Temperature of TIG Welding: Arc, Pool & Heat Guide

A shop apprentice once turned a clean 1/8-inch aluminum T-joint into a sagging, porous mess and insisted his machine was ‘too cold’ — while the tungsten glowed cherry red an inch above the puddle. The real problem was never the dial setting: it was not knowing what temperature he was actually creating, or where that heat was going once the arc struck.

Why TIG Welding Temperature Matters More Than the Dial Setting

The apprentice from our opening story did exactly what most beginners do: he stared at the amperage dial and concluded the machine was lying to him. His tungsten was glowing cherry red, the puddle was wandering, and the aluminum was soaking up heat faster than he could push it. What he actually lacked was a mental model of temperature in gas tungsten arc welding (GTAW) — how hot the arc gets, how hot the metal gets, and how much of that heat stays where you put it.

Here is the short answer to the question people search for. TIG welding produces one of the hottest and most controllable arcs in all of welding. The arc region generally sits in the range of roughly 10,000–20,000°F (about 5,500–11,100°C), and physics reference compilations report peak values near 35,000°F (around 19,400°C) at the core of an arc column. For perspective, the surface of the sun is about 10,000°F. Yet a TIG arc is gentle enough to fuse a hair-thin tab of sheet aluminum, because temperature and heat are not the same thing — and TIG gives you unusually fine control over both.

The Three Different “Temperatures” of TIG Welding

When someone asks about the temperature of TIG welding, they are usually collapsing three separate numbers into one. Keeping them apart is the single most useful thing a new welder can learn.

Zone	Typical temperature	What it tells you
Arc column	~10,000–20,000°F, peaks near 35,000°F	How intensely the plasma ionizes and how easily it starts and holds an arc
Weld pool	At or just above the base metal’s melting point (for steel, about 2,500–2,800°F)	Whether the metal actually fuses, wets out, and stays clean
Base metal and heat-affected zone (HAZ)	Anything from room temperature up to just below melting	Where metallurgy changes, distortion grows, and cracking risk lives

The arc can be astronomical while the puddle sits politely at melting and the HAZ a half-inch away never gets hot enough to matter. Conversely, a welder who keeps the arc small and moves fast can melt metal without cooking the surrounding structure. That gap between arc temperature and metal temperature is where skill lives.

Why GTAW Behaves This Way

GTAW was developed in the early 1940s by Russell Meredith at Northrop, who used a tungsten electrode with helium shielding to weld magnesium aircraft frames — the process was briefly marketed as “heliarc” welding (history of the GTAW process). Two design choices explain the temperature behavior you see today. First, the electrode is tungsten, which melts at 3,422°C (6,192°F), so it can sit inside a plasma that would vaporize almost any other metal without being consumed. Second, the filler metal is fed by hand and carries no current, so the arc remains stable and concentrated. That stability is also why TIG produces very little welding fume compared with stick or flux-cored processes.

Who This Guide Is For — and What It Covers

This article is written for people who need real numbers rather than folklore: beginner welders setting up their first machine, fabrication students preparing for open-book tests and aerospace TIG welding standards work, hobbyists troubleshooting a ruined aluminum project, and inspectors verifying preheat records against a written procedure. If you have ever scrubbed a soiled aluminum bead and wondered whether cleaning chemistry was the real culprit, our aluminum prep guide covers the same heat-and-contamination logic from the other side.

Here is the path through the rest of the guide:

1. Actual arc temperature figures, and why published numbers disagree.
2. Melting points and typical TIG settings for steel, stainless, aluminum, copper, and titanium.
3. The heat input formula — the practical version of “temperature” you can control.
4. Preheat and interpass limits under AWS D1.1 and how to measure them.
5. Heat-affected zone behavior and cooling rate.
6. How gas, electrode geometry, and polarity shift the heat.
7. Measurement tools, common temperature mistakes, and safe working practices.

The theme running through all of it: the dial is only an input. Understanding where the heat goes is what turns a settings chart into a weld.

How Hot Is the TIG Arc? Actual Numbers Explained

When people ask about the temperature of TIG welding, the answer isn’t a single number. What they’re really looking for is how hot the arc gets, and that number can swing wildly depending on what part of the arc you’re measuring. The key difference is that the arc itself is far hotter than the metal you’re melting, and understanding that gap is what explains why the tungsten electrode can survive while steel turns to liquid.

The Range of TIG Arc Temperatures

At its core, the TIG (GTAW) arc is an ionized stream of plasma gas, which is what allows it to reach some of the highest temperatures seen in common arc welding processes. Published figures vary based on the measurement method, but generally accepted numbers place the arc column anywhere between 10,000°F and 30,000°F (5,540°C and 16,649°C). In the Kelvin scale, that comes out to roughly 5,000 K to 19,000 K.

More specifically, sources like the Hypertextbook and technical discussions from the American Welding Society show that the arc core, the narrowest and most concentrated part of the plasma column, is the hottest. Measurements have placed it near the upper end of that range, while the outer plume of the arc cools off significantly. Lincoln Tech further notes that the TIG molten pool region can reach about 19,000 K (over 33,000°F), putting it well above the sun’s surface temperature of roughly 10,000°F (5,537°C).

Why Do Published Numbers Vary So Much?

There are a few reasons why you’ll see such a wide range across different sources. First, where you measure matters. The arc isn’t uniform, so readings from the tight core, the wider arc column, or the loose plasma plume will all be different. Second, your measurement method matters. Optical emission spectroscopy, thermocouples, and calorimetry all produce different results. Third, your setup matters. Gas type, amperage, arc length, electrode size, and even your polarity can all shift the temperature. For example, adding helium to argon creates a hotter, more conductive plasma than pure argon, raising temperatures even further.

How Can the Tungsten Survive?

The reason the non-consumable tungsten electrode doesn’t instantly vaporize is due to its sheer heat resistance. Tungsten has the highest melting temperature of any pure metal at 3,422°C (6,192°F). While the arc core is far hotter than that, the electrode isn’t sitting in the absolute center of that core unprotected. With proper gas coverage, correct tip geometry, and the use of DCEN for most steels, the heat is drawn down the electrode and dissipated, allowing it to withstand the plasma around it. It’s a delicate balance, which is exactly why contamination or incorrect polarity can cause it to overheat in an instant.

How Does It Compare to Other Processes?

While TIG is known for its precision, it’s not the only hot arc out there. The table below breaks down the approximate arc temperatures of the most common processes to put these numbers into perspective:

Welding Process	Approx. Arc Temperature (°F)	Approx. Arc Temperature (°C)	Notes
TIG (GTAW)	10,000 – 30,000	5,540 – 16,649	Highly focused plasma, great for precision.
MIG (GMAW)	9,000 – 16,000	4,982 – 8,871	Slightly cooler and wider than a TIG arc.
Stick (SMAW)	6,500 – 10,000	3,593 – 5,537	Lower arc temperature, but very robust in the field.

Ultimately, the arc itself can be hotter than the surface of the sun, but that’s not the number that will burn through your aluminum. What matters is that this intense, ionized plasma is so concentrated that a tiny bit of amperage can create enough heat to melt metal. With techniques used for aluminum boat welding, for example, that concentration is put to use with extreme precision. The takeaway is simple: the arc temperature is astronomical, but control over it is what separates a clean TIG weld from a blown hole.

Weld Pool and Base Metal Temperatures by Material

The arc is only half the story. Once it touches the joint, the number that actually matters is the temperature of the metal in front of it. Every base metal has a specific melting point, and your job as a TIG welder is to bring the puddle just past that point, hold it long enough to fuse, and move on before the heat runs away. Push past it and you burn through; fall short and you get a bead sitting on top of the plate instead of in it.

What Each Metal Actually Needs to Reach

Here is the useful part: the arc column may sit in the tens of thousands of degrees, but the puddle only has to reach the base metal’s melting point. That is why one amperage setting that welds steel beautifully will simply scorch and ball aluminum, and why copper makes so many beginners question their machine.

Base Metal	Approx. Melting Point	Typical TIG Amperage Range	Notes
Mild / carbon steel	2,500–2,800°F (1,370–1,540°C)	40–150 A for most sheet	Forgiving; ~1 A per 0.001 in thickness
Stainless steel (304/316)	2,550–2,650°F (~1,400–1,450°C)	40–120 A, often lower than steel	Lower heat input to avoid sensitization
Aluminum (6061)	1,220°F (660°C)	60–200 A depending on thickness	High conductivity demands more amps
Copper	1,984°F (1,085°C)	100–300 A+ with preheat	Extreme heat sinking
Titanium (Grade 2/5)	~3,034°F (1,668°C)	40–120 A, tight control	Requires full back purge

Those figures are starting points, not gospel. Joint design, fit-up, position, and whether the piece is clamped to a heavy table all shift the number. A butt joint on 1/8-inch plate needs noticeably less current than a T-joint of the same thickness because the T-joint has two planes pulling heat away.

Why Aluminum Eats So Much More Heat

This is the single most important thermal fact in TIG welding: aluminum conducts heat roughly 4–5 times faster than carbon steel and about 10–12 times faster than stainless steel. The moment the arc strikes, heat sprints away from the puddle into the surrounding plate. That is why aluminum settings feel absurdly hot compared to steel — you are not melting more metal, you are paying a conduction tax on every amp you push in.

Copper is worse still, and titanium is the opposite problem: it conducts slowly, so heat piles up locally and stays there. Titanium also becomes a sponge for oxygen and nitrogen at temperature, which is why it needs strict shielding and a back purge on anything open-root.

The practical consequence is that “right” temperature control looks different on every material. On steel you dial in a setting and refine with travel speed. On aluminum you often need more amperage but less dwell time, or a pedal you can snap back on as soon as the puddle breaks through the oxide layer. That oxide skin, which melts around 3,700°F (2,037°C) while the aluminum underneath melts at 1,220°F (660°C), is exactly why surface prep matters so much — a dedicated aluminum cleaner before you strike an arc saves more heat-related defects than any dial adjustment.

The Amperage Reference: Haynes International’s GTAW Table

If you want a credible starting point rather than a forum guess, Haynes International’s GTAW parameter table is a good anchor. Their published ranges start at 15–75 A for 0.030–0.062 in material and climb to 125–200 A for material over 0.250 in. Note how wide those bands are: the low end suits thin, well-supported work with fast travel; the thick end assumes heavier sections acting as heat sinks.

Titanium has its own house rules. Because it melts around 3,034°F and tolerates no contamination, it is commonly welded with 2% thoriated (red) tungsten electrodes on DC, which hold a point well and resist contamination better than pure tungsten — though the thoriated variant requires grinding and careful dust handling. Beyond electrode choice, one thing stays constant across every material: the machine setting is only an input. What the metal experiences is defined by heat input, and that is where the real control lives.

Related reading: if you are cross-shopping processes to decide where TIG fits, this aluminum MIG welding guide lays out how MIG’s higher deposition and different heat profile compare against TIG on the same aluminum alloys.

Heat Input: The Formula That Controls TIG Temperature

An arc reading of 20,000°F sounds dramatic, but it tells you very little about what your plate is actually doing. The arc column is only the delivery system. What determines whether your bead sinks in smoothly or blows a hole is the energy your joint receives per inch of travel. Welders call that number heat input, and it is the practical, controllable version of temperature.

The important part is that heat input is not something you dial in. Your machine has knobs for amperage, and some machines let you set voltage or arc length indirectly, but heat input only exists once you combine those values with how fast you move. It is an outcome you calculate after the fact, which is exactly why codes regulate it rather than trusting a setting on a front panel.

The Formula Welding Codes Actually Use

The standard expression found in welding procedure literature is simple:

Here is a worked example. Suppose you are running 300 A on thick plate with an average measured arc voltage of 20.5 V, cruising along at 18 in./min.:

• At 18 in./min.: (60 × 300 × 20.5) ÷ 18 = 369,000 ÷ 18 ≈ 20,500 J/in. (20.5 kJ/in.)
• At 13.5 in./min.: 369,000 ÷ 13.5 ≈ 27,400 J/in. (27.4 kJ/in.)

That is a 25% cut in travel speed producing roughly a 33% jump in heat input. Nothing on the machine changed. The amperage dial stayed put, the arc looked identical, yet the joint soaked in a third more energy simply because the arc lingered longer over each inch. Slow down slightly and you can move a weld from an acceptable range straight into a procedure violation or a warped panel.

Amperage, Arc Length and the 1 Amp per 0.001 In Rule

Amperage is where most welders start. The classic rule of thumb for TIG on mild steel is roughly 1 amp per 0.001 in. of material thickness for a flat butt joint, so 1/8-in. (0.125 in.) stock starts around 125 A. Bump the number up for vertical or overhead positions, thicker fillet legs, or material that is acting as a heat sink, and trim it back on thin edges and root passes. It is a starting point, never a procedure.

Arc length is the quiet second lever. Amperage sets the current, but arc voltage climbs as you pull the tungsten away from the puddle. Because voltage sits in the numerator of the formula, a long, lazy arc quietly adds joules per inch even when your amperage never moves. Keep the tungsten close, roughly one electrode diameter off the work, and you get a tight, focused arc with lower voltage and a narrower, more controlled bead. This matters doubly on thin material, where the difference between a sound joint and a blowout is often an extra eighth-inch of standoff.

Pulsed TIG: Turning Temperature Down Without Losing the Arc

Pulsed TIG alternates between a high peak current that melts the puddle and a low background current that lets it solidify slightly. The average current, and therefore the average heat input, drops well below a comparable constant-current setting while penetration stays adequate. The practical payoff shows up on heat-sensitive work: on stainless steel, pulsing cuts input and distortion and improves first-pass yield, meaning fewer sections need to be cut out and re-welded. Thin aluminum jobs benefit the same way — a concern anywhere distortion decides the outcome, from alloy wheel repair to precision aerospace assemblies where aerospace TIG welding procedures limit total energy strictly.

Think of amperage as the faucet and travel speed as how long you hold it under the joint. Heat input is the volume of water that actually lands. Manage that number deliberately, and the temperature of TIG welding stops being an abstraction and becomes something you can plan, measure, and repeat.

Preheat and Interpass Temperature Requirements

Everything so far has been about the heat you apply during the weld. This section is about the heat you put into the metal before the arc strikes, and the ceiling on heat you can leave behind between passes. Those two numbers — preheat and interpass temperature — are what an inspector actually checks, and codes specify them for a reason: they control how fast the weld cools, and cooling rate decides whether a joint survives or cracks weeks later on the job.

What Preheat and Interpass Actually Mean

Preheat is the temperature the base metal is raised to, and held at, before welding begins. Interpass temperature is the maximum temperature the previously deposited weld and adjacent base metal may reach before the next pass goes on top. As Lincoln Electric’s preheat guidance explains, both exist to slow the cooling rate of the weld and the heat-affected zone, not to make the metal hotter for its own sake.

The mechanism is simple. A hot joint cools slowly, giving dissolved hydrogen time to diffuse out before it gathers at stress points in the HAZ. A cold, thick, heavily restrained joint cools almost instantly, trapping hydrogen in a shrinking-stressed microstructure with little ductility to absorb it. That combination — hydrogen, hard microstructure, and restraint — is the classic recipe for hydrogen-induced cracking.

What AWS D1.1 Actually Requires

For structural steel in the United States, AWS D1.1 governs preheat and interpass control. Its prequalified joint tables (Table 5.8 in recent editions) list minimum preheat and minimum interpass temperatures by material group and thickness. For common mild steel in light sections, that floor can be as low as 70°F (20°C) — essentially ambient shop temperature. For heavier sections, higher-strength groups such as Group D steels, and restrained joints, the requirement steps up to 150°F (65°C), sometimes more.

Just as important as the number is where you measure it. D1.1 requires preheat to be verified at a distance from the joint equal to the thickness of the thickest member being welded, but never less than 3 inches (75 mm) from the point of welding. Measuring right at the bevel edge gives a falsely high reading; the joint root can be far colder than the glowing surface suggests, especially on thick plate where the surrounding metal acts as a heat sink.

Material	Typical preheat	Typical interpass limit
Carbon steel, light section	70°F (20°C)	600°F (315°C)
Carbon steel, heavy/restrained (per D1.1)	150°F (65°C) minimum	600°F (315°C)
Aluminum (GTAW guidance)	175–200°C (347–392°F)	Varies by alloy
Thick magnesium	Up to 150°C (302°F) maximum	150°C (302°F)
Austenitic stainless	Usually none	Kept low to avoid sensitization

Preheat Beyond Steel: Aluminum and Magnesium

Non-ferrous metals play by different rules. Standard GTAW reference guidance lists a preheat of 175–200°C (347–392°F) for aluminum and a maximum of 150°C (302°F) for thick magnesium. Note the wording for magnesium: it is a ceiling, not a floor. Magnesium loses strength and becomes dangerously oxidizing if pushed too hot, so the goal is gentle, controlled warmth — enough to drive off moisture and soften the thermal shock of a high-conductivity metal meeting an arc, never a glowing red heat.

Aluminum preheat is likewise more about moisture and cleanliness than metallurgy. Because aluminum sheds heat roughly four to five times faster than carbon steel, a preheated joint can drop back toward ambient in seconds, and any oil, cutting fluid, or water baked into the surface turns straight into porosity. If you are preheating an aluminum joint, surface prep is half the battle — see Aluminum Cleaner for Welding: How to Prep Aluminum Right for the degreasing and oxide-removal sequence that makes preheat worth doing at all.

Annex B and the Carbon Equivalent Route

D1.1 also offers an alternative path. Its Annex B preheat provisions let you calculate requirements from the steel’s carbon equivalent (CE), its hydrogen level, joint restraint, and planned heat input, rather than following the fixed prequalified tables. Under favorable conditions — low CE, low-hydrogen consumables, moderate restraint — Annex B can justify heat inputs as high as 100 kJ/in with reduced preheat, because the slower cooling that comes with high heat input does some of the hydrogen’s work for it. This is where the trade becomes explicit: more heat input means less cracking risk but a larger, softer HAZ. Procedures for high-alloy and specialty steels handle the same balancing act — see Alloy 20 Welding: Procedures, Filler Metals, and Best Practices for how preheat and interpass limits are written into procedures for corrosion-resistant alloys.

Practical Rules for the Shop Floor

• Measure preheat at the required offset — at least the thickest member’s thickness, and never less than 3 in (75 mm) from the weld point.
• Use the right tool: a calibrated contact thermometer, an IR pyrometer with emissivity set correctly, or temperature-indicating crayons as a backup check.
• Hold preheat long enough for heat to equalize through the full thickness, not just the surface.
• Watch interpass with the same discipline. Letting a multi-pass weld climb above the code maximum undoes the benefit of preheating it correctly in the first place.
• Record the readings. A WPS that requires documented preheat is only as good as the log proving it was done.

Preheat is the least glamorous part of a TIG procedure and the one most often faked with a propane torch waved at the bevel for ten seconds. Done properly — right temperature, right measurement point, right hold time — it is the cheapest insurance against cracking you will ever buy.

The Heat-Affected Zone and Cooling Rate

There is a third temperature zone in TIG welding, and it is the one that catches most welders off guard. It sits just outside the shiny weld bead, it never melts, and yet it can quietly wreck the strength of a joint. That zone is the heat-affected zone, or HAZ, and understanding it is the difference between a weld that passes inspection and one that cracks months later in service.

What Exactly Is the HAZ?

According to TWI’s technical definition, the heat-affected zone is the area of base metal that has not been melted, but whose mechanical properties or microstructure have been changed by the heat of welding. In plain terms: the metal around your bead got hot enough to rearrange its internal grain structure, but not hot enough to turn to liquid.

That distinction matters. The weld metal itself you control with filler choice and amperage. The HAZ you control almost entirely with heat management. Every metallurgical complaint about welded joints, from softening in aluminum to hard, brittle zones in steel, has its roots in the HAZ.

Why Cooling Rate Is the Real Story

Heat input gets all the attention, but what actually determines HAZ properties is how fast the metal cools after the arc passes. This is why codes and researchers talk about cooling time, not just amperage.

The most widely referenced metric is t8/5 — the time it takes the metal to cool from 800°C to 500°C (some standards use 800°C to 400°C). This temperature window is where the critical phase transformations happen in steel: where austenite decomposes into ferrite, pearlite, bainite, or martensite. Cool slowly through that window and you get soft, ductile structures. Cool quickly and you can form hard martensite that is prone to hydrogen cracking.

Research funded through DTIC used infrared thermography to measure weld metal cooling rates, tracking both the cooling rate at 538°C (1,000°F) and the total time to cool from 800°C to 400°C. That work confirmed what welding engineers had long observed in the field: cooling rate is measurable, it varies dramatically with process parameters, and it directly predicts final properties.

What Grows or Shrinks the HAZ

Three variables dominate HAZ size:

• Heat input. More joules per inch means a larger volume of metal gets pushed above transformation temperature. Low heat input cools faster and produces a smaller, narrower HAZ with less grain growth.
• Travel speed. Slower travel keeps the arc in one spot longer, pushing heat deeper and widening the HAZ. This is why rushing nothing and dragging your puddle are both enemies of metallurgy.
• Material thickness. Thick plate acts as a heat sink, pulling heat away rapidly and shrinking the HAZ. Thin sheet has nowhere to send the heat, so the HAZ spreads wide. As a general rule, a larger weld heat sink cools faster and shrinks the heat-affected zone.

Graphically, a low-heat-input TIG weld on thick steel might show a HAZ only a few millimeters wide. A high-heat, slow-travel weld on thin plate can push the HAZ far beyond the visible discoloration, sometimes several times the weld width on each side.

What Goes Wrong in the HAZ

Different metals fail in the HAZ in characteristic ways:

• Grain growth. Excessive heat coarsens grains in the HAZ, reducing toughness and fatigue strength. This is a particular concern in fine-grained and micro-alloyed steels.
• Hardening and cracking. In carbon and low-alloy steels, fast cooling through the critical window can create hard martensite. Combined with hydrogen from moisture or contaminated filler, that martensite can crack. This is the reason preheat and interpass temperature rules exist.
• Sensitization in stainless steel. Hold stainless in the 425–870°C range too long and chromium carbides precipitate at grain boundaries, depleting the adjacent metal of chromium and destroying corrosion resistance. Slower travel speeds and excessive interpass temperatures are the usual culprits.
• Softening in aluminum. Heat-treatable aluminum alloys can lose strength in the HAZ as precipitation-hardened phases dissolve or over-age. On thin aluminum, distortion is often a bigger practical problem than strength loss, as anyone who has warped an alloy wheel during repair can confirm.
• Residual stress. Uneven heating and cooling locks stress into the joint. High heat input, thick sections, and restraints all increase it.

Practical Control Levers

You cannot avoid the HAZ, but you can keep it tight. Keep travel speed steady and as fast as the joint allows while still achieving full fusion. Avoid wandering the arc or pausing unnecessarily outside the puddle. On multi-pass welds, keep interpass temperatures in check. On thin sections, use pulse settings or chill blocks. On stainless, keep interpass below 175°C (350°F) unless a procedure says otherwise.

The takeaway is simple: temperature in welding does not end at the puddle. Managing how quickly that heat leaves is just as important as how much you put in.

How Gas, Electrode and Polarity Change the Heat

Two welders can set the same machine to 120 amps and still produce completely different welds, because amperage is only one of three levers. The shielding gas you pick, the tungsten grind, and the polarity you run all decide how much heat actually reaches the puddle, how wide it spreads, and how fast it climbs back out. If the dial setting is the throttle, these three variables are the steering.

Shielding Gas: The Invisible Heat Setting

According to Miller Welds, 100% argon is the best all-around TIG shielding gas, and for good reason: it starts easily, runs stably on DC, and gives a calm, predictable arc that beginners can actually learn on. Argon also forgives a slightly long arc without wrecking the weld, something hydrogen and helium blends do not.

But argon is not the hottest option. Argon/helium blends ionize differently and produce a hotter, stiffer arc that concentrates more energy into the joint, giving deeper penetration and faster travel on thicker material. Pure helium runs hotter still, which is why it appears on thick copper, thick aluminum, and heavy-section production work where conductivity works against you. The trade-off is real: helium arcs are harder to start, more sensitive to arc length, and they push extra heat into the tungsten, so you may need a larger electrode and a more deliberate technique.

As The Fabricator explains, shielding gas choice influences arc stability, heat input, weld appearance, and arc starting characteristics together, not one at a time. That is why a gas change can fix a bead no amperage adjustment seemed to touch.

Gas choice	Heat effect	Best suited to
100% argon	Balanced, stable, forgiving arc	Most steel and stainless TIG, general shop work
Argon + 10–25% helium	Hotter arc, deeper penetration, faster travel	Thicker mild steel, stainless, production joints
Argon + 5–10% hydrogen	Sharper, hotter arc, better wetting	Austenitic stainless only, thin sections
100% helium	Highest heat, broad arc footprint	Thick copper, heavy aluminum, high-conductivity metals

Tungsten Geometry: Where the Heat Points

The ground profile of the electrode controls how tightly the arc is focused. The generally suggested tungsten geometry is a 30–60° cone with a 0.040–0.060 in (1.0–1.5 mm) flat ground at the tip. Think of it as a flashlight lens:

– A sharper 20–30° grind narrows the arc, concentrates heat, and drives deeper penetration on steel and stainless. It also makes the arc more directional and slightly more sensitive to hand position.
– A blunter 60–90° grind spreads the arc wider, softening heat over a larger area, which is friendlier for thin sheet and for aluminum, where the puddle wants time to wet out.
– The flat at the tip protects against balling and contamination. Grind it lengthwise, parallel to the electrode axis, so the scratch lines run toward the puddle and the arc starts straight.

Electrode diameter matters just as much. A 1/8-inch tungsten dissipates heat through more mass than a 3/32-inch one, so stepping up a size can stop tungsten overheating at high amperage or on helium blends. Keep the tungsten clean as well: a contaminated tip changes the arc shape, which changes the heat pattern before you notice the bead looking wrong.

Polarity, AC Balance and Frequency

Polarity decides which side of the arc absorbs the heat. On DCEN (direct current electrode negative), roughly two-thirds of the arc energy goes into the workpiece, which is why it is the standard for steel, stainless, titanium, and copper. Flip to DCEP and most of the heat migrates into the tungsten instead, producing shallow penetration but an aggressive cleaning action that blasts surface oxides away.

That cleaning action is exactly why aluminum runs on AC. Aluminum oxide melts around 3,700°F (2,040°C) while the base metal melts near 1,220°F (660°C), so the arc has to break the oxide skin before it can melt anything beneath it. Proper surface prep still comes first; an aluminum cleaner for welding removes the contaminants no arc setting should be asked to fix.

Modern inverter machines let you shape that compromise two ways:

– Balance sets the ratio of cleaning to penetration. Shift toward more cleaning and you widen the etched zone and soften penetration; shift toward more penetration and the bead gets narrower and deeper with less surface etching.
– AC frequency (typically 60–200 Hz) controls arc width. Higher frequency tightens and directs the arc, adding penetration and reducing the cleaning band, which is useful on thicker aluminum and out-of-position work.

Run the two together and you can dial heat where you want it without touching amperage at all. If you are comparing processes on aluminum, our aluminum MIG welding guide shows how much of this balancing act transfers to wire processes, and where TIG still wins on control.

How to Measure and Control Temperature While Welding

Here is the uncomfortable truth about TIG: your machine dial does not display temperature. It displays amperage, and amperage only becomes temperature after it interacts with travel speed, arc length, material thickness, and how fast the surrounding metal steals heat away. If you never measure the result, you are guessing. That is why weld procedures, aerospace shops, and inspection crews treat temperature measurement as documented work rather than a matter of feel.

Five Ways to Actually Read Temperature

Each method trades convenience against accuracy, so most shops end up using more than one:

• Infrared pyrometers. Non-contact, point-and-shoot readings in a fraction of a second. Ideal for checking interpass temperature between beads without stopping the job for long. The catch is aiming: the measurement spot must be small and fully inside the area you care about, or you average hot and cold zones together.
• Temperature-indicating sticks and crayons. A wax-based marker rated to a specific temperature that melts or smears when the steel reaches it. Cheap, portable, and hard to misread, which is why they show up constantly in preheat work. They give you a pass/fail answer rather than a number, and they leave a mark you must clean off.
• Thermocouples. Small sensors clamped or tack-welded to the joint, wired to a logger. This is the method that produces a defensible record: temperature versus time, pass by pass, exactly what a procedure review or a contested inspection calls for.
• Contact thermometers. Probe-style instruments pressed against the surface. Simple and reasonably accurate on clean, flat steel, but slow, and they read low on freshly ground or reflective surfaces.
• Infrared thermography cameras. The high-end option. Instead of one spot, you get a full thermal image of the pool, the heat-affected zone, and the surrounding structure at once. Modern infrared thermography research published by NIST reflects how mature this technique has become, and industrial weld-monitoring cameras now capture hundreds of frames per second, which is fast enough to follow puddle dynamics and HAZ width in real time rather than after the fact.

ISO 13916 and What Your WPS Expects

When a procedure calls for a preheat or interpass temperature, someone has to prove it happened. ISO 13916 is the referenced standard for monitoring preheat and interpass temperatures using thermal devices, and it covers the things auditors actually ask about: which instrument, how it was calibrated, where the measurement was taken, and how the reading was recorded. A crayon mark on a plate, a logged thermocouple trace, or a timestamped pyrometer reading all satisfy that requirement as long as the method is specified in the procedure and repeatable by the next welder. In regulated work such as aerospace fabrication, undocumented temperature control is effectively no temperature control at all, which is a theme you see throughout aerospace TIG welding practice.

The Control Levers You Can Pull

Once you can see the temperature, you can manage it. These are the practical levers, roughly in order of how often they should be used:

Lever	Effect on heat
Amperage	Sets the baseline energy per second. Change last, not first.
Travel speed	The most efficient adjustment: faster travel drops heat input almost proportionally.
Arc length and weave	A longer arc raises voltage and spreads heat wider; a tight, narrow bead keeps it focused.
Pulsed TIG	Background current lets the pool cool between peaks, cutting average heat without losing penetration.
Back purge and trailing gas	Protects the underside of stainless and titanium so excess heat does not turn into oxidation.
Staggered welds and chill blocks	Copper backing bars, heat sinks, and skipping around the part spread and absorb heat before it accumulates.

The goal is never to eliminate heat, which is impossible, but to keep the metal inside the temperature window the filler, the alloy, and the procedure were chosen for. Measure, adjust one variable, and measure again. That loop, not the dial, is what separates a repeatable weld from a lucky one.

Common Temperature Mistakes and How to Fix Them

Almost no temperature-related welding defect is mysterious. Burn-through, sugaring, porosity, distortion and cold cracks record a decision made seconds earlier: too much amperage, travel too slow, an interpass too hot, or a shield that never worked. Read the bead like a thermometer and most fixes take seconds.

Burn-Through: Too Much Heat, Too Slow

Burn-through shows as a hole, a sagging root or a blown-out edge, with three usual causes: amperage too high, travel speed too slow, or an arc left too long, which adds voltage and widens the arc cone. The Fabricator’s breakdown of welding parameters shows why amperage and travel speed dominate heat input, and thin stock punishes both far faster than thick plate does.

The counterintuitive fix: move faster instead of just turning the dial down. Faster travel cuts heat input, and on heat-sensitive metals like aluminum it is the most effective correction. Also try short stitched segments, a copper chill block behind the joint, a shorter arc, or pulsed TIG so background current lets the puddle cool.

Lack of Fusion and Cold Joints

The opposite failure is a bead sitting on top of the metal instead of bonded to it: rounded, ropey, no wetting. Too little amperage, travel too fast, a long arc or filler fed into the arc cone all produce it. Slow slightly, shorten the arc and let the puddle wet both toes before adding rod. For overhead and vertical rod choices see our All Position Welding Rod Guide.

Sugaring and Oxidation on Stainless

That blue-grey crust on a stainless root is sugaring: chromium meeting oxygen while hot, from an overheated joint, a missing purge or an interpass left to climb. Stainless is welded cooler and faster than carbon steel to limit heat input and carbide precipitation. Cap interpass (many procedures allow only 300–400°F / 150–200°C), purge the back side and skip-weld. AWS ties preheat and interpass limits to metallurgy, not comfort, in both carbon and stainless steels.

Porosity: When More Gas Makes It Worse

New TIG welders crank the flow meter at porosity, but excessive flow creates turbulence that pulls air into the arc. Miller Welds recommends moderate flows — commonly 15–25 CFH for argon on a standard cup, less with a gas lens — and warns that leaks, drafts and dirty filler are common culprits in TIG shielding setups. Keep the nozzle off the puddle and clean oily filler.

Tungsten Contamination

A grey, flat, sputtering tungsten means the electrode touched the puddle, usually because the arc was too long, the amperage too low, or the rod dipped into the tungsten. Break the arc, regrind the electrode lengthwise on a dedicated diamond wheel, shorten the arc and raise amperage if it wanders. Tungsten inclusions are rejectable under most codes.

Aluminum Oxide: The Heat You Can’t See

Aluminum oxide melts near 3,700°F (2,035°C) while the aluminum beneath melts around 1,220°F (660°C), so the skin you weld through can be hotter than the puddle looks. A dirty joint forces extra amperage and then burn-through. Our Aluminum Cleaner for Welding: How to Prep Aluminum Right covers the degrease, etch and stainless-brush routine; on thin alloy wheel repair add a chill block.

Distortion, Warping and Cracking

Distortion comes from uneven expansion and contraction: long beads, poor fit-up, missing clamps and high heat input. Counter it with skip-welding, rigid fixturing, alternating stitch sequences and lower amperage with faster travel. Large fabrications like aluminum boat hulls need this because aluminum’s conductivity spreads heat fast.

Cracking splits into two families. Hot cracking usually means contamination, the wrong filler for the alloy, or a joint restrained too rigidly. Cold or hydrogen cracking appears after cooling, driven by hard metallurgy plus hydrogen plus restraint — which is why preheat and slow cooling exist. TWI’s summary of HAZ behavior explains why the metal beside the weld is where hardness and residual stress concentrate in steels and alloys.

Symptom	Likely temperature cause	Fix
Burn-through or blown edge	Too much amperage, slow travel, long arc	Speed up, trim amps, add chill block
Ropey bead, no wetting	Too little heat, long arc	Add amps, slow down, tighten arc
Stainless sugaring or tint Common Temperature Mistakes and How to Fix Them Almost no temperature-related welding defect is mysterious. Burn-through, sugaring, porosity, distortion and cold cracks record a decision made seconds earlier: too much amperage, travel too slow, an interpass too hot, or a shield that never worked. Read the bead like a thermometer and most fixes take seconds. Burn-Through: Too Much Heat, Too Slow Burn-through shows as a hole, a sagging root or a blown-out edge, with three usual causes: amperage too high, travel speed too slow, or an arc left too long, which adds voltage and widens the arc cone. The Fabricator’s breakdown of welding parameters shows why amperage and travel speed dominate heat input, and thin stock punishes both far faster than thick plate does. The counterintuitive fix: move faster instead of just turning the dial down. Faster travel cuts heat input, and on heat-sensitive metals like aluminum it is the most effective correction. Also try short stitched segments, a copper chill block behind the joint, a shorter arc, or pulsed TIG so background current lets the puddle cool. Lack of Fusion and Cold Joints The opposite failure is a bead sitting on top of the metal instead of bonded to it: rounded, ropey, no wetting. Too little amperage, travel too fast, a long arc or filler fed into the arc cone all produce it. Slow slightly, shorten the arc and let the puddle wet both toes before adding rod. For overhead and vertical rod choices see our All Position Welding Rod Guide. Sugaring and Oxidation on Stainless That blue-grey crust on a stainless root is sugaring: chromium meeting oxygen while hot, from an overheated joint, a missing purge or an interpass left to climb. Stainless is welded cooler and faster than carbon steel to limit heat input and carbide precipitation. Cap interpass (many procedures allow only 300–400°F / 150–200°C), purge the back side and skip-weld. AWS ties preheat and interpass limits to metallurgy, not comfort, in both carbon and stainless steels. Quick Note: If a stainless weld discoloured to straw, blue or black, the metal got too hot or lost its gas shield. Discoloration is not always rejectable, but it is always a signal to reduce heat input next pass. Porosity: When More Gas Makes It Worse New TIG welders crank the flow meter at porosity, but excessive flow creates turbulence that pulls air into the arc. Miller Welds recommends moderate flows — commonly 15–25 CFH for argon on a standard cup, less with a gas lens — and warns that leaks, drafts and dirty filler are common culprits in TIG shielding setups. Keep the nozzle off the puddle and clean oily filler. Tungsten Contamination A grey, flat, sputtering tungsten means the electrode touched the puddle, usually because the arc was too long, the amperage too low, or the rod dipped into the tungsten. Break the arc, regrind the electrode lengthwise on a dedicated diamond wheel, shorten the arc and raise amperage if it wanders. Tungsten inclusions are rejectable under most codes. Aluminum Oxide: The Heat You Can’t See Aluminum oxide melts near 3,700°F (2,035°C) while the aluminum beneath melts around 1,220°F (660°C), so the skin you weld through can be hotter than the puddle looks. A dirty joint forces extra amperage and then burn-through. Our Aluminum Cleaner for Welding: How to Prep Aluminum Right covers the degrease, etch and stainless-brush routine; on thin alloy wheel repair add a chill block. Distortion, Warping and Cracking Distortion comes from uneven expansion and contraction: long beads, poor fit-up, missing clamps and high heat input. Counter it with skip-welding, rigid fixturing, alternating stitch sequences and lower amperage with faster travel. Large fabrications like aluminum boat hulls need this because aluminum’s conductivity spreads heat fast. Cracking splits into two families. Hot cracking usually means contamination, the wrong filler for the alloy, or a joint restrained too rigidly. Cold or hydrogen cracking appears after cooling, driven by hard metallurgy plus hydrogen plus restraint — which is why preheat and slow cooling exist. TWI’s summary of HAZ behavior explains why the metal beside the weld is where hardness and residual stress concentrate in steels and alloys. Symptom Likely temperature cause Fix Burn-through or blown edge Too much amperage, slow travel, long arc Speed up, trim amps, add chill block Ropey bead, no wetting Too little heat, long arc Add amps, slow down, tighten arc Stainless sugaring or tint Overheating, no purge, high interpass Purge, lower interpass, skip-weld Porosity Turbulence, leaks, dirty filler Reduce flow, shield area, clean filler Sputtering arc Tungsten contamination, low amperage Regrind tungsten, raise amps Warping or oil-canning Excessive heat, no restraint Clamp, skip-weld, use pulse Crater cracks at stop Arc broken on a hot pool Fill crater, overlap stop, taper current Overnight cracking in steel Fast cooling, hard HAZ, hydrogen Correct preheat, control interpass, slow cooling Work the table from the symptom backwards. The fix is almost always one of four things: change travel speed, change amperage, control interpass, or fix the gas envelope. Safety, Practical Settings and Final Takeaways Every temperature covered in this article carries a safety consequence with it. An arc hot enough to boil tungsten also throws out ultraviolet and infrared radiation intense enough to burn skin and cornea within seconds, and base metal that looks only mildly orange can still be sitting near interpass temperature long after the arc stops. Heat control and personal protection are one discipline, not two separate chores. What the Heat Actually Threatens Start with radiation. The TIG arc produces UV that causes photokeratitis (arc eye) and flash burns on exposed skin, plus IR that heats tissue deeper than a surface burn. A correctly shaded helmet, typically shade 10 to 13 across common GTAW amperage ranges, plus safety glasses underneath and flame-resistant leathers are the baseline. Next comes stored heat: a thick steel plate can still be near 150°F minutes after a pass, and the tungsten, filler rod stubs, clamps and fixtures all hold heat longer than beginners expect. The final hazard is airborne. OSHA’s welding fact sheet lists hazards from the shielding gases themselves (argon and helium can quietly displace oxygen in a confined space) alongside process-generated gases such as nitric oxide, carbon monoxide and ozone, and calls for ventilation and PPE controls to manage them. Quick Note: Acute exposure to welding fume can cause eye, nose and throat irritation, dizziness and nausea, while prolonged exposure may cause lung damage and cancer. That is OSHA’s warning, not shop folklore, and it applies to “clean” TIG work too, since fume comes from the base metal, coatings and the arc’s own reactions. PPE and Ventilation, Summarized Arc protection: auto-darkening helmet with the right shade, safety glasses under it, hearing protection when grinding. Body protection: flame-resistant jacket and sleeves, cuff-length leather gloves (thin enough for filler-rod control, still rated for the heat), no synthetic fabrics exposed. Air: local exhaust or fume extraction positioned at the arc, supplemented by general shop ventilation; in confined spaces, test oxygen first and never rely on argon’s invisibility to warn you. Gas handling: secure cylinders, check regulators and hoses, and buy from suppliers who document gas purity and handling, as covered in guides like AllGas Welding Supply: Gases, Services & Safety Guide. Quick-Start TIG Settings by Material Thickness These are starting points for a 3/32-inch electrode on clean, fit-up-ready material, not a substitute for a written WPS: Material Thickness Typical Amps Notes Mild steel (DCEN) 1/16 in (1.6 mm) 40–60 A Short arc length, fast travel Mild steel (DCEN) 1/8 in (3.2 mm) 80–120 A 1 A per 0.001 in baseline Mild steel (DCEN) 3/16 in (4.8 mm) 110–160 A Preheat if restrained or cold Stainless 304 1/8 in (3.2 mm) 70–100 A Run hotter, then move faster to avoid tint Aluminum 6061 (AC) 1/8 in (3.2 mm) 110–150 A Clean with Aluminum Cleaner for Welding: How to Prep Aluminum Right Copper / brass 1/8 in (3.2 mm) 120–180 A Helium blend or preheat helps Titanium (DCEN) 1/16 in (1.6 mm) 40–70 A Full back purge, no compromises Amperage is only the entry point. GTAW is a low-deposition, high-skill process chosen for precision work rather than heavy plate production, which is why the fine adjustments, not the raw setting, decide the result. That is exactly what Aerospace TIG Welding: Standards, Techniques, and Training emphasizes: procedure control over brute heat. The Core Answer: What Temperature Is TIG Welding? The arc column sits in a published range of roughly 10,000 to 30,000°F, hot enough to keep argon ionized and the tungsten intact at its 3,422°C melting point. The weld pool never needs to match that: it melts only as far as the base metal’s melting point requires, about 2,500°F for steel and about 1,220°F for aluminum. Between those sits the heat-affected zone, which never melts but still changes. And your only real lever over all three zones is heat input, calculated from amps, volts and travel speed, not read off a dial. Set amperage from thickness, then correct with travel speed, arc length and weave. Check your preheat and interpass temperatures with a real instrument, not color judgment. Watch the heat-affected zone: slow it down with chill blocks or faster travel when grain growth matters. Ventilate and extract fume at the arc, every time, regardless of how clean the joint looks. When a job demands repeatable temperature control, invest in training rather than guesswork. That final point is where welders separate themselves from trial and error. Knowing the temperature you are creating, where it goes, and how to verify it is the whole difference between the apprentice in our opening story and a welder who can dial in the same joint the next morning. Frequently Asked Questions How hot is a TIG welding arc really? Published figures for the GTAW arc range from roughly 10,000°F to 30,000°F (about 5,500–16,600°C), with some physics references quoting peak values near 35,000°F. The exact number depends on the arc region measured, current, electrode diameter and shielding gas. Is TIG hotter than MIG welding? Both processes produce arcs in a similar high range — often cited around 6,000–10,000°F for typical MIG arcs and higher for TIG’s constricted arc core. TIG’s real advantage is control: concentrated heat, low spatter and adjustable heat input rather than raw peak temperature. What temperature does the TIG weld pool reach? The puddle only needs to reach the melting point of the base metal — about 2,500°F for mild steel and roughly 1,220°F for aluminum. The far higher arc temperature is what allows rapid, deep melting at the arc root. What is the correct preheat temperature before TIG welding? It depends on the code, material and thickness. AWS D1.1 tables set minimum preheat and interpass temperatures (commonly 150°F in prequalified joints), while aluminum is typically preheated to 175–200°C (347–392°F) and thick magnesium to a maximum of 150°C. How do I calculate heat input when TIG welding? Use Heat Input (J/in.) = (Voltage × Amperage × 60) ÷ Travel Speed in inches per minute. Divide by 1,000 for kJ/in. Because travel speed sits in the denominator, slowing down increases heat input sharply. Why is my TIG weld overheating and blowing through thin metal? Usually amperage is too high for the thickness, travel speed too slow, or arc length too long (which raises voltage and heat input). Reduce amps, shorten the arc, move faster, or use pulsed TIG to cut average heat. What interpass temperature is too high for stainless steel? Excessive interpass temperature promotes carbide precipitation and loss of corrosion resistance in austenitic stainless. Weld stainless cooler and faster, control heat input, and follow your WPS limits — many procedures cap interpass around 300–350°F (150–175°C). How do I measure weld and preheat temperature accurately? Use calibrated infrared pyrometers or contact thermometers for preheat and interpass checks, temperature-indicating crayons for quick verification, and thermocouples or thermal cameras for research-grade cooling curves. Clean the surface first — shiny or oxidized metal skews infrared readings. TOPICS: TIG Welding Procedure Inspection NH Nicholas Harper Editorial Team Covering welding processes, equipment selection, and shop-floor practice for WeldZen — with every claim checked against the governing code. Share this technical standard COPY LINK Related Studies Field Study Hot Plate Plastic Welding: How It Works and How to Do It Oct 25, 2026 · 55 min Buying Guide Argon Welding Tank Sizes: Complete Guide to Choosing the Right Cylinder Oct 25, 2026 · 44 min Safety How to Connect PVC Pipe to Copper Pipe Without Welding Oct 25, 2026 · 51 min Technical Dispatch Get The Next Benchmark First New field studies and calibration sheets, once a week. No spam. Email address Subscribe