Welding 1045 Steel: Preheat, Procedures, and Crack Prevention

When a 1-1/2 inch diameter 1045 shaft needs repair welding on heavy equipment, a rushed job without proper preheat can lead to hairline cracks that only appear days later. Understanding the weldability of medium carbon steel is critical to avoiding these costly, dangerous failures.

Introduction to 1045 Steel and Its Weldability

AISI 1045 is one of those steels that shows up everywhere in the real world of maintenance and fabrication. You’ll find it in shafts, axles, gears, sprockets, pins, tie rods, hydraulic rods, hammer handles on equipment, and countless machined parts that need strength but not the cost of an alloy grade

Understanding the Metallurgy: Why 1045 is Prone to Cracking

The biggest difference between welding 1045 steel and common mild steels comes down to its chemistry. With a carbon content between roughly 0.43% and 0.50%, 1045 is classified as a medium carbon steel. While this higher carbon content gives the material excellent strength and wear resistance in its heat-treated form, it also makes it far less forgiving to weld than lower carbon grades. The root of its cracking susceptibility lies in its hardenability, the way it transforms on cooling, and its affinity for hydrogen.

Hardenability and Martensite Formation

Hardenability is simply a steel’s ability to form hard microstructures when cooled at a certain rate. For 1045, its higher carbon content means it has a much greater hardenability than mild steel. When the base metal in the heat-affected zone (HAZ) is rapidly heated to austenitizing temperatures and then cooled quickly, the austenite transforms into martensite.

Martensite is incredibly hard and strong, but also extremely brittle with very little ductility. Rapid cooling can form hard, brittle martensite in the heat-affected zone, creating a localized area that is far more crack-prone than the surrounding base metal. This hardened zone has little ability to accommodate the stresses that come from welding, setting the stage for cracking before any other factors even come into play.

Hydrogen-Induced Cracking: The Hidden Threat

Martensite alone is dangerous, but it becomes even more problematic when combined with hydrogen. Hydrogen embrittlement is a primary concern with medium carbon steels like 1045. Moisture on the base metal, damp electrodes, contaminated flux, or even atmospheric humidity can all introduce hydrogen into the weld pool. As the weld cools, this hydrogen diffuses into the HAZ and weld metal.

When hydrogen finds itself trapped within the brittle martensitic structure under tensile stress, it creates internal pressure at the atomic level. This can lead to hydrogen-induced cracking (also known as cold cracking), which is often delayed. Instead of cracking immediately after welding, these flaws can appear hours, or even days, later. This delayed nature is what makes them so costly and dangerous in repairs on heavy components.

Transformation Temperatures and Cooling Rate

Every steel has critical transformation temperatures where its microstructure changes. For 1045, the key is that its transformation to martensite occurs at relatively fast cooling rates compared to mild steel. Factors that speed up cooling, such as welding thin passes, working in cold environments, or welding without insulation, make martensite formation far more likely.

This is exactly why preheat is necessary. By raising the base metal temperature before welding, preheat slows the cooling rate of the HAZ, giving the austenite more time to transform into softer, more ductile microstructures like ferrite and pearlite instead of brittle martensite. Slowing cooling also allows more time for hydrogen to diffuse out of the weld zone before it can become trapped.

Carbon Equivalent and Real-World Risk Factors

Not all medium carbon steels are created equally, which is why welders rely on carbon equivalent (CE) calculations to help assess cracking susceptibility. The CE takes into account not only carbon, but also other alloying elements like manganese, chromium, molybdenum, nickel, and copper, all of which increase hardenability.

While 1045 doesn’t have heavy alloy additions, its carbon content alone gives it a notably higher CE than A36 mild steel. This higher CE directly correlates to a greater need for controlled cooling.

Beyond chemistry, two other factors drastically raise the risk: thicker sections and higher restraint increase cracking risk. Thicker plates absorb and conduct heat differently, and more importantly, they create larger, stiffer joints that resist contraction. This added restraint generates higher tensile stresses as the weld cools and contracts. Combine that with martensite and hydrogen, and the odds of cracking multiply very quickly.

These metallurgical realities are exactly why, when working with 1045, proper procedure selection matters so much. Even when choosing consumables from resources covering alloy steel welding electrodes, the steel’s own nature will dictate the need for preheat and low-hydrogen practices. For a deeper look into the transformation behavior of steels, references such as the ASM Handbook, Volume 6A provide valuable context for understanding these changes.

Preheat Requirements for Welding 1045 Steel

Preheat is the difference between a 1045 repair that lasts and one that cracks after the machine is back in service. It does two jobs at once: it slows the cooling rate so the heat-affected zone (HAZ) does not transform into brittle martensite, and it gives hydrogen trapped in the weld time to escape before it causes cold cracking.

Because 1045 contains roughly 0.45% carbon—far more than common mild steel—it has much higher hardenability. A fast-cooled weld on 1045 can produce a HAZ harder than many file tests will comfortably cut, even when the weld itself looks sound. Preheat buys the time needed to avoid that outcome. It is not a ritual; it is a metallurgical control.

Recommended Preheat by Thickness

The most widely quoted starting points come from historical Welding Research Council (WRC) data for medium-carbon steels welded with low-hydrogen processes. For 1045, those recommendations look like this:

Thickness	Typical minimum preheat
Up to 1/2 in (13 mm)	About 300°F (150°C)
Over 1/2 in up to 4 in (13–100 mm)	About 400°F (205°C)
Heavy restraint or adverse conditions	392–572°F (200–300°C) depending on the case

Treat these values as floors, not universal recipes. The AWS preheat guide makes clear that preheat depends on carbon equivalent, thickness, restraint, process, and hydrogen level. A thin, free-to-move bracket is not the same problem as a 3-inch shaft keyed into a housing. The 400°F figure is common for heavier sections, but a highly restrained repair may justify the upper end of the 392–572°F range. Use alloy steel welding electrodes with a reputable low-hydrogen classification, and let a qualified procedure—not a shop-floor guess—set the final number.

This is also where code language matters. AWS D1.1 does not list 1045 among its prequalified base metals in many cases, so a fabricator often cannot rely on a generic prequalified joint detail. The AWS D1.1 structural welding code expects a procedure qualification when the base metal falls outside the prequalified envelope. That means the preheat you use should be written down, tested if required, and followed consistently.

Measuring and Maintaining Preheat

Temperature measurement is where good intentions often fall apart. A torch playing over the surface does not prove the part is at temperature. Use calibrated temperature-indicating sticks for quick checks, contact thermocouples for critical work, or a properly set infrared thermometer with an awareness of emissivity error. Infrared guns read surface temperature and can be fooled by scale, shine, and distance. Measure near the weld zone on both sides where possible, and allow thick sections time to soak so the core is not dramatically colder than the skin.

Interpass temperature matters as much as initial preheat. The workpiece should not be allowed to cool below the specified preheat between passes. Keep it covered with insulating blankets, maintain gentle heating, and verify before each pass. Excessive interpass heat is also a problem, so follow the WPS上限 rather than simply “adding more heat.” Controlled warmth is the goal; uncontrolled overheating can coarsen the HAZ and degrade properties.

Beware the shortcuts. The old “add a zero to the carbon content” rule gives 450°F for 1045—not far from common heavy-section practice, but it ignores thickness, restraint, and hydrogen. The “100°F per inch” rule is even rougher and can badly underheat thick parts. ESAB’s guidance on preheating reinforces the point: these are approximations to be adjusted, never a substitute for a procedure matched to the actual joint.

If you remember one thing, remember this: preheat is a controlled variable, not a quick pass with a rosebud. Measure it, maintain it, and document it. The next section explains how to turn that number into a repeatable welding procedure from joint prep through completion.

Selecting the Right Welding Process, Electrodes, and Filler Metal

Once you’ve decided that 1045 needs preheat, the next question is what you’ll actually strike an arc with. This is where a lot of well-intentioned repairs go sideways, because process choice quietly controls two things that matter enormously in medium carbon steel: how much hydrogen gets into the weld, and how fast the joint cools afterward.

Pick the wrong combination and you can preheat perfectly, weld beautifully, and still find cracks under the toe a week later. Pick the right one and the job becomes surprisingly forgiving.

The Core Rule: Low Hydrogen, Moderate Heat Input

Everything in this section comes back to two principles. First, minimize diffusible hydrogen. Second, avoid cooling rates fast enough to transform the heat-affected zone into untempered martensite. Process and filler selection is really just a way of controlling those two variables.

AWS D1.1 treats hydrogen control as a structural requirement rather than a suggestion, and its preheat and electrode conditioning tables are built around exactly this logic (AWS D1.1 Structural Welding Code). For 1045, that logic applies with extra weight because the base metal itself already contributes a lot of carbon to the HAZ.

Shielded Metal Arc Welding (SMAW)

For most 1045 repair work, SMAW with a low-hydrogen electrode is the default answer, and for good reason. It’s portable, tolerant of field conditions, handles dirty or awkward joints better than most

Welding Procedure Steps: From Prep to Completion

A qualified procedure is only as good as its execution. With 1045 steel, small shortcuts in cleaning, preheat, or interpass control can undo an otherwise sound welding plan. The steps below turn the metallurgy and filler-metal choices into a repeatable shop-floor sequence.

1. Clean the Joint and Surrounding Metal

Start with bare, dry steel. Remove oil, grease, rust, mill scale, paint, and moisture from the joint faces and at least one inch of surrounding base metal. Use a dedicated solvent for grease, then grind or wire-brush to bright metal. Do not rely on a quick wipe: oil and moisture are hydrogen sources, and hydrogen

Post-Weld Heat Treatment (PWHT) for 1045 Steel

Post-weld heat treatment is not a automatic finish line for every 1045 weld. It is a deliberate thermal step that solves specific problems: residual stress, hardness, delayed cracking risk, and dimensional movement after machining. On a restrained repair or a thick shaft, skipping it can undo an otherwise sound weld. On a thin, lightly loaded bracket, adding it may create more risk than it removes.

The decision starts with three questions. How thick is the section? How much restraint does the joint see? And what does the applicable code or customer specification require? A 1-inch plate welded into a rigid frame behaves very differently from a free-floating 3/8-inch tab. The first may need stress relief; the second often does not.

When Does 1045 Actually Need PWHT?

PWHT is commonly recommended for 1045 after welding in critical applications, especially where sections are thick, joints are highly restrained, or the part sees fatigue, impact, or precision machining after welding. The same logic applies to repair welds on shafts, pins, and heavy equipment components, where a hard heat-affected zone plus trapped hydrogen is a recipe for delayed cracking.

It is less likely to be necessary on thin sections with low restraint and noncritical service. That does not mean “never” or “always.” Code requirements, thickness, service conditions, and criticality should drive the call. AWS D1.1, for example, ties heat treatment and qualification to specific fabrication and service conditions rather than a single blanket rule, which is why reading the governing specification matters more than following a shop-floor rumor. The AWS D1.1 structural welding code is the place to confirm those requirements.

Stress Relief vs. Tempering vs. Normalizing

These three treatments are often confused, but they do different jobs.

• Stress relief: heats the weldment to a temperature below the lower critical temperature, holds it, and cools slowly. The goal is to relax residual stresses and give hydrogen time to escape, not to change the basic microstructure.
• Tempering: follows hardening. It heats an already hardened part to improve toughness and ductility, with the exact temperature chosen to hit a target hardness. It is a property adjustment, not merely a stress treatment.
• Normalizing: heats above the upper critical temperature and air-cools to refine grain structure and homogenize the microstructure. It is not a substitute for stress relief, and on a finished 1045 part it can introduce distortion and unwanted hardness changes.

For welded 1045, stress relief is the usual concern. Normalizing is a different metallurgical reset and should be specified only when the design actually calls for it.

Temperature Range and Hold Time

For stress relief of 1045 weldments, a common range is 1100–1250°F (593–677°C). The part should be heated uniformly, held long enough for the center of the section to reach temperature, and then cooled slowly. A practical starting point is about one hour per inch of thickness, with a one-hour minimum, though the governing code or procedure qualification may specify otherwise. ESAB’s guidance on preheating and post-weld heat treatments is a useful practical reference for setup and control.

Heating and cooling rates matter as much as the hold temperature. Fast heating can distort a part before it ever reaches the soak; fast cooling can reintroduce residual stress. Furnace cooling, or cooling under insulation, is preferred for critical work. Thermocouples attached to the part give far better assurance than watching a torch flame or trusting an infrared gun on a shiny surface.

What PWHT Buys You — and What It Costs

The benefits are real. Stress relief reduces the risk of delayed cracking and distortion, lowers residual stress around the weld, and can improve toughness in the heat-affected zone. It also makes later machining more predictable because the part is less likely to move when metal is removed.

The trade-off is that PWHT can affect hardness and strength depending on the original condition of the 1045 and the parameters used. A quenched-and-tempered shaft and a normalized bar will not respond identically. The filler metal matters too; select an electrode whose deposited weld metal is compatible with the treatment, as discussed in this guide to alloy steel welding electrodes. The metallurgical background behind these transformations is covered in the ASM Handbook on welding metallurgy.

Finally, document the cycle: heating rate, hold temperature, hold time, cooling method, and the instrument used. A chart recorder or digital log is not bureaucracy. It is the evidence that the procedure actually happened, and it is often the difference between a accepted repair and a disputed one.

Common Welding Defects, Causes, and Troubleshooting

With 1045 steel, most welding defects won’t reveal themselves until after cooling, and some won’t show until days later. Because of its medium carbon content, the margin for error is slim. By focusing on the root causes, most of these flaws can be prevented entirely.

Hydrogen-Induced Cracking (Cold Cracking)

Cold cracking is the most notorious issue with 1045. It forms hours or even days after welding, triggered by the combination of hydrogen, hard martensite, and residual stress. Moisture from damp electrodes, rust, oil, or grease is often the source of that hydrogen, while rapid cooling creates the brittle microstructure that allows it to propagate.

Prevention and correction:

• Consumables: Use low-hydrogen electrodes such as E7018 kept in a holding oven at 250–300°F, or E7015 where DC+ is available.
• Prep: Remove rust, mill scale, grease, and paint from the joint before striking an arc.
• Thermal control: Maintain proper preheat and interpass temperatures, and allow for slow cooling under a blanket.
• Repair: If a crack is found, gouge it out completely to sound metal, re-preheat, and reweld. Never cap over a crack.

Toe Cracks and Underbead Cracks

Toe cracks start at the weld toe, where geometry creates a natural stress riser and cooling is at its fastest. Underbead cracks are even harder to catch, hiding beneath the weld in the coarse-grained heat-affected zone (HAZ). Both are almost always a product of hydrogen paired with a hard, untempered microstructure.

Adequate preheat, controlled interpass temperature, clean low-hydrogen consumables, and a slow cool will address the vast majority of these cases. Grinding the weld toe to create a smooth transition also helps relieve stress concentration. For hydrogen control, the filler metal matters just as much as technique, and a refresher on alloy steel welding electrodes can help match the classification to your base metal and service conditions.

Excessive HAZ Hardness

Without preheat, rapid cooling of 1045 will transform austenite into martensite, often pushing coarse-grained HAZ hardness above 400 HV. This brittle martensite is far more prone to cracking when pulled by weld shrinkage.

Hardness can be managed by keeping heat input moderate and consistent, with a weave no wider than about three electrode diameters. Where specifications call for it, post-weld tempering is the most reliable way to restore ductility. The ESAB guide to preheating and post-weld heat treatment does an excellent job of laying out the link between cooling rate, hardness, and cracking risk.

Porosity and Lack of Fusion

Porosity on 1045 is typically tied to contamination. Damp electrodes, dirty base metal, a compromised gas supply, or poor shielding can all trap gas, and with 1045’s quick freeze time, there’s little opportunity for it to escape.

Lack of fusion, on the other hand, is almost always a technique issue. Since medium carbon steel conducts heat away from the arc rapidly, traveling too fast or running too low of an amperage can fail to melt the sidewall. Slowing travel, using correct amperage, and pausing briefly at the toes will correct most cases. If either defect is found, it must be gouged out and rewelded, as neither can be reliably fused over.

Distortion and Residual Stress

Heavily restrained parts, such as shafts and brackets, are especially vulnerable to distortion on 1045. As the weld shrinks, that force has nowhere to go, locking in residual stress that can directly feed cracking. Balanced weld sequences, the backstep technique, proper fixturing, and preheat all help mitigate this. Most importantly, slow, controlled cooling takes a large amount of that stress out of the equation.

For a broader look at how filler and process selection impact defect risk, the ASM Handbook volume on welding fundamentals is a solid reference.

Ultimately, troubleshooting 1045 comes down to discipline. Trace any defect back to one of three roots: hydrogen, hardness, or restraint. Fix that root, and you’ll give your weld the best chance to hold for good.

Practical Tips, Code Considerations, and Real-World Advice

Everything covered so far tells you what 1045 needs in theory. The real world adds variables: codes, inspectors, cold weather, unknown base metal history, and the pressure to get a machine back in service by morning. This section is about closing the gap between a good procedure and a job that actually passes inspection.

Code Compliance: 1045 Is Usually Not Prequalified

Here is the first thing many fabricators learn the hard way. Under AWS D1.1, prequalified joint details apply only to the base metals listed in the code, and medium-carbon steels like 1045 generally fall outside that list. That means you cannot simply grab a generic WPS and start welding. You typically need a procedure qualification record backed by tensile and bend testing, or at minimum a WPS supported by existing qualification data that your engineer and inspector accept.

The essential variables matter enormously: preheat and interpass temperature, heat input, filler metal classification, and joint design. Change any of them outside the qualified range and the paperwork no longer covers the work. On structural or pressure-retaining repairs, budget for qualification before you strike an arc. It is far cheaper than cutting out a rejected weld.

Thickness Changes Everything

A 3/8-inch bracket and a 3-inch shaft are not the same problem. Thick sections conduct heat away quickly, increase restraint, and raise the risk of a hard, crack-prone heat-affected zone. They need more preheat, more careful interpass control, and often a post-weld stress relief. Thin sections can sometimes be welded with modest preheat, but they bring their own trap: it is easy to overheat them and lose toughness.

Match your preheat to the thickest part of the joint, not the average. When a thin plate is welded to a heavy forging, the forging governs.

Welding 1045 to Mild Steel

Dissimilar joints such as 1045 to A36 are common in repair work, and they are manageable with the right approach. Dilution from the mild steel side lowers carbon content in the weld pool, which helps, but the 1045 side still forms a hardened HAZ. Govern preheat by the 1045 component, use a low-hydrogen electrode such as E7018, and consider buttering the 1045 face before making the final joint on highly restrained work. Filler selection deserves real thought; our guide to alloy steel welding electrodes walks through matching strength and hydrogen control.

Repair Welding: The Highest-Risk Scenario

Repair work concentrates every hazard. The part may have seen years of service, unknown prior welds, or subsurface cracks. Clean the area to bare metal, inspect with magnetic particle testing before welding, and remove defects completely rather than welding over them. Gouge or grind out cracks to sound metal with a gentle profile, preheat the whole repair zone, and verify temperature on the far side of the section. After welding, re-inspect. A shaft repair that passes visual inspection can still hide a toe crack that opens under load.

Field vs. Shop Practice

In the shop you have ovens, positioners, and stable ambient conditions. In the field you have wind, rain, and a January morning. Cold ambient air accelerates cooling and effectively reduces your preheat, so the temperature you measured at the start may not hold through the pass. Build an enclosure, use blankets, block the wind, and check interpass temperature with a calibrated device rather than guessing. The AWS preheat guidance is a useful reference for thinking about heat flow and measurement rather than relying on feel.

Practical Habits That Pay Off

• Write the preheat, interpass, and heat input limits on the WPS and keep a copy at the joint.
• Calibrate temperature measurement tools and record readings, especially on code work.
• Keep low-hydrogen electrodes in a holding oven; a damp rod undoes a good preheat.
• Document repairs with photos and inspection results, not just a verbal handover.
• When in doubt about a procedure, qualify it. Experience is valuable, but it is not a substitute for testing.

Field experience and published guidance agree on one point: 1045 rewards preparation and punishes shortcuts. Treat the code, the thickness, and the environment as part of the weld, and the metallurgy will cooperate.

Conclusion: Keys to Successful 1045 Steel Welds

At the end of the day, welding 1045 steel isn’t about forcing it to act like mild steel. It’s about respecting the fact that its medium carbon makeup drastically changes how it reacts to heat. Every step that has been covered throughout this guide all funnels down to one goal: controlling the cooling rate from the moment the arc is struck, all the way to a fully stable, stress-relieved weld.

Without that control, the heat affected zone is far too susceptible to forming hard, brittle martensite, opening the door for the dreaded hydrogen-induced and transformation cracks that have plagued this grade for decades.

Respect the Metallurgy First

Before any amperage is set, the most important tool is an understanding of why this steel is finicky to begin with. As noted by Get Metals, AISI 1045 carries a carbon content high enough to greatly increase its hardenability compared to low carbon steels. This is exactly what makes adequate preheat and post-weld practices the difference between a sound joint and a failure. For thicker sections, references such as the AWS Preheat Guide should be used to determine appropriate values, rather than relying on blanket sayings such as “100°F per inch”.

Clean, Dry, and Low-Hydrogen

Controlling the cooling rate is only half of the battle. Moisture is one of the biggest contributors to cracking with this grade, which is why low-hydrogen consumables and proper storage are non-negotiable for many applications. Electrodes, such as the low-hydrogen options found within any proper selection of alloy steel welding electrodes, must be kept in a rod oven and only taken out as needed. Any consumable that has been exposed to shop humidity for an extended period should be reconditioned or replaced. These small habits take minutes, yet prevent some of the hardest to detect underbead cracks.

Control Cooling and Consider PWHT

Successful 1045 welding hinges on controlling cooling rate through preheat and post-weld practices. Maintaining a proper minimum interpass temperature, utilizing insulated blankets to slow cooling, and avoiding any unnecessary exposure to cold air or wet surfaces will go a long way in preventing martensitic hardening. For highly restrained joints, thick sections, or code driven repairs, Post-Weld Heat Treatment (PWHT) for stress relief in the range of roughly 1100-1250°F (593-677°C), as outlined by ESAB, can drastically improve toughness and relieve dangerous residual stresses.

Follow Qualified Procedures, Not Guesswork

No two 1045 repairs are identical. Joint restraint, thickness, service loading, and applicable codes all play a massive factor in what is acceptable. When in doubt, consult a qualified WPS, or reference authoritative standards such as AWS D1.1/D1.1M for projects that fall under its scope. This isn’t a matter of being overly cautious, but of ensuring the weld is fit for the load it’s designed to carry.

Most importantly, prevention of cracking is far more reliable than attempting to repair after cracking occurs. Grinding out a tight, hydrogen induced crack is often a deceptive fix, as micro-cracks can extend far past what is visible to the naked eye, and re-welding without correcting the original cause will almost always reintroduce the same problem.

So, keep it simple: understand the metallurgy, use adequate preheat for your thickness, employ and properly store low-hydrogen consumables, control your cooling, consider PWHT when the conditions call for it, and follow qualified procedures. Do those things consistently, and you’ll find that 1045 steel, while demanding, can be welded to produce strong, reliable, and long lasting joints.

Frequently Asked Questions

Do I need to preheat 1045 steel before welding?

In most cases yes, especially for sections over 1/4 inch or when using higher restraint. For 1045 (0.45% carbon), preheat is typically recommended around 300-400°F depending on thickness, welding process, and hydrogen levels. Thin sections with low-hydrogen processes may need less, but skipping preheat increases cracking risk significantly.

What is the recommended preheat temperature for 1045 steel?

Recommendations vary by source, but common guidance based on WRC/Stout data suggests ~300°F for thicknesses up to 1/2 inch and ~400°F for thicknesses from 1/2 inch to 4 inches when using low-hydrogen electrodes. Some practical sources recommend 200-300°C (392-572°F). Always follow a qualified welding procedure if available.

Can you weld 1045 steel without preheat?

Welding very thin sections of 1045 with low-hydrogen electrodes and minimal restraint might be attempted in some cases, but it is generally not recommended. The risk of hydrogen-induced cracking and hard martensite formation in the HAZ is high due to 1045’s medium carbon content and good hardenability.

What electrodes should I use to weld 1045 steel?

Low-hydrogen electrodes such as E7018 or E7015 are strongly recommended. These minimize diffusible hydrogen which is a major contributor to cold cracking in medium carbon steels like 1045. Proper storage and baking of low-hydrogen electrodes is essential for best results.

Is post-weld heat treatment necessary for 1045 welds?

Not always mandatory, but often beneficial for critical applications. Stress relief between 1100-1250°F (593-677°C) is commonly recommended to reduce residual stresses and lower cracking risk. PWHT requirements depend on service conditions, codes (like ASME/AWS), thickness, and the criticality of the weld.

Is 1045 steel prequalified for welding under AWS D1.1?

Generally no – AISI/SAE 1045 is not listed in AWS D1.1 Table 3.1 as a prequalified base metal in most editions. This means welding procedures for 1045 often need to be qualified per AWS D1.1 Section 4 unless an applicable code provides different provisions. Always check the current code edition being used.

Why does 1045 crack after welding even if it looks fine?

This is typically hydrogen-induced (cold) cracking. Hydrogen can diffuse into the weld and HAZ, and combined with high hardness from rapid cooling and tensile stresses, cracks can form hours or even days after welding. Adequate preheat, low-hydrogen consumables, proper cleaning, and slow cooling help prevent this delayed cracking.

Can I weld 1045 to mild steel (A36)?

Yes, but it requires careful procedure development. The higher carbon/hardenability of 1045 drives the preheat and hydrogen control needs. Often the procedure must be based on the more hardenable material (1045). Use low-hydrogen electrodes and follow preheat requirements appropriate for 1045 and the thickness/restraint of the joint.

What happens if I don’t preheat thick 1045 steel?

Without adequate preheat, thick sections cool rapidly creating a hard martensitic microstructure in the HAZ. This makes the steel brittle and highly susceptible to cracking under weld stresses. Cracks may appear immediately or be delayed (cold cracking), potentially leading to catastrophic failure in service.

Is the ‘carbon content times 100’ preheat rule accurate for 1045?

This is a very rough approximation (suggesting ~450°F for 0.45%C) and should not be used as the sole basis for critical work. Factors like thickness, alloying elements, restraint, hydrogen level, and cooling rate all affect required preheat. Authoritative references (WRC/Stout data, qualified WPS, applicable codes) should guide the actual temperature.