Welding 1045 Medium Carbon Steel: Preheat, Filler Selection & HAZ Control

1045 steel contains 0.43-0.50% carbon, which puts it squarely in the “weldable with precautions” category. Skip the preheat or use high-hydrogen consumables and the heat-affected zone forms hard, brittle martensite that cracks under residual welding stress. Follow the right procedure and 1045 welds reliably for shafts, gears, axles, and machine components.

The jump from 1018 to 1045 is a big one in welding terms. That extra 0.27% carbon triples the hardenability. The HAZ on 1045 can reach 55-60 HRC (Rockwell C) under fast cooling conditions, which is harder than a file. At that hardness, the microstructure is almost entirely untempered martensite, and it’ll crack before you finish the weld if you don’t control the thermal cycle.

1045 Composition and Metallurgy

The carbon equivalent (CE) of 1045 runs 0.55-0.65, well above the 0.45 threshold where hydrogen cracking becomes a serious concern. Every weld on 1045 needs to address three things: preheat to slow cooling, low-hydrogen filler to minimize diffusible hydrogen, and controlled cooling or PWHT to temper any martensite that does form.

What Happens in the HAZ

When you weld 1045, the base metal adjacent to the fusion line heats above its critical temperature (roughly 1350F for 1045) and transforms to austenite. As that zone cools, the austenite transforms to either soft pearlite/ferrite (slow cooling) or hard martensite (fast cooling). The cooling rate depends on material thickness, preheat temperature, heat input, and ambient conditions.

Without preheat, a 1/2-inch section of 1045 cools fast enough to form nearly 100% martensite in the HAZ. That martensite has high residual stress, zero ductility, and a strong tendency to crack. With a 400F preheat, the same section cools slowly enough to form a mixed microstructure of bainite, pearlite, and only partial martensite. That’s far more ductile and crack-resistant.

Preheat Requirements

Preheat is mandatory on 1045. The temperature depends on section thickness, joint restraint, and filler hydrogen level.

How to preheat properly:

1. Heat the area 3 inches on each side of the joint using a rosebud (multi-orifice) torch or an electric resistance heating pad.
2. Measure temperature on the side opposite the heat source to ensure through-thickness heating, not just surface temperature.
3. Use temperature-indicating crayons (Tempilstik) or contact thermocouples. Don’t guess.
4. Maintain preheat as minimum interpass temperature throughout welding. If the piece cools below preheat between passes, reheat before welding again.

Filler Metal Selection

The filler for 1045 must be low-hydrogen. Period. High-hydrogen consumables (E6013, E6010) introduce diffusible hydrogen into a HAZ that’s already crack-prone from high hardenability. That combination is the recipe for delayed hydrogen cracking.

Stick Electrodes

E7018 is the baseline choice. Low-hydrogen coating (H4-H8 designation), 70 ksi tensile deposit, smooth arc. For most 1045 repair and fabrication, 7018 provides adequate strength. The weld metal won’t match 1045’s heat-treated strength, but that’s acceptable for many applications.

E8018-C1 provides 80 ksi tensile and is the better match when welding 1045 in the quenched-and-tempered condition. The 1% nickel content improves toughness in the weld metal.

E11018 and higher-strength electrodes match Q&T 1045’s full strength range but require even more careful hydrogen control and preheat. These are specialist rods for specific engineering applications.

Critical: Keep all 7018 and 8018 rods in a holding oven at 250-300F after opening the hermetically sealed container. Exposed rods absorb moisture within hours. Moisture in the flux coating is the primary source of diffusible hydrogen in stick welding. If rods have been exposed to ambient air for more than 4 hours, re-bake at 700-800F for 1-2 hours before use.

MIG Wire

ER70S-6 is usable for non-critical 1045 welding. Solid MIG wire inherently has very low hydrogen levels (typically under H4) because there’s no flux to absorb moisture. This is an advantage over stick welding on hydrogen-sensitive steels.

ER80S-D2 provides 80 ksi tensile strength and better matches the properties of heat-treated 1045. It contains ~0.50% molybdenum for improved high-temperature strength and toughness.

Run 75/25 argon/CO2 or straight CO2. Straight CO2 provides deeper penetration but slightly higher hydrogen levels from the CO2 decomposition. For critical work, 75/25 is the safer choice.

TIG Rod

ER70S-2 or ER80S-D2 depending on strength requirements. TIG has the lowest hydrogen potential of any arc welding process because there’s no flux and the argon shielding is completely inert. This makes TIG a good process choice for 1045 when the application allows it.

Welding Procedure Step-by-Step

1. Identify the Condition

Before welding 1045, determine if it’s hot-rolled, normalized, or quenched-and-tempered (Q&T). Ask the customer or check drawings. If unknown, a hardness test tells you: 170 BHN is hot-rolled/normalized, 250+ BHN is heat-treated. Q&T material is harder to weld because the HAZ will have even more dramatic property changes.

2. Joint Preparation

Grind or machine the weld joint clean. Remove all surface contamination, rust, and scale. On thick sections, bevel to a 60-degree included V-groove with a 1/16 inch root face and 1/16 inch root opening. Tight fit-up reduces the volume of weld metal needed, which reduces heat input and shrinkage stress.

3. Preheat

Heat per the chart above. Verify temperature. Don’t start welding until through-thickness preheat is confirmed.

4. Weld

Run stringer beads only. No wide weaving patterns. Keep heat input moderate; high heat input doesn’t help and actually expands the HAZ. Short arc length on stick (one rod diameter or less). For MIG, use short-circuit transfer on thinner material and spray transfer on thicker sections with multiple passes.

Use a backstep or skip welding sequence to distribute heat and minimize distortion. On shafts, weld a short section, rotate 180 degrees, weld the opposite side, then fill in the gaps.

5. Post-Weld Cooling

Do not let the part cool rapidly. After welding, maintain the preheat temperature for at least 1 hour per inch of thickness. Then slow cool by wrapping the part in ceramic fiber blanket, burying in dry sand, or placing in a furnace set to preheat temperature and shutting it off.

Forced air cooling, water quenching, or setting the part on a steel bench to cool are all ways to crack a 1045 weld. Slow cooling gives hydrogen time to diffuse out and allows partial tempering of any martensite in the HAZ.

Post-Weld Heat Treatment (PWHT)

PWHT isn’t always required on 1045, but it significantly improves joint reliability. The decision depends on the application.

When PWHT is required:

• Q&T 1045 being restored to service at original strength levels
• High-cycle fatigue applications
• Parts that will see impact loading
• Code-governed pressure or structural applications

Standard PWHT for 1045:

• Stress relief: 1100-1200F for 1 hour per inch of thickness, furnace cool
• Full re-temper (Q&T material): Match the original tempering temperature from the material spec

When PWHT can be skipped:

• Non-critical repairs on hot-rolled 1045
• Low-stress applications
• When the weld is in a low-load area

Without PWHT, the HAZ on 1045 retains some as-welded hardness (typically 35-50 HRC depending on cooling rate and preheat). That hardness won’t increase over time, but it does create a residual stress pattern that reduces fatigue life. PWHT softens the HAZ martensite to tempered martensite (much more ductile) and reduces residual stress by up to 80%.

Hydrogen Cracking on 1045

Hydrogen cracking (also called cold cracking or delayed cracking) is the primary weld failure mode on 1045. It requires three simultaneous conditions:

1. Hydrogen - Diffusible hydrogen in the weld zone from consumable moisture, contamination, or ambient humidity
2. Stress - Residual tensile stress from welding shrinkage and joint restraint
3. Susceptible microstructure - Hard martensite in the HAZ (above roughly 350 HV / 35 HRC)

Eliminate any one of these three and cracking won’t occur. A good 1045 welding procedure attacks all three:

• Low-hydrogen consumables with proper storage reduce hydrogen
• Preheat and slow cooling reduce HAZ hardness and allow hydrogen to diffuse out
• Joint design and welding sequence minimize restraint and residual stress

Hydrogen cracks are insidious because they often don’t appear until 24-72 hours after welding. Inspect 1045 welds at least 48 hours after completion. For critical applications, use magnetic particle inspection (MPI) on the completed weld after the hydrogen waiting period.

Common Mistakes on 1045

Skipping preheat. The number one cause of cracked 1045 welds. “It’s just carbon steel” is how shops justify it, right before the repair cracks.

Using E6013 or E6010. These are not low-hydrogen electrodes. On 1045, they introduce hydrogen into a HAZ that’s already susceptible to cracking. Always use E7018 or better.

Welding in the quenched condition without identifying it. Q&T 1045 at high hardness is dramatically harder to weld than hot-rolled 1045. The HAZ is more crack-prone, and the property mismatch between weld metal and base metal is larger. Always check hardness before welding 1045 of unknown history.

Rapid cooling after welding. Setting a hot 1045 part on a steel table or in a draft accelerates cooling and promotes martensite formation. Wrap it up, slow it down.

Welding over fatigue cracks without proper prep. On shafts and rotating components, you must excavate the entire crack before welding. Grinding a groove, checking with dye penetrant to confirm complete crack removal, and then filling with weld metal is the correct approach. Welding over a crack just buries it.

1045 isn’t as forgiving as 1018 or A36, but it’s completely weldable with the right discipline. Preheat, low hydrogen, and slow cooling are the three pillars. Skip any one and expect cracks.