Steel is a cornerstone material in manufacturing, construction, and industrial applications, and metal welding is one of the most essential processes for joining steel components. However, not all steels behave the same during welding.
In this article, we delve into three common grades of steel—1018, 1045, and 4140—and explore their differences in welding behavior, best practices, and recommended precautions.
Introduction to Steel Grades
Before diving into the welding specifics, it’s important to understand the composition and characteristics of each of these steel grades:
1018 Steel
- Type: Low carbon steel (also known as mild steel)
- Carbon Content: ~0.18%
- Key Properties:
- Excellent weldability
- Good machinability
- Moderate strength
- Easily cold formed and machined
1045 Steel
- Type: Medium carbon steel
- Carbon Content: ~0.45%
- Key Properties:
- Higher strength and hardness than 1018
- Moderate weldability
- Requires preheat and post-weld treatment
4140 Steel
- Type: Alloy steel (chromium-molybdenum steel)
- Carbon Content: ~0.40%
- Alloying Elements: Chromium (~0.8–1.1%), Molybdenum (~0.15–0.25%)
- Key Properties:
- High strength and toughness
- Wear resistance
- Poor weldability without preheat/post-heat
- Commonly heat-treated (quenched and tempered)
Weldability Overview
| Property | 1018 Steel | 1045 Steel | 4140 Steel |
|---|---|---|---|
| Carbon % | ~0.18% | ~0.45% | ~0.40% |
| Weldability | Excellent | Moderate | Difficult |
| Preheat Requirement | None | Yes (100–300°C) | Yes (200–400°C) |
| Post-Weld Heat Treat | Not required | Recommended | Required |
| Cracking Risk | Low | Moderate | High |
1. Welding 1018 Steel
Characteristics:
1018 is one of the easiest steels to weld due to its low carbon content. It responds well to both MIG (GMAW), TIG (GTAW), and Stick (SMAW) welding processes.
Welding Considerations:
- Preheat/Postheat: Not required under normal conditions.
- Filler Material: ER70S-6 (for MIG/TIG) or E7018 (for Stick)
- Weld Appearance: Clean, minimal porosity
- Shielding Gas: 75% Argon / 25% CO₂ (for MIG)
Advantages:
- Excellent ductility and toughness post-welding
- Little to no risk of cracking
- Minimal residual stress
Common Applications:
- Structural components
- General fabrication
- Furniture and frames
2. Welding 1045 Steel
Characteristics:
1045 steel contains more carbon than 1018, offering greater hardness and strength, but it also presents a higher risk of cracking during welding.
Welding Considerations:
- Preheat: Required to reduce thermal shock and prevent cracking (typical range: 200–300°C)
- Post-Weld Heat Treatment: Recommended to relieve stress and restore mechanical properties
- Filler Material:
- ER70S-6 or ER80S-D2 (for MIG/TIG)
- E7018 (for Stick)
- Shielding Gas: Same as 1018
Precautions:
- Avoid welding in a cold environment
- Ensure slow cooling post-welding (e.g., with a welding blanket)
- Use stringer beads instead of weaving for better control
Potential Issues:
- Formation of hard, brittle microstructures in the heat-affected zone (HAZ)
- Risk of cold cracking if not properly preheated
Common Applications:
- Shafts
- Gears
- Bolts and axles
3. Welding 4140 Steel
Characteristics:
4140 is a chromium-molybdenum alloy steel valued for its exceptional strength and hardness, particularly after heat treatment. However, these qualities can make welding more challenging.
Welding Considerations:
- Preheat: Mandatory to prevent cracking (200–400°C depending on thickness)
- Post-Weld Heat Treatment:
- Stress relief at 600–650°C
- Tempering if quenched and tempered beforehand
- Filler Material:
- ER80S-D2 or ER90S-B3 (to match strength)
- E10018-D2 (for Stick)
- Shielding Gas: Argon/CO₂ blend or pure Argon for TIG
Challenges:
- High hardenability increases the likelihood of hydrogen-induced cracking
- Significant heat-affected zone hardness
- Potential loss of heat treatment (tempering) in welded area
Welding Technique Tips:
- Maintain consistent preheat throughout the part
- Minimize interpass temperature fluctuations
- Allow slow cooling under insulation
Common Applications:
- High-stress parts (crankshafts, drive shafts, molds)
- Oil and gas tools
- Heavy machinery components
Welding Process Recommendations
| Process | 1018 Steel | 1045 Steel | 4140 Steel |
|---|---|---|---|
| MIG (GMAW) | Highly suitable | Suitable with preheat | Use with care, pre/post heat needed |
| TIG (GTAW) | Excellent | Good with skilled welder | Difficult, high risk without control |
| Stick (SMAW) | Easy to apply | Common for structural work | Used with pre/post weld procedures |
| FCAW | Applicable | Applicable | Only with proper procedure |
Preheat and Post-Weld Heat Treatment Summary
1018 Steel:
- Preheat: Not needed
- Post-Heat: Not needed
1045 Steel:
- Preheat: 200–300°C
- Post-Heat: Stress relief recommended, 550–650°C
4140 Steel:
- Preheat: 200–400°C depending on thickness
- Post-Heat: Mandatory stress relief at ~600°C, tempering if required
Common Welding Defects and Their Mitigation
| Defect | Cause in 1045/4140 | Prevention Method |
|---|---|---|
| Cold Cracking | High carbon/hard martensite | Preheat, controlled cooling, low-H electrodes |
| Porosity | Contaminants | Clean surface, use dry rods/wire |
| Underbead Cracks | High hardenability | Slow cooling, post-weld tempering |
| Lack of Fusion | Poor technique | Proper travel speed, correct amperage |
Conclusion
Choosing the right steel for welding requires a clear understanding of its chemical composition and how it responds to heat to ensure structural integrity and long-term reliability. Here’s a quick recap:
- 1018 Steel is the most weld-friendly option, ideal for beginners and general-purpose fabrication.
- 1045 Steel offers greater strength but needs preheating and post-weld care to prevent brittleness and cracking.
- 4140 Steel, while highly durable, is the most difficult to weld due to its alloy content and heat treatment sensitivity. It demands careful control of temperature before, during, and after welding.