Choosing the Right Filler Metal for Welding S355J2 and S690QL
This is my first post on Weld Feed. After a lot of persistent suggestions to write some blog content now and then, I finally decided to roll up my sleeves and give it a go.
I can say that I decided to write this post after seeing the incorrect responses to a poll I did on LinkedIn a few weeks ago—the poll was actually on the very topic that’s now the title of this post.
Material Properties
S355J2 and S690QL are steels with distinct mechanical properties and application areas:
S355J2
- Yield Strength: ~355 MPa
- Tensile Strength: 490-630 MPa
- Commonly used in low-cost structural applications.
S690QL
- Yield Strength: ~690 MPa
- Tensile Strength: 770-940 MPa
- Designed for applications requiring high strength.
The most commonly encountered brands include:
- SSAB: Strenx 700 (formerly Weldox 700), Domex 700, Optim 700QL
- ThyssenKrupp: N-A-XTRA 70
- ArcelorMittal: Ultra 700, Amstrong 700
The significant strength difference between these two steels is a critical factor to consider in designing the welded joint. After welding, the structure under load is generally limited by the mechanical properties of the weakest material in the joint.
Filler Metal Options
The selection of filler metal for welded joints impacts both the mechanical properties of the joint and economic considerations. For joining S355J2 and S690QL, three commonly used filler metals are examined:
- ER110S-G (SFA/AWS A5.28)
Yield Strength: ~760 MPa
Tensile Strength: 830-930 MPa
Applications: Welding of high-strength steels.
Advantages
- Matches the strength of S690QL.
- Provides high strength in the weld zone.
Disadvantages
- Costly option.
- May offer excessive strength relative to S355J2, potentially leading to economic inefficiency.
Suitability:
- ER110S-G can be considered if cost is not a primary concern or is deemed irrelevant. This filler metal is particularly suitable for applications where the performance and reliability of the weld are prioritized, and substituting S355J2 with another material is not an option. Additionally, it is the preferred choice for welding S690QL to itself, ensuring compatibility with its mechanical properties and performance requirements.
- ER70S-6 (SFA/AWS A5.18)
Yield Strength: ~470 MPa
Tensile Strength: 550-620 MPa
Applications: Welding of low- to medium-strength steels.
Advantages
- Provides mechanical properties compatible with S355J2.
- Economical option.
- Ensures homogeneous welds.
Disadvantages
Does not match the high strength of S690QL.
Suitability:
Best choice if the structural design limits are based on S355J2’s properties.
- ER309L (SFA/AWS A5.9)
Yield Strength: ~350 MPa
Tensile Strength: ~520 MPa
Applications: Welding of stainless steel to carbon steel (dissimilar joining).
Advantages
- Capable of joining dissimilar steels.
- Provides high corrosion resistance.
Disadvantages
- Limited strength.
- More expensive than ER70S-6.
Suitability
- Typically used when one of the steels (e.g., S355J2 or S690QL) needs to be joined with a stainless steel such as 304L. Not ideal for this case.
Conclusion and Recommendations
The selection of filler metal for welding S355J2 and S690QL depends entirely on design requirements and expected post-weld loading conditions. Considering the strength difference between these two steels:
- ER70S-6: The most suitable and economical choice if the loading is limited by S355J2’s strength. Using a higher-strength filler metal would be unnecessary since the joint’s capacity will already be constrained by S355J2.
However, a critical point to emphasize is the management of the thermal regime during welding. When selecting consumables suited for low-strength steel, it is essential to strictly control key parameters such as heat input and interpass temperature, aligning them with the requirements of S690QL. This ensures that the thermal cycle does not compromise the mechanical properties of the high-strength steel and prevents issues such as excessive softening or cracking in the weld zone.
Discussion