Welding of stainless steel to mild steel/ Carbon steel/ Low alloy steel
Dissimilar metal welding (DMW)
Dissimilar metal welding (DMW) is frequently used to join stainless steels to other materials. This approach is most often used where a transition in mechanical properties and/or performance in service are required. For example, austenitic stainless-steel piping is often used to contain high-temperature steam in power generation plants. Below a certain temperature and pressure, however, carbon steels or low alloy steels perform adequately, and a transition from stainless to other steels is often used for economic purposes (carbon steel, or low-alloy steel, is much less expensive than stainless steel).
Welding of stainless steel to mild steel/ Carbon steel/ Low alloy steel (Temperature upto 600 °F (315 °C)
The most common Electrode/ filler wire used to join stainless steel or duplex stainless steel to mild steel is E309L/ ER309L for normal temperature service. For high temperature Nickel base consumables are preferred.
Here E309L, ENiCrFe-2, ENiCeFe-3 & ENICrMo-3 are SMAW Consumables. Their equivalent for TIG/ MIG shall be: ER309L, ERNiCr-3 & ERNiCrMo-3.
The table below shows the combination of various dissimilar welding combination between stainless, duplex stainless steel & carbon steel and Cr-Mo steels.
When joining dissimilar ferritic steels (P-No. 1 though P-No. 5), the filler metal shall conform to the nominal chemical composition of either base metal or an intermediate composition. However, when attaching non-pressure parts to pressure parts, the filler metal chemical composition shall match the nominal chemical composition of the pressure part.
When joining ferritic steels (P-No. 1 through P-No. 5 and P-No. 15E) to:
- a) martensitic stainless steels (P-No. 6); or
- b) ferritic stainless steels (P-No. 7); or
- c) austenitic stainless steels (P-No. 8), the filler metal shall be selected based on the following criteria:
1) Type 309 and Type 309L may be used for design temperatures not exceeding 600 °F (315 °C. For higher temperatures Nickel base welding consumables are preferred.
Welding of Mild steel or low alloy steel (P1, P3, P4 & P5) to Stainless steels (P6, P7 & P8) for high temperature applications
Nickel-base alloy filler materials may be selected using design conditions shown in Table below:
The Schaeffler diagram is useful in providing a microstructure approximation for dissimilar metal welds, since stainless steels, carbon steels, and low-alloy steels can be plotted on the diagram, and microstructure predictions can be made for all of these steels.
Watch this interactive video on Schaeffler Diagram and its practical uses: