The Weldability of Stainless Steel

Types of Stainless Steel

Austenitic

We carry: 301, 302, 303, 304, 316, 321, 347, N50 and N60

This class of stainless steel is highly corrosion-resistant, strong, and highly formable. But it is also prone to stress cracking. These are considered the most easily weldable stainless steel. There is no need for pre- or post-weld heat treatment.

Austenitic alloys are normally welded with fillers with matching composition to the base material. There are a few exceptions though; 308 filler is used for alloys 302 and 304, and type 347 filler used for 321.

Ferritic

We carry: 430

All ferritic alloys are in the 400 family, but not all 400s are ferritic. They have lower ductility, are more brittle, prone to hot cracking, and possess lower corrosion resistance than the austenitic grades. But they offer higher resistance to stress corrosion cracking. This type is generally considered to have poor weldability because at high temperatures it undergoes rapid grain growth. This leads to brittle, heat affected zones.

If ferritic alloys are being welded, it is in sections less than 6mm thick. Any loss of toughness is negligible in a piece that thin. When welding the ferritic stainless, filler metals should be used which match or exceed the chromium level of the base alloy. 409 and 430 are commonly used as fillers, and austenitic types 309 and 312 for dissimilar joints.

Martensitic

We carry: 410, 420, and 440C

The 400 and 500 series make up the martensitic grades. These alloys have higher strength, wear resistance and fatigue resistance than the austenitic and ferritic grades. But they are less corrosion resistant. This grade becomes hard and brittle upon cooling, making it a great material for wear resistance but more difficult to weld as it tends to weld crack on cooling.

However, martensitic stainless can be welded with careful precautions. The filler metals should generally match the chromium and carbon content of base martensitic metal. Type 410 filler is used to weld types 402, 410, 414 and 420 steels. Austenitic types 308, 309 and 310 are also used to weld martensitic steels to themselves or dissimilar metals.

Precipitation-Hardening

We carry: 455, 13-8, 15-5, and 17-4

Precipitation-hardening stainless steels contain both chromium and nickel. These metals provide a combination of the properties of martensitic and austenitic grades. They can be hardened through heat treatment to levels comparable to Martensitic steels while also being corrosion resistant like austenitic steels.

P-H steels can be readily welded using procedures similar to those for 300-series stainless steels. Grade 17-4 is commonly welded with 17-7 filler and can be welded without preheating. As with many other alloys, achieving the same mechanical properties in the weld as in parent material is difficult for P-H steels. Even when utilizing matching filler, it requires some careful preparation. Heat treatment after welding can be used to help the weld achieve close similarities to the parent metal.

Duplex

Duplex stainless steels are “duplex” because they possess a two-phase microstructure. This contains grains of both ferritic and austenitic stainless steel. These steels have significantly better toughness and ductility than ferritic grades. However, they do not reach the excellent values of austenitic grades. But they share a comparable corrosion resistance to the austenitic steels.

Modern duplex steels are readily weldable. But the procedure to maintain the heat input range must be strictly followed. Because of the material’s complex chemical composition, too much heat also adversely affects duplex stainless steels. Likewise, selecting a filler metal is slightly more challenging. Many types of duplex stainless base metals are not available as filler metals due to the fact that filler metal cools much more quickly than the base metal.