Investigation and comparison of ferritic, austenitic and stabilised stainless steels weldability

Stainless steels are the alloys which contains mainly Cr and mostly Ni, and they are obligedthe corrosion resistance properties to chromium. For obtaining corrosion resistance to steels12% Cr must be added. To the classical theories, Cr forms an oxide film on surface of themetal and makes passive the surface of the metal. This can briefly described as passive filmformation.Stainless steels are find a wide range of usage area for many applications in the industry. Thetypes of stainless steels which have usage area in industry today can be divide in five groups.These are martensitic, ferritic, austenitic, precipitation hardening and duplex stainless steels.But for our investigations necessity, we have examined ferritic (in theoretic), austenitic andstabilised stainless steel which can be used by welding.Some difficulties can occur while welding the austenitic and ferritic stainless steels. The mostimportant thing and which must be controlled is, chromium depletion and losing resistance tointergranular corrosion in welded parts, which are cooling in air at a temperature range (450-850ºC) at the reason of intersititial chromiumcarbur precipitation. For preventing theintergranular corrosion, Ti, Nb and Ta must be added for binding C and N.In experiments, 4 types of stainless steels are welded and electric arc and TIG weldingmethods are applied for every type. In electric arc method, materials are welded with suitableelectrode and not suitable electrode. In addition, for suitable electrode, different current valuesare applied. The aim of this operation is determining the effects of current and electrodes tothe weldability of the material. In TIG method, different current values with suitable rodmaterial tested. After this, different tests are applied according to standards and the datas fromexperiments are compared with datas from literatures.Key words: Stainless steel, austenitic, ferritic, stabilised, electric arc welding, TIG welding.JURY:1. Prof. Dr. Ahmet ÜNAL (Supervisor) Date : 05.10.20052. Prof. Dr. Ahmet TOPUZ Page : 1503. Prof. Dr. Erhan ALTAN