What Is Stainless Steel?
Ferritic Stainless Steel
Ferritic stainless steels have a Cr content of 11-28%. Commonly used alloys include the 430 grade, having 16-18% Cr and 407 grade having 10-12% Cr. As these alloys can be considered to be predominantly single phase and non-hardenable, they can be readily fusion welded. However, a coarse grained HAZ will have poor toughness.
Avoiding weld imperfections – The main problem when welding this ferritic stainless steel is poor HAZ toughness. Excessive grain coarsening can lead to cracking in highly restrained joints and thick section material. When welding thin section material (less than 6 mm), no special precautions are necessary. In thicker material, it is necessary to employ a low heat input to minimize the width of the grain-coarsened zone and an austenitic filler to produce a tougher weld metal. Although preheating will not reduce the grain size, it will reduce the HAZ cooling rate, maintain the weld metal above the ductile-brittle transition temperature, and may reduce residual stresses. Preheat temperature should be within the range 50-250°C, depending on material composition.