| 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.
|
|
|
