Development of Heat Treatment Parameters to Enhance HAZ Impact Toughness of SS 430 Material

Abstract

Pressure Housing, used in the Grid Mechanisms Motor, is manufactured from ferritic stainless steel, SS430 bar of 120mm diameter. The application demands an alternative non-magnetic and magnetic material (austenitic and ferritic) on the outside. This is manufactured by making longitudinal machined slots on the outside surface of SS430 bar which is ferritic and magnetic and the machined slots are filled up by depositing SS347 which is an austenitic and non-magnetic stainless steel material. In order to weld SS430 # SS430 with SS347, welding procedure was to be qualified as per ASME Sec IX with additional requirements of impact specimens from weld and HAZ at temperature +20°C, microstructure examination and intergranular corrosion test as per ASTM A763 Pr.Z. It was the first time, SS430 # SS430 welding procedure qualification with SS347 was to be carried out as no earlier cases required this qualification. SS430 ferritic stainless steel bar exhibits stringers of ferrite and martensite and in cases of stingers of two phase structures like duplex stainless steel, it has been reported that the transverse impact properties drops to half to two-third the longitudinal values. In the welded coupon, the impact property on the HAZ was located in the transverse direction and extremely difficult to meet the requirements. Welding qualification with impact requirement in transverse direction in HAZ was a challenging task and this paper addresses the issues encountered and the work carried out in literature study on the metallurgy, heat treatment and experimental trials to meet the specification requirement.