Effect of welding technique on weld morphology and hardness of supermartensitic 13%Cr steels

Abstract

The 13%Cr supermartensitic stainless steels are a new group of steels for use as pipelines for oil and gas transport. Sheet and strip material from the supermartensitic stainless steels containing 11.5–12%Cr and different Ni (4.6 and 6.4%) and Mo (1.3 and 2.3%) contents were welded using several techniques including Plasma/TIG, EB and EB/ TIG. Post-heat treatment was also applied. The effect of welding technique on the weld morphology and hardness distribution was studied. The structure obtained included a variety of phases which are roughly identified as ferrite and austenite with Ni, Cr, Mo and Si in solid solution with the absence of conventional martensite owing to the very low carbon content of the steels. Hardness values as high as 350 HV were obtained in the fusion zone in the EB+TIG/tempered and in Plasma+TIG/tempered states, whereas it reached 360–370 HV in the fusion zone in EB with and without filler independent of the composition. A lower hardness of around 300 HV was obtained in the fusion zone of Plasma+TIG/tempered and Plasma+TIG/as welded in the alloys containing lower Si (0.177%) and higher Mn (1.76%).