Weldability, microstructure and properties of precipitation strenghtened martensitic stainless steels. [Custom 450; PH 13-8 Mo]

We have investigated the influence of welding on the mechanical properties and corrosion resistance of two precipitation strengthened martensitic stainless steels: Custom 450 and PH 13-8 Mo. The two alloys exhibited very good weld cracking resistance, although the formation of a low melting NbC eutectic constituent did cause some solidification cracking in Custom 450. The effects of aging temperature on tensile and impact properties were similar in the base metal and Gas-Tungsten-Arc (GTA) weldment for both alloys. The similarity of weld and base metal properties is attributed to the uniform precipitate distribution throughout the weld, as shown by Transmission Electron Microscopy (TEM) and electron microprobe analyses. The susceptibility to pitting corrosion was not impaired by aging or by welding, with the possible exception of a narrow band in the heat-affected zone (HAZ), and both materials were more resistant than 304 stainless steel. The narrow band is identified by electrochemical reactivation testing as a region of increased matrix activity likely caused by localized Cr and/or Mo depletion.