Mechanism of the Embrittlement in the 30 Cr-2 Mo Steel Overlay Weld

Study on Welding of the Low Interstitial Ferritic Stainless Clad Steel (Report 2)

Abstract

A study on the mechanism of the embrittlement in the low interstitial ferritic stainless overlay welds has been undertaken using 26Cr-1Mo steels with carbon content ranging 20 to 490 ppm. Tensile test was performed on 26Cr-1Mo steels with various carbon contents and grain diameters in order to obtain the fracture stress, friction stress and Hall-Petch slope of the steels. Various mechanisms proposed in the literatures for brittle fracture were evaluated with comparison the experimental results and the calculated fracture stresses through each models. It was elucidated that the embrittlement of 26Cr-1Mo steel examined could best be explained by Almond's model involving the embrittler effect of grain boundary carbides to give lower crack initiation energy, and it was suggested that the increase in the thickness of grain boundary carbide due to pick-up of carbon from the base metal during welding might be the main cause of the overlay weld embrittlement in the low interstitial ferritic stainless steels.