EFFECT OF HYDROGEN ON DYNAMIC PRECIPITATION OF CARBIDE IN TYPE 304-STAINLESS-STEEL DURING CREEP PROCESS

Effect of hydrogen on the creep behavior of type 304L, the solution-tr eated and sensitized type 304 stainless steels was investigated in 9.9 MPa argon and hydrogen at 823 K. Hydrogen did not affect the creep pr operties of 304L stainless steel and slightly affected those of the se nsitized 304 stainless steel, however, hydrogen decreased the creep st rength and increased the creep ductility of the solution-treated 304 s tainless steel above the rupture time of 153 h when carbides were prec ipitated on the grain boundaries. Hydrogen affected the dynamic precip itation of carbide. especially the morphology of the carbide on the gr ain boundary in the solution-treated 304 stainless steel. The shape of the carbides was changed from granular carbides in argon to plate-sha ped carbides in hydrogen. It is suggested that hydrogen decreased ;he interfacial energy of the carbide. The influence of hydrogen on creep properties of the solution-treated 304 stainless steel was mainly due to a change in the shape of the carbide on the grain boundary caused b y the hydrogen. The plate-shaped carbide covered a wider area of the g rain boundary than granular carbide at the same volume, so grain bound ary sliding was more effectively blocked by the carbide in hydrogen. ( C) 1997 Acta Metallurgica Inc.