EFFECT OF HEAT TREATED STRUCTURE ON DIFFUSION OF HYDROGEN IN MARTENSITIC TYPE 403 STAINLESS STEEL.

Abstract

The commercial steel investigated contained 0. 12% C, 11. 86% Cr, and 0. 31% Ni. The specimens were heated at 980 degree C for 1 hr, water quenched, and then tempered by air cooling after holding at 100 to 950 degree C for 1 hr in vacuum. A second series was annealed at 100 to 980 C for 1 hr without being quenched. It was found that diffusivity and solubility vary with the microstructure, and the diffusion coefficient increases from a structure tempered around 500 C to the as-quenched martensitic structure, to tempered martensite around 300 degree C, and coarse spheroidal pearlite tempered between 700 and 800 degree C. Hydrogen solubility has the opposite relation to structure. The variation in solubility and diffusion coefficient can be explained in terms of a hydrogen trapping process involving the lattice imperfections such as dislocations, lattice vacancies, etc. , produced by martensitic transformation and or by the precipitation of chromium carbides.