Physical metallurgy basis for broader and safe use of 13Cr-4Ni-0.5Mo steel in nuclear power engineering

VITKOVICE as one of the first companies exploited 15 years ago successfully the secondary metallurgy in the production of martensitic-austenitic 13Cr-4Ni-0.5Mo and 13Cr-6Ni-0.5Mo stainless steels of very low carbon content and the products in cast or wrought form exhibited excellent ductility and toughness in a wide range of testing temperatures. Noteworthy was the finding that such very low carbon grades are highly resistant against the temper embrittlement, even after prolonged tempering against the temper embrittlement, even after prolonged tempering at temperatures close to 500 deg. C. As a reason for such behaviour serves the presence of only small amount of carbides at the grain boundaries which leads to the elimination of one of conditions necessary to originate the intergranular fracture. Such controlled carbide-free microstructure of martensite and certain percentage of reversion austenite further performs high resistance to intergranular corrosion and other type of local corrosion events in high temperature water as well as the low susceptibility to hydrogen embrittlement. (author). 19 refs, 9 figs, 3 tabs