Studies were made in connection with the development of a new steel for low-temperature use.The ef-fects of alloying elements on the toughness of6%Ni steel were examined in relation to metallurgical factors such as temper brittleness, microstructure and the stability of temper-formed austenite (reverted austenite). The results are as follows:(1) The addition of manganese refines the microstructure and improves toughness but promotes susceptibility to temper brittleness.(2) The addition of molybdenum or tungsten is bene ficial in preventing temper brittleness of6%Ni steel with a high manganese content and in producing finely dispersed and stable austenite islands, but has the disadvantage of retarding recovery on tempering.(3) The addition of chromium is useless in improving the toughness of 6% steel.(4) The addition ofcopper has similar effects to those of manganese, that is, it refines the microstructure and improves toughness.
Based on these results, a new steel has been developed with 6%Ni, 1-2%Mn and 0.2%Mo or 0.45%W, which has good toughness, such as 13kgm at-196°C.
