Abstract
In order to develop the austenitic steel for cryogenic use, micro structure, mechanical properties especially low temperature toughness, and thermal expansion coefficient of manganese-chromium steels with much amount of manganese as an austenitizing element, have been investigated.The results obtained are as follows.
It is found that 25 Mn-5Cr-1Ni steel, selected as optimum base composition, has excellent notch toughness and low thermal expansion coefficient of6.7-7.2×10-6/°C. Further the addition of niobium, vanadium and titanium to base composition result in the refinement of austenite grain size which increase the strength considerably but decrease the notch toughness a little. Especially the addition of 0.1% niobium contribute to the high tensile strength of 70 kg/mm2 and keep the low temperature toughness υE-196 more than 5 kgm. The addition of nitrogen increases only the 0.2% proof strength.
