Yunoshin Imai and Kenzaburo Kumada
The cause of the so-called 475° brittleness of high chromium steels has not yet been determined. To study this phenomenon, the hardness, thermal expansion, electric resistance, thermal magnetic analysis, tensile test, and microstructure of high chromium steels which contain chromium 15 ∼ 35%, were studied. At the neighbourhood of 500°, the hardness and also the tensile strength increase, reduction of area, decrease in elongation and expansion is observed, electric resistance and magnetic intensity decrease, magnetic transformation point shifts to high temperature with holding time and no clear difference of microstructure is seen between the long annealed specimen at about 500° and a specimen not so annealed, but the former shows a clearer grain boundary etching. From these experimental results, it is concluded that this phenomenon is not caused by the usual precipitation but the formation of a superlattice.
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