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(一)前言钢在回火时的脆性最先是在比较镍铬钢在回火后快冷和慢冷试样的冲击韧性的差别时发现的。Гуляев指出合金钢的冲击韧性曲线一般地具有两个极小值:一个在300℃左右;另一个在550℃左右。并称在残余奥氏体分解温度内出现的脆性为“第一种回火脆性”或“不可逆脆性”;而由于在～500～600℃回火慢冷而出现的脆性,称之为“第二种回
(I) Preface The brittleness of steel during tempering was first found in comparing the differences in the impact toughness of fast-cooled and slowly-cooled specimens of nickel-chromium steels after tempering. Гуляев pointed out that the impact toughness of alloy steel generally has two minimum: one at about 300 ℃; the other at about 550 ℃. It is also said that the brittleness occurring at the residual austenite decomposition temperature is “first temper brittleness” or “irreversible brittleness”, while the brittleness due to temper slow cooling at ~ 500-600 ° C is called " Two kinds of back