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作者采用X—射线,金属薄膜透射等手段研究了淬火W6Mo5Cr4V2,W18Cr4V,W2Mo9Cr4VCo8(M42)及65Cr4W3Mo2VNb(65Nb)钢中残余奥氏体回火转变规律及电镜形貌。发现:(1)淬火高速钢在250～400℃范围回火吋,部分残余奥氏体转变为贝氏体。在320～350℃回火1b,其最大转变量可达7%。(2)由残余奥氏体生成的下贝氏体与过冷奥氏体形成的下贝氏体相比,其贝氏体针粗而短,M_3C碳化物密度大,贝氏体形成时引起周围残余奥氏体发生塑性变形。(3)淬火高速钢中残余奥氏体形成贝氏体的动力学具有“C”曲体特征,“C”曲线的鼻子温度约在320～350℃。其转变动力学与过冷奥氏体向贝氏体转变动力学相似。但残余奥氏体贝氏体转变的温度范围和“C”曲线的鼻子温度均向高温方向移动。(4)淬火高速钢在320～380℃范围低温回火1h,不会增加残余奥氏体的回火稳定性。(5)一部分残余奥氏体转变成贝氏体对高速钢的二次硬化和红硬性有一定贡献。
The authors studied the residual austenite transformation and microstructure of the as-quenched W6Mo5Cr4V2, W18Cr4V, W2Mo9Cr4VCo8 (M42) and 65Cr4W3Mo2VNb (65Nb) steels by means of X-ray and metal thin film transmission. It is found that: (1) Quenched HSS is tempered at 250-400 ℃, some retained austenite is transformed into bainite. Tempered at 320 ~ 350 ℃ 1b, the maximum change of up to 7%. (2) The lower bainite formed by the retained austenite has coarse and short bainite needles, large M 3 C carbide density, and bainite formation when compared with the lower bainite formed by the supercooled austenite Surrounding retained austenite plastic deformation. (3) The kinetics of retained austenite formation bainite in quenched high speed steel has the character of “C”, and the temperature of nose of “C” curve is about 320 ~ 350 ℃. Its transformation kinetics is similar to that of undercooled austenite to bainite transformation. However, both the temperature range of residual austenite bainite transformation and the nose temperature of the “C” curve are shifted toward high temperature. (4) quenching high-speed steel in the range of 320 ~ 380 ℃ tempering 1h, will not increase the residual austenite tempering stability. (5) A part of retained austenite transformed into bainite contributes to secondary hardening and red hardness of HSS.