高碳钢的热物性与显微组织的关系

THE RELATIONSHIP OF THERMOPHYSICAL PROPERTIES TO MICROSTRUCTURE OF HIGH-CARBON STEEL

采用激光脉冲法和比较法测量了不同组织状态下的高碳钢的导温系数α、比热容CP和导热系数λ等热物性参数。并对高碳钢的热物性与显微组织、力学性能之间存在的某些对应关系做了初步讨论。结果表明,高碳钢的α和λ值按珠光体、回火索氏体、回火马氏体和淬火马氏体的顺序依次减小,且在500℃以后趋于一致,这恰好与硬度、强度值随回火温度变化的规律吻合。通常随着合碳量的增加,高碳钢的α和λ值降低。碳以固溶形式存在于基体时对钢导热能力的损害比以第二相形式存在时大。与强度和塑性等力学性能不同,高碳钢的晶粒越小,其α和λ值越低。淬火后的高碳钢在100℃附近回火,α和λ值出现最小值与硬度出现峰值相对应,在750℃附近存在居里点,比热容出现最大值。

The thermal conductivity, thermal diffusivity and specific heat capacity of high-carbon steels having different microstructure have been measured by laser pulse method and comparing method. The relation among the thermophysical properties, the microstructure and mechanical properties was discussed. The result showed that the a, λ of high-carbon steel decrease in the order of pearlite, temper sorbite, temper rnartensite, and quench martensite, and the a, λ go to the same after 500℃. This law is the same with the law of hardness and strength with the temper temperature. In general the a,λ of high-carbon steel decrease with the quantity of carbon. The reducing of carbon existing by the form of solid solution in the matrix to the heat conduction is more than it existing by the form of secondary phase. The a.λ decrease with the decrease of the size of crystal grain, this law is opposite to the law of some mechanical properties-for example strength and ductility-with the size of crystal grain. The a,λ of quenching rnicrostructure is the smallest at about 100℃, this corresponds with that high-carbon steel has hardness peak value at the temperature. High-carbon steel has curie point at about 750℃, and the specific heat capacity is the maximum there.