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

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 α、λ of high-carbon steel decrease in the order of pearlite, temper sorbite, temper martensite, and quench martensite, and the α、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 α、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 α、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 α、λ of quenching microstructure 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.