Effect of Carbon Content on Grain Boundary Cementite of Hypereutectoid Steel

The precipitation of grain boundary cementite for hypereutectoid steels with different carbon contents of 1.06%, 1.09%, 1.16% and 1.24% were investigated. The thermal simulation results show that the minimum cooling rate for inhibition the formation of grain boundary cementite increases from 15 ℃/s to 30 ℃/s when the carbon content increases from 0.96% to 1.24%. In industrial hot rolling test, when the carbon content increases from 1.06% to 1.24%, the grain boundary carbonbon length per unit area increases from 9.0×10⁵ μm/mm² to 6.17×10⁶ μm/mm², the reduction of area of the steel wire rod decreases from 24% to 14%. The results of hot rolled strip salt bath show that the salt bath temperature decreases from 450℃-600 ℃ to below 450 ℃, when the carbon content increases from 1.06% to 1.24%. The maximum carbon content of the best microstructure（sorbite without grain boundary cementite） of the steel wire rod is 1.09% and the maximum salt bath temperature is 500℃.