Abstract: Taking C38+N non-quenched and tempered steel for heavy-duty vehicle crankshafts as the object, the thermal deformation behavior of the steel was studied experimentally.The austenite grain growth behavior of C38+N steel when held at 850-1250℃for different time was studied. It is concluded that the activation energy of austenite grain growth of model-casting rolling material and continuous casting-rolling material C38+N steel is 7.49×10⁴ J/mol and 7.87×10⁴ J/mol, respectively.The austenite grain growth models under different experimental conditions were calculated and established.The reason for the difference in the austenite grain growth behavior of C38+N steel model-casting-rolling material and continuouscasting-rolling material is that the MnS distribution of continuous-casting-rolling material is more dispersed than that of model-casting-rolling material, and MnS has a pinning effect on austenite grain boundaries.