DP강에서 등온 상변태시 오스테나이트내의 탄소 농도 분포 계산

초록

Recently, 3 step cooling method(intercritical annealing(MT) - rapid cooling to low temperature - holding at low temperature(CT)) is used in production of hot rolled dual phase steels. Intercritical annealing is practically adopted by air cooling, which results in a deviation of fractions of polygonal ferrite. With less ferrite, intermediate phases such as acicular ferrite / upper bainite are inevitable in final products. Thus, the proper carbon enrichment in austenite are required in order to prohibit the formation of intermediate phases during cooling. In this study, thermodynamic analysis of Fe-Mn-Si-C system was conducted by a Thermo-Calc and the thermodynamic program developed was based on the sub-lattice model using para-equilibrium condition including the metastable mixtures such as Widmanstatten ferrite, bainite and martensite. Using results of the linear diffusional equation in the finite media, analysis of γ/α transformation rate and carbon profile in residual austenite during γ/α transformation were conducted.