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以改进的KRC模型决定AG~(γ→α)的方法,计算了Fe-C合金贝氏体相变可能机制:γ→α+γ_1,γ→α+Fe_3C以及γ→α(浓度相同)和α′→α_B~″(贝氏体铁素体碳浓度)+Fe_3C的相变驱动力和长大(形核)驱动力.相变驱动力以γ→α+Fe_3C为最大,γ→α+γ_1次之,γ→α最小.由奥氏体转变成同成分铁素体(γ→α)的长大驱动力远小于γ→α+γ_1的长大驱动力.在贝氏体形成温度范围内,γ→α的驱动力远小于切变机制所需的驱动力.0.1—0.55wt,%C合金在B_s温度时γ→α+γ_1的相变驱动力仅约—45Jmol~(-1).0.8wt %C合金在贝氏体形成上限温度(823K)时γ→α的相变驱动力为137Jmol~(-1),而α→α+Fe_3C的相变驱动力为-527Jmol~(-1);两者相加,即在贝氏体铁素体析出渗碳体的情况下,相变总驱动力也仅有约-390Jmol~(-1).上述结果表明,贝氏体铁素体很难以切变机制形成和长大.
Based on the improved KRC model for determining AG ~ (γ → α), the possible mechanism of bainite transformation for Fe-C alloys was calculated: γ → α + γ_1, γ → α + Fe_3C and γ → α The driving force of phase transformation and the driving force of growth (nucleation) are α ’→ α_B ~’ (bainitic ferrite carbon concentration) + Fe_3C.The driving force of phase transformation is γ → α + Fe_3C, γ → α + γ_1 and γ → α, the driving force for the growth of the ferrite (γ → α) transformed from austenite to the same composition is much smaller than that of γ → α + γ_1. In the bainite formation temperature range , The driving force of γ → α is far less than the driving force required for the shear mechanism.The phase change driving force of γ → α + γ_1 is only about -45 Jmol -1 at B_s temperature for 0.1-0.55wt% The kinetics of γ → α phase transformation was 137Jmol -1 at the maximum bainite temperature (823K) and the phase transformation driving force of α → α + Fe_3C was -527Jmol ~ (- 1), and the sum of the two, that is, the total driving force for phase transformation is only about -390 Jmol -1 in the case of precipitation of cementite by bainitic ferrite.The above results show that the bainitic ferrite Difficult to change the mechanism to form and grow up.