本文用有限元网格模拟12CrMo钢铁素体(F)+马氏体(M)双相组织的显微结构,利用轴对称弹塑性大应变有限元程序,计算了几种不同马氏体含量12CrMo钢的应力应变曲线,和相应的实验结果吻合较好.结果表明:马氏体含量是影响双相组织强度的主要因素。在低应变时,双相组织的流变应力和马氏体含量成线性关系,在高应变时呈非线性关系.强度随马氏体岛的直径减小而略增大.当马氏体含量为50％时,以马氏体为基体的双相组织强度高于以铁素体为基体的.计算的应力应变曲线在颈缩之前可用两段幂硬化规律近似,第一阶段的硬化指数n_1≈0.30—0.45,n_1对基体相比较敏感,而对第二相的尺寸、形状变化不敏感.硬化的第二阶段代表了12CrMo钢双相组织的应力应变曲线上绝大部分硬化规律。和n_1相反,n_2对第二相尺寸、形状变化比较敏感.对基体相不敏感.n_2在数值上约等于(1/2)n_1,和Mileiko理论值接近,但n_2大于实际测量的最大均匀应变ε_u.
An elastic-plastic axisymmetric increment finite element program based on f inite deformation theory has been applied to calculate the stress-strain curves of 12CrMo ferrite-martensite steel with different martensite contents The fraction and shape of martensite in the finite element meshes should be the same as those in actual materials. The calculated stress-strain curves are consistent with experimental ones. The flow stresses at low strain stage are directly proportional to the martensite content, but at high strain stage, the effect of martensite content dies down. The strength of the steel increases slightly with decreasing martensite size. When the martensite content is 50%, the strength of steel becomes higher than that of those with ferrite matrix. At uniform strain stage, the calculate stress-strain curves on Log-Log scales show two straight lines with slopes n_1 and n_2. The strain hardening exponent n_1 at the first strain hardening stage is sensitive to the character of matrix, while n_2 at the second stage is sensitive to that of particle phase.
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