在应变控制下,试验了5CrNiMo和5Cr2NiMoVSi两种热作模具钢的循环软化特性及其微观结构的变化。结果表明:在应变幅为Δεt/2=0.6—1.8×10~(-2)范围内,不同硬化状态的试验钢均表现为循环软化特性;软化效应主要集中在前几周,在随后的循环过程中应力幅变化较小,软化效应减弱;整个循环过程中,未观察到明显的应力饱和现象。TEM分析表明,循环软化与塑性变形的不均匀性有关。试验钢的软化是由于在循环变形中位错结构转变成低密度、低内应力的位错胞状组织,以及细小碳化物在位错往复切割下碎化而重新回溶引起的。
The feature and microstructure change of cyclic softening in hot-working die steels 5CrNiMo and 5Cr2NiMoVSi were studied under strain controlledlow-cycle fatiguing. The results show that the cyclic softening is featured in bothvariedly hardened steels under strain controlled in the amplitude range of Δε_t,/2=0.6 - 1.8×10~(-2). The softening effect is mainly gathered in the prior some cycles.And the stress amplitude varies slightly in the sequential cycles, i. e. the softeningeffect is minified. No obvious saturation phenomenon of stress is observed duringthe whole cyclic deformation. The cyclic softening was analyzed under TEM thatit is related to heterogeneity of plastic deformation. The softening of the steelstested is caused by the formation or the dislocation cell structure with low densityand low internal stress, and by the redissolution of fine carbides into matrix.
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