基于应变控制的4Cr5MoSiV1热作模具钢热机械疲劳行为

采用MTS?热机械疲劳电液伺服试验机研究了4Cr5MoSiV1热作模具钢400～700℃范围内拉压对称机械应变控制的同相及反相热机械疲劳行为.结果表明:当应变幅为±0.50％时,4Cr5MoSiV1钢反相热机械疲劳寿命约为同相的60％;无论同相还是反相加载,应力-应变滞后回线均呈现不对称性,同相加载时表现为平均压缩应力,反相加载时表现为平均拉伸应力.两种加载方式下,最大应力与最大应变及峰值温度均不同步,在高温半周出现应力松弛现象.此外,高温半周呈现持续循环软化,而低温半周呈现初始循环硬化,随后持续循环软化的特征.同相加载时断口以主裂纹、撕裂脊和准解理特征为主,裂纹少而深;反相加载时断口以疲劳条纹和大量的凹坑特征为主,裂纹多而浅.

Strain-controlled thermal-mechanical fatigue behavior of 4 Cr5 MoSiV1 hot work die steel

In-phase (IP) and out-of-phase (OP) thermal-mechanical fatigue (TMF) tests of 4Cr5MoSiV1 hot work die steel were conducted in full reverse mechanical strain control in the temperature range of 400-700℃ by a TMF servo-hydraulic testing system (MTS?). The results indicate that, when the strain amplitude is ±0. 50％, the OP TMF life of 4Cr5MoSiV1 steel is ～60％ of the IP TMF life. The stress-strain hysteresis loops show asymmetries for both IP and OP loading. IP loading leads to comprehensive mean stress, while OP loading gives rise to tensile mean stress in the temperature range of 400-700℃. The changes of maximum strain and peak temperature with maximum stress are inconsistent, and the stress relaxation phenomenon could be observed under IP and OP load-ing. Moreover, two kinds of TMF cycling exhibite continuous cyclic softening in the high temperature half stage, while in the low tem-perature half stage, cyclic hardening occurs initially and is then followed by continuous cyclic softening. The fractured surfaces under IP TMF loading display striation and tear ridge, and exhibits quasi-cleavage characteristics. In addition, the cracks are less but longer. However, fractured surfaces under OP TMF loading mainly display striation and dimple characteristics, and the cracks are shorter and more abundant.