Strain-controlled thermal-mechanical fatigue behavior of 4Cr5MoSiV1 hot work die steel
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摘要: 采用MTS®熱機械疲勞電液伺服試驗機研究了4Cr5MoSiV1熱作模具鋼400~700℃范圍內拉壓對稱機械應變控制的同相及反相熱機械疲勞行為.結果表明：當應變幅為±0.50%時，4Cr5MoSiV1鋼反相熱機械疲勞壽命約為同相的60%；無論同相還是反相加載，應力-應變滯后回線均呈現不對稱性，同相加載時表現為平均壓縮應力，反相加載時表現為平均拉伸應力.兩種加載方式下，最大應力與最大應變及峰值溫度均不同步，在高溫半周出現應力松弛現象.此外，高溫半周呈現持續循環軟化，而低溫半周呈現初始循環硬化，隨后持續循環軟化的特征.同相加載時斷口以主裂紋、撕裂脊和準解理特征為主，裂紋少而深；反相加載時斷口以疲勞條紋和大量的凹坑特征為主，裂紋多而淺.Abstract: 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 loading. Moreover, two kinds of TMF cycling exhibite continuous cyclic softening in the high temperature half stage, while in the low temperature 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.
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參考文獻
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