预应变亚稳态奥氏体不锈钢(S30408)深冷低周疲劳性能

Cryogenic low-cycle fatigue performance of pre-strained metastableaustenitic stainless steel (S30408)

为了研究冷成形和温成形对深冷容器低周疲劳性能的影响,通过液氮温度(77 K)下的拉伸试验和低周疲劳试验,分析预应变(0和0.35)和预应变温度(293 K和363 K)对亚稳态奥氏体不锈钢(S30408)深冷低周疲劳性能的影响机制.0.35预应变使试样内部位错密度增加和产生强化相体心立方马氏体,与母材试样相比,293 K预应变试样初始循环应力幅增大,疲劳辉纹宽度减小,深冷低周疲劳寿命增加显著.随着预应变温度由293 K升高到363 K,奥氏体相稳定性增加,马氏体相变受到抑制,初始循环应力幅减小,疲劳辉纹宽度增大,预应变对深冷低周疲劳寿命的增益作用减弱.总体来看,0.35预应变对S30408深冷低周疲劳性能有明显增益作用,但增益程度受预应变温度的限制.

Cryogenic pressure vessel’s low-cycle fatigue performance is greatly affected by cold forming and warmforming. Tensile experiments and low-cycle fatigue experiments of metastable austenitic stainless steel S30408 atliquid-nitrogen temperature (77 K) were conducted to analyze the influences of pre-strain (0 and 0.35) and pre-straintemperature (293 K and 363 K) on the cryogenic low-cycle fatigue performance. Due to 0.35 pre-strain resulting inthe increase in dislocation density and formation of strain-induced body centered cubic martensite, 293 K pre-strainspecimen shows higher initial cyclic stress amplitude, smaller fatigue striation width and longer low-cycle fatiguelife than base metal specimen at 77 K. When the pre-strain temperature changes from 293 K to 363 K, the austenitephase owns higher stability, martensitic transformation is blocked, the initial cyclic stress amplitude decreases, thefatigue striation width increases, and the strengthening effects on the cryogenic low-cycle fatigue life caused by 0.35pre-strain is weakened. In general, 0.35 pre-strain shows significant strengthening effects on the S30408’s cryogenic low-cycle fatigue performance, and the effects are limited by the pre-strain temperature.