Effect of Relative Humidity on Mechanical Degradation of Medium Mn Steels
Effect of Relative Humidity on Mechanical Degradation of Medium Mn Steels
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DOI：
10.3390/ma13061304
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发表时间：
2020-03
期刊：
影响因子：
3.4
通讯作者：
Qingyang Liu;Juanping Xu;Liancheng Shen;Qingjun Zhou;Yanjing Su;L. Qiao;Yu Yan
中科院分区：
文献类型：
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作者：
Qingyang Liu;Juanping Xu;Liancheng Shen;Qingjun Zhou;Yanjing Su;L. Qiao;Yu Yan
中锰钢由于其优异的强度和延展性平衡而被认为是汽车工业中使用的下一代材料。为了减轻车辆的总重量，提高车辆的安全性，中锰钢具有广阔的应用前景。然而，氢致延迟开裂是使用高强度钢的一个问题。本文研究了两种中锰钢在不同相对湿度（40%、60%、80%和100%）条件下的使用特性。在25 ℃正常相对湿度（约40%）下，钢中的氢浓度为0.4ppm。当暴露于较高的相对湿度时，钢中的氢浓度缓慢增加，并达到一个稳定值，约为0.8 ppm。在不同相对湿度条件下的慢应变速率拉伸试验中，拉伸强度发生变化，氢浓度增加，延伸率降低，从而增加了氢脆敏感性。换句话说，施加的拉伸速率越小，氢脆敏感性越大。在不同相对湿度条件下的恒载荷试验中，M7 B（“M”为Mn，“7”为Mn含量，“B”为罩式退火）钢的延迟开裂门槛值保持在0.82 σB（抗拉强度）的稳定值。M10 B的延迟开裂门槛值随相对湿度的变化沿着发生显著变化。当相对湿度从60%增加到80%时，阈值从0.63 σB急剧下降到0.52 σB。我们将80%的相对湿度定义为M10B的“阈值湿度”。
Medium Mn steels have been considered as the next-generation materials for use in the automotive industry due to their excellent strength and ductility balance. To reduce the total weight and improve the safety of vehicles, medium Mn steels look forward to a highly promising future. However, hydrogen-induced delayed cracking is a concern for the use of high strength steels. This work is focused on the service characteristics of two kinds of medium Mn steels under different relative humidity conditions (40%, 60%, 80% and 100%). Under normal relative humidity (about 40%) at 25 °C, the hydrogen concentration in steel is 0.4 ppm. When exposed to higher relative humidity, the hydrogen concentration in steel increases slowly and reaches a stable value, about 0.8 ppm. In slow strain rate tensile tests under different relative humidity conditions, the tensile strength changed, the hydrogen concentration increased and the elongation decreased as well, thereby increasing the hydrogen embrittlement sensitivity. In other words, the smaller the tensile rate applied, the greater the hydrogen embrittlement sensitivity. In constant load tests under different relative humidity conditions, the threshold value of the delayed cracking of M7B (‘M’ referring to Mn, ‘7’ meaning the content of Mn, ‘B’ denoting batch annealing) steel maintains a steady value of 0.82 σb (tensile strength). The threshold value of the delayed cracking of M10B significantly changed along with relative humidity. When relative humidity increased from 60% to 80%, the threshold dropped sharply from 0.63 σb to 0.52 σb. We define 80% relative humidity as the ‘threshold humidity’ for M10B.