300M超高强度钢电化学性能及应力腐蚀开裂

采用动电位扫描技术和慢应变速率拉伸试验研究了超高强度钢300M在3.5%NaCl溶液中的应力腐蚀行为,并利用扫描电镜观察了不同外加电位下的断口形貌.300M钢在3.5%NaCl溶液中开路电位下的应力腐蚀开裂机制为阳极溶解型,Cl-的存在明显地增加了材料的应力腐蚀开裂敏感性.阳极电位-600 mV下300M钢溶解速率加快,表现出较高的应力腐蚀开裂敏感性,断面收缩率损失由开路电路下的52.6%升高至99.5%,裂纹起源于表面点蚀坑处,应力腐蚀开裂为阳极溶解型机制.阴极电位-800 mV下材料处于阴极保护电位范围,表现出较低的应力腐蚀开裂敏感性,强度和韧度与空气中拉伸的数值相近,开裂机制为阳极溶解和氢致开裂协同作用.在更低电位(低于-950 mV)下,300M钢的应力腐蚀开裂机制为氢致开裂,在氢和拉应力的共同作用下表现出很大的应力腐蚀开裂敏感性.

Electrochemical behavior and stress corrosion cracking of 300M ultrahigh strength steel

The stress corrosion cracking(SCC) behavior of an ultrahigh strength steel 300M in a 3.5% NaCl solution was studied by potentiodynamic polarization and slow strain rate tests(SSRT),and the fracture surfaces at different applied potentials were observed by scanning electron microscopy(SEM).The SCC mechanism of 300M steel in the NaCl solution at open circuit potential is attributed to anodic dissolution.Cl-ions significantly increase the SCC sensitivity of 300M steel.At the anodic applied potential of-600 mV the anodic dissolution rate and SCC susceptibility of 300M steel increase,represented by the loss of reduction-in-area at open circuit potential increasing from 52.6% to 99.5%.Cracks generally initiate at corrosion pits and the SCC mechanism remains anodic dissolution.At the cathodic potential of-800 mV,300M steel exhibits a lower SCC sensitivity due to cathodic protection.Its strength and toughness values are close to those in air.The SCC is controlled by anodic dissolution and hydrogen induced cracking.When the applied potential is more negative than 950 mV,300M steel exhibits a higher SCC sensitivity.The SCC mechanism is hydrogen induced cracking due to a synergistic action of stress and hydrogen.