深海用沉淀硬化不锈钢力学化学效应机理的研究

This project aims to study the corrosion mechanism of precipitation hardening stainless steel under the coupled mechanical and electrochemical effects in simulated deep-sea high-pressure low-temperature high-chloride ion environment. Firstly, the transmission electron microscope (TEM) and scanning electron microscope (SEM) will be employed to characterize the structural difference of the material under no load, elastic load and plastic strain conditions and the deformation regularity of various phases in the precipitation hardening stainless steel in the process of deformation. Secondly, using SKP, SVP, LEIS and SDC techniques to study the micro-scale surface electrochemical properties of the precipitation hardening stainless steel under different stresses and speculate the impact mechanism of the stress on the corrosion behaviour of various phases in the material. Finally, the high temperature and high pressure electrochemical test autoclave with heat exchange tube will be used to simulate deep-sea environment including different hydrostatic pressures, different sea water temperatures, different dissolved oxygen and flow rates, and then comparatively investigate the corrosion behaviour of the precipitation hardening stainless steel under no load, elastic load and plastic strain conditions in simulated deep-sea environment, so the mechanochemical effect (MCE) of the precipitation hardening stainless steel in deep-sea environment could be analyzed and revealed. Based on the experimental results and mechanism study, this project will have great significance as the theoretical guidance to life prediction, service safety evaluation, reasonable material selection and optimization microstructure for the service materials in actual deep-sea engineering structures.

本项目旨在研究沉淀硬化不锈结构钢在模拟深海高压低温高氯离子环境中力学因素与电化学腐蚀耦合作用下材料的腐蚀机理。利用透射电镜、扫描电镜观察并表征材料在无载荷、弹性载荷、塑性应变作用时的结构区别及其在形变过程中沉淀硬化不锈钢中各相的形变规律；利用SKP、SVP、LEIS、SDC等技术对沉淀硬化不锈钢在不同应力作用下微观尺度的表面电化学性质进行研究，推测应力对材料中各相的腐蚀行为的影响机制；利用带有热交换管的高温高压电化学测试反应釜模拟不同静水压、不同海水温度、不同溶解氧、不同水流速度等深海环境并对比研究无载荷、弹性应力、塑性应变作用下沉淀硬化不锈钢在模拟深海环境中腐蚀行为的规律，从而分析揭示在深海环境下沉淀硬化不锈钢的力学化学效应机理。本项目的开展对实际深海工程中服役材料的寿命预测、服役安全评价、合理选材并优化材料显微组织具有重要的理论指导意义。

本项目旨在研究沉淀硬化不锈结构钢在模拟深海环境中力学因素与电化学腐蚀耦合作用下材料的腐蚀机理。研究结果表明，PH13-8Mo沉淀硬化不锈钢随着回火温度的升高，显微组织中镍铝化合物析出相会随之改变，Ni/Al比值会明显增加且其力学性能随之改变。应力作用会增加沉淀硬化不锈钢显微组织中位错密度；应力作用会降低PH13-8Mo沉淀硬化不锈钢在深海环境中的开路电位、自腐蚀电位、点蚀电位、传质电阻及点蚀阻抗；降低其钝化膜的钝化效果并促进材料的腐蚀；其电化学性能与显微组织的析出物及位错密度有关。静水压的增加会降低PH13-8Mo沉淀硬化不锈钢在3.5% NaCl溶液中的开路电位、点蚀电阻及传质电阻且其对腐蚀产物没有明显影响。随海水流速的增加，不锈钢的腐蚀电流密度明显增加；冲刷角度对金属腐蚀的热力学稳定性有明显影响，海水的流速比冲刷角度对金属腐蚀速率的影响更加敏感；不锈钢在25 ℃深海环境下具有良好的耐点蚀能力；在65 ℃下不锈钢表面会出现明显的点蚀；在150和200 ℃时，不锈钢表面会产生裂纹状点蚀坑；随着温度的升高点蚀坑扩展的速率随之加快；65 ℃时点蚀坑的发生位置主要在奥氏体相内，100~200 ℃时点蚀坑发生的位置主要在铁素体相内；不锈钢在20 MPa静水压下的模拟深海溶液中，其阴极反应为析氢反应；20 MPa环境除氧后易产生氢致开裂现象，裂纹均处于铁素体相内。阳极金属溶解不会明显引起PH13-8Mo沉淀硬化不锈钢在深海环境中应力腐蚀开裂；表面的点蚀坑往往是裂纹的形核点，沉淀硬化不锈钢在深海环境中发生应力腐蚀开裂的主要是由氢致开裂导致的裂纹开裂；裂纹扩展既包含沿晶应力腐蚀开裂又包含穿晶应力腐蚀开裂；不锈钢随着充氢电流密度的增加或者充氢时间的增加会使其表面开裂现象加剧。本项目的开展对实际深海工程中服役材料的寿命预测、服役安全评价、合理选材并优化材料显微组织具有重要的理论指导意义。