节Ni型双相不锈钢时效行为的Mn影响机制研究

The shortage of Ni resources is an obstacle to the promotion and application of duplex stainless steels, thus, the development of low nickel type duplex stainless steels is an effective way to solve the problem. Meanwhile, the brittle precipitates will lower mechanical property and corrosion resistance of duplex stainless steels in high temperature appilication environment and under high temperature working. Therefore, it is key to investigate their aging mechanism and properties for improving high temperature performance of duplex stainless steels. The low nickel type duplex stainless steels are to stabilze the austenite phase by substituting Mn and N elements for Ni element. it is difficult to increase N content in the smelting process of low nickel type duplex stainless steels, thus, the effect of Mn on aging microstructure and properties become the central issues for their development. For certain Cr cntents series low nickel type duplex stainless steels for engineering application, this project intends to study the influencing mechanism of Mn on the aging behavior. The following study will be conducted. To study the effect of Mn contents variation on the precipitation phase type and distribution in two phase, and to investigate the thermodynamic mechanism and kinetics process of precipitation formation with different Mn contents during aging treatment. To investigate the influencing mechanism of Mn contents variation on mechanical properties after aging treatment. To study the influencing rules and mechanism of Mn contents variation on pitting corrosion and intergranular corrosion and stress corrosion after aging treatment, so as to establish corresponding physical model of corrosion. Therefore, the influencing mechanism of Mn on precipitation phase formation and performance properties of low nickel type duplex stainless steels will be revealed during aging treatment, which is of great significance to promote their research and development and application.

Ni资源短缺是双相不锈钢推广和应用的障碍，发展节Ni型双相不锈钢是解决该问题的有效途径。同时，在高温使用环境和热加工过程中，脆性相的析出会降低双相不锈钢力学和耐腐蚀性能，故研究其时效机理和相关性能是改善高温使用性能的关键。节Ni型双相不锈钢以Mn、N代Ni稳定奥氏体相，因实际生产中增N困难，Mn对时效组织和性能的影响成为其发展的核心问题。对工程用一定Cr含量范围内节Ni型双相不锈钢，本项目拟对其时效行为的Mn影响机制进行研究。研究Mn含量变化对时效过程中析出相类型及在两相中分布规律的影响，探讨Mn影响并参与时效过程中析出相形成的热力学机理及动力学过程；分析Mn含量变化对时效力学性能的影响机制；研究Mn含量变化对时效点蚀、时效晶间腐蚀和应力腐蚀的影响规律和机理，并建立相应的腐蚀物理模型。通过揭示Mn对节Ni型双相不锈钢时效过程中析出相形成及相关性能的影响机制，对推进其研发和应用具有重要意义。

Ni资源短缺严重阻碍了双相不锈钢的应用和推广，且其在高温使用和热加工过程中析出相的形成会降低其使用性能。对于以Mn、N代Ni 稳定奥氏体节Ni型双相不锈钢，因实际生产中加N困难，为推进以Mn代Ni节Ni型双相不锈钢的发展和应用，探讨Mn添加对其高温条件下析出相形成和性能影响机制，针对Mn添加对不同Cr含量系列节Ni型双相不锈钢时效组织和性能影响进行了深入研究。对于19%Cr、22%Cr和25%Cr节Ni型系列双相不锈钢，获得了Mn对其固溶态两相体积分数变化、力学性能和耐点蚀性能影响规律，发现Mn添加导致的奥氏体比例变化对塑韧性影响较大，而对强度影响较小，固溶温度升高使高Cr含量实验钢Mn稳定奥氏体的能力减弱和耐点蚀性降低。揭示了19%Cr实验钢1040～1220℃固溶温度下Mn添加导致合金元素含量在两相中分配机理。揭示了Mn含量变化对500～800℃时效析出相组织演变影响规律，Mn对时效析出相形成和分布不仅受时效温度和时间的影响，还与Cr含量的变化存在紧密关系。鉴别了500～800℃条件下不同Mn含量下析出相类型，并获得了Mn添加对析出相元素分布的影响规律，探讨了Mn参与析出相形成的机理，发现Mn参与不同类型时效析出相的质量百分比存在较大差异。获得了Mn对22%Cr实验钢时效析出动力学影响规律和机制，首次探讨了不同时效温度下Mn含量变化对析出动力学参数和析出相形核方式的影响。获得了Mn含量增加导致奥氏体相体积分数变化、时效析出相数量和类型变化对冲击韧性的影响规律。揭示了Mn含量变化导致的时效析出相形成对点腐蚀电位和再钝化性能的影响规律和机理，发现Mn含量变化导致析出相的数量和类型的变化对耐点蚀性能影响较大，随时效温度增加，Mn含量增加提高了点蚀电位降低的敏感程度，且对点蚀再钝化性能影响增强。获得了Mn含量变化对晶间腐蚀影响规律，建立了不同Mn含量下时效σ相析出影响耐蚀性的电化学阻抗模型。