低成本双相不锈钢设计及制备的基础研究

To meet the demand for high durability steel bar in marine architecture, research on scientific issues of low-cost design and manufacture of lean duplex stainless steel is intended to carry out in this project. Firstly, alloy compositions will be optimally designed considering of low cost, corrosion resistance and the equilibrium of α/γ phase ratio. And then the poor hot plasticity of lean duplex stainless with Mn and N composites in place of Ni will be studied under the condition of thermal-mechanical coupling. It concludes that A. diffusion, migrate and redistribution of alloys elements between α and γ phases, B. α↔γ phase transformation, C. precipitation of carbonitride, intermetallic phase and secondary γ phase, D. coordinate softening between α and γ phase, E. deformation induced diffusion, phase transition and other complex microstructural evolutions. In order to explore the mechanism of increasing the hot workability of duplex stainless steel by means of optimal compositions design and microstructural control, the effects of materials microstructural evolution on hot plasticity are thoroughly discussed and analyzed. Finally, cold rolling of the billets or ingots right after homogenization will be carried out, and then the feasibility of the saving processing will be estimated after analysis of corrosion resistance and mechanical properties of the products. It is respected to lay the foundation for the application of high durability stainless steel bar instead of ordinary carbon steel bar in the field of marine engineering through the research in this project.

以海洋建筑对高耐久性钢筋的需求为背景，开展双相不锈钢的节约型成分设计和低成本加工制造两个方面的相关科学问题研究。开展兼顾低成本和耐蚀性、并保持α/γ两相比例平衡的合金成分优化设计；重点解决以Mn、N代Ni后双相不锈钢热塑性差的问题，拟在温度-变形耦合条件下研究：a.合金元素在α/γ两相间的扩散迁移与再分配，b.α↔γ相转变，c.(碳氮化物、金属间相、二次奥氏体相)析出，d.两相协调软化机制，e.形变诱导扩散、相变等复杂的微观组织演化行为，全面分析材料组织演化规律对热塑性的影响机制，从而探明通过成分优化、组织调控提高双相不锈钢热加工性的科学机理；另外还拟探索节约型双相不锈钢钢坯经均质化热处理后直接冷轧的工艺路线，研究短流程制备产品的组织变化及其对产品耐蚀性和力学指标的影响，进而探讨其可行性。通过以上科学问题的研究，为高耐久性不锈钢钢筋替代普通碳素钢筋在海洋工程领域推广应用奠定基础。

为替代普碳钢筋获得满足海洋工程用高耐久性双相不锈钢为背景，围绕双相不锈钢节约型成分设计、稀土合金化改性夹杂、热加工中N原子迁移行为、热力耦合条件下变形协调性及动态软化机制、短流程加工工艺探索等相关基础问题展开研究，主要取得以下进展：.1）探明了Mn、N代Ni的低成本双相不锈钢中Mn元素含量对相转变、相比例、显微硬度、冷变形性能及腐蚀性能的影响规律，揭示了冷变形加工硬化行为及应变诱导马氏体相变抑制裂纹的作用机理，掌握了较高Mn含量有利于轧制性能但有损耐点蚀性能。.2）分析了RE-Al复合脱氧对改性双相不锈钢中夹杂物的影响，探明了多组元复杂结构稀土夹杂物诱发腐蚀的微观机理，明确了电偶腐蚀诱发条件及电偶腐蚀顺序。稀土合金化的双相不锈钢凭借改性的含阳极相的夹杂物使其具有更优异的耐点蚀性能。.3）掌握了升温、温降及热变形下N在α↔γ相转变中迁移再分配行为及其对两相硬度的影响规律，阐明了Mn、Ni对N在两相间迁移的影响机制，获得N迁移影响双相不锈钢热塑性的本质原因。经缓冷或增加热变形能促进N回迁至奥氏体从而避免Cr2N析出。.4）揭示了变形温度、应变速率及压下量对双相不锈钢的流变应力、变形协调性及软化机制的影响机制，掌握合理的提高热塑性的热机械加工工艺制度。适当提高变形温度、降低应变速率及增加变形道次可获得良好的热塑性。.5）探明了不同变形条件对双相不锈钢应力-应变曲线及表面缺陷的影响规律，基于DMM与塑性功方法绘制了适用于低成本双相不锈钢的热加工图，确定了1050-1200℃与0.01-1s-1条件下处于低成本双相不锈钢的安全加工区域。.6）分析了不同变形条件下双相不锈钢中两相亚结构演变规律，探明了不同应变速率下两相动态软化机制，明确了高温高应变速率下DDRX机制有助于提高材料的热塑性。.7）对比了传统轧制与直接冷轧工艺的组织及性能，验证了均质化铸坯直接冷轧的可行性，确定了短流程制备冷轧钢筋工艺路线。经950℃退火处理的钢筋可获得符合要求的性能。