Ti-Zr微合金化工程机械用钢控轧过程中奥氏体组织超细化及均匀化调控机制

The combination of Ti microalloying method with controlled rolling and controlled cooling is an economic and effective way to produce engineering mechanical steel with high strength and high toughness.It is some key problems in Ti microalloying low carbon steel that unstable Ti precipitated phases, austenite coarsening and mixed grain phenomenon during controlled rolling process.For these problems, Ti-Zr microalloying method would be adopted . By using the addition of Zr to influence precipitation of Ti compounds in different periods, the influence of Ti carbides on recrystallization would be given play to its function and austenite grains would be fully recrystallized to make the austenite grian size being fully ultra-refined and homogenized, and then it is expected to search for new technologies for improving and stabling the properties of Ti microalloying steel in this project. First of all, the controlling precipitation mechanism of Ti carbonitrides in different periods and the effect of Zr would be studied using application of precipitation transformation theory and stress relaxation test. Then, the influence of Ti, Zr and hot rolling process on hot deformation behavior, dynamic recrystallization and static recrystallization of austenite grain would be investigated by theoretical calculation and thermal simulation test. Thus, new technologies for austenite refinement would be obtained. Based on the above work, microstructure evolution rules under actual controlled rolling conditions would be investigated. The aim of this study is to clarify general scientific problems such as coupling relationship between austenite recrystallization and precipitation in Ti-Zr microalloying steel, the detailed microstructure controlling mechanism of ultra-refinement and homogenization of austenite grains, and finally exploring a new way for ultra-refinement of austenite. The implementation of this project will enrich the strengthening and toughening theory of microalloying high strength steel, and also is of great scientific importance to promote the further development of engineering mechanical steel with high strength, high toughness in our country.

钛微合金化结合控轧控冷技术是生产高强度高韧性工程机械用钢经济有效的方法。针对钛微合金化钢Ti析出相不稳定以及控轧过程中奥氏体组织晶粒粗大且具有混晶现象等问题，提出Ti-Zr复合微合金化，利用Zr来影响Ti的化合物析出相，发挥轧制阶段钛的碳化物对再结晶的作用，使奥氏体晶粒尺寸超细化和均匀化，探讨改善和稳定钛微合金化钢性能的新途径。首先应用析出相变理论和应力松弛试验研究钛的碳氮化物不同阶段析出的控制以及Zr的影响，然后利用理论计算结合热模拟试验研究Ti、Zr和热轧工艺对奥氏体热变形行为及动态和静态再结晶的影响。在此基础上，研究实际控轧条件下组织演变规律，阐明钛锆复合微合金化钢奥氏体再结晶与析出的耦合关系以及奥氏体晶粒超细化和均匀化的调控机制等共性科学问题，探寻奥氏体组织超细化的新途径。项目的实施将丰富微合金化高强度钢的强韧化理论，对推进我国工程机械用钢的进一步发展具有重要的科学意义。

钛微合金化结合控轧控冷技术是生产高强度高韧性工程机械用钢经济有效的方法。针对钛微合金化低碳钢中Ti析出相不稳定及控轧过程中奥氏体组织晶粒粗大且具有混晶现象等问题，本项目提出了采用Ti-Zr复合微合金化，利用Zr来调控钛析出相，提高钢中有效Ti，综合发挥Ti和Zr的作用，使轧制阶段奥氏体组织超细化和均匀化，获得了改善和稳定钛微合金钢综合力学性能的新途径。探明了Zr对钛微合金化低碳钢不同阶段Ti化合物固溶和析出的影响规律。发现Zr能减少钛的氮化物和碳硫化物从铸态组织和高温奥氏体中析出，提高钛在奥氏体中的固溶度，使轧制阶段形变诱导析出相增多并且细化。对不同工艺条件下Zr含量对热变形及动态和静态再结晶行为和析出的影响进行了研究，明确了Ti-Zr复合微合金化低碳钢热变形和奥氏体再结晶行为以及析出规律，揭示了形变奥氏体再结晶与析出相的耦合关系。研究了主要轧制工艺参数和Zr、Ti含量对轧制阶段奥氏体组织的影响，获得了奥氏体组织演变和析出规律，阐明了轧制阶段奥氏体组织细化和均匀化的调控机制，实现了轧制阶段奥氏体组织细化到10μm以下且均匀。利用Ti-Zr复合微合金化结合控轧控冷技术成功制备出屈服强度在700MPa以上兼具延伸率在20%、-20℃夏比冲击吸收功在140J以上的高强度和高韧性低碳钢板，为新型高强度高韧性工程机械用钢板的开发奠定了基础。本研究成果对促进复合微合金化技术和低合金高强度钢的发展具有重要的科学意义和实用价值。