稀土对低合金耐磨铸钢微观组织的影响机理

Low-alloy wear-resistant cast steel is one kind of wear resistant materials which has bright developing prospect in recent years. The researches have shown that adding rare earth in low-alloy wear-resistant cast steel can improve the microstructure and then increase the wear resistance, which results in extending its application range. But the study on the effect mechanism of RE on the microstructure of low-alloy wear-resistant cast steel from the aspect of the interaction between RE and other elements in steel appears very rare. The low-alloy wear-resistant cast steel widely used at present was used to prepare the experimental steel by adding different amounts of the elements of La and Ce. The method combined the detection and characterization techniques of minute RE with the simulating calculation was adopted to study the solid solution of RE in the low-alloy wear-resistant cast steel. The effects of RE on the inclusions, microstructure, mechanical properties, solid-state phase transformation dynamics and the precipitation behavior of the low-alloy wear-resistant cast steel were investigated by microstructure observation, mechanical properties test and thermal simulation experiments. The researches aims to ravel the existential state of RE in low-alloy wear-resistant cast steel and the interaction between RE and other elements in steel, and then understand fully the effect mechanism of RE on the microstructure. The research achievements can enrich the theory system of the effect mechanism of RE in steel, at the same time, they can provide the theory basis for the quantitative control of RE addition in low-alloy wear-resistant cast steel.

低合金耐磨铸钢是近年来一类很有发展前途的耐磨材料，研究表明，添加稀土可改善铸态组织，进而提高耐磨性，达到进一步扩大应用范围的目的，但从稀土与钢中其它元素交互作用的角度揭示稀土对低合金耐磨铸钢微观组织影响机理的研究，未见报导。本项目针对目前使用较为广泛的低合金耐磨铸钢，通过加入不同量的镧、铈稀土元素冶炼制备试验钢。通过微量稀土检测与表征技术，结合模拟计算分析研究微量镧、铈稀土在低合金耐磨铸钢中的固溶及固态反应；通过显微组织观察与力学性能检测，结合热模拟实验，研究镧、铈稀土加入量对低合金耐磨铸钢组织学、固态相变动力学与析出行为的影响。目的是从根本上弄清稀土镧、铈在低合金耐磨铸钢中的存在形式，弄清稀土与钢中其它元素的交互作用，进而揭示稀土对低合金耐磨铸钢微观组织的作用机理。研究结果能够丰富稀土在钢中作用机理的理论体系，也能够为稀土在低合金耐磨铸钢中加入的定量控制提供理依据。

铸钢由于是非变形材料，通过添加稀 土改善组织、提高性能非常重要。针对20MnCrNi2Mo低合金耐磨铸钢，通过加入不同量的镧、铈混合稀土冶炼制备试验钢；通过测定稀土残留量和固溶量，用物理化学相分析方法对试验钢中不同存在形式的稀土进行测量分析，结合第一性原理计算，研究了镧铈稀土在低合金耐磨铸钢中的固溶及固态反应，并探究了稀土在钢中的存在形式；通过显微组织观察与力学性能检测，结合对过冷奥氏体连续冷却转变动力学曲线的测定，并通过对以粒状贝氏体为主的贝氏体组织的回火转变过程的分析，研究了镧铈稀土对低合金耐磨铸钢组织学、固态相变动力学与析出行为的影响。.研究结果表明，钢中添加稀土，除了形成夹杂物，还能够微量固溶；固溶稀土更倾向于在晶界偏聚，此外，晶内也会有微量的稀土原子存在，相比而言，稀土固溶于Fe3C较之固溶于铁素体的倾向更大些。镧铈混合稀土使得试验钢连续冷却转变动力学曲线整体向右下方移动，增加了过冷奥氏体的稳定性，延缓了过冷奥氏体的转变，改善了20MnCrNi2Mo低合金耐磨铸钢的铸态显微组织，改变了夹杂物的类型，使夹杂物形状趋于圆整、尺寸减小，还改善了试验钢的断口形貌，使得试验钢的综合力学性能得到改善。镧铈稀土提高了20MnCrNi2Mo耐磨铸钢的抗回火稳定性，使得试验钢贝氏体组织回火过程中合金元素向θ-渗碳体的扩散富集形成平衡态碳化物合金渗碳体的过程受阻，并推迟了α相的回复、再结晶，延缓了M/A岛的分解，将回火转变推向高温。.研究搞清了镧铈稀土在钢中的存在形式，揭示了镧铈稀土对低合金耐磨铸钢微观组织的影响机理，为镧、铈稀土在钢中的有效利用提供了一定的理论基础。