稀土低合金贝氏体耐磨铸钢回火过程中的组织演变

Microstructure Evolution of Low-alloy Bainite Wear-resistant Cast Steel with Rare Earth in Tempering Process

摘要:

针对添加镧铈混合稀土的20MnCrNi2Mo低合金贝氏体耐磨铸钢,将其铸态组织分别加热到200~650 ℃并保温1 h进行回火处理,采用扫描电镜和透射电镜观察回火过程中的显微组织,采用物理化学相分析方法对析出相进行定性与定量分析,采用X射线衍射仪对不同温度回火组织中残留奥氏体量进行定量测定,分析回火过程中的组织演变。结果表明,实验钢的铸态组织为粒状贝氏体,回火过程中析出的平衡相碳化物为合金渗碳体,且其中有微量稀土固溶；500 ℃回火时未观察到明显的回复现象,650 ℃回火时有亚晶形成,发生明显的回复；200 ℃回火时M/A岛基本未发生分解,随回火温度的升高,M/A岛逐渐发生分解,到450 ℃回火时,M/A岛大量分解。

Abstract:

The cast samples of low-alloy bainite wear-resistant cast steel of 20MnCrNi2Mo with anthanum-cerium mischmetal were tempered at 200, 250, 300, 350, 400, 450, 500, 550, 600 and 650 ℃ respectively for 1 h. The microstructure was observed by QUANTA-400 environmental scanning electron microscope and JEM-2100 transmission electron microscope, the precipitation was qualitatively and quantitatively analyzed by using physicochemical phase analysis, and the retained austenite after different temperature tempering was measured quantitatively by D8 ADVANCE X ray diffracmeter. The microstructure evolution during the tempering was investigated. The results show that the microstructure of the tested steel as cast is granular bainite. The precipitated equilibrium-phase carbide during the tempering is alloying cementite with trace amount of solid-solution rare earth. The recovery has not been found during tempering at 500 ℃. The subgrains are found become distinctly and the recovery is observed clearly during tempering at 650 ℃. The M/A islands do not decompose tempered at 200 ℃, with the increase of the tempering temperature, the M/A islands gradually decompose, and the amount of the M/A islands decreases so obviously that it can not be detected when the tempering temperature is up to 450 ℃.