Bainite Tempering Transformation Of20MnCrNi2Mo Steel And Effect Of Rare Earth On The Process

Low alloy wear-resistant cast steel has good property and low cost, so it has goodprospect. The application of RE on low alloy wear-resistant cast steel also attracts moreattention. The bainite low alloy wear-resistant cast steel is becoming a widespread researchdirection. Toughness and hardness is enhanced by proper heat treatment and multi-component alloying. It is important to improve abrasive resistance. A lot of researchs havebeen done about tempering process of bainite. The tempering process of granular bainiteneeds further research. And there is few report about the effect of RE on bainite temperingtransformation. The research of bainite tempering process and the effect of RE is importantin theoretical research and engineering application.For20MnCrNi2Mo wear-resistant cast steel with different content of mischmetal ofLa and Ce, they are respectively heated to200,250,300,350,400,450,500,550,600and650℃keeping for1hour. Firstly, the hardness after tempering is measured by Rockwellapparatus. In the next step, the microstructure after tempering is observed by SEM, TEMand EDS. The qualitative analysis of precipitated phase during tempering process is usedby electrowinning and XRD. Quantitative analysis of retained austenite for test steelbainite is used by XRD. Inclusions are separated by non-aqueous electrolyte at lowtemperature. And solid solubility of RE is measured by ICP-MS. The distribution of soliddisloved RE is resrarched by TEM and EDS. Bainite tempering transformation process oftest steel is researched, and effect of RE is analyzed. The bainite tempering transformationof20MnCrNi2Mo wear-resistant steel and the effect of RE is researched,The results show that: the granular bainite of20MnCrNi2Mo wear-resistant steel istempered at200～650℃keeping for1hour. The decomposition of M/A island isobserved when tempering at250℃. The content of M/A island decreases obviously whentempered at350℃. The type of precipitated carbides is M3C in the tempering process.Sub-grain is observed when tempered at500℃. But the boundary is dim. Sub-grain turns distinct when tempered at650℃. When RE is added in, the temperature for thedecomposition of M/A island increases in tempering process. The type of precipitatedphase is not changed. But RE hinders alloy element diffuse and enrich to Fe3C intempering process. RE restrain the formation of sub-grain. The testing results show thatthere is little RE dissolved in20MnCrNi2Mo wear-resistant cast steel. The solid solutionRE atom is apt to segregate in grain boundary and other crystal imperfection, and it hindersthe diffusion of carbon and alloy element. The dislocation movement is hindered too. Thechange of microstructure and hardness in the tempering process of granular is influenced.