A Study On Processes And Properties Of Y-base Rare Earth Inoculating High Manganese Steel

Effects of Y-base rare earth inoculation process on microstructure, properties, as well as the work-hardening rate of high manganese steel (ZGMnl3-1) were studied. Inoculation technology in this paper included the amount addition of heavy rare earth yttrium, the adding temperature and the methods of adding.Results showed that for the inoculated as-cast samples, the effect of rare-earth was mainly reflected in purifying grain boundary and refining the grain. The rare earth played a key role in cleanup when its residual level is low (0.018wt.%). Austenite grain size is relative fine compared with un-inoculated microstructure. Thus, the number of carbides on grain boundary decreased significantly, impact toughness and tensile strength were increased. When the rare earth content in the steel was 0.023 wt.%, austenite grain size decreased from 197.6μm to the 109.9μm, tensile strength and impact toughness values remained at a high level. Excessive amount addition can not refine austenite grain further. In contrast, the tensile strength and impact toughness were deteriorated because of the large number of impurities connected with each other while as-cast hardness improved with the amount of residual rare earth increasing.After solution treatment, the primary role of rare earth was solution strengthening and refining strengthening. Low amount addition (0.018wt.%) of rare earth did not have an important effect on microstructure and properties. However, when the residual level of rare earth reached to 0.024wt.%, austenite grain were refined from 255.4μm to the 136.5μm; tensile strength increased from 479.3MPa to 802.6MPa; impact toughness increased from 68.4 J/cm2 to 108.8 J/cm2, abrasive wear resistance properties also improved obviously. Excessive rare earth (>0.047wt.%) destroyed tensile strength, impact toughness, abrasion resistance due to there are many rare earth compounds still remained along the grain boundary after solution treatment. The hardness improved with the amount of in- solution rare earth compounds increasing. At the same adding temperature, adding rare earth into ladle can purify molten steel more effectively than adding into steel spout:the former samples obtained higher tensile strength, impact toughness, and abrasive wear resistance properties. With the same adding method (adding into ladle), casting temperature plays an important role in refining austenite grain. Smaller austenite grain size and well properties (including tensile strength, impact toughness, abrasive wear resistance) can be obtained under lower adding temperature.The stacking fault density ofε-martensite of the steel is higher than that of the steel without inoculation under the same impact energy. The micro-hardness increases from 341.7 HV0.2 to 517.3 HV0.2. The work-hardening rate of high-manganese steel was increased by Y rare earth-based inoculation.A well processes of Y-base rare earth inoculation high manganese steel including the following three aspects:adding rare earth into ladle, the residual rare earth level between 0.023%～0.035%, and a lower adding temperature.