The Solidification Characteristics Of Rare Earth Microalloy Austenite Stainless Steels With Low Nickel

Since the low nickel austenitic stainless steel has the advantages of small harm to human and the low cost of production, it has a very good market prospects. However, it is easy to appear defects such as crack in the rapid casting and hot working process. This has a close relation with the solidification of steel. Rare earth can improve the microstructure and properties of cast steel. Combined with the effects of directional solidification technology research of rare earth on microstructure and properties of the cast of the low nickel austenitic stainless steel, the rare application in stainless steel becomes one of the most important researches.In this paper, we use rare earth low nickel austenitic stainless steel as the research object to do the directional solidification experiment with electromagnetic induction directional growth furnace. Using differential thermal analyzer, Caisi optical microscope, scanning electron microscope with energy spectrum analyzer, the microstructure of rare earth influencing low nickel austenitic stainless steel under different solidification rate, the type of solidification, the solute distribution and the second phase were researched. The effect of rare earth on the casting microstructure and mechanical properties was discussed.The research shows that, in low nickel austenitic stainless steel, Ce refine the microstructure of the cast. Without rare earth, the austenitic stainless steel is coarse. The mean grain size is103.7um. When rare earth reached0.002%, grain became thinner. When rare earth reached0.067wt%, the mean grain size reduced to be53.4um.Through differential thermal analysis and directional solidification experiments, in air cooling condition, solidification mode of low nickel austenite stainless steel is austenitic mode. When the solidification rate is30μm/s and200μm/s, solidification is AF mode..Through directional solidification experiment, under the certain solidification rate, with the increase of the content of rare earth, the solidification structure is better, and the refinement of the primary dendrite and the second dendrite arm spacing have also been improved. When the content of rare earth is certain, under the solidification rate30μm/s, the solid-liquid interface of low nickel austenitic stainless steel presents cellular. When the solidification rate reached200μm/s, solid-liquid interface become columnar dendrite crystal. With the solidification rate increasing, the primary dendrite and the second dendrite arm spacing significantly reduced. Increasing the solidification rate and adding rare earth both can increase the micro-hardness values of low nickel austenitic stainless steel.Analysis by energy spectrum, rare earth can reduce the micro segregation of other elements. In addition, the rare earth cerium can also change the low nickel austenitic stainless steel inclusion shape. Without containing the rare earth, the most of the inclusion is irregular angular and inclusion is hercynite inclusions. When the content of rare earth reached0.002%, the inclusion became the oval and the number decreased. When the content of rare earth reached0.067%, the inclusion was the spherical rare earth aluminates and distributed in the grain interior.