Effect of Cu alloying on cryogenic-temperature toughness of Fe-18Mn-0.6C TWIP steel
TWIP(twinning induced plasticity)steel t has the advantages of high strength and ductility,high impact toughness and high low-temperature performance.At present,the Fe-18Mn-0.6C based TWIP is widely used in the market.The industrial production and promotion of high-performance TWIP steel can achieve complete variety specifications of China's steel industry and promote high value-added steel materials.Through a certain alloying design to further improve its low-temperature strength and toughness,it can become an effective alternative steel for energy storage and transportation.Cu with different contents were added to Fe-18Mn-0.6C TWIP steel.Through tensile test at room temperature and impact test from room temperature to low/ultra-low temperature,with OM,XRD,SEM and EBSD et al.for characterization to found the effect of Cu alloying on the microstructure and mechanical properties of hot-rolled TWIP steel,especially the improvement effect of cryogenic toughness at low tem-perature/ultra-low temperature by Cu alloying.The results show that the hot-rolled TWIP steels had single austen-itic microstructure,and the Cu alloying had significant grain refining effect on the TWIP steel,and also increased the uniformity of grain boundary orientation difference.At room temperature,the TWIP steel without Cu shows higher strength and better plasticity because of its larger average grain size,showing higher strain strengthening effect and higher strength and plasticity balance.The effect of Cu alloying on the impact toughness of TWIP steel is distinct.The impact energy of TWIP steel increased with the increasing Cu content.The impact energy of TWIP steel with 2.9%Cu alloying at room temperature reached 375 J.The impact toughness of TWIP steel without Cu alloying decreased significantly with the decreasing temperature.The impact energy of TWIP steel with Cu alloying remained above 200 J at-180℃.This is related to Cu alloying increasing SFE,reducing SFE decline at low tem-perature,inhibiting ε-martensitic transformation and improving solution strengthening effect at low temperature.TWIP steel can still maintain ductile fracture characteristics with the decreasing temperature to-180℃.Only TWIP steel without Cu alloying had a small amount of local brittle fracture morphology impacted at-180℃.
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