Study On Improvement Of Hot Ductility And Hot Shortness Of Steel Containing Copper And Arsenic By Rare Earth

With the advent of the"dual carbon"era,scrap steel would play an important role as a green recycling resource.However,the residual elements in scrap steel were difficult to economically remove by current smelting methods because of their lower oxygen potential than iron,and then harmed to the steel properties.In this thesis,rare earth were added to improve the hot ductility and hot workability problems caused by the coexistence of copper and arsenic,and the improvement effect and mechanism by rare earth are studied.For the hot ductility,0.0022～0.0290wt%Ce improved the hot ductility of steel with0.16wt%Cu+0.10wt%As.When Ce content in steel were 0.0022wt%and 0.0058wt%,the temperature range for hot ductility improvement was 950～1100℃.When Ce content was0.0100wt%,the hot ductility was enhanced in the whole temperature range of 700～1100℃,and the hot ductility of steel with 0.0100wt%Ce returned to the similar level of 0.17 wt%Cu bearing steel without As.As further increased to 0.0290wt%Ce,the hot ductility continued to be improved,and hot ductility was much higher than that of 0.17wt%Cu bearing steel without As in the temperature range of 800～1100℃.The reason for the hot ductility improvement was that Ce completely inhibited the formation of intergranular proeutectoid ferrite and simultaneously promoted the dynamic recrystallization occurrence.Furthermore,the inclusion composition combined with gain boundary element analysis implied that Ce and As did not interact with each other at low Ce content such as in steel with 0.0022wt%Ce,and the competitive grain boundary segregation of Ce and As was another reason for the hot ductility improvement.However,the As-containing rare earth inclusions was formed at the higher Ce content such as in steel with0.0290wt%Ce.This would reduce the amount of solution arsenic into the matrix,which in turn decreased the grain boundary segregation of As and enhanced the hot ductility except for the competitive grain boundary of Ce and As.Therefore,the hot ductility improvement effect of the interaction between RE and As was superior to that of the single competitive grain boundary segregation.For the high temperature oxidation and hot shortness behavior,0.0022～0.0290wt%Ce decreased the weight gain,increased the oxidation activation energy and high temperature oxidation resistance.The oxidation enrichment mapping analysis suggested that the enrichment of Cu and As was the most serious at 1000℃ and 1050℃,the enrichment phenomenon was not distinguished at above 1100℃.When oxidized at 1000 and 1050℃,increasing Ce content reduced Cu and As enrichment at the scale/steel matrix interface and even eliminated the Cu-rich liquid phase containing As when Ce content in steel exceeded 0.0100wt%.Furthermore,the hot compression experiments suggested that when Ce content was 0.0022 and 0.0058wt%,the surface cracking caused by the grain boundary penetration of Cu-rich liquid phase containing As at 1050℃ was alleviated,and the hot cracking is basically eliminated when Ce content was0.0100 and 0.0290wt%.The refined austenite grain size,the densified oxide layer,the formation of Fe₂Si O₄layer and As-containing rare earth inclusions in steel with higher Ce content was responsible for the reduction of Cu and As enrichment.Considering the hot ductility improvement and surface cracking suppression,0.0100 and 0.0290wt%Ce in steel with0.16wt%Cu+0.10wt%As was more appropriate.