| Based on the promotion of the two-stage carbon emission reduction goal proposed by China,scrap steel resources become more and more important due to the green and low-carbon advantages.However,the problem of deteriorating steel properties caused by residual elements would be inevitably faced during scrap recycling process.In this paper,the effect of As on the hot ductility and hot workability of steels with two levels of Cu content as well as deterioration mechanisms was investigated by hot tensile and isothermal oxidation testing,respectively.This provided theoretical basis and technical support to avoid crack-sensitive areas for the operation of continuous casting straightening step and subsequent rolling step.The results of high temperature hot tensile test show that when the content of Cu is 0.17mass%or 0.22mass%,the loss of hot ductility of the test steel increases with the increase of arsenic content at 700～1100℃;However,the As content that seriously harms hot ductility was 0.10mass% for steel with 0.17mass% Cu,while this As content was decreased to 0.04mass% for steel with0.22mass%Cu.The fracture morphology results show that the fracture of the experimental steel changes to intergranular brittle fracture with the increase of arsenic content under the two copper content levels.Thermal dilatometric curve combined with microstructure observation indicated that the increase of As content suppressed the formation of intergranular proeutectoid ferrite and thereby triggered in the hot ductility deterioration in the austenite+ferrite two phase region.The analysis results of stress-strain curves and transmission electron microscopy(TEM)showed that the inhibition of dynamic recrystallization by As and the grain boundary segregation of Cu and As resulted in the poor hot ductility in the austenite single phase region.The effect of Cu and As on the hot workability of steel is closely related to its high temperature oxidation.The results of oxidation kinetics show that no matter the Cu content level is 0.17mass%or 0.22mass%,the increase of As content improved the oxidation weight gain and reduce the oxidation activation energy of steel.At the same time,the oxidation activation energy of steel with copper content level of 0.22mass% is lower than that of steel with copper content level of0.17mass%.The oxidation enrichment mapping analysis suggested that the enrichment of Cu and As was the most serious at 1050°C and the enrichment phenomenon was not distinguished at above1100°C.Meanwhile,the penetration into grain boundary by Cu and As enriched liquid phase was gradually obvious with increasing As content at 1050°C.Increasing As content reduced the melting point of the copper-rich phase,which promoted the more precipitation of copper-rich liquid phase containing As and then penetrated grain boundaries at 1050°C determined by energy dispersive spectroscopy(EDS)and Cu-As phase diagram analysis.In addition,the As content that initiated the grain boundary penetration by Cu-rich liquid phase containing As was 0.10mass% for steel with0.17mass%Cu,while the As content level was 0.04mass% for steel with 0.22mass%Cu.The simulated hot compression experiment confirmed that the surface cracking was most severe at1050°C and exacerbated with increasing As content,in consistent with Cu and As enrichment during high temperature oxidation experiment.In order to avoid the hot crack sensitive area,the final rolling temperature of copper-arsenic steel should be higher than 1100℃ as much as possible. |
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