Synergistic effect of Cu and Ni on microstructure properties and second phase precipitation behavior of micro-alloyed high-strength steel
The effects of the relative contents of Cu and Ni on the microstructure and second phase precipitation behavior of copper-bearing aged steel with the same Cu/Ni ratio were investigated.SEM,TEM,EBSD,XRD and other analytical characterization methods were used to analyze the microstructure and mechanical properties of low carbon micro-alloyed high strength steel with different Cu and Ni contents under quenching and tempering treatment.The results show that the strength and toughness of the test steel are improved with the increase of Cu and Ni content(tensile strength increased by 3.3%,impact toughness increased by 10%).In the microstructure,some granular bainite is transformed into tempered sorbite(the proportion of tempered sorbite increased by 10%),the content of large-angle grain boundaries increases,and the substructure and dislocation density improve significantly.It is found that the austenite phase transition temperature decreases with the increase of Ni content by Thermo-Calc thermodynamic calculation.The addition of Ni element refines the tempered sorbite lath(from 332nm to 264nm)and increases the lath bundles in the structure.A large number of dislocation entanglement in the slat boundary provides more nucleation sites for the second phase precipitation,reduces the form energy of Cu precipitation,promotes and refines Cu precipitation,and then improves the strength and toughness of micro-alloyed high strength steels.
copper-nickel compositetempering treatmentfine grain strengtheningsecond phase reinforcementlow temperature toughness
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