| Based on the role of each element in IQ process,a kind of Cu-bearing low carbon steel with component of 0.18 C-1.58 Si-2 Mn-0.41 Cu-0.33 Ni was designed under the premise of fully considering.The analysis method combines testing by SEM,EPMA,X-ray diffractometer,tensile test,phase transformation thermal dilatometer,and thermodynamic and kinetic calculation by Thermo-Calc and Dictra software.In this paper,the effects of intercritical heat preservation process on microstructure,element partition and mechanical properties were investigated and the following results were obtained.The thermodynamic calculation results show that under equilibrium state the Ae1 and Ae3 temperature of experimental steel are 660 ? and 819 ? respectively in the equilibrium state of test steel.With the increase of equilibrium temperature,the fcc phase fraction increases and the mass fraction of alloy elements in fcc phase decreases.The results of Dictra show that the rate of partition and homogenization of C atom is much higher than that of Mn and Cu atom,while that of Mn atom is slightly higher compared with Cu atom.The interface migration rate is 11900 nm/s under the control of C atom partitioning,while only 0.25 nm/s under the control of Mn and Cu atom partitioning.The results of EPMA show that the relative partition and homogenization rate of C,Mn and Cu are consistent with the calculated results,but the actual rate is smaller.SEM examination showed that the microstructure was mainly composed of ferrite,martensite and a small amount of retained austenite after IQ treatment.The block-shaped martensite nucleates at the boundaries of the ferrite.The tensile test shows that when the heat preservation temperature is 740 ?,the maximum value of the strength-plasticity balance is 16963.24 MPa·% at 600 s.When the heat preservation time is 1200 s,the maximum value reached 15963.04 MPa·% at 760 ?.Figure 36;Table 3;Reference 84... |
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