Low-Temperature Creep Behavior Of 60Si2MnA Steel

The tensile properties of 60Si2MnA steel in the conditions of room temperature and in 2.1×10^-42.1×10^-1/s strain rate were researched, under the temperature range of 573K⁷23K studied the low-temperature creep properties of 60Si2MnA steel in the stress of 0.63σ_0.2⁰.95σ_0.2, the stress was loaded by the strain rate of 1.9×10^-2/s. Optical microscope, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) observation of the 60Si2MnA steel were taken. Described the low temperature creep law of the 60Si2MnA steel by power law breakdown equation, finally, obtained the low-temperature creep model of the 60Si2MnA steel.As the velocities of tensile rise, yield strength and tensile strength of 60Si2MnA steel show a rising trend, while the elongation and reduction in area decline with increasing velocities. As the temperatures rise, yield strength and tensile strength of 60Si2MnA steel show a trend of decline, while the elongation and reduction in area of 60Si2MnA steel show a rising trend. Macroscopic observation shows a fracture characteristic of ductile fracture. SEM micrograph observes that with the tensile speed decreases, the size of dimple gradually become larger and deeper, that indicate the plasticity of 60Si2MnA steel increases and plastic deformation capacity enhancement.Get the creep activation energy of 60Si2MnA is 191kJ/mol in the temperature range of 573K⁷23K by using The Arrhenius equation, get the stress exponent of 60Si2MnA steel by using the power-law creep equation in 623K, 673K and 723K, the stress exponent of the mean value is 7.00 and the constant B on the average is 8.66×10-3, which in connection with the material properties. By comparison, the steady creep rate calculated by the PLB equation compared with the power law equation is much closer to the measured values, the deviation is a lot smaller, therefore, under the experimental conditions the creep law of 60Si2MnA steel more in line with the power law breakdown creep failure(PLB), that is low temperature (T<0.5Tm) under high stress, the mechanism of creep deformation is the dislocation glide mechanism. Metallographic observation shows that after creep the organization and distribution were not changed, the organization is still the tempered troostite with needle-like morphology of martensite. TEM observation shows that after creep the boundary of subgrain is clear, the phase difference between subcrystals is very small, while the subgrain boundary dislocation spacing decreases, the dislocation density within subgrain almost unchanged. There are dislocations of the multilateral phenomenon. EDX analysis shows that the carbide precipitates in the subgrain boundary containing mainly Fe, Si, Mn and other elements, it shows that after creep the carbide alloy appear precipitation and the structure did not have changed. SEM micrograph observation shows that the creep fracture mode of 60Si2MnA steel in 673K, 0.85σ_0.2 and 723K, 0.85σ_0.2 both are transgranular fracture mode.