Microstructure,properties and strengthening mechanism of carbon-strengthened ultra-low carbon steel
In order to find out the effect of carbon content on the mechanical properties of ultra-low carbon steel,three types of ultra-low carbon steel with carbon mass fraction of 0.002％,0.005％,and 0.008％were smelted in the laboratory,which were rolled as hot steel sheet.Mechanical properties,microstructure and second phase precip-itation of the steel sheet were observed.The results show that,with the increase of carbon mass fraction from 0.002％to 0.008％,the yield strength and tensile strength of the steel significantly increase,while the elongation after fracture decreases.With the increase of carbon content,the strength change at 580 ℃ coiling is more signifi-cant than that at 730 ℃ coiling.The grain size of test steel decreases from 22 μm at carbon mass fraction of 0.002％and coiling temperature of 730 ℃ to 11 μm at carbon mass fraction of 0.008％and coiling temperature of 580 ℃,and second phase TiC particles average size decreases from 35 nm at carbon mass fraction of 0.002％and coiling temperature of 730 ℃ to 10 nm at carbon mass fraction of 0.008％and coiling temperature of 580 ℃.When the car-bon mass fraction is 0.008％and the coiling temperature is 730 ℃,the yield strength of the steel sheet reaches more than 230 MPa,the calculated grain-refining strengthening value is 64.5 MPa and the precipitation strengthening val-ue is 56.8 MPa.Industrial production data show that when the carbon mass fraction of the ultra-low carbon steel is 0.008％,the mechanical properties can meet the standard requirements of high-strength IF steel.
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