Study On The Modification Of Allotype Steel By Rare Earth Elements And Surface Treatment

There are defects in the joint,fatigue and stress concentration in the special-shaped steel structure.The cracking in the cold bending process of the special shaped steel in the fields of tunnel and bridge is easy to crack.Therefore,the flexural performance and toughness of the special-shaped steel must be improved from the point of view of safety and saving the resources.In order to solve this problem,this paper uses the I-steel as the base material,modifier by adding rare earth element Ce,as well as the bending resistance modification and the corrosion resistance modification of hot dipped aluminum by shot peening treatment,in order to improve the performance of the I-steel.The metallographic structure,surface stress,microhardness,mechanical properties and fracture analysis of I-steel were analyzed by means of metallographic microscope,micro dimensional hardness tester,microcomputer controlled electronic universal testing machine,stress tester,X ray diffraction analyzer,scanning electron microscope and so on.The results show that when the shot peening time is 30 s,the microhardness value of the sample surface reaches the maximum value of 474 HV,and the microhardness value 230 HV is increased by 106.1% compared with that of the unpeening sample,the surface stress value reaches the maximum value 436 MPa,and the surface stress 299.4MPa of the specimen without shot peening can be raised by 45.8%,and the shot peening sample is relatively not shot peening sample.The critical temperature of transition is changed from 743.2 ?to 739?,which is reduced by 4.2 degrees Celsius.The diffraction angle of shot peening samples increased by 0.024 degrees at 46.592 degrees than that of non shot peening samples.The spacing of the crystal surface decreased from 0.22644 nm to 0.22633 nm,and the spacing of the crystal surface decreased by 0.00011 nm,and the bending strength was 2.03 GPa,and the bending strength of the shot peening was 36.24% higher than that of the unshot peening.The diffusion temperature of hot dipped aluminum at 890? that can not only ensure the maximum strength of the matrix 162.6HV,but also obtain a small thickness of 140?m,which can improve the corrosion resistance and oxidation resistance of the sample.When the rare earth element Ce is added,the maximum grain degree is 7.05 when the residual amount is 0.024%,and the grain degree of the rare earth sample is increased by 19.9%.The sample with the residual amount of 0.024% of the rare earth is tested by the X ray diffraction method.The surface stress value is 13 MPa and the surface stress value changes to 348.6 MPa through the shot peening 30 s treatment,and its bending resistance is reduced.The bending strength of the sample is increased by 15.17% from 1.45 GPa to 1.67 GPa,and the bending strength of the sample is 16.27% higher than that of the rare earth specimen without the rare-earth specimen,and the bending strength of the sample is combined with the rare-earth modification.When the residual Ce of rare-earth element is 0.024%,the impact energy reaches the maximum value of 33 J,which is 46.67% higher than that of the rare earth sample without impact on the 22.5J.After shot peening 30 s,the impact energy of the sample is changed to 34 J,and shot peening has little effect on the impact work.