Effect Of Rare Earth Treatment On Microstructure And Properties Of Ferritic Stainless Steel Bearing Tin And Copper

The application of rare earth in steel has been paid more and more attention,and some achievements have been made.It has been proved that adding proper amount of rare earth into steel by suitable method has great potential to improve the properties of steel material and reduce the production cost.Based on the 430 ferritic stainless steel bearing Sn and Cu,the effects of rare earth elements on the purification of molten steel,modification of inclusions and microalloying of ferritic stainless steel were studied in this paper.The mechanism of rare earth elements on the non-metallic inclusions,microstructure,mechanics and corrosion resistance of 430 ferritic stainless steel bearing Sn and Cu was investigated.Six groups of 430 ferrite stainless steels bearing Sn and Cu with different rare earth contents were smelted in a 30 kg vacuum induction furnace by means of Al pre-deoxidation,vacuum decarburization,deoxidation and rare earth deep deoxidation and desulfurization.The results showed that proper amount of rare earth played an important role in deep deoxidation and desulfurization.The lowest oxygen content was 0.00086%,and the lowest sulfur content was 0.002%.When the content of rare earth was above 0.0018%,the proportion of equiaxed grain zone of stainless steel ingot increased to above 53%.The highist properity could reach 82.7%,which effectively avoided the wrinkle problem in the process of steel processing.At the same time,with the increase of RE content,the inclusions in the steel were transformed in the order of MnS·Al2O3→ CeAlO3→ Ce2O2S→ Ce2O3,and the inclusions were further refined and spherically dispersed in the steel.The amount of inclusions,the average diameter and the proportion of inclusions in the steel treated with RE had a tendency to decrease,so as to improve the cleanliness of steel.The addition of rare earth can effectively improve the mechanical properties of hot rolled annealed stainless steel.With the increase of RE content,the grain size of stainless steel first decreased and then increased.The yield strength and tensile strength of the stainless steel containing 0.012%RE were 337.02 MPa and 455.55 MPa respectively,which was 21 MPa higher than that of the steel without RE.At the same time,when the content of rare earth was 0.012%,the best plasticity was obtained.The elongation was 37.4%,the reduction of area was 52.2%,and the mixed fracture of ductile and brittle was transformed into ductile fracture.In addition,the plastic strain ratio along rolling direction of stainless steel treated with rare earth was increased.When the content of rare earth was 0.003%,r>1,the deep drawing property of stainless steel was improved effectively.When the rare earth content was 0.012%,the self-corrosion potential of stainless steel after hot-rolling annealing can reach-227 mV.The self-corrosion current decreased to 306 nA·cm-2,which was was 30%of that stainless steel bearing Sn and Cu without rare earth.The pitting potential reached 148 mV,the impedance reached 2.45 E+5 Ω·cm2,the intergranular corrosion reactivation rate decreased to 12.5%,and the intergranular corrosion sensitivity decreased by 50%compared with that of the stainless steel bearing Sn and Cu without rare earth addition.