Study Of Effect Of Residual Element Tin On Microstructure And Properties Of High Carbon Steel

It is an inevitable trend that scrap steel will become the main raw material for steel production as the rapid increasing stock of iron and steel in China and the requirement of environmental protection.However,as one of the main residual elements in scrap steel,tin(Sn)with a lower oxidation potential than that of iron is difficult to economically remove in the current steelmaking process,resulting in an accumulation in the recycling process of scrap steel.Tin usually segregates to grain boundaries and the interfaces of the matrix and oxidation layer,so as to affect the hot working and mechanical properties of steel.It is of great practical significance for improving the steel quality and the utilization of scrap steel to explore the mechanism that how tin affects the properties of steel and to determine the allowable tin content in steel.Therefore,from the point of view of the occurrence state of Sn and its effect on the microstructures,the effects of Sn on the mechanical properties,high temperature oxidation properties and the kinetic characteristics of oxidation for high carbon steels with 0.003% to 0.120% Sn were investigated.The results show that tin affected the mechanical properties of high carbon steels by affecting the interlamellar spacing of the sorbite but had no significant effect on the microstructure type.The interlamellar spacing of sorbite first decreased and then increased as Sn content increased from 0.003% to 0.120%,and it reached the minimum value of 0.16 ?m when Sn content was 0.060%.Yield strength and tensile strength with opposite variation trends to the interlamellar spacing of sorbite reached the maximum values of 1064.89 MPa and 1333.25 MPa as Sn content was 0.060%,respectively.In addition,the elongation,percentage reduction of area and impact absorbing energy of high carbon steels decreased significantly with the increasing Sn content.Tin also affected high temperature oxidation properties of high carbon steels.Under the temperature from 990°C to 1110°C,tin significantly segregated in the oxide layer.As the oxidation time increased from 1800 s to 10800 s,the amount of oxide layers increased,and the presence of air gaps between oxidation layers significantly inhibited the diffusion of tin.The enrichment position of tin gradually migrated from the matrix to the surface of the oxide layer.The influence of Sn content on the high temperature oxidation characteristics of high carbon steel reflected in two aspects: oxidation weight gain and oxidation activation energy.The increase of Sn content inhibited the weight gain in the early stage of oxidation,and its inhibitory effect gradually decreased with the increase of oxidation temperature.The oxidative weight gain curves conformed to the parabolic law only at 990°C,and the increasing temperature significantly accelerated the oxidation process.The oxidation activation energy increased first and then decreased gradually with the increase of Sn content,which reached the maximum value of 737.635 kJ/mol as Sn content was 0.060%.In order to obtain good comprehensive mechanical properties and to ensure the heat processing properties of steel,Sn content should be controlled lower than 0.060%.