Research On Single-phase Ferrite Structure Of 45 Steel Surface

Steel material with gradient structure is one of the goals of modern steel material performance development.This gradient material can bring some special structural or functional properties.The single-phase ferrite structure was obtained on the surface of the 45#steel sample by accurately designing the heat treatment process,and the carbon diffusion behavior in the process of forming the surface single-phase ferrite structure was studied.Through the precise design of the cooling rate,a local ferrite phase transformation occurs on the surface of the sample within a certain cooling rate range,and the structure gradient material is finally formed.This material has dual advantages: on the one hand,the high-plasticity ferrite structure of the surface and the high-strength martensite structure of the core can make the whole material obtain a better combination of strength and bending performance;on the other hand,The pure ferrite layer on the surface of the steel material improves the surface corrosion resistance of the steel material due to the lower carbon content.Moreover,this process has the advantages of simple equipment,low cost,less energy consumption,and convenient operation.In this paper,the following conclusions have been obtained through research: in the range of cooling rate of 0.02?0.08 ?/s,45# steel has successfully prepared a surface ferrite layer;through the iron-carbon phase diagram,it is analyzed whether the cooling rate is caused by local ferrite transformation.The important factor is that the cooling rate needs to be accurately designed to form a suitable temperature gradient,and local ferrite phase transformation occurs on the surface of the sample,which leads to ultra-long-range diffusion of carbon atoms;the EPMA test results after the slow cooling experiment show that carbon Atoms undergo ultralong-range diffusion from the surface to the core;the result of EPMA quenched at 770 ?shows that a peak of carbon appears near the austenite/ferrite interface,which provides a direct way for the diffusion of carbon during the formation of surface ferrite.The results of the Monte Carlo simulation are qualitatively consistent with the results of EPMA quenched at 770 ?,which gives a statistical theoretical explanation;the corrosion resistance experiment shows that the presence of the surface ferrite layer does improve the corrosion resistance of the material.The research in this paper provides a theoretical explanation and direct experimental evidence for the formation of the surface ferrite layer and also provides a statistical simulation and explanation for the carbon diffusion behavior during the formation of surface ferrite.The scope of steel grades that realize local ferrite transformation has been expanded,and the structure gradient material has been successfully prepared.