GRADIENT STEEL MATERIAL HAVING SURFACE LAYER WITH FERRITE AND INNER LAYER WITH FERRITE + PEARLITE AND MANUFACTURING METHOD

摘要

Provided are a gradient steel material having a surface layer with ferrite and an inner layer with ferrite + pearlite, and a manufacturing method, the weight percentage of the components are: C≤0.15%, Si≤1%, Mn≤1.5%, the remaining are Fe and inevitable impurities, and the surface layer of the steel material is ferrite tissue, the inner layer is ferrite + pearlite tissue. The manufacturing method thereof includes: smelting, casting, rolling, heat treatment; wherein, in the heat treatment step, the steel material is heated above the austenite temperature Ac3, and the temperature is kept above 3 min to ensure that the material is completely austenitized; subsequently, it is cooled to a temperature below Ar1 at a cooling rate of less than 0.5°C/s. The steel material does not require to be compounded with two materials, and is only processed and prepared on a single material, the process is short, the procedure is simple, and the cost is low.