In order to obtain ultra-fine-grained steel, a variety of process methods have been developed: repeat heat treatment under the same rapid heating condition, mechanical grinding of metal powder, controlled rolling, controlled cooling, TMCP, composite TMCP method, etc. The ultrafine grains is the determinant of the excellent strength and toughness of ultrafine grain steels. Therefore, the difference between ultrafine grain steels and traditional steels is that their chemical composition cannot be used to predict strength of steel.
Compared with traditional steels of the same strength, the main feature of ultrafine grain steel is its low carbon content, which is conducive to improving its weldability. Therefore, the strengthening means is not by increasing the carbon content and alloy element content, but by grain refinement, phase transformation strengthening, precipitation strengthening and other methods are combined to achieve the purpose of improving toughness.
Grain refinement (including deformation refinement and phase refinement) is the only method that can simultaneously improve the strength and toughness of steel, thus becoming the best strengthening mechanism for ultrafine grain steel. Precipitation strengthening by the precipitation of second-phase particles is another strengthening mechanism adopted by ultrafine grain steel. Although particles formed in austenite at high temperature are effective for controlling grain growth, they will not cause strengthening. It is formed in austenite or ferrite at low temperature. Dislocation and substructure strengthening is also an effective strengthening method.
Henan Jinrui Machinery © Co., Ltd. All Rights Reserved |