.45 Steel Boron - Rare Earth (chromium) Alloying Process And Organizational Performance

To reduce the boronizing temperature and improve the structure and properties of boride layer was the purpose of this paper. The method of multi-boronizing was used. The elements of multi-boronizing were Rare Earth element and Chromium element as well as Boron element. The method of orthogonal experiment was used to investigate the effect of parameter of boronizing process on the thickness of the boride layer. The parameter of boronizing process included boronizing temperature, boronizing time, the addition of Rare Earth and the addition of Chromium. Then the proper parameters of boronizing process were determined. Devices and equipments such as optical microscope, metallographic microscope, scanning electron microscope (SEM), X-ray diffractometer, microhardness tester, wear tester and so on, were used to observe the structure of boride layer and test properties of boride layer.The conclusions as follows:The higher boronizing temperature, the more the thickness of the boride layer. The relation between the thickness of the boride layer and boronizing time obeyed the parabolic law. Rare Earth could accelerate the growth of the boride layer. But there was optimal range for the addition of Rare Earth. The rational boronizing process as follows: Boronizing temperature: 880-920. Boronizing time: 4-6h. The addition of Rare Earth: 4-6%. The addition of Chromium: 1-3%.The structures of all boride layers consisted of simple Fe2B phase. The tooth-like structure of the boride layer inserted the matrix. The growth of the boride layer appeared sharp texture. From the surface of the boride layer to the matrix, the structures were Fe2B phase, the transition zone, the matrix, respectively. The high temperature oxidation resistance and the corrosion resistance in sulfuric acid solution(15%) of the boride layer were better than these of 45 steel.Comparing with the case of boronizing, the structure of the boride layer of multi-boronizing was improved. The degree of outermost rarefaction of the boride layer of multi-boronizing was relieved. Rare Earth element and Chromium element existed in the boride layer, buttheir distributions in the boride layer were non-uniform. Themicrohardness gradient of the boride layer contained Rare Earth elementwas improved. The brittleness and the wear resistance of the boride layerof multi-boronizing were better. Particularly, the wear resistance of boridelayer contained Rare Earth element was best.