Research On Re-Al-boronizing On The Surface Of Steels

This subject aims to improve service ability of hot-pinch mould and raise its life-span on active service. So the experimental study of Re-Al-boronizing on the surface of steels has been carried on.In this paper, the influences of different boronizers, boriding temperature, content of carbon and alloying elements in steel, the content of Re and Al in boronizers on the microstructure and properties for steels were investigated. And the microstructure of Re-Al-boronized layer and distribution of every element were researched by SEM, energy spectrum and X ray diffraction analysis. This paper put forward the function of Al in the process of Re-Al-boronizing and studied low temperature boriding for alloy-steel 4Cr5MoSiVl for the first time. Moreover, the thermodynamics analysis of boriding course was carried on and Re-Al-boronized mechanism was discussed systematically and deeply.The results of study indicate that no matter high temperature Re-Al-boronizing or the low temperature boriding, the most strong capability of boronization is for borax, carbonization boron takes second place, LSB is the worst in three boronizers. Low temperature Re-Al-boronizing on the surface of steel can be realized. With increasing the amount of carbon and alloying element in steel, the thickness of boriding layer reduces , the transition zone increases, and the needle like structure tends towards stability. The optimum value of the content of Re-Mg in the boronizers is 10%~15%. When the content of Al is smaller than 6%, increasing the content of aluminium, the thickness of boriding layer reduces. Al mainly plays a reducing role to promote the production of active B atom. Phase structure of boriding layer is connected with boron-tendency. When boron-tendency is higher, the layer is mainly consisted of phases FeB; when the boron-tendency is lower, it is mainly phases Fe2B.The results of X ray diffraction and energy spectrum analysis show that phases structure of Re-Al-boronized layer is without (Fe, Al) B, (Fe,Al) 2B existing at Al<2%.The microstructure of the layer is continuous and compact, the layer possess high micro-hardness. When corrode medium density is lower, corrosion resistance of low-temperature Re-Al-boronized layer for steel 45 is superior to one of high temperature, but as corrode medium density is higher, corrosion resistance of high-temperature layer is better. Compared with nitriding and simple boriding, Re-Al-boronized layer has the higher red hardness and anti-oxidation property. The above-mentioned results of study offer the reliable craft parameter and theoretical foundation for superficial strengthening, production and development of mould.