СТРУКТУРА И СВОЙСТВА ПОВЕРХНОСТИ НАПЛАВКИ, ОБЛУЧЕННОЙ ИНТЕНСИВНЫМ НИЗКОЭНЕРГЕТИЧЕСКИМ ИМПУЛЬСНЫМ ЭЛЕКТРОННЫМ ПУЧКОМ

Abstract

To substantiate the selection of a coatings material conforming to the operating conditions of the products and the subsequent electron-beam processing conditions, the authors studied the microhardness, Young’s modulus and the microstructure of modified surface layer deposited on the martensitic low-carbon Hardox 450 steel with the high-carbon powder wires of various chemical composition (No. 258 (NbC-G), No. 720 (DT-DUR), No. 760 (DT-DUR)) and further modified by the irradiation with the intense pulsed electron beam using the two-step method. The formation of fused layer on steel surface was carried out in the shielding gas environment containing 98 % Ar, 2 % CO 2 , with the welding current of 250–300 A and the arc voltage of 30–35 V. The modifying of a fusion layer was carried out by irradiating the fusion layer surface with a high-intensity electron beam in the mode of melting and high-speed crystallization. The load on the indenter was 50 mN. The Young’s modulus microhardness was determined in 30 arbitrarily selected points of the modified surfacing surface. The structure of modified by electron beam surfacing surface was studied with the scanning electron microscopy methods. It is determined that the increase in strength properties of the modified by the electron beam weld layer is caused by the formation of a sub-microsized structure, the hardening of which is caused by the quenching effect and the presence of the second phase inclusions (borides, carboborides, carbides). It was found that the maximum hardening effect is observed when surfacing with a flux-cored wire containing 4.5 % of boron. The study shows that the microcracks systems are formed on the surfacing surface formed by a wire, the elemental composition of which includes 4.5 % of boron, and additionally irradiated with the intense pulsed electron beam. While the surface surfacing formed by the powdered wires free of boron after the pulsed electron beam treatment demonstrated the absence of microcracks on the modified surface. The authors determined the significant spread in nanohardness and Young’s modulus values that was apparently conditioned by the nonuniform distribution of strengthening phases.