Известия Томского политехнического университета: Инжиниринг георесурсов (May 2019)
Influence of heat input at plasma powder surfacing of M2 steel on structure and hardness of the coating. Single roller surfacing (P. I)
Abstract
Heat input is a determining parameter in plasma surfacing. It can be controlled by welding current power and displacement rate of heating source. Increasing the heat input can affect significantly the formation of structure and properties of the deposited material. Therefore, the choice of plasma powder surfacing parameters, for example sealing ends, which are used for oil extraction pumps, oil transportation and oil refining, is relevant for restoration or hardening a part surface. The authors have carried out the single-pass plasma surfacing with industrial powder of M2 steel which had a particle size distribution about 100…350 microns on the rectangular 400х150х10 mm plate of steel C1020. Argon was used as the conveying, protective and plasma gas. Surfacing was performed on UPN303UHL4. The authors used the plasma torch with an internal circuit of powder input into the arc. To change the heat input the authors used the modes with different values of current and deposition rate. The authors analyzed the influence of the heat input during plasma powder surfacing of a single roller on formation of its structural and phase composition and hardness. The microstructure evolution analysis was carried out using optical microscope Olympus GX 51, which has a set of application 700 SIAMS programs, and scanning high resolution electron microscope JSM-7500FA, equipped with energy dispersive microanalysis system manufactured by JEOL. The X-ray diffraction, which was carried out using X-ray diffractometer XRD-7000S in the filtered CuK-radiation, was used in the work. It is shown that increasing heat input from 20 to 42 kJ/cm the width of the deposited bead increases twice and the depth of penetration of the base metal from grows from 0,2 to 0,9 mm. It was found that when increasing the heat input the proportion of eutectic reduces in 2 times, increasing the amount of martensite in the matrix volume from 72 to 84 % and an average particle size of the vanadium carbide from 0,75 to 2 microns. А layer of material thickness of about 100... 150 mm is formed near the fusion boundary and upper bead, where the increasing number of dispersed carbides to ~ 4 % is fixed and there is no eutectic net of carbides. When increasing heat input to 25 kJ/cm the average microhardness remains at 860 HV. Hardness decreases to 780...790 HB, when the heat input increases to 30 kJ/cm. Hardness remains unchanged with further increase of heat input.
