Effect of heating VK and TK group hard alloys in various media on surface quality

Abstract

The studies carried out to explore the modifying effect on the surface of a hard alloy, surface alloying and thermochemical treatment of metal, thermal diffusion saturation, vacuum ion-plasma deposition demonstrated changes in surface roughness and performance. This paper used roughness to evaluate the behavior of various hard alloy groups when heated in various media. The samples were 5× 5× 35 mm bars and 15.8 ×15.8 mm tetrahedral plates made of VK8 and T14K8 hard alloys. Surface roughness parameters were measured on the profilometer implementing the contact (probe) method. Roughness values obtained were analyzed in the Microsoft Excel system based on an integral percentage and histograms were constructed. The effect of the heating medium on the surface roughness was studied both on bars and plates (with and without holes) using the saturating element/buffer substance (50–100 % BaCl2) melt. K4(Fe(CN)6 potassium ferrocyanide and Na2B4O7 borax were used as a saturating element (25 %). Microhardness and cutting wear were determined directly on the products (after determining the heating media effect on roughness). The heating of VK8 and T14K8 hard alloys in various media increases roughness and reduces cutting wear up to 2 times. The structure of initial materials before and after heating in various melts was studied using the JCM-6000 scanning electron microscope (Jeol Ltd., Japan) at a magnification of 1000–3000×. Plates in their initial state and after heating in various melts were subjected to resistance tests on the 1A616 screw-cutting lathe by face turning of an axle billet made of OS steel (similar in structure and properties to St45) 210 ×1650 mm in size of continuously cast metal (GOST 4728-2010). X-ray diffraction analysis of the VK8 hard alloy after heating in various media demonstrated the absence of changes in the phase composition. Along with this, there was a slight change in the carbide phase fine structure parameters of the alloy, namely a slight increase in micro-stresses with a simultaneous decrease in mosaic blocks.