Correlation Between the Indentation Properties and Microstructure of Dissimilar Capacitor Discharge Welded WC-Co/High-Speed Steel Joints

Abstract

The welding of cemented carbide to tool steel is a challenging task, of scientific and industrial relevance, as it combines the high level of hardness of cemented carbide with the high level of fracture toughness of steel, while reducing the shaping cost and extending the application versatility, as its tribological, toughness, thermal and chemical properties can be optimally harmonised. The already existing joining technologies often impart either insufficient toughness or poor high-temperature strength to a joint to withstand the ever-increasing severe service condition demands. In this paper, a novel capacitor discharge welding (CDW) process is investigated for the case of a butt-joint between a tungsten carbide-cobalt (WC-Co) composite rod and an AISI M35 high-speed steel (HSS) rod. The latter was shaped with a conical-ended projection to promote a high current concentration and heat at the welding zone. CDW functions by combining a direct current (DC) electric current pulse and external uniaxial pressure after a preloading step, in which only uniaxial pressure is applied. The relatively high heating and cooling rates promote a thin layer of a characteristic ultrafine microstructure that combines high strength and toughness. Morphological analysis showed that the CDW process: (a) forms a sound and net shaped joint, (b) preserves the sub-micrometric grain structure of the original WC-Co composite base materials, via a transitional layer, (c) refines the microstructure of the original martensite of the HSS base material, and (d) results in an improved corrosion resistance across a 1-mm thick layer near the weld interface on the steel side. A nano-indentation test survey determined: (e) no hardness deterioration on the HSS side of the weld zone, although (f) a slight decrease in hardness was observed across the transitional layer on the composite side. Furthermore, (g) an indication of toughness of the joint was perceived as the size of the crack induced by processing the residual stress after sample preparation was unaltered.

Nano-Indentation Properties of Tungsten Carbide-Cobalt Composites as a Function of Tungsten Carbide Crystal Orientation

“…Nevertheless, some large voids may also have been caused by the concomitant pulling out of some WC grains. A similar situation has been observed for a martensitic matrix in tool steels [16] which, because of the intrinsic different etching rate of its dispersed carbides, after chemomechanical polishing, presents a characteristic multi-level topological surface [16]. Figure 6 clearly indicates that the number of indentations over the prismatic planes is much larger than that over the basal ones, which is in fair agreement with refs.…”

“…The present work has been aimed at developing a new experimental methodology, which relies on a limited number of nanoindentation tests, to successfully relate the indentation properties of WC grains (dispersed in a WC-10Co composite) to their crystal orientation. This paper is a preliminary study of a wider industrial oriented research that is focused on the mechanical characterisation of solid-state tool-steel/WC-Co welded joints by means of nanoindentation [16]. The nanoindentation property distributions were sampled using a suitable Gaussian mixture model [17].…”

Study on the Tribological Behavior of Wear and Friction Coefficient on AISI M35 High-Speed Steel with and without DLC Coating

“…The presence of vanadium and chromium in the analysis, however in low intensity showed by the EDS, also exposes that the microstructure may be constituted by vanadium (MC) and chromium (M 23 C 6 ) carbides 25 . found MC carbides in AISI M35 steel, but in a smaller volume (0.9%) when compared to M 6 C (7.8%) 29 . also found carbides MC (rich in vanadium) and M 6 C (rich in molybdenum and tungsten).…”

“…The presence of chromium improves the conditions of hardness and toughness, showing an average of 4.42% in the composition 28 . Molybdenum, with an average of 3.83%, partially replaces tungsten and has the same type of double carbide with iron and carbon 29 . Vanadium increases the hot hardness, presenting an average of 1.39% and the tungsten element that improves shock resistance, hot hardness presented an average of 5.36%.…”

Rapid Joining of Commercial-Purity Ti to 304 Stainless Steel Using Joule Heating Diffusion Bonding: Interfacial Microstructure and Strength of the Dissimilar Joint

“…A newly developed JHDB system with high power source induces the local heating of the abutted surfaces to the target temperature, without overshooting, at a heating rate higher than 1000 • C/s. Therefore, JHDB results in the rapid fabrication of joints without the macroscopic deformation of the workpieces, which is a unique superiority of JHDB, which the other bonding processes using Joule heating could hardly achieve [14]. This results in the effective suppression of the formation and growth of IMCs during the dissimilar bonding of CP-Ti to 304 stainless steel.…”