Microstructure and hardness characterisation of laser coatings produced with a mixture of AISI 420 stainless steel and Fe-C-Cr-Nb-B-Mo steel alloy powders

Fe-C-Cr-Nb-B-Mo alloy powder and AISI 420 SS powder are deposited using laser cladding to increase the hardness for wear resistant applications. Mixtures from 0 to 100 wt.% were evaluated to understand the effect on the elemental composition, microstructure, phases, and microhardness. The mixture of carbon, boron and niobium in the Fe-C-Cr-Nb-B-Mo alloy powder introduces complex carbides into a Fe-based matrix of AISI 420 SS which increases its hardness. Hardness increased linearly with increasing Fe-C-Cr-Nb-B-Mo alloy, but substantial micro-cracking was observed in the clad layer at additions of 60 wt.% and above; related to a transition from a hypoeutectic alloy containing α-Fe/α' dendrites with an (Fe,Cr)2B and γ-Fe eutectic to primary and continuous carbo-borides M2B (where M represents Fe and Cr) and M23(B,C)6 carbides (where M represents Fe, Cr, Mo) with MC particles (where M represents Nb and Mo). The highest average hardness, for an alloy without micro-cracking, of 952 HV was observed in a 40 wt.% alloy. High stress abrasive scratch testing was conducted on all alloys at various loads (500, 1500, 2500 N). Alloy content was found to have a strong effect on the wear mode and the abrasive wear rate, and the presence of micro-cracks was detrimental to abrasive wear resistance.

Effect of retained austenite on wear resistance of nanostructured dual phase steels

Nanostructured super bainitic and quenching-partitioning (Q&P) martensitic steels with a significant amount of retained austenite obtained by low temperature bainitic transformation and Q&P respectively were studied to explore the effect of retained austenite on stirring wear resistance. The results suggest that the Q&P martensitic steel significantly enhanced the hardness of the worn surface (from 674 to 762 HV1) and increased the thickness of the deformed layer (,3.3 mm), compared to the nanostructured bainitic steel. The underlying reason is that the Q&P martensitic steel has a higher stability of retained austenite thereby providing a superior transformation induced plasticity effect to increase surface hardness and reduce wear rate during the wear process.

Tool wear and surface integrity analysis of machined heat treated selective laser melted Ti-6Al-4V

In this study, the tool wear and surface integrity during machining of wrought and Selective LaserMelted (SLM) titanium alloy (after heat treatment) are studied. Face turning trails were carried out onboth the materials at different cutting speeds of 60,120 and 180 m/min. Cutting tools and machinedspecimens collected are characterized using scanning electron microscope, surface profiler and opticalmicroscope to study the tool wear, machined surface quality and machining induced microstructuralalterations. It was found that high cutting speeds lead to rapid tool wear during machining of SLMTi-6Al-4V materials. Rapid tool wear observed at high cutting speeds in machining SLM Ti-6Al-4Vresulted in damaging the surface integrity by 1) Deposition of chip/work material on the machinedsurface giving rise to higher surface roughness and 2) Increasing the depth of plastic deformationon the machined sub surface.

Impacts of wear and geometry response of the cutting tool on machinability of super austenitic stainless steel

This paper presents a study of tool wear and geometry response whenmachinability tests were applied under milling operations onthe Super Austenitic Stainless Steel alloy AL-6XN. Eight milling trials were executed under two cutting speeds, two feed rates, andtwo depths of cuts. Cutting edge profile measurements were performed to reveal response of cutting edge geometry to the cuttingparameters and wear. A scanning electron microscope (SEM) was used to inspect the cutting edges. Results showed the presenceof various types of wear such as adhesion wear and abrasion wear on the tool rake and flank faces. Adhesion wear represents theformation of the built-up edge, crater wear, and chipping, whereas abrasion wear represents flank wear.Thecommonly formed wearwas crater wear. Therefore, the optimum tool life among the executed cutting trails was identified according to minimum lengthand depth of the crater wear.The profile measurements showed the formation of new geometries for the worn cutting edges due toadhesion and abrasion wear and the cutting parameters.The formation of the built-up edge was observed on the rake face of thecutting tool. The microstructure of the built-up edge was investigated using SEM. The built-up edge was found to have the austeniteshear lamellar structure which is identical to the formed shear lamellae of the produced chip.

Understanding wear conditions during hot stamping

Wear and galling are significant issues during production hot stamping processes. This paper uses thermo-mechanical finite element analysis to study the contact pressure, sliding distance and temperature conditions that occur at the wearing interface during hot stamping. Several hot stamping processes are studied, representing the numerous methods that are used in industry to form a typical hat-shaped channel component. These process include crash forming (without blankholder), stamping with a blank holder with an applied blank holder pressure, and stamping with a clearance blank holder (i.e. with spacer blocks). This paper identifies the distinct contact pressure and temperature conditions that occur for each of these forming methods. The regions of the most severe contact conditions are notably different for each of the forming methods. The work from this paper will form the basis for the development of suitable temperature dependent wear models and low cost wear tests for industrial hot stamping applications.

In-situ synthesis of titanium carbides in iron alloys using plasma transferred arc welding

The synthesis of Fe-TiC metal matrix composite during metal deposition with laser and arc welding techniques is of technical and economic interest for hard surfacing of engineering components. Recent studies linked the resistance to abrasive wear with the size and morphology of TiC precipitates, which are strongly dependent on the deposition conditions and, more importantly, on the alloy chemistry. In this study, the effect of silicon and manganese on the TiC precipitates was explored and different processing conditions were assessed. The characterisation included optical and scanning electron microscopy, X-ray diffraction and microhardness testing. The results indicate that silicon and manganese can have a significant effect on TiC size and morphology. Therefore, the composition of the matrix alloy offers an effective pathway to modify the microstructure of in-situ precipitated Fe-TiC metal matrix composites. © 2013 Elsevier B.V.

In-situ precipitation of TiC upon PTA hardfacing with grey cast iron and titanium for enhanced wear resistance

Titanium and grey cast iron powders were blended and deposited by plasma transferred arc onto mild steel substrates. The powders were injected directly into the arc by a stream of inert gas. The grey cast iron provided the iron matrix and the excess carbon content for reaction and precipitation of titanium carbides. The microstructure of the overlay was analysed by optical microscopy and scanning electron microscopy, and the respective phases were identified by X-ray diffraction. Microhardness measurements were taken from representative areas and the wear behaviour was assessed under low-stress abrasion conditions. The results show that the addition of titanium produced a significant change in the microstructure of the overlays, increased surface hardness and enhanced wear resistance compared to overlays produced without titanium.

Dry sliding wear of active screen plasma carburised austenitic stainless steel

Low temperature diffusion treatments with nitrogen and carbon have been widely used to increase the tribological performance of austenitic stainless steels. These processes produce a layer of supersaturated austenite, usually called expanded austenite or S-phase, which exhibits good corrosion and wear resistance. The novel active screen technology is said to provide benefits over the conventional DC plasma technology. The improvements result from the reduction in the electric potential applied to the treated components, and the elimination of such defects and processing instabilities as edge effects, hollow cathode effects and arcing. In this study, AISI 316 coupon samples were plasma carburised in DC and active screen plasma furnaces. The respective layers of carbon expanded austenite were characterised and their tribological performance was studied and compared. Detailed post-test examinations included SEM observations of the wear tracks and of the wear debris, EDX mapping of the wear track, EBSD crystal orientation mapping of the cross sections of the wear tracks, and cross-sectional TEM. Based on the results of wear tests and post-test examinations, the wear mechanisms involved are discussed.

Wear mechanisms and microstructure of pulsed plasma nitrided AISI H13 tool steel

AISI H13 tool steel discs were pulsed plasma nitrided during different times at a constant temperature of 400 °C. Wear tests were performed in order to study the acting wear mechanisms. The samples were characterized by X-ray diffraction, scanning electron microscopy and hardness measurements. The results showed that longer nitriding times reduce the wear volumes. The friction coefficient was 0.20 ± 0.05 for all tested conditions and depends strongly on the presence of debris. After wear tests, the wear tracks were characterized by optical and scanning electron microscopy and the wear mechanisms were observed to change from low cycle fatigue or plastic shakedown to long cycle fatigue. These mechanisms were correlated to the microstructure and hardness of the nitrided layer.