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Anti-wear performance of hot work tool steels is influenced by various parameters during their application lifetime as they are exposed to complex loading including heat, mechanical loading and sliding. Aim of this research work was to correlate different microstructures obtained by various heat treatments with hardness and anti-wear properties of hot work tool steel. For this purpose, modified 1.2367 hot work tool steel was used in this investigation. Two different austenitizing temperatures (1030 °C and 1150 °C) were used. Martensitic matrix was obtained after quenching, with two different austenitizing temperatures showing considerable difference in volume fraction of undissolved carbides (carbo-nitrides), being mainly vanadium rich MC type. Wear performance, which was influenced by austenitizing and tempering temperature, was evaluated by reciprocating sliding wear tests carried out at room temperature and pin-on-disc contact configuration. To simulate adhesive and abrasive wear component, 100Cr6 and Al2O3 balls were used as counter-body material, respectively. Lower wear rate at similar hardness over 50 HRc was observed comparing 100Cr6 counter-body results in favour to 1150 °C austenitized specimens where adhesive and abrasive wear components took place. Higher or comparable wear rate was obtained in the case of ceramic counter body where abrasive wear was prevailing.

Hot stamping is a well-established technology for producing safety relevant car components. The use of hot stamped components in modern car bodies offers the possibility of improving crash performance due to their high strength while simultaneously decreasing the fuel consumption by reducing sheet thicknesses and thus weight. Hot stamped components are mainly produced using the boron-manganese-alloyed steel 22MnB5. To prevent formation of oxide layer during heat treatment and subsequent forming process, AlSi-coatings are applied on the workpiece surface. Since hot stamped parts are formed at temperatures between 600 °C and 800 °C, no suitable lubricants have been found yet. Thus, severe wear and high friction occur during the forming process affecting final part quality as well as life-time of hot stamping tools. Consequently, measures for reducing tribological load during the forming operation have to be found in order to improve part quality and increase efficiency of industrial hot stamping applications. Within this study, the impact of the tool material on friction and wear is analyzed by comparing the tribological behavior of the newly developed high thermal conductivity hot work tool steel Thermodur 2383 Supercool with the reference material 1.2367. Both are characterized by means of flat strip drawing experiments under hot stamping conditions. The experiments are performed with different hardness values for each of the two tool materials. Furthermore, wear behavior is analyzed using scanning electron microscope and confocal microscope measurements of workpiece and tool. Hereby, fundamental wear and friction mechanisms within hot stamping applications are identified. The results of this study help to increase the process understanding regarding the tribological conditions during hot stamping. In future research work tool-side measures for increasing the life-time of hot stamping tools will be developed.

The increasing demands for light-weight components in vehicles contribute to the global expansion of hot sheet metal forming technologies. Structural components are typically produced using hot sta ...

The tribological behaviour of two sets of industrial hot stamping tools, one tool made of uncoated hot work tool steel and another PVD coated hot work tool steel set, were analysed by means of a surface replication technique. This technique allows using laboratory equipment and methodology for the inspection of tools without removing them from production. By means of this procedure, on the one hand adhesive wear mechanism can be identified and properly described and, on the other hand, the morphology and thickness of adhered material on tool surface is measured. The tribological behaviour of different industrial tools can be compared objectively.

Metal sheet shearing is necessary for dimensional control during steel forming. Due to the extreme operating conditions, like elevated temperatures, high contact stresses and corrosive environment, shearing blades suffer from severe wear and need frequent repair or outright replacement. This of course increases the maintenance costs for steel fabricators. Therefore, the goal of the current project was to gain insight into the wear phenomena that occur at high temperatures during sheet shearing. A comprehensive damage analysis was undertaken on a hot work tool steel used for such blades (steel type 1.2367) by means of optical microscopy, 3D surface topography, SEM/EDS and X-ray computed tomography. The structure of micro- and macroscopic cracking was characterised and linked to wear mechanisms. Corrosion phenomena such as oxide growth and oxidation-enhanced crack propagation were also analysed. Results indicated that the predominant wear mechanisms were thermal and mechanical fatigue in a corrosive environment leading to accelerated crack growth and material removal.

The wear mechanisms during dry sliding of two representative tool steel grades, one of lower and one of higher percentage of carbide-forming elements—AISI H13 hot work and Cr–Mo–V cold work steels respectively—were investigated. Prior to testing, both grades were properly subjected to heat treatments aiming to their hardening up to final values of 40, 45 and 50 HRC. After heat treatments, a part of the specimens from each hardness level was subsequently surface treated via liquid nitrocarburizing (Tufftriding), under typical industrial processing conditions. The sliding friction behavior of all specimens was studied on a ball-on-disc apparatus, applying normal loads in the range of 1–10 N. The continuous recording of the friction coefficient, the measurement of the wear volume, together with the post-testing microscopic observation of the wear surfaces provided for the evaluation of material removal mechanisms and of the effects of prior heat and surface treatments on the response of the material under surface loading. It was found that the dry friction coefficient remained practically constant (0.80–0.95) for all specimens. The hardening heat treatment did not affect substantially the wear coefficient, in contrast to the surface treatment that resulted in its significant reduction. Finally, in the case of the grade with the higher percentage of carbide-forming elements, it was found that both the wear coefficient and related mechanisms are strongly affected by the presence of coarse chromium carbides within the metallic matrix.

The high temperature wear performance of Inconel 617 and Stellite 6 alloys was investigated and compared with that of the X32CrMoV33 hot work tool steel. The wear performance of the latter at 750 degrees C is judged to be very poor due basically to its inferior oxidation resistance. Extensive oxidation co-occurring with wear at 750 degrees C leads to substantial material loss basically due to the lack of an adhesive oxide scale, sufficiently ductile to sustain the wear action without extensive spalling. The wear resistance of the Inconel 617 and Stellite 6 alloys at 750 degrees C is relatively superior. The adhesive oxides growing slowly on Inconel 617 and Stellite 6 alloys sustain the wear action without spalling and are claimed to be responsible for the superior wear resistance of these alloys at 750 degrees C. (C) 2010 Elsevier B.V. All rights reserved.

An alternative possibility to increase exposure time of hot work tools is the modification of the tool's surface. The most common method of surface modifying for this kind of tools is nitriding. Unfortunately, nitrided cases often suffer from severe impact wear. Therefore, the development of graded surface layers for backing of the nitrided cases by hard metal monocarbides like TiC, Cr 3 C 2 , WCCo and WCCoCr, alloyed in the tool's surface could be promising. To cut back expensive production trials, impact wear tests of the duplex-coatings were carried out by a special apparatus where a fixed tungsten carbide ball periodically stroke on the specimens’ surface. In time, an indentation dome was developed which could be evaluated by its diameter. Results have shown that the best impact wear resistance is provided by duplex-layer WCCoCr-plasmanitrided. After the laboratory experiments some of the duplex-layers were tested on simple high speed forging tools for screw-production. With duplex-layer WCCoCr-plasma a 50% increase of tool life time was achieved, though the transferability of laboratory experiment and industrial application proved to be rather unsteady.

A great deal of research has been conducted to clarify the role of oxide films in the wear of metals. Oxides formed during dry sliding of steels at high temperatures determine their tribological behavior. The present work deals with the influence of the oxide-forming alloying elements aluminum and silicon on the oxidation and wear of three selected hot work steels. For this investigation, ball-on-disc experiments were carried out in ambient air and 500 °C. Wear tracks on the disks and balls were characterized using both a scanning electron microscope and an optical profiler. The oxidation products were characterized using X-ray photoelectron spectroscopy and energy-dispersive electron probe microanalysis. The results show that the alloying elements aluminum and silicon yield a reduction of the oxide film thickness and thus lead to an increase in mechanical wear as temperature rises.

Pin-on-disc wear tests of tungsten carbide inserts against hot-work tool steel disc were carried out, with loads of 40 and 50 kgf, speeds of 100 and 130 m/min; and temperatures of 25, 200, 400 and 600 °C. Two types of insert (pin) settings were used. With the first type, the insert was set in full contact with the disc throughout the whole testing cycle. In the second type, the insert was set with an initial angle with the disc at the beginning of the wear test, but would have a full contact at the end of the testing cycle. It was found that, with the same testing parameters, the wear coefficient values of the inserts with an initial angular setting were significantly lower than those obtained with inserts that maintained a full contact setting with the counter disc throughout the testing cycle. The ratio of these two wear coefficient values, the wear coefficient ratio, was also found to be an important parameter. Lower wear coefficient ratios were generally obtained in the early stage of transient wear as well as with higher testing temperatures. This work has, therefore, provided a significant new insight into the discrepancy of the wear coefficient values obtained previously by the turning method and those by the standard pin-on-disc testing method.

An extensive study has been performed to investigate the tool-wear mechanisms of CBN cutting tools in finish turning of the following hardened steels: X155CrMoV12 (AISI D2) cold work steel, X38CrMoV5 (AISI H11) hot work steel, 35NiCrMo16 hot work steel and 100Cr6 bearing steel (AISI 52100), treated at 54 HRC. A large variation in tool-wear rate has been observed in machining of these steels. The generated tool flank grooves have been correlated with the hard carbide content of the workpieces. A crater wear study has also been performed and, it is shown that the appearance of an adhesive third body could induce a chemical wear in the tool.

Dies for extrusion of aluminium alloys are exposed to severe thermal, chemical and mechanical conditions. Extrusion dies are usually made from hot work tool steels such as AISI H13. In order to reduce wear they are almost always surface treated by various forms of nitriding. Surface-coating by physical vapour deposition (PVD) or chemical vapour deposition (CVD) is currently being introduced as a means to further improve the wear resistance. The present study aims at elucidating the life limiting wear mechanisms of gas nitrided tools, and duplex coated tools. The latter has been plasma nitrided and subsequently PVD coated with CrN in the same process. The duplex coating is included for its potential to effectively reduce the wear of extrusion dies. It is estimated that duplex coating prolongs the tool life at least five times as compared to conventional nitriding. The reason is that the superficial PVD-layer shows a combination of high resistance to mechanical wear and resistance to corrosive attack by hot aluminium. Eventually, the PVD-layer fractures and delaminates due to fatigue. When the nitrided substrate is exposed, the wear accelerates significantly.

Hot extrusion is a very cost efficient method of aluminium forming. One limitation for further improvement of cost reduction is wear of the bearing surface on the die which deteriorates the dimensional tolerance and surface quality of the profile. Nitrided hot work tool steels are commonly used as die material but new surface treatments are being introduced. This paper describes a new block on disc test machine and a corresponding methodology for simulating tribological interactions on the die bearing surface. The applicability of the test is demonstrated in a comparison between traditional nitriding and a CVD coating by TiC+TiN. The same kind of wear mechanisms were found on actual dies as well as on tests specimens. Thus, the new test method proved to simulate realistic extrusion conditions. Chemical wear dominates the deterioration for the two surface treatments. Both in actual extrusion and in the laboratory tests, the CVD coating had a superior resistance to wear compared to the nitrided steel.

Soldering and abrasive wear of die-casting tools are some of the biggest problems facing the aluminium die-casting industry. The understanding of the tribological behaviour is crucial to design new tool steels and tool steel-coating systems. The present study aims at investigating aluminium adhesion of aluminium/tool steel pair, performing sliding tests at high temperature with ball-on-disc configuration to reproduce solid/solid interaction. Different test conditions have been conducted in order to select the optimal test parameters to obtain aluminium adhesion on disc surface. Once the lab test has been designed, the high temperature tribological performance of different hot work tool steels (uncoated and coated by PVD) sliding against aluminium has been studied to allow proper die material design and selection.

Two-body abrasive resistance has been determined as a function of tempering temperature for a conventional hot work die steel and two experimental hot work die steels. After tempering in the secondary hardening range both experimental steels exhibit abrasive wear resistance comparable with or superior to that of the conventional die steel. In addition, the abrasive wear behavior of the three steels has been assessed using an approach suggested by one of the authors which emphasizes the role of ductility in determining abrasive wear resistance. As suggested by that approach, the product of the wear ratio and the bulk hardness tends to decrease with increasing tensile strain to fracture.