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.
•Improved resistance against adhesive wear with increasing tool hardness revealed.•Material transfer, ploughing and flattening identified as main friction mechanisms.•New hot stamping tool steel with high thermal conductivity has been presented.
This paper reports the outcome of a numerical study of ultrasonic cavitation using a CFD flow algorithm based on a compressible density-based finite volume method with a low-Mach-number consistent ...flux function and an explicit time integration 15; 18 in combination with an erosion-detecting flow analysis procedure. The model is validated against erosion data of an ultrasonic horn for different gap widths between the horn tip and a counter sample which has been intensively investigated in previous material studies at the Ruhr University Bochum 23 as well as on first optical in-house flow measurement data which is presented in a companion paper 13. Flow features such as subharmonic cavitation oscillation frequencies as well as constricted vapour cloud structures can also be observed by the vapour regions predicted in our simulation as well as by the detected collapse event field (collapse detector) 12. With a statistical analysis of transient wall loads we can determine the erosion sensitive areas qualitatively. Our simulation method can reproduce the influence of the gap width on vapour structure and on location of cavitation erosion.
Steels for the production of frames for plastic molds frequently need to exhibit resistance to corrosion while at the same time requiring large amounts of machining. Machinability as a crucial ...property can be enhanced by the addition of sulfur, resulting in the formation of favorable sulfides, which in turn can deteriorate mechanical properties and corrosion resistance. The detrimental effect on mechanical properties is caused, among others, by the elongation of sulfides during rolling or forging. In a novel approach, a special wire treatment of the melt is performed, which results in improved spherical morphology and chemical composition of the inclusions, yet leading to even enhanced machinability (tested, among others, by means of milling). Milling tests reveal increased productivity compared to conventionally manufactured material, which means an improved lifetime of milling inserts even at the highest cutting speeds. In addition, orthogonal cutting trials are performed aiming at understanding differences in machinability. At the same time, mechanical properties, in particular toughness, are slightly improved, while corrosion resistance is not severely affected.
Plastic mold steels frequently require good mechanical properties and high resistance to corrosion; thus, martensitic stainless steels are widely applied. Furthermore, machinability can be important, which is improved by re‐sulfurization. However, this may cause drawbacks in mechanical and corrosion properties. Herein, the influence of a novel metallurgical treatment in addition to re‐sulfurization is investigated.
Hot stamped high‐strength steel components for car bodies become increasingly important due to the need to save weight for multiple reasons such as fuel conservation regulations. Tribological systems ...in tools for hot stamping depend on process parameters and may include, e.g., mechanical and thermal loads as well as adhesive and abrasive wear. Furthermore, the process cycle time should be as short as possible due to economic reasons. Commonly used hot work tool steels mainly suffer from rather low wear resistance, whereas in terms of process cycle time, a high thermal conductivity is desired. Thus, solutions showing optimized combination of key properties for application in hot stamping such as wear resistance, high thermal conductivity, toughness, and hardening behavior need to be found. In this contribution, novel high thermal conductivity hot work tool steels, especially designed for application in hot stamping, are presented and some key properties are compared, e.g., to those of conventional hot work tool steels like 1.2367, which is commonly used in this application. Furthermore, tribological investigations are performed in laboratory tests according to ASTM G65 and G75 as well as a flat strip‐drawing test setup using sheets of 22MnB5 under hot stamping conditions.
Hot stamping of high‐strength steel components for car bodies becomes increasingly important. Tool steels for this application need to exhibit optimized combination of key properties such as wear resistance, thermal conductivity, toughness, and hardening behavior. In this contribution, novel, especially designed tool steels are presented and key properties including wear resistance are compared to those of conventional steel 1.2367.
Herein this investigation, profiled high interstitial austenitic stainless steel parts are burnished on a profile‐rolling machine, and afterward, the wear behavior is analyzed in a melt of ...glass‐reinforced polypropylene. Wear and corrosion resistance are significant properties of steel parts in the plastics and food industries. The high work‐hardening ability of high interstitial austenitic stainless steel enables burnishing parts with a significant local hardness to increase up to maximum values of ≈600 HV 1. Wear tests on a recently developed test stand reveal that the burnished austenitic stainless steel surface performs similarly to a nitrided surface of the standard nitriding steel 31CrMoV9 + QT with a hardness of ≈830 HV 0.5. Regarding the given advantage of corrosion resistance, it is concluded that roller burnishing supports the applicability of high interstitial austenitic stainless steel in plastics and food industries.
Herein, it is shown that roller burnishing of high interstitial austenitic stainless steel parts results in high material hardness without the need for subsequent heat treatment and fine processing. A test stand is developed to simulate wear conditions in a plastics extruder. Wear is analyzed on the profiled geometry.
Usually, tool steels are used in quenched and tempered conditions. Due to the phase transition from austenite to martensite and the volume change during the transformation, controlling distortion ...might be challenging. A newly developed steel focusing on a bainitic structure, even for bigger dimensions, shows a lower hardness at ambient temperature than conventional hot working tool steels but with a lower temperature dependency. Therefore, at service temperature, the mechanical properties are comparable to established grades. Heat treatment is simplified by a simple austenitization and cooling process without special requirements on the cooling rate. Due to a generally lower cooling rate and lower hardness compared to a quench and tempering process, the risk of cracking is reduced while machinability is improved. With the combination of good weldability and rather low hardness after rapid cooling, this grade can also be processed in additive manufacturing and is well suited for a hybrid process of conventional and additive manufacturing.
A new tool steel with a bainitic microstructure is presented in this study. The low hardness due to a rather carbon content compared to standard tool steel leads to good machinability. At elevated temperatures, the decrease in yield strength is very low, and therefore the mechanical properties at in‐service temperatures are comparable to usually used ones.
High interstitial austenitic stainless CrMn steels are characterised by significantly increased work hardening ability and strength compared with conventional CrNi austenites, yet maintaining very ...high ductility and toughness. The machining of high interstitial CrMnCN steels is challenging in terms of process stability and economic efficiency. In this context, unfavourable chip forms, high thermomechanical loads and the superposition of different wear mechanisms in particular lead to challenges in turning operations. In the following article, different lubricant strategies are analysed for machining of CrMnN and CrMnCN austenitic stainless steels regarding chip form, mechanical tool loads and wear. Furthermore, the workpiece properties are considered with regard to surface roughness and microstructural changes.
High interstitial austenitic stainless CrMn steels are characterised by significantly increased work hardening ability and strength compared with conventional CrNi austenites, yet maintaining very ...high ductility and toughness. The machining of high interstitial CrMnCN steels is challenging in terms of process stability and economic efficiency. In this context, unfavourable chip forms, high thermomechanical loads and the superposition of different wear mechanisms in particular lead to challenges in turning operations. In the following article, different lubricant strategies are analysed for machining of CrMnN and CrMnCN austenitic stainless steels regarding chip form, mechanical tool loads and wear. Furthermore, the workpiece properties are considered with regard to surface roughness and microstructural changes. Keywords High-strength materials; stainless austenitic steels; cooling lubricants; corrosion resistance; Interstitials; work hardening; turning Nichtrostende, austenitische CrMn-Stahle zeichnen sich durch ein deutlich hoheres Kaltverfestigungsvermogen und sowie eine gesteigerte Festigkeit im Vergleich zu konventionellen CrNi-Austeniten aus, wobei sie eine sehr hohe Duktilitat und Zahigkeit aufweisen. Die Zerspanung von CrMnCN-Stahlen gestaltet sich in Bezug auf Prozessstabilitat und Wirtschaftlichkeit dabei als sehr herausfordernd. In diesem Zusammenhang fuhren insbesondere ungunstige Spanformen, hohe thermomechanische Belastungen und die Uberlagerung verschiedener Verschleissmechanismen zu Herausforderungen bei der Drehbearbeitung. Nachfolgend werden zwei unterschiedliche Schmierstoffstrategien fur die Zerspanung von austenitischen CrMnN--und CrMnCNEdelstahlen hinsichtlich Spanform, mechanischer Werkzeugbelastung und Verschleiss analysiert. Daruber hinaus werden die Werkstuckeigenschaften im Hinblick auf Oberflachenrauheit und Gefugeveranderungen betrachtet. Schlusselworter Hochfeste Werkstoffe; Nichtrostender, austenitischer Stahl; Kuhlschmierstoffe; Korrosionsbestandigkeit; Interstitielle Elemente; Kaltverfestigung; Drehbearbeitung
FeCrMnCN stainless austenitic high‐interstitial steels (HIS) combine the properties of conventional FeCrNi austenites (superior ductility and surface corrosion resistance) with the potential of ...significant strengthening. This combination of properties makes them promising candidates for environments that require resistance to both wear and corrosion, e.g., processing of plastics. The aim herein is to make use of the high work‐hardening ability of HIS. Thus, machined preforms with an application‐related design are formed by profile cross rolling. The preform design enables a hardness increase in component regions that are most subjected to wear. Rolling of the specimens results in a very high surface quality with a roughness Rz in the range of 1 μm. Hardness measurements in rolled specimens confirm a significant hardness increase in the subsurface up to a depth of ≈2.5 mm. Hardness values of about 600 HV1 are yielded within a surface distance of ≈0.3 mm. Furthermore, tests on a modified pin‐on‐disc tribometer suggest that the wear behavior of the work‐hardened HIS is comparable with nitriding steel. Thus, the results of this study support the development of a forming technology for screws in corrosive environments.
Cold rolling is applied to machined preforms to strengthen the subsurface. Together, the outstanding work‐hardening potential of the corrosion‐resistant steel and the forming procedure facilitate a novel wear protection method for axisymmetric and helical parts. Wear test results for the sliding contact between steel and glass‐reinforced plastics indicate an abrasion resistance comparable with nitriding steel.
High interstitial steels (HIS) are based on the joint addition of carbon and nitrogen, which resulted in an austenitic FeCrMn steel grade. In contrast to high nitrogen steels (HNS), they can be ...produced by conventional metallurgy and offer a unique combination of mechanical properties and corrosion resistance. This makes them promising candidates for the use in environments featuring corrosive or wear attack or even both. Corrosion resistance can be improved by the addition of molybdenum, particularly in the case of media containing chloride ions. In this study, different FeCrMnCN alloys were investigated by means of pitting corrosion testing in sodium chloride solution, as well as cavitation erosion resistance. These properties were examined depending on prestraining, since the latter is used to strengthen this kind of alloys.
High interstitial austenitic stainless steels offer a unique combination of mechanical properties and corrosion resistance. Their mechanical properties can even be improved by cold working. In this study different FeCrMnCN alloys are investigated by means of pitting corrosion and cavitation testing. The results show higher cavitation resistance and no significant deterioration of corrosion properties due to the prestraining.
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