Fostabericht P 942 - Entwicklung intelligenter Werkstoffe zur Verschleißreduzierung bei SchmiedegesenkenFostabericht P 942 - Entwicklung intelligenter Werkstoffe zur Verschleißreduzierung bei Schmiedegesenken

P 942 – Increase of the wear resistance of hot forging tools by utilization of the cyclical edgezone hardening


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P 942 – Increase of the wear resistance of hot forging tools by utilization of the cyclical edgezone  hardening

The life span of hot bulk metal forming tools is limited by damage resulting from a complex combination of cyclic loads. Especially the surface layer of a tool is under a high amount of thermal, mechanical, tribological and chemical stress during the production process. The resulting load spectrum leads to tool failure with smaller life span  quantities compared to other manufacturing methods. The main cause of failure is wear in the shaping areas of the  tool. That is why different wear  reduction techniques for  hot forging dies have been discussed in a number of  research studies so far. Despite the significant progress  being made by applying hard coatings or nitriding the tool  surface, no solution with a satisfying cost-benefit ratio has been found so far. Recent measures to reduce wear require  either a high investment or high tool costs which outweigh the life span benefit by far.
This study analyses a simpler  and more economic method of wear reduction. A new hot  working tool steel has been developed for this purpose  reducing the expenses to the costs of the additional  alloying elements. The alloying composition is based on  the hot working tool steel 32CrMoV12-28 (material no.  1.2365 / AISI H10) with varying ratios of the austenite  stabilizing eleUmformments manganese, nickel and cobalt . The objective is to lower the material’s austenite start   temperature and manipulate the microstructure in the  tool’s surface layer. The material’s intelligent reaction to  the  thermomechanical loads should induce an increased  rehardening effect maintained over a great deal of forging cycles. This hardened surface layer acts as continuous wear  rotection.
The research has shown that lowering the  austenite start temperature through alloying can increase the rehardening effect if the thermomechanical loads  duringforging cause the surface layer to austenize. In the tool’s thermomechanically highly stressed regions   exceeding the austenite start temperature the following quenching lead to the formation of a re-hardened layer. The tool regions where the thermomechanical stress is  insufficient for microstructural transformation and re-hardening develop tempered layers with less hardness.  These increase wear and decrease tool’s  ife span. The new alloy’s full potential can only be benefitted from if the  process parameters and thermomechanical loads are  known and optimized. The study has also shown that  further improvement is possible by combining the new  alloy steel with a nitriding treatment. This caused higher  wear resistance in the tool regions that were not re- hardened leading to an overall increase of the tool life  quantity.
The research project IGF-No. 445 ZN from the  Research Association for Steel Application was supported by the Ministry of Economic Affairs and Energy through  the German Federation of Industrial Research Associations (AiF) as part of the programme for promoting industrial  cooperative research (IGF) on the basis of a decision by  German Bundestag. The research project has been carried  out at Institut für Umformtechnik und Umformmaschinen, of Gottfried Wilhelm Leibniz Universität Hannover and at  Institut für Werkstoffkunde, of Gottfried Wilhelm Leibniz Universität Hannover.

Only available in german language.

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B.-A. Behrens, J. Puppa, H.-J. Maier, F. Nürnberger