New type of high-performance hybrid roll to substitute hard chrome plated layers – Hybrid-Roll

As part of a new research project, a collaboration with the Materials Technology Chair at the Ruhr University Bochum, Deutsche Edelstahlwerke Specialty Steel GmbH & Co. KG and C.D. Wälzholz GmbH & Co KG has been entered into with the intention of developing a hybrid roll for cold-rolling applications. The work is being based on an entirely new combination of materials and processes. It means that it will possible to replace the hard-chromium-plated rolls that are produced using melting metallurgy, which are currently being employed across the world. It also means that the very detrimental effects on health and the environment resulting from the use of chromium (VI), which is released during the process of plating with hard chromium, can be prevented. It is hoped at the same time that the new process will allow a significant increase in the rolls' wear resistance, which will, as a result, help improve economic efficiencies during the rolling of high-strength products destined for lightweight construction applications.

The highly wear-resistant working areas on the hybrid rolls are to made from an alloy produced using powder metallurgy. The core and journal areas on the rolls are to be made using an alloy that is cheaper to manufacture and that is produced by melting metallurgy. The aim is to employ powder metallurgy to develop a highly wear-resistant alloy that is specifically adapted to the requirements encountered in the cold-rolling industry, i.e. an alloy that impossible to realise using melting metallurgy due to the high proportion of specially formed hard phases.

Another aim is to utilise a completely new compaction / forming technology to overcome the size limitations that currently exist for composite rolls that are manufactured using powder metallurgy.

The vacuum-heat-treatment process, which is currently used to adapt rolls manufactured with the help of powder metallurgy to the required material properties and which is also associated with a size-limiting effect, is to be replaced by a new type of inductive surface-layer-hardening process that may be used on all sizes of rolls.

The project's scope also includes an investigation into the behaviour of the new type of composite roll blanks during inductive surface hardening. These investigations will focus particularly on the complex interactions between the temperature- and phase-dependent material properties. Research into heating and quenching conditions is also to be carried out. The geometric conditions, which are to be examined using FEM simulations with special emphasis on how stress develops and the adjustment of the desired hardening structure, will also be part of our work.

The heat-treatment parameters developed in the simulations and the knowledge gained from the research are then going to be applied to the actual heat-treatment processes that are to be used in the production of the new type of hybrid rolls.

A quenching shower for sequential quenching with pure compressed air and a mixture of air and water, including the necessary measuring and control technology, is being developed specifically for these uses.

In the context of the quenching shower, the mutual interactions between the nozzle type, the operating parameters and the temperature of the roll surfaces and the effects on the transfer of heat are also going to be investigated. The relative movement between the roll and quenching nozzles is also going to be examined.

This project is supported by the European Union and the state of North Rhine-Westphalia within the framework of the ERDF, to whom we express our thanks at this point.

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