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Effect of Austenitising Temperature and Cooling Rate on Microstructure in a Hot-Work Tool Steel
University West, Department of Engineering Science, Division of Manufacturing Processes. (PTW)ORCID iD: 0000-0001-5249-4207
Uddeholms AB.
The Swedish School of Mining and Metallurgy.
Nuclear Physics Institute ASCR.
Show others and affiliations
2014 (English)In: Proceedings of the 6th International Swedish Production Symposium / [ed] Stahre, Johan, Johansson, Björn & Björkman, Mats, 2014, p. 1-7Conference paper, Published paper (Refereed)
Abstract [en]

The effects on microstructucture of austenitising temperature and cooling rate during hardening were studied for a hot-work tool steel. Transformation temperatures were determined by dilatometry, scanning electron microscopy was used to characterise the microstructure and both retained austenite contents and their lattice parameters were measured by neutron diffraction. For lower cooling rates, lower austenitising temperatures produce larger amounts of both retained austenite and bainite. Retained austenite in bainitic structures is higher in carbon than in martensitic structures. Consequently, lowering the austenitising temperature will affect microstructure and properties.

Place, publisher, year, edition, pages
2014. p. 1-7
Keywords [en]
Austenitising temperature, bainitic reaction, retained austenite, lattice parameter
National Category
Production Engineering, Human Work Science and Ergonomics
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-7009ISBN: 978-91-980974-1-2 (print)OAI: oai:DiVA.org:hv-7009DiVA, id: diva2:764703
Conference
The 6th Swedish Production Symposium
Available from: 2014-11-20 Created: 2014-11-19 Last updated: 2015-11-11Bibliographically approved
In thesis
1. Effect of austenitising temperature and cooling rate on microstructures of hot-work tool steels
Open this publication in new window or tab >>Effect of austenitising temperature and cooling rate on microstructures of hot-work tool steels
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The average size of hot-work tools has gradually increased over the past years.This affects the effective temperature cycle tools experience during hardening,as large dimensions prevent uniform and rapid cooling, and thereby the resulting microstructures and properties. In order to avoid the formation of coarse structures or cracking during heat treatment it has become common practise to lower the austenitising temperature below that recommended by the steel manufacturer.In this work, therefore, the effects of austenitising at temperatures lower thancommonly recommended are investigated. Three 5% Cr hot-work tool steelsalloyed with Mo and V were heat treated, resulting microstructures andtempering carbides were studied and transformation characteristics determined for different austenitising temperatures and different cooling rates. The temperatures and cooling rates have been chosen to be representative for heat treatments of different sizes of tools. Bainite rather than martensite formed during slow cooling regardless of austenitising temperature. A lowered austenitising temperature produced largeramounts of both bainite and retained austenite while a higher caused graingrowth. Carbon partitioning during the bainitic transformation resulted in anincrease of the carbon content in the retained austenite of at least 0.3 wt.%. The austenitising temperature influences also the type and amount of tempering carbides that precipitate, which affects the properties of the steel. Higher austenitising temperatures favour the precipitation of MC carbides during tempering. The Mo rich M2C type carbides were proven to be more prone to coarsening during service at 560°C-600°C, while V rich MC carbides preserve their fine distribution. A best practice heat treatment needs to balance the increase of grain size with increasing austenitising temperatures, with the possibility to form more tempering carbides. Higher austenitising temperatures also give less retained austenite, which can affect dimensional stability and toughness negatively after tempering

Place, publisher, year, edition, pages
Trollhättan: University West, 2015. p. 85
Series
Licentiate Thesis: University West ; 4
Keywords
Tool steel, Heat Treatment, Austenitising Temperature, Large Tools, Tempering Carbides, Bainitic Microstructures
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-8614 (URN)978-91-87531-16-3 (ISBN)978-91-87531-15-6 (ISBN)
Opponent
Supervisors
Available from: 2015-11-11 Created: 2015-11-02 Last updated: 2015-11-11Bibliographically approved

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Coll Ferrari, Maria Teresa

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