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On the evolution of tempering carbides in a modified H!# and a modified H11 when hardening at 1000°
University West, Department of Engineering Science, Division of Manufacturing Processes. (PTW)ORCID iD: 0000-0001-5249-4207
2013 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Hot- work tool steels require high austenitising temperature during hardening in order to yield the high tempering resistance that vanadium- rich carbides supply. Such grades, when offering high cleanness, are also used for plastic injection molding. The hardening temperature can then be lower, yielding a lower content of vanadium in the martensitic matrix and precipitating instead molybdenum-rich carbides, M2C- type, during tempering. M2C- type carbides are metastable and have high carbide/ matrix interface energy, which implies a greater driving force for coarsening than that in the MC- type. In this paper the carbide evolution in two hot- work grades hardened at 1000˚C, is studied after two and threetemperings. Type, size and distribution of tempering carbides were investigated with the help of TEM. Undissolved carbides were documented by SEM investigation and the microstructures classified by LOM. Hardness levels and Charpy V test results are also reported here.

Place, publisher, year, edition, pages
2013.
Keyword [en]
hardening, tempering carbides, hot-work tool steel, lowered austenitising temperature, carbide coarsening
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
URN: urn:nbn:se:hv:diva-8612OAI: oai:DiVA.org:hv-8612DiVA: diva2:866255
Conference
4th Heat Treatment Symposium,24 - 25 October 2013, Istanbul
Note

Ingår i lic uppsats

Available from: 2015-11-02 Created: 2015-11-02 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. 85 p.
Series
Licentiate Thesis: University West, 4
Keyword
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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