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Influence of nickel content on machinability of a hot-work tool steel in prehardened condition
Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.ORCID iD: 0000-0001-6029-2613
Research and Development, Uddeholms Tooling AB.
Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering. (Materials Engineering, Materials Science)ORCID iD: 0000-0002-9441-2502
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2011 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 32, no 2, 706-715 p.Article in journal (Refereed) Published
Abstract [en]

In the present study, the influence of nickel content on the machinability of a prehardened hot-work tool steel was investigated. The machinability with varying nickel content from 1 to 5 wt% was characterized in end milling and drilling by evaluating tool life, cutting forces, and tool/chip interface temperature.

Nickel content showed to have a positive effect on the machinability of the hot-work tool steel; with increasing nickel content in the steel, the longer tool life was reached in end milling and drilling operations. Machining the higher nickel containing steels generated lower cutting forces and tool/workpiece interface temperature. In addition, less adhesive wear and built-up edge formation were observed on the tools.

The difference in the steel machinability was discussed in terms of their microstructure and mechanical properties. Increasing nickel content tends to decrease the carbon in the martensite and to retain a fine distribution of small primary carbides. It resulted in a reduction in yield strength with increasing nickel content related to the cutting force reduction and machinability improvement.

Place, publisher, year, edition, pages
Amsterdam: Elsevier, 2011. Vol. 32, no 2, 706-715 p.
Keyword [en]
tool steel, machinability, nickel content
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
URN: urn:nbn:se:kau:diva-5628DOI: 10.1016/j.matdes.2010.07.037ISI: 000284788300028OAI: oai:DiVA.org:kau-5628DiVA: diva2:318415
Available from: 2010-05-12 Created: 2010-05-07 Last updated: 2017-06-22Bibliographically approved
In thesis
1. Performance of advanced tool steels for cutting tool bodies
Open this publication in new window or tab >>Performance of advanced tool steels for cutting tool bodies
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Performance of indexable insert cutting tools is not only about the performance of cutting inserts. It is also about the cutting tool body, which has to provide a secure and accurate insert positioning as well as its quick and easy handling under severe working conditions. The common damage mechanisms of cutting tool bodies are fatigue and plastic deformation. Cutting tools undergo high dynamic stresses going in and out cutting engagement; as a result, an adequate level of fatigue strength is the essential steel property. Working temperatures of tool bodies in the insert pocket can reach up to 600°C, why the tool steel requires high softening resistance to avoid plastic deformation. Machinability is also essential, as machining of the steel represents a large fraction of the production cost of a cutting tool.

The overall aim of the study is to improve the tool body performance by use of an advanced steel grade with an optimized combination of all the demanding properties. Due to the high-temperature conditions, the thesis concerns mostly hot-work tool steels increasing also the general knowledge of their microstructure, mechanical properties and machinability.

Knowing the positive effect of sulphur on machinability of steels, the first step was to indentify a certain limit of the sulphur addition, which would not reduce the fatigue strength of the tool body below an acceptable level. In tool bodies, where the demand on surface roughness was low and a geometrical stress concentrator was present, the addition of sulphur could be up to 0.09 wt%.

Fatigue performance of the cutting tools to a large extent depended on the steel resistance to stress relaxation under high dynamic loading and elevated temperatures. The stress relaxation behaviour, material substructure and dislocation characteristics in low-alloyed and hot-work tool steels were studied using X-ray diffraction under thermal and mechanical loading.  Different tool steels exhibited different stress relaxation resistance depending on their microstructure, temper resistance and working temperature. Hot-work tool steels showed to be more preferable to low-alloyed tool steels because of their ability to inhibit the rearrangement and annihilation of induced dislocations.

High-temperature softening resistance of the hot-work tool steels was investigated during high-temperature hold-times and isothermal fatigue and discussed with respect to their microstructure. Carbide morphology and precipitation were determined using scanning and transmission electron microscopy.

Machinability of a prehardened hot-work tool steel of varying nickel content from 1 to 5 wt% was investigated in end milling and drilling operations. Machining the higher nickel containing steels resulted in longer tool life and generated lower cutting forces and tool/workpiece interface temperature. The difference in machinability of the steels was discussed in terms of their microstructure and mechanical properties. 

Place, publisher, year, edition, pages
Karlstad: Karlstad University, 2010. 80 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2010:17
Keyword
tool steel, cutting tool body, fatigue strength, stress relaxation, machinability, high-temperature properties, microstructure
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-5630 (URN)978-91-7063-307-2  (ISBN)
Public defence
2010-09-03, Ljungbergssalen 21A244, Karlstads iniversitet, Karlstad, 10:15 (English)
Opponent
Supervisors
Available from: 2010-06-17 Created: 2010-05-07 Last updated: 2011-10-31Bibliographically approved

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