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Inclusions, Stress Concentrations and Surface Condition in Bending Fatigue of an H13 Tool Steel
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, Uddeholm Tooling AB.
2008 (English)In: Steel research, ISSN 0177-4832, ISSN 1869-344X, Vol. 79, no 5, 376-381 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Wiley-Blackwell, 2008. Vol. 79, no 5, 376-381 p.
Keyword [en]
fatigue life, inclusions, tool component, surface roughness, stress concentrator
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
URN: urn:nbn:se:kau:diva-3011OAI: oai:DiVA.org:kau-3011DiVA: diva2:117455
Available from: 2008-11-18 Created: 2008-11-13 Last updated: 2016-09-07Bibliographically approved
In thesis
1. Tool steel for tool holder applications: microstructure and mechanical properties
Open this publication in new window or tab >>Tool steel for tool holder applications: microstructure and mechanical properties
2008 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Large improvements in cutting tool design and technology, including the application of advanced surface engineering treatments on the cemented carbide insert, have been achieved in the last decades to enhance tool performance. However, the problem of improving the tool body material is not adequately studied.

Fatigue is the most common failure mechanism in cutting tool bodies. Rotating tools, tool going in and out of cutting engagement, impose dynamic stresses and require adequate fatigue strength of the tool. Working temperatures of milling cutter bodies in the insert pocket can reach up to 600°C depending on the cutting conditions and material of the workpiece. As a result, steel for this application shall have good hot properties such as high temper resistance and high hot hardness values to avoid plastic deformation in the insert pocket of the cutting tool. Machinability of the steel is also essential, as machining of steel represents a large fraction of the production cost of a milling cutter.

This thesis focus on the improvement of the cutting tool performance by the use of steel grades for tool bodies with optimized combination of fatigue strength, machinability and properties at elevated temperatures.

The first step was to indentify the certain limit of the sulphur addition for improved machinability which is allowable without reducing the fatigue strength of the milling cutter body below an acceptable level. The combined effect of inclusions, surface condition and geometrical stress concentrator on the fatigue life of the tool steel in smooth specimens and in tool components were studied in bending fatigue.

As the fatigue performance of the tools to a large extent depends on the stress relaxation resistance at elevated temperature use, the second step in this research was to investigate the stress relaxation of the commonly used milling cutter body materials and a newly steel developed within the project. Compressive residual stresses were induced by shot peening and their response to mechanical and thermal loading as well as the material substructures and their dislocation characteristics were studied using X-ray diffraction.

Softening resistance of two hot work tool steels and a newly developed steel was investigated during high temperature hold times and isothermal fatigue and discussed of with respect to their microstructure. Carbide morphology and precipitation as well as dislocation structure were determined using transmission electron microscopy and X-ray line broadening analysis.

Place, publisher, year, edition, pages
Karlstad: Karlstad University, 2008. 38 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2008:44
Keyword
tool steel, tool holder, microstructure, mechanical properties, machinability
National Category
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-2872 (URN)978-91-7063-203-7 (ISBN)
Presentation
2008-11-28, 21A 342, Karlstads universitet, Karlstad, 10:15 (English)
Opponent
Supervisors
Available from: 2008-11-18 Created: 2008-10-17 Last updated: 2011-11-30Bibliographically approved
2. 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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