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Inclusion Characteristics and Their Link to Tool wear in Metal Cutting of Clean Steels Suitable for Automotive Applications
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.ORCID iD: 0000-0001-7707-5631
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis covers some aspects of hard part turning of carburised steels using a poly‑crystalline cubic boron nitride (PCBN) cutting tool during fine machining. The emphasis is on the influence of the steel cleanliness and the characteristics of non‑metallic inclusions in the workpiece on the active wear mechanisms of the cutting tool. Four carburising steel grades suitable for automotive applications were included, including one that was Ca‑treated.

A superior tool life was obtained when turning the Ca-treated steel. The superior machinability is associated with the deposition of lubricating (Mn,Ca)S and (CaO)x-Al2O3-S slag layers, which are formed on the rake face of the cutting tool during machining. Moreover, the transfer of work material to the rake face crater is characteristic in hard part turning of clean steels. It can be because of the lack of sulfides that protect the cutting edge when turning machinability treated steels. This corresponds to the more pronounced crater wear caused by the low‑sulfur steels than that of the steels with higher sulfur contents. It was also concluded that the composition of the non‑metallic inclusions in the Ca‑treated steel is a more important factor than the inclusion number and size, in hard part turning using a PCBN cutting tool. Also, a 3D analysis after electrolytic extraction was found to give a more precise characterisation of non‑metallic inclusions than the conventional 2D analysis by SEM‑EDS. In turn, better correlations to machinability and mechanical properties can be obtained. Hence, the use of this technique is beneficial for future material development.

Finally, the challenge for future metallurgy is to manufacture high‑performance steels with improved combined properties of mechanical strength and machinability.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , 41 p.
Keyword [en]
Tool wear, PCBN, Machinability, Steel, Non-metallic inclusions
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
URN: urn:nbn:se:kth:diva-164875ISBN: 978-91-7595-505-6 (print)OAI: oai:DiVA.org:kth-164875DiVA: diva2:806392
Presentation
2015-05-05, Sal Sefström, M131, Brinellvägen 23, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
VINNOVA
Note

QC 20150422

Available from: 2015-04-22 Created: 2015-04-20 Last updated: 2015-04-22Bibliographically approved
List of papers
1. The Effect of Different Non-Metallic Inclusions on the Machinability of Steel
Open this publication in new window or tab >>The Effect of Different Non-Metallic Inclusions on the Machinability of Steel
2015 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 8, no 2, 751-783 p.Article in journal (Refereed) Published
Abstract [en]

Considerable research has been conducted over recent decades on the role of non-metallic inclusions and their link to the machinability of different steels. The present work reviews the mechanisms of steel fractures during different mechanical machining operations and the behavior of various non-metallic inclusions in a cutting zone. More specifically, the effects of composition, size, number and morphology of inclusions on machinability factors (such as cutting tool wear, power consumption, etc.) are discussed and summarized. Finally, some methods for modification of non-metallic inclusions in the liquid steel are considered to obtain a desired balance between mechanical properties and machinability of various steel grades.

Place, publisher, year, edition, pages
Basel, Schweiz: MDPI AG, 2015
Keyword
inclusions, machinability, steel
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-164860 (URN)10.3390/ma8020751 (DOI)000352052600026 ()2-s2.0-84923692993 (Scopus ID)
Funder
VINNOVA
Note

QC 20150422

Available from: 2015-04-20 Created: 2015-04-20 Last updated: 2017-12-04Bibliographically approved
2. The effect of inclusion composition on tool wear in hard part turning using PCBN cutting tools
Open this publication in new window or tab >>The effect of inclusion composition on tool wear in hard part turning using PCBN cutting tools
Show others...
2015 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 334, 13-22 p.Article in journal (Refereed) Published
Abstract [en]

This work reports on hard part turning of carburizing steels using a PCBN cutting tool in fine machining. Emphasis is on the link between composition of the inclusions in work material and wear mechanisms of the cutting tool. A Ca-treated machinability improved 20NiCrMo steel was included together with three other carburizing steels with different inclusion characteristics.

Machining tests were conducted to examine cutting tool life and its balance between excessive flank wear or crater wear. The wear mechanisms were examined using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS) and a secondary electron (SE) detector.

The longest tool life was obtained when cutting the Ca-treated steel. The improved machinability is linked to the deposition of complex (Mn,Ca)S and (Ca,Al)(O,S) protective slag layers that form on the rake face of the cutting tool during machining. Cutting in this steel also resulted in a typical ridge formation in the tool edge crater. Transfer of workpiece material to the rake face crater is characteristic in hard part turning of steel with high cleanliness. This is suggested to be related to the lack of the sulphides that lubricate conventional machinability treated steels, and that the crater wear of low-sulphur steel is more pronounced than for steels with higher sulphur content.

Place, publisher, year, edition, pages
Elsevier, 2015
Keyword
Tool wear, PCBN, Machinability, Steel, Inclusions
National Category
Manufacturing, Surface and Joining Technology
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-164862 (URN)10.1016/j.wear.2015.04.008 (DOI)000357543300002 ()2-s2.0-84928546529 (Scopus ID)
Note

QC 20150421

Available from: 2015-04-20 Created: 2015-04-20 Last updated: 2017-12-04Bibliographically approved
3. Effect of Different Inclusions on Mechanical Properties and Machinability of 20NiCrMo Carburizing Steels
Open this publication in new window or tab >>Effect of Different Inclusions on Mechanical Properties and Machinability of 20NiCrMo Carburizing Steels
2015 (English)In: The 6th International Congress on the Science and Technology of Steelmaking (ICS2015), Beijing: The Chinese Society for Metals , 2015, 805-808 p.Conference paper, Published paper (Refereed)
Abstract [en]

In modern steelmaking, carburizing steels are often used for production of automotive components with elevated levels of toughness and fatigue strength. This study is focused on the link between the characteristics of non-metallic inclusions in the steel and the machinability of the given steel grades. For this purpose, inclusion characteristics (such as composition, number, size, morphology etc.) in steel samples were determined by common two-dimensional (2D) observations of inclusions on polished metal surface of samples as well as by three-dimensional (3D) investigations of inclusions after electrolytic extraction from steel samples. The inclusion characteristics were investigated in the three types of 20NiCrMo carburizing steel grades: Steel A ‑ reference steel (410ppm S) having a common level of mechanical properties and machinability, Steel B ‑ steel grade (having 340ppm S) with an improved machinability due to the Ca-treatment and modification of MnS inclusions and Steel C ‑ clean steel grade (40ppm S) having a small amount of inclusions and a higher fatigue strength. It was found that the number of inclusions in Steel B is smaller than that in Steel A and that the inclusion composition is different. At the same time, the estimated machinability (tool life) of the Ca‑treated steel was superior to that of the reference steel. However, the significant decrease of the number of inclusions in the clean steel (Steel C) resulted in a lower machinability in comparison to the reference steel grade.

Place, publisher, year, edition, pages
Beijing: The Chinese Society for Metals, 2015
Keyword
Non-metallic inclusions, carburizing steel, machining, PCBN cutting tool
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-164866 (URN)2-s2.0-84983137878 (Scopus ID)
Conference
The 6th International Congress on the Science and Technology of Steelmaking (ICS2015), Beijing, May 12-14, 2015
Note

QC 20150422

Available from: 2015-04-20 Created: 2015-04-20 Last updated: 2016-05-17Bibliographically approved

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