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Steel characteristics and their link to chip breaking and tool wear in metal cutting
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.ORCID iD: 0000-0001-7707-5631
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The vision of this thesis is to study how it is possible to obtain optimised workpieces during metal cutting processes in industry. Specifically, the work is aimed to increase the understanding between the steel characteristics and their link to the chip breaking and tool wear during metal cutting. The emphasis is on the influence of the cleanliness and the characteristics of non-metallic inclusions in the workpiece on the machinability of carburising steel grades. The machinability of a case hardening steel is improved by a M-treatment (additions of Ca). Also, the improved machinability of the M-steels offers an attractive potential to save money which makes it possible to reduce the tooling costs with up to 50%. The improved machinability of Ca-treated steels is correlated to the formation of lubricating slag layers consisting of Ca-enriched sulfide inclusions and oxy-sulfide inclusions, which are formed on the rake face during the machining operation. It is proposed that the formations of slag layers from the workpiece constituents are essential to minimise the chemical degradation of the tool edge due to a contact with the chip. During this process, sulfur minimises the material transfer from the chip flow, whilst Ca-treated impurities have a stabilising effect on the protective deposits made of slag layers.

Since there is a remaining industrial need to increase the production rate, whilst maintaining a high quality of the finished parts, the future production will continue to require extreme demands on the quality of workpieces. If the emphasis is focused on the workpiece, it should be possible to obtain a robust manufacturing process. Therefore, the challenge for future steel metallurgists is to develop high performance grades with optimised combined properties.

Abstract [sv]

Syftet med denna avhandling är att studera hur det är möjligt att framställa optimala ämnen för skärande bearbetning i industriell skala. Målsättningen med arbetet är att öka förståelsen för ståls egenskaper och dess inverkan på spånbrytning och slitage av verktyg vid skärande bearbetning. Avhandlingen fokuserar på kopplingen mellan arbetsstyckets renhet och inneslutningskarakteristik och dess inverkan på skärbarhet hos sätthärdningsstål. Skärbarheten hos vanligt sätthärdningsstål kan förbättras markant genom en Ca-behandling, dvs. en så kallad M-behandling. Den förbättrade skärbarheten hos M-stål möjliggör stora kostnadsbesparingar, som uppskattas kunna reducera verktygskostnader med upp till 50%. Den förbättrade skärbarheten hos M-stål beror på bildningen utav tribologiska skikt som är anrikade med (Mn,Ca)S- och (CaO)x-Al2O3-S-slagg. Dessa tribologiska skikt bildas på skärverktygets spånsida under ingrepp vid skärande bearbetning och består utav vissa atomer som överförts från det bearbetade ämnet till skäret. Bildandet av ett skyddande skikt anses nödvändigt för att undvika att verktygets skäregg utsätts för ett kemiskt angrepp i kontaktytan med spånflödet. Svavel anses minimera att rent arbetsmaterial överförs till skärverktyget medans kalcium-berikade inneslutningar hjälper till att bilda ett stabilt och skyddande tribologiskt skikt.

Det eviga behovet att öka produktionstakten, utan att för dess skull riskera slutproduktens kvalité ställer stora krav på framtidens material. Med utgångspunkt från arbetsstycken så ska det vara möjligt att uppnå en robust industriell produktion. Utmaningen är därför att utveckla högpresterande stål med en förhöjd kombinerad funktionsegenskap.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. , 73 p.
Keyword [en]
machinability, steel, non-metallic inclusions
Keyword [sv]
skärbarhet, stål, icke-metalliska inneslutningar
National Category
Materials Engineering
Research subject
Materials Science and Engineering
Identifiers
URN: urn:nbn:se:kth:diva-187156ISBN: 978-91-7595-949-8 (print)OAI: oai:DiVA.org:kth-187156DiVA: diva2:929065
Public defence
2016-06-08, Sal B3, Brinellvägen 23, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2016-05-17 Created: 2016-05-17 Last updated: 2016-05-17Bibliographically 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 Cleanliness and Micro Hardness on the Machinability of Carburizing Steel Grades Suitable for Automotive Applications
Open this publication in new window or tab >>The Effect of Cleanliness and Micro Hardness on the Machinability of Carburizing Steel Grades Suitable for Automotive Applications
2016 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 87, no 4, 403-412 p.Article in journal (Refereed) Published
Abstract [en]

This work reports on soft part turning of carburizing steels using cemented carbide (CC) cutting tools. The emphasis is on the influence of the cleanliness and micro hardness on the machinability of carburizing steel grades. A reference steel grade is included in this study together with a clean steel and an ultra-clean steel. Machining tests are conducted to examine the cutting tool life, the balance between the excessive flank or crater wear and the chip formation. The wear mechanisms are examined by using a scanning electron microscope (SEM) equipped with a back-scatter (BS) detector. It is possible to differentiate between the machinability of the clean steel grades, having only a minor difference in the sulfur and oxygen contents. Furthermore, the longest tool life is obtained when machining the reference steel. The superior machinability of the reference steel R is linked to its high content of sulfur. It is believed that MnS inclusions act as stress raisers in the primary shear zone. Hence, this will improve the chip formation process.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2016
Keyword
non-metallic inclusions, automotive, machinability, steel, micro hardness
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-185993 (URN)10.1002/srin.201500243 (DOI)000373608300001 ()2-s2.0-84963517149 (Scopus ID)
Note

QC 20160504

Available from: 2016-05-04 Created: 2016-04-29 Last updated: 2017-11-30Bibliographically approved
3. The influence of microstructure and non-metallic inclusions on the machinability of clean steels
Open this publication in new window or tab >>The influence of microstructure and non-metallic inclusions on the machinability of clean steels
(English)Manuscript (preprint) (Other academic)
Abstract [en]

This study focused on the evaluation of the machinability of different carburising steel grades by using a cemented carbide cutting tool during semi finishing of steel. The effect of the steel composition, microstructure and inclusion characteristics on the cutting tool wear in the soft part turning was evaluated for a reference steel R (0.028% S, 0.0009% O), a clean C steel (0.003% S, 0.0005% O), and an UC ultra clean steel (0.002% S, 0.0004% O). An improved cutting tool life of about 10-25% was obtained when machining the reference steel R. The favorable machining performance of this steel was attributed to its higher content of non-metallic inclusions, larger grain size and lower micro hardness than that of the clean steels.

Keyword
carburising steel, grain size, non-metallic inclusions, machinability
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-187154 (URN)10.1002/srin.201600111 (DOI)
Funder
VINNOVA
Note

QC 20160518

Available from: 2016-05-17 Created: 2016-05-17 Last updated: 2016-05-18Bibliographically approved
4. 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
5. 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
6. Steel characteristics and their link to tool wear in hard part turning of transmission components
Open this publication in new window or tab >>Steel characteristics and their link to tool wear in hard part turning of transmission components
(English)Manuscript (preprint) (Other academic)
Abstract [en]

This study describes the influence of the steel characteristics of Ca-treated carburising steel grades during hard part turning of synchronising rings in gearbox production. The main focus was on the chemical composition of the non-metallic inclusions in the evaluated workpieces and their effect on the PCBN tool wear. In addition, a Ca-treated carburising steel grade was compared to a standard steel grade.

Machining tests were performed at the transmission machining site at Scania in order to evaluate the PCBN cutting tool life as defined by the generated surface roughness during actual production. The progression of flank and crater wear was evaluated by using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS) and a secondary electron (SE) detector.

The Ca-treated steel showed a more than doubled tool life than that of the standard steel grade. The superior machinability was linked to the formation of a Ca-enriched slag barrier composed of (Mn,Ca)S and (Ca,Al)(O,S). It is believed that the stability of the protective deposits is essential to minimise diffusion-induced chemical wear of the PCBN tool. Furthermore, the improved machinability corresponds to a reduced tooling cost of 50% during an industrial production of transmission components at the site of Scania. Therefore, to implement the M-steel on a wider range of components would lead to a significantly reduced manufacturing cost per produced component. However, the capability of Ca-treated steels through the complete production route must be further investigated in order to allow for a large scale introduction of Ca-treated steels in the production.

Keyword
wear, PCBN, machinability, steel
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-187155 (URN)
Note

QC 20160518

Available from: 2016-05-17 Created: 2016-05-17 Last updated: 2016-05-18Bibliographically approved

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