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The Effect of Cleanliness and Micro Hardness on the Machinability of Carburizing Steel Grades Suitable for Automotive Applications
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
2016 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 87, no 4, 403-412 p.Article in journal (Refereed) PublishedText
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. Vol. 87, no 4, 403-412 p.
Keyword [en]
non-metallic inclusions, automotive, machinability, steel, micro hardness
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-185993DOI: 10.1002/srin.201500243ISI: 000373608300001ScopusID: 2-s2.0-84963517149OAI: oai:DiVA.org:kth-185993DiVA: diva2:926096
Note

QC 20160504

Available from: 2016-05-04 Created: 2016-04-29 Last updated: 2016-05-17Bibliographically approved
In thesis
1. Steel characteristics and their link to chip breaking and tool wear in metal cutting
Open this publication in new window or tab >>Steel characteristics and their link to chip breaking and tool wear in metal cutting
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
machinability, steel, non-metallic inclusions, skärbarhet, stål, icke-metalliska inneslutningar
National Category
Materials Engineering
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-187156 (URN)978-91-7595-949-8 (ISBN)
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

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