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Mangans inverkan på skärbarhet och mekaniska egenskaper i ett varmarbetsstål
Karlstad University, Faculty of Technology and Science.
2010 (Swedish)Independent thesis Basic level (degree of Bachelor), 15 credits / 22,5 HE creditsStudent thesisAlternative title
Influence of Mn content on the machinability and mechanical properties of a hot-work tool steel (English)
Abstract [sv]

Syftet med examensarbetet var att undersöka manganhaltens inverkan på skärbarheten och de mekaniska egenskaperna i varmarbetsstål Dievar samt kontrollera och undersöka hypotesen att material med låga Ac1 temperaturer maskinbearbetas svårare än material med högre temperaturer. 

Skärbarhet hos Dievar med olika Mn-halt från 0,084 till 1,59 vikts% studerades i härdat tillstånd med ett pinnfräsningstest. Skärbarheten karakteriserades genom mätning av verktygslivslängd och skärkrafter. Verktygslivslängd bestämdes av fasförslitningsutvecklingen på verktyget. Förslitningsmekanismer studerades på verktygets spån- och släppningssidor med hjälp av svepelektronmikroskop (SEM). Dragprov vid rums- och förhöjd temperatur genomfördes för att studera mangans inverkan på hållfasthetsegenskaper hos Dievar. Mikrostrukturen av stålen i härdat och anlöpt tillstånd undersöktes i SEM. Ac1 temperatur i stålen uppmättes med dilatometer.

Mangan visade sig ha en positiv inverkan på skärbarheten i Dievar. Verktygets livslängd var två gånger längre vid pinnfräsning av Dievar 1,59 vikts% Mn i jämförelse med Dievar 0,084 och 0,27 vikts% Mn. Mer påkletningsbenägna stål med lägre Mn-halt orsakade mer adhesiv nötning och urflisning av fräsens skäregg. Detta ledde till att förslitningen utvecklades hastigare under bearbetningen av Dievar med lägre Mn-halt.

De uppmätta skärkrafterna under bearbetning förklarade inte skillnaden i skärbarheten mellan Dievar med olika Mn-halt; skärkrafter var lika i alla material.

Dievar med högre Mn-halt innehöll mindre primära molybdenrika karbider än Dievar med lägre Mn-halt. Detta berodde på att manganet minskade Ac1 temperaturen i Dievar.

Mn-halten i Dievar påverkade inte hållfasthetsegenskaperna vid rumstemperatur men visade en tendens att minska stålets hållfasthet vid hög temperatur.

De genomförda undersökningarna bekräftade inte hypotesen att material med lägre Ac1 temperaturer har sämre maskinbearbetbarhet än material med högre temperaturer. Dievar 1,59 vikts% Mn hade betydligt lägre Ac1 temperatur än andra Dievar-material samt modifierat Orvar men visade sig vara lättare att bearbeta.

Abstract [en]

The aim of the study was to investigate influence of manganese content on the machinability and mechanical properties of a hot-work tool steel Dievar and verify a hypothesis that materials with low Ac1 temperatures are more difficult to machine than steels with higher Ac1 temperatures.

Machinability of Dievar with varying manganese content from 0,084 to 1,59 wt% was investigated in the hardened condition in the milling operation. The machinability of the steels was characterized by measuring tool life and cutting forces during machining. The tool life was estimated by measuring flank wear on the tools. Wear mechanisms were investigated on the clearance and rake faces of the tools by SEM. Tensile tests at room and elevated temperatures were carried out to examine the manganese influence on the mechanical properties of Dievar. Microstructure of the steels in hardened and tempered condition was investigated by SEM. Dilatometer tests were done to determine the Ac1 temperature for the steels.

Manganese content showed to have a positive effect on the machinability of Dievar. Two times longer tool life was reached when end milling Dievar 1,59 wt% Mn comparing to end milling Dievar 0,084 and 0,27 wt% Mn. More adhesive wear and chipping were observed on the tools after end milling the lower manganese containing steels. This resulted in more progressive wear and shorter tool life during machining of these steels.

The measured cutting forces could not be related to the difference in machinability of the steels with different manganese content. The generated cutting forces were similar for all the tested steels.

Dievar with higher manganese content contained less primary molybdenum-rich carbides in the microstructure. It was related to the lower Ac1 temperature of Dievar 1,59 wt% Mn comparing to the lower manganese containing steels.

The manganese content showed no influence on the tensile properties of Dievar at room temperature and a tendency to a slight decrease in yield and ultimate strength at the elevated temperature.

The machinability tests carried out in the present study did not confirm the hypothesis that materials with low Ac1 temperatures have poor machinability.  Dievar 1,59 wt% Mn had much lower Ac1 temperatures than the other Dievar steels and the modified Orvar steel but showed to have an improved machinability compared to the others.

Place, publisher, year, edition, pages
2010. , p. 38
Series
Karlstad University Studies, ISSN 1403-8099
Keywords [sv]
varmarbetsstål, skärbarhet, mekaniska egenskaper, manganhalt
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kau:diva-5917OAI: oai:DiVA.org:kau-5917DiVA, id: diva2:325654
Presentation
2010-06-10, 21A342, Karlstads universitet, Karlstad, 10:30 (Swedish)
Uppsok
Technology
Supervisors
Examiners
Available from: 2010-06-28 Created: 2010-06-18 Last updated: 2010-06-28Bibliographically approved

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