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Partial Remelting of Powder Metallurgy Tool Steels During Hot Isostatic Pressing
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. (Materials Design)
2019 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Abrasive wear is one of the most common failure modes in cold work tool steels. Apart from the material’s hardness, large undissolved carbides, i.e., primary- or eutectic carbides, can further increase the abrasive wear resistance. Therefore, the present work has investigated whether a partial remelting process of two powder metallurgy tool steel grades, during hot isostatic pressing, can cause in situ formation of large carbides not achievable through conventional powder metallurgical manufacturing methods. Where one of the investigated steel grades have vanadium as dominating alloy element and the other chromium.   

The obtained results show that large carbides can indeed be formed by a partial remelting process; with carbides several factors larger than those found in conventionally manufactured material of the two grades. Which consequently results in significantly improved abrasive wear resistance, compared to the conventional equivalents. The ductility is however reduced to low values as a result of grain coarsening, large carbides and carbide networks in the grain boundaries, and also existence of porosity in one of the grades.

The high-vanadium grade shows best prerequisites for continued trials. Explained by a larger temperature interval were the dominant carbide phase is stable in semi-solid state, better carbide distribution and morphology, and showing the highest abrasive wear resistance.

Abstract [sv]

Abrasiv nötning är en av de vanligaste förslitningsmekanismerna för kallarbetsstål. Vid sidan av materialets övergripande hårdhet kan stora karbider, det vill säga primära eller eutektiska, öka det abrasiva nötningsmotståndet. Således har denna studie undersökt om en partiell omsmältningsprocess av två pulvermetallurgiska verktygsstål, under hot isostatic pressing, kan leda till karbidstorlekar som inte kan uppnås genom konventionella pulvermetallurgiska tillverkningsmetoder. Där den ena undersökta stålsorten har vanadin som dominerande legeringselement, medan den andra har krom.

De erhållna resultaten visar att stora karbider kan bildas genom en partiell omsmältnings-process. Med karbider flera faktorer större än dem i konventionellt producerat material av de två stålsorterna. Följaktligen resulterade detta i betydande förbättring av det abrasiva nötningsmotståndet, jämfört med de konventionellt producerade materialen. Duktilitet reducerades emellertid till låga värden till följd av kornförgrovning, stora karbider och karbidnätverk i korngränserna, samt även porositet för en av stålsorterna.

Stålsorten med högt vanadin-innehåll uppvisar bäst förutsättningar för fortsatta försök. Vilket förklaras av ett större temperaturintervall där den dominerande karbidfasen är stabil i semisolitt tillstånd, bättre distribution och morfologi hos karbiderna samt att den uppvisade bäst abrasivt nötningsmotstånd.      

Place, publisher, year, edition, pages
2019. , p. 59
Series
TRITA-ITM-EX ; 2019:626
Keywords [en]
Tool steels, Carbides, Partial remelting, HIP, Abrasive wear resistance
Keywords [sv]
Verktygsstål, Karbider, Partiell omsmältning, HIP, Abrasivt nötningsmotstånd
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-259738OAI: oai:DiVA.org:kth-259738DiVA, id: diva2:1353290
External cooperation
Uddeholms AB - Voestalpine High Performance Metals Sweden AB
Educational program
Master of Science - Engineering Materials Science
Supervisors
Examiners
Available from: 2019-09-24 Created: 2019-09-22 Last updated: 2019-09-24Bibliographically approved

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