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Dissertation
Processing, microstructure and property relationships in a powder metallurgy high speed steel
Doctor of Philosophy (Ph.D.), Drexel University
1985
DOI:
https://doi.org/10.17918/00008052
Abstract
REX 25('TM) high speed steel, processed from rapidly solidified gas atomized powder, has been studied in detail with respect to microstructure, strength, toughness, grindability, wear resistance and hardness at elevated temperatures. Powders were nitrogen gas atomized, screened to specific size fractions and consolidated to full density by hot isostatic pressing. The HIPed material was either heat-treated or hot-worked by forging prior to heat-treatment. Two HIPing temperatures, two austenitizing temperatures and three tempering temperatures were evaluated. X-ray diffraction, optical and scanning electron microscopy were utilized to characterize the microstructure in the atomized and consolidated conditions. Atomized powders exhibit segregated structures, with MC and M(,2)C carbides present in the form of an interconnected network. The proportion of MC carbides increases and the scale of microstructure is refined, with decreasing powder particle size. Traces of M(,6)C carbides are observed in the coarse size fractions. The matrix phase in the fine powders is (delta)-ferrite. Slower cooling promotes the formation of martensite. After HIPing, the carbide networks observed in the atomized powders are replaced by individual MC, M(,6)C and M(,23)C(,6) carbides in a ferritic matrix. Carbide size distributions are independent of prior particle size fraction, but are displaced towards coarser carbides with increasing HIPing temperature. Carbide volume fractions are independent of size fraction and HIPing temperature. Prior austenite grain size is a function of the HIPing and austenitizing temperature, and of the intermediate forging step. In the tempered condition, carbide volume fractions are independent, whereas carbide size distributions are a function of the HIPing temperature and the introduction of an intermediate forging operation. Strength and toughness are enhanced by hot forging. Austenitizing at a lower temperature results in improved strength and decreased hot hardness. Strength, toughness, hot hardness and wear resistance are similar to those in the corresponding commercial P/M high speed steel.
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Details
- Title
- Processing, microstructure and property relationships in a powder metallurgy high speed steel
- Creators
- Ali S. Fareed
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- xvii, 208 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- Materials (Science and) Engineering (Metallurgical Engineering) [Historical]; College of Engineering (1970-2026); Drexel University
- Other Identifier
- 991021888867104721