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Effect of Nitrogen on the Mechanical Properties of Microstructures of Hot Isostatically Pressed Nanograined Fe

Published

Author(s)

A Munitz, Z Livne, J C. Rawers, J S. Adams, Richard J. Fields

Abstract

The effect of nitrogen content in Fe powders on the mechanical properties and microstructure of cold isostatic pressed (CIPed) and sintered or hot isostatic pressed (HIPed) Fe powders which produced by attrition ball milling was investigated. Microhardness and compression tests were used to determine the mechanical properties. Optical, scanning, and transmission electron microscopy were used to investigate the microstructural changes that occurred during consolidation. Sintering of the CIPed bodies at temperatures below 850 degrees Celsius} caused no change in density, with only minor mechanical improvement, and the bodies remained friable. HIPing was found to be essential for effective consolidation of ball-milled powders. Increasing Hiping temperatures increased the density, the compression yield stress, the maximum compressive strength, and the hardness to a maximum value and then decreased. The maximum in density preceded the maximum in the compression yield stress, and its value depends on the nitrogen content in the powder. At low HIPing temperatures (< 580 degrees Celsius}) the nitrogen content has no influence on the mechanical properties. However, above 580 degrees Celsius}, the nitrogen content reduces the mechanical properties as well as density, and increases the oxide precipitation. There are two microstructural effects of nitrogen on the microstructure: void formation in the Fe powder above 580 degrees Celsius} for the higher nitrogen concentrations, and severe grain boundary embrittlement above 965 degrees Celsius}. Iron bodies processed in argon has a smaller grain size than iron bodies processed in nitrogen throughout the entire consolidation temperature range. However due to the smaller grain size, the optimum in mechanical properties (maximum strength with reasonable elongation) is reached only above 965 degrees Celsius}. Processing in argon improves mechinability.
Citation
NIST Interagency/Internal Report (NISTIR) - 6141
Report Number
6141
Volume
37

Keywords

ball-milled powder, cold and hot isostatic pressing, effect of argon & nitrogen, iron sintering, mechanical properties, microstructure, nanograin

Citation

Munitz, A. , Livne, Z. , Rawers, J. , Adams, J. and Fields, R. (2006), Effect of Nitrogen on the Mechanical Properties of Microstructures of Hot Isostatically Pressed Nanograined Fe, NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=852876 (Accessed April 15, 2024)
Created May 31, 2006, Updated October 12, 2021