Effects of Ni and Ni + Co Additions in P/M Stainless Steel 316L on Sigma Phase and Oxide Formations after Long Term Heating

Abstract:

The effects of various Nickel and Nickel with Cobalt additions in P/M 316L stainless steel on sigma phase and oxide formations were investigated. Various powder mixtures of P/M316L with Ni and both Ni + Co powders as 1, 2, 3 and 4% by wt.%, were compacted using single action press under 498 MPa and sintered at 1300 °C for 30 minutes in hydrogen atmosphere. Then specimens were exposed at temperature of 800 °C and 900 °C for 25, 50, 75 and 100 hours in order to investigate the microstructural stability. It was found that specimens with both Co and Ni additions could reduce amount of sigma phase formation especially at heating of 900 °C. After all heat treatments, oxide scales had grown in closed pores during heating, therefore, the amount and size of internal porosity were decreased. It was also observed that the amount and size of porosity of heated specimens still have the same tendency as sintered specimens. The oxide scale in the matrix is mainly composed of Fe3O4 and Cr2O3 in the closed pores.

• Periodical: Advanced Materials Research (Volume 894)
• Pages: 227-233
• DOI: https://doi.org/10.4028/www.scientific.net/AMR.894.227
• Online since: February 2014
• Authors: Panyawat Wangyao, Nantawan Pichaiwong, Visuttipitukul Patama, Nutthita Chuankrerkkul, Jirutthitikalpongsri Hirunyagird
• Keywords: 316L Stainless Steel, Powder metallurgy, Sigma Oxidation, Sigma Phase

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