On-line Control of Processing Atmospheres for Proper Sintering of Oxidation-Sensitive PM Steels
Journal article, 2012

Changes of atmosphere composition during sintering of water atomized powder prealloyed with Mn and Cr (up to 2% of both) were studied. Increasing sensitivity to atmosphere purity with increasing alloying elements content was registered. Continuous monitoring of sintering atmosphere composition (CO/CO2/H2O) indicates three critical stages during the heating up to final sintering temperature: the importance of rapid atmosphere purification after lubricant decomposition and removal; the reduction of the iron oxide layer by hydrogen at temperatures up to ~500°C and by carbon at temperatures around ~720°C; the reduction of the spinel oxides on the powder surface at above 900°C and further reduction of thermodynamically stable surface oxides and mixed internal oxides close to the sintering temperature. The measured ratio of CO/CO2 indicates favorable thermodynamic conditions for reduction of stable oxides as (Cr,Mn)xOy close to sintering temperature (1120C) for the applied sintering conditions. The experimental results were confirmed by modeling the metal-gas interactions using the thermodynamic/thermochemical softwares ThermoCalc and HSC Chemistry. The modeling indicate the significance of maintaining a sintering atmosphere with high reducing potential during heating stage for minimizing oxidation before high-temperature carbothermal reduction starts.

atmosphere monitoring

carbothermal reduction

sintering

processing atmosphere

oxide reduction

prealloyed powder

Author

Eduard Hryha

Chalmers, Materials and Manufacturing Technology, Surface and Microstructure Engineering

Eva Dudrova

Slovak Academy of Sciences

Lars Nyborg

Chalmers, Materials and Manufacturing Technology, Surface and Microstructure Engineering

Journal of Materials Processing Technology

0924-0136 (ISSN)

Vol. 212 4 977-987

Driving Forces

Sustainable development

Areas of Advance

Production

Subject Categories

Other Chemistry Topics

Other Materials Engineering

DOI

10.1016/j.jmatprotec.2011.12.008

More information

Latest update

6/10/2019