Sulfoxidation and Gaseous Nitrocarburizing of Sintered Steels
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To decrease the treatment time and to obtain better properties of the layers, the authors studied a cycle consisting in a pre-oxidation with sulfur dioxide, effected with the purpose of reducing the interconnected porosity, and a nitrocarburizing stage. Steel samples, containing little carbon (0. 01 wt pct) and copper (2 wt pct), with three different density ranges (6. 3 multiplied by (times) 10**3, 6. 7 multiplied by (times) 10**3 and 7. 2 multiplied by (times) 10**3 kg/m**3), were treated in a laboratory furnace with a small flow of SO//2 (1. 4 multiplied by (times) 10** minus **6 Nm**3/s) for different times and temperatures. After the sulfoxidation stage the samples were nitrocarburized at 630 degree C with a gaseous atmosphere ammonia ( approximately equals 3 multiplied by (times) 10** minus **5 Nm**3/s) and methanol (5, 10 and 20 vol. pct) mixtures for times varying between 1 and 8 h.