Effects of Nitrogen on Powder Metallurgical Propertics of Water-atomized Stainless Steel Powders

Abstract

An investigation was made on the pressing and sintering behavior of water-atomized 15/25% Cr-Ni stainless steel powders bearing 0.34% or less of nitrogen.
The results were summarized as follows:
(1) Nitrogen was successfully added into powders up to near the nitrogen-solubility in the molten state at pulverizing temperature, on account of rapid solidification by quench-atomization.
(2) Compressibility was found to be higher in nitrogen-rich lower Cr powders, only in the case that athermal martensite was less formed under the favorable influence of nitrogen as an austenite stabilizer, with less affecting sintering behavior.
(3) Compressibility was appreciably improved by heat-decomposing (in the range 600-700°C) metastable phases quenched from high temperatures, especially for 15/17% Cr powders with the normal amount of nitrogen.
(4) Excess nitrogen-added powders were outgassed in the early stage of vacuum-sintering at temperatures higher than 1000°C.
As a result, it was found that fairly good mechanical properties of sintered materials can be obtained irrespective of the original amount of nitrogen.