Sintering of powders without a circulating gas environment (review)

Abstract

621.762The paper summarizes and analyzes the known literature and data obtained by the authors on the development, use, and evolution of methods for nonoxidation sintering and chemical/thermal treatment of powders without protective gas environments. The efficiency of the method, including that for sintering of materials with high affinity to oxygen, is shown.The production of parts from structural metal materials with powder metallurgy methods involves nonoxidation sintering conventionally conducted in protective gas environments [1][2][3][4][5] in continuous (conveyer, pusher) furnaces. However, the development of small production enterprises (including powder metallurgy ones) that are rarely equipped with expensive and high-output continuous furnaces has necessitated the wider use and improvement of nonoxidation sintering of powder compacts in containers with an isolated protective atmosphere in ordinary chamber furnaces [5][6][7].Although these processes hold much promise, they still have to be examined. They are scarcely described in fundamental literature and powder metallurgy textbooks and, thus, process engineers have insufficient knowledge about them.The objective of this paper is to summarize and analyze the known literature and our data needed to use and develop nonoxidation sintering in standard heat-treatment furnaces.It should be emphasized that nonoxidation heating processes during sintering and chemical/thermal treatment have much in common and often use identical equipment. Sintering in steel containers is combined with chemical/thermal treatment, for example, manganizing [8], carburizing [9], boronizing [10,11], or simultaneous diffusion alloying with carbon and sulfur [12] using one or another method to isolate the container from penetration of air, which is a mixture of oxidizer (O 2 ) and molecular nitrogen, being practically inert to iron. The isolation of a steel container from air by welding is perfectly reliable and has been used in laboratory practices [8], but the high cost and technical complexity of this sealing method have not permitted its commercial application.