High-chromium cast iron sintered of sprayed powders

Abstract

621.762The paper examines basic technological characteristics of high-chromium cast iron powders resulting from gas or water melt spraying. Sintering of billets made of these powders is investigated. It is shown that Fe-Cr-Mo-Cr powder alloys can combine high hardness and thermal stability. Therefore, they are candidate materials for operation in intensive wear and at high temperatures.An efficient way to enhance the wear resistance of components operating at high loads and subjected to different types of wear is to use powder composites with special properties, including tungstenfree hard alloys and carbide steels [1][2][3]. Moreover, there is a need to create cheaper composites (as compared with conventional hard alloys) since wear-resistant materials have widespread application. These materials include carbide steels based on the Fe-Cr-C system [4,5] and stainless austenitic steels with chromium carbide additions [6][7][8].Based on preliminary efforts by the UkrNIIspetsstal' (Zaporozh'e) and Institute for Problems of Materials Science, high-chromium cast iron produced from sprayed powders of relevant alloys is considered as a candidate for structural wear-resistant and tool materials. The production technology of these materials includes cast iron smelting in an induction furnace, melt spraying with an inert gas or water, powder mixing with a plasticizer, compaction and sintering of billets in the presence of a controlled amount of liquid phase.This study focuses on four chromium-containing alloys (Table 1) sprayed with nitrogen and water at high pressure.Based on a morphology analysis of sprayed particles, grain-size analysis, and chemical analysis of powders in comparison with sprayed powders of high-speed steels [8,9] have shown that a greater carbon content in the melt somewhat reduces the content of oxygen in the powder (spraying conditions being equal). On the other hand, a watersprayed powder contains much more oxygen than gas-sprayed powders of the same composition.The medium used for spraying substantially influences the bulk density of powders. If γ b = 4.9 to 5.1 g/cm 3 for the nitrogen-sprayed powder, the bulk density of the water-sprayed powder (alloy) is only 2.76 g/cm 3 . This substantial difference is attributed to a more developed surface of water-sprayed powder particles as compared with gas-sprayed ones. Gas-sprayed particles are almost spherical and the powder has better yielding properties, while water-sprayed powders have irregular shape, which greatly improves their technological characteristics (compactibility and moldability [10]). A comparative analysis of gas-sprayed powders of different chemical composition produced under equal conditions has shown that the mean particle size essentially decreases with increasing carbon content of the alloy. For example, the fraction ≤160 µm for sprayed powder of composition 1 amounts to 83% and does not exceed 40% (Table 2) for R6M5K5 steel powders containing about 1 wt.% C. This seems to result from substantial decrease of the melt surface tensio...