New alloying systems for ferrous powder metallurgy precision parts

Abstract

Traditionally, the common alloy elements for sintered steels have been Cu and Ni. With increasing requirements towards mechanical properties, and also as a consequence of soaring prices especially for these two metals, other alloy elements have also become more and more attractive for sintered steels, which make the steels however more tricky to process through PM. Here, the chances and risks of using in particular Cr and Mn alloy steels are discussed, considering the different alloying techniques viable in powder metallurgy, and it is shown that there are specific requirements in particular for sintering process. The critical importance of chemical reactions between the metal and the atmosphere is described, and it is shown that not only O2 and H2O but also H2 and even N2 can critically affect sintering and microstructural homogenization

Degradation of alumina refractory bricks by sintering Mn low-alloy steels

“…for alumina is ρ th E 4.088 g/cm 3 ; therefore, the porosity of this material is approximately 65.2%.…”

“…This work discusses the effects of Mn (g) on the chemical corrosion mechanism of refractory brick. The renewed interest in Mn as an alloy element in sintered steels is due to its low cost compared to the cost of, for example, Ni or Mo and because of the excellent properties that can be attained either in the as-sintered state or after heat treatment, irrespective of its high oxygen affinity, which has previously limited its use in powder metallurgy [2][3][4][5][6].…”

Dimensional Changes, Microstructure, Microhardness Distributions And Corrosion Properties Of Iron And Iron-Manganese Sintered Materials

“…Pores remain on the sites of the Mn carrier particles, and as the sample cools, they are filled with agglomerates of tiny Mn particles. The consequence of these processes is a macroscopic expansion [9].…”

Application of thermal analysis techniques to study the oxidation/reduction phenomena during sintering of steels containing oxygen-sensitive alloying elements

“…Hydrogen is the most effective reducing agent at low temperatures, taking care of the reduction of iron oxides layers covering most of the surface of the steel powders at temperatures around 400°C. However, the reduction of more stable oxides, or internal oxides that need high temperatures to diffuse to the powder surface, necessarily takes place at higher temperatures at which the dominant mechanism is the carbothermal reduction [1][2][3].…”

“…However, it is still not well known how the specific composition of the master alloy affects the oxidation/reduction phenomena and therefore how the processing conditions have to be adapted for these new materials. Thermogravimetry analysis coupled with mass spectrometry has proved to be the most effective method for analyzing the oxidation/reduction reactions at different stages of sintering [1][2][3]. Identification of critical temperature ranges with these techniques has provided the tools for an optimum design of the sintering cycles for conventional steels and even for Cr-prealloyed grades [1,[7][8][9].…”