Sinter Hardening PM Steels Prepared through Hybrid Alloying

Abstract

In powder metallurgy (PM), there are several ways of introducing alloying elements into a PM material in order to adjust a certain alloying element content. Each alloying route has its advantages and disadvantages. Master alloys (MA), powders with a high content of typically several alloying elements, can be added in small amounts to a base powder, especially to introduce oxygen sensitive elements such as Cr, Mn, and Si. In addition, the master alloy can be designed in such a way that a liquid phase is formed intermediately during the sintering process to improve the distribution of alloying elements in the material and to accelerate homogenization. In this study, such master alloys were combined with pre-alloyed base powders to form hybrid alloyed mixtures with the aim of improving the material‘s sinter hardenability. The hybrid alloys were compared with mixtures of master alloy and plain Fe as reference material. The sinter hardenability of all materials was determined by generating CCT diagrams recorded with 13 different cooling rates. These were verified by metallographic cross-sections of specimens treated at common cooling rates of 3 and 1.5 K/s and subsequent hardness measurements of the microhardness (HV 0.1) of the microstructural constituents and the apparent hardness (HV 30). ◼

Transient Liquid Phase Sintering of PM Steel—A Matter of the Heating Rate

“…The martensite start (Ms) temperature is affected by the C content and the alloying elements distributed in the material. In a previous study [26], the measured Ms temperatures were shown to be in good agreement with Steven and Haynes' calculations [27] for Ms. This means that if deviations between the measured and the calculated Ms temperature occur, remaining MA particles might be an explanation for this case, since they "trap" alloying elements and C away from the materials matrix which are subsequently not available for hardening.…”

Microstructural evolution during sintering of Fe-Cr-C steels prepared from admixed elemental powders

“…Also, the masteralloy route, e.g. as ferroalloys or as complex carbidic masteralloys has been regarded as an option [8][9][10], in particular, since new atomising techniques can yield high output of fine, rounded particles [11][12][13][14]. On the other hand, adding Cr as elemental alloying particles has not been studied too frequently, although the mechanical properties reported are quite attractive [15].…”