Master Alloy Compositions for Tailoring Liquid Phases in Lean Steels

Paper i proceeding, 2014

Optimized Cu-Ni-Si master alloys (MA) have been used to tailor the properties of lean PM steels by means of a liquid phase. The degree of intersolubility between MA and iron base powder has been used as a key factor for controlling the amount and time interval when liquid is available, the distribution of the liquid and even the impact on dimensional behavior. Two MA compositions -with dissimilar dissolutive character in contact with iron- are used to clarify the effect of solubility on microstructure development and dimensional response: a Cu-based MA able to dissolve up to 2 wt.% of iron is compared to a Ni-based MA which favors higher degrees of iron dissolution, 35 wt.%. Solid-liquid interactions taking place at high temperatures (iron dissolution and wettability) are characterized through the use of thermodynamic calculations and monitored wetting experiments. Microstructure development and dimensional behavior is evaluated through interrupted sintering trials in a quench dilatometer under different sintering conditions. The results show how critical aspects for the steel performance (densification, dimensional behavior, microstructure, etc.) can be specifically tailored (during the design step) through the proper characterization of the degree of interaction between the phases.