Effect of Iron Powder Preparation Method on Powder Steel Compact Formation During Electric-Contact Compaction

Abstract

A dependence is given for porosity of iron powder and iron-graphite composite based on atomized and reduced powders on different electric-contact compaction regimes. A dependence is determined for the amount of bonded carbon on process regime. Limiting processes are established during the formation of powder steel by electric-contact compaction.Development of powder metallurgy assumes the development of methods for preparing objects based on combining different forms of action on a compacted charge. One of these methods is electrical contact compaction (ECC) with which the compacting force applied is accompanied by passage of an electric current through a compacted charge [1].The underlying processes of powder steel formation with ECC are charge compaction and material homogenization [2][3][4][5]. The aim of this work is to study the effect of powder particle surface condition, depending on its preparation method, on these process kinetics. Results of this work may serve as a rough guide for production services of industrial enterprises in the technological development of powder steel object production by ECC.Currently in industry iron powder used is prepared by reducing scale and melt atomization. The starting materials used for the study were iron powders PZhR 3.200.28 and PZhV 3.160.26 (GOST 9849−86) and pencil graphite GK-1 (GOST 4404−78). The carbon content in the original iron powder was 0.05%. In subsequent studies, iron powder produced by the fi rms Höganäs (Sweden) and Quebec Metal Powder (Canada) will be used.Studies were performed in an ECC laboratory unit (Fig. 1) in the following sequence. A powder sample weighing 1.6 g was weighed with an accuracy of ±0.1 g and poured into a die with a lower piston 1 installed in the starting position. The wall of the die was treated with calcium fl uoride CaF 2 , and the piston ends in contact with a charge were treated with graphite GK-1. Then the die was placed in a chamber 2 and fl ushed with argon, after which the upper piston 1 was installed in the die cavity. Chamber sealing was provided by rubber gaskets 3.Dielectric plates 6 serve for preventing development of a harmful voltage within the body of the laboratory unit. Regulator 7 is intended for controlling argon supply to the chamber. Ammeter 8 controls current strength supplied from source 9.The chamber prepared for pressing is installed on the press table. Specimens were prepared by two-sided compaction in a laboratory hydraulic press 4 (maximum force 7600 N) making it possible to control pressing force both with respect to magnitude and duration of its application during sintering powder material 5 by direct passage of an electric current.