The Role of Oxygen Transfer in Sintering of Low Alloy Steel Powder Compacts: A Review of the “Internal Getter” Effect

Christian Gierl-Mayer,Herbert Danninger,Raquel De Oro Calderon

doi:10.1007/s11837-016-1819-z

Abstract

The chemical aspects of sintering have to be considered, in particular the role of oxygen. For sintered alloy steels used for highly stressed components, traditional alloy elements have been Cu, Ni and Mo, which in their oxygen affinity are very similar to the base constituent iron. Advanced alloying systems however contain Cr, Mn and/or Si. In the present study it is shown that one of the principal aspects of sintering to be considered is oxygen transfer from the base iron oxides to the alloy elements, which then form oxides that are more difficult to reduce. This process, defined as “internal gettering”, occurs both in mixed powder compacts and in prealloyed materials, although through different mechanisms. The effect can at least be alleviated by presintering in H2 in the 400°C range, part of the oxygen being removed as H2O before internal gettering becomes kinetically effective. However, in industrial practice, this collides with delubricaton. Furthermore for both alloy variants high temperature sintering is advantageous because it enhances reduction of the more stable oxides, thus eliminating the effects of internal gettering.

Highlights

Studying the fundamental mechanisms of sintering has been focused on physical processes such as: solid state sintering, densification and grain growth,[1] the role of contact geometry,[2,3,4] of defects[5,6] and of liquid phase.[1,7] The chemical side, in particular the role of oxygen, has received much less attention by science, except the effect of oxide layers on wetting[8] and atmosphere effects in some cases (See Ref. 9)
For sintered alloy steels used for highly stressed components, traditional alloy elements have been Cu, Ni and Mo, which in their oxygen affinity are very similar to the base constituent iron
The effect can at least be alleviated by presintering in H2 in the 400°C range, part of the oxygen being removed as H2O before internal gettering becomes kinetically effective

Summary

INTRODUCTION

Studying the fundamental mechanisms of sintering has been focused on physical processes such as: solid state sintering, densification and grain growth,[1] the role of contact geometry,[2,3,4] of defects[5,6] and of liquid phase.[1,7] The chemical side, in particular the role of oxygen, has received much less attention by science, except the effect of oxide layers on wetting[8] and atmosphere effects in some cases (See Ref. 9). The main amount of oxygen is always introduced through the base iron powder, even if the content is

Base Fe Powder

CONCLUSION

Findings

OPEN ACCESS