Influence of Geometry and Cooling Rate on Properties of Sinter-Hardened Steels

Abstract

The aim of this paper is to deepen the understanding of the influence of the cooling step on the final properties of sinter-hardened components, mainly focusing on part geometry (through the definition of an A/M ratio) and cooling rate. A commercial Distaloy DH powder has been uniaxially pressed in different shapes, identified in terms of area/mass index, at three different compacting pressures (500, 600 and 800 MPa). During the sinter-hardening process, conducted in a belt-furnace, temperature profiles and atmosphere have been sampled and analysed. Particular attention has been paid to the cooling step, carried out at different furnace settings (10 to 80% of the maximum cooling capability in terms of fan speed). Sintered samples have been analysed in terms of carbon and oxygen content, hardness and microstructure. The considered properties have then been compared with dilatometer data, derived from literature. Matching these properties, a correlation between furnace setting, shape and microstructure has been drawn.

The Study of Local Effect of Manganese on Microstructure Development of Admixed Fe-Mn-C Sintered Steels

“…As the temperature increases, Mn vapor reacts with oxygen and water vapor. Formed oxides are accumulated in residual pores, in accordance with other authors [1,6,9,11,28]. Salak [15] suggested that to utilize to the maximum extent the effect of sublimation and condensation of manganese vapors as a primary alloying mechanism, iron compacts must have mainly open pores, at least at the start of sintering, this ensures that by filling these pores the manganese vapors can affect the surface of all particles.…”

“…During the past decade huge expansion [1][2][3][4][5][6][7][8][9][10][11] in manganese sintered steels research is evident, where manganese additions have been tried in various forms, starting from elemental blended addition of various grades of ferromanganese and master-alloy powders up to fully pre-alloyed powder. However, its industrial utilization is still very limited [12,13] as sintering of admixed combinations leads to high risk of oxidation during heating stage and the high vapor pressure can result in significant loss of manganese even during the heating up phase [14][15][16][17].…”

Dry sliding wear behaviour of low alloyed sintered steels in relation to microstructure and fracture behaviour

“…In general, the presented microstructures are heterogeneous and depend on local atmosphere conditions, which are in good agreement with previous studies. 4,5,7,8,11,[15][16][17]19,20,23,24,[27][28][29]31,[34][35][36][37] 13b Wear tracks morphology for alloy A sintered in industrial atmosphere with detrimental effect of intensive plastic deformation in soft structure regions 14 Area of first sites of crack initiation and local damage in vacuum sintered steel B…”

“…In general, the presented microstructures are heterogeneous and depend on local atmosphere conditions, which are in good agreement with previous studies. 4,5,7,8,11,15–17,19,20,23,24,27–29,31,34–37…”

“…1,2 In the last years, the research in PM has been focused on the possibility to substitute expensive, carcinogenic and toxic nickel by introducing manganese and chromium into sintered steels. [3][4][5][6][7][8][9] In addition, Mn improves strength of ferrite and both Mn and Cr increase the hardenability of steels. However, their application in PM products finds some difficulties, mainly related to the high affinity for oxygen, leading to the formation of continuous oxide networks during conventional sintering in atmospheres, and therefore failing to satisfy the requirements of the Ellingham-Richardson diagram (related to dew point).…”