The following exclusive review for www.ipmd.net by Professor Ramamohan Tallapragada reports on a paper presented by the College of Engineering at Pune, India, discussing the effect of iron powder dilution on M3/2 sintered compacts. The event took place in Pune, India, from the 3rd to 5th February 2011
The presentation by A. A. Manwatkar, J. B. Suryawanshi and N. B. Dhokey from the College of Engineering at Pune, India, entitled “Effect of dilution by iron on sintered properties of M3/2” was judged as the best research paper related to industrial research presented by a student at the conference.
The objective of the paper was to analyse the effect of dilution of M3/2 HSS with iron powder. M3/2 HSS is used in manufacturing valve train components due to its high hardness, mechanical strength and high temperature and wear resistance.
Fully pre-alloyed water atomised and vacuum annealed powder of M3/2 was obtained from Höganäs India. Iron powder in varying proportions, 10, 20, 30, and 40 wt% was introduced into M3/2 powder and blended for 1 hour in a double cone mixer. Electrolytic copper powder (99%) of size 2-8 µm was used for infiltration.
Green compacts of 10mm diameter and 10mm height were die pressed at 600MPa, and sintered at 1140°C in hydrogen atmosphere for 30 minutes. These were cooled in furnace to 850°C followed by air cooling to room temperature.
Some sintered samples were subjected to cryogenic treatment at -185°C and soaked in the bath for 16 hours followed by soft tempering at 100°C for 1 hour to relieve cold stresses. Another set of sintered samples were copper infiltrated at 1180°C in a hydrogen atmosphere. After measuring the density and Rockwell hardness using 150kgf loads, a dry sliding wear test was performed using a computerised Pin-on-Disc machine. The wear test was carried out using a fixed normal load of 6kg at constant sliding distance of 3000mm for 21 minutes. Metallography was conducted using both image analyser as well as scanning electron microscope.
Sintered density of samples showed an initial increase (7.0 g/cc) with increase in iron additions up to 20%. Further increase in iron had no effect. Density of copper impregnated samples showed no variation in density (about 7.5 g/cc) with increasing iron additions.
The hardness of both sintered as well as impregnated samples decreased with the increase in iron content. Cryo-treated samples showed improved hardness, possibly due to the transformation of retained austenite into martensite.
Wear analysis indicated that the wear rate followed a trend opposing the hardness values. Wherever an increase in hardness was observed due to either cryogenic treatment or due to iron additions, a decrease in wear rate was observed.
Non-cryogenic treated samples showed heavy segregation of carbides. Cryogenic treated samples showed a homogeneous structure with uniformly dispersed fine carbides that might be responsible for the increase in hardness and decrease in wear rate.
Thus, the combination of dilution with iron and cryogenic treatment improves the overall mechanical properties of M3/2 steels.