Microstructure and mechanical properties of sintered (2-4)Mn-(0¿6.-0¿8)C steels.

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426-464 MPa, tensile strengths R m were 724-780 MPa and strains to failure were 1•6-2•0% after sintering at Dr A. Cias, Mr K. Pilch, Mrs H. Cias and Mr 1250°C. The 1120°C sintering temperature resulted in M. Sulowski are with the Academy of Mining and 10-15% lower strength values. The microstructures, Metallurgy, AGH, Al. Mickiewicza 30, 30-059 Krakow, signi cantly devoid of oxide networks, comprised

The potential of PM Mn steels has been established yield, tensile and bend strengths of 499, 637 and in laboratory experiments. This paper deals with 1280 MPa, respectively, with impact energy of 18 J, and sintering of Fe-(2-4)Mn-(0•3/0•7)C, also with 0•85%Mo tensile and bend strains of 1•17 and 1•57%, were achieved addition, in an industrial pusher furnace at 1180°C in an for the Fe-2Mn-0•85Mo-0•5C alloy, marginally superior atmosphere of 25% hydrogen plus 75% nitrogen, to Fe-2Mn-0•7C. For the sinter hardened Fe-4Mn-0•3C obtained from a cryogenic liquid, giving an inlet dew-alloy yield, tensile and bend strengths were 570, 664 and point of −55°C. Tensile, bend (including fatigue) and 1263 MPa, respectively, at an acceptable impact energy miniature Charpy specimens were sintered in flowing of 14 J, with tensile and bend strains of 0•52% and 1•8%. gases and in semiclosed containers with a getter of ferro-Many of the results compare favourably with the requiremanganese, carbon and alumina. The quenched and tem-ments of MPIF standard 35. Mn is a more effective pered state was investigated, as was sinter hardening strengthening agent than either Ni or Cu, or their combi-(cooling rate of 55 K min−1), simulated for comparison nation, though generally at reduced plasticity. with slow cooling at 10 K min−1. As there was no forma-PM/1086 tion of oxide networks at the combination of sintering temperature and dewpoint, in accordance with the Dr Dudrova ´(

Calculated multicomponent phase diagrams were used to identify high speed steel (HSS) type alloys having the potential to exhibit enhanced sinterability. The requirement was for an extensive austenite+carbide+liquid phase field. Of the six tungsten and molybdenum based systems studied, Fe-14Mo-C+4Cr-8Co systems were potentially the most promising. Appropriate compositions were water atomised and additional alloys prepared by blending annealed powders with graphite powders. Powders were compacted to green densities of about 70% theoretical and then vacuum sintered. Sinterability was assessed in terms of sintered densities and microstructures. Alloys containing Fe-13Mo-1•3C, Fe-14Mo-4Cr-1•3C, and Fe-14Mo-8Co-4Cr-1•4C were sintered to full density at temperatures as low as 1170°C, 70-150 K lower than for existing HSSs. Sintering windows were 20-30 K, a significant improvement on existing HSSs. As sintered microstructures consisted of angular M 6 C carbides dispersed in martensitic matrixes, which is typical for correctly sintered HSS. Heat treatment response and cutting performance for the sinterable grades were assessed and found to be comparable to existing HSS. The cutting performance of Fe-14Mo-8Co-4Cr-1•4C tools at 45 and 52•5 m min−1 was superior to both cast wrought M2 and T1 tools of identical geometry. Lower carbon contents resulted in an increase in sintering temperature and a reduction in the width of the sintering window. Higher carbon contents destroyed sinterability, since they led to the formation of M 2 C eutectic structures in the undersintered condition. Alloy sinterability was correlated to differential thermal analysis data obtained during heating of powders. The variations in sinterability with alloy composition are discussed with reference to phase diagrams; the degradation in sinterability observed at carbon contents above 1•4% is attributed to the presence of ternary eutectic phase fields. The commercial implications of the relationship between sinterability and alloy composition are discussed.