Fatigue properties and fracture of plasma nitrided sintered iron and steel

Fatigue properties and fracture of plasma nitrided sintered iron and steel

EFFECT OF PORE SIZE ON MECHANICAL PROPERTIES OF SINTERED STEEL J.&i et al. (Central Iron and Steel Research Inst., Beijing, China.) The influence of p...

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EFFECT OF PORE SIZE ON MECHANICAL PROPERTIES OF SINTERED STEEL J.&i et al. (Central Iron and Steel Research Inst., Beijing, China.) The influence of pore size on mechanical properties of sintered steels was reviewed. Experimental studies showed that, at constant density, fatigue strength, tensile strength and elongation decrease with increase in mean pore size. Effect of pore morphology was discussed. The importance of control of pore size was emphasized. PROPERTIES OF SINTERED AND COLD ROLLED COPPER-NICEELGOLD ALLOYS SNestorovic, D.Markovic. (University of Belgrade, Bar, Yugoslavia.) It was reported that Cu-2wt%Nil%Au elemental electrolytic powders had been cold pressed and sintered in pure dry H. The cold rolling characteristics of the alloy were investigated under different degrees of deformation to the limit of plasticity. ELASTIC PROPERTIES OF SINTERED IRON AND STEEL PBeiss. (RWTH, Aachen, Germany) Elastic properties of porous materials were reviewed and it was noted that while the effect of porosity on some elastic constants is well documented, such as Young’s modulus, others are not, including Poisson’s ratio. A study of samples of steels with low density, to examine effects of low density by means of transverse and longitudinal ultrasonic velocities, was described. The results agreed with the trend, the literature, that reported in Poisson’s ratio declines at lower densities. It was shown that it is possible to describe the dependence on density of all the elastic constants. MICROSTRUCTURAL EFFECTS ON DYNAMIC BEIIAVIOUR OF HIGH DENSITY SINTERED STEELS O.Mars. (Hogan& AB, Hoganas, Sweden.) The dynamic properties of sintered steel were discussed with reference to the influences of structure and density. Possible conflict between structure and density for optimum properties was noted. Investigations of the effects of density, in the range 7.0 to 7.4 g.cmm3, and varying microstructures, on dynamic properties, were described. The object was to determine optimum combinations of structure and density for best dynamic properties. Pore size distribution and sintering neck sizes were considered.

EFFECT OF ADDITIONS OF CARRONYL IRON ON PROPERTIES OF A STEEL AS-SINTERED AND HEAT TREATED D.Lohe et al. (University of Karlsruhe, Germany) It was suggested that addition of fine carbonyl Fe to PM steels may improve mechanical properties, and investigations to study this were described. 5% carbonyl Fe powder was added to Fe1.5%Mo-0.5%C and properties were investigated in as-sintered and heat treated conditions. Samples with carbony1 Fe had rounder and smaller pores with larger sintering necks. In the as sintered state there was little difference between properties. After heat treatment there was a small increase in strength and a significant increase in endurance limit for the steels with carbony1 Fe. BEIIAVIOUR OF SINTERED IRON AND STEELS IN IMPACT BEND TESTS D.Lohe et al. (University of Karlsruhe, Karlsruhe, Germany.) Impact properties of a range of sintered ferrous materials, with densities in the range 6.6 to 7.4 g.cme3, were investigated using different specimen types. The impact energy-temperature curves had typical S-shapes. Impact strength was shown to be increased by more rounded pores, more homogeneous structures and elimination of microporosity by sintering above 1150°C. The factors also lowered the ductile/brittle transition temperature. Un-notched samples had higher impact energy than Charpy specimens with notch radius less than 1 mm. MECIIANICAL PROPERTIES OF BORON-MOLYBDENUM-ASTALOY STEEL ALLOYS

RELATIONSHIP BETWEEN MICROSTRUCTURE AND PROPERTIES OFSINTERIIARDENEDPMMATERIALS S.Stedman et al. (GKN Sintermetals Ltd, Lichfield, UK.) It was reported that a range of sinterhardening steels had been processed in a purpose built furnace. The structures of the steel varied from ferrite-bainite to predominantly martensite and were compared with structures of conventionally sintered alloys. Correct selection of composition and cooling rates was shown to allow direct production of parts with martensitic structures. FATIGUE PROPERTIES AND FRACTURE OF PLASMA NITRIDED SINTERED IRON AND STEEL H.de B. Costa et al. (University of St. Caterina, Florianopolis, Brazil.) Fatigue and fracture of sintered Fe and low alloy MO steel were investigated in an attempt to establish the micromechanisms leading to fracture by use of scanning electron microscopy of fracture surfaces. Some samples were plasma nitrided, others were not.

Post-sintering treatment

A.Molinari et al. (University of Trento, Trento, Italy.) The market for sintered structural materials was discussed with reference to properties and their relationship to density, production processes and costs. It was suggested that elements such as B, which stabilizes ferrite and promotes liquid phase sintering, may be a cost effective means of attaining high values of properties. An investigation of the effects of adding various amounts of B to a 1.5%Mo steel was described, the object being to increase mechanical properties. The B-MO steel had good properties for nitriding. DEFORMATION INDUCED VOLUME CHANGES IN SINTERED FERROUS MATERIALS O.Vohringer et al. (University Karlsruhe, Karlsruhe, Germany.1

Volume changes during plastic deformation of Fe, Fe-Cu, Fe-Cu-C and Fe-P alloys were investigated by measurement of axial and transverse strains. The volume changes were shown to be proportional to plastic strain and were larger in tension than in compression. This was attributed to different changes in pore volume and crack initiation. It was shown that there is a strength-differential effect, which increases with increase in porosity

COMPARISON OF HEAT TREATMENT OF PM AND WROUGHT STEELS IN AUTOMATIC EQUIPMENT A.Navazio, G.F.Bocchini. (PM Consulting, Rapallo, Italy.) Equipment for heat treatment of steel parts was described. Hardness tests were carried out on steel parts and the results were analysed statistically to determine scatter within batches and spread between batches. Scatter, in macrohardness measurements within batches, was similar for PM and for wrought steels. Microhardness showed up structural inhomogeneities. It was suggested that computer control of heat treatment processes leads to consistent results. NITRIDING AND N&TEMPERING OF PM BASE ALLOYS

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H.O.Gulsol, S.Salman. (University Marmara, Istambul, Turkey.)

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MPR January 2000 37