- Email: [email protected]
Porosity and properties of warm compacted high strength sintered steels
SIZE O F W P O W D E R SYNTHESIZED BY SELF PROPAGATING HIGH TEMPERATURE SYNTHESIS
C.W.Won et al. (Chungnam National University, Taejon, Korea.) Production of W powder by reaction between W oxide and Mg was investigated to determine W powder size distribution and morphology. MgO was leached out with HCI. The W powder was 99.98% pure, impurities being volatilized during the exothermic reaction. 33% excess Mg above stoichiometry was required.
higher densities attainable and the requirement for tight control over powder and lubricant characteristics. The paper considered powder mixture property requirements and how part density is influenced by compaction parameters. Compaction conditions to optimize density, surface finish and part-to-part consistency were discussed. STRENGTH AND MICROSTRUCTURE D U R I N G WARM C O M P A C T I O N O F IRON POWDERS
CREEP RESISTANCE OF HIGH SPEED S T E E L S C O M P A R E D WITH CAST A N D FORGED MATERIALS
H.F.Hinz, H.Berns. (Ruhr University, Bochum, Germany.) Creep of PM, as-cast and forged grades of high speed steels were investigated and compared in cutting tool uses. Coolant/lubricant was used to keep temperatures below 650°C. The steels are subject to thermal cycling. Short time creep tests, up to 500 hours, showed that the as-cast materials had the lowest secondary creep rate and that the PM material had the highest elongation to fracture. The forged alloy was in between. The differences were attributed to variations in size and distribution of eutectic carbides. Failure was due to decohesion of carbide in the PM steel and carbide fracture in others. It was suggested that the higher ductility of the PM steel is beneficial under thermal cycling.
Warm compaction
K.Pischang et al. (Dresden University of Technology, Dresden, Germany.) Density of materials processed by warm compaction was discussed. In particular it was noted that green strength can be increased by up to 100% and that increased mechanical properties cannot be explained solely by reference to increased density. Investigations of correlations between t e m p e r a t u r e , yield strength and influence on plastic deformation of powder particles were described.
A CRITICAL E V A L U A T I O N O F H I G H DENSITY PROCESSES FOR PM PARTS
Tool steels
COMPACT SWELLING DURING LIQUID PHASE SINTERING
J.Wahnschaffe et al. (GKN Sinter Metals Radewormwald, Germany.) The demand for higher strength PM steels permitting smaller sized parts was noted. To satisfy this, higher density and/or greater use of alloy elements are required. Die wall lubrication and warm compaction are two of the strategies that can be used. Warm compaction was reviewed with respect to lubricants, conventional or isostatic pressing, and component design.
SINTERING AND MICROSTRUCTURE OF HIGH VANADIUM HIGH SPEED STEELS
A.Savitskii et al. (Inst. of Strength Physics and Materials Science, Tomsk, Russia.) Dimensional changes, in liquid phase sintering, were discussed in terms of diffusion-based mechanisms, interchange of atoms between solid and liquid. Dilatometry and interrupted quenching were used to determine dimensional changes. X-ray diffraction was used to measure changes in lattice parameters. A1-Cu and A1-Mg were used in experiments.
EVOLUTION OF DEFECT STRUCTURE OF NON-EQUILIBRIUM POWDERS
A.A.Smetkin. (RETCPM, Perm, Russia.) The defect structure of Ti powder, produced by attrition of Ti sponge, was investigated. Two types of defect were found in the powder and the evolution of these was demonstrated.
POROSITY AND PROPERTIES OF WARM C O M P A C T E D H I G H S T R E N G T H SINTERED STEELS
U.Engstr~im et al. (HSgan~s AB, H6gan~is, Sweden.) Use of warm compaction to produce parts with densities of 7.1 to 7.4 g.cm 3 was discussed with regard to part precision, cost, porosity and pore size distribution. It was shown t h a t w a r m compaction reduces pore size by a factor of up to 2 and t h a t pore distribution is more uniform than in conventional processing. Characteristics of parts made by warm compaction, single-press-andsinter and double-press-double-sinter routes were compared. BEHAVIOUR OF STEEL POWDER M I X T U R E S P R O C E S S E D BY WARM COMPACTION
S.St.Laurent, F.Chagnon. (Quebec Metal Powders Ltd, Quebec, Canada.) Warm compaction of metal powders was discussed with reference to the
42 MPR March 1999
C.S.Wright et al. (University of Bradford, Bradford, Yorkshire, UK.) Reasons why sintering in N reduces the sintering t e m p e r a t u r e for high speed steels containing V were investigated for a steel containing 9%W-9%Co3%Mo4%-Cr-(6 to 12)%V-(1.6 to 4)%C. Powders were pressed at 770 MPa and sintered in N-7vol%H at a dew point less than -67°C. Above 600°C N reacted with V rich MC carbides to form carbonitrides. The C released formed various additional carbides. Densification was by supersolidus liquid phase sintering. Alloys with high %C were unsinterable due to excessive amounts of liquid phase and resulting distortion. The results were discussed in t e r m s of phase diagrams. A model was presented. Implications of the lower sintering temperature were discussed. P M T O O L S T E E L S F O R COLD W O R K APPLICATIONS
O.Sandberg, L.J6nson. (Uddeholm Tooling AB, Hagfors, Sweden.) PM tool steels, produced using rapid solidification technology, were discussed with respect to applications for cold working of metals. PM tool steels were shown to have properties capable of withstanding these applications, that is, a good combination of toughness and wear resistance. Comparison was made between PM steels and steels made in other ways.
Sintering
DEPENDENCE OF GRAIN GROWTH O N S O L I D : L I Q U I D RATIO IN L I Q U I D PHASE SINTERING
E.Olevski, R.M.German. (Pennsylvania State University, Pennsylvania, USA.) A model for diffusion-controlled grain growth during liquid phase sintering, based on a Rayleigh grain size distribution and theoretical and experimental studies, was presented. Asymmetric distribution provides the driving force for grain growth. The model used solid grain contiguity to determine the contributions of solid and liquid states to grain coarsening. Grain agglomeration influences diffusion distances and surface areas. Cumulative grain growth rate was calculated. Only solid volume fraction and solid-liquid dihedral angle are need to predict grain coarsening rate. The model was shown to allow prediction in multi-phase materials, notably where vapour phase transport may be involved.
C.W.Won et al. (Chungnam National University, Taejon, Korea.) Production of W powder by reaction between W oxide and Mg was investigated to determine W powder size distribution and morphology. MgO was leached out with HCI. The W powder was 99.98% pure, impurities being volatilized during the exothermic reaction. 33% excess Mg above stoichiometry was required.
higher densities attainable and the requirement for tight control over powder and lubricant characteristics. The paper considered powder mixture property requirements and how part density is influenced by compaction parameters. Compaction conditions to optimize density, surface finish and part-to-part consistency were discussed. STRENGTH AND MICROSTRUCTURE D U R I N G WARM C O M P A C T I O N O F IRON POWDERS
CREEP RESISTANCE OF HIGH SPEED S T E E L S C O M P A R E D WITH CAST A N D FORGED MATERIALS
H.F.Hinz, H.Berns. (Ruhr University, Bochum, Germany.) Creep of PM, as-cast and forged grades of high speed steels were investigated and compared in cutting tool uses. Coolant/lubricant was used to keep temperatures below 650°C. The steels are subject to thermal cycling. Short time creep tests, up to 500 hours, showed that the as-cast materials had the lowest secondary creep rate and that the PM material had the highest elongation to fracture. The forged alloy was in between. The differences were attributed to variations in size and distribution of eutectic carbides. Failure was due to decohesion of carbide in the PM steel and carbide fracture in others. It was suggested that the higher ductility of the PM steel is beneficial under thermal cycling.
Warm compaction
K.Pischang et al. (Dresden University of Technology, Dresden, Germany.) Density of materials processed by warm compaction was discussed. In particular it was noted that green strength can be increased by up to 100% and that increased mechanical properties cannot be explained solely by reference to increased density. Investigations of correlations between t e m p e r a t u r e , yield strength and influence on plastic deformation of powder particles were described.
A CRITICAL E V A L U A T I O N O F H I G H DENSITY PROCESSES FOR PM PARTS
Tool steels
COMPACT SWELLING DURING LIQUID PHASE SINTERING
J.Wahnschaffe et al. (GKN Sinter Metals Radewormwald, Germany.) The demand for higher strength PM steels permitting smaller sized parts was noted. To satisfy this, higher density and/or greater use of alloy elements are required. Die wall lubrication and warm compaction are two of the strategies that can be used. Warm compaction was reviewed with respect to lubricants, conventional or isostatic pressing, and component design.
SINTERING AND MICROSTRUCTURE OF HIGH VANADIUM HIGH SPEED STEELS
A.Savitskii et al. (Inst. of Strength Physics and Materials Science, Tomsk, Russia.) Dimensional changes, in liquid phase sintering, were discussed in terms of diffusion-based mechanisms, interchange of atoms between solid and liquid. Dilatometry and interrupted quenching were used to determine dimensional changes. X-ray diffraction was used to measure changes in lattice parameters. A1-Cu and A1-Mg were used in experiments.
EVOLUTION OF DEFECT STRUCTURE OF NON-EQUILIBRIUM POWDERS
A.A.Smetkin. (RETCPM, Perm, Russia.) The defect structure of Ti powder, produced by attrition of Ti sponge, was investigated. Two types of defect were found in the powder and the evolution of these was demonstrated.
POROSITY AND PROPERTIES OF WARM C O M P A C T E D H I G H S T R E N G T H SINTERED STEELS
U.Engstr~im et al. (HSgan~s AB, H6gan~is, Sweden.) Use of warm compaction to produce parts with densities of 7.1 to 7.4 g.cm 3 was discussed with regard to part precision, cost, porosity and pore size distribution. It was shown t h a t w a r m compaction reduces pore size by a factor of up to 2 and t h a t pore distribution is more uniform than in conventional processing. Characteristics of parts made by warm compaction, single-press-andsinter and double-press-double-sinter routes were compared. BEHAVIOUR OF STEEL POWDER M I X T U R E S P R O C E S S E D BY WARM COMPACTION
S.St.Laurent, F.Chagnon. (Quebec Metal Powders Ltd, Quebec, Canada.) Warm compaction of metal powders was discussed with reference to the
42 MPR March 1999
C.S.Wright et al. (University of Bradford, Bradford, Yorkshire, UK.) Reasons why sintering in N reduces the sintering t e m p e r a t u r e for high speed steels containing V were investigated for a steel containing 9%W-9%Co3%Mo4%-Cr-(6 to 12)%V-(1.6 to 4)%C. Powders were pressed at 770 MPa and sintered in N-7vol%H at a dew point less than -67°C. Above 600°C N reacted with V rich MC carbides to form carbonitrides. The C released formed various additional carbides. Densification was by supersolidus liquid phase sintering. Alloys with high %C were unsinterable due to excessive amounts of liquid phase and resulting distortion. The results were discussed in t e r m s of phase diagrams. A model was presented. Implications of the lower sintering temperature were discussed. P M T O O L S T E E L S F O R COLD W O R K APPLICATIONS
O.Sandberg, L.J6nson. (Uddeholm Tooling AB, Hagfors, Sweden.) PM tool steels, produced using rapid solidification technology, were discussed with respect to applications for cold working of metals. PM tool steels were shown to have properties capable of withstanding these applications, that is, a good combination of toughness and wear resistance. Comparison was made between PM steels and steels made in other ways.
Sintering
DEPENDENCE OF GRAIN GROWTH O N S O L I D : L I Q U I D RATIO IN L I Q U I D PHASE SINTERING
E.Olevski, R.M.German. (Pennsylvania State University, Pennsylvania, USA.) A model for diffusion-controlled grain growth during liquid phase sintering, based on a Rayleigh grain size distribution and theoretical and experimental studies, was presented. Asymmetric distribution provides the driving force for grain growth. The model used solid grain contiguity to determine the contributions of solid and liquid states to grain coarsening. Grain agglomeration influences diffusion distances and surface areas. Cumulative grain growth rate was calculated. Only solid volume fraction and solid-liquid dihedral angle are need to predict grain coarsening rate. The model was shown to allow prediction in multi-phase materials, notably where vapour phase transport may be involved.