Steel Preforms Research Articles

Cold and hot deformation and densification studies on sintered Fe-C-Cr-Ni low alloy P/M steels

The present research work pertains to the study of the densification behaviour of sintered low alloy P/M steels with Ni and Cr during cold and hot deformation processing. Elemental powders of atomized iron, graphite, chromium and nickel were mixed in suitable proportions using a ball mill, compacted and sintered in order to yield the following alloy compositions: Fe-0.2% C, Fe-0.2% C-1% Cr, Fe-0.2% C-2% Cr and Fe-0.2% C-1% Cr-2% Ni. The compaction was performed in a 1000 kN hydraulic press using suitable cylindrical die-punch combination. Sintering of the ceramic-coated cylindrical preforms was carried out at 1000 ± 10°C in a muffle furnace for a period of 180 minutes. Cold and hot upsetting studies on the sintered preforms were undertaken in order to study the densification and plastic deformation behaviour of the low alloy P/M preforms under various applied loads. Further, microstructural analysis was done on the cold and hot worked alloy preforms in order to correlate the deformation behaviour with the metallurgical structure of the alloys. Among the various alloys under consideration, the plain carbon steel preforms exhibit better densification and deformation behaviour under hot upsetting. The addition of Ni and Cr as alloying elements to the plain carbon steel preforms promotes better densification characteristics during cold upsetting. However, the deformation of the alloy preforms with Ni and Cr is found to be sluggish compared to that of the plain carbon steel preforms. So, it is contended that the presence of carbide phase in the case of alloy steel preforms containing Ni and Cr additions strongly influences the deformation behaviour of alloy preforms.

Experimental study of the plastic deformation and densification behaviour of some sintered low alloy P/M steels

Abstract Elemental powders of atomized iron, graphite, molybdenum, copper and titanium were mixed in suitable proportions using a ball mill, then compacted and sintered in order to yield the alloy compositions such as Fe–0.5% C, Fe–0.5% C–2% Mo, Fe–0.5% C–2% Cu, Fe–0.5% C–2% Mo–2% Cu–2% Ti, Fe–0.5% C–2% Mo–2% Cu–4% Ti. The compacts were prepared in a 1000 kN hydraulic press using suitable cylindrical die-punch combination. Indigenously developed ceramic coated cylindrical preforms were sintered at 1000 ± 10 °C in a muffle furnace for a period of 120 min. In order to study the plastic deformation and densification characteristics of the low alloy powder metallurgy (P/M) preforms under various axial loads, the sintered cylindrical preforms were subjected to cold upsetting, hot upsetting and cold repressing. Further, microstructural analysis was carried out on the cold forged, hot forged and cold repressed alloy samples in order to correlate the plastic deformation and densification characteristics with the metallurgical structure of the sintered and forged alloys. Plain carbon steel preforms were observed to attain the highest levels of densification and axial deformation. Addition of Ti and Mo resulted in reduced levels of deformation as well as densification, irrespective of the mode of forming. The behaviour of the preforms containing Cu and Mo was intermediate between the plain carbon steel and the Ti-based steel. Microstructures of the Mo-containing alloy reveal the presence of fine particulates of Mo, TiC and pearlites, which account for the reduction in densification and deformation levels.

Sintered Fe-0.8%C-1. 0%Si-0.4%Cu P/M Steel Preform Behaviour During Cold Upsetting

Cold upsetting experiments were carried out on sintered Fe-0.8%C-1.0%Si-0. 4%Cu steel preforms in order to evaluate their deformation characteristics. Powder preforms of 86% of theoretical density, with two different ratios of height to diameter, were prepared using a suitable die set assembly on a 1.0 MN capacity hydraulic testing machine. Sintering was carried out in an electric muffle furnace for 1.5 h at 1 150 °C. Each sintered compact was subjected to incremental loading of 0.04 MN under dry friction condition till a crack appeared at the free surfaces. The experimental results were critically analysed, the stress as a function of strain and densification was obtained, then the work hardening behaviour was analyzed. It has been found that in the process of enhancing densification, strength and strain hardening is also induced during upsetting, but the work hardening behaviour is not homogenous-ly enhanced against strain and densification.

Sintered eutectoid P/M steel behaviour during cold upsetting

Cold upsetting experiments were carried out on sintered Fe-0.8%C steel preforms in order to evaluate the technical relationship that exist between the applied stresses against continuous deformation and densification. Powder preforms of 86% theoretical density and 0.40 of initial aspect ratio were subjected to incremental compressive loading of 0.04 MN under three different friction conditions such as dry, graphite and zinc stearate employed during deformation until fracture appears at free surfaces. Experimental results revealed that the response of applied stresses with induced strain and attained densification exhibits a continuous enhancement but with three different stages. Irrespective of friction conditions the first and third stage shows steep rise, which offers high resistance to deformation, whereas the second stage shows virtually steady state; deformation needed gradual increase in applied stresses but with high rate of densification. Further, preform deformed under without lubricant exhibited maximum strain hardening as well as an enhanced rate of strain hardening through out the deformation in comparison with lubricants employed conditions.

Some investigation on the cold deformation behaviour of sintered iron–0.8% carbon alloy powder preforms

Powder metallurgy (P/M) manufacturing route has wide industrial applications due to a host of techno-economic advantages. However, the production of highly dense product for structural application with pore free at open surface is a challenging endeavour for the investigators. Thus, present investigation pertains to describe cold deformation behaviour and to develop forming limits for iron–0.8% carbon sintered P/M steel preforms. Experiments were conducted on 0.40 and 0.75 initial aspect ratio of 86 ± 1% initial fractional theoretical densities under two different lubricant constraints namely, nil/no lubricant and graphite lubricant. The deformations were confined till the appearance of visible crack on the free surface of the deforming compacts. This aspect was quantized to evaluate the densification behaviour against compressive strain and to provide guidelines for introducing external constraints so as to produce components free from open surface pores.

Some aspects of workability studies on sintered high strength P/M steel composite preforms of varying TiC contents during hot forging

Workability is a measure of the extent of deformation that powder metallurgy materials can withstand prior to fracture occurred in the forming or upsetting processes. Workability of a material is obtained from several parameters namely strain, strain rate and temperature. Hot upsetting of the composite steel preforms with varying TiC contents, namely, 3% and 4%, and aspect ratios, namely, 0.45, 0.71 and 1.25, was carried out at a temperature of 1120 °C and the formability behaviour of the same under triaxial stress state condition was determined. The curves plotted for different preforms were analysed and a relationship was established between the axial strain and the formability stress index (β). The influence of TiC addition, in the steel composite, on the formability stress index, the relative density (R) and various stress ratio parameters, namely, (σθ/σeff), (σm/σeff) and (σz/σeff) were studied. An attempt is also made to relate the fracture strain of the preforms with the formability stress index (β) under triaxial stress state condition.

Some features on hot forging of powder metallurgy sintered high strength 4%titanium carbide composite steel preforms under different stress state conditions

In this paper, the authors propose mathematical expressions for the determination of different stress ratio parameters under plane and triaxial stress state conditions. Experiments were carried out to evaluate the hot forging features in the high strength sintered powder metallurgy 4%titanium carbide composite steel performs under different stress states, namely, plane stress and triaxial stress states. Cylindrical compacts with aspect ratios 0.45, 0.75 and 1.25 were prepared, sintered and forged at the temperatures of 1120 ± 10 °C. The investigation suggests that the experimentally determined relative density has a straight-line relationship with the new geometrical shape factor. The measured barrel radius of curvature is found to have a circular arc. Relationship is established between the measured barrel radius and the stress ratio parameters under plane and triaxial stress state conditions. An attempt is also made to establish a relationship between the various stress ratio parameters under plane and triaxial stress state conditions and the relative density.

Some aspects of workability studies on P/M sintered high strength 4% Titanium carbide composite steel preforms during cold upsetting

Workability is concerned with the extent to which a material can be deformed in a specific metal working process without the initiation of cracks. Ductile fracture is the most common failure in bulk forming process. The formability is a complicated phenomenon which depends on the friction between the preform and the die surface in cold upsetting. A complete experimental investigation on the workability behavior of the steel composite of 4%TiC was performed under different stress states, namely, plane and triaxial stress state conditions. Cold upsetting of the Fe–1.0%C–4%Ti steel composite preforms was carried out applying different lubricants, namely, graphite, zinc stearate and molybdenum disulphide, and without lubricant, and the formability behaviour of the same under plane and triaxial stress state conditions was determined. The curves plotted for different preforms were analysed and relationship was established between the axial strain and the formability stress index under plane and triaxial state conditions. A relationship between the relative density and the axial strain was also established. Various stress ratio parameters, namely, (σθ/σeff), (σm/σeff) and (σz/σeff), under plane and triaxial stress state conditions were determined empirically as a function of the relative density. An attempt is also made to study the variation of slope of the relative density versus stress ratio parameters under plane and triaxial stress conditions with respect to the relative density to identify the pore closure mechanism.

Effect of titanium carbide particle addition on the densification behavior of sintered P/M high strength steel preforms during cold upset forming

Experimental investigation has been carried out to evaluate the effect of titanium carbide addition on the composite steel preforms. The cold upsetting of the composite steel preforms with varying TiC contents, namely, 3% and 4%, and different aspect ratios, namely, 0.42, 0.67 and 1.0, and lubricating conditions namely, nil lubricant, graphite and zinc stearate lubricants, was carried out using 100 tonnes capacity Universal Testing Machine (UTM) and the deformation behavior of the same was determined. The influence of TiC addition, in the steel composite, on the percent theoretical density attained, axial stress and Poisson's ratio were studied. The effect of initial preform geometry and lubricating conditions on the densification and deformation behavior have been studied.

Investigations on the continuous drive friction welding of sintered powder metallurgical (P/M) steel and wrought copper parts

The present investigation attempts to understand the friction welding characteristics of sintered P/M steel preforms–wrought copper dissimilar parts. In order to achieve sound weld between these two materials the process parameters were optimized and inferred that the preforms of lower densities with lower process parameters yields quality weldments, established through post-weld tests. This study also envisages the influence of process parameters which include resident preform densities, friction pressure, upset pressure, and burn-off length on microstructure and mechanical properties of the welds. This work consolidates information on the aspects of joining P/M component with wrought materials for practical execution.

Deformation, densification, and corrosion studies of sintered powder metallurgy plain carbon steel preforms

Sintered plain carbon steels containing carbon up to 1% with density near theoretical have potential applications requiring high strength, high hardness, and wear resistance. In the forged conditions such steels are suitable materials for tools, cutters, bearing rollers, fasteners, and cams. In the present study, experimental investigations were under taken in order to understand the mechanism of densification and deformation during cold and hot upset forming operations on sintered cylindrical performs of Fe and Fe–1%C. Effect of addition of 1%C to Fe on the corrosion behavior of the steel has also been considered. Cylindrical preforms of aspect ratio of 0.5 were prepared out of mixed elemental powders of Fe and C, sintered at 1100 °C for 120 min and subsequently hot/cold forged in flat dies. Density as well as dimension measurements were carried out on the forged billets after each step of deformation during the forging operations. Further, aqueous corrosion tests were conducted on the forged alloys by immersing them in 1% HNO 3 solution for 25 h. Weight loss measurements were made on the corroded samples. The densification rate is found to depend on the flow stress as well as the deformation rate of the preforms. Further, the densification rate increases monotonically up to an axial deformation level of about 0.5 (true strain) and thereafter slightly reduced in both Fe and Fe–1%C alloy. The applied stress during cold upsetting increases with densification. But the rate of increase is not uniform. The rate of densification is also observed to be on the higher side with the addition of 1%C with Fe during both cold and hot forging. The corrosion rate of pure iron samples has been observed to be invariably higher compared to that of Fe–1%C steels irrespective of the method of deformation. Corrosion rate is found to decrease drastically with increase in the percentage theoretical density in both materials. The highest density obtained in both alloys is seldom exceeding 98% of theoretical density irrespective of the mode of deformation. Presence of porosity leads to enhanced rate of uniform corrosion in both Fe and Fe–1%C carbon steels. Microstructure of the forged alloys revealed the presence of numerous fine rounded pores both within grains and along grain boundaries.

Some Aspects on Hot Forging Features of P/M Sintered High-Strength Titanium Carbide Composite Steel Preforms Under Different Stress State Conditions

Experiments were carried out to evaluate the hot forging features in the high-strength sintered Powder Metallurgy TiC composite steel performs under different stress states, namely, plane and triaxial stress. Cylindrical compacts with aspect ratios 0.45, 0.75, and 1.25 were prepared, sintered and forged at the temperatures of 1120°C+10°C. The investigation suggests that the experimentally determined relative density has a straight line relationship with the new geometrical shape factor (ρ0∕ρth)(h0∕hf)(3D02∕(2Db2+Dc2)). The measured barrel radius of curvature is found to have a circular arc because the above relation is a straight line one. Relationship is established between the measured barrel radius and the stress ratio parameters namely (σθ∕σz), (σz∕σm) and (σeff∕σz) under plane stress and triaxial stress state conditions. An attempt is also made to establish a relationship between the various stress ratio parameters namely (σθ∕σz), (σz∕σm), and (σeff∕σz) under plane stress and triaxial stress state conditions and the relative density.

Some aspects of workability studies on hot forging of sintered high strength 4% titanium carbide composite steel preforms

The aim of the paper is the study of workability of Fe–1.0% C–4% TiC steel composite during hot upsetting. Ductile fracture is the most common failure acting in bulk forming process. The formability during hot upsetting depends on the temperature, strain and strain rate. A complete experimental investigation of the workability behaviour of Fe–1.0% C–4% TiC steel composite was performed under the triaxial stress state condition. Hot upsetting of Fe–1.0% C–4% TiC steel composite preforms was carried out at a temperature of 1120 °C and the formability behaviour of the same at triaxial stress state condition was determined. The curves plotted for different preforms were analysed and the relationship between the axial strain and the formability stress index were obtained. A relationship between the relative density and the axial strain was also established. A particular attempt was made to relate the various stress ratio parameters, namely, ( σ θ / σ eff), ( σ m/ σ eff) and ( σ z / σ eff) with the relative density.

Preliminary studies on friction welding of sintered P/M steel preforms to wrought mild steel

Continuous drive friction welding studies on sintered powder metallurgical (P/M) steel preforms–wrought mild steel combination are reported in the present study. The work is a preliminary study to optimise the friction welding parameters and data generated by the present work is expected to contribute to friction welding of dissimilar and similar sintered P/M preforms to wrought metals or sintered P/M preforms – a planned future research work. Sound welds were obtained with all welding parameter combinations studied. The mechanical properties of welds were comparable to those of sintered P/M steel. Sintered P/M preforms deformed to a greater extent than wrought mild steel due to their low flow stress and thermal conductivity. The sintered density and other properties of the P/M preforms were found to dictate the deformation at the interface and consequently the weld strength. The results indicate that the current approach can be extended to other combinations of sintered P/M preforms.

Solid state infiltration of porous steel with aluminium by the forcefill process

We report first results on producing a metal - metal composite by forcing solid aluminium to fill a porous steel preform. This process is akin to forcefill used for filling of vias when producing metallic interconnects inmicroelectronics. Using scanning electron microscopy with energy-dispersive X-ray spectroscopy, it was shown that for nominal pore size as small as 100 um, the pores could be filled with aluminium throughout the entire preform used, thus demonstrating the viability of the process. An interesting aspect of this solid state 'infiltration' is that the tortuous random paths taken by the plastically flowing Al involve numerous kinks. Some of them may induce large localised shear deformation similar to that produced by equal channel angular pressing, which is used to fabricate bulk ultra-fine-grained materials. It is, therefore, conjectured that towards the exit end of the channels the infiltrating material may develop an ultra-fine grain structure and exhibit enhanced strength. It is suggested that the process described can be used to produce metal-metal (or ceramic-metal) composites with unusual mechanical properties. Thin fibres of the material that has percolated through the porous preform can be expected to have a sub-micron grain structure and to possess improved mechanical properties.

Selected Problems of Die‐Forging of PM Steel Products

The paper discusses the selected technological and material problems of closed‐die forging of PM steel preforms. The first part presents technological variants of hot forging routs of PM materials. In the second part the influence of hot forging parameters on the density, mechanical properties and structure are discussed. The influence of the size of powder particles, powder manufacturing method, chemical composition and heat treatment conditions on mechanical properties after forging is shown. The research on thermomechanical forging of PM preforms has resulted in potential possibilities of shortening of the manufacturing route to obtain products with high density and good mechanical properties from one heating before forming.

Inferences on plastic properties and coefficient of friction during simultaneous compression deformation of dissimilar sintered powder metallurgical preforms

Plastic working of powder metallurgical (PM) material necessitates the development of fundamental data such as flow stress, densification behaviour, coefficient of friction, apparent strength coefficient, apparent strain hardening exponent, plastic Poisson's ratio, etc. In the present work compression and standard ring compression tests have been carried out to generate the fundamental data for simultaneous deformation of sintered steel and copper powder metallurgical preforms. The results reveal that the behaviour of individual materials during simultaneous deformation is strongly influenced by local micromechanical interactions at the metal - metal interface. In addition to this, the test conditions (iso-stress and iso-strain) strongly influence the severity of interaction. The interfacial friction coefficients are less than that of the same material when tested between hard tools. The optimal process parameters with higher interfacial friction, which can enhance the solid state joining of dissimilar materials, have been identified. The flow stress of the composite (steel - copper combination) during simultaneous deformation can be estimated if the flow stress of the individual materials comprising the combination/composite are known. With these studies, it should be possible to extend the inferences to the major deformation processes.

Impact forging of sintered steel preforms

The treatment of heavy metal–cyanide complex in industrial wastewater generally involves various processing units, such as chemical oxidation, hydrolysis precipitation and coagulation. A novel dual function reagent (PACC), which contains high content of active chlorine and Al13 polymer, shows a promising potential to shorten the process and heighten the treatment efficiency for cadmium–cyanide complex ([Cd(CN)4]2−). The results indicated that PACC is able to simultaneously achieve the complete oxidation of cyanide (CN−) by active chlorine and the subsequent coagulation of cadmium ion (Cd2+) by Al13 polymer. Two stages were carried out for complete CN− oxidation and effective Cd2+ coagulation. The first stage involves the conversion of CN− to cyanate (CNO−), and the second stage involves the conversion of CNO− to nitrogen and the coagulation of the liberated Cd2+. The optimum pH values for the first stage and the second stage are pH 11 and pH 8.5, respectively. The two stages for effective treatment of [Cd(CN)4]2− at the optimal pH condition totally need about 43 min at active chlorine dosage 130% of the theoretical requirement for CN− decomposition. Under the optimal conditions for [Cd(CN)4]2− treatment, the stoichiometric weight ratio of Cl2/Al in PACC is 2. This study presents a novel reagent and method to remove heavy metal–cyanide complexes from wastewater.

Impact forging of sintered steel preforms

The results of a fifteen year research and development programme on the application of forge hammers to the impact powder forging of 46xx steel preforms are reviewed and assessed. The main topics are suitability of forge hammers to powder forging; effects of forging strain and forging pressure on core residual porosity; importance of pressure dwell or contact time in determining residual porosity near the surfaces and corners of powder forgings; dependence of tensile ductility, toughness, and fatigue strength on high strength, impact powder forged 46xx steel on lateral strain, residual porosity, oxygen, and sulphur contents; and inclusion volume fraction and spacing. It is shown that impact forged steels can achieve mechanical property parity at very high strength levels with high quality wrought steels. State of the art forge hammers have significant technical and economic advantages over presses in powder forging applications and are best suited to powder forging processes for which the forging strains and energy requirements are small.

Impact forging of sintered steel preforms: D.W.Smith et al. (Michigan Technological University, USA.)

Impact forging of sintered steel preforms: D.W.Smith et al. (Michigan Technological University, USA.)