Ananthanarayanan Rajeshkannan

Strain hardening behaviour in sintered Fe—0.8%C—1.0%Si—0.8%Cu powder metallurgy preform during cold upsetting

Abstract Cold upsetting experiments were performed on sintered Fe—0.8%C—1.0%Si—0.8%Cu steel preforms in order to evaluate the strain hardening characteristics. Powder preforms of 86 per cent theoretical density and an initial aspect ratio of 0.4 were prepared using a suitable die and a 1 MN capacity hydraulic press. Sintering was carried out in an electric muffle furnace for a period of 90 min at 1150 °C. Each sintered compact was subjected to an incremental compressive loading of 0.04 MN until fractures appeared on the free surface. Experiments were performed with no lubricant and using graphite as a lubricant. The behaviour of the applied stress as a function of both strain and densification level exhibits a continuous enhancement over three different response modes. The first and third stage responses offer a high resistance to deformation, whereas the second stage shows virtually steady-state behaviour. The instantaneous strain hardening exponent ni and strength coefficient Ki of the steel preforms were calculated and found to continuously increase with an increase in the deformation and densification levels.

Workability Studies on Cold Upsetting of Sintered Copper Alloy Preforms

The major concern of the design for manufacturability is to accomplish the require deformation without failure of work material. The degree of deformation that can be achieved in a particular metal forming process without creating condition is termed as workability. The present investigation pertains to study the cold workability behaviour of Cu-7%Al-1.8%Si sintered preforms. Cold upsetting of these preforms with various aspect ratios were carried out and the working behaviour of the preforms at various stress state conditions was computed. The analysis measured for different components such as stress formability index and obtained density during secondary deformation as a function of induced strain. Similarly various computed stress ratio parameters with induced strain.

Workability Studies in Forming of Sintered Fe-0. 35C Powder Metallurgy Preform During Cold Upsetting

An experimental investigation on the workability behaviour of sintered Fe-0. 35C steel preforms under cold upsetting, have been studied in order to understand the influence of aspect ratio and lubrication condition on the workability process. The above mentioned powder metallurgy sintered preform with constant initial theoretical density of 84% of different aspect ratios, namely, 0. 4 and 0. 6 respectively were prepared using a suitable die-set assembly on a 1 MN capacity hydraulic press and sintered for 90 min at 1 200°C. Each sintered preform was cold upset under nil/no and graphite frictional constraint, respectively. Under the condition of triaxial stress densification state, axial stress, hoop stress, hydrostatic stress, effective stress and formability stress index against axial strain relationship was established and presented in this work. Further more, attained density was considered to establish formability stress index and various stress ratio parameters behaviour.

Influence of Carbon Content on Strain Hardening Behaviour of Sintered Plain Carbon Steel Preforms

Complete experimental investigation on the instantaneous strain hardening behaviour of powder metallurgy (P/M) preforms of pure iron, Fe-0. 35%C, Fe-0. 75%C and Fe-1. 1%C was carried out. The strain hardening behaviour of the above-mentioned P/M sintered steel preforms with aspect ratio of 0. 4 under triaxial stress state condition was determined by cold upsetting under nil/no and graphite lubricant conditions. The instantaneous strain hardening value (ni), strength coefficient (Ki), and the stress as a function of strain and densification were obtained and analyzed. Furthermore, a relation was obtained from a semi-log plot of stress against relative density and analyzed to study the hardening behaviour owing to densification as stress was a function of induced strain as well as densification in the P/M materials.

Deformation Study of Sintered Iron–Carbon–Silicon–Copper Steel Compacts during Cold Forging

Cylindrical preforms of 0.4 initial aspect ratio with 86 ± 1% initial theoretical density has been prepared for iron–0.8%carbon–1%silicon with 0.4% and 1.2% copper added steel preforms through classical powder metallurgy route. These preforms are then subjected to secondary deformation such as cold upsetting to evaluate the deformation characteristics. The cold upsetting is carried out in an incremental step of 0.04 MN under two different frictional media using 100 tons capacity hydraulic press. Plasticity theories have been portrayed for various stresses, strains and Poissons ratio under triaxial condition. The results revealed that the compositional effect on deformation is quite evident under dry friction condition than at graphite employed lubricant condition; on the other hand, both the friction condition shows a phenomenal effect on densification characteristics. Further, it is found that increase of copper content and frictional condition proportionally increases axial and hoop stress but there is a nil effect on mean stress.

Phenomenon of Instantaneous Work Hardening Characteristics of Sintered Cold Deformed Cu Alloy Preforms

Work hardening behavior is an important phenomenon especially when a material is subjected to cold work. The two important parameters that expose this study are strain hardening exponent, n, and strength coefficient, K, according to ludwik equation, σ=Kε^n. In addition to strain as influencing factor for work hardening behavior, the attained density during deformation is also considered in the present investigation; a rational approach and its characteristic evaluation has been proposed. Thus a copper alloy preforms of three different aspect ratios prepared using conventional powder metallurgy method and a secondary deformation such as cold deformation were carried out till maximum density or fracture appears at the outer surface of deforming preforms. The dimensional and density measurements were carried out carefully and the same is utilized to explain the instantaneous work hardening behavior with respect to induced strain and attained density.

Strain hardening behaviour in forming of sintered iron-0.35% carbon powder metallurgy preform during cold upsetting

A complete experimental investigation on the instantaneous strain-hardening behaviour of powder metallurgy preforms of Fe-0.35%C was carried out. The strain hardening behaviour of the above-mentioned P/M sintered steel preforms with aspect ratio of 0.4 and 0.6, respectively, under triaxial stress state condition was determined by cold upsetting under nil/no and graphite lubricant conditions. The instantaneous strain hardening value (ni), strength coefficient (Ki), and the stress as a function of strain and densification were obtained and analyzed. Further, a relation is obtained from a semi-log plot of stress against relative density. This was analyzed to study the hardening behaviour due to the densification as applied stress is a function of induced strain as well as of densification in the powder metallurgy materials.

Forming Limit Analysis of Molybdenum Reinforced Carbon Steels

The occurrence of ductile fracture during the plastic deformation of powder metallurgy materials is adverse and damaging and the prediction of fracture is very important in the early stages as early modifications will prevent failure. This will tend to save a lot of money and forming limit studies in many metal forming processes is up most important. Forming limit analysis on the cold forged molybdenum reinforced carbon steels were carried out in this work. In this study two key strain hardening parameters are used to study the formability characteristics. This analysis is effectively used for design of powder metallurgy parts and most importantly the die design as repressing needs to be employed before pores appear as cracks on the free surface. The cold forging was carried out on Fe-0.8%C, Fe-0.8%C-1%Mo, Fe-0.8%C-1.5%Mo and Fe-0.8%C-2.0%Mo and the formability behavior of the same is presented.

Study on Densification Behaviour under Cold Forging of Sintered High Carbon Alloy Steels

Densification behaviour of sintered Fe-0.8%C-1%Si-0.8%Cu powder metallurgy steel under the influence of two different aspect ratios subject to cold forging is studied in the present investigation. The critical evaluation of cold deformation exercise revealed that induced strains are linearly contributing to enhance densification till the specimen fracture; however overall resistance to deformation of material is exhibiting in three different responses with respect to improvement in densification. That is at initially, high resistance to deformation followed by high kinetics of deformation and finally exhibiting little resistance against overall deformation. Although, the aforementioned criteria is common for both the aspect ratios, the applied deformation is little homogeneous when aspect ratio is less that directly contributes to enhance the rate of attainment of densification as little faster in the later stage of densification on the other hand the higher aspect ratio preform is bit non-linear in nature and retards stress in the later stage.

Some Studies on the Bulging Characteristics of Cold-Upset Steel Preforms

Present investigation pertains to establish the bulging characteristics of sintered steel preforms under cold upsetting. Cylindrical preforms of Fe-0.8%C and with 1%Mo and 2%Mo of 86% initial theoretical density and 0.4 initial aspect ratio have been produced through conventional powder metallurgy techniques. These preforms were further subjected to secondary deformation, that is, cold upsetting under nil and zinc stearate lubricant conditions. The results obtained from this experiment were used to study the bulging characteristics with densification and hoop stress. An empirical equation is determined between these parameters and is found to follow a power law relationship.