Barrelling Aspects and Microstructure Examination of Sintered AISI 8620 P/M Steel during Hot Upset Powder Preform Forging (original) (raw)
Related papers
International Journal of Engineering Research and Technology (IJERT), 2014
https://www.ijert.org/barrelling-aspects-and-microstructure-examination-of-sintered-aisi-8620-pm-steel-during-hot-upset-powder-preform-forging https://www.ijert.org/research/barrelling-aspects-and-microstructure-examination-of-sintered-aisi-8620-pm-steel-during-hot-upset-powder-preform-forging-IJERTV3IS080664.pdf Present investigation is to generate experimental data on AISI 8620 steel through hot axial upset forging in order to reveal the densification mechanisms under bulging and further to examine the microstructural development at different height strains.. Compacts of initial aspect ratios of 0.60, 0.90 and 1.20 were prepared from homogeneously blended powders corresponding to AISI 8620 steel in the pressure range of 480±10M Pa maintaining the density in the range of 85±1% of theoretical. Sintering operation was carried out at 1150 ± 10°C for a period of 90 minutes in an electric muffle furnace under the protection of ceramic coating. Sintered compacts were hot upset forged to various height strains except one sample from each aspect ratio kept as in sintered condition for comparison purposes. Analysis of experimental data, calculated parameters with series of plots and microstructural details have resulted in several empirical relationships relating densification, Poisson's ratio, and new Poisson's ratios while considering typical bulging such as circular and parabolic arcs for the mechanism/s of densification studies.
Experimental work has been carried out to reveal quantitative data on some aspects of deformation and barrelling characteristics on hot deformation of sintered low alloy high strength AISI 8640 steel containing the composition of 0.4%C , 0.28%Si, 0.83%Mn, 0.5%Cr, 0.55%Ni and remaining 97.24%Fe, during axial hot upset forging at 1100°±10°C through powder preform forging in the way of powder metallurgy process. Cylindrical green compacts of three different aspect ratios of 0.6, 0.9and 1.2 were prepared from homogeneously blended powders respect to AISI 8640 steel composition in the pressure range of 480±10MPa with the compact density in the range of 85±1% of theoretical using 1.0MN capacity UTM. Sintering was carried out at 1100°±10°C for a period of 120 minutes in an electric muffle furnace under the protection of ceramic coating. Sintered compacts were hot upset forged to different height strains using 1.0MN capacity Friction Screw Press and quenched in the linseed oil bath to cool down to the room temperature. Analysis of experimental data and calculated parameters based on the forged preform geometry have resulted in several empirical relations relating Densification, Poisson's ratio, new Poisson's ratio and arc radius by considering circular arc of bulging.
The present investigation pertains to generate experimental data in order to establish the influence of initial preform geometries on the material behaviour and the operative densification mechanism/s during hot upsetforging of sintered AISI 9840 P/M Steel composition prepared from the elemental powders. Powder blend corresponding to AISI 9840= C(0.4%), Mn(0.8%), Si(0.3%), Ni(1.0%),Cr(0.8%), Mo(0.25%) and Fe(96.4%) composition was prepared on a pot mill and the blending was carried out for a period' of 16hrs. while maintaining the powder to ball ratio 1.1: I by weight. Compacts of 27.5mm diameter and 12 - 24mm heights were prepared from the aforesaid blend in the density range of 84±1 percent of theoretical density by applying accurately controlled pressures in the range of 460±10 MPa and by taking pre-weighed powders. Indigenously developed ceramic coating was applied all over the compact surfaces and dried under an ambient conditions for a period of 10- 12 hrs. These ceramic coated compacts were recoated 90° to the previous coating and re- dried under the aforesaid conditions. These ceramic coated preforms were sintered in an electric muffle furnace for a period of 90 minutes at 11500±10°C. Immediately after the completion of the sintering schedule, the preforms corresponding to 0.45, 0.68 and 0.92 initial aspect ratios were axially hot forged to different height strains. Analysis of the experimental data has revealed that the lower aspect ratio preforms densified rapidly compared to higher aspect ratios and the densification curves corresponded to a third order polynomial of the form:(ρf/ρth) = ao +al €h + a2€h2 +a3€h3; where, €h= ln (Ho/Hf) and a0, al, a2 anda3 are empirically determined constants. Further analysis has established that the Poisson's ratio would always remain less than one half and will have the tendency to approach to a limiting value of 0.5 in the near vicinity of the theoretical density. Influence of the preform geometry is established to be quite pronounced and has affected the densification curves and Poisson's ratio with density.
Hot upset forging experiments were carried out on sintered Iron and AISI 3115 Powder Metallurgy (P/M) steel preforms at 1120˚±10˚C which were sintered at the same temperature for a period of sixty minutes. Present investigation, therefore, pertains to evaluate the effect of initial preform geometry on how the densification mechanism/s operate/s during hot upsetting mode. Preforms of initial aspect ratios of 0.6, 0.85 and 1.05 respectively were prepared on a 1.0 MN capacity Universal Testing Machine from Iron as well as from AISI 3115 composition powder blend using suitable die punch and bottom insert assembly in the pressure ranges of 537±10M Pa; 557±10M Pa; and 578±10MPa respectively. With the control of pressure and powder weights, the initial compact densities were maintained in the range of 0.91±0.01 of theoretical density. All compacts were coated with a thin film by using indigenously developed ceramic coating twice and at each time they were dried for a period of twelve hours under an ambient conditions. Ceramic coated compacts were sintered in an electric muffle furnace for a period of sixty minutes at 1120˚±10˚C. All sintered compacts except one from each aspect ratios were hot upset forged to different height strains and suitable plots were drawn between fractional theoretical density and the true height strains, true diameter strain and the true height strains, Poisson’s ratio and the fractional theoretical density, the fractional theoretical density and the bulging ratio to establish empirical relations in the above said parameters. Analysis of the experimental and the calculated parameters along with the various plots have yielded several empirical relationships of practical as well as of theoretical importance.
TJPRC, 2014
"Present experimental work has been evaluated the densification behaviour and mechanical properties of sintered hot forged AISI 8720 PM Steels by elemental powder through Powder Metallurgy techniques. Three aspect ratios were selected namely 0.55, 0.92 and 1.28 were prepared from Fe-0.20% C-0.28%Si-0.80%Mn-0.50%Cr-0.25%Mo-0.55%Ni powder blends using suitable die, punch and bottom insert on 1.0 MN capacity U.T.M in the pressure range of 480 ± 10 M Pa, 520 ±10 M Pa and 540 ± 10 M Pa respectively. The green Compacts were sintered at 1120 ±100 C for a period of 120 minutes under the protective ceramic coating. Sintered compacts were axially hot upset forged to different height strains with hydraulic screw press. The forged steels were heat treated in five different methods. The investigation on densification behaviour and Mechanical properties were studied with the calculated parameters. The sintered forged AISI 8720 steels show the existence of third and second order polynomial densification w.r.t height strain, bulging ratio, diameter strain, relative density and poisson’s ratio. The lower aspect ratio 0.55 densified better than other aspect ratio performs. Sintered forged homogenised heat treatment samples shows better mechanical properties then sintered forged heat treated samples. Microstructure of the forged steels exhibited the presence of alloy carbides in ferrite matrix with the traces of martensite needles and bainite, pearlite grains. Fractography reveals mixed mode of fracture."
Hot powder forging behavior analysis of sintered AISI 8740 PM steels for automotive application
Elsevier: Materials Today, 2020
Present study deals with hot forging behavior of the sintered AISI 8740 powder metallurgy steels through powder metallurgy route. These steels extensively used for automobile application for its strength and elongation. Green compacts were fabricated with aspect ratios 1.28, 0.92 and 0.55. These green compacts were fabricated using appropriate die set assembly with 0.6 MN capacity Universal testing machine at 550 ± 10 MPa pressure and subsequently sintered at an elevated temperature in a protective atmosphere using Muffle furnace. Green compacts were forged and analysed with different densification and properties evaluation. Structure property correlation were analysed systematically. The fractography of all compacts show fine dimples and cleavage kind of fracture that confirms mixed mode of fracture due to the existence of multi-phase combination of different alloying elements.
Materials & Design, 2010
Sintered low alloy steels containing the alloying elements molybdenum, copper and titanium were synthesised through powder metallurgy route from mixed elemental powders to yield the compositions: Fe-0.5% C, Fe-0.5% C-2% Cu, Fe-0.5% C-2% Mo and Fe-0.5% C-2% Cu-2% Mo-2% Ti. Green cylindrical compacts were made using a 1000 kN hydraulic press using suitable cylindrical die-punch combination. The ceramic coated cylindrical preforms were sintered at 1000 ± 10°C in a muffle furnace for a period of 120 min. After sintering, the preforms were subjected to different heat treatment processes, namely, heating to 900°C, soaking for 60 min and quenching in air or oil or cooled inside the furnace. The heat treated preforms were subject to axial upsetting deformations, at various applied loads and their densification behaviours were compared. The influence of various heat treatment processes on deformation and densification of the alloys was studied and correlated with their microstructures. The plain carbon steel preforms were observed to respond well to the three heat treatment cycles by way of exhibiting the highest levels of densification and plastic deformation. However, both alloy addition and heat treatment have led to a reduction in densification and deformation of the alloy steel preforms. Presence of titanium carbide particulates in the microstructure of the Ti-alloyed steel has played a significant role in reducing the densification as well as deformation. The basic ferritic-pearlitic microstructure of Fe-0.5% C steel has essentially promoted the largest deformation levels coupled with higher densification.
Materials & Design, 2009
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.
A Review of the Physical Metallurgy related to the Hot Press Forming of Advanced High Strength Steel
2009
The automotive industry requirements for vehicle weight reduction, weight containment, improved part functionality and passenger safety have resulted in the increased use of steel grades with a fully martensitic microstructure. These steel grades are essential to improve the anti-intrusion resistance of automotive body parts and the related passenger safety during car collisions. Standard advanced high strength steel (AHSS) grades are notoriously difficult to be press formed; they are characterized by elastic springback, poor stretch flangeability and low hole expansion ratios. Hot press forming has therefore received much attention recently as an alternative technology to produce AHSS automotive parts. In this contribution, the physical metallurgy principles of the hot press forming process are reviewed. The effect of composition on CCT curves of standard CMnB hot press forming steels is discussed taking the deformation during press forming into account. Furthermore,the effect of the static strain ageing processes occurring during the paint baking cycle on the in-service mechanical properties of press hardened steel will be presented. The influence of temperate and strain rate on the flow stress during press forming and the final room temperature mechanical properties will be discuss ed. Moreover, the issues related to coatings on B-alloyed CMn hot press forming steel will be critically reviewed. In particular the combined effects of thermal cycle and deformation on the degradation of the Al-10%Si coating will be discussed in detail. Finally, the properties of both Al-based and Zn-based coating systems are compared, and the possibility of the formation of a diffusion barrier during press forming is discussed.
Tool Steels: Forging Simulation and Microstructure Evolution of Large Scale Ingot
Acta Physica Polonica A, 2015
The aim of this paper is to analyze the hot working behavior of two dierent steels based on 3% and 5% Cr steel chemistry, respectively. Hot deformation is studied by hot torsion tests in the range of temperatures 10001200 • C and strain rates 0.01, 0.10, 1.00 s −1. At given temperatures and strain rates ow curves exhibit a peak followed by a decline towards a steady state which is indicative of dynamic recrystallization. At constant strain, ow stress increases with increasing strain rate and decreasing temperature. The analysis of the constitutive equation relating peak ow stress, strain rate and temperature shows high activation energy values for both steels. Recrystallized volume fraction of steels after hot deformation is estimated based on the grain orientation spread as measured by electron backscattered diraction technique, on the hot deformed and quenched materials.