Ferrous Powder Metallurgy Research Articles

Hardenability of PM Steel Alloyed Using Tailored Master Alloys

Abstract The ferrous powder metallurgy industry is facing major upheavals currently, which, however, also offer opportunities. New materials and concepts, made possible by tailored design, are a way to prepare for new challenges. Alloying of PM steel through the master alloy route is a concept that combines efficient usage of alloying elements, also of such with high oxygen affinity, with accelerated homogenization via liquid phase sintering. Thus, improved properties can be attained while maintaining dimensional precision, which makes the PM route more attractive. In the present study, different master alloys containing Fe, Si, C, Cr and / or Mn have been admixed to plain iron base powder, the mixes then being consolidated by pressing and sintering. The materials thus produced are compared to two commercial sinter hardening PM steel grades in terms of hardenability. CCT diagrams are presented for all materials, and hardness data from quenching dilatometer experiments are compared to the hardness values achieved by sinter hardening in the lab furnace as well as by a classical quench-and-temper treatment.

Thermoanalytical techniques for characterizing sintering processes in ferrous powder metallurgy

For powder metallurgy processing, the sintering stage, i.e. the heat treatment of a the powder compact below the melting point of -at least- the major component, is decisive for establishing microstructure and properties. Thorough studying of the chemical and metallurgical processes occurring during sintering is essential for attaining optimal product properties, and sintering has therefore been the focus of investigations for many decades. Thermoanalytical techniques, at best combined with chemical analysis, enable in-situ characterization of the sintering process from many perspectives. When using these techniques in powder metallurgy, it should be considered that the very large specific surface of a powder compact, compared to a solid metallic body, results in much higher reactivity with the surrounding atmosphere. This atmosphere is on the one hand the “external” one, outside the body in the free space of the furnace, and on the other hand the “internal” one within the pore network of the specimen. This paper shows different examples of how critical information about the sintering process can be described by using thermoanalytical techniques combined with mass spectroscopy: e.g. phase transformations and liquid phase formation in the powdered compact, deoxidation and decarburization reactions, and interstitial redistribution in sintered alloy steels prepared through different alloying techniques.

Study of dry wear behavior of Novel ferrous samples prepared by powder metallurgy method

The sliding wear behavior of newly developed ferrous powder metallurgy samples was investigated under dry sliding conditions. Wear tests were conducted by varying the normal loads of 30 N, 40 N, and 50 N at a constant velocity of 1 m s−1 and then at a constant load of 30 N by varying the sliding velocities by 0.5 m s−1, 1 m s−1, and 2 m s−1 at room temperature. Furthermore, the variations in the wear rate and coefficient of friction at a constant sliding distance of 5400 m were studied at different normal loads keeping sliding velocity constant at 1 m s−1 as well as at different sliding velocities and maintaining normal load at 30 N. The wear characteristics were evaluated using weight loss measurements. The mechanism of wear was observed using a scanning electron microscope and compositional analysis using energy-dispersive X-ray spectroscopy (EDX). It was found that increased normal load had a dominant effect on the wear loss in comparison to increased sliding speed during the tribological testing of the powder metallurgy samples.

The Use of Transient Liquid Phases in Powder Metallurgy

Liquid phase sintering is most widely known in its variant „persistent liquid phase sintering“, in which case the liquid phase is present in constant quantity during the entire isothermal period. There is however also the variant „transient liquid phase“, the melt being present only for a short period in the first stage of sintering and then solidifying through diffusional processes. In this presentation, the preconditions for both variants are presented, in particular with regard to the starting materials. The benefits of transient liquid phases are described, both for sintering – to accelerate material transport, contact formation and microstructural homogenization compared to standard solid state sintering – and for transient liquid phase bonding, a brazing variant which is an attractive method for joining porous powder compacts. Both techniques are highly useful in particular for ferrous powder metallurgy precision components, etc.

Sintering behaviour of compacted water-atomised iron powder: effect of initial state and processing conditions

ABSTRACT Conventional ferrous powder metallurgy relies on uniaxial die-pressing of powder before sintering. The operation causes particle rearrangement and deformation and the initial state of the compact ultimately determines the sintering behaviour. In this study, sintering was investigated for water-atomised iron powder compacted at three different pressure levels, with and without admixed graphite. Electron back-scatter diffraction of the powder and compacts showed a large increase in low-angle grain boundaries after compaction. The sintering of the compacts was investigated by means of dilatometry in hydrogen. The initial compaction strongly influences sintering shrinkage, particularly in the low-temperature, high-diffusivity ferrite region which can account for up to 80% of the recorded shrinkage. Only a small fraction of the total shrinkage originates from the austenite phase, even at high sintering temperatures. However, the ratio of sintering shrinkage in ferrite and austenite changes with compaction pressure, carbon content and heating rate.

Microstructural Evolution during Sintering and Fracture Behavior of Iron-Copper-Carbon Compacts Made with Elemental Powders

Abstract Iron-copper and iron-copper-carbon have been significant alloy compositions in the ferrous powder metallurgy industry for decades. In most applications in which these alloys are used, the copper is mixed into an iron or low-alloy steel base powder as an elemental particulate additive, with alloying accomplished by diffusion during sintering. In this manuscript, the effect of sintering on the development of the microstructure is investigated, where the copper particles melt and flow into the interconnected pore structure, relocate within the iron-base matrix, and create more interfacial area for diffusion. With this combination of enlarged copper-iron contact area and the presence of the liquid phase, diffusion is improved and enhancements in both physical and mechanical properties are realized. The mechanisms for both alloying and the evolution of the microstructure are described through changes in both compact temperature and the time at sintering temperature. It is demonstrated that alloying strengthens not only the surfaces of the particles, but also many of the most vulnerable sites in the compact, i.e., the locations where neighboring particles are forced into contact during compaction. These sintered particle-to-particle contacts are frequently small in cross-sectional area and often the weakest sites in the final microstructure. Fractography is used to show the change in fracture behavior as copper diffusion is affected by sintering times and temperatures.

Investigation of Sinter Braze Ferrous Powder Metallurgy to Wrought Substrates by Ancorbraze 72 Filler Metal Alloy

Brazing processes were carried out using a Ancorbraze 72 and BAg8 fillers alloy, and furnace with Argon gas, characterization of the final joint is supported with optical microscopy, SEM, EDS and Hardness tests. This research is focused on the two steps, the first step is preparing the samples from powder metallurgy of pure Fe, Ni and Fe, Ni alloys. Second step, brazing these samples. Finally, experimental illustrated that BAg8 filler metal was not suitable for protact brazing due to its narrow melting range while protact brazing was suitable for Ancorbraze 72. The Ancobraze filler metal alloy contains boron, silicon elements make affinity for iron and nickel to make joint. It seem that the iron base metal joint more affinity to make a joint with respect to the selected filler metal (nickel, copper, manganic, silicon and boron). This positive effect was obtained due to the effect of Ancorbraze 72 filler metal elements and the distribution of these elements in the joined powder matallurage (P/M) samples after brazing processes.

A Metallographic Study on the Diffusion Behavior and Microstructural Transformations in Silicon-Containing Powder Metallurgy Steels

The choice of alloying method for ferrous powder metallurgy alloys is often dictated by the oxidation potential of the alloying elements used in powder and compact manufacture. Silicon is effective in improving properties of ferrous PM steels; however, if added to the melt prior to atomization, the likelihood of oxidation is high. Alternatively, Si-rich and more complex particulates can be combined with the base powder, i.e., iron or low-alloy steel, with alloying occurring by solid-state diffusion during sintering. The effectiveness of these additives to improve material properties is dependent on their distribution throughout the material volume, as determined by diffusion of each added element. In this study, the distribution of silicon was quantified using energy-dispersive spectroscopy on an iron-based alloy composition. These data were compared with the volume fraction of the various transformation products in cross sections of hardenability samples using both light and electron microscopy. Predictions on the effects of local chemical composition, cooling rate, and microstructure are made.

Raw materials management in iron and steelmaking firms

This paper adds new knowledge on how raw materials should be managed in iron and steelmaking firms. While previous research has contributed significantly to how firms should deal with functional challenges related to raw materials, the understanding of Raw Materials Management from a holistic perspective is largely lacking, and extant research does not provide qualified advice to firms on this matter. This study provides such knowledge by drawing on insights from Höganäs AB, a world leader in ferrous powder metallurgy, and their efforts to identify key aspects and principles of raw materials management. Our elaboration of a more holistic view on raw materials management builds on two elements. First, we depict five external uncertainties and three internal conditions that impact firm-level raw materials management. Second, we present six critical capabilities that underpin proficient firm-level raw materials management. The paper concludes with a discussion of implications for both firms aiming to increase their raw materials proficiency and to future investigations into this important area.

Role of Cu During Sintering of Fe0.96Cu0.04 Nanoparticles

Nanoparticle agglomerates of passivated Fe (n-Fe) and Fe0.96Cu0.04 (n-Fe0.96Cu0.04), synthesized through the levitational gas condensation (LGC) process, were compacted and sintered using the conventional powder metallurgy method. The n-Fe0.96Cu0.04 agglomerates produced lower green density than n-Fe, and when compacted under pressure beyond 200 MPa, they underwent lateral cracking during ejection attributed to the presence of a passive oxide layer. Sintering under dynamic hydrogen atmosphere can produce a higher density of compact in n-Fe0.96Cu0.04 in comparison to n-Fe. Both the results of dilatometry and thermogravimetric (TG) measurements of the samples under flowing hydrogen revealed enhancement of the sintering process as soon as the reduction of oxide layers could be accomplished. The shrinkage rate of n-Fe0.96Cu0.04 reached a value three times higher than n-Fe at a low temperature of 723 K (450 A degrees C) during heating. This enhanced shrinkage rate was the manifestation of accumulation of Cu at the surface of the particles. The formation of a thin-surface melted layer enriched with copper during heating to isothermal holding facilitated as a medium of transport for diffusion of the elements. The compacts produced by sintering at 773 K (500 A degrees C), with relative density 82 pct, were found to be unstable and oxidized instantly when exposed to ambient atmosphere. The stable compacts of density more than 92 pct with 300- to 450-nm grain size could only be produced when sintering was carried out at 973 K (700 A degrees C) and beyond. The 0.22 wt pct residual oxygen obtained in the sintered compact is similar to what is used for conventional ferrous powder metallurgy products.

Embrittling Components in Sintered Steels: Comparison of Phosphorus and Boron

AbstractIn ferrous powder metallurgy, both boron and phosphorus have been known to be sintering activators for a long time. However, the use has been widely different: while P is a standard additive to sintered iron and steels, boron has been frequently studied, but its use in practice is very limited. Both additives are also known to be potentially embrittling, though in a different way. In the present study the differences between the effects of both elements are shown: while P activates sintering up to a certain threshold, in part by stabilizing ferrite, in part by forming a transient liquid phase, boron is the classical additive enhancing persistent liquid phase, being virtually insoluble in the iron matrix. The consequence is that sintered steels can tolerate quite a proportion of phosphorus, depending on composition and sintering process; boron however is strongly embrittling in particular in combination with carbon, which requires establishing a precisely defined content that enhances sintering but is not yet embrittling. The fracture mode of embrittled materials is also different: while with Fe-P the classical intergranular fracture is observed, with boron a much more rugged fracture surface appears, indicating some failure through the eutectic interparticle network but mostly transgranular cleavage. If carbon is added, in both cases transgranular cleavage dominates even in the severely embrittled specimens, indicating that no more the grain boundaries and sintering necks are the weakest links in the systems.

Friction and wear behavior of steam-oxidized ferrous PM compacts

This study determines density effect by assessing sintering temperature and graphite content on the dry sliding wear characteristics of steam-treated iron materials using a pin-on-disk wear test. The specimens were prepared from atomized premixed iron base powders and contained 0.1 to 1.0 wt.% carbon compacted at different densities (5.9 g/cc to 6.8 g/cc). The specimens were sintered for 1 h at different sintering temperatures (1090°C to 1130°C), and then subjected to continuous steam treatment at 540°C for 95 min through in situ Powder metallurgy (PM) technique. Steam treatment was proposed to improve the wear performances of the components of PM. Wear tests were conducted using a pin-on-disk-type machine. Load ranged from 20 N to 60 N. Sliding distance and sliding velocity of 312 m and 0.26 m/s, respectively, were adopted for all tests. Scanning electron microscope was used to analyze wear surface. Increased density and graphite content reduced the wear rate of steam-treated materials. Hardness increased with increasing graphite content. Wear mechanism, wear rate map, and wear maps were drawn for the test result data. Wear transition map identified mild, severe, and ultra-severe wear regimes as functions of applied load.

Sinterability and microstructure evolution during sintering of ferrous powder mixtures

The present work is focused on ferrous powder metallurgy and presents some results of a development of a suitable masteralloy for use as an additive to iron powder for the production of sintered steels. The masteralloy was produced by melting a powder mixture containing approximately Fe + 20% Ni + 20% Mn + 20% Si + 1% C (wt%), in order to obtain a cast billet that was converted into fine powder by crushing and milling. It was observed presence of SiC in the masteralloy after melting that is undesirable in the alloy. Si element should be introduced by using ferrosilicon. Sintered alloys with distinct contents of alloying elements were prepared by mixing the masteralloy powder to plain iron powder. Samples were produced by die compaction of the powder mixtures and sintering at 1200 °C in a differential dilatometer in order to record their linear dimensional behaviour during heating up and isothermal sintering, aiming at studying the sinterability of the compacts. Microstructure development during sintering was studied by SEM, XRD and microprobe analyses.

ANCORLOY HP-1

Abstract Ancorloy HP-1 is a press-ready, engineered binder-treated premixed ferrous powder metallurgy material designed for enhanced as-sintered mechanical properties. This datasheet provides information on composition, physical properties, hardness, and tensile properties as well as fracture toughness. It also includes information on powder metal forms. Filing Code: SA-676. Producer or source: Hoeganaes Corporation.

Effect of Bio Field Treatment on the Physical and Thermal Characteristics of Silicon, Tin and Lead Powders

Silicon, tin and lead powders belong to group IV in periodic table and exhibit decreasing semi conducting nature towards the bottom of the group. These are very useful in producing non ferrous powder metallurgy components. In the present investigation silicon, tin and lead powders are exposed to bio field. Both the exposed and unexposed powders are later characterized by various techniques. The average particle size, after an initial decrease is found to increase with increase in number of days after treatment although the size is lee than that exhibited by untreated powder, suggesting the operation of competing mechanisms fracture and sintering. The BET surface area increased slightly in silicon powder but did not change in tin and lead powders. SEM photographs showed that samples exposed to bio field after 20 days showed fracture paths and fractures at inter and intra particle boundaries in treated powders. Thermal analysis indicated a decrease in heat of reaction and decrease in mass in treated samples. X-ray diffraction of the powder samples indicated both increase and decrease in crystallite size, unit cell volume and molecular weight of samples exposed to bio field even after 179 days. These results indicate that the properties of the metallic powders can be controlled even up to atomic level by exposing to bio field.

The Use of Metallographic Techniques in Failure Analysis Examinations of Ferrous Powder Metallurgy (PM) Materials

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Effect of copper and graphite addition on sinterability of iron

In ferrous powder metallurgy, copper and graphite are used as common alloying elements. Copper melts at low temperature compared to iron and forms liquid which promote interparticle bond formation. However, it also results in compact swelling. To negate this, graphite is used as an additive. This study examines the influence of copper and graphite addition on the densification, dimensional changes, and mechanical properties of iron compacts sintered at 1120°C. These properties have been correlated with the microstructure.

Analysis of Density of Sintered Iron Powder Component Using the Response Surface Method

The continued growth of ferrous powder metallurgy in automobile and others engineering application is largely de-pendent on the development of higher density materials and improved mechanical properties. Since density is a predominant factor in the performance of powder metallurgy components, it has been primarily considered for the present investigation. An experimental investigation have been undertaken in order to understand the variation of density with respect to the variation of process parameters viz., compaction load, sinter temperature and sintering time. The relation among the various process parameters with density has been observed. A mathematical model has been developed using second order response surface model (RSM) with central composite design (CCD) considering the above mentioned process parameters. The developed mathematical model would help in predicting the variation in density with the change in the level of different parameters influencing the density variation. This model also can be useful for setting of optimum value of the parameters for achieving the target density.

Microstructure analysis of microwave sintered ferrous PM alloys

The properties and microstructure of microwave and conventional sintered Fe-2Cu-0.6C powder metallurgy (PM) alloys were investigated. The experimental results show that microwave sintered alloy has the better properties (sintered density 7.20 g/cm3, Rockwell hardness 75 HRB, tensile strength 413.90 MPa and elongation 6.0%), compared with the conventional sintered counterpart. Detailed analyses by using optical microscopy and scanning electron microscopy (SEM) reveal that microwave sintered sample has finer microstructure with small, rounded and uniformly distributed pores, and also demonstrate the presence of more flaky and granular pearlite in the microwave sintered body, both of which account for the property improvement. SEM images on the fracture morphology indicate that a mixed mode containing ductile and brittle fracture is presented in microwave sintered alloy, in contrast with the brittle fracture in conventional sintered counterpart.

Effect of molybdenum addition on workability of powder metallurgy steels during cold upsetting

Ferrous powder metallurgy preforms containing 0%, 0.5%, 1.0% and 1.5% of molybdenum were completely investigated experimentally to study workability behaviour. The formability behaviour of the above-said powder metallurgy sintered steels preforms with aspect ratio of 0.75 under triaxial stress state condition was determined by cold upsetting them with graphite as lubricant. The formability stress parameter was evaluated for all the above-mentioned steel preforms and its variation with respect to axial strain was plotted, studied and discussed relative to their as-sintered microstructures. Also the characteristics of various stresses and stress ratio parameters with respect to axial strain were analyzed and presented.