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Sintered Structural Steels Containing Mn, Cr And Mo – The Summary of the Investigations

Metallurgy and Particulate Materials. Vol. 10, 2001, p. 131 [11] Šalak, A.: Powder Metallurgy International, vol.16, 1984, p. 6 [12] Šalak, A., Leitner G., Hermel, W.: Powder Metallurgy International, vol. 13, 1981, p. 1 [13] James, J., Lindsley, B., Rutz, B., Narasimhan, KS. In: Proc. Euro PM2009. Vol. 1, 2009, p. 23 [14] Lindsley, B., James, J. In: Proc. 2010 PM World Congress&Exhibition. Vol. 3. Sintered steels, 2010, p. 151 [15] Bergman, O., Bengtsson, S. In: Euro PM2009, Sintered Steels II

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Phosphorus in Sintered Steels: Effect of Phosphorus Content and P Carrier in Sintered Steel Fe-C-P

Abstract

Phosphorus as an alloy element is quite common in powder metallurgy, the contents industrially used being markedly higher than those present in wrought steels. In this study, the influence of phosphorus addition through different P carriers was investigated. PM steels of the type Fe-0.7%C-x%P (x = 0.0 … 0.8%) were manufactured by pressing and sintering in H2. It showed that Fe3P is the best phosphorus carrier, resulting in fine and regular microstructure and in high impact energy data at 0.3 … 0.45%P while red P and also Fe2P showed a tendency to agglomeration, with resulting secondary porosity. At high P levels the mechanical properties tend to drop, for the tensile strength at P > 0.60%P while for the impact energy the threshold is 0.45%P. The dimensional behaviour of Fe-C-P can be related to PM aluminium alloys, expansion by transient liquid phase being followed by shrinkage by persistent liquid phase, at least at higher temperatures. In contrast to the dimensional behaviour, degassing and reduction is hardly affected by the phosphorus content.

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Density, Microstructure, Strength and Fractography of Spark Plasma and Conventionally Sintered Mn Steels

REFERENCES [1] Hryha, E., Nyborg, L., Dudrova, E., Bengtsson, S. In: Proc. Euro PM2009 - Sintered Steels 1 – Composition. International powder metallurgy congress et exhibition. Copenhagen, 12.-14.10.2009. Vol. 1. Shrewsbury: EPMA, 2009, p. 17 [2] Taylor, GF.: US Patent No. 1,896,854, 1933 [3] Taylor, GF.: US Patent No. 1,896,853, 1933 [4] Crèmer, GD.: US Patent No. 2,355,954, 1944 [5] Lenel, VF.: JOM – the Journal of The Minerals, Metals & Materials Society (TMS), Trans. AIME, vol. 7, 1955, no. 1, p. 158 [6] Song, X., Liu, X

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Phosphorus in Sintered Steels: Interaction of Phosphorus with Mo

Abstract

Phosphorus as an alloy element is quite common in powder metallurgy, the contents industrially used being markedly higher than those present in wrought steels. However, embrittlement effects are reported also for sintered steels, in part depending on the alloy elements present. In this study, the influence of phosphorus addition on the mechanical properties of PM steels alloyed with Mo, as the most common VI group element in sintered steels, was investigated. PM steels of the type Fe-x%Mo-0.7%Cy% P were manufactured with varying contents of Mo and P, respectively. It showed that P activates sintering also in these materials and enhances Mo homogenization, but there is in fact a risk of embrittlement in these steels that however strongly depends on the combination of Mo and P in the materials: If a critical level is exceeded, embrittlement is observed. At low Mo contents, higher P concentrations are acceptable and vice versa, but e.g. in a material Fe-1.5%Mo-0.7%C-0.45%P, pronounced intergranular embrittlement occurs, further enhanced by sinter hardening effects. This undesirable phenomenon is more pronounced at higher sintering temperatures and in case of faster heating/cooling; it was observed both in materials prepared from mixed and prealloyed powders, respectively. This typical intergranular failure observed with embrittled specimens, in particular after impact testing, indicates the precipitation of brittle phases at the grain boundaries, apparently when exceeding the solubility product between Mo and P.

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Embrittling Components in Sintered Steels: Comparison of Phosphorus and Boron

Abstract

In 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.

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The Role of the Atmosphere on Boron-Activated Sintering of Ferrous Powder Compacts

Abstract

Boron has been known to activate densification during sintering of ferrous powder compacts, though with risk of embrittlement. In the present study, specimens Fe-B and Fe-C-B prepared from standard atomized iron powder with addition of ferroboron Fe-21%B were sintered in different atmospheres, and the resulting microstructures and properties were studied. It showed that the activating effect of boron is observed during sintering in argon and in hydrogen while sintering in N2 containing atmospheres results in rapid deactivation of boron, through formation of stable BN. In hydrogen atmosphere, surface deboronizing was observed to considerable depth. Ar is chemically inert, but Ar trapped inside closed pores tends to inhibit further densification. The impact energy data indicated that the embrittling effect of boron is enhanced significantly by presence of carbon. In the fracture surfaces, transgranular cleavage fracture can be observed both at very low and high impact energy values.

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Prediction of Wear Behavior in Porous Sintered Steels: Artificial Neural Network Approach

REFERENCES [1] Khorsand, H., Abdoos, H.: The mechanical behavior and fatigue of porous sintered steel, K. N. Toosi university of Technology press, Tehran, Iran, 2015 [2] Khorsand, H., Abdoos, H., Amirjan, M.: Metallurgical Engineering Journal, vol. 43, 2011, p. 3 [3] Aliabadi, A., Heydarzadeh Sohi, M., Ghambari, M., Sheikhi Moghadam, K.: Advance Material, vol. 7, 2017, no. 28, p. 27 [4] Sahri, SM., Ghayour, H., Amini, K., Naseri, M., Morteza, H., Rastegari, H., Golparvar, M., Javaheri, V.: The effect of quench and temper treatment on

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Studying the Progress of Sintering in Ferrous Powder Compacts by In-Situ Measuring the Thermal Conductivity

Abstract

In situ characterization of the sintering process is a difficult task, in particular for systems without pronounced dimensional changes. Dilatometry is not too helpful in those cases, and therefore other properties have to be recorded. In the present study, sintering of ferrous powder compacts was studied in situ by measuring the thermal diffusivity a using a laser flash apparatus. This property is a measure to characterise the heat flow through a material; it depends on the contact area between the particles and thus reveals their change during sintering. It is shown that the change of a during sintering of ferrous compacts is much less pronounced than in the case of cemented carbides which is not surprising when regarding the widely differing porosity changes. The results are however in good agreement with expectations when considering some experimental limitations. The trend for the thermal conductivity λ. which can be calculated from a, the specific heat and the density, is in good agreement with that found for the electrical conductivity, both properties being linked through Wiedemann-Franz’ law.

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Applying “Spark Plasma Sintering” Technology to Enhance the Resistance to Contact Fatigue of Sintered Steel Based on Astaloy CRL

Abstract

The article deals with the effect of porosity on the contact fatigue of sintered material type Astaloy CrL with 0.3 and 0.4% C. Sets of samples were used with densities beginning from the value of 7000 kg.m−3 to the value of almost 7859 kg.m−3 which represents almost zero porosity (compact material). It has been found out that the increase of compacting pressure applied simultaneously with temperature results in the reduction of porosity from the value of 9.10% to 0.0005% and increase in hardness from 145 to 193 HV10, depending on the carbon content. Logically there is also an increase in the fatigue life by the contact fatigue tests for the value of 50×106 cycles from the value of 900 MPa to 1150 MPa for samples with 0.3% of C and from 900 MPa to 1300 MPa for samples with 0.4% C. These investigations were also carried out in the past, but to achieve the reduction of porosity, different technonologies were used at each level such as double pressing, hot pressing, saturation, hot forging, etc. In this case, the single technology of “spark plasma sintering” making use of compacting at high temperatures is capable to continuously reduce porosity to zero.

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Surface Hardening Vs. Surface Embrittlement in Carburizing of Porous Steels

Abstract

Carburizing increases the contact fatigue resistance of sintered steels, but the surface hardening may result the formation of surface brittle cracks due to the combined effect of high hardness and porosity. The effect of carburizing on the embrittlement of the case of a 7.3 g/cm3 1.5%Mo - 0.25%C sintered steel was studied. The phenomenon was analyzed theoretically and verified by experiments. The resistance of the carburized steel to surface brittle cracking increases with the load bearing surface and the decrease of the maximum pore size, of the surface microhardness and the friction coefficient. The theoretical analysis was implemented in a design procedure for parts subject to contact stresses.

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