Andrej Šalak

Comparison of Mn, Cr and Mo alloyed sintered steels prepared from elemental powders

Abstract Molybdenum, chromium and manganese offer considerable potential as alloy elements in sintered steels, especially for PM precision parts used, for example, in automotive engines and transmissions. This holds in particular for recycling and health/safety aspects. Within this work, the influence of these elements as admixed alloy metals on the sintering behaviour and the properties of structural PM steels is discussed. The considerable differences in the homogenisation behaviour during sintering are described as well as the respective advantages and drawbacks. It is shown that for high density PM steels, Cr and Mo are better suited while for conventionally produced mass products Mn is attractive, its affinity to oxygen being less of a problem today than commonly assumed and since Mn addition promotes swelling, this element might be a replacement for Cu. For Mn, admixing is the more attractive route, for Cr, in contrast, prealloying offers advantages, while for Mo both alloying techniques are feasible.

Durability and failure of powder forged rolling bearing rings

Abstract The rolling contact fatigue endurance of case-hardened powder forged Fe–2Ni–0.5Mo and Fe–0.7Mn–1Cr–0.2Mo steels is presented. The contact fatigue endurance of the Fe–Mn–Cr–Mo powder steel is higher than that of the Fe–Ni–Mo and of wrought bearing steel. The basic data of 17 powder forged outer and inner bearing rings are given. The durability of case-hardened powder forged rings reached the basic dynamic load rating up to ∼150% for Fe–Ni–Mo steel and up to ∼200% for Fe–Mn–Cr–Mo steel. Beside the rolling stress conditions, there are some special powder metallurgy reasons for failure of the rings by spalling which are initiated to a certain depth below the raceway in the zone of maximum shear stresses. These are pores, “free” unforged surfaces, hard white etching areas with microcracks in the form of white bands and/or butterflies generated by pores. The highest durability was recorded for the rings with transcrystalline ductile morphology verified on failure tested rings. Failure of the rings can be minimized by manufacturing under optimal technological conditions.

The Influence of Iron Powder Grade and Manganese Carrier on the Homogeneity Modulus of Sintered Mn Steels

The use of Mn in PM steels has been recently reconsidered because of the possibility of alloying through the gaseous phase. In the present work the reliability of Fe-Mn-C sintered steels is evaluated in dependence on powder grade and manganese carrier type employed for sintered steel production. Three types of iron powders were used for confection of sintered samples: two of them were sponge iron powders, the third was a water atomised one. Manganese was added in the from of high- and low carbon ferromanganese and as electrolytic manganese to achieve 5 wt.% Mn. Vickers hardness measurements were used to calculate the homogeneity moduli h. Significant differences in dependence of powder and manganese carrier type were found. The use of water atomised powder resulted in low reliability, the best performance showed the sponge iron NC 100.24. Best results were obtained using high-carbon ferromanganese and electrolytic manganese, the worst with low-carbon ferromanganese.

Mechanical and Tribological Characteristics of Sintered Manganese Steels

The effect of three iron powder grades and three manganese carrier types on mechanical and tribological characteristics of sintered 1 -5% Mn steels was investigated. The different effect of iron powder grades in dependence on manganese addition expressed oneself in strength and in wear. The highest strength and highest wear attained the steels with 3% Mn added as high carbon ferromanganese. The components – rollers - prepared from manganese steel exhibited lower wear than that from Fe-4Ni-1.5Cu-0.5Mo powder. The gears for hydrogenerator prepared from Fe-3.5Mn-0.5Mo-0.3C steel exhibited longer life time at increased oil pressure compared with that from through hardened sintered Fe-4Ni-1C steel.

Rolling contact fatigue endurance of powder-extruded bearing steel

Abstract The mechanical and toughness properties and rolling contact fatigue endurance of powder-extruded bearing steel made from nitrogen atomized remelted turning powder in as-extruded and as-heat treated state are presented. The mechanical and toughness properties are comparable with those of wrought bearing steel. Rolling contact fatigue endurance was tested by the AXMAT method in as-extruded and as-spheroidizing annealed states depending on the austenitizing temperature, which ranged from 790 °C to 870 °C. Powder-extruded bearing steel in both states showed slightly higher hardness (63 HRC), higher contact fatigue resistance ( L 10 = 80.7 and 55.2 million load cycles, respectively) in comparison with wrought steel ( L 10 = 31.8 million load cycles). The results demonstrate the advantageous properties of powder-extruded bearing steel for high dynamic loading.

Properties of Sintered and Powder Forged Steels Based on Prealloyed Powders

Using manganese as alloy element in sintered steels, also in combination with Cr, is an attractive alternative to the more common but expensive alloy additives, especially Ni, Cu and Mo, also in high concentrations. The main peculiarities of Mn that should be considered is its high affinity for oxygen which is slightly higher than that of Cr—and much higher than that of Cu, Ni and Mo. Chapters 2 and 3 refuted in detail concerns regarding the oxidation of manganese in the samples during sintering in the atmosphere which does not meet thermodynamic requirements on the purity of the sintering atmosphere.

Effect of additional elements on the properties of manganese steels

This chapter provides information and knowledge about the wider impact of the additional elements, i.e. molybdenum, copper, tin, phosphorus and boron, on the mechanical and other properties of sintered mixed manganese steels and some steels alloyed with manganese, chromium and other elements. Particular attention in this chapter is devoted to boriding of sintered steels to produce hard coatings on their surfaces resistant to wear under the technical and technological conditions in which they were produced. Samples of these steels were prepared under different forming and sintering conditions with respect to the possible application of such materials for the production of sintered parts with the characteristics of each system achieved under the particular conditions.

Processing and Properties of Hybrid Fe–(Cr)–xMn–(Mo)–(V) Steels

This chapter describes the methods for preparation of hybrid sintered steels on the basis of prealloyed Fe–Cr–Mo–(V) and Fe–(0.85,1.5)Mo powders with a manganese addition and their mechanical, toughness, structural and fracture characteristics in the as sintered and as sinter hardened conditions.

Effect of Processing Conditions and Materials on Properties of Sintered Fe, Cr, Mo, C Steels Containing Manganese

The study [259] investigated possibility to determine the optimum addition of manganese and molybdenum for preparing the combination of compressibility and mechanical properties of sintered steels.

Effect of Variable Processing Conditions and Materials on Properties of Sintered Mn–C Steels

The goal of the following research and development work in terms of thermodynamics was to reduce the high demands on the purity of the sintering atmosphere at sintering of manganese alloy steels, because when the samples are covered with a getter manganese oxides can be reduced what could occur only at sintering temperatures over 1200°C. Therefore, tests were carried out to determine whether the addition of some low-melting elements would allow sintering and homogenisation of the structures of sintered iron–manganese samples also at lower temperatures.