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The possibility of replacing nickel by manganese in Cu − Ni steels is studied. The physicomechanical properties, composition, and production conditions for manganese-containing steels sintered in hydrogen and converted gas are determined. It is established that they may replace standard steel grade PK40N2D2.Currently in the powder metallurgy industry there is extensive use of structural steels alloyed with copper and nickel. The most widespread of them correspond in chemical composition and properties to steel grades PK40N2D2 and PK70N2D2 according to GOST 28378-89. In view of the cost of alloying elements, particularly nickel, it is important to study the possibility of its partial or total replacement by other less expensive alloying metals. One version of this substitution is the use of manganese. As is well known, in the Ukraine there are no large reserves of nickel but there are considerable natural reserves of manganese-containing ores and production of ferroalloys based on them. Therefore the aim of this work is to develop compositions, study preparation conditions and properties of manganese-containing low-alloy powder structural steels.Partial or total replacement of nickel and molybdenum in powder structural steels by manganese, chromium, silicon, and other less expensive alloying elements has been studied in [1][2][3]. However, substitution conditions have not been studied while this would make it possible in particular to prepare manganese-containing steels with a high level of physicomechanical properties comparable with the properties of the steels being replaced. Methods for introducing manganese into structural powder steels, production regimes for preparing them and the optimum compositions providing the required level of properties were not considered in [1][2][3].Manganese may be introduced into powder structural steels by different methods: using alloyed powders, manganese-containing readily-melting and carbide master alloys, and also fine powders of metal manganese and ferromanganese [4][5][6]. Previously alloyed powders containing manganese are prepared by diffusion impregnation from point sources or atomization. The first method has been developed in the Institute for Problems of Materials Science, National Academy of Sciences of Ukraine [7], and the second has been developed abroad where atomization of powders containing manganese, chromium, and other readily-oxidizing elements is accomplished predominantly on a testindustrial scale with nitrogen [8] or oil [9].Most often Cu − Mn and more rarely Cu − Mn − Zn are used as readily-melting master alloys for introducing manganese into powder steels. On sintering these master alloys form a liquid phase that markedly accelerates homogenization [10,11]. Use of multicomponent carbide master alloys of the MCM type (25% Mn, 23 Cr, 22 Mo, 22 Fe, and 7% C) and MVM (25.5% Mn, 23 V, 25.5 Mo, 20 Fe, 5 C, and 0.2% O) in which the alloying elements, including
The influence of the temperature of heating for drop-forging on the fine structure of the ferrite of powder steel Kh17 is investigated. On the basis of structural characteristics obtained from different drop-forging sites by means of harmonic analysis, substantial differences in the degree of structural defectiveness in the crystal lattice between the outer faces and an internal layer of the samples has been established. The highest degree of structural defectiveness is found in the structure of the outer faces following heating for drop-forging to 1050°C while a uniform structure throughout the drop-forging volume is created following heating to 1100°C.Keywords: porous green body, heating temperature, drop-forging, deformation, structural defectiveness of crystal lattice.It is well known that alloying of steels with chromium leads to refinement of the grain and an increase in hardness, strength, and wear resistance [1] as well as to heterogeneity of the structure of powder steels obtained by means of hot drop-forging [2]. Moreover, the fact that such steels are prone to self-hardening affects the evolution of its structure [1]. The slow development of the processes of softening in steels that have been alloyed with chromium is related to the difference in the diffusion constants and the retarding influence of carbide inclusions [3].Chromium steels containing 17% Cr and a small quantity of carbon belongs to the class of semiferrite and ferrite steels in which a γ → α transformation occurs only in one phase or does not occur at all [1]. The entire spectrum of structures is observed in chromium steel that has been sintered of a mechanical mixture, from ferrite to troostitemartensite [4]. The hardness of the base may vary from 1.02 to 6.52 GPa. The properties of semiferrite steels depends on the ratio between the γ and α phases. It has been noted that cracks appear as the carbon content is increased upon rapid cooling of steels [1] containing 17% Cr. Moreover, the properties of powder chromium steels depend to a significant extent on the method used to add the chromium and the type of structure that forms as a result. The production of chromium steels out of alloy powders leads to the creation of the most homogeneous structure [5].Kh17 alloy chromium powder produced by diffusion saturation from point sources is the starting material for fabrication of green body with porosity of about 15% [6]. The porosity of the drop-forged pieces following heating to 950, 1000, 1050, 1100, and 1150°C for 15 min amounts to 3.96, 3.33, 2.68, 2.94, and 2.5%, respectively.The chemical composition of the samples following forging in the temperature interval 950-1150°C is presented in Table 1. The carbon content in the drop-forged pieces is basically 0.11-0.12% while that of chromium, 17.9%. The chemical composition of the sample following heating for drop-forging to 1100°C is slightly different, with the carbon content down to 0.10% and the chromium content down to 17.8%.The intragranular structural defectiveness of Kh17 powder steels ...
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