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It is shown that machines of the SI series for wear fatigue tests make it possible to measure the fric tion torque during rolling with a sufficient accuracy. For this purpose, methods for the calibration and deter mination of the accuracy of all parameters and characteristics being specified and measured are developed. A method for the determination of the coefficient of resistance to rolling depending on the value of the off con tact load is also developed and exemplified. Analysis of the experimental results and analytical description of the complex of these studies will be presented in subsequent papers.

The properties of sintered steels doped with manganese and copper and produced using copperbearing ferromanganese master alloys are examined with respect to temperature and concentrations of the master alloy (3-10%) and graphite (0-1.0%) in the charge. It is shown that increase in the concentration of the master alloy and graphite leads to the relevant increase in steel strength. The hardness of steel with the minimum content of the master alloy (3%) becomes substantially higher when carbon is introduced and weakly depends on sintering temperature. If the concentration of the master alloy is higher (7 and 10%), the effect of sintering temperature on hardness noticeably increases, while the effect of graphite content substantially decreases. With increasing concentration of the master alloy, the hardness of the sintered steel becomes higher regardless of sintering temperature and graphite content of the charge.Keywords: sintered steel doped with manganese and copper, master alloy, graphite, iron powder, ferromanganese, sintering.Sintered steels doped with manganese have increasingly been used for the manufacture of products for structural purposes. The economic and technical effectiveness of manganese for doping sintered structural steels is due to the relatively low cost and availability of this element, which is ascertained by a number of papers [1][2][3][4].Ferromanganese is commonly used as the main raw material for the introduction of manganese in the production of sintered manganese steels [4]. Nevertheless, the papers [5,6] show that copper-bearing ferromanganese master alloys can efficiently be used for this purpose over a wide range of ratios between elements. Owing to the presence of a low-melting eutectic in the Mn-Cu system with a melting point below the sintering temperature of compacts, these master alloys not only activate sintering but also largely prevent the formation of oxide films on ferromanganese particles.The study of basic mechanical properties of sintered steels [6] has shown that increase in the concentrations of copper-bearing ferromanganese master alloys in the charge leads to higher hardness and strength of the alloys. However, the introduction of more than 5 wt.% master alloy is feasible neither technically nor economically. This has necessitated a search for other ways to improve the main mechanical properties of sintered steels. One of the ways may be to introduce additional carbon to the charge (in excess of that contained in the starting ferromanganese) as graphite powder.

The results o f special experiments on the size effect in contact fatigue are presented. It is established that under constant contact loading conditions the durability is higher, the larger is the diameter o f a tested element. The methods fo r estimation o f contact fatigue resistance o f gear wheels, which is based on the statistical model fo r a deformable solid body having a critical volume, are proposed. The limiting stresses o f a gear wheel are estimated using a regulated base fo r this machine parts. K e y w o r d s : size effect, contact fatigue, gear wheels.The durability and fatigue resistance o f com ponents operating under cyclic loading by bending, tension, com pression, twisting, etc. appear to be the lower, the larger are the com ponent dim ensions [1,2] Since the phenom ena o f contact fatigue are based on the same processes as those occurring under other types o f fatigue, it is natural to expect that increasing the absolute dim ensions o f a com ponent w ould decrease its contact fatigue limit. However, by analyzing the available results o f studies on the size effect in contact fatigue it is im possible to get a definite opinion on this problem [2][3][4][5][6][7][8][9][10][11][12][13].Some researchers state that the size effect in contact fatigue undergoes inversion, i.e., as the diam eter o f contacting parts is increased, the durability grows [4][5][6]. However, others assert that increase in a com ponent size leads to reduction o f bending and contact fatigue lim its [7,10].For the basic regularities o f the size effect in contact fatigue to be elucidated, special experim ental studies have been m ade. The test schem e is shown in Fig. 1. C ylindrical sam ple 2 serves as a tooth o f a gear wheel. A counterbody -roller 1 -is pressed to the surface o f sam ple 2 by a contact load F N in the contact zone x. R oller 1 serves as a tooth o f the second gear w heel that transm its the contact load F n to sam ple-m odel 2 .Sam ple 2, w hich is fastened in spindel 3, is rotated w ith an angular velocity « 1. C ounterbody 1 is rotated w ith an angular velocity « 2 , its rotation axis being parallel to that o f sam ple 2. R egulating the ratio o f the velocities «1 and « 2 allows one to obtain the required slip coefficient, im itating the slip in gearing. The contact load F N provides a sim ultaneous excitation both o f contact and bending stresses in the corresponding zones, w hereas the distance betw een these zones is chosen tobe equal to that betw een the pitch point and the tooth root.U sing the counterbody (roller) w ith a constant diam eter D =100 m m and sam ple-m odels o f various diam eters d (Fig. 2) m akes it possible to change two m ain curvatures and to obtain the size ratio o f the contact area (a /b ) w ithin the range 0.4-0.8, w hich is satisfactory for practical purposes.