Behavior of materials under different types of loading has attracted the attention of many researchers due to their fundamental and applied significance [1-2]. The most time-consuming are the tests to determine the mechanical characteristics of identifying the optimal regime of heat treatment [3-4]. In the present work we studied the 6ХС steel oil-hardened and tempered in a zone temperature 260-650° С. The test results showed that the highest value of fatigue limit σ-1 are the samples subjected isothermal tempering (280° С), with σ-1 = 700MPa. Steel 6ХС was also tested in the double holiday at temperatures from 150+250° С to 150+600° С. The greatest value of the fatigue limit σ-1 = 720 MPa was obtained at a tempering temperature of 150 + 370° С. Rather high value of σ-1 = 650 MPa, have samples, tempered at a temperature of 150+250° С. From the previously obtained data on fatigue and static tests it follows that the steeper the slope of the hardening curves, the more sloping the slopes of the fatigue curves are. The tangent of the slope of the left branch of the curve lg σ – lg ε is the strain hardening coefficient. It is defined by the expression lg αк=, or rather, and as a rule:

tg αк; where lg σвист – the true tensile strength; σт = σεi; εi – is the deformation that is determined by the yield strength (e.g., εi = 0,002 и σт = σ0,002); εР – uniform deformation, which corresponds σвист.

В результате обработки данных испытаний на однократное разрушение нескольких температур отпуска были построены кривые упрочнения. Наблюдается зависимость, что чем больше параметр деформационного упрочнения tg αк ,тем меньше показатель tg αω, т.е. сталь лучше сопротивляется усталости. Описанная связь представляет собой обратную корреляцию между tg αω и tg αк , т.е. ее можно представить в виде выражения:

As a result of processing test data for a single destruction of several temperatures was constructed hardening curves. The observed dependence that the larger the parameter strain hardening tg αк ,the lower the rate tg αω, i.e. steel better resists fatigue. Describes the relationship is an inverse correlation between tg αω and tg αк , i.e. it can be represented in the form of the expression:

tg α_ω= К_ус/ tg α_к or К_ус= tg αω tg α_к .

Analyzing the obtained results, it should be noted that steel 6ХС shows the average value of the parameter Кус equal 0.0213. Comparing the parameter Кус obtained in the present work, with the same parameter, less durable materials, it should be noted that high-strength steel gives a lower value (К_{ус ср} = 0.0213) in comparison with less durable materials (Кус ср = 0.05). This dictates the need to apply the parameter Кус in the calculations of the parameters tg αω and tg αк, guided by the class of structural materials.

2. Suresh S. Fatigue of metals. – Cambridge University Press, 2006. – 701 p.

3. Mylnikov V.V., Shetulov D.I., Chernyshov E.A. Influence of the heat treatment of 03H18K9M5T-E{CYRILLIC}L{CYRILLIC} steel on its microplastic and cyclic deformation // Steel in Translation. 2013. Т. 43. No. 11. рр. 695-697.

4. Mylnikov V.V., Romanov A.D., Shetulov D.I., Khlybov A.A. Effekt of the aging temperature of steel on the parameters of fatigue resistance and microstrain // Metal Science and Heat Treatment. 2016. рр. 1-3.