OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 1 2022 The steels were smelted in an induction steel furnace. The resulting ingots were forged into blanks with a cross section of 30 × 40 mm and a diameter of 20 mm. The forging temperature was chosen to be 1,000–1,250 °С. The resulting workpieces were subjected to heat treatment, consisting of austenitization for steel 10Cr14NMn20 at a temperature of 900–950°C and 1,000–1,050°C for steel 10Cr14Mn14Ni4Ti with cooling in water. The phase composition of the samples was studied on a DRON-3.0 X-ray diffractometer. Mechanical tests were carried out in the temperature range from +20 to –196 °C. Static uniaxial tensile tests were carried out on a R-20 tensile testing machine; cylindrical specimens with threaded heads were prepared according to GOST 11150–84 “Metals. Methods of tension tests at low temperatures”, as well as samples with a circumferential notches. Dynamic bending tests were carried out on a pendulum impact tester, using samples according to GOST 9454–78 “Metals. Method for testing the impact strength at low, room and high temperature”. Results and discussion It is known that in metastable austenitic steels, phase transformations can occur during the manufacture of products using forging, stamping, and other types of impact, as well as during operation under dynamic loading conditions at low temperatures. Taking into account the degree of responsibility of low-temperature equipment, a set of studies was carried out to determine the dependence of martensitic transformations in industrially used metastable austenitic steels 10Cr14NMn20 and 10Cr14Mn14Ni4Ti on the strain rate and test temperature. In the process of analyzing phase transformations occurring under deformations and low temperatures in steel 10Cr14NMn20 at different strain rates, the following was revealed. When steel 10Cr14NMn20 is deformed at 20 °C at a rate of έ = 0.34 × 10– s–1, ε-martensite is formed immediately. At the same time, an increase in the rate to έ = 0.34 × 10–1 s–1 causes the formation of ε-martensite only after deformation by 25 %, and at a rate equal to έ = 0.34 × 102 s–1, the solid solution remains stable up to the destruction of the samples (Figure 1). Lowering the test temperature to –100 °C and further to -196 °C is accompanied by the appearance of α-martensite. Characteristically, at –100 °C, α-martensite appears after 10–15 % strain, and its amount increases with further deformation. The amount of ε-martensite under these conditions fi rst increases and Fig. 1. Dependence of martensitic transformations in steel 10Cr14NMn20 on the strain rate at a test temperature of 20 °C
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