Z. I. Nekrasov Institute of Ferrous Metallurgy of NAS of Ukraine (Dnipro, Ukraine):

Lutsenko V. A., Dr. Eng., Leading Researcher, e-mail: lutsenko@optima.com.ua
Golubenko T. A., Cand. Eng., Researcher
Lutsenko O. V., Cand. Eng., Researcher

JSW «BSW — Management Company of Holding «BMC», (Zhlobin, Belarus):
Glazunova N. A., Head of the Laboratory of Metallurgy central laboratory

Сhromium-molybdenum-bearing steels (grades 42CrMo4 and 31CrMoV9) are used for production of the details of responsible application that are working in the conditions of heavy loads. The content of carbon and alloying elements in these steels, as well as the grain size have significant impact on a complex of mechanical properties. Influence of austenitization temperature on austenite grain size of chromium-molybdenum and chromium-molybdenum-vanadium steels is studied. It was revealed that the structure of both a.m. steels consisted of tempered martensite after pilot heat treatment. Dispersion of grain size values for austenite in both steel grades makes 4–7 points, while the most part of austenite grains were characterized as 5–6 points. Increased chromium content in 31CrMoV9 steel (compared with 42CrMo4 steel) and vanadium alloying resulted in obtaining of more fine austenite grain. It is shown that increase of austenitization temperature from 850 to 1050 °С leads to variation of the average nominal diameter of austenitic grain in the structure of chromium-molybdenum steel from 0.053 to 0.060 mm, and in chromium-molybdenum-vanadium steel — from 0.044 to 0.078 mm. Thereby, size of martensite plates increased from 2.5 to 3 points with the same increase of austenitization temperature from 850 to 1050 °С To form the coarse-grained structure, heating for an austenitization of the steels, containing chromium and molybdenum, should be made at high temperatures above A1+200 °C.

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