The formation оf the bainite structure during heat treatment of the rail steel (analogue J13052)

The shortcomings of the existing normalization regime with annealing of the 1st kind of large-sized parts made of rail steel analogue J13052 are investigated. The increasing of toughness was obtained by controlled quenching air to the bainitic structure with the use of an orthogonal matrix of planning for 15 modes. Allowable hardness interval was determined to provide the value of shock viscidity no less than 20 J/cm2. On the basis of statistical data and the series of experimental heat treatment processes, optimal interval of hardness 165 … 180 HB was defined. This interval of hardness provides desired impact strength characteristics. According to the method above, heat treatment modes on the planning matrix were established in laboratory conditions. Critical points of the cooling Ar1 and Ar3 were determined by the thermograms. Then obtained thermograms results are used to select the cooling mode of castings of different masses and sizes, by setting the temperature control sensors during the heat cycle. Due to the fact that the austenite transformation temperature range is influenced by heating, holding time and cooling air flow rate. While using controlled heat treatment in the production, correction of holding time and of cooling rate of bulk product is being adjusted to reach the predetermined interval of intermediate conversion. Regressive equalizations of polynomials of 2nd degree were expected for determination of the shock viscidity of KCV-60, hardness, microhardness of structural constituents as a ferrit, alloyed ferrit, pearlite. Applying of controlled cooling process includes controlled isothermal quenching with self-tempering, where pearlite transformation region is transferred to the low temperature interval. This transfer provides obtaining of maximal degree of grain refinement and getting of structural component in the form of bainite till 3% in ferrite-pearlite structure. The difficult cycle of heat treatment is offered for massive railway details with conservation of internal energy of founding for recrystallization.

bainite, toughness, ferrite-pearlite structure, low carbon steel