Increasing the Service Life of Large Rolling-Mill Rolls by Using the Reserve Hardenability of the Steel

Abstract

Roll steel with a high chromium content (steel 45Kh5MF) is characterized by good hardenability, which provides an opportunity to significantly increase the durability of rolling-mill rolls. Here, the surface layer (working layer) of the rolls is strengthened thanks to the use of a heat treatment that forms a structure of lower bainite while blocking the pearlite transformation of austenite. At the same time, occurrence of the bainite transformation in high-chromium steel requires that the steel be kept in the narrow temperature range associated with this conversion (290–410°C) for a considerable length of time. Large rolls made of steel 45Kh5MF are quenched on a horizontal unit in two stages: intensive water-air cooling for 30–35 min (stage 1); cooling with compressed air for 4–5 h (Stage 2). Such quenching blocks the conversion of austenite to pearlite and ensures the formation of a satisfactorily developed bainitic structure. Efficient regimes for quenching and tempering large rolling-mill rolls were found by using integrated software that makes it possible to track the dynamics of the formation of temporary and residual stresses in rolls.