In-situ observation of pearlite transformation in a hypoeutectoid steel under different cooling rates

The pearlite transformations of a typical hypoeutectoid steel (0.56C–1.44Si–0.66Mn–0.68Cr) under different cooling rates (6, 12, 30 and 60 °C min −1 ) were studied using a confocal laser scanning microscope. Initially precipitated spherical carbides grew into clavate shapes, gradually interconnecting to form a lamellar carbides structure. As the cooling rate increased from 6 to 60 °C min −1 , the initiation temperature of carbide precipitation decreased from 819 to 768 °C, while the subsequent lattice reconstruction temperature decreased from 669 to 625 °C. Simultaneously, the average pearlite lamellar spacing decreased from 258.1 to 168.3 nm. This refinement was accompanied by an increase in quantity of spheroidal and clavate carbides, which exhibited a more random distribution. In addition, there existed a non-linear relationship between the average pearlite lamellar spacing and undercooling.