Rails are an important component of railways and mainly bear the impact and wear from wheels. Therefore, it is necessary to improve the strength and toughness of rails and increase the service life of rails. After continuous practice, we found that using a medium frequency induction heating machine to perform SQ treatment on the rails can meet the working requirements of the rails. Today, the editor will tell you about the basic principles of SQ treatment using medium frequency induction heating machines on rails.
When eutectoid steel is quenched, the supercooled austenite produces the following phase transformation reaction: austenite transforms into pearlite, A-P. The reaction product is pearlite composed of a layer of ferrite and a layer of cementite. The distance between ferrite and cementite lamellae determines the strength and toughness of pearlite. The thicker the lamellar spacing, the lower the strength of the pearlite and the worse the toughness; conversely, the thinner the lamellar spacing, the higher the strength of the pearlite and the stronger the toughness. During SQ treatment, we strive to obtain a pearlite structure with a fine lamellar structure. To this end, take the following measures to achieve good SQ processing results.
(1) Use a medium frequency induction heating machine for induction heating to obtain fine initial austenite grains. This fine initial grain of austenite creates favorable structural conditions for the next step to obtain pearlite with fine lamella spacing. Because coarse grains will inevitably produce pearlite with thick interlamellar spacing, and the finer the grains, the smaller the interlamellar spacing of pearlite will be. When rail SQ is processed, it is hoped to obtain pearlite with a lamella spacing less than 80.
(2) By controlling the transformation temperature and cooling rate of the A-P transformation process, a pearlite structure with small lamellar spacing can be obtained. As the degree of supercooling increases during the transformation process and the cooling rate accelerates during the transformation process, the lamellar spacing of pearlite decreases, and the strength and toughness of the steel increase. Therefore, using an austenitizing temperature close to the Ac1 point and rapid cooling is another important means to obtain fine pearlite lamellar spacing.
In short, using a medium frequency induction heating machine for induction heating and then quickly raising the temperature to the austenitizing temperature to reduce excessive temperature rise and rapid quenching and cooling are the keys to obtaining a fine lamellar spacing pearlite structure.