Study On The Behavior Of Dynamic Surface Oxide Film Of High-speed Steel Working On Hot-rolled

With the rapid development of rolling technology, the rolling industry thrives as well.A group of new rolling materials successively come to appear, and among themHigh-speed steel (HSS) rolls are in the leading place and develop at a fastest speed. Forthe special materials of HSS and the unique hot strip rolling working condition where ex-ist high temperature, large stress, water vapor and so on, working rolls are easily to forma layer of thin oxide scales. When the oxide scales form completely, they can slow downthe wear which caused by hot strip touching the roll surface, and extend the period of theworking roll, in that way, the shape of the roll can keep its original one, and the quality ofthe strips has been improved, and the roll wear has been decreased. The oxide scales haveits own procedure from forming, developing and peeling off, when the oxide scales peeloff, the roll surface will affect the product quality apparently. So there is a necessity toresearch the mechanism of the oxide scales above the roll surface.In this paper, the working layer of HSS roll are used as experiment material, makingthem oxide thermostatically and under thermal cycling condition respectively, in whichway the mechanism of the oxidation could be studied at various temperatures and forvarious time, then get the knowledge of the temperature field developing in rolls duringhot rolling from the existing literature, by changing peak temperature, obtain oxide scalesof various peak temperature and oxidation time, then use millionth of a gram electronicbalance and scanning electron microscope, study respective oxidation kinetics, observethe sample s surface morphologies, from them find out the most suitable oxidation tem-perature and time, then use this to guide rolling mills.The results are as follows: under constant temperatures the curves of oxidation ki-netics are in accordance with parabola tendency, this shows the oxidation formationsmainly are completed by diffusion mass transfer, and the oxidation rate rises as the oxida-tion temperatures and the oxidation time rise, furthermore, the oxidation temperatures have a larger influence about the oxidation rate. Under800℃the oxidation rises rapidly,this is because of Mo in the HSS. From SEM image, we can know about that the oxida-tion resistance of MC carbides ranks last place, at the same time the oxide grains willbecome bigger as the time rises.Under thermal cycling condition, the curves of oxidation kinetics are in accordancewith linear tendency, and the oxidation grains become smaller than ones under constanttemperatures, their shapes change as well, all these are owing to the inner stress whichappears in the oxidation scales forming under rapidly heating and cooling, in thisway,the scales will peel off and smash in portion, newly formed scales will not gathertogether rapidly, so the oxidation grains will appear small. Fe substrate oxidation scalesappear acicular, at the same time, MC oxidation formations appear irregular columnar,under700℃peak temperature the oxidation rate will increase, and also the oxidationscales will rapidly grow into pieces, while there are still a lot of cracks.