In-situ observation of surface oxidation of roll

 During the use of the roll, due to the surface contact between the roll and the hot billet, an oxide film is formed on the surface under the action of heat. The formation and peeling of the oxide film have a significant impact on the consumption of the hot roll and the quality of the hot rolled product. In situ observations were made on the surface oxidation of hot rolling rolls of three materials: high chromium cast iron, high chromium cast steel, and high-speed steel rolls.

In-situ observation of surface oxidation during continuous heating (a→l arranged from left to right, from top to bottom)

(a) High chromium cast iron 250℃; (b) High chromium cast iron 400℃; (c) High chromium cast iron 500℃; (d) High chromium cast iron 650℃;

(e) High chromium cast steel 250℃; (f) High chromium cast steel 400℃; (g) High chromium cast steel 500℃; (h) High chromium cast steel 650℃;

(i) High-speed steel 250℃; (j) High-speed steel 400℃; (k) High-speed steel 500℃; (l) High-speed steel 650℃.

In situ observation of surface oxidation at 650℃ isothermal process (a→l arranged from left to right, from top to bottom)

(a) High chromium cast iron 0min; (b) High chromium cast iron 10min; (c) High chromium cast iron 30min; (d) High chromium cast iron 60min;

(e) High chromium cast steel 0min; (f) High chromium cast steel 10min; (g) High chromium cast steel 30min; (h) High chromium cast steel 60min;

(i)High-speed steel 0min; (j) High-speed steel 10min; (k) High-speed steel 30min; (l) High-speed steel 60min.

The influence of the number of heating and water cooling cycles on the oxidation morphology of the sample surface (a→l arranged from left to right, from top to bottom)

(a) High chromium cast iron 10 times; (b) High chromium cast iron 30 times; (c) High chromium cast iron 50 times; (d) High chromium cast iron 100 times;

(e) High chromium cast steel 10 times; (f) High chromium cast steel 30 times; (g) High chromium cast steel 50 times; (h) High chromium cast steel 100 times;

(i) High-speed steel 10 times; (j) High-speed steel 30 times; (k) High-speed steel 50 times; (l) High-speed steel 100 times.

Conclusion

In the continuous heating process, the oxide film formation temperature of high chromium cast iron and high chromium cast steel is lower, about 300 ℃, but the oxide film is dense and uniform, which inhibits the growth of the oxide film in the high temperature and isothermal process; while the high speed steel oxide film is formed The temperature of the oxide film is higher, and the temperature at which the oxide film is formed quickly is about 480°C, but the oxide film has poor uniformity and has a faster growth rate.

At high temperatures, due to the poor compactness of the oxide film formed around the granular MC-type carbides in the high-speed steel, the formation of a uniform oxide film is split, resulting in the oxidation resistance of high-speed steel lower than that of high-chromium cast iron and high-chromium cast steel. Therefore, compared with high-chromium cast iron or high-chromium cast steel rolls, high-speed steel rolls must achieve better results during use, and require higher production processes and equipment.

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