Tungsten and Molybdenum inhigh speed steel rollrole in

Tungsten and molybdenum are the main alloying elements in ordinary high-speed steel rolls. The chemical properties of tungsten and molybdenum are similar, and their effects on the microstructure transformation and properties of high-speed steel rolls are almost the same. The difference is that molybdenum causes a lower temperature of the structural transition. The main reason for using high-speed steel to manufacture rolls is to use the excellent red hardness of high-speed steel to improve the high-temperature wear resistance of rolls. The excellent red hardness of high-speed steel rolls is firstly attributed to the strong aggregation resistance of M2C and MC. A large amount of retained austenite can also be obtained in the quenched structure of ordinary carbon steel and low alloy steel. Decomposition of this retained austenite at high temperatures rarely increases the hardness. The austenite in these steels usually decomposes at a lower temperature, while the precipitated Fe3C type carbides rapidly aggregate at a slightly higher temperature, and the aggregation of carbides is the direct cause of softening. In high-speed steel, the precipitation of carbides into very fine particles and the decomposition of residual austenite jointly cause secondary hardening, and the carbides always maintain their fine size, so high-speed steel has good red hardness. In high-speed steels, the elements that influence this phenomenon are tungsten and molybdenum. The atomic size of tungsten and molybdenum in high-speed steel is much larger than that of any other element, and the diffusion rate is slower. In order for the accumulation of carbides to continue, the diffusion of not only chromium and vanadium, but also tungsten (molybdenum) and carbon is required. Therefore, in order to ensurehigh speed steel rollWith good red hardness and high temperature wear resistance, it is reasonable to add appropriate amount of tungsten and molybdenum in the roll structure.

High-speed steel roll: From the development history of high-speed steel, tungsten is also an element that improves the tempering stability and red hardness of high-speed steel. Tungsten mainly exists in the form of M6C in high-speed steel, which plays an important role in improving the wear resistance of high-speed steel. During the high-temperature quenching process, a part of M6C is dissolved in austenite to improve the hardenability of high-speed steel. Tungsten dissolved in the matrix can effectively prevent precipitation during tempering. Tungsten atoms have a large radius and a high elastic modulus. It interacts with the dislocation and is concentrated on the dislocation line. Dislocations are locked, making it difficult to move, forming large solid solution strengthening. The bonding force between tungsten atoms and carbon atoms is large, which improves the stability of martensite decomposition at high temperatures, maintains the martensite lattice characteristics at high temperatures, and maintains high hardness. Undissolved M6C during quenching and heating can prevent austenite grains from growing at high temperatures. During the high-temperature tempering process, part of the tungsten is dispersed and precipitated in the form of W2C, resulting in secondary hardening and increasing the red hardness of high-speed steel. It is these characteristics that make the dispersion strengthening and solid solution strengthening of tungsten-containing high-speed steel improve with the increase of tungsten content during heating and insulation, which determines that tungsten has a strong ability to improve the thermal stability of high-speed steel.high speed steel roll: The effect of tungsten on the structure and main properties of high-speed steel is not proportional to its content. High-speed steel containing 7%-8% W can obtain satisfactory secondary hardness and thermal stability, but at this time the carbide phase contains too much M23C6 and too little M6C. Therefore, the quenching temperature should not be too high, otherwise very coarse grains will be produced, and the strength and toughness will be significantly reduced. If the tungsten content continues to increase, the M6C produced will increase, which will significantly improve the overheating stability of the steel. However, if the tungsten content is too high, the leburite content in the roll structure will increase, and the carbide particles will be large and uneven, which will adversely affect the thermal fatigue performance of the roll.