What are the types of heat treatment commonly used for rollers?
发布日期：2019-09-19 浏览次数：307
What are the types of heat treatment commonly used for rollers?
The commonly used heat treatment types of rollers are stress annealing, isothermal spheroidization annealing, diffusion annealing, normalizing, tempering, quenching and cryogenic treatment.
Why do metallurgical steel rolls undergo high temperature diffusion treatment?
Due to the presence of dendritic crystals during the solidification of cast steel rolls, intratrystalline segregation of alloy components is caused by the failure of the inner and outer layers of the rolls to solidify in sequence during the solidification of the rolls. The larger the diameter of the roll body, the longer the length of the roll body, the greater the solidification temperature gradient, and the more serious the alloy solidification segregation. With the increase of alloy content in alloy cast steel roll, the segregation index during solidification increases, and the degree of inhomogeneity is also increased. Therefore, in order to fully diffuse the atoms of alloying elements and obtain uniform austenitic structure, it is necessary to heat the high alloy cast steel roll to 150-250℃ above Ac3 for a certain period of time. This heat treatment method is called high-temperature diffusion treatment.
Why do alloy cast steel rolls need spheroidizing annealing treatment?
The spheroidization annealing treatment of alloy cast steel roll is mainly to improve the cutting performance of the roll, improve the cutting efficiency and prepare the structure for the subsequent quenching treatment. The spheroidization annealing treatment makes the carbide in the tissue change from flake to sphere, that is, the spherical or granular carbide is evenly distributed on the ferrite matrix, and the structure becomes spherical pearlite. The spheroidization temperature is generally slightly higher than the critical point of Ac1. If the temperature is too low, the required spheroidization time is too long. If the temperature is too high, the granular pearlite with different particle sizes will appear.
Why do alloy cast steel rolls undergo quenching heat treatment?
The quenching process of alloy cast steel roll is to heat it to the critical temperature (Acm or Ac1) above, and then to make it fully austenitized for a certain period of time, and then to cool it sharply to the bainite transition zone at a cooling rate greater than the critical cooling speed, so that the working layer of the roll body can obtain the bainite structure heat treatment process.
The purpose of quenching and heat treatment of alloy cast steel roll is to make the working layer of the roll be well organized, to give full play to the role of alloying elements in the roll, and to improve the hardness and wear resistance of the working layer of the roll body.
