HOT LINE: +86-510-80628100At present, the materials of forged steel cold rolling rolls in China are mainly Cr2, Cr3, Cr5, as well as semi high speed steel, high-speed steel, etc. Among them, the technology of Cr2 and Cr3 forged steel cold rolling work rolls is relatively mature, while Cr5 forged steel cold rolling rolls have higher hardness and deeper quenching layer depth. Due to the significant increase in alloy composition, the heat treatment process of semi high speed steel and high-speed steel cold rolling rolls has undergone significant changes, with high hardness, high wear resistance, heat shock resistance and accident resistance.
The heat treatment process of forged steel cold rolling rolls mainly includes post forging heat treatment, overall quenching and tempering treatment of the roll, deep quenching and tempering treatment of the roll body. Some cold rolling work rolls also require deep cryogenic treatment to increase the depth of the quenching layer and reduce the residual austenite content. Among them, post forging heat treatment, as a heat treatment process for roll forging, includes forms such as normalizing and spheroidizing annealing, mainly used to improve the matrix structure, eliminate stress, and improve machining and cutting performance. The overall quenching and tempering treatment of the rolling mill includes quenching and high-temperature tempering. After quenching and tempering treatment, the rolling mill substrate has good strength, toughness, plasticity, and mechanical processing properties. Deep quenching of the roll body is the most important heat treatment process that affects the performance of the roll, including roll preheating, continuous quenching of the roll body, cold treatment, and tempering treatment.
Preheating treatment is required for forged steel cold rolling rolls after post forging heat treatment and rough machining, in preparation for continuous quenching heating. The preheating process temperature is generally 210 ℃ -420 ℃, and the preheating temperature for Cr2, Cr3, and Cr5 rolling rolls is basically the same. Due to the high quenching temperature, the preheating temperature needs to be correspondingly increased for semi high speed steel and high-speed steel. Depending on the size specifications of the rolling rolls, the insulation time varies from 20 to 30 hours. Adequate preheating can enhance the quenching effect of the rolling mill and reduce internal stress. Controlling the preheating temperature at a lower level can effectively reduce stress, but it weakens the heat storage capacity for quenching and makes quenching heating more difficult. Therefore, setting an appropriate preheating process temperature can have a positive impact on continuous quenching while ensuring controllable stress and minimal subsequent effects.
Continuous quenching of the roll body is a heat treatment process that involves continuous induction heating on the surface of the roll body using an inductor, and continuous cooling with a water medium. According to different materials such as Cr2, Cr3, Cr5, as well as semi high speed steel and high-speed steel, the heating temperature ranges from 860 ℃ to 1120 ℃. The appropriate quenching temperature can fully austenitize the surface structure of the rolling mill body. Heating at a too low temperature can lead to the structure not being austenitized or insufficiently austenitized, resulting in uneven structure and poor performance after quenching. Heating at a too high temperature can cause the structure to become coarse, resulting in a significant decrease in the strength, plasticity, and toughness of the matrix, and even overheating, which seriously affects the final performance of the rolling mill.
Quenching and cooling to around 100 ℃ before cold treatment, with a cooling temperature of -80 ℃ to -160 ℃ and holding for 8 hours, can further transform residual austenite into martensitic structure. Reducing residual austenite can make the structure more uniform and stable, while improving the hardness of the roller body. The material of forged steel cold rolling rolls ranges from Cr2, Cr3, Cr5 to high-speed steel. With the gradual increase of chromium alloy content, the hardness, wear resistance, and quenching depth continue to increase, and the surface hardness of the roll body can reach 95HSD-103HSD.
After quenching and cold treatment of the roller body, tempering treatment is required to stabilize the structure, size, timely eliminate internal stress, avoid deformation and cracking, and further homogenize the structure and adjust the hardness performance indicators. The tempering temperature of cold rolling rolls made of Cr2, Cr3, and Cr5 materials is generally between 90 ℃ and 160 ℃, while the tempering temperature of cold rolling rolls made of high-speed steel materials can reach up to 450 ℃ to 540 ℃. The high-speed steel forging cold rolling mill adopts a heat treatment process of two tempering steps followed by a deep cold treatment. The second tempering process takes twice the time of the first tempering step, and the two tempering temperatures are the same. Conducting a tempering treatment before the cold treatment can effectively control the residual stress after quenching and avoid fracture of the rolling mill during cold treatment due to high comprehensive stress.
