Preheat treatment method for large-size forged steel supporting roller

Abstract

The invention discloses a preheat treatment method for a large-size forged steel supporting roller. The after-forging heat treatment process is technically characterized in that high-temperature normalizing and high-temperature tempering processes are adopted under the normalizing heating temperature of 800 to 970 DEG C and the heating rate of less than 90 DEG C / h; after the temperature is averaged, the heat insulation time is determined according to the diameter of a roller body of the supporting roller; the heat insulation time for the supporting roller with the diameter of Phi 1,000-1,700 mm is 10 to 40 hours; after the roller is cooled in air, high-temperature tempering is carried out under the tempering temperature of 500 to 750 DEG C and the heating rate of less than 60 DEG C / h; after the temperature is averaged, the heat insulation time is 40 to 90 hours. A hardening and tempering process is as follows: an oil quenching and high-temperature tempering process is adopted; the preheat temperature for the supporting roller is 550 to 700 DEG C and is insulated for 5 to 20 hours; then the supporting roller is heated to the quenching temperature of 800 to 970 DEG C under the heating rate of 80 DEG C / h; after the heat is insulated for certain time, oil quenching is carried out for cooling time of 100 to 400 min; once oil is discharged, tempering is carried out immediately under the tempering temperature of 500 to 750 DEG C and the heating rate of less than 50 DEG C / h; after being averaged, the temperature is insulated for 20 to 90 hours.

Description

technical field [0001] The invention relates to a preparatory heat treatment method for a large forged steel support roll, belonging to the technical field of large forging heat treatment technology. Background technique [0002] The large forged steel back-up roll is an important core part of the strip mill, which plays the role of supporting and stabilizing the work roll. Because it works under high load for a long time, it has high mechanical performance requirements: the working layer has high wear resistance and fatigue resistance Uniformity and uniformity of hardness; the core requires good strength and toughness. As the demand for modern steel rolling continues to increase, the size and specifications of forged steel backup rolls have also increased, and some diameters have reached one and a half meters or even more than two meters. However, the problems of brittle fracture and premature failure of backup rolls have become increasingly prominent, and Due to improper ...

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Problems solved by technology

At present, the main materials of back-up rolls commonly used in rolling mills are 50Cr3MoV, 70Cr3NiMo, 45Cr4NiMoV, 50Cr5NiMoV, etc. However, with the increase of alloying elements, the types of carbides and the dissolution temperature of different materials vary widely, and it is necessary to obtain an excellent structure at the center of the back-up roll distribution, the process of heat treatment is more difficult to formulate

[0004] At present, there are deficiencies in the preparatory heat treatment process of backup rolls: the purpose of spheroidizing annealing in post-forging heat treatment is to reduce hardness, improve cutting performance, and prepare for spheroidized pearlite obtained by quenching and tempering treatment; and the quenching temperature range of quenching and tempering treatment Too broad, too high quenching and tempering temperature and long-term heat preservation will easily lead to the dissolution of all carbides in the core, and the austenite composition is relatively uniform. After tempering and high-temperature quenching, the effect has been eliminated, and the spheroidization effect has not been achieved, and the process is lengthy, time-consuming and labor-intensive, and leads to a sharp decline in impact toughness, increasing the risk of backup roll fracture

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