Method for heat treatment of a repair welding of a blooming mill hot rolling roll

Abstract

The application belongs to the technical field of metal material heat treatment, and provides a kind of roughing mill hot rolling roller welding repair heat treatment method, comprising: roughing roller, remove damaged site oxide skin, repair roller contour;Resistance furnace preheating, remove water;Roller welding repair, adopt automatic welding repair machine to the damaged site of hole type and carry out welding repair;According to the annealing treatment of ladder temperature process;According to the requirements of rolling, the hole type of roller is finished;The quality, hardness, size of roller surface are detected accurately;The application optimizes roller preheating and annealing heat treatment process, solves the quality defects such as surface porosity, high hardness, network crack and local block in the repair process of traditional 60CrMnMo hot rolling roller;At the same time, the comprehensive mechanical properties of roller after welding repair are improved through process, the wear resistance, thermal fatigue resistance and spalling resistance are significantly enhanced, the service life of single repair is prolonged, and the maintenance cost is reduced.

Description

Technical Field

[0001] This invention belongs to the field of heat treatment technology for metallic materials, and relates to the welding repair and supporting heat treatment process of hot rolling rolls of large primary rolling mills in the metallurgical industry after use. Specifically, it is a method for welding repair heat treatment of hot rolling rolls of primary rolling mills. Background Technology

[0002] As a core component of the rolling mill, the hot rolling rolls of the primary rolling mill are prone to wear, cracks and spalling under high temperature, high pressure and thermal fatigue environment. Taking 60CrMnMo hot rolling rolls as an example, the common damage types and their proportions are as follows: roll surface wear accounts for 45%, roll pass deformation accounts for 20%, surface cracks account for 18%, local spalling accounts for 12%, and roll surface porosity accounts for 5%.

[0003] The traditional welding repair process involves preheating the roll (200℃ / 24 hours) before welding, followed by furnace cooling to room temperature and then annealing in an annealing furnace (550℃ / 4 hours). Although 60CrMnMo rolls possess high strength and hardenability, after repair using the traditional welding process, the roll only achieves a reduction in hardness on the surface, and the annealing depth is insufficient (welding depth 15-20mm). At the same time, the short preheating time prevents the complete removal of moisture inside the roll, leading to porosity at high temperatures. Uneven heating causes internal stress concentration, resulting in cracks and spalling. The process often faces technical bottlenecks such as poor wear resistance and short service life (less than half that of a new roll).

[0004] As companies develop high-end products such as low-density steel and nickel-based alloys, more stringent requirements are placed on the high-temperature strength and corrosion resistance of rolling mill rolls. Traditional repair processes can no longer meet the demands of high-end rolling and suffer from problems such as porosity and rapid crack propagation, severely restricting production efficiency and product quality. Summary of the Invention

[0005] The purpose of this invention is to provide a method for heat treatment of welding repair of hot rolling rolls in primary rolling mills. The aim is to solve the quality defects such as surface porosity, high hardness, network cracks and local spalling that exist in the traditional hot rolling roll repair process by optimizing the preheating and annealing heat treatment process parameters of the rolls.

[0006] The technical solution adopted by the present invention to achieve the above objectives is as follows: A method for heat treatment of weld repair of hot rolling rolls in a primary rolling mill, comprising: S1. Rough turning of the rolls to remove oxide scale from damaged areas and repair the roll shape; S2. Preheat the resistance furnace, hoist the rolls into the resistance furnace, and bake at a constant temperature of 200℃ for 48 hours; S3. Roll welding repair: Automatic welding repair machine is used to weld and repair the damaged parts of the roll. S4. Annealing treatment according to the stepped heating process: S5. Finish-machine the roll pass according to rolling requirements; S6. Perform precision testing on the quality, hardness, and dimensions of the roll surface.

[0007] Furthermore, the stepped heating process includes: S41, heat to 400℃ at 30℃ / h and hold for 4 hours; S42, heat to 550℃ at 30℃ / h and hold for 8 hours; S43, furnace cooling at 30℃ / h to <100℃ before tapping; S44. Allow to cool naturally to room temperature.

[0008] The beneficial effects of this invention are: The dual dehydration process, which combines preheating and heat preservation, completely removes moisture from the inside of the rolls, eliminates air holes on the roll surface, improves the surface quality of the rolls, and avoids stress concentration. By using two-stage heat preservation annealing, the annealing depth covers the weld repair layer (≥20mm), making the hardness distribution of the roller body, roller ring, and roller diameter uniform (240-260HB), with a deviation of ≤5HB, and basically eliminating network cracks and spalling phenomena.

[0009] The wear resistance and thermal fatigue resistance of the rolls are significantly improved, and the life of a single repair is increased by 80%, which can stably roll high-end steel products and reduce the overall production cost. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the annealing process temperature control of the present invention; Figure 2 This is a table showing the quality inspection results of the repaired rolls in this embodiment of the invention. Detailed Implementation

[0011] The method of the present invention will be further described below with reference to embodiments: Example

[0012] Taking five 60CrMnMo rolls (numbered 84#, 86#, 90#, 77#, and 91#) from the company's 1000mm roughing mill as an example, batch repairs were carried out, with a weld depth of 15-20mm. Specific implementation steps included: S1. Rough turning of the rolls: remove oxide scale from damaged areas, trim the roll shape, and ensure that the weld repair surface is flat and clean. S2. Preheat the resistance furnace, hoist the rolls into the resistance furnace, bake at a constant temperature of 200℃ for 48 hours, and cool to a suitable welding temperature after thorough dehydration.

[0013] S3. An automatic welding repair machine is used with 30Cr13 welding wire to repair the damaged hole area, and the welding parameters are strictly controlled to ensure the bonding strength.

[0014] S4. After welding repair, the welded parts are placed in a pit-type annealing furnace and annealed according to the following process: S41, heat to 400℃ at 30℃ / h and hold for 4 hours; S42, heat to 550℃ at 30℃ / h and hold for 8 hours; S43, furnace cooling at 30℃ / h to <100℃ before tapping; S44. Allow to cool naturally to room temperature.

[0015] S5. Precision machining: Precision machine the roll profile according to the rolling requirements to ensure the dimensional accuracy and surface roughness of the rolls.

[0016] S6. Inspection and Production Line: The surface quality, hardness, and dimensional accuracy of the rolls are inspected. The inspection results are shown in Table 2. Once no defects are found, the rolls can be put into production and their usage is tracked and recorded.

[0017] After repair, the surface of the five rolls is free of pores and cracks, with a hardness of 245-252HB and uniform distribution, and a roll size deviation of ≤0.03mm. After being put into operation, there are no issues with chipping or crack propagation. It can stably roll low-density steel and nickel-based alloys. The service life of a single repair is 88-92 days, with an average of 90 days, which is 80% faster than the traditional process, fully verifying the practicality and effectiveness of the process of this invention.

[0018] This invention addresses quality defects such as surface porosity, high hardness, network cracks, and localized spalling that exist in the traditional 60CrMnMo hot rolling roll repair process by optimizing the roll preheating and annealing heat treatment process.

[0019] Meanwhile, by improving the overall mechanical properties of the repaired rolls through process enhancement, the wear resistance (increased by 36.4%), thermal fatigue resistance (increased by 400%), and spalling resistance are significantly improved, extending the service life of a single repair (increased by 80%) and reducing maintenance costs. Furthermore, this method aims to enable the repaired rolls to meet the rolling requirements of high-end products such as low-density steel and nickel-based alloys, providing equipment assurance for the stable and efficient operation of the production line.

Claims

1. A method for heat treatment of weld repair of hot rolling rolls in a primary rolling mill, characterized in that: include: S1. Rough turning of the rolls to remove oxide scale from damaged areas and repair the roll shape; S2. Preheat the resistance furnace, hoist the rolls into the resistance furnace, and bake at a constant temperature of 200℃ for 48 hours; S3. Roll welding repair: Automatic welding repair machine is used to weld and repair the damaged parts of the roll. S4. Annealing is performed according to a stepped heating process; S5. Finish-machine the roll pass according to rolling requirements; S6. Perform precision testing on the quality, hardness, and dimensions of the roll surface.

2. The method for heat treatment of weld repair of hot rolling rolls in a primary rolling mill according to claim 1, characterized in that: The stepped heating process described in S4 includes: S41, heat to 400℃ at 30℃ / h and hold for 4 hours; S42, heat to 550℃ at 30℃ / h and hold for 8 hours; S43, furnace cooling at 30℃ / h to <100℃ before tapping; S44. Allow to cool naturally to room temperature.

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