A heating method for large rectangular billet 42CrMo used in engineering machinery
By employing a precisely designed heating method, the problems of oxidation and decarburization of large rectangular billets and loss of machining allowance were solved. This achieved 100% austenitization of the billet core and control of the decarburized layer, improving the adaptability of billet performance and reducing processing costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-03-24
- Publication Date
- 2026-06-26
AI Technical Summary
Traditional heating methods result in severe oxidation and decarburization of large rectangular billets, increasing processing costs and processing allowance losses, and making it difficult to meet the high requirements of core density and surface quality for engineering machinery components.
By employing precisely designed preheating, heating, and homogenization zone temperatures, times, and atmosphere parameters, the austenitization rate and grain size are controlled. Through a walking beam continuous heating furnace, 100% austenitization of the billet core is achieved, reducing the decarburized layer thickness and internal-external temperature difference, minimizing oxidation, and adapting to the performance requirements of engineering machinery components.
It achieves 100% austenitization of the billet core, with a decarburized layer thickness of ≤0.2mm, reducing machining allowance loss by 15%–20%, reducing energy consumption by 16%–19%, improving billet performance adaptability, and reducing processing costs.
Smart Images
Figure CN122279158A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of profiled tube rolling technology, and in particular to a heating method for a large rectangular billet 42CrMo for engineering machinery. Background Technology
[0002] 42CrMo steel, due to its high strength (Rm≥1080MPa) and good low-temperature impact toughness, has become the preferred material for core load-bearing components of engineering machinery. Its large rectangular billets have large cross-sectional dimensions, and engineering machinery components have much higher requirements for the billet's "core density, surface quality, and performance uniformity" than ordinary structural parts. Traditional heating methods have the following specific technical challenges: Excessive oxidation and decarburization increases processing costs: To ensure core heating, traditional processes require extended heating time (5-6 hours), resulting in an oxidation loss rate of 2.5%-3% on the billet surface and a decarburized layer thickness exceeding 0.5mm. Engineering machinery parts are mostly processed with "minimal cutting and near-net-shape forming," requiring additional cutting to remove the decarburized layer. This not only increases processing allowance loss (wasting 25-30 tons of steel per 10,000 tons of billet) but may also affect the surface hardness of the parts due to insufficient cutting depth. Summary of the Invention
[0003] This invention provides a heating method for large rectangular billets of 42CrMo used in engineering machinery. By precisely designing the temperature, time, and atmosphere parameters of the preheating section, heating section, and soaking section, the method achieves 100% austenitization of the billet core, no surface cracks after rolling, and a decarburized layer thickness of ≤0.2mm, while controlling the austenite grain size to level 5-8.
[0004] To achieve the above objectives, the present invention employs the following technical solution: A heating method for a large rectangular billet (42CrMo) used in engineering machinery includes the following steps: (1) Preheating section: The cold billet enters the preheating section, the preheating temperature is ≤720℃, and the preheating time is 1.5~1.8h; (2) Heating section: temperature 950~1100℃, heating period 3.0~3.5h; (3) Heat soaking section: temperature 1160~1240℃, heat soaking section time 2.0~2.2h.
[0005] Furthermore, the dimensions of the large rectangular 42CrMo billet are (380~500) mm. (400~600)mm.
[0006] Furthermore, the initial temperature of the cold billet entering the preheating section is ≤50℃.
[0007] Furthermore, the preheating section controls the austenitic phase transformation initiation temperature of the large rectangular billet 42CrMo to be below 720℃.
[0008] Furthermore, the heating section controls the grain size of the billet to be 5 to 8 levels, while maintaining a slight positive pressure of 20 to 30 Pa inside the furnace.
[0009] Furthermore, the heat preservation temperature of the heat soaking section is 360-440°C higher than the austenitic phase transformation end temperature of the large rectangular billet 42CrMo.
[0010] Furthermore, the air-coal ratio in the homogenization section is controlled at 0.60 to 0.65, reducing the oxygen supply by 6% to 9%.
[0011] Compared with the prior art, the beneficial effects of the present invention are: 1) Improve the adaptability of billet performance: After heating, the austenitization rate of the billet core is 100%, and the grain size is grade 5-8; 2) Reduced defect rate and cost: With a decarburized layer ≤0.2mm, the machining allowance can be reduced by 0.3~0.5mm, reducing subsequent cutting costs by 15%~20%; 3) Adapting to mass production needs: The total heating time has been optimized from the traditional 8-9 hours to 6.5-7.5 hours, and the unit energy consumption has been reduced to 430-490 m³ / t, a reduction of 16%-19% in energy consumption. Attached Figure Description
[0012] Figure 1 This is a metallographic image showing the thickness of the decarburized layer in an embodiment of the present invention.
[0013] Figure 2 This is a metallographic image of austenite grain size grade 6.0 in an embodiment of the present invention. Detailed Implementation
[0014] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings: This invention discloses a heating method for a large rectangular 42CrMo billet used in engineering machinery. Based on phase change temperature control adapted to the operating conditions of engineering machinery, the method is implemented in three stages within a walking beam continuous heating furnace. The large rectangular 42CrMo billet has a size of 390 mm. 510mm (thickness 390mm, width 510mm), the core parameters are designed to meet the performance requirements of engineering machinery components. The specific steps are as follows: (1) Preheating section: The cold billet enters the preheating section. The initial temperature of the cold billet entering the preheating section is ≤50℃, the preheating temperature is ≤720℃, and the preheating time is 1.5~1.8h. The furnace temperature is controlled below the austenitic phase transformation initiation temperature of the large rectangular billet 42CrMo of 720℃. By raising the temperature at a low speed, the temperature difference between the surface and the core of the billet is reduced to ≤40℃, eliminating the initial temperature stress. At the same time, it avoids entering the phase transformation zone in advance, which leads to "local phase transformation stress", laying the foundation for subsequent uniform phase transformation.
[0015] (2) Heating section: Temperature 950~1100℃, heating section time 3.0~3.5h; ensure that the surface of the billet and the core enter the phase transformation zone synchronously, avoid the internal stress caused by asynchronous phase transformation, and reduce the risk of corner cracking; accelerate the uniform growth of austenite grains in the core, control the grain size at level 5~8, adapt to the fatigue resistance requirements of engineering machinery, and at the same time maintain a micro-positive pressure of 20~30Pa in the furnace to reduce local oxidation caused by cold air intake.
[0016] (3) Soaking section: temperature 1160~1240℃, soaking section time 2.0~2.2h; the heat preservation temperature is higher than the austenitic phase transformation end temperature of the large rectangular billet 42CrMo by 360~440℃, ensuring that the core temperature reaches 1170~1190℃ and the internal and external temperature difference is ≤30℃; at the same time, the air-coal ratio is adjusted to 0.60~0.65, reducing the oxygen supply by 6%~9%, and inhibiting surface oxidation and decarburization reaction.
[0017] To meet the fatigue resistance requirements of engineering machinery components, the austenite grain size is controlled within the range of 5 to 8 to avoid fatigue performance degradation caused by coarse grains. Size and performance synergistic heat homogenization design: Combining the thermal conductivity characteristics of 390×510mm billet, the preheating time is extended (1.5~2h, traditionally 1h) and the heat homogenization temperature is optimized (1160~1240℃) to ensure 100% austenitization of the core. At the same time, through micro-positive pressure and air-coal ratio control of 0.60~0.65, the iron oxide scale thickness is controlled to ≤2mm and the decarburized layer thickness is controlled to ≤0.2mm, which is suitable for the "less cutting" processing requirements of engineering machinery.
[0018] The following embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments. Unless otherwise specified, the methods used in the following embodiments are conventional methods.
[0019] Example: 1. Implementation conditions A dual-regenerative walking beam continuous heating furnace is adopted, with a furnace length of 36.5m and effective zones: a preheating zone of 12.5m, a heating zone of 12m, and a soaking zone of 12m. The billet to be heated is a 42CrMo continuous casting billet with a diameter of 390×510×5800mm and a chemical composition of: C: 0.39%~0.45%, Si: 0.19%~0.25%, Mn: 0.63%~0.74%, Cr: 1.03%~1.11%, Mo: 0.17%~0.20%, with the remainder being Fe and impurities.
[0020] 2. Implementation Steps Preheating stage: Load the cold billet at 28℃ into the preheating section, set the furnace temperature to 700℃, and hold for 1.8 hours; Heating stage: The billet is moved into the heating section, the furnace temperature is set to 1050℃, and it is held for 3.2 hours; the furnace pressure is controlled at 20Pa slightly positive pressure. Soaking stage: Move to the soaking zone, set the furnace temperature to 1210℃, adjust the air-coal ratio, reduce oxygen by 8%, and hold for 2 hours; Test results: surface temperature 1221℃, core temperature 1195℃, iron oxide scale thickness 1.5mm, decarburized layer thickness 0.11~0.12mm, etc. Figure 1 As shown, the austenite grain size is 6.0 grade, as... Figure 2 As shown.
[0021] 3. Implementation Results The billet was subsequently rolled into a φ120mm forging. After testing, the product surface was free of cracks, the core hardness of the forging was 185-195HBW (uniformity deviation ≤6%), and the tensile strength Rm=1320MPa, which met the requirements for forging.
Claims
1. A heating method for a large rectangular billet (42CrMo) for engineering machinery, characterized in that, Includes the following steps: (1) Preheating section: The cold billet enters the preheating section, the preheating temperature is ≤720℃, and the preheating time is 1.5~1.8h; (2) Heating section: temperature 950~1100℃, heating period 3.0~3.5h; (3) Heat soaking section: temperature 1160~1240℃, heat soaking section time 2.0~2.2h.
2. The heating method for a large rectangular billet 42CrMo for engineering machinery according to claim 1, characterized in that, The dimensions of the large rectangular 42CrMo billet are (380~500) mm. (400~600)mm.
3. The heating method for a large rectangular billet 42CrMo for engineering machinery according to claim 1, characterized in that, The initial temperature of the cold billet entering the preheating section is ≤50℃.
4. The heating method for a large rectangular billet 42CrMo for engineering machinery according to claim 1, characterized in that, The preheating section controls the austenitic phase transformation initiation temperature of the large rectangular billet 42CrMo to be below 720℃.
5. The heating method for a large rectangular billet 42CrMo for engineering machinery according to claim 1, characterized in that, The heating section controls the grain size of the billet to be 5-8 grades, while maintaining a slight positive pressure of 20-30 Pa inside the furnace.
6. The heating method for a large rectangular billet 42CrMo for engineering machinery according to claim 1, characterized in that, The heat preservation temperature of the heat soaking section is 360-440°C higher than the austenitic phase transformation end temperature of the large rectangular billet 42CrMo.
7. The heating method for a large rectangular billet 42CrMo for engineering machinery according to claim 1, characterized in that, The air-to-coal ratio in the homogenization zone is controlled at 0.60–0.65, reducing oxygen intake by 6%–9%.