As the requirements for rolling processes and rolled material quality continue to rise in modern rolling mills, enhancing the wear resistance, roughness retention, and accident resistance of rolls has become a crucial research topic. Semi-high-speed steel, known for its excellent high-temperature performance and secondary hardening phenomenon during tempering, is widely used in the production of high-speed steel rolls. This paper explores the forging process of semi-high-speed steel rolls, including chemical composition, ingot quality, heating standards, deformation process, and post-forging heat treatment, and presents a series of optimized forging processes, successfully producing semi-high-speed steel roll billets that meet technical specifications.
1. Introduction
The increasing demands of modern rolling mills for higher material quality and longer roll lifespans have led to a focus on improving roll durability, extending roll change intervals, and ensuring superior performance. Due to their excellent wear resistance, accident resistance, and secondary hardening phenomenon during high-temperature tempering, semi-high-speed steel rollshave become a key material in improving roll quality. This paper systematically investigates the forging process of semi-high-speed steel rolls, examining its application potential in modern rolling mills.
2. Forging Process Analysis of Semi-High-Speed Steel Rolls
2.1 Ingot Quality and Metallurgical Process
The quality of the ingot is critical in determining the overall quality of the roll billet. To meet the required chemical composition and ingot purity standards and reduce component segregation, we employ a double-refining method, which involves ladle refining and electroslag remelting (ESR). This metallurgical method effectively reduces gas content in the steel, minimizes non-metallic inclusions, and controls component segregation, providing a high-quality raw material foundation for subsequent forging.
2.2 Heating Standards
The temperature range for forging semi-high-speed steel is narrow, with high deformation resistance, making the material prone to cracking. Therefore, the heating process plays a critical role in ensuring quality. A combination of slow heating and high-temperature homogenization ensures uniform temperature distribution within the steel ingot. This prevents cracks during forging. The starting forging temperature is set between 1130°C and 1150°C. The final forging temperature is maintained between 850°C and 900°C to avoid excessive deformation temperatures that can cause cracks.
2.3 Forging Process
The forging process involves several key steps to ensure the billet meets technical requirements. We utilize a “split forging method,” which effectively fractures the eutectic carbides and improves the internal structure of the ingot. The choice of die shape is critical for semi-high-speed steel forging due to its high deformation resistance. We use one set of flat dies and two sets of V-shaped dies for the forging process. This combination ensures uniform deformation, preventing cracks that might arise from improper die selection. Additionally, a four-pass forging process is implemented, with the light-heavy-light forging sequence, to control plastic deformation and avoid crack formation.
2.4 Heat Treatment Process
The purpose of post-forging heat treatment is to eliminate residual stresses from the forging process, homogenize the microstructure, and improve carbide spheroidization. The heat treatment process consists of normalizing, spheroidizing annealing, and hydrogen expansion. These steps are essential for reducing the hardness of the forged material, improving its machinability, and preventing white spots.
3. Production Process Flow of Semi-High-Speed Steel Rolls
The production process for semi-high-speed steel rolls includes casting the electrode, electroslag remelting, forging, and post-forging heat treatment. After that, rough machining, flaw detection, and high/low magnification inspection are performed. Each step is crucial to meet the required specifications.
3.1 Flaw Detection and Inspection
Each roll billet undergoes ultrasonic testing to detect cracks, white spots, voids, and other defects. High magnification inspection ensures that the pearlite grade does not exceed level 3, and that eutectic carbide segregation is controlled to below level 2.
3.2 Quality Control
We adopt double-refining techniques along with strict forging and heat treatment processes. This ensures the steel is free of significant inclusions and segregation. As a result, it meets the high standards required for semi-high-speed steel rolls.Each stage of the production process is closely controlled, ensuring precision and consistency in the final product.
4. Conclusion
This study successfully produced two semi-high-speed steel roll billets that met all technical requirements, proving the feasibility of the proposed forging methods. The key findings include:
The use of the “split forging method” combined with one set of flat dies and two sets of V-shaped dies effectively fractured eutectic carbides and improved the internal quality of the billets.
The “light-heavy-light” forging technique minimized the risk of crack formation during the forging process, ensuring thorough deformation of the billet.
The heat treatment process includes normalizing, spheroidizing annealing, and hydrogen expansion. These steps significantly improve the roll’s wear resistance and accident resistance. They meet the demanding requirements of modern rolling mills.
With further optimization of production and quality control, semi-high-speed steel rolls can better meet the growing demands of rolling mills. This will help extend roll change intervals and improve overall service life.
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