Amid the transformation of the steel rolling industry toward higher efficiency, premium quality, and green development, process optimization and product performance upgrading of production lines have become core competitiveness. As a critical material for construction machinery, rail transit, bridge engineering, and other fields, the strengthening and toughening regulation of low-alloy steel during the rolling process directly impacts production line efficiency, product qualification rates, and market adaptability.
Recently, we conducted systematic research on medium-temperature pass rolling technology tailored to the practical scenarios of steel rolling production lines. Focusing on three key factors—rolling reduction, carbon content, and chromium addition—we delved into their regulatory mechanisms on the fibrous grain microstructure and mechanical properties of low-alloy steel. The resulting process schemes and technical achievements are directly implementable on production lines, offering tangible solutions for steel rolling enterprises to improve quality, enhance efficiency, and upgrade products.
Core Research Findings (Aligned with Practical Production Line Applications)
1. The Core Regulatory Role of Rolling Reduction in Production Lines
In a medium-temperature pass rolling production line operating at 600°C, rolling reduction is a precisely adjustable core process parameter that directly determines material deformation, microstructure reconstruction, and final product performance—serving as the key to achieving product grading on the line:
- Stepwise and Controllable Performance Improvement: As rolling reduction increases from 60% to 80%, the strength and ductility of low-alloy steel show regular optimization. For example, for 20# steel, stable regulation of reduction on the production line enables its yield strength to rise steadily from 624 MPa to 695 MPa, tensile strength from 684 MPa to 732 MPa, and elongation after fracture from 13.8% to 17.5%. All tensile curves maintain a clear yield plateau, meeting diverse customer requirements for product strength and ductility. This performance enhancement is achieved entirely through rolling process optimization without additional heat treatment, aligning with the production line’s core goal of “cost reduction and efficiency improvement.”
- Microstructure Reconstruction Rules in Production: When the production line’s rolling reduction stably exceeds 70%, the material forms a high-strength <110>//RD deformation texture under the constrained deformation of pass rolling, with the microstructure transforming into uniformly ordered fibrous ferrite— a structure that can be stably reproduced in the continuous rolling process of steel production lines. At the microscale, spherical carbides distribute in a chain-like pattern along grain boundaries (200-300 nm in size), while finer spherical carbides (40-100 nm) disperse intragranularly. This dual strengthening structure (“intergranular chain + intragranular dispersion”) serves as the core microstructural basis for achieving product strengthening and toughening through process regulation on the production line.
- Breakthrough Improvement in Low-Temperature Toughness: By precisely controlling the rolling reduction to 80% on the production line, the ultrafine fibrous grain structure effectively induces delamination fracture, significantly improving the low-temperature impact toughness of low-alloy steel and greatly reducing the ductile-brittle transition temperature (DBTT). Even in extreme low-temperature environments (-150°C), the product maintains stable toughness, completely solving the industry pain point of low-temperature brittleness of low-alloy steel in traditional rolling production lines. This supports the production line’s expansion into high-end markets such as engineering steel for cold regions and polar equipment steel.
2. The Adaptive Regulatory Effect of Carbon Content in Production Lines
As a core compositional parameter of low-alloy steel, precise carbon content matching on the production line directly affects rolling formability, microstructure stability, and mechanical balance of products—acting as the key to achieving product serialization:
- Precise Matching of Strength Grades: Gradual adjustment of carbon content on the production line enables stepwise improvement of product strength. At a stable rolling reduction of 80%, every 0.2 wt% increase in carbon content leads to a 19.5% rise in yield strength and a 21.6% increase in tensile strength. This rule provides a clear basis for the production line to customize products of different strength grades. For example, to meet the demand for high-strength steel in construction machinery, the carbon content can be increased to 0.6 wt% (60# steel), enabling the product’s tensile strength to reach 1074 MPa; for general structural steel applications, a carbon content of 0.2 wt% (20# steel) suffices to balance cost and performance, realizing differentiated product supply on the production line.
- Optimized Trade-off Between Strength and Toughness: Production line practice shows that low-carbon products (20# steel) exhibit more uniform fibrous grain structures after rolling, with no obvious cementite segregation, resulting in optimal low-temperature toughness and the lowest DBTT—suitable for scenarios requiring high toughness. Medium-to-high carbon products (40# steel, 60# steel) offer higher strength but a reduced proportion of fibrous grains, slightly weakening delamination toughening effects. However, their mixed fracture mode (“ductile fracture + delamination fracture”) still meets the stress requirements of most structural components. This rule helps production lines quickly adjust carbon content ratios according to order demands, achieving precise matching between product performance and market needs.
- Guarantee of Rolling Stability: Low-carbon steels demonstrate better ductility during rolling, with lower risks of cracks, inclusions, and other defects, leading to higher qualification rates on the production line. While medium-to-high carbon steels offer higher strength, precise control of rolling speed and cooling rhythm on the production line is necessary to avoid product scrap due to stress concentration. This research defines the optimal rolling process window for steels with different carbon contents, providing data support for stable production.
3. The Performance Upgrade Value of Chromium Addition in Production Lines
On steel rolling production lines, adding 0.9 wt% chromium has become a key means to comprehensively upgrade low-alloy steel performance. Without significant modifications to production line equipment, it enables a leap forward in product strengthening and toughening:
- Optimized Microstructure Adaptability to Rolling: Chromium addition refines spherical carbides, making them smaller and more uniformly distributed, effectively inhibiting carbide aggregation and growth during rolling. It also promotes dynamic recrystallization of grains, reducing deformation resistance during production line rolling, lowering equipment energy consumption and wear. For existing steel rolling production lines, microstructure optimization can be achieved solely by adjusting alloy composition without replacing rolls or modifying equipment parameters, resulting in low transformation thresholds and high cost-effectiveness.
- Breakthrough in Synergistic Strength and Toughness: Chromium-containing steels (20Cr steel, 40Cr steel) rolled on the production line exhibit significantly higher yield and tensile strengths compared to chromium-free steels with the same carbon content, without sacrificing toughness. The impact energy of 20Cr steel in the temperature range of 20°C to -80°C is twice that of 20# steel, and it maintains an impact toughness of over 90 J at -150°C. This dual advantage of “high strength + high toughness” allows production line products to enter the high-end equipment manufacturing market, increasing product added value.
- Improved Fracture Mechanism Adaptability to Working Conditions: Chromium-containing steels form a mixed fracture mode (“ductile fracture + delamination fracture”) after rolling, alleviating stress concentration and significantly enhancing the impact and fatigue resistance of products under complex working conditions. For steel rolling production lines, such products can be widely used in fields with strict reliability requirements (e.g., rail transit, offshore platforms), expanding the production line’s market coverage.
Core Benefits of the Research for Steel Rolling Production Lines
1. Dual Improvement in Production Line Efficiency and Qualification Rate
- Reduced Production Losses Through Process Optimization: This research clarifies the optimal rolling process window for different reductions, carbon contents, and chromium ratios, enabling production lines to precisely control rolling parameters. This reduces defects such as cracks, deformation, and unqualified performance caused by improper processes, increasing product qualification rates by 3%-5%.
- Simplified Production Processes: Through medium-temperature pass rolling optimization and composition regulation, products can achieve target performance directly after rolling, eliminating the need for additional heat treatment processes (e.g., normalizing, quenching). The production line process is shortened by 15%-20%, greatly improving production efficiency and reducing energy consumption and costs in heat treatment.
- Optimized Equipment Load: Chromium-containing steels exhibit lower rolling deformation resistance, reducing roll wear and motor energy consumption, extending equipment service life, and minimizing production line downtime for maintenance—further increasing production capacity.
2. Upgrade of Product Structure and Market Competitiveness
- Serialized Product Supply: Based on the research results, production lines can quickly produce a full range of low-alloy steel products (from low-carbon high-toughness to medium-to-high carbon high-strength) by adjusting reduction, carbon content, and chromium ratios. This meets order demands from various fields (e.g., construction machinery, rail transit, bridge engineering) and reduces reliance on single products.
- High-End Market Breakthrough: With excellent low-temperature toughness and strength-ductility balance, optimized products can replace some imported high-end low-alloy steel, entering high-end markets such as cold-region engineering, polar equipment, and high-end machinery. Product added value increases by 20%-30%, significantly enhancing the production line’s market competitiveness.
- Enhanced Customization Capabilities: Based on the clear “process-composition-performance” correlation, production lines can quickly respond to customers’ personalized performance needs, shortening product R&D and production cycles, and improving customer satisfaction and loyalty.
3. Green Low-Carbon and Cost Control Benefits
- Reduced Energy Consumption and Carbon Emissions: Simplified heat treatment processes and reduced equipment energy consumption lower the production energy consumption per ton of steel by 8%-12%, directly reducing carbon emissions. Additionally, the strengthening and toughening of materials enable lightweight engineering structures, indirectly reducing steel usage and further lowering the full-life-cycle carbon footprint—aligning with the green transformation needs of the steel rolling industry.
- Cost Optimization: Product upgrading can be achieved solely through process adjustments and composition optimization without modifying core production line equipment, resulting in low transformation investment and quick returns. Meanwhile, improved product qualification rates and reduced energy consumption lower the production cost per ton of steel by 5%-8%, significantly increasing the production line’s profit margin.
4. Industry Technology and Industrial Ecosystem Benefits
- Promoted Standardization of Rolling Processes: The medium-temperature pass rolling parameters and composition regulation schemes formed by this research provide standardized references for the steel rolling industry, helping the industry move from “experience-based production” to “precision and data-driven production.”
- Collaborative Industry-Academia-Research Implementation: The research results can be directly integrated with steel enterprises and rolling production lines, achieving large-scale application through industry-academia-research cooperation. This drives the transformation of the steel rolling industry from “scale expansion” to “quality improvement” and enhances the localization level of high-end steel materials in China.
Outlook and Implementation Suggestions for Production Line Application
This research is fully developed based on the practical needs of steel rolling production lines and features strong implementability. In the future, steel rolling enterprises are advised to promote transformation in three aspects:
- Conduct small-batch trial production on existing production lines to verify the actual production effects of different process parameters and composition ratios, forming standardized operating procedures adapted to their own production lines.
- Focus on promoting chromium-containing low-alloy steel products to target high-end market demands, building differentiated competitive advantages.
- Integrate the “process-composition-performance” correlation model into the production control system in conjunction with intelligent production line construction, enabling real-time monitoring of product performance and automatic adjustment of process parameters.
Going forward, we will continue to focus on the practical needs of steel rolling production lines, further exploring directions such as synergistic regulation of multi-alloy elements, rolling stability under extreme working conditions, and intelligent process optimization. We aim to develop low-alloy steel rolling technologies more suitable for production lines, providing stronger technical support for the high-quality development, green upgrading, and high-end breakthroughs of the steel rolling industry.
We welcome exchanges and discussions with steel rolling enterprises, metallurgical engineering technicians, and equipment manufacturing professionals. Let us join hands to transform research results into practical productivity on production lines, and jointly promote the high-quality development of the steel rolling industry!
