This segment tackles core pain points in hot-rolled reinforcing steel bar production via targeted process optimization and cutting-edge R&D, unlocking impactful technological breakthroughs:
I. Core Challenges
Hot-rolled reinforcing steel bar manufacturing faces critical pain points that drive technological R&D:
- High alloy costs: Excessive vanadium (V) in HRB500E and HRB600E leads to low resource utilization and unsustainable production.
- Poor quality stability: A 4.7% unqualified rate in national spot checks, with significant fluctuations in microstructure and mechanical properties, plus unstable seismic performance.
- Prominent surface defects: Traditional water quenching often causes red rust, resulting in customer returns or forced price reductions.
- Insufficient process adaptability: Water quenching is prone to martensite tempering and welding softening, with water temperature exerting a notable impact—making it hard to balance low cost and high surface quality.
- Weak homogenization control: Unreasonable alloy ratios and insignificant precipitation strengthening effects.
II. Key Technological Breakthroughs
(1) Graded Air-Mist Cooling Process & Equipment Technology
- Core Innovation: Replaced traditional water quenching’s centralized cooling and temperature recovery with “segmented graded cooling + segmented temperature recovery.” It achieved breakthroughs in efficient heat transfer, layout design, composite strengthening, and high surface quality control, earning inclusion in the MIIT Recommended Catalog of Energy-Saving Technologies and Equipment in the Industrial and Information Technology Field.
- Technical Advantages: Eliminated surface red rust—optimized scale structure (60-90% Fe₃O₄ + 40-10% FeO) is dense, uniform, and weather-resistant, with no large-area rusting after one month of outdoor exposure. Vanadium utilization rate increased by 20-40%, alloy content of HRB400E-HRB500E reduced by 0.02-0.04% V, and average yield strength boosted by 20-30MPa.
- Application Results: Multiple pilot lines and production demonstration lines have been established. Costs are cut by $3-9 per ton of steel, driving substantial increases in output value and saving over $28 million in alloy costs over three years. Relevant technologies have secured 3 scientific and technological achievements (internationally leading level) and 3 provincial/ministerial-level awards, including the first prize for Metallurgical Science and Technology Progress.
(2) Stable Nitrogen Enrichment & Precipitate Control Process
- Core Objective: Reduce microalloy addition and lower production costs without compromising mechanical properties, via precise nitrogen control and optimized nitrogen-vanadium (N/V) atomic ratio.
- Key Measures: Optimized converter tapping carbon control, aluminum-iron pre-deoxidation, vanadium-nitrogen alloy addition, and continuous casting processes, targeting nitrogen control at 140ppm. Defined optimal composition ratios for different strength grades: HRB500E (0.06-0.07% V + 0.012-0.016% N) and HRB600E (0.10-0.12% V + 0.020-0.026% N).
- Technical Achievements: Advanced the controlled precipitation theory for V-N reinforcing steel bars—identifying optimal V (C,N) precipitation temperatures (800-900℃ in the austenite region, 650-800℃ in the ferrite region). Precipitates are predominantly fine, uniform V (C,N) (10-50nm), delivering significant strengthening effects.
(3) Double Low-Temperature Rolling + Graded Cooling Process
- Process Characteristics: Integrated low-temperature heating rolling, low-temperature rough rolling, low-temperature finish rolling, and graded controlled cooling. Improved core-surface temperature difference and as-cast structure uniformity through cooling path optimization.
- Core Advantages: Dramatically reduced billet heating fuel consumption and metal loss, enhanced rolling material core compactness. Refined pearlite lamellar spacing and nodule size, boosting cross-sectional structure uniformity (hardness difference between core and edge <15HV).
- Supporting Technologies: Developed precise pearlite component control technology and built a process-structure-property model based on strengthening mechanisms—strength prediction accuracy reaches ≥85% for ±20MPa and ≥90% for ±30MPa.
(4) Development of Ultra-High-Strength & Ductile Reinforcing Steel Bars
- Product Series: Launched ultra-high-strength seismic and weather-resistant bars (HRB600E, HRB700E, HRB800E, YS700E) covering composition systems like VNCr, VNCrNb, and NiCrVN.
- Performance Indicators: HRB600E (yield strength 620-680MPa, tensile strength 790-860MPa, yield ratio ≥1.25); HRB700E+ (yield strength ≥700MPa, microstructure F+B+P) — meeting high-strength, high-ductility, and seismic requirements.
- Application Verification: Passed comprehensive tests (high-temperature mechanical properties, weather resistance, welding performance). Outperforms conventional bars in low-cycle fatigue life and cumulative absorbed energy, adapting to complex service environments.
III. Overall Value
Through collaborative innovation across multiple processes, this technical system systematically solves core industry pain points (high alloy costs, unstable quality, surface defects). It provides actionable cost-saving and efficiency-boosting solutions, while driving the upgrade of high-strength reinforcing steel bars toward higher grades, greater stability, and greener development.
