High Strength, Low Relaxation + Precision Craftsmanship: Prestressed Steel Strands Empower Super Engineering Construction
Driven by national major projects such as the Yarlung Zangbo River Super Hydropower Station and the Xiongshang High-Speed Railway, prestressed steel strands, as core load-bearing materials, have become indispensable key products in the infrastructure sector due to their excellent mechanical properties and stable reliability. The domestic market size of prestressed steel strands is expected to exceed 58 billion yuan in 2025, with a year-on-year growth of 8.5%. The refined upgrading of production processes and technological innovation are driving the product iteration towards "ultra-high strength, low relaxation, and long durability," providing solid support for more extreme engineering scenarios.
Core Features: Three Core Advantages Forge Engineering Necessity
The core competitiveness of prestressed steel strands stems from the triple empowerment of "strength + stability + adaptability," making them irreplaceable in high-stress and complex environments. Firstly, ultra-high mechanical strength is the core highlight. Mainstream products have a tensile strength ranging from 1860MPa to 2400MPa, and 2200MPa-class ultra-high strength products have been widely used in high-speed railway and hydropower projects. Compared with traditional products, their strength is increased by more than 40%, which can effectively reduce engineering material consumption and realize structural lightweighting. Secondly, excellent low relaxation performance: under long-term stress, the residual deformation is controlled within 2.5%, and the 1000-hour relaxation rate is ≤2.0% (for 1860MPa class), which can maintain the prestressing effect for a long time and ensure the long-term stability of bridges, tunnels and other structures. Thirdly, wide scenario adaptability: product specifications cover φ12.7mm-φ21.6mm, with structures mainly 1×7 and 1×19. Anti-corrosion treatments such as epoxy coating and hot-dip galvanizing can be customized according to engineering needs, adapting to bridges, wind power towers, LNG storage tanks and other different scenarios, while meeting the use requirements of extreme environments such as -40℃ alpine and coastal high salt spray.
Production Process: Full-Process Precision Control Creates High-Quality Products
The production of prestressed steel strands is a systematic project of "raw material selection - processing and forming - performance enhancement." Each process directly determines the mechanical properties and stability of the product. The core process is divided into four major links:
Step 1: Raw Material Preparation and Wire Drawing Strengthening
High-quality high-carbon steel wire rod (carbon content 0.75%-0.95%) is selected as the base material. First, strict surface treatment is carried out - removing oxide scale by pickling, degreasing by alkali washing, and neutralizing by water washing to ensure the steel base surface is clean and free of impurities. Then it enters the continuous wire drawing process, adopting the "multi-pass progressive diameter reduction + online heat treatment" technology to draw the steel wire to the preset diameter (such as φ5.0mm for 1×7 structure φ15.2mm steel strand). At the same time, sorbitic transformation is achieved by temperature control (450-550℃) to improve the tensile strength and toughness of the steel wire. A special lubricant is used during wire drawing to avoid surface scratches affecting subsequent performance.
Step 2: Stranding Forming to Ensure Structural Uniformity
Multiple drawn steel wires (such as 6 side wires + 1 central wire for 1×7 structure) are fed into the stranding machine, and stranded according to the preset lay length (usually 12-16 times the diameter of the steel strand) and lay direction (left lay or right lay) to form the steel strand blank. To reduce residual stress, some high-end products adopt the "pre-deformation process" - pre-bending the steel wire into an arc before stranding, making the stranded steel strand structure tighter, the stress distribution more uniform during loading, and avoiding the risk of local fracture.
Step 3: Stabilization Treatment to Achieve Low Relaxation Characteristics
This is the core process of prestressed steel strand production, realizing low relaxation performance through "continuous tempering + stress relief." The stranded steel strand is sent to a continuous stabilization furnace, held at 420-460℃ for 2-3 hours, and a certain prestress (about 20%-30% of the nominal tensile strength) is applied at the same time. Residual stress inside the steel wire is eliminated through thermomechanical treatment, and organizational stabilization is promoted. For ultra-high strength products (above 2200MPa), "zonal temperature control" technology is added to ensure the consistency of the through-length performance of the steel strand, and the relaxation rate is further reduced to ≤1.5%.
Step 4: Anti-Corrosion Treatment and Finished Product Inspection
According to the needs of application scenarios, the steel strand is subjected to anti-corrosion treatment: chrome-free passivation treatment is adopted for general scenarios to enhance corrosion resistance; for harsh environments (such as marine and chemical fields), epoxy coating (thickness ≥0.18mm) or hot-dip galvanizing treatment (zinc layer weight ≥300g/m²) is adopted to improve corrosion resistance. The finished product inspection link adopts "online + offline" dual inspection: online control of outer diameter tolerance (±0.02mm) through laser diameter gauge and eddy current detection of surface defects; offline sampling for tensile strength, relaxation rate, bending test, salt spray test, etc., to ensure the product meets the requirements of GB/T 5224-2014 national standard, and unqualified products are directly rejected.
Technological Upgrading: Simultaneous Advancement of Intelligence and Greenization
Currently, the prestressed steel strand industry is accelerating the transformation towards "precision and low carbonization." In terms of intelligence, leading enterprises have introduced AI closed-loop control systems to real-time adjust wire drawing speed, tempering temperature, and lay length parameters, controlling the product strength fluctuation range within ±30MPa and increasing the first-pass qualification rate to over 98%; machine vision inspection technology realizes millisecond-level identification of surface defects, and the inspection efficiency is 15 times higher than that of manual inspection. In terms of greenization, the penetration rate of cyanide-free passivation technology has reached 90%, replacing traditional chrome-containing processes and reducing environmental pollution; enterprises such as Hebei Iron and Steel Group and Baowu Group have reduced unit product energy consumption by 18% compared with 2020 through green power substitution and waste heat recovery systems, and carbon emission intensity has been reduced to below 0.7tCO₂/t, meeting the compliance requirements of the EU CBAM.
Market Application: Dual-Drive of Super Engineering and New Scenarios
The application scenarios of prestressed steel strands continue to expand, forming a dual-growth pattern of "traditional infrastructure + new scenarios." In the field of traditional infrastructure, transportation projects such as the Xiongshang High-Speed Railway and the Sichuan-Tibet Railway drive the demand for 1860MPa-2200MPa class products, and the Yarlung Zangbo River Hydropower Project alone needs to purchase more than 100,000 tons; in the field of new scenarios, the demand for offshore wind power tower anchoring, LNG low-temperature storage tank reinforcement, and UHV power grid tower support is growing rapidly. In 2025, the proportion of new scenario demand is expected to reach 35%, driving the sales of special prestressed steel strands such as epoxy coating and hot-dip galvanizing to increase by 28% year-on-year.
Industry experts said that in the future, prestressed steel strands will develop towards "higher strength (above 2500MPa, better corrosion resistance, and intelligent perception)." Intelligent prestressed steel strands integrated with optical fiber sensing technology will realize real-time stress monitoring, further improving engineering safety. Enterprises need to continue to focus on raw material formula optimization, precise process control, and green production transformation to seize the competitive high ground in the wave of super engineering construction.