Steel wire: an indispensable metal basic material in many fields​

In modern industrial systems and daily life scenarios, steel wire, as a specially processed metal wire, has become a key material for connecting basic manufacturing and high-end applications due to its excellent mechanical properties and flexible form adaptability.From the leads of tiny electronic components to the load-bearing steel cables of large-scale projects, the figure of steel wires runs through all walks of life, and its technological iteration and quality improvement have always kept up with the needs of industrial development.​
1. Definition and core classification of steel wire​
Steel wire is a round and special-shaped (such as square and hexagonal) wire made of high-quality steel as raw material and processed through multiple processes such as drawing, heat treatment, and surface treatment. The diameter is usually between 0.1mm and 20mm. The diameter of steel wire for some special scenes can break through this range.According to different classification standards, steel wires can be divided into various types to meet differentiated needs.：​
1. Classification by material and performance​
Low-carbon steel wire: the carbon content is less than 0.25%, it has good plasticity and weldability, and moderate strength. It is mainly used for the preparation of barbed wire, nails, hooks and other daily necessities and lightly stressed components, such as lashing steel wires for construction and protective mesh skeletons for agriculture.​
Medium carbon steel wire: the carbon content is between 0.25%-0.6%, the strength and hardness are significantly improved, and the toughness can be improved after proper heat treatment. It is commonly used in industrial components such as automobile shock absorption springs, mechanical transmission chains, and ordinary bolts.​
High-carbon steel wire: the carbon content exceeds 0.6%, the hardness is extremely high after quenching and tempering, and the wear resistance is excellent. It is mainly used in the production of high-strength and high-loss products such as wire ropes, steel strands, cutting saw blades, bearing balls, etc. It is indispensable in heavy equipment such as mines, bridges, and elevators.​
Special alloy steel wire: Adding chromium, nickel, molybdenum, titanium and other alloying elements to the steel can give the steel wire special properties such as corrosion resistance, high temperature resistance, and fatigue resistance. For example, stainless steel wire is used in medical equipment and food processing equipment, and heat-resistant steel wire is used in aviation engine blades and industrial kiln heating elements.​
2. Classification by surface treatment process​
Glossy steel wire: There is no additional coating on the surface to maintain the metallic luster of the steel itself. It is mainly used in scenes where there are no special protection requirements for the surface, such as ordinary iron wire and steel wire for temporary fixation.​
Galvanized steel wire: A zinc layer is formed on the surface of the steel wire by hot-dip zinc or electroplating zinc process, which can effectively isolate air and moisture and greatly improve corrosion resistance. It is widely used in outdoor fences, power transmission lines, communication cable armor and other products exposed to harsh environments for a long time.​
Plastic-coated steel wire: The surface of the steel wire is coated with polyethylene, polyvinyl chloride and other plastic coatings, which combine the strength of steel with the weather resistance and insulation of plastic. It is commonly used in gardening brackets, internal wiring of household appliances, and protective nets for children's amusement facilities.​
Phosphated steel wire: The surface is phosphated to form a phosphate film, which can enhance the binding force with the subsequent coating, and at the same time has a certain anti-rust ability. It is mainly used as a semi-finished product for subsequent processing, such as the pretreatment process of spring steel wire and radial steel wire for tires.​
2. The core production process of steel wire​
The production of steel wire is a process of “reducing diameter and increasing quality”. It needs to be controlled through multiple precision processes to ensure the dimensional accuracy and performance stability of the final product. The core process mainly includes the following links：​
1. Raw material pretreatment​
The high-quality hot-rolled wire rod (the original raw material of the steel wire) is selected as the substrate, and the surface is cleaned first, and the iron oxide and oil stains on the surface of the wire rod are removed by pickling to avoid impurities in subsequent processing affecting the quality of the steel wire; then phosphating or borating treatment is carried out to form a lubricating film on the surface to reduce friction for the drawing process.​
2. Drawing processing​
Drawing is the key process of steel wire forming. The pretreated wire rod is passed through the tapered hole on the mold and forced through the mold under the action of traction, so that the steel cross-section is reduced, the length is elongated, and the target diameter is gradually reached.According to the final size and performance requirements of the steel wire, drawing can be divided into single drawing and multiple continuous drawing, and some high-demand products need to be interspersed with intermediate annealing treatment during the drawing process-by heating to a specific temperature and keeping warm, the stress inside the steel is eliminated, the plasticity is restored, and the steel wire is avoided from breaking during subsequent drawing.​
3. Heat treatment strengthening​
According to the material and purpose of the steel wire, targeted heat treatment is required: low-carbon steel wire usually only needs to be annealed at low temperature to eliminate drawing stress; medium and high-carbon steel wire needs to be quenched (heated to austenitic temperature and quickly cooled) to increase hardness, and then tempered (low temperature heating and heat preservation) to adjust toughness to achieve “hard but not brittle” performance balance; special alloy steel wire needs to adopt high-precision processes such as vacuum heat treatment and controlled atmosphere heat treatment to ensure uniform distribution of alloying elements and avoid surface oxidation.​
4. Surface treatment and finished product inspection​
After completing the size and performance processing, surface treatments such as galvanized and plastic coating are carried out according to demand; finally, the finished product inspection link is entered, the dimensional accuracy is tested by a diameter measuring instrument, the tensile strength and elongation are tested by a tensile testing machine, and the internal organization is observed with the help of a metallographic microscope. Some key products also need to be tested for corrosion resistance (such as salt spray test) and fatigue life test to ensure that each batch of steel wire meets national standards or industry specifications.​
3. Typical application scenarios of steel wire​
With its diverse properties and forms, steel wire plays an irreplaceable role in construction, industry, transportation, medical and other fields. The following are some typical applications.：​
1. Construction and infrastructure​
Steel wire for steel bar binding: Low-carbon galvanized steel wire is used to fix the steel bar skeleton in construction. It has the characteristics of easy operation and firm binding, which can improve the integrity and stability of the concrete structure.​
Steel strand: It is made of a number of high-carbon steel wires twisted together, with extremely high strength. It is widely used in bridge prestressed tensioning, high-rise building foundation reinforcement, and large storage tank top cover support. For example, the core of the cable for a long-span cable-stayed bridge is a high-strength steel strand.​
Steel wire for protective nets: A protective net woven from plastic-coated or galvanized steel wire, which is used for highway isolation, protection along railway lines, and safety barriers around foundation pits. It has both impact resistance and weather resistance.​
2. Industrial manufacturing field​
Mechanical transmission and shock absorption: springs and gears made of medium-carbon steel wire, chains and wire ropes made of high-carbon steel wire are the core transmission components of machine tools, cranes, automobiles and other equipment to ensure stable and efficient power transmission.​
Electronics and home appliances: fine-diameter low-carbon steel wire or stainless steel wire, used to make motor stator windings, transformer coil leads, and support skeletons inside household appliances, which need to meet the requirements of high precision and low loss.​
Metal product processing: Steel wire can be further processed into nails, rivets, fasteners, wire brushes and other basic metal products, covering many scenes such as mechanical maintenance, home decoration, and daily necessities.​
3. Transportation and Logistics​
Automobile industry: automobile suspension springs and valve springs made of high-carbon steel wire, and exhaust pipe fastening belts made of stainless steel wire, need to withstand high-frequency vibration and high-temperature environments, and have extremely high requirements for fatigue life and corrosion resistance.​
Logistics and transportation: Wire rope (made of multiple strands of steel wire twisted together) is used in the lifting mechanism of cranes and forklifts, as well as the traction system of freight elevators. It needs to have the characteristics of high strength, wear resistance and impact resistance to ensure the safety of cargo transportation.​
4. Medical and livelihood fields​
Medical equipment: stainless steel wire or titanium alloy composite steel wire, used to make surgical sutures, orthopedic fixation nails, dental correction wire, must meet the requirements of biocompatibility, corrosion resistance, and high precision to ensure medical safety.​
Agriculture and horticulture: greenhouse skeletons made of galvanized steel wire, orchard fences, and plant climbing brackets made of plastic-coated steel wire can adapt to outdoor humid and pest-prone environments, with long service life and low maintenance costs.​
Daily life: steel balls and wire brushes are used for cleaning, nets woven with thin steel wire are used for filtering, and steel wire hangers are used to dry clothes, which have become practical tools that can be seen everywhere in people's daily lives.​
Fourth, the quality control and purchase points of steel wire​
1. Core indicators of quality control​
Dimensional accuracy: Diameter deviation and ovality must meet the requirements of the standard, especially in precision application scenarios (such as electronic leads and medical steel wires), and the dimensional error is too large to affect product assembly and performance.​
Mechanical properties: tensile strength, yield strength, elongation, and hardness need to match the application requirements. For example, steel ropes for load-bearing need high tensile strength, and steel wires for springs need high elastic limits.​
Surface quality: no cracks, scratches, oxide skin, rust and other defects, the surface coating (galvanized, plastic coated) must be uniform and have strong adhesion to avoid corrosion caused by the coating falling off during use.​
Internal quality: There are no internal defects such as pores, inclusions, segregation, etc., which can be detected by ultrasonic flaw detection, metallographic analysis, etc. to ensure that the internal organization of the steel wire is uniform and dense.​
2. Purchase points​
Clarify application requirements: according to the use scenario (such as outdoor / indoor, force size, environmental corrosion degree), choose the appropriate material (low carbon steel / high carbon steel / stainless steel) and surface treatment process (galvanized / plastic coated / glossy) steel wire to avoid excess or insufficient performance.​
Check qualifications and standards: choose products that meet national standards (such as GB/T 3428 "Steel Wire Classification and Terminology", GB/T 1179 "Round Wire Concentric Twisted Overhead Wire") or industry standards, and require suppliers to provide quality inspection reports to ensure reliable product quality.​
Pay attention to the appearance and feel: the surface of the high-quality steel wire is smooth, the color is uniform, and there are no obvious defects; the toughness is moderate when bending (according to the material characteristics), there is no brittleness or cracks, and the purchase of inferior products with rough surfaces and easy to rust is avoided.​
5. The development trend of the steel wire industry​
With the continuous progress of industrial technology, the steel wire industry is developing in the direction of “high performance, refinement and greening”：​
High performance: Through the optimization of alloy composition and the upgrading of heat treatment technology (such as low-temperature nitriding and isothermal quenching), the strength, toughness and corrosion resistance of steel wire are improved, and higher-strength steel strands for bridges and longer-life automobile spring steel wires are developed.​
Refinement: For high-end fields such as electronics and medical care, ultra-fine steel wires with smaller diameters (such as micrometers) and higher dimensional accuracy are developed, while mass production of steel wires with special-shaped cross-sections (such as flat and triangular) is realized to meet special structural design needs.​
Greening: promote acid-free drawing processes (such as physical rust removal) and environmentally friendly surface treatment technologies (such as chromium-free passivation) to reduce pollutant emissions in the production process; at the same time, develop recyclable and degradable coating materials to enhance the environmental friendliness of steel wire products.​
As a basic metal material, the technological development and industrial upgrading of steel wire will continue to provide better quality and more efficient material solutions for the modern industrial system and people's livelihood, and become an important support for promoting the high-quality development of various industries.​