Production Process and Optimization of 0.04mm Ultra-Fine Stainless Steel Wires (Chapter Ⅰ)
Stainless steel ultra-fine wire production is a new type technique that integrates with metallurgy, model manufacture, chemical process etc. techniques, which is the deep extension of common steel wire drawing technique. This article sets the uni-drawing ultra-fine stainless steel wire production technique as the research aim.
Production Process and Optimization of 0.04mm Ultra-Fine Stainless Steel Wires (Chapter one)
ABSTRACT
Stainless steel ultra-fine wire production is a new type technique that integrates with metallurgy, model manufacture, chemical process etc. techniques, which is the deep extension of common steel wire drawing technique. This article sets the uni-drawing ultra-fine stainless steel wire production technique as the research aim. Starting to analyze from the wire drawing performance of different production technique processes, and combining metallographic analysis, wire drawing mechanics performance test, SEM micro-structure observation, XRD analysis etc. different experiment research methods. Specifically researches the differences of product's characteristics and the influence to the wire drawing performance. During the period of wire drawing, it occurs the crystal lattice distortion due to the big uneven deformation, and the crystal grain broken phenomenon is very serious. With the wire drawing process, the crystal grain along the pulling direction is pulled into fiber and appeared like a silk structure, its macro appearance is with the reduced of fine wire's diameter, the tensile strength is bigger and bigger, whereas the elongation is greatly decreased, With the super large of deformation, the ultra-fine austenitic stainless steel fine wire appears more and more strong magnetism, The magnetism disappears after annealing. Corresponding to the different hot processing, there is large difference between the before and after of annealing fine wire mechanics performance and metallographic structure.
Through theoretical analysis and great amount of direct actual productions, it is found that the wire broken rate is obviously different while pulling the same specification's fine wire in the case of annealing and non-annealing. The easiest occurrence of wire broken is at the beginning of wire drawing; the wire broken rate is higher and higher with the increase of wire drawing speed at the same process condition and same specification, The model consumption of high speed pulling is lower than the low speed one, the specification of model-match is the most key factor of affecting the smooth of wire drawing, the size of model input angle has great influence on the wire drawing broken rate.
This thesis is finally made a set of actual production criterion that is suitable forthe actual production condition of enterprise. The parameter setting, lubrication condition, annealing parameter, model selection, model-match specification of wiredrawing machine after optimization may provide theoretical and practical guide line for the future ultra-fine wire production.
Key Words: micro-structure, mechanics performance, model consumption; technique optimization
Chapter 1 Introduction
1.1 Overview
Stainless steel is one of the important inventions of the 20th century. After nearly a century of continuous development and innovation, there are now more than 300 different grades of stainless steel. Stainless steel ultra fine wires are among its significant varieties. With the advancement of modern industrial production technology, especially the increasingly demanding requirements of modern petrochemical technology on stainless steel filter screens in terms of precision and high mesh numbers, for instance, the single filament diameter required for woven screens above 500 mesh has reached as fine as Ф0.025mm, Ф0.020mm, down to Ф0.018mm, and other ultra-fine stainless steel ultra fine wires, depending on the different opening areas. The development of special textile industries has also driven the production of stainless steel ultra fine wires towards dimensions that are precise, surfaces that are smooth, high strength, good ductility, strong corrosion resistance, and stable performance.
The production of stainless steel ultra fine wires (or stainless steel fibers) involves knowledge from multiple disciplines and industries such as metallurgy, fiber science, textile engineering, mold manufacturing, and chemical processes. It represents an important new frontier in the development of materials science.
Currently, there is no strict differentiation in concept between stainless steel fibers and stainless steel ultra fine wires both domestically and internationally. In the production market, it is generally customary to refer to filaments produced by single wire drawing processes with diameters ranging from 0.025mm to Ф0.1mm and lengths ranging from tens of meters to hundreds of kilometers as microfilaments. The category of stainless steel fibers includes not only long filaments but also short filaments ranging from a few centimeters to several meters, produced using processes such as bundle drawing, melting and spinning, and cutting. In this paper, the term "ultra-fine stainless steel microfilaments" specifically refers to long filaments with diameters ranging from Ф0.03mm to Ф0.05mm produced by single wire drawing methods.
Currently, the mainstream products in the ultra fine wire production market are various specifications with diameters ranging from Ф0.035mm to Ф0.025mm. There are also a few ultra-fine wires below the 0.02mm specification available for sale. However, these products are either of poor quality or produced in small quantities by manufacturers at high cost to enhance their corporate image and brand effect. High-quality, profitable ultra-fine stainless steel ultra fine wires below the Ф0.02mm specification have not yet been mass-produced domestically. In terms of both quantity and quality, domestic production of stainless steel ultra-fine wires lags behind the development of ultra-fine wire products, especially in the production of ultra-fine ultra fine wires with diameters below Ф0.02mm. According to literature, the domestic annual demand for high-quality stainless steel ultra fine wires is no less than 9,000 tons, while current domestic production is only over 2,000 tons, with ultra-fine stainless steel ultra fine wires being completely dependent on imports.
Therefore, by researching different preparation processes such as various heat treatment processes, different die parameters, different drawing speeds, different lubrication conditions, and different raw materials, and analyzing their effects on wire breakage rate, die wear, and product performance during the wire drawing process, it has become imperative for domestic stainless steel ultra-fine wire production enterprises to develop and optimize ultra-fine stainless steel ultra fine wire production processes with independent intellectual property rights. This will further improve product quality and application performance and expand the application fields of the products.
1.2 Applications of Stainless Steel Ultra fine wires
The unique preparation process of stainless steel ultra fine wires has resulted in significant changes in their product structure and performance in many aspects, including conductivity, thermal conductivity, corrosion resistance, high wear resistance, surface stability, high strength and ductility, excellent radiation protection, superior shielding against electromagnetic interference, and good sound absorption effects . These properties make stainless steel ultra fine wires widely used in modern industries and civilian sectors such as petrochemical, textile, metallurgy, automotive manufacturing, construction, pharmaceuticals, biochemical engineering, national defense, and aerospace. Applications include the production of high-precision filter meshes, shielding and sound-absorbing materials, microwave absorption devices, battery electrodes, fiber-reinforced composite materials, protective clothing, and more.
Additionally, due to significant changes in their microstructure and the nanoscale grain size effect, stainless steel ultra fine wires exhibit some new properties that the raw materials do not possess . All these factors provide a broad scope for expanding the application fields of ultra fine stainless steel wires.
The most traditional and primary use of stainless steel ultra-fine wires is in the production of water, gas, and oil separation filters for industries such as petrochemical, aerospace, pharmaceuticals, brewing, and environmental protection. These filters are characterized by good permeability, easy cleaning, high tensile strength, high-temperature resistance, and excellent corrosion resistance. With the advancement of modern petrochemical technology, filters now require higher precision and finer mesh, increasing the demand for thinner stainless steel ultra fine wires.
Stainless steel ultra fine wires are also thriving in the textile industry due to their excellent flexibility, fine diameter, good hand feel, and transparency, making them widely used in recent years. They are an essential raw material for manufacturing explosion-proof clothing and electromagnetic wave radiation-proof clothing for employees in industries like oil and gas, liquefied gas, and chemical products, offering unparalleled performance compared to other materials. According to tests conducted by overseas textile research institutes, woven fabrics containing 3% stainless steel ultra fine wires achieve a shielding rate of 98.43% at 1800MHz and 98.49% at 2450MHz. When blended with 5% stainless steel ultra fine wires, the products have an electromagnetic shielding rate of over 99%.
Currently, most sound-absorbing materials are made from ultra-fine glass wool, slag wool, and wood fiberboard, which are typically structured as either porous or perforated plates. However, in environments with high oil, water, and gas content, as well as high temperatures and strong corrosive conditions—such as in gas turbine power systems on ships, offshore platform gas turbines, gas turbine trailer power stations, and gas turbine locomotives—there is a need for efficient, long-lasting, and lightweight exhaust silencing devices. The performance of traditional materials in these conditions is often unsatisfactory. Experiments have shown that 1Cr18Ni9 stainless steel fiber is an ideal porous sound-absorbing material with excellent sound absorption properties and strong resistance to harsh conditions.
Porous metal materials made from stainless steel ultra fine wires, compared to traditional porous ceramic materials and porous metal materials prepared using powder sintering methods, offer equal or superior corrosion and high-temperature resistance. Additionally, they exhibit better elasticity, permeability, higher efficiency, lighter weight, and higher purification precision. These advantages make stainless steel ultra fine wires highly applicable in the fields of aerospace, marine, environmental protection, electronics, chemical engineering, and energy.
Exploratory research in other areas includes reinforcing concrete and composite materials, where stainless steel ultra fine wires' properties, such as anti-static and radiation protection, can be leveraged. In the future, these materials could be used in radiation-protective buildings or for anti-radiation and anti-static casings for machines and vehicles.
1.3 Overview of Stainless Steel Fiber Production Methods
The production processes for stainless steel fibers can be broadly categorized into three methods: wire drawing, mechanical cutting, and melt extraction. The latter two methods are primarily used for producing short fibers.
Mechanical Cutting Methods
Mechanical cutting includes various techniques such as vibration cutting, scraping, milling, unit turning, coil turning, and cold-rolled forming shearing. These methods involve physically cutting the material into fibers.
Melt Extraction Method
The melt extraction method involves solidifying the molten metal on the circumference of a rotating disc. As the disc spins at high speed, the solidified metal is continuously drawn out in fiber form. This method can produce fibers with a minimum equivalent diameter of Ф0.025mm, depending on the disc's speed.
Wire Drawing Method
The wire drawing method is divided into bundle drawing and single-wire drawing:
Bundle Drawing: This method involves grouping multiple stainless steel wires produced by single-wire drawing into a bundle, which is then coated with an outer material (typically medium carbon steel due to its similar work-hardening properties to stainless steel) and subjected to a second drawing process. Bundle drawing significantly reduces the number of drawing cycles needed, thereby improving production efficiency. It also prevents production interruptions due to breakage of individual fine wires. However, the product’s diameter uniformity and surface smoothness are not as good as those achieved by single-wire drawing. Currently, the bundle drawing method can produce stainless steel fibers with diameters as small as 2 micrometers (μm), primarily for fiber production. To prevent adhesion between individual fibers in the bundle, their surfaces are usually coated with materials like copper, which can be chemically removed after the drawing process to obtain bundled stainless steel fibers.
Single-Wire Drawing: This method involves drawing individual wires to achieve the desired diameter. While more labor-intensive and time-consuming, it results in fibers with better diameter uniformity and surface smoothness compared to bundle drawing.
Stainless steel ultra fine wires are typically produced using base materials such as 304, 304L, 316, and 316L stainless steel wire. These wires undergo processes such as single-wire drawing, heat treatment, winding, and finishing to produce soft stainless steel wires with diameters less than 0.060mm.
During the production of ultra fine wires with diameters below 40 micrometers (μm) using domestically produced stainless steel, wire breakage is a significant factor affecting productivity. For ultra-fine ultra fine wires with diameters below 20μm, it is extremely challenging to produce them using domestic stainless steel wire. The quality of the raw material is a crucial factor that directly determines whether production can proceed smoothly.
For ultra-fine stainless steel wires, the raw material must undergo induction furnace melting followed by secondary refining outside the furnace. Processes such as vacuum refining or electroslag remelting are necessary to control impurity content. If the levels of impurities and gases exceed standards, it often leads to irregular wire breakage during drawing, disrupting normal production. This results in small coil weights and unstable mechanical properties of the finished product. Cannot meet the weaving requirements of the wire mesh
A single wire drawing process utilizes a series of dies with progressively smaller diameters for continuous drawing. The specifications of the dies are crucial factors affecting the smoothness of the product surface, the uniformity of the wire diameter, the accuracy of dimensions, and the weight of the coils in the single wire drawing process, as illustrated in Figure 1.1. It is important to control the winding tension as evenly as possible during the drawing process, as this significantly influences the breakage rate of the wire. Reducing the breakage rate is essential to achieve the coil weight targets set by the company.
Heat treatment is a critical factor in determining the quality and yield of soft stainless steel ultra-fine wires. The control of the furnace temperature and the bright heat treatment in a protective atmosphere are fundamental to ensuring the surface quality and mechanical properties of the ultra-fine wires. The reliable operation of the wire feeding and winding mechanisms during the heat treatment process directly impacts the final product's coil weight. The unwinding and winding systems must have reliable and effective tension control and adjustment mechanisms to prevent the fatal defect of coil slackness. The heat treatment winding equipment should be adaptable to various types of spools and winding methods, as shown in Figure 1.2.
Factors affecting the breakage of ultra fine wires also include the degree of die wear, lubrication conditions, drawing process parameters, and the quality of raw materials. Whether it is single wire drawing or bundle drawing, the following key performance indicators are generally used to measure product performance:
1. Strength: This typically refers to the maximum breaking strength, defined as the maximum breaking force divided by the cross-sectional area.
2. Elongation: This refers to the percentage increase in length of the metal wire after passing through the die and being stretched.
3. Tolerance (Roundness): This indicates the degree of deviation in the product's diameter.
4. Smoothness: This refers to the smoothness and flatness of the product surface, which is generally assessed by inspectors based on their experience.
1.4 Current Status of Research and Production of Ultra Fine Stainless Steel Wires Domestically and Internationally
The production and application research of stainless steel fibers in China began in the mid-1980s. Currently, the main research institutions in this field domestically are the Changsha Mining Research Institute, the Northwest Institute for Non-ferrous Metal Research, and the General Research Institute for Non-ferrous Metals in Beijing. The Northwest Institute for Non-ferrous Metal Research has achieved significant progress in the modification research of stainless steel fibers and the bundle method for producing stainless steel short fibers. The production of ultra fine wires with a diameter of 0.025mm represents the current near-limit level of single wire drawing technology. The University of Science and Technology Beijing has a project under the 863 Program, one aspect of which is drawing stainless steel ultra fine wires with a diameter of 0.01mm, but no results have been reported so far.
On the international market, several strong competitors are engaged in the production of stainless steel ultra fine wires. However, due to the high requirements for raw materials and production processes, as well as the complexity of the equipment, many stainless steel wire producers around the world, except for a few companies like Riken and Nippon Seisen in Japan, Trak-Su in Germany, Ugine-Savoie Imphy in France, Bekaert in Belgium, and Memtec in the United States, dare not venture into the production of ultra-fine stainless steel ultra fine wires with diameters below 25 micrometers. Recently, there have been reports of a newly developed production line in Belgium capable of producing stainless steel short fibers with a diameter of 0.3 micrometers.
Internationally, although there has been considerable research focused on short fibers, most of it is concentrated on theoretical studies and product characteristics. There is very little research on the processes for producing ultra-fine stainless steel ultra fine wires. Domestically, research on the development and optimization of the manufacturing processes for ultra-fine stainless steel ultra fine wires is almost non-existent. Therefore, it can be said that the current research on the processes for producing ultra-fine stainless steel ultra fine wires has not yet garnered significant attention in the materials science community.
The production of stainless steel ultra fine wires is a crucial intermediate stage in the stainless steel wire mesh products industry. On one hand, it relies on the product quality provided by upstream raw material suppliers. On the other hand, it influences downstream manufacturing companies involved in weaving and textile production. Therefore, stainless steel ultra-fine wires hold a pivotal position in the entire product chain of stainless steel ultra fine wire products.
Domestically, stainless steel ultra fine wire production enterprises are mainly concentrated in Anping County in Hebei Province, Jiangyin City in Jiangsu Province, and Hangzhou in Zhejiang Province. The products are primarily ultra fine wires with diameters ranging from 0.025mm to 0.1mm, but their quality has not yet reached the level of similar foreign products. Major foreign suppliers of wire materials include Nippon Steel, Nippon Seisen, and Riken in Japan. The main domestic suppliers are Tengda, Kangrui, Hairun, and several manufacturers in Jiangyin, Jiangsu.
The downstream weaving companies are mainly located in Anping County, Hebei Province, Tianjin, Xingtai, and some old state-owned enterprises in Shanghai. These companies have very stringent quality requirements for the stainless steel ultra fine wires used in weaving, often benchmarking against the quality of similar foreign products. This has led to improvements in technology among Chinese stainless steel ultra fine wire manufacturers. However, it has also resulted in the closure of some small and medium-sized stainless steel ultra fine wire producers with insufficient technical capabilities and outdated equipment, while simultaneously driving up the prices of high-quality stainless steel ultra fine wires and intensifying competition.
With the progress of society and the development of science and technology, stainless steel wire mesh has become an indispensable consumable material in aerospace, aviation, petroleum, chemical, electromechanical, textile, and printing fields. This has made the production of stainless steel ultra fine wires a highly active and emerging material processing industry.
1.5 Research Content and Objectives of This Paper
The main content and objectives of this paper are to leverage the existing production experience of a collaborating company in producing 0.035mm stainless steel ultra fine wires and to use metallographic analysis, energy spectrum testing, and mechanical performance tensile experiments to preliminarily explore methods for inspecting the quality of raw materials. By studying the effects of raw material quality, optimization of die specifications, stretching machine parameters, annealing process optimization, and improvements in the lubrication and cooling systems on wire breakage rates, die wear, and the final product performance during the drawing process, this research aims to establish a production process specification for producing 0.04mm stainless steel ultra fine wires that suits the company's production conditions. The goal is to ensure a product yield (with spool weights above 100 grams) of 70% to 80% and achieve a drawing speed of 10 to 12 meters per second.
Through this research, the paper not only aims to effectively promote the refinement and perfection of ultra fine wire preparation processes but also hopes to discover some unique deformation phenomena and patterns by studying the mechanisms of large deformations during the wire drawing process.