Introduction of Japanese high-strength rods and wires
(1) Rods and wires can be processed into a variety of products
In addition to being directly used in construction, rods and wires can also be processed into various parts for other purposes. Taking a common car as an example, each car uses about 150Kg of rods and wires, which is about 10% of the car’s weight. Among them, the materials used for engine components (crankshafts, camshafts, valve springs, etc.) and drive system components (various gears, screw shafts, etc.) are inseparable from rods and wires. “Driving, turning and stopping” are the basic actions of a car. If a component supporting these actions is damaged, the car will stop running. This shows their importance.
In addition, as a reinforcing material for automobile tires, some organic fibers were used in the past. Later, the rigidity of automobile tires has been significantly improved after the use of radial steel wires. Therefore, in recent years, the tire damage and deflation accidents during automobile driving have been greatly reduced; now as a standard The Φ0.3mm radial steel wire used in the product has made a significant contribution to saving resources and improving tire performance through high-strength (an annual output of 300,000 tons). According to statistics, the amount of meridian steel wire in 1975 was ~ 20,000 tons, which increased sharply to 100,000 tons in 1985, 200,000 tons in 1995, and 300,000 tons in 2005, showing its rapid development.
In buildings and steel structures, high-strength rods and wires have also begun to be widely used. Among them, such as telegraph poles and concrete reinforcement materials, suspension bridges, cable-stayed bridges, etc., their strength is generally reinforced 3 to 4 times, which also brings many benefits.
In addition, various bolts, nuts and springs made of rods and wires are also widely used in various aspects, led by the machinery industry; even our common daily necessities such as piano wires, guitar strings and fishing wires are processed by wires. Become. Although their final products have different shapes and properties, they have in common that they are all processed from steel rods and wires. Nippon Steel produces rods and wires, including Muroran Steel Plant, Kamaishi Steel Plant, and Junjin Steel Plant. The classification and use of wire products are shown in Table 1.
Table 1 Classification and use of rods and wires
Classification specification name JIS symbol main purpose
Ordinary wire, mild steel wire SW(-)RM nail, steel wire, traveller, etc.
Special wire rod hard steel wire rod
Spring steel wire
Very low carbon steel wire SW(-)RH
Steel rope, tire wire, spoke wire
Meridian steel wire, steel wire for bridge, steel wire for compaction of concrete
Suspension spring, valve spring
Steel wire for glass enclosure
Wire rod for cold working Wire rod for cold rolling
Low alloy steel spring wire
Wire rod for polished steel
Wire for reinforced concrete SW(-)RH
SD various steel bolts, nuts, mechanical parts
Various steel bolts, nuts, mechanical parts
Polished rod, wire
(2) Bars and wires supplied as semi-finished products
The difference between bars, wire rods and other hot-rolled steels is that they are supplied as semi-finished products in a hot-rolled state, which are then processed and heat-treated by users such as automobile manufacturers and component manufacturers to become final products; and medium-thick plates and thin plates Steels such as steel pipes, steel pipes and H-beams are supplied by steel mills rolled into finished steel products of a certain shape and strength.
Take the processing process of a pinball as an example. The brief introduction is as follows: the wire produced by the steel plant is sent to the secondary processing factory, and is cold drawn -> molded into a ball -> rough polishing -> surface marking -> heat treatment -> grinding -> mirror Polished -> After chrome plating, the product is formed. The small pinball section has three different structures: the surface layer is 3um chromium-plated, the lower 1mm thickness is the martensite structure with 0.8% carbon after carburizing treatment, and the inside is iron with only 0.2% carbon. The soft structure of body + martensite. The above structure makes the surface of the pachinko ball have high hardness and strong impact resistance, and the interior of the pachinko ball can absorb the impact and make the ball difficult to break. This carburizing treatment is also applied when using rods and wires to produce gears and other parts.
In addition, the size, weight, and processing accuracy of the pinball depend on the molding process. The general size tolerance is controlled within 0.01mm and the weight error is within 0.01g. For this reason, the requirements for the workability of the wires used are very strict. This shows the difference between bars, wires and other steels.
(3) Consider the adjustment and cooling of the processing procedure
Generally, the cost of materials made of rods and wires only accounts for 20% of the production cost of the parts (the remaining 80% is forging 20%, cutting 40%, heat treatment 10% and other 10%). Due to the high cost of secondary processing, the development of steel should focus on favoring secondary processing. Even if the final product requires high strength, the rods and wires supplied by steel mills are also required to be “easy to process in order to simplify the processing procedures.” In other words, the rods and wires provided should be the opposite of the high strength required by the final product, that is, they should be softer, thus creating a contradiction. In order to meet this requirement, “adjusted cooling” technology has been adopted. Generally, the strength of the hot-rolled steel material is increased after rapid cooling, and the strength is decreased after slow cooling. “Slow cooling” equipment is to keep the rolled wire coils warm and slowly cool them to reduce their strength. For example, bolts are cold forged with wires at room temperature. The processed steel must be soft to make it easy to form. For this reason, the above-mentioned slow cooling measures are taken for the hot-rolled material to improve its cold forgeability, and the strength is increased by heat treatment after processing to reach the required level.
Due to the different strength requirements of various products, there are also many cooling methods. In addition to the above-mentioned “slow cooling” equipment, there are also cooling methods such as “air cooling” where air is fed for faster cooling, “DLP” through 550°C salt bath cooling, and “EDC” through hot water cooling. Among them, the “DLP” equipment has obvious adjustment effects on the strength and extensibility of high-carbon steels that require high strength, which is beneficial to users to simplify the process in the subsequent toughening treatment, especially the use of salt baths that do not contain metals such as lead, not only thermal conductivity Good, and the salt adhering to the wire can also be simply washed with hot water to remove it and recycled and reused, and it has less pollution than the lead bath treatment.
(4) Master the strength of steel through organizational control
As mentioned above, adapting the properties of rods and wires to the user’s processability is the first condition. However, due to the wide range of purposes and applications, the required strength level of the final product is in the range of 300-5000 MPa. For example, ordinary wires for steel wire and wire mesh are only 300 MPa, while the aforementioned radial steel wires for automobile tires and wire saws for cutting silicon wafers require high-strength wires up to 4000 MPa. For this reason, the chemical composition and crystalline structure of rods and wires are also diversified, because the strength of steel increases with the increase in carbon content, but the corresponding extensibility needs to be considered in thin and medium plate products, so carbon is contained The amount is generally kept below 0.2%. However, in order to meet the requirements of various strengths for rods and wires, the range of carbon content has been expanded to between 0.01 and 1.1%; with such a wide range of carbon content, the organizational forms that affect strength, elongation and toughness are also diverse.