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Classification and characteristics of free cutting steel
According to the different cutting elements, it can be divided into sulfur free cutting steel, lead free cutting steel, calcium free cutting steel, titanium free cutting steel and composite free cutting steel. According to their different uses, free-cutting steel is divided into automatic machine steel, structural free-cutting steel and special free-cutting steel (heat-resistant steel, stainless steel, tool steel, etc.). According to the different cutting performance, it can be divided into general free cutting steel, super free cutting steel and so on.
- sulfur free cutting steel
Sulfur free-cutting steel accounts for 70% and 90% of the world's total free-cutting steel output. Sulfur free-cutting steel can be divided into low-sulfur steel, medium-sulfur steel and high-sulfur steel according to different sulfur content: S≤0.025% of general low-sulfur steel, and some even S<0.01%; S=0.04～ of medium sulfur steel 0.09%; S=0.1-0.3% of high-sulfur steel. Among them, medium-sulfur steel has been widely used in industrial production due to its good cutting performance and mechanical properties, while high-sulfur steel is a steel for special cutting performance requirements.
It is generally believed that as the sulfur content increases, the cutting performance of the steel is better, but for ordinary steel, a slight increase in sulfur can have a significant effect of improving the machinability; adding appropriate sulfur (especially in the case of sulfur) Below 0.1%), the effect on improving the machinability of steel is very significant. Its main functions are: not only reduce the cutting force and cutting temperature, but also significantly improve the tool life, but also reduce the surface roughness of the workpiece and improve the chip handling.
The sulfur in the steel is mainly present in the form of (Mn, Fe)S. The MnS inclusions cut off the continuity of the matrix and the stress concentration source, so that the scraps are easily broken, and the lubrication reduces the wear of the cutter, thereby improving The cutting performance of steel. In order to make the steel have better cutting performance, the MnS in the steel should have a certain aspect ratio (L/W). Studies have shown that the inclusions are spherical and spindle-like than the line shape, which is more favorable for cutting. Therefore, it is hoped that steel The MnS in the form is spindle-shaped or approximately spherical. However, MnS is elongated along the rolling direction during the hot rolling process, which significantly reduces the transverse mechanical properties of the sulfur free-cutting steel and exacerbates the anisotropy of the steel. By adding elements such as barium, calcium, zirconium, rare earth and titanium to the free-cutting steel to form sulfides with the sulfur in the steel, the inclusions have poor high-temperature plastic working properties, and it becomes difficult to extend the pressure delay. The anisotropy is also suppressed to achieve the purpose of changing the shape of the sulfide. At the same time, it should ensure that the steel has a certain ratio of manganese to sulfur to reduce the adverse effects caused by the high sulfur content in the steel to ensure the mechanical properties of the steel.
-Lead free cutting steel
Lead free-cutting steel has been developed on the basis of sulfur free-cutting steel. In 1932, inspired by lead-brass with excellent machinability, it began to produce lead-free free-cutting steel. However, technical problems such as smelting and pollution prevention (PbO was highly toxic) were not solved. Until a US research institute and inland steel company published the patent for lead free-cutting steel in 1937, Japan and Germany began production. China has been developing lead free-cutting steel since the 1970s, mainly adding different amounts of lead in carbon structural steel, alloy structural steel, tool steel and stainless steel. The lead-adding method has separate lead and composite lead and sulfur. And lead-sulfur-碲. The lead content in lead free-cutting steel is generally 0.15-0.35%, and the lead content in quenched and tempered steel in Japan JASO is 0.04-0.09%.
Lead is distributed in steel with tiny elemental metal particles and does not solidify in steel. During the cutting process, strong friction is generated between the tool and the workpiece, so that the lead particles in the steel are melted and thus lubricated. The function is to improve the cutting performance of the steel, to make the steel chips finely crushed, reduce the tool wear and finally extend the tool life. Compared with lead-free steel, the cutting performance of lead-containing steel can be improved by 20 to 50%, while the mechanical properties and heat treatment properties remain basically unchanged, and have no effect on cold, hot workability and weldability. Lead free-cutting steel has been widely used as an important part in the manufacture of precision instrument parts, auto parts, and various types of machinery. However, lead free-cutting steel has low contact fatigue, so it is not suitable for parts such as gears and bearings that are subjected to fatigue stress loads.
Due to the large lead ratio, the molten steel is prone to segregation during the solidification process, and lead is poisonous. The pollution caused by lead vapor in the production process is difficult to solve, so a special lead-adding process is required. The lead-adding process of foreign smelting lead free-cutting steel is classified as patent and confidential. In the long-term production practice, Tianjin Special Steel Factory has done a lot of work on lead-adding process and control of lead pollution, and summarizes the basis of production practice. Four methods of adding lead were tried: 1) ladle lead method; 2) electroslag remelting and lead method; 3) ladle bottom blowing argon and lead method; 4) ladle blowing and lead method. However, based on the consideration of lead quality and environmental protection, only the electroslag remelting and lead method and the ladle injection and lead method are applied to production practice. Although great progress has been made in smelting lead free-cutting steel, from the environmental point of view, the use of lead free-cutting steel has been limited and will eventually be eliminated.
-Calcium free cutting steel
Since the 1960s, another way has been to study the improvement of the machinability of steel by adding a special deoxidizer to control the oxide inclusions required for the formation. In 1964, the Federal Republic of Germany first proposed a patent for calcium decalcification free cutting steel. It was introduced to Japan three years later and officially put into production. In the 1980s, China successfully developed calcium free-cutting steel, also known as deoxidized adjustable free-cutting steel, which refers to the use of metal calcium and calcium-silicon alloy deoxidizer instead of metal aluminum for deoxidation. Generally, calcium free cutting steel contains only 0.001 to 0.006% Ca. After deoxidation with calcium or calcium-silicon, calcium, silicon, and aluminum in the steel are usually oxidized to form CaO·Al 2 O 3 · 2 SiO 2 (calcium plagioclase) and 2 CaO·Al 2 O 3 · SiO 2 (calcium feldspar) composite oxide. When the cutting temperature rises, these inclusions soften and accumulate on the cutting edge of the cemented carbide tool, forming a built-up edge, the so-called Belag attachment, which prevents the chip from coming into contact with the tool and inhibits tool wear. . Calcium alone is only suitable for high-speed cutting. In order to improve the cutting performance of steel during medium and low speed cutting, sulfur, lead and antimony are added to the steel. Therefore, generally simple calcium free cutting steel is rarely used, and calcium-sulfur and calcium-sulfur-lead composite free cutting steel is more common. It is worth noting that the calcium-containing free-cutting steel can significantly extend the tool life when using high-speed cutting with cemented carbide tools, but the effect is not significant when using high-speed steel tools. This is because the high-speed steel cutting tool does not form a high temperature during cutting. The melting point of the calcium composite oxide does not form a cover film, so the wear of the tool cannot be reduced.
The strength, plasticity, impact value, fatigue performance, wear resistance and heat treatment properties of Ca-S composite free-cutting steel which is added to steel are comparable or slightly lower than that of the base steel. Calcium free-cutting steel is used for more important structural parts such as shafts, gears and spline shafts. In actual mass production, cemented carbide and high speed are often used.
-Titanium free cutting steel
Titanium free cutting steel is another new type of free cutting steel developed on the basis of calcium free cutting steel. In December 1969, the Japan Institute of Metal Materials Technology proposed the first patent for titanium free cutting steel. Free-cutting steel with Ti alone is especially suitable for high-speed cutting of more than 200m/min. To improve its cutting performance at medium and low speeds, a certain amount of S can be added, and other free-cutting elements can be combined to produce titanium composite free-cutting steel. . In the 1980s and 1990s, China successfully developed titanium-sulfur composite free-cutting steels Y35TiS and Y45TiS, which are currently in the leading position in the world. Like the Ca-S free-cutting steel, Ti-S free-cutting steel forms a layer of Belag cover film on the tool for high-speed cutting, which can extend the tool life by 3 to 9 times. Titanium free-cutting steel has better hardenability, wear resistance, and deformation of the machined parts than the base steel, and the fatigue properties, anisotropy and other properties are equivalent to or slightly lower than the base steel. Ti-S free-cutting steel has a small reduction in lateral mechanical properties, so it can be used for important structural parts such as lead screws, light bars, shafts, gears and fasteners on machine tools.
Hot-Dip Galvanized Welded Wire Mesh: Hot-dip galvanized welded wire mesh is a type of welded wire mesh that has undergone a galvanizing process. In this process, the mesh is immersed in a bath of molten zinc, which forms a protective coating on the surface of the wires. The zinc coating provides excellent corrosion resistance, making hot-dip galvanized welded wire mesh suitable for outdoor applications where exposure to moisture and harsh environments is expected. It is commonly used for fencing, construction, and industrial purposes.
Hot-Dip Zinc Welded Wire Mesh: Hot-dip zinc welded wire mesh is another term used for hot-dip galvanized welded wire mesh. It refers to the same type of mesh that has been galvanized through the hot-dip process, resulting in a protective zinc coating. The zinc coating helps prevent rust and corrosion, ensuring the long-term durability of the wire mesh. Hot-dip zinc welded wire mesh is widely used for various applications, including fencing, animal enclosures, and reinforcement in concrete structures.
Hot Dip Galvanized Iron Wire Mesh: Hot-dip galvanized iron wire mesh is a type of wire mesh that is made from galvanized iron wires and has undergone the hot-dip galvanizing process. The iron wires are immersed in molten zinc, resulting in a protective zinc coating on the surface. This coating provides excellent corrosion resistance, making hot-dip galvanized iron wire mesh suitable for outdoor applications, especially in environments where rust and corrosion are concerns. It is commonly used for fencing, agriculture, and industrial purposes.
These different types of wire mesh, including welded wire mesh rolls, hot-dip galvanized welded wire mesh, hot-dip zinc welded wire mesh, and hot-dip galvanized iron wire mesh, offer varying levels of corrosion resistance and durability. The specific choice depends on the intended application, environmental factors, and the level of protection required.
Brief description of classification and characteristics of free-cutting steel
The so-called free-cutting steel refers to steel with excellent machinability. The improvement of the machinability of steel is mainly through the addition of free-cutting elements (S, P, Pb, Se, Te, Bi, Zr, Re, etc.) to the steel alone or in combination. ). The superiority of cutting performance of free-cutting steel is generally evaluated by several comprehensive indexes such as tool life, machined surface finish, chip handling, tool force and energy consumption.