high speed steel High-speed steel invented by American […]
high speed steel
High-speed steel invented by American mechanical engineer F.W. Taylor and metallurgical engineer M. White in 1898 is still a common tool material. High-speed steel is a kind of high-alloy tool steel with more alloy elements such as w, Mo, Cr and V. Its carbon content is 0.7%-1.05%. High-speed steel has high heat resistance and its cutting temperature can be Up to 6000 ° C, the cutting speed can be doubled compared with carbon tool steel and alloy tool steel. High-speed steel has good toughness and formability and can be used to manufacture almost all types of tools such as taps, twist drills, gear cutters, broaches, and small diameter milling cutters. However, high-speed steel also has defects such as poor wear resistance and poor heat resistance, and it has been difficult to meet the increasing requirements of modern cutting tools for tool materials; in addition, the storage of some major elements (such as tungsten) in high-speed steel materials. The resources are depleting in the world. It is estimated that the reserves are only enough to be re-exploited for 40 to 60 years, so the high-speed steel materials are facing a severe development crisis.
Ceramic materials have higher hardness, red hardness and wear resistance than cemented carbide. Therefore, when machining steel, the durability of the ceramic tool is 10 to 20 times that of the cemented carbide tool, the red hardness is 2 to 6 times higher than that of the cemented carbide, and the chemical stability and oxidation resistance are superior to those of the hard alloy. . The disadvantages of ceramic materials are high brittleness, low transverse rupture strength, and poor impact load capacity, which is the focus of people's continuous improvement in recent decades. Ceramic tool materials can be divided into three categories: 1 alumina-based ceramics. Usually, TiC, WC, SiC, TaC, ZrO2 and other components are added to the Al2O3 matrix material, and the composite ceramic cutter is hot pressed to have a hardness of 93-95 HRA. To improve the toughness, a small amount of metal such as Co and Ni is often added. . 2 silicon nitride based ceramics. The commonly used silicon nitride-based ceramics are SiN+TiC+Co composite ceramics, and their toughness is higher than that of alumina-based ceramics, and the hardness is equivalent. 3 silicon nitride-alumina composite ceramic. Also known as Sialon ceramics, its chemical composition is 77% Si3N4 + 13% A12O3 + 10% Y2O3, hardness up to 1800HV, bending strength up to 1.20GPa, most suitable for cutting superalloys and cast iron.
Unlike cermets composed of WC, cermets are mainly composed of ceramic particles, TiC and TiN, binders Ni, Co, Mo, and the like. The hardness and red hardness of cermets are higher than that of cemented carbides, lower than that of ceramic materials; the transverse rupture strength is greater than that of ceramic materials, less than that of hard alloys; good chemical stability and oxidation resistance, resistance to peeling abrasion, oxidation and diffusion resistance, Lower bonding tendency and higher blade strength. The cutting efficiency and working life of cermet cutters are higher than that of cemented carbide and coated carbide tools, and the surface roughness of the machined workpiece is small. Because of the low adhesion between cermet and steel, the cermet cutter is used instead of coating. When a layer of cemented carbide tool is used to process steel workpieces, the chip formation is relatively stable, and long chip winding is less likely to occur during automated machining, and the edges of the parts are substantially free of burrs. The disadvantage of cermet is that it is less resistant to thermal shock and is easily broken, so it has a limited range of use.