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According to different purposes, high-speed steel can be divided into general-purpose high-speed steel and high-performance high-speed steel.

⑴ General-purpose high-speed steel cutter

General purpose high speed steel. Generally can be divided into two types of tungsten steel, tungsten molybdenum steel. This kind of high speed steel containing (C) is 0.7~0.9%. According to the different tungsten content in steel, it can be divided into tungsten steel containing 12% or 18% W, tungsten molybdenum steel containing 6% or 8% W, and molybdenum steel containing 2% or no W. General-purpose high-speed steel has a certain hardness (63-66HRC) and wear resistance, high strength and toughness, good plasticity and processing technology, so it is widely used in the manufacture of various complex tools.

① Tungsten steel: The typical grade of general-purpose high-speed steel tungsten steel is W18Cr4V (W18 for short), which has good comprehensive performance and high temperature hardness of 48.5HRC at 6000C, which can be used to manufacture various complex tools. It has the advantages of good grindability and low decarburization sensitivity, but due to the high carbide content, uneven distribution, large particles, low strength and toughness.

2 tungsten and molybdenum steel: refers to a part of tungsten in tungsten steel with molybdenum instead of a high-speed steel. The typical grade of tungsten molybdenum steel is W6Mo5Cr4V2 (M2 for short). The carbide particles of M2 are fine and uniform, and the strength, toughness and high temperature plasticity are better than W18Cr4V. Another kind of tungsten molybdenum steel is W9Mo3Cr4V steel (W9 for short), its thermal stability is slightly higher than M2 steel, bending strength and toughness are better than W6M05Cr4V2 steel, and it has good processability.

(2) High-performance high-speed steel cutting tools

High-performance high-speed steel refers to a new steel that adds some carbon content, vanadium content and Co, Al and other alloying elements to the general-purpose high-speed steel composition, which can improve its heat resistance and wear resistance. There are mainly the following categories:

① High carbon high speed steel. High-carbon high-speed steel (such as 95 W18Cr4V), room temperature and high temperature hardness, suitable for manufacturing and processing of ordinary steel and cast iron, high wear resistance requirements of drill bits, reamers, taps and milling cutters, etc. or processing of harder materials, should not withstand large impact.

② high vanadium high speed steel. Typical brands, such as W12Cr4V4Mo,(EV4 for short), contain V up to 3%-5%, have good wear resistance, and are suitable for cutting materials with great tool wear, such as fiber, hard rubber, plastic, etc., and can also be used for processing stainless steel, high-strength steel, high-temperature alloy and other materials.

Cobalt high speed steel. It is a cobalt-containing superhard high-speed steel, a typical brand, such as W2Mo9Cr4VCo8 (M42), with high hardness, its hardness can reach 69-70HRC, which is suitable for processing high-strength heat-resistant steel, high-temperature alloy, titanium alloy and other difficult-to-machine materials. M42 has good grindability and is suitable for making precision and complex tools, but it is not suitable for working under impact cutting conditions.

④ Aluminum high speed steel. It is an aluminum-containing superhard high-speed steel with typical brands, such as W6Mo5Cr4V2Al (501 for short), and its high-temperature hardness at 6000C also reaches 54HRC, and its cutting performance is equivalent to M42. It is suitable for manufacturing milling cutters, drill bits, reamers, gear cutters, broaches, etc. and is used for processing alloy steel, stainless steel, high-strength steel, high-temperature alloy and other materials.

⑤ nitrogen superhard high speed steel. Typical grades, such as W12M03Cr4V3N, referred to as (V3N), are nitrogen-containing superhard high-speed steel, hardness, strength, toughness and M42, can be used as a substitute for cobalt-containing high-speed steel, used for low-speed cutting of difficult-to-process materials and low-speed high-finish processing.

(3) Melting high speed steel and powder metallurgy high speed steel

According to different manufacturing processes, high-speed steel can be divided into smelting high-speed steel and powder metallurgy high-speed steel.

① smelting high-speed steel: ordinary high-speed steel and high-performance high-speed steel are manufactured by smelting method. They are made into cutting tools through smelting, ingot casting and plating rolling. The serious problem of melting high-speed steel is carbide segregation, hard and brittle carbides are not evenly distributed in high-speed steel, and the grains are coarse (up to tens of microns), which has a negative impact on the wear resistance, toughness and cutting performance of high-speed steel tools.

② Powder metallurgy high speed steel (PM HSS): Powder metallurgy high speed steel (PM HSS) is a molten steel melted in a high-frequency induction furnace, atomized with high-pressure argon or pure nitrogen, and then quenched to obtain a fine and uniform crystal structure (high-speed steel powder), and then the obtained powder is pressed into a blank at high temperature and high pressure, or the blank is first made into a blank and then forged and rolled into a tool shape. Compared with high-speed steel manufactured by melting method, PM HSS has the advantages that the carbide grains are fine and uniform, and the strength, toughness and wear resistance are improved a lot compared with melting high-speed steel. In the field of complex NC tool PM HSS tool will be further development and occupy an important position. Typical grades, such as F15, FR71, GF1, GF2, GF3, PT1, PVN, etc., can be used to manufacture large size, bear heavy load, large impact tools, can also be used to manufacture precision tools.

Selection Principle of 3. NC Tool Material

At present, the widely used CNC tool materials mainly include diamond tools, cubic boron nitride tools, ceramic tools, coated tools, carbide tools and high-speed steel tools. There are many total grades of tool materials, and their performance varies greatly. The following table shows the main performance indicators of various tool materials.

The tool material for CNC machining must be selected according to the workpiece and the nature of the machining. The selection of tool materials should be reasonably matched with the processing object. The matching of cutting tool materials and processing objects mainly refers to the matching of mechanical properties, physical properties and chemical properties of the two, so as to obtain longer tool life and greater cutting productivity.

1. Matching the mechanical properties of the cutting tool material and the machining object

The problem of matching the mechanical properties of the cutting tool and the processing object mainly refers to the matching of the mechanical properties parameters such as the strength, toughness and hardness of the tool and the workpiece material. Tool materials with different mechanical properties are suitable for processing different workpiece materials.

① Tool material hardness sequence: diamond tools> cubic boron nitride tools> ceramic tools> carbide> high speed steel.

The order of the bending strength of the tool material is: high-speed steel> cemented carbide> ceramic tools> diamond and cubic boron nitride tools.

The order of the toughness of the tool material is: high-speed steel> cemented carbide> cubic boron nitride, diamond and ceramic tools.

The workpiece material with high hardness must be processed with a higher hardness tool, and the hardness of the tool material must be higher than the hardness of the workpiece material, which is generally required to be above 60HRC. The higher the hardness of the tool material, the better its wear resistance. For example, when the amount of cobalt in cemented carbide increases, its strength and toughness increase, and its hardness decreases, which is suitable for roughing; when the amount of cobalt decreases, its hardness and wear resistance increase, which is suitable for finishing.

2. The cutting tool material matches the physical properties of the processed object

Tools with different physical properties, such as high thermal conductivity and low melting point of high-speed steel tools, high melting point and low thermal expansion of ceramic tools, high thermal conductivity and low thermal expansion of diamond tools, etc., are suitable for the processing of workpiece materials are different. When machining workpieces with poor thermal conductivity, the tool material with good thermal conductivity should be used to make the cutting heat quickly pass out and reduce the cutting temperature. Due to the high thermal conductivity and thermal diffusion rate of diamond, the cutting heat is easy to dissipate and will not produce great thermal deformation, which is particularly important for precision machining tools with high dimensional accuracy.

① Heat-resistant temperature of various tool materials: diamond tools are 700 ~ 8000C, PCBN tools are 13000 ~ 15000C, ceramic tools are 1100 ~ 12000C, TiC(N)-based cemented carbide is 900 ~ 11000C, WC-based ultrafine grain cemented carbide is 800 ~ 9000C, HSS is 600 ~ 7000C.

The thermal conductivity of various tool materials: PCD>PCBN>WC-based cemented carbide> TiC(N)-based cemented carbide> HSS>Si3N4-based ceramics> A1203-based ceramics.

③ The order of thermal expansion coefficient of various tool materials is: HSS>WC-based cemented carbide> TiC(N)> A1203-based ceramics> PCBN>Si3N4-based ceramics> PCD.

④ The order of thermal shock resistance of various tool materials is: HSS>WC-based cemented carbide> Si3N4-based ceramics> PCBN>PCD>TiC(N)-based cemented carbide> A1203-based ceramics.

3. Matching the chemical properties of cutting tool materials and processing objects

The problem of matching the chemical properties of cutting tool materials and processing objects mainly refers to the matching of chemical properties parameters such as chemical affinity, chemical reaction, diffusion and dissolution of tool materials and workpiece materials. Different materials of the tool for the processing of the workpiece material is different.

① The anti-bonding temperature of various tool materials (with steel) is: PCBN> ceramic> cemented carbide> HSS.

The oxidation temperature of various tool materials is: ceramic> PCBN> cemented carbide> diamond> HSS.

The diffusion strength of the tool material (for steel) is: diamond> Si3N4 based ceramics> PCBN>A1203 based ceramics. The diffusion strength (for titanium) is: A1203 based ceramics> PCBN>SiC>Si3N4> diamond.

4. Reasonable choice of CNC tool materials

In general, PCBN, ceramic tools, coated carbide and TiCN-based carbide tools are suitable for CNC machining of ferrous metals such as steel, while PCD tools are suitable for the processing of non-ferrous metal materials such as Al, Mg, Cu and their alloys and non-metallic materials. The following table lists some of the workpiece materials that are suitable for machining with the above tool materials.