Metal Cutting Tools Materials--High-speed Steel

The high-speed steel is alloy tool steel containing more alloying elements such as W, Mo, Cr, V, and better overall performance, the widest range of applications of a cutting tool materials. After heat treatment hardness of 62-66HRC, flexural strength of about 3.3GPa, heat resistance to 600 ℃, addition, has the advantages of heat deformation small, can be forged, and easy to grind the sharp edge. The use of high-speed steel is a large proportion, especially for the manufacture of a complex structure of the forming tool. Such as various types of hole machining tools, milling cutters, broaches, thread cutting tools, gear cutting tools, etc.

Types of high-speed steel:

General-purpose high-speed steel

General-purpose high-speed steel is the most widely used, accounting for about 75% of the total high-speed steel. The carbon content of 0.7% -0.9%, at different containing tungsten, molybdenum content is divided into tungsten series, Department of tungsten and molybdenum. The main grades are the following three:

1. Tungsten high-speed steel of W18Cr4V (18-4-1): has good overall performance. Vanadium containing is less and has good sharpening process. Overheating tendencies small quenching, heat treatment is easier to control. The drawback is the uneven distribution of carbides, not bigger section of the tool; poor thermoplastic any, animal husbandry; gradually reduced because of tungsten high prices, domestic use abroad has been rarely used.

2. W6M05Cr4V2 (6-5-4-2) tungsten molybdenum high speed steel: grade is widely used at home and abroad. Instead of two because of a Mo W, this can reduce the alloying elements in steel, to reduce the number of carbides in the steel and the uneven distribution of favorable to improve thermoplastic, flexural strength and toughness. The mass fraction of 3% -5% of molybdenum, the sharpening process can be improved. 6-5-4-2 high temperature plasticity and toughness than 18-4-1, it can be used in the manufacture of hot-rolled tool such as twisted system twist drill. The main disadvantage is the narrow range of quenching temperature, decarburization overheating sensitivity large.

3. W9M03Cr4V (9-3-4-1) tungsten molybdenum high speed steel: the grades developed according to the country's resources. The bending strength and toughness are better than 6-5-4-2. Good high temperature thermoplastic and quenching overheating decarburization sensitivity, good cutting.

High-productivity high-speed steel

High-productivity high-speed steel refers to the increase in the general-purpose high-speed steel, carbon, vanadium, adding alloying elements such as cobalt or aluminum, new steel grades. Its hardness at room temperature up to 67-70HRC, significantly improved wear resistance and heat resistance, and can be used in the processing of stainless steel, heat resistant steel and high strength steel.

The carbon content of the high-carbon high-speed steel is improved, so that all alloying elements forming carbides, thereby improving the hardness and wear resistance of the steel in the steel, but its strength and toughness are decreased slightly, has been rarely used.

High Speed Steel is the mass fraction of vanadium steel increased by 3% -5%. Vanadium carbide hardness silicon is up to 2800HV, higher than the ordinary corundum. So, on the one hand to increase the wear resistances of the steel, but also increase the difficulty of sharpening steel grades.

Cobalt high speed steel grades W2Mo9C4VC08 (M42). Steel added cobalt, can improve the high-temperature hardness and antioxidant capacity of the high speed steel, and therefore can be applied to the high cutting speeds. Drilling in the steel can promote the steel during tempering martensite in the precipitation of carbides of tungsten, molybdenum, improving tempering hardness. Cobalt in higher thermal conductivity, it is advantageous for improving cutting tools. Add drill steel can still reduce the friction coefficient, to improve their grinding.

Aluminum high-speed steel is the original high-productivity, high-speed steel. The typical grades are W6Mo5Cr4V2A1 (501). The aluminum is not carbide-forming elements, but it can improve the solubility of the W, Mo and other elements in the steel, and can prevent grain growth. Therefore aluminum high-speed steel can improve the high-temperature hardness, thermoplastic and toughness. The aluminum speed steel under the effect of temperature in the cutting tool surface may be formed on the alumina film, to reduce friction with the chips and the adhesive. 501 mechanical properties of high-speed steel cutting performance with American M42 high-speed steel equivalent to its lower price, the more stringent requirements of aluminum heat treatment process of high-speed steel.

PM HSS

PM HSS is obtained by the high speed of molten steel in a high pressure inert gas or a high-pressure water atomizing brightly small, high-speed steel powder, and then pressing or hot forming, and then by sintering the high-speed steel. PM HSS was first developed in the 1960s by Swiss success, made of powder metallurgy high speed steel began to trial in the 1970s. Its increasing application performance.

PM HSS has the following advantages compared with smelting high-speed steel:
1) Since the small uniform crystalline structure (carbonization Item tablets 2 - 51 μm) can be obtained, so as to completely avoid the segregation of carbides, and to improve the hardness and strength of the steel, can achieve the hardness 69.5-70HRC, flexural strength σbb 2.73 ~ 3.43 GPa.
2) due to the physical and mechanical properties of isotropic heat treatment deformation and stress reduction, can be used in the manufacture of precision tools.
3) Since the carbides fine and uniform, so that the grinding resistance has been significantly improved, containing the amount of vanadium amount, the degree of improvement on the more remarkable. These unique advantages, making the powder metallurgy high speed steel can be used for the manufacture of new, increasing the alloying elements, the addition of a large number of carbide superhard speeds steel without reducing its sharpening process. This is unmatched by melting high-speed steel.
4) PM HSS improve material utilization

PM HSS is still less used because of the higher cost. Main use is to create forming complex tool, such as precision threading tool, broaches, gear cutting tool, as well as the processing of high-strength steels, nickel-based alloys, titanium, titanium and other difficult-to-machine materials with planer, drill, milling cutter.

Coated high speed steel

A surface coating of the high-speed steel cutting tool is the use of physical vapor deposition (PVD) method, to the vaporized titanium ions react with the nitrogen in a suitable high degree of vacuum and temperature environment, are generated on the anode surface of the tool of TiN. The thickness thereof is decided by the time of the vapor deposition, is generally 2-8μm, has little effect on the accuracy of the dimensions of the tool.

The new coating equipment using nanometer composite vacuum ion plating process control 500 ℃ environment. Usually tool coated with TiN, dura mater, a thickness of approximately 2μm. The surface of the coating is firmly bonded, golden yellow, hardness up to 2200HV, have high thermal stability, low coefficient of friction with steel.

Coated high speed steel cutting tools, cutting force, cutting temperature decrease of approximately 25%, cutting speed, feed rate, and tool life increased significantly. Even if the tool regrinding, its performance is still better than the ordinary high-speed steel. Suitable for drills, taps, shaping cutters, gear cutting tool widely used.

In addition to TiN coating, the new coating process coating more functions, typically including: of TiN, TiC, TiCN, TiAlN, Al-TiN, TiAlCN, DLC (diamond-like Coating diamond-like coating), CBC (Carbon-base class based coating carbide coating).

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