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Heat treatment method of high speed steel products

High-speed steel is widely used in the manufacture of large size, high cutting speed, heavy load, high working temperature of a variety of machining tools, but also for the manufacture of high wear resistance of cold and hot mold.
Today, we start from the common features of HSS and list the heat treatment process of various tools, dies, gauges and other products made of HSS steel wire. Point out that the mysteries of high-speed steel, but as long as we master the composition, organization, performance and service life (product lifeline) of the relationship (referred to as “three points a line”), will be able to produce high-quality products.

What is high-speed steel

High-speed tool steel (also known as high-speed steel), since its introduction in 1900 has been more than 120 years of history. The steel because of its unique metallurgical composition and subsequent products obtained by heat treatment of excellent performance, causing machine tools and tool manufacturing, mold industry and other revolutionary changes, promoting the development of the national economy and social progress, so the study of high-speed steel and its products performance is of practical significance. In this paper, we try to introduce the heat treatment process of various tools made of high speed steel, starting from the common features of high speed steel, in order to attract the attention of the industry, to improve the heat treatment of high speed steel, and make a contribution to society.

Commonality of high-speed steel materials

High-speed steel is a lainitic steel, in addition to containing high C, but also contains more W, Mo, Cr, V and other important alloying elements, thus creating a special high-speed steel process performance.
According to the chemical composition of high-speed steel, it can be divided into low-alloy high-speed steel (HSS-L), ordinary high-speed steel (HSS), high-performance high-speed steel (HSS-E); according to the forming method is divided into metallurgical high-speed steel, powder steel, injection steel. Regardless of the method of production of high-speed steel, it has the following commonalities.

  • 1) High C content, generally > 0.70% (mass fraction, the same below).
  • 2) All are high-alloyed steel (containing a total alloy of > 10%).
  • 3) Most of them contain Cr up to 4%.
  • 4) All contain very high alloying elements and sufficient carbon with the formation of different carbides in the heat treatment process.
  • 5) The normal quenching and heating temperature is lower than the steel melting point of about 80 ℃.
  • 6) Quenched and tempered hardness are ≥ 63HRC.
  • 7) Quenching and tempering after the metallurgical organization of the same.
  • 8) After quenching and tempering are to be tempered for several times before the full, there are secondary hardening phenomenon, secondary hardening peak temperature in 540 – 560 ℃.
  • 9) In addition to the turning tool products, the quenching grain size of popular products tool in 9.5 – 10 grade, the grain are relatively fine.
  • 10) Good hardenability, <200mm products in the whole section can get uniform high hardness, small pieces of air-cooled self-hardening.
  • 11) It has high thermal hardness.
  • 12) It can make many kinds of tools.
  • 13) Excellent hot and cold workability.
  • 14) Various tools and dies made of HSS can be surface strengthened in many ways.
  • 15) Expensive, more than 10 times the price of the same specification 45 steel.
  • 16) Heat treatment is difficult, the influence of many factors, the quality and stability of the manufactured product is not easy to control.

Heat treatment process of high speed steel wire tool products

GB/T3080-2001 “high-speed tool steel” and YB/T5302-2010 “high-speed tool steel” are specified in the diameter of the wire 1.0 – 16.0mm. the following is a brief description of the nominal diameter of the products in this range of heat treatment process.

Diameter ≤ 3.0mm heat treatment process of the product

For the heat treatment of small drill bits with straight shanks, JB/T9986-2013 “Tool Heat Treatment Metallographic Inspection” stipulates that: the quenching grain size of drill bits with a diameter of ≤ 3mm is 10-11.5 (W-Mo system), superheat ≤1, and the tempering degree is qualified. Quenching and tempering hardness 62 – 65 HRC. the author developed and implemented a practical process: If the M2 steel manufacturing, preheating, 870 – 880 ℃ salt bath heating (installed sleeve), 1215 – 1220 ℃ salt bath heating, grain size control in 11 – 12, diameter 2.5 mm M2 steel small drill quenching metallographic organization as shown in Figure 1. 500 – 550 ℃ neutral salt (50% CaCl2 + 30% BaCl2 + 20% NaCl), triangular box clamps straight tempering, 560 – 570 ℃ × 1h × 4 times after tempering hardness 63 – 65.5 HRC. hardness exceeds the standard (≥ 65.1 HRC) should be made for metallographic testing, such as not overheating should be cutting test, to meet the standards of qualified products should be released.

Diameter 3 – 16mm steel wire products heat treatment process

Diameter > 3mm above the high-speed steel wire, you can make a variety of drills, straight shank end mills, keyway milling cutters, cylindrical milling cutters, straight shank T-slot milling cutters, dovetail milling cutters, chamfering cutters, center drill, straight shank machine reamer, machine taps and round hole broaches and dozens of metal cutting tools. Because of the different shapes of such tools, cutting objects are different, so can not implement the same process, the development of heat treatment process must be personalized. The general principle is that both high hardness and good toughness, in the case of ensuring toughness, strive for high hardness. Diameter > 3-6mm tools, quenching and heating temperature with the middle limit, diameter > 6-15mm tools, quenching and heating temperature selected upper limit, carbide dissolution to be adequate, the former quenching and tempering hardness in 64.5 – 66HRC better, the latter hardness in 65 – 66.5HRC more competitive market. Take M2 (W6Mo5Cr4V2) steel straight shank twist drill for example: 1220 – 1225 ℃ salt bath heating quenching, grain size 9.5, M2 steel wire φ8mm straight shank drill quenching metallurgical organization as shown in Figure 2, tempered hardness 66 – 66.5 HRC. by the production practice proved that the highest life of the drill bit heat treatment with this process. If the M8 machine tap, quenching and heating temperature should be appropriately low, grain size control in 10.5 – 10, hardness in 65 – 66 HRC more appropriate. The development of heat treatment process to understand the processing object of the tool, highlighting a certain aspect of performance, so that the manufacture of tools will be popular in the market.
20220119020426 36346 - Heat treatment method of high speed steel products
Figure 1 φ2.5mm drill bit quenching metallographic organization (500 x)
20220119020512 44266 - Heat treatment method of high speed steel products
Figure 2 φ8mm drill quenching metallurgical organization (500 x)

Heat treatment of high-speed steel mold products

The author is one of the early application of high speed steel mold manufacturing technology personnel. 1975 in Guilin, an arsenal work, at the request of a hardware factory in Guilin, with M2 steel manufacturing M12 specifications plum hexagonal wrench has been successful, its life for the original Cr12MoV steel several times. 1984 in Zhejiang with M2 steel manufacturing punch bar, life than the original Cr12MoV increased by more than 10 times, for this The factory set up a workshop for manufacturing high-speed steel punching bars, and the products are exported to all over the country. After a long period of practice, the author figured out a more mature heat treatment process of high-speed steel die salt bath, is introduced as follows.

  • 1) Quenching heating temperature is much lower than the same size of the tool.
  • 2) The heating time is a little longer.
  • 3) The first tempering temperature with 580-590℃.
  • 4) It is important to determine the hardness according to the working condition of the die such as punching bar.

The author in practice summed up a very applicable high-speed steel die quenching temperature and hardness of the empirical relationship between the formula, namely

  • W18Cr4V steel: T=1260-10(64-H)
  • W6Mo5Cr4V2 steel T=1190-10(64-H)

In the formula:

  • T – determined quenching heating temperature (℃);
  • H – the average value of the required hardness (HRC).

Here we should especially emphasize that the first tempering temperature of the mold after quenching with 580 – 590 ℃, such as the tool quenching after tempering at 550 ℃, the calculated heating temperature to subtract 20 ℃.

Heat treatment of high speed steel high temperature bearings

In more than 500 ℃ high temperature service bearing parts, in addition to the requirements of > 62HRC high hardness, but also must have wear resistance, fatigue resistance, oxidation resistance, corrosion resistance, impact resistance, good dimensional stability, and good machinability, high-speed steel is one of the few steel with the above properties. The following is a brief introduction to several high-speed steel production of high-temperature bearing heat treatment process, for reference only.

  • (1) M50 steel heat treatment M50 (equivalent to China’s Cr4Mo4V steel) is a low-alloy high-speed steel, China’s high-temperature bearing steel standard GB/T38886-2020 will also be included in the steel, the production of high-temperature bearing heat treatment process [2] can be selected: 1130 – 1140 ℃ heating, grain size 10 – 11, 540 – 550 ℃ × 1h × 4 times. 550 ℃ × 1h × 4 times after tempering, hardness up to 63 – 65 HRC.
  • (2) China’s own low-alloy high-speed steel 301, 4341 steel heat treatment 301 (W3Mo2Cr4VSi) and 4341 (W4Mo3Cr4VSi) steel 1175 – 1180 ℃ heating and quenching, grain size 10 – 11, 540 – 560 ℃ × 1h × 4 times after tempering, hardness up to 64 – 66 HRC.
  • (3) M2 and 9341 steel heat treatment M2 (W6Mo5Cr4V2) and 9341 (W9Mo3Cr4V) steel 1155 – 1165 ℃ heating quenching, grain size 10.5 – 11.5 grade, 550 – 560 ℃ × 1h × 4 tempering, hardness up to 64 – 66.5 HRC.

Heat treatment of high speed steel plug gauge gauges

Plug gauge is a commonly used gauge, the domestic had 20Cr steel carburizing quenching, but also with CrWMn, 9SiCr and other alloy steel production. High-speed steel heat treatment has a very high hardness, saw blade milling cutter, three-sided milling cutter, screw slot and other tools with bore, the operator is often measured in the machine tool is not stopped, which makes 9SiCr and other alloy steel plug gauge wear quickly and failure, the author used high-speed steel scrap head and 45 steel friction welding manufacturing plug gauge, received an unexpected effect.
Plug gauge material selection of high carbon saturation of M2 or high-performance high-speed steel manufacturing, quenching heating temperature to take the upper limit of the furnace before the grain size control in 9.5 – 10, 550 ℃ × 1h × 4 times after tempering, hardness ≥ 65HRC, service life of 9SiCr steel is more than 20 times.

Deal with the composition – organization – performance, product life “three points a line” relationship

I was in charge of the plant when the hot processing of all technical matters, in addition to the implementation of high-speed steel furnace number management, but also adhere to the raw materials into the plant trial quenching system. Only those who pass the test quenching system are allowed to enter the warehouse, and the test quenching data is used as a reference for mass production. Therefore, the technical personnel engaged in heat treatment must study the material, if you do not understand the material is the same as no introduction. 50 years, I have learned a truth, to improve heat treatment must deal with the composition, organization, performance and life of the workpiece (product lifeline) between the complex relationship (can be called “three points a line”). Material is the foundation, the foundation is not firm, the composition determines the organization, the organization determines the performance, the performance determines the life. According to the use of the workpiece, we should recommend the procurement of suitable components of steel, the implementation of the best heat treatment process, to obtain the outstanding performance required by the product, so that the manufactured products are high-grade, tasteful, and not just qualified products. Today’s society to qualified products do not have much room for survival, we must produce high-quality products.

Conclusion

High-speed steel compared with other steel, there are a variety of characteristics. With high-speed steel made of drill bits, milling cutters, taps, punches, bearings and plug gauge products, due to the different performance requirements, failure forms vary, so the heat treatment process must be personalized. Heat treatment workers to properly handle the composition, organization, performance and product life “three points a line” of the relationship, the unit of product quality up, to win market share is the hard truth.

Source: China Stainless Steel Pipes Manufacturer – Yaang Pipe Industry (www.epowermetals.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at [email protected]

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