Vacuum Heat Treatment of Hand Hacksaw Blades

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With the development of manufacturing technology, the high-carbon steel hand-used hacksaw blades that have been used in China for many years will gradually be replaced by high-speed hacksaw blades. The high-speed steel hand saw blade has undergone three stages of development. The first generation is made of full high-speed steel, and it is heated, quenched and tempered in a salt bath furnace. The material and manufacturing cost are high, and it is easy to chip and break; the second generation uses high-speed steel. Electron beam welding of steel and spring steel is used to make bimetal saw blades. The manufacturing process is complex, which solves the problem of broken bars, but it is also prone to tooth chipping and high cost.

On the basis of the double-layer glow ion infiltrating metal hand hacksaw blade metal infiltration process developed by Taiyuan University of Technology, we have developed the third-generation special high-speed steel hand hacksaw blade, and developed a complete set of vacuum heat treatment process. The vacuum heat treatment production line of hand-used hacksaw blade completely replaces the heating, quenching and tempering process of salt bath furnace commonly used in China.

This paper introduces the main characteristics of vacuum heat treatment of special high-speed steel hand hacksaw blades. The whole heat treatment process includes six processes including vacuum ion infiltration metallization, vacuum solution treatment, vacuum ion carburization, vacuum quenching, vacuum tempering and vacuum nitriding.

1.Characteristics of special high speed steel hand hacksaw blades

Use ordinary low carbon steel or low alloy steel to process into hand-use hacksaw blades, infiltrate special alloy elements (including tungsten, molybdenum, chromium, vanadium and cobalt, etc., with a total content of not less than 10%) on the surface of the saw teeth, and then carry out Carburizing, so that the carbon content of the saw tooth surface reaches more than 0.70%, and the carbon content of the saw back is kept below 0.45%, and the saw tooth material becomes a special high-speed steel. After strict heat treatment, the saw tooth has the performance of high-speed steel and the saw back Has the toughness of the base material. A diffusion layer transition is formed between the saw tooth and the saw back. This is a saw blade with a new structure, which eliminates the welding process of the two materials of the bimetal saw blade.

The special high-speed steel hand-used hacksaw blade we have successfully developed has stable product quality, small deformation, smooth surface and high degree of equipment automation due to the vacuum heat treatment process, which completely eliminates the pollution to the environment. This product has been affirmed by foreign users.

2.Vacuum Ionizing Metal

In a specially designed vacuum ion infiltration metal furnace, the ion infiltration metal treatment is carried out, the vacuum degree is 10~100Pa, argon gas protection, and the temperature is kept at 1150~1250℃ for 2~6h, so that the saw blade teeth can be obtained 0.2~0.5mm deep special Alloy layer of high speed steel composition.

3.Vacuum solution treatment

After the saw blade teeth are infiltrated with metal, the distribution of alloying elements in the infiltrated metal layer is not uniform, and the metallographic structure of the infiltration layer does not fully meet the requirements of the subsequent heat treatment process. Treatment, supplemented by rapid cooling, homogenizes the alloying elements of the infiltrated metal layer. If the salt bath furnace is used for heating, the surface of the saw blade will be corroded, the alloy layer will also be partially dissolved, and the pollution will be serious. This process is heated by vacuum furnace, kept at 1200～1300℃ for 5～60min, and then cooled with high pressure gas or cooled in oil. After treatment, the deformation is small, the surface is smooth, and the metallographic structure achieves the purpose of solution treatment.

4.Vacuum ion carburizing and vacuum quenching

The three processes of vacuum solution treatment, vacuum ion carburizing and vacuum quenching are carried out continuously in the same vacuum furnace according to the set program.

The saw blade is prepared for subsequent carburizing after solution treatment. Vacuum ion carburizing can ensure that the saw teeth are carburized and the saw back is not carburized, the carburizing layer is uniform, the sea carbon concentration is high, and the infiltration rate is fast. Direct heating and quenching after carburizing is another feature of this process. In the ordinary gas carburizing furnace, the high-speed steel after carburizing cannot be heated and quenched at high temperature, but the equipment used in this process can directly heat up to 1200-1300 ℃ for quenching after carburizing.

In vacuum ion carburization, the saw blade is used as the cathode to carry out glow discharge carburization in a carbon-containing atmosphere, and the temperature is kept at 850 to 1050 ° C for 1 to 2 hours, and a carburized layer with a depth of 0.2 to 1.0 mm can be obtained. After carburizing, it is directly heated to the quenching heating temperature of 1200-1300°C, kept for 5-30 minutes, and then quenched with high pressure gas or oil.

5.Vacuum tempering

After quenching, the surface hardness of the saw teeth of the special high-speed steel saw blade is 62-66HRC. After 2 or 3 times of tempering at 520-560℃×1h, the hardness is 62-65HRC. At the same time, the back of the saw blade has suitable strength and toughness, and the hardness is 25-35HRC.

In order to further improve the performance of the special high speed steel hand hacksaw blade, vacuum nitriding can be carried out after the first vacuum tempering. Passing through ammonia gas and keeping the temperature at 500-560C for 1-5h can obtain a nitriding layer of 0.05-0.15mm, which significantly improves the red hardness and wear resistance of the saw blade.

Equipment selection: The VOGQ series vacuum heat treatment furnace produced by SIMUWU is a high-quality product for the vacuum heat treatment of tooling and molds. The good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum heat treatment process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.