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Plasma Arc Welding of Bimetallic Saw Blades
Generally, machine saw blades are made of high-speed steel. In fact, only the teeth of the saw blade need to be made of high-speed steel. The method of plasma arc welding bimetal can use high-speed steel reasonably and save precious materials. The shape of the welded saw blade is shown in Figure Welding saw blade shape. The teeth are made of high-speed steel and the back is made of low-alloy steel. Toughness, not easy to break. See Table The chemical composition and hardness of the material of the bimetallic saw blade for the chemical composition and hardness of bimetallic saw blades. The blade material is W18Cr4V, 490 mm x9.5mmx1.8 mm cold-rolled strip steel. The back material is 65Mn, 490mmx30mmx1.8mm cold-rolled strip steel. The above materials are all in the annealed state.
Craft equipment of plasma arc welding and cutting
The simple tooling for welding saw blades is shown in Figure Simple Tooling for plasma arc Welding Saw Blades. The welding torch is fixed, the saw blade is moved by the moving fixture, and the back of the weldment is ventilated with protective gas. There is no adaptive control sensor in the lower part of the weldment, which can automatically adjust welding parameters (such as welding speed) to ensure uniform and stable welding quality.
Plasma Arc Welding parameters
A three-hole nozzle is used, the hole diameter is 2 mm, the hole length is 2.4 mm, the diameter of the small holes on both sides of the nozzle hole is 0.8 mm, and the hole spacing is 6 mm. Both shielding gas and ion gas are argon. See table Welding parameters for welding saw blades for welding parameters
Hardness test results
The hardness of the weld seam after welding is very high, and the hardness of the tooth base metal and heat-affected zone is also significantly increased, while the hardness of the back base metal is low.
Microstructure Analysis of Welded Joints
The hardened structure appeared in the weld seam and the heat-affected zone of the bimetallic welded joint. There is more ledeburite in the weld, and there is also a small amount of ledeburite in the heat-affected zone near the high-speed steel. The heat-affected zone of the backrest is wider (2.65 mm), and the heat-affected zone near the teeth is narrower. (0.81mm). The weld width is 2.50 mm. From the perspective of metallographic structure, the metallographic properties of the weld seam and the near seam area are very poor, especially the weld seam is very hard and brittle. This unqualified structure can be improved by post-weld heat treatment.
Post-weld annealing
Annealing treatment is required within 24 hours after welding, and the annealing process curve is shown in Figure Annealing process curve. After annealing, the ledeburite structure in the weld is largely eliminated, and the hardness of the teeth, weld and back are all less than 24 HRC, which can meet the processing requirements. In short, the technical requirements are basically met after annealing. The metallographic structure distribution of each zone after the welded joint is annealed is shown in Figure Distribution of metallographic structure in each area after annealing.
Quenching treatment
The quenching treatment is carried out according to the performance of the high-speed hacksaw blade, and the performance of the back material is also taken into consideration. The quenching process curve is shown in Figure Quenching process curve. After quenching, the hardness of the teeth is 67 HRC, the hardness of the weld is 65.1 HRC, and the hardness of the back is 52.4 HRC. The hardness value is greatly increased, and the ledeburite in the weld and heat-affected zone basically disappears, but there is more residual ledeburite.
Tempering treatment
After quenching, three tempering treatments are required, and the tempering process curve is shown in Figure Tempering process curve. After quenching, it must be tempered in time, generally not exceeding 24h
Metallographic structure after tempering
The metallographic structure after tempering, the teeth are tempered martensite + a small amount of residual carbide; the weld is tempered martensite + fine mesh of residual carbide; the back is acicular sorbite + a small amount of feathery bainite Body + Troostite.
Performance of bimetallic saw blades
The saw blade processed by the above process can be used to saw round steel or square steel with a diameter of 40~130mm (the material is 45 steel). Bi-metal saw blades can completely replace saw blades made of high-speed steel.