At present, there are ten brands of steel bonded carbide in China, mainly used for making cold working die, blanking die, cold pier die, cold punching die, cold drawing die, cold extrusion die and so on. But there are still some problems in using steel bonded tungsten carbide to make hot working die.

 

The flash butt welding process can be used for the welding of 3Cr2W8 heat resistant steel. Taking Acu ψ-75akMCP1-100 as welding equipment, which can be calculated according to the 0.08-0.2 kVA/cmz performance. Bar below ψ50 mm can adopt MCP-75 flash butt welding. Before welding, it is necessary to check the quality of the two welding faces to ensure that the ellipticity of the ends is no more than 1.5mm, and the butt surface of the two weldments is not more than 0.7 mm. The full length bending rate is not more than 0.7 mm. and the diameter difference of the two weldments is not more than 1.3 mm.

 

 

When welding, the resistance of workpiece contacts is the largest, resulting in high temperature and semi molten metal. Then welding with pressure at the speed of 1-1.8mm/s. The pressure should be uniform and not interruptible, and the duration is about 10s. After annealing, the workpiece is directly annealed in annealing furnace to eliminate stress. Annealing can be done by closed isothermal annealing.

 

After welding, 100-150 mm thick iron filings are added to protect the workpiece from oxidation and decarburization than heating. Preserving heat for 4-6 h when the temperature is between 880-900℃. Then as the furnace cooled to 730-750℃, heat preservation was 3-5 h, the cooling rate below 30 C was reduced to 550-600℃, and then the furnace cover was opened half, the furnace temperature was reduced to 450-500℃, and the annealing cycle was usually 24 h, and the workpiece could be refined according to the requirements of the drawings.

 

The GT-35 steel bonded tungsten carbide is a chromium steel indium bonding phase, with tungsten carbide as a hard phase, which is produced by powder metallurgy. It not only has the performance of die steel and steel bonded hard alloy, but also has high red hardness and ideal thermal expansion coefficient, and its service life is 2-4 times higher than that of the heat-resistant die steel 3CrW8.

 

Due to the weldability of the GT-35 steel knot cemented carbide, the GT-35 steel knot hard alloy can be used as the working part (contact part with the hot workpiece) and the other parts of the mold (not directly contact with the heated workpiece) when the structure of the hot die is designed. The combination of the two through welding can not only guarantee the hardness and wear resistance of the die, but also keep the whole plasticity of the die, and greatly reduce the cost of the mold.