W18Cr4V steel is one of the most important tool materials in machining. It has high metal cutting performance (such as thermosetting and wear resistance), but its hardness is high, plasticity is low, forgeability is poor, mainly forging The deformation resistance is large, the forming is difficult, and it is prone to defects such as overheating, over-burning, cracks, and white spots. In the past few years, the forging of W18Cr4V cake-type milling cutters produced by our factory often has cracks in the forging process (in the actual production, metal ingots and steels of other materials also occur in the forging process during the forging process). This has resulted in varying levels of raw material waste and production losses. In particular, in recent years, companies have faced various difficulties (sufficient funds, shortage of raw materials, etc.), and conducted multi-party investigations and data collection, and conducted more thorough research on such issues. The promotion of the results will inevitably bring certain economic benefits to the production of the enterprise.
1. Performance characteristics and chemical composition
The outstanding features of W18Cr4V steel are: high heat hardness, high strength, hardness and wear resistance. At the same time, it also has high hardenability. However, the plasticity is low, the toughness is poor, the deformation resistance is large, and the forgeability is poor.
The chemical composition of W18Cr4V is shown in Table 1. The function of each alloying element is that W, V and Cr respectively form a composite carbide with C, so that the high speed tool steel maintains a high hardness at a relatively high temperature. W and V together create a thermosetting property, and the improvement of W and C greatly improves the wear resistance of steel. Cr increases the hardenability of steel, which together with W forms a composite carbide that prevents the accumulation of carbides at high temperatures.
2. High-speed steel organization
The as-cast microstructure of high-speed tool steel usually consists of three forms of carbide: nascent carbide precipitated by liquid alloy, which is coarse fish bone (called Leysite), which has high brittleness and low plasticity; reticulated secondary carbide The mechanical properties of the material are reduced; finally, the finely uniformly dispersed eutectoid cubic carbide is precipitated by transformation from austenite to pearlite. These composite carbides are difficult to completely dissolve into austenite and cannot be dispersed by heat treatment. Only the crude primary carbide and another part of the secondary carbide can be crushed by forging and uniformly distributed by metal flow. . The high-speed tool steel is rolled into steel (this material is used to form a sheet-milling forging blank). Due to the different degree of deformation, the degree of carbide fracture (called carbide segregation) and distribution in the steel is also different. Due to the segregation of carbides and other factors, the defects of the as-cast microstructure cannot be completely eliminated in the steel structure after rolling, and further forging is required.
For more details, please see the attached content or "Metal Processing (Hot Processing)" No. 19
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