Since the 1970s, the market share of high-speed steel tools has gradually been eroded by cemented carbide tools. However, in recent years, with the improvement of cutting performance of powder metallurgy high speed steel (P/M HSS) tools, the market share of high speed steel tools has rebounded. Compared with ordinary high-speed steel tools, powder metallurgy high-speed steel tools have higher hardness, better toughness and wear resistance. Therefore, in some applications (such as high impact, large cutting processing), powder metallurgy high speed steel Knives have a tendency to gradually replace solid carbide tools that are more brittle and prone to chipping under cutting impact.
The powder metallurgy high-speed steel manufacturing process was successfully developed in Sweden in the late 1960s and entered the market in the early 1970s. The process can add more alloying elements in high-speed steel without damaging the toughness or grindability of the material, so that it can be made with high hardness, high wear resistance, absorbable cutting impact, suitable for high resection rate processing and breaking. Continued cutting tools.
High-speed steel tool materials are mainly composed of two basic components: one is metal carbide (tungsten carbide, molybdenum carbide or vanadium carbide), which gives the tool better wear resistance; the other is distributed around the steel matrix, which makes The tool has good toughness and the ability to absorb shock and prevent chipping. When preparing ordinary high-speed steel, the molten steel is injected into the mold from the ladle, and it is slowly cooled and solidified. At this time, the metal carbide precipitates from the solution and forms a large agglomerate. The higher the alloy content added to the high speed steel, the larger the carbide agglomerates. When a critical point is reached, a very large carbide mass (up to 40 mm in diameter) can be formed. The critical point at which large carbide agglomerates appear varies slightly depending on the size of the ingot and other factors, but generally occurs when the vanadium carbide content reaches about 4%. By subjecting the ingot to subsequent processing such as forging and rolling, a part of the carbide agglomerates can be pulverized, but it is impossible to completely eliminate it. Although increasing the amount of metal carbide particles in the steel can improve the wear resistance of the material, as the alloy content increases, the size of the carbide and the number of agglomerates increase, which is extremely unfavorable for the toughness of the steel. Impact, because large carbide clusters can quickly become the starting point for cracking.
The preparation process of powder metallurgy high-speed steel is different from that of ordinary high-speed steel. The molten steel is not directly injected into the mold, but is blown into a nitrogen stream through a small nozzle for atomization, and the sprayed molten steel is rapidly cooled to Small steel particles (less than 1mm in diameter). Since the carbides in the aqueous steel solution are too late to precipitate and form a cluster during the rapid cooling process, the obtained carbide particles have fine and uniform distribution of carbide particles. The steel powder is sieved, placed in a steel drum, and the air in the middle of the steel powder is vacuumed to form a vacuum state, and then the steel powder in the steel drum is pressed and formed under high temperature and high pressure to obtain a density of 100. % of powder metallurgy high speed steel blanks. This preparation process is called hot isostatic pressing (HIPing) molding. The blank can then be subjected to subsequent processing such as forging, rolling, and the like.
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