Tool Steel Oil Qenching

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Tool steel oil qenching, carbon tool steel has a very short temperature range in the transition tendency, and the incubation time is very short and the hardenability is very poor. In order to avoid non-M transitions before the formation of martensite, an extremely high critical cooling rate is required, and in order to achieve complete hardening, a violent coolant, typically water and an aqueous solution, is required. In order to prevent the formation of soft spots, 10% NaOH (sodium hydroxide) can be added to the water to increase the quenching intensity. Even so, the martensitic hardened layer is still very shallow, only 2 to 3 mm. In the core region, it is lower than the critical cooling rate, and the transformation is carried out in the pearlite and bainite regions. Thus, the carbon tool steel has good toughness after quenching, which is an advantage. The inclusion of Si, Mn and residual Ni, Cr, Cu (from scrap) can reduce the critical cooling rate, increase the hardenability, and increase the depth of the hardened layer. However, this increases the risk of cracking during quenching during quenching. Therefore, oil quenching can sometimes be performed on such steels, which is difficult to grasp. Generally, the use of water-oil two-liquid quenching has a good effect.

Tool Steel Quenching
It must be heated slowly and evenly to the quenching temperature. Generally, it is very important to transfer the preheated workpiece to the furnace which is already in the quenching temperature and heat the salt bath furnace. Firstly, it is easy to avoid the explosion due to the moisture (water content) of the workpiece directly into the salt bath; The stress of initial heating can be avoided. Domestic heat treatment workers do not pay enough attention to it. It is believed that only high alloy steels do so because of poor thermal conductivity and high quenching temperature. In fact, it is also necessary to preheat the carbon tool steel during the initial low temperature stage (≤600 °C). It is preferably heated in a deoxidized salt bath furnace or a vacuum furnace or a furnace with a protective atmosphere.

The quenching temperature is 780-800 °C for the hypereutectoid steel. The workpiece with a complicated shape or a small size takes the lower limit; the large workpiece with a simple shape takes the upper limit, even a slightly higher temperature such as 820 °C. After the temperature is reached, it should be kept for a considerable period of time, then quenched in water or salt water, and appropriate movement according to the specific conditions of the workpiece. The water temperature is preferably 20 to 30 ° C (that is, room temperature). When quenching oil, the oil temperature is preferably 50-60 ° C, and the best quenching effect can be obtained. Water-oil two-liquid quenching is recommended for workpieces that may generate large stresses or quench cracks.

Tool Steel Tempering
Immediately after quenching, tempering should be carried out immediately. It is best to remove the workpiece from the quenching medium when quenched to 100 ° C, and then temper at a suitable temperature between 150 and 300 ° C to meet the required hardness and toughness. The tempering needs to be kept for a sufficient period of time and then cooled in still air. For mold working parts, rapid tempering, self-tempering, partial tempering and other processes are not suitable, tempering must be composed of components, quenching stress is not completely eliminated, and cracks are likely to occur in subsequent processing such as grinding and wire cutting, even There is no problem in the subsequent processing, and it is prone to early failure and shorten the life of the mold.

Carbon tool steel is hot-processed between 1050 and 800 °C. When the temperature is too high, coarse grain structure is formed, and hypereutectoid steel also forms coarse cementite. At this point, a normalizing or quenching and tempering treatment can be performed to improve. After forging, in order to improve the workability, annealing is necessary, and the annealed structure is the most recent original structure quenched. Sometimes, in order to eliminate the processing stress, stress relief annealing is performed.

The chemical composition of carbon tool steel, especially the amount and purity of P, S and Si, Mn can be divided into three precision grades. That is, high-quality steel, high-quality steel (steel No. A) or premium quality steel (steel with E). China’s carbon tool steel is only high-quality steel and high-grade steel. The specific provisions of P, S and Si, Mn and impurity alloying elements Cr, Ni and Cu are listed in the relevant standards.

Tool Steel Oil Qenching Furnace