On 2018-08-08 14:48:54
Salt bath quenching process
The heating temperature and holding time of the salt bath quenching process should not be too high, otherwise the surface decarburization will be caused. If the heating temperature is too high, the austenite grains will be coarse, the heating temperature will be too low, and the holding time will be insufficient, the carbide in the structure will not be fully dissolved, and the uniform troostite and sorbite will not be obtained after tempering in the industrial electric furnace. All these shortcomings will reduce the elastic and fatigue strength of steel. Decarburization on the surface will reduce the fatigue strength strongly. Therefore, measures should be taken to prevent oxidation and decarburization during heating. Heating is carried out in a salt bath or controlled atmosphere furnace. When heating in the air furnace, the heating gas should be slightly reductive, and the furnace load should not be too large; high temperature and rapid heating can also be adopted to shorten the holding time.
Salt bath quenching process operation of spring steel: generally, the heat preservation coefficient of heating in air furnace shall not exceed 2 min / mm, and heating in salt bath shall not exceed 0.5 min / mm. The quenching and holding time is longer than that of general alloy steel, so that the carbide in the steel can be fully dissolved. The hot formed spring shall be hot formed at a temperature higher than the quenching temperature, and the residual heat shall be quenched after forming; the forming temperature shall not be too high to prevent overheating. The critical points of heating and cooling of common spring steel are shown in relevant chapters. When the spring is quenched, the quenching temperature shall be ensured.
Salt bath quenching medium should have enough cooling capacity to ensure that enough martensite structure and hardness are obtained, and no ferrite appears in the center. Generally, spring quenching is oil cooling or isothermal quenching in 350 ℃ salt bath. For steel or large spring with poor hardenability, water quenching oil cooling can be used, but the water quenching time shall be strictly controlled to prevent cracking. In order to reduce the deformation of the spring, do not erect or stack it when charging, and the cooling mode shall be correct. If the deformation after quenching exceeds the specified requirements, tempering shall be carried out after correction. Use fixture to heat and cool.
Salt bath quenching heat treatment has the advantages of high thermal efficiency, no thermal inertia, fast heating speed, uniform heating, convenient operation, preventing oxidation and decarburization, and the furnace temperature can rise to 1300 ℃. It is suitable for steel quenching and tempering heating and liquid chemical heat treatment, especially for high temperature quenching heating. Piston pin (including automobile) is connected with piston and connecting rod. When it moves, it is equivalent to two-point beam, which bears asymmetric alternating load and certain impact load. Its surface works under the condition of friction for a long time, and it should have enough strength, toughness, wear resistance and fatigue limit. Generally, no matter the piston pin is made in the form of bar, hot-rolled tube or cold drawn tube, it is processed by machining, carburizing, quenching, tempering and finishing. So salt bath quenching can not take place of carburizing quenching, but salt bath furnace can carry out carburizing process. After salt bath quenching, tempering process is usually required.
The vacuum quenching furnace is suitable for solution treatment and aging treatment of large and medium vacuum parts. Vacuum high pressure gas quenching furnace is a very advanced vacuum heat treatment equipment. Its outstanding performance and unique design provide a wide range of vacuum bright gas quenching, annealing and magnetic materials suitable for high-precision parts of alloy materials such as high-speed steel, die steel, stainless steel, alloy steel and titanium alloy.