The determination of quenching and heat preservation time of the induction heating quenching machine
in rapid heat treatment
It is the characteristic of rapid heat treatment of induction heating to shorten the heat preservation time by improving heat treatment heating temperature.In special cases, it is necessary to maintain a short heat preservation time, which is the same for quenching and tempering.
Determination of steel quenching and heat preservation time.
When hardening of carbon steel and low alloy steel, the carbon content in steel is high (carbon quality score is above 0.06%).Steel containing carbon, nitrogen has strong affinity for the alloy elements, such as chromium, vanadium, niobium and titanium, tungsten, molybdenum, etc, in order to make the formation of carbides, nitrides can be fully dissolved in heating process, at the same time of raising temperature increase a certain time of heat preservation is good, homogenization of austenite carbon content is also good.
The heating temperature and thermal insulation time of 21-4n steel and the relationship between undissolved carbide content are given in the table below.From the comparison data in the table, it can be seen that induction heating insulation 30s and electric furnace heating 3600s heat preservation, the total amount of undissolved carbide in steel after quenching is at the same level.At the same time, during the study of the quenching process of 35CrMo steel tube induction heating, the quenching temperature was extended from30sto 60s, and no change was found in the room temperature performance of steel after quenching.Ordinary carbon steel and low alloy steel, therefore, induction heating quenching heat preservation time, keep around 30 s is feasible, will not affect the performance of hardened steel, in contrast, if the hardening holding time is too long, not only to increase the burden on process equipment, and will cause grain growth, reduce the quenching treatment effect.
The heating temperature and heat preservation time and the total amount of undissolved carbide of induction quenching machine
The heating temperature / ℃
Total amount of undissolved carbide /%
Induction heating (30s insulation)
Electric furnace heating（360s insulation）
Note: the test steel is 21-4n hot strong valve steel
The method of extending quenching and retaining time
In the case of continuous rapid heating, the specific method of extending quenching and retaining time is to install the thermal insulation device after quenching the final sensor.Keep the steel in the device to keep the quenching temperature.The insulation can be heated by induction heating, or by using resistance wire or other forms of heat source, but the temperature should be kept constant.The length of the insulation device can be calculated by L=Vt formula.Which is suitable for steel speed V (cm s - 1), t need to extend the time of heat preservation for the length of the insulation device (s), L (cm), L value can be decomposed into several only insulation devices to facilitate operation.
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