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What is the difference between steel induction hardening process

In the induction heat treatment production, you may encounter problems of one kind or another, how to solve them quickly, neither delay production nor ensure quality is the key. In the future, we will edit some questions and answers from time to time and push them in time. I hope to have reference to colleagues in the industry.
One question: What is the difference between steel induction hardening and what should be noted?

Positive solution: In all kinds of cast iron, the induction hardening of gray cast iron is the most difficult. Induction hardening of gray cast iron is similar to steel, and the quenching equipment used is similar. Pay attention to the following differences:
1) The heating time is longer than steel, generally should be more than a few seconds, and should be kept for a period of time, so that the insoluble structure is dissolved into austenite. If the heating speed is too fast, it will lead to excessive thermal stress and crack.
2) The heating temperature should not be too high, the upper limit is 950 ° C, generally 900-930 ° C, different grades have an optimal temperature, when the heating temperature reaches 950 ° C, there will be phosphorus eutectic on the surface of the part, and there will be coarse residual Clan.
3) In order to make the temperature transition from the surface to the core slowly, it is best not to quench immediately after heating. Pre-cooling is preferably 0.5-2.0s.
4) Induction quenching of cast iron parts generally uses polymer solution or oil as quenching medium. Some parts such as cylinder liners directly use water as quenching medium, and more cylinder seat adopts self-cooling quenching.
5) After induction quenching of gray cast iron parts, low temperature tempering should be carried out to eliminate stress. For example, the cylinder liner adopts power frequency tempering, 220 °C × 1h.
The matrix of ferritic malleable cast iron is ferrite and graphite carbon. In order to dissolve carbon into austenite, it is necessary to increase the heating temperature (up to 1050 ° C) and extend the heating time (up to 1 min). In some graphite carbon lysites, a higher surface can be obtained after quenching.
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