Precautions for induction hardening of cast iron in high-frequency hardening machine

Among various cast irons, induction hardening of gray cast iron is the most difficult. Gray cast iron induction hardening is similar to steel, and the quenching equipment used is also similar. The following differences should be noted:

1) The heating time is longer than that of steel parts, generally more than a few seconds, and should be kept for a period of time, so that the insoluble structure can be dissolved into austenite. If the heating speed is too fast, it will lead to excessive thermal stress and easy to crack.

2) The heating temperature should not be too high, the upper limit is 950℃, generally 900-930℃, different grades have an optimal temperature, when the heating temperature reaches 950℃, phosphorus eutectic will appear on the surface of the part, and there will be coarse residues. Austenite.

3) In order to make the temperature slowly transition from the surface to the core, it is best not to quench immediately after heating, and pre-cooling 0.5 to 2.Os is best.

4) Induction quenching of cast iron parts generally uses polymer aqueous solution or oil as the quenching cooling medium, and some parts such as the cylinder liner are directly used as the quenching cooling medium with water, and the valve seat of the cylinder body is self-cooling quenching.

5) After induction hardening, gray iron castings should be tempered at low temperature in order to eliminate stress. For example, the cylinder liner should be tempered at 220℃x 1h. The matrix of ferritic malleable cast iron is ferrite and graphitic carbon. In order to dissolve carbon in austenite, it is necessary to increase the heating temperature (up to 1050℃) and extend the heating time (up to 1min or more), so as to make small Part of graphitic carbon is dissolved in austenite, and higher surface hardness can be obtained after quenching.