Steel surface quenching method: steel pipe surface quenching is a local quenching method, in the workpiece surface to obtain a certain degree of hardening layer, while the heart remains undisturbed state. Surface quenching the surface of the workpiece quickly heated, and soon reached the quenching temperature, the heat has yet to spread to the workpiece has been cooling the heart to achieve the effect of local quenching. The surface of the workpiece should be carefully cleaned to remove burrs, iron and oil, etc., the surface state will significantly affect the quenching effect.
Commonly used steel pipe surface quenching
(1) induction hardening
In a induction coil through a certain frequency of alternating current (sub-high frequency, intermediate frequency and power frequency three), so that the induction coil around the same frequency of alternating magnetic field, placed in the magnetic field of the workpiece to produce the same frequency with the induction coil , The opposite direction of the induced current, known as the eddy current. Due to the skin effect, the eddy current is mainly concentrated in the surface of the workpiece. The heat generated by the eddy current heats the surface of the workpiece quickly to the quenching temperature, then the water is sprayed to the part, so that the surface of the workpiece is hardened and the thickness of the hardened layer is thinner with increasing frequency. This is the induction heating surface hardening. Heating speed is very fast, only in the vortex through the surface within a few seconds will be able to surface temperature rise to 800 ~ 1000 ℃, and the heart too late to heat up. So the principle of induction hardening is caused by the electromagnetic induction in the workpiece surface eddy current heating the surface of the workpiece, then quickly cold, so that the surface hardened surface hardening technology. The actual application of the current frequency from 50Hz ~ 500KHz. Among them, 50Hz ~ 10KHz for the intermediate frequency, mainly to the thyristor (thyristor), for deep hardened layer depth, such as roll, etc .; 10KHz ~ 50KHz for the super audio to IGBT (insulated gate bipolar transistor is BJT (bipolar transistor) and MOS (insulated gate type field effect transistor) composed of composite full control voltage drive power semiconductor devices), the most widely used; 50KHz above known as high frequency, used in fine workpiece processing , Mainly to the tube, useful MOS tube.
(2) flame quenching
A process of maximizing the surface of a workpiece with a flame, making it austenitized and quenched. The heat of the flame supply surface must be greater than the heat from the surface to the heart and the loss of heat to achieve surface hardening. The oxygen-acetylene mixture has the highest temperature, up to 3100 ℃, and the gas-oxygen mixture gas; the natural gas-oxygen mixture; the propane-oxygen gas mixture, wherein the propane-oxygen mixture Gas produces the lowest flame temperature, 2650 ℃. The advantage is simple equipment, easy operation, low cost, free from the workpiece size limit, after quenching the surface without oxidation and decarburization phenomenon, deformation small. Disadvantages are easy to overheat, subject to surface shape restrictions, heating gas explosion hazard.