Gas quenching method

Abstract

This gas quenching method comprises a first phase (t1-t2) for quenching a workpiece by forcibly circulating a cooling gas, a second phase (t2-t3) for stopping the circulation of the cooling gas, reducing the pressure inside the furnace and thermally insulating same, and a third phase (t3 and beyond) for cooling the workpiece again using the cooling gas. In the second phase, the workpiece is maintained at an intermediate temperature that is higher than the martensitic transformation starting temperature and during this period, the temperatures of various parts of the workpiece equalize. Accordingly, it is possible to achieve uniform quenching and warping due to differences in cooling rate can be limited.

Description

technical field [0001] The present invention relates to a gas quenching method in which a workpiece is heated and then cooled using a cooling gas as quenching of steel. Background technique [0002] Quenching of steel is a heat treatment technique in which steel is brought into a high-temperature state and then rapidly cooled to obtain a martensitic structure. At present, for quenching large parts, liquid quenching methods in which liquids such as oil, water, or polymer solutions with high cooling properties are used as coolants are used in many cases to cool after heating. However, in this liquid quenching, boiling occurs unevenly during quenching, and as a result, the cooling rate becomes uneven and the quality becomes unstable. In addition, after quenching, a cleaning step for removing the coolant is required, and the treatment of waste water generated by cleaning is also a big problem. [0003] From the above point of view, in recent years, attention has been paid to a...

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Problems solved by technology

[0006] However, as in Non-Patent Document 1, in the conventional method of realizing multi-stage quenching using a plurality of gases with different temperatures, a heat exchanger for gas heating, a cooler for gas cooling, and a gas furnace are required. The damper for switching the flow path, etc., complicates the equipment

[0007] In addition, isothermalization is achieved by the balance between the temperature of the hot gas and the temperature of the workpiece. Therefore, it takes time until the temperature of the workpiece converges to the target isothermal treatment temperature, and the cycle time of the entire quenching treatment becomes longer.

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