Hot gas quenching devices, and hot gas heat treating system

Abstract

A metal heat treatment method includes quenching a workpiece by blowing an inert gas onto the workpiece, adjusting the temperature of the inert gas to approximately an isothermal holding temperature of the workpiece for transformation of the workpiece, holding the isothermal holding temperature within a margin of error of approximately plus or minus five degrees Celsius for a given period, and performing a metal heat treatment with the isothermal holding temperature kept statically or dynamically by varying the temperature of the hot-gas.

Description

TECHNICAL FIELD [0001] The present invention relates to a metal heat treatment method, a hot-gas quenching apparatus and a hot-gas heat treatment system to heat-treat effectively without a salt bath by use of hot-gas adjusted to hold a given intermediate temperature of an inert gas such as N2 or Ar in accordance with a transformation temperature of a metal. BACKGROUND ART [0002] A well-known quenching method for metal is to quench a workpiece preheated at an initial quenching temperature to room temperature before annealing the workpiece. Also, there is an austempering method, a martempering method and a marquenching method, referred to as “isothermal holding heat treatment”, to hold a given intermediate temperature based on an S-curve (T, T, T curve) for a certain period. [0003] Another well-known method is isothermal holding heat treatment with a salt bath disclosed in “Heat Treatment with Salt Bath” published by The Japan Society for Heat Treatment, Aug. 30th, 2000, p. 144-147. T...

AI Technical Summary

Benefits of technology

[0012] It is an object of the present invention to provide a metal heat treatment method to perform heat treatment with an isothermal holding temperature, a hot-gas quenching apparatus, and a hot-gas heat treatment system for the heat treatment method. According to the present invention, a heat treatment with hot-gas is performed more safely and more effectively than in the related art. Controlling the temperature of the hot-gas provides a new metal heat treatment method, which is not achieved by the prior method using a salt bath.

[0054] In a heat treatment using the above described hot-gas quenching apparatuses and hot-gas heat treatment system according to the present invention, since a heat treatment by a isothermal holding is performed, a risk of surface deterioration such as decarbonization and oxidation can be prevented. In addition, since surface roughness and warping do not occur, costs for refinishing can be reduced. By this heat treatment, a workpiece can have toughness, and can avoid a crack. Also, life of the workpiece can be made longer. Automation of the system enables management parameters to be observed surely and quality to be assured. The system eliminates uncomfortable environments, and does not cause problems of pollution or waste water. Smooth operation can be performed, and processing costs can be reduced. In this way, various benefits can be brought about.

Problems solved by technology

The solution has a problem in that there are many restrictions for the workpiece under the austempering operation.

Therefore, means for soaking and removing the workpiece in those solutions creates a restriction on the heat treatment in itself.

A plurality of salt bathes are required, and means for moving the workpiece to the salt bathes for these complicated steps, increases the scale of a plant and the cost of the products.

However, the blast furnace is not able to hold the isothermal holding temperature at an intermediate temperature for the heating treatment required by the austempering method, the martempering method and the marquenching method.

Because of the drastic variation of temperature, the blast furnace is unable to hold an isothermal holding temperature.

Because the inert gas introduced into the furnace is at room temperature, a problem of partial undercooling arises.

It is difficult to heat the inert gas to solve the problem.

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