JP2017006945A - Hot forging method and hot forging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hot forging method and a hot forging device by which generation of an oxidized scale during forging can be suppressed.SOLUTION: A hot forging method comprises: a temperature rising process in which a temperature of billet is risen to a first prescribed temperature (1,200°C); a cooling process in which the billet, of which the temperature is risen to the first prescribed temperature, is cooled to a second prescribed temperature (900°C), which is equal to or higher than A3 transformation point, at a prescribed cooling rate; a descaling process in which an oxidized scale on a surface of the billet, which is cooled to the second prescribed temperature, is removed; and a forging process in which the billet which is cooled to the second prescribed temperature and from which the oxidized scale is removed, is forged.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a hot forging method and a hot forging apparatus.

  Patent Document 1 discloses a hot forging method in which forging is performed at a temperature of 1,050 ° C. or higher.

JP 2007-84909

However, in the above prior art, since the temperature during forging is high, there is a problem that a large amount of oxide scale is generated during forging, which causes a decrease in mold life and seizure.
The objective of this invention is providing the hot forging method and hot forging apparatus which can suppress generation | occurrence | production of the oxide scale at the time of forging.

  In order to achieve the above object, in the hot forging method of the present invention, a temperature raising step of raising the temperature of the workpiece to the first predetermined temperature, and a temperature of the workpiece heated to the first predetermined temperature to a predetermined cooling rate A cooling step for cooling to a second predetermined temperature not lower than the A3 transformation point, a descaling step for removing oxide scale on the surface of the workpiece cooled to the second predetermined temperature, cooling to the second predetermined temperature, and And a forging step for forging the workpiece from which the oxide scale has been removed.

  In this invention, since the temperature at the time of forging is low, generation | occurrence | production of the oxide scale at the time of forging can be suppressed.

It is a figure which shows the structure of the hot forging apparatus of Example 1. FIG. It is a figure which shows the heat history of the billet 5 in the hot forging method of Example 1. FIG.

[Example 1]
First, the hot forging device of Example 1 will be described. 1 is a diagram illustrating a configuration of a hot forging device according to a first embodiment.
The hot forging device of Example 1 includes a temperature raising device (temperature raising means) 1, a cooling device (cooling means) 2, a descaling / forging device (descaling means, forging means) 3 and a cooling apparatus (cooling means) 4 Is provided.
As the temperature raising step, the temperature raising device 1 uses an induction heater, for example, to heat the billet (steel material) 5 that is a workpiece and raise the temperature to the first predetermined temperature. The first predetermined temperature is 1,200 ° C.

  As a cooling step, the cooling device 2 cools the billet 5 heated by the temperature raising device 1 to a second predetermined temperature at a predetermined cooling rate. The second predetermined temperature is a temperature equal to or higher than the A3 transformation point and is 900 ° C. close to the A3 transformation point. The A3 transformation point is the temperature at which the transformation from a low-temperature body-centered cubic lattice to an austenite face-centered cubic lattice. The cooling device 2 includes a belt conveyor 2a, a fan 2b, temperature sensors 2c and 2d, and a stopper 2e. The belt conveyor 2a conveys the billet 5 heated by the temperature raising device 1 to the descaling / forging device 3. The fan 2b blows each billet 5 on the belt conveyor 2a, and the fan 2b cools each billet 5 being conveyed by the belt conveyor 2a by blowing. The temperature sensors 2c and 2d are provided upstream and downstream of the belt conveyor 2a, and measure the temperature of each billet 5. The stopper 2e is provided on the belt conveyor 2a, and when the temperature of the billet 5 measured by the temperature sensor 2d exceeds 900 ° C., the billet 5 is prohibited from being transferred to the descaling / forging device 3, and the billet 5 When the temperature is 900 ° C. or lower, transfer of the billet 5 to the descaling / forging apparatus 3 is permitted. That is, the cooling device 2 causes the billet 5 to wait until it is cooled until the temperature of the billet 5 reaches 900 ° C.

The descaling / forging apparatus 3 performs a descaling process and a forging press as a descaling process and a forging process. The descaling process is a process of removing the oxide scale on the surface of the billet 5 by performing a slight upsetting process while blowing high-pressure air to the billet 5. The upsetting process is a process of compressing the billet 5 in the axial direction.
As a cooling process, the cooler 4 leaves the billet 5 forged by the descaling / forging device 3 on the belt conveyor 4a and cools it by natural cooling. The belt conveyor 4a conveys the billet 5 forged by the descaling / forging device 3 to a predetermined position. The billet 5 transported to a predetermined position is put into a container 6 and transported to a shot blasting device (not shown), and subjected to a descaling process for removing oxide scale generated during forging. After the descaling process, a carburizing process is performed on the surface of the billet 5 as a post process. The wear resistance of the billet 5 is improved by the carburizing process.

[Oxidation scale suppression]
FIG. 2 is a diagram showing the thermal history of the billet 5 in the hot forging method of the first embodiment.
The billet 5 is heated from room temperature to 1,200 ° C. in the temperature raising process and transformed into austenite, and then cooled at a predetermined cooling rate to 900 ° C. higher by the A3 transformation point in the cooling process. When the temperature of the billet 5 is cooled to 900 ° C., the billet 5 is forged by a forging process after the oxide scale on the surface is removed by the descaling process and given a predetermined shape. After forging, it is cooled at a predetermined cooling rate (cooling rate due to natural cooling) by a cooling step, and the austenite phase is transformed into a ferrite + pearlite phase.
The flow of the hot forging method of Example 1 is shown below.
Example 1: Temperature rise to 1,200 ° C → Cool to 900 ° C → Descale → Forging

Here, as a comparative example of Example 1, two hot forging methods performed along the following flow will be considered.
Comparative Example 1: Temperature rise to 1,200 ° C → Descale → Forging Comparative Example 2: Temperature rise to 1,200 ° C → Descale → Cool to 900 ° C → Forging First, in the hot forging method of Comparative Example 1, the temperature during forging is high More oxide scale is generated during forging. Next, in the hot forging method of Comparative Example 2, although the temperature at the time of forging is low, the temperature immediately after the descaling is high, so that the oxide scale generated immediately after the descaling until forging increases. That is, in the hot forging methods of Comparative Examples 1 and 2, there is a problem of die life reduction and seizure due to the oxide scale.

  In contrast, in the hot forging method of Example 1, the billet 5 is cooled to 900 ° C., and then descaling and forging are performed. Thereby, since the temperature at the time of forging is low compared with the hot forging method of the comparative example 1, generation | occurrence | production of the oxide scale at the time of forging can be suppressed. Moreover, since the temperature immediately after de-scaling is lower than that in the hot forging method of Comparative Example 2, it is possible to suppress oxidized scale generated between immediately after de-scaling and forging. As a result, it is possible to suppress a decrease in mold life and seizure due to the oxide scale.

  In the hot forging method of Example 1, the billet 5 is forged at a temperature equal to or higher than the A3 transformation point and 900 ° C. close to the A3 transformation point. When forging at a temperature above the A3 transformation point (austenite region), the lower the temperature, the smaller the recrystallized grains. Since the hardenability is lowered as the crystal grains are smaller, the formation of bainite during subsequent cooling can be suppressed. If bainite is contained in the ferrite + pearlite metal structure, the mechanical strength and machinability are deteriorated, so that high mechanical strength and machinability can be secured by suppressing the formation of bainite. Moreover, in the hot forging method of Example 1, the billet 5 is naturally cooled after forging. The smaller the crystal grain, the higher the critical cooling rate for bainite generation. Therefore, the bainite generation can be prevented by allowing the billet 5 to cool naturally.

  In the hot forging method of Example 1, the billet 5 is once heated to 1,200 ° C. Here, if the descaling and forging are performed by raising the temperature to 900 ° C. without raising the temperature to 1,200 ° C., the effect of preventing grain coarsening in the carburizing process in the subsequent process is not possible because the aluminum-nitrogen compound is not sufficiently dissolved. Loses sight. Therefore, once the billet 5 is heated to 1,200 ° C., the aluminum-nitrogen compound can be sufficiently dissolved in a short period of time, so that the reduction in the effect of preventing grain coarsening in the subsequent carburizing process can be suppressed. The wear resistance of billet 5 can be improved.

In Example 1, the following effects are exhibited.
(1) A temperature raising step for raising the billet 5 to a first predetermined temperature (1,200 ° C.) and a second predetermined temperature (above the A3 transformation point) at a predetermined cooling rate for the billet 5 heated to the first predetermined temperature. A cooling process for cooling to 900 ° C., a descaling process for removing oxide scale on the surface of the billet 5 cooled to the second predetermined temperature, and a billet 5 cooled to the second predetermined temperature and from which the oxide scale has been removed. And a forging process for forging.
Therefore, since both the oxide scale generated immediately after the descaling and forging and during forging can be suppressed, it is possible to suppress die life reduction and seizure due to the oxide scale. Moreover, the loss of the effect of preventing grain coarsening in the subsequent carburizing treatment can be suppressed, and the wear resistance can be improved.

(2) A cooling step for cooling the forged billet 5 at a predetermined cooling rate is provided, and the cooling rate in the cooling step is higher than the cooling rate in the cooling step.
Therefore, the cooling rate is such that bainite is not generated during cooling, that is, the cooling rate is lower than the critical cooling rate for bainite generation. A balance can be realized.

(3) The cooling step is a step of measuring the temperature of the billet 5 and waiting the billet 5 until the billet 5 is cooled to the second predetermined temperature.
Therefore, temperature variation of billet 5 at the time of forging can be suppressed.

(4) The temperature raising device 1 that raises the billet 5 to the first predetermined temperature (1,200 ° C.) and the second predetermined temperature that is equal to or higher than the A3 transformation point at the predetermined cooling rate of the billet 5 that is heated to the first predetermined temperature. The cooling device 2 that cools to (900 ° C.) and the billet 5 that has been cooled to the second predetermined temperature while removing the oxide scale on the surface of the billet 5 that has been cooled to the second predetermined temperature, and the oxide scale has been removed. And a descaling and forging device 3 for forging.
Therefore, the oxide scale generated immediately after the descaling to the forging and the oxide scale generated during the forging can be suppressed, and the reduction in die life and seizure due to the oxide scale can be suppressed. Moreover, the loss of the effect of preventing grain coarsening in the subsequent carburizing treatment can be suppressed, and the wear resistance can be improved.

(5) A cooler 4 is provided for cooling the forged billet 5 at a predetermined cooling rate, and the predetermined cooling rate is higher than the predetermined cooling rate.
Therefore, the cooling rate is such that bainite is not generated during cooling, that is, the cooling rate is lower than the critical cooling rate for bainite generation. A balance can be realized.

(6) The cooling device 2 measures the temperature of the billet 5 and causes the billet 5 to wait until the billet 5 is cooled to the second predetermined temperature.
Therefore, temperature variation of billet 5 at the time of forging can be suppressed.

[Other Examples]
As mentioned above, although the form for implementing this invention was demonstrated based on the Example, the concrete structure of this invention is not limited to the structure shown in the Example, and is the range which does not deviate from the summary of invention. Any design changes are included in the present invention.
For example, the first predetermined temperature may be any temperature that can sufficiently dissolve the aluminum-nitrogen compound in a short time. Further, the second predetermined temperature may be a temperature not lower than the A3 transformation point.
The cooling rate in the cooling step may be less than the critical cooling rate for bainite generation.
A descaling means and a forging means may be provided separately.

1 Temperature raising device (temperature raising means)
2 Cooling device (cooling means)
2a Belt conveyor
2b fan
2c, 2d temperature sensor
2e Stopper
3 Descaling and forging equipment (descaling means, forging means)
4 Cooling device (cooling means)
4a belt conveyor
5 Billet (workpiece)
6 containers

Claims (6)

A temperature raising step for raising the temperature of the workpiece to a first predetermined temperature;
Cooling the workpiece heated to the first predetermined temperature at a predetermined cooling rate to a second predetermined temperature not lower than the A3 transformation point;
A descaling step of removing oxide scale on the surface of the workpiece cooled to the second predetermined temperature;
A forging step of forging the workpiece that has been cooled to the second predetermined temperature and from which the oxide scale has been removed;
A hot forging method comprising: In the hot forging method according to claim 1,
A cooling step of cooling the forged workpiece at a predetermined cooling rate;
The hot forging method, wherein the predetermined cooling rate is higher than the predetermined cooling rate. In the hot forging method according to claim 1 or 2,
The hot forging method is characterized in that the cooling step is a step of measuring the temperature of the workpiece and waiting the workpiece until the workpiece is cooled to the second predetermined temperature. A temperature raising means for raising the temperature of the workpiece to a first predetermined temperature;
Cooling means for cooling the workpiece heated to the first predetermined temperature to a second predetermined temperature not lower than the A3 transformation point at a predetermined cooling rate;
Descaling means for removing oxide scale on the surface of the workpiece cooled to the second predetermined temperature;
Forging means for forging the workpiece that has been cooled to the second predetermined temperature and from which the oxide scale has been removed;
A hot forging device comprising: In the hot forging device according to claim 4,
A cooling means for cooling the forged workpiece at a predetermined cooling rate;
The hot forging device, wherein the predetermined cooling rate is higher than the predetermined cooling rate. In the hot forging device according to claim 4 or 5,
The hot forging apparatus characterized in that the cooling means measures the temperature of the workpiece and waits the workpiece until the workpiece is cooled to the second predetermined temperature.

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