JPH0331414A - High-frequency hardening method - Google Patents

Abstract

PURPOSE:To allow a high-frequency hardening treatment with which quenching crack does not arise by subjecting a cam shaft made of cast iron to a high-frequency induction beating to an austenitization temp., then to a continuous cooling by a primary cooling stage in which the cam shaft is cooled by a specific liquid for hardening and a secondary cooling stage in succession thereto at the time of the highfrequency hardening of the cam shaft. CONSTITUTION:The machine part made of the cast iron, such as cam shaft, for which strength is required, is heated to the austenitization temp. by a high- frequency heating coil and is then cooled down to the Ms point or below by spraying the cooling liquid added with a hardening agent, such as polyalkylene glycol, which is uniformly mixed in a base liquid for cooling, such as water at the prescribed state change temp. lower than the Ms point to transform the steel to martensite or below and is separated from the base liquid in the temp. state higher than this state change temp. The cam shaft is in succession subjected to the secondary cooling to cool the cam shaft down to the state change temp. after the cooling or below by spraying the above-mentioned cooling liquid again after the spraying of the cooling liquid is once stopped.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an induction hardening method for induction hardening a heat-treated material such as an engine camshaft made of materials such as cast iron and cast steel. .

(Prior art) Generally, metal parts that require strength, such as the camshaft of a vehicle engine, have been subjected to heat treatment such as induction hardening to increase the strength of the parts. . In this heat treatment such as induction hardening, the material to be heat treated, such as a camshaft, is heated with high frequency to a high temperature of, for example, 900°C to change the metal structure of the material to austenite, and then rapidly cooled at a cooling rate higher than the critical cooling rate. According to
It is a heat treatment that generates a martensitic structure and makes it extremely hard and strong, and it is known that good heat treatment effects can be obtained when induction hardening steel materials such as carbon steel.

However, when engine camshafts, etc. are made of cast iron, and this cast iron heat-treated material is induction hardened in the same way as steel materials such as carbon steel, the martensitic structure expands during martensitic transformation. Since cracks are likely to occur, it is difficult to stabilize the hardening quality of cast iron heat-treated materials subjected to induction hardening.

Therefore, when mass-producing induction hardened products made by applying induction hardening to cast iron heat-treated materials, the yield tends to be poor, and there is a problem in that it is difficult to increase the mass production of cast iron induction hardened products. Ta.

(Problem to be solved by the invention) When heat-treated materials such as engine camshafts are made of cast iron, and this cast iron heat-treated material is induction hardened in the same way as steel materials such as carbon steel, quenching cracks occur. It is difficult to stabilize the hardening quality of cast iron heat treated materials that have been induction hardened, so when mass producing induction hardened products that have undergone induction hardening treatment of cast iron heat treated materials, However, there was a problem in that the yield rate was poor and it was difficult to increase the mass production of induction hardened cast iron products.

This invention was made in view of the above-mentioned circumstances, and aims to stabilize the quenching quality of heat-treated materials that are susceptible to quenching cracks when subjected to induction hardening, such as cast iron heat-treated materials. The object of the present invention is to provide an induction hardening method that can increase the mass productivity of processed products.

[Structure of the Invention] (Means for Solving the Problems) The present invention includes a heating step of high-frequency heating to a high temperature state that transforms a heat-treated material into austenite, and after this heating step, the heat-treated material transforms into a martensitic structure. A cooling liquid added with a quenching agent that is uniformly mixed into the base liquid at a temperature below a predetermined state change temperature that is lower than the Ms point and is separated from the base liquid at a high temperature higher than this state change temperature is applied to the heat-treated material. A first cooling step in which the material to be heat treated is cooled down to the Ms point or below by spraying, and after this first cooling step, the appropriate cooling liquid spraying is stopped and the cooling liquid is again applied to the material to be heat treated. This method includes a second cooling step of cooling the material to be heat treated by spraying to a temperature below the state change temperature of the cooling liquid.

(Function) During induction hardening, the material to be heat-treated is subjected to high-frequency heating to a high temperature state that turns it into austenite, and then the material to be heat-treated is heated to a predetermined temperature lower than the Ms point at which the material to be heat-treated transforms into a martensitic structure. The material to be heat treated is sprayed at a predetermined flow rate with a cooling liquid containing a quenching agent that is uniformly mixed into the base liquid at a temperature below the state change temperature and separated from the base liquid at a high temperature above the state change temperature. The heat-treated material undergoes first cooling relatively slowly to below the Ms point at which it transforms into a martensitic structure, and after this first cooling, the appropriate cooling liquid spraying is stopped for a period of time, and then the cooling liquid is sprayed from the nozzle again. By cooling the heat-treated material by spraying it again at a flow rate lower than the flow rate during the primary cooling, it is possible to cool the heat-treated material, which is likely to cause quench cracking when induction hardened, such as cast iron heat-treated materials. This stabilizes the hardening quality of the material and increases the mass productivity of induction hardened cast iron products.

(Example) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the state of temperature change of a heat-treated material during induction hardening treatment according to an embodiment of the present invention. Also, the second
The drawings and FIG. 3 schematically show the overall structure of an induction hardening apparatus for carrying out an induction hardening method according to an embodiment of the present invention. That is, the induction hardening apparatus of this embodiment includes a first processing section 1 and a second processing section 2, as shown in FIG.
, a third processing section 3, and an annealing section 4 are provided, respectively.

These first processing section 1, second processing section 2, third processing section 3, and slow cooling section 4 are provided independently, and the fourth
As shown in the figure, the material to be heat treated such as the camshaft 5 of the engine is 1
The first transport mechanism 6 between one processing section 1 and the second processing section 2, the second transport mechanism 7 between the second processing section 2 and the third processing section 3, and the third The third transport mechanism 8 between the processing section 3 and the slow cooling section 4 sequentially transports the materials. In this case, the camshaft 5 of the material to be heat treated is made of a material such as cast iron or cast steel. The cam shaft 5 has cam portions 5b at multiple locations on the substantially cylindrical shaft body 5a.
...is installed protrudingly.

Further, the first processing section 1 includes a first support mechanism 9 that rotatably supports a heat-treated material such as a camshaft 5, and a heat-treated material such as a camshaft 5 supported by the first support mechanism 9. A first rotational drive mechanism 10 that rotationally drives a material, a plurality of first heating coils 11 for high-frequency heating that locally covers the periphery of a material to be heat treated such as a camshaft 5, and a camshaft 5 and the like. A plurality of first spray nozzles 12 for spraying the cooling liquid onto the heat-treated material are respectively provided. In this case, the first heating coils 11... have a substantially semicircular cross section as shown in FIG.
... are arranged at positions corresponding to the cam portions 5b... of the camshaft 5, respectively. Further, for the first spraying, nozzles 12 are appropriately arranged around the camshaft 5, for example, on the top, bottom, left and right sides. Further, the first rotation drive mechanism 10 and the first heating coils 11 are connected to a heating control means 14 of a control section 13 formed by, for example, a microcomputer and its peripheral circuits. The heating control means 14 controls the operations of the first rotational drive mechanism 10 and the first heating coil 11 . Furthermore, this control section 13 includes a heating control means 1.
4, a primary cooling control means 15, a secondary cooling control means 16, and a tempering heating means 17, which will be described later, are provided, respectively.

Further, for the first spraying, the tip of the liquid feeding passage 19 of the first cooling liquid control mechanism 18 is connected to the nozzle 12 . The first coolant control mechanism 18 is provided with a liquid feeding pump (not shown) connected to the base end side of the liquid feeding passage 19, a flow rate control valve (not shown) interposed in the liquid feeding passage 19, and the like. Ori,
In the first spraying, a predetermined flow rate of the cooling liquid is supplied to the nozzle 12 via the first cooling liquid control mechanism 18 . In this case, the ζ coolant is cooled at a temperature below a predetermined state change temperature (for example, about 74 degrees Celsius or 90 degrees Celsius), which is lower than the Ms point (for example, about 200 degrees Celsius) at which the heat-treated material such as the camshaft 5 transforms into a martensitic structure. A hardening agent (for example, polyalkylene glycol (PAG)) that is uniformly mixed in a liquid (for example, water) and separated from the base liquid at a high temperature above the state change temperature is used at a predetermined concentration. .In addition, as a cooling liquid, Ura,
It may also be made of vinyl or the like.

Furthermore, this first coolant control mechanism 18 is connected to the first cooling control means 15 of the control section 13 . The primary cooling control means 15 is further connected to a first transport mechanism 6, a first temperature sensor 20a, and a second temperature sensor 20b, respectively.

In this case, the first temperature sensor 20a is in a high temperature state (9
The second temperature sensor 20b is in the state of being subjected to high frequency heating (high frequency heating temperature) to a temperature of about 00°C (approx. (first cooling temperature).

Further, the second processing section 2 includes a first support mechanism 9 of the first processing section 1, a first rotational drive mechanism 10. A second support mechanism and a second rotary drive mechanism 21 having substantially the same configuration as the nozzles 12 are provided for the first spraying, and a nozzle is provided for the second spraying. In this case, the second spraying nozzle of the second processing section 2 is connected to a second cooling liquid control mechanism 22 having substantially the same configuration as the first cooling liquid control mechanism 18 of the first processing section 1. There is.

The second rotational drive mechanism 21 and the second coolant control mechanism 22 of the second processing section 2 are connected to the secondary cooling control means 16 of the control section 13.

A second transport mechanism 7 and a third temperature sensor 20c are further connected to the secondary cooling control means 16, respectively. In this case, the third temperature sensor 20c detects a state in which the quenching agent in the coolant is lowered to a predetermined state change temperature (for example, about 74°C or 90°C) at which it is uniformly mixed into the base liquid (secondary cooling). temperature).

Furthermore, the third processing section 3 includes a support mechanism 9 for the first processing section 1, a first rotational drive mechanism 10, a first heating coil 11, and a first rotational drive mechanism 10.
A third support mechanism, a third rotational drive mechanism 23, a second heating coil 24, and so on, each having substantially the same configuration as . . . , are provided. In this case, the third rotational drive mechanism 23, second heating coil 24, . . . of the third processing section 3 are connected to the tempering heating means 17 of the control section 13. A third conveyance mechanism 8 is further connected to this temper heating means 17.

Next, an induction hardening method using the induction hardening apparatus configured as described above will be explained.

First, during induction hardening of a material to be heat treated, such as the camshaft 5 of an engine, the material to be heat treated, such as the camshaft 5, is first set on the first support mechanism 9 of the first processing section 1. Then, when the power switch (not shown) of the induction hardening device is turned on in this state, the heating control means 14 of the control section 13 controls the first
The first rotational drive mechanism 10 of the processing unit 1 is driven, the camshaft 5 is rotationally driven, and the first heating coil 11 is
. . , and the camshaft 5 is high-frequency heated by the first heating coil 11 . . . (heating step). Further, the operation signal of this heating control means 14 is outputted to the primary cooling control means 15.

Furthermore, when the operation signal from the heating control means 14 is input to the primary cooling control means 15, the first temperature sensor 20a
Based on the detection signal from the camshaft 5, the metal structure of the heat-treated material such as the camshaft 5 is detected to be high-frequency heated to a high temperature (approximately 900°C) where the metal structure becomes austenitic (indicated by A in Fig. 1). Then, a signal to cut off the energization to the first heating coils 11 is output to the heating control means 14, and the energization to the first heating coils 11 is cut off. A drive signal is output to the control mechanism 18, and a predetermined flow rate of the cooling liquid is supplied to the nozzles 12 through the first cooling liquid control mechanism 18. ... is sprayed onto the heat-treated material such as the camshaft 5, and the heat-treated material such as the camshaft 5 is cooled (first cooling step). In this case, the coolant sprayed onto the heat-treated material such as the camshaft 5 is heated to a temperature higher than the predetermined state change temperature (for example, about 74°C or 90°C) at which the quenching agent is uniformly mixed into the base liquid. Since it is heated, in this state, the quenching agent in the coolant separates from the base liquid, and this quenching agent forms a coating layer (film) on the surface of the material to be heat treated, such as the camshaft 5.

Therefore, the coating layer (film) of the quenching agent component can prevent the base liquid of the coolant from evaporating from the surface of the heat-treated material such as the camshaft 5, so the cooling rate can be adjusted (delayed). can.

Further, when the second temperature sensor 20b detects that the material to be heat treated, such as the camshaft 5, is primarily cooled to below the Ms point where it transforms into a martensitic structure (indicated by B in FIG. 1), The drive of the first coolant control mechanism 18 is stopped by the control signal from the primary cooling control means 15, and a drive stop signal to the first rotary drive mechanism 10 is output to the heating control means 14, After the drive of the first rotational drive mechanism 10 is stopped, a drive signal is subsequently output to the first transport mechanism 6. Then, the material to be heat treated, such as the camshaft 5, is transported from the first processing section 1 to the second processing section 2 by this first transport mechanism 6, and is transferred to the second support mechanism of this second processing section 2. Set. Note that during the time during which the first transport mechanism 6 transports the material to be heat treated, such as the camshaft 5 (B- in FIG.
Between C), the spraying of the coolant is stopped, and the materials to be heat treated, such as the camshaft 5, are gradually cooled in an air-cooled state.

Further, when the material to be heat treated such as the camshaft 5 is set on the second support mechanism of the second processing section 2, the secondary cooling control means 16
The second rotational drive mechanism 21 of the second processing section 2 is driven, and the camshaft 5 is rotationally driven, and a drive signal is output to the second coolant control mechanism 22, so that the second coolant In the second spraying, a predetermined flow rate of cooling liquid is supplied to the nozzle via the control mechanism 22, and in the second spraying, the cooling liquid is sprayed from the nozzle to the heat-treated material such as the camshaft 5. The material to be heat treated is cooled (secondary cooling step). In this case, in the second spraying, the flow rate of the coolant sprayed from the nozzle is set to a smaller flow rate than the flow rate during the first cooling, and cooling is performed more slowly than during the first cooling (cooling time is relatively long). Then, at the time when the third temperature sensor 20c detects that the material to be heat treated such as the camshaft 5 has been cooled to the secondary cooling temperature (indicated by D in FIG. 1), the second cooling liquid is At the same time as the drive of the control mechanism 22 is stopped, a drive stop signal is output to the second rotational drive mechanism 21, and the drive of the second rotational drive mechanism 21 is stopped. In this case, when the third temperature sensor 20c detects that the material to be heat treated, such as the camshaft 5, has been cooled to the secondary cooling temperature, the material to be heat treated, such as the camshaft 5, is in a predetermined state of the coolant. Change temperature (e.g. 74℃ or 90℃)
℃) or below, all of the quenching agent in the coolant is evenly mixed into the base liquid. Therefore, when the material to be heat treated such as the camshaft 5 is cooled to the secondary cooling temperature, the quenching agent component formed on the surface of the material to be heat treated such as the camshaft 5 between A and C in FIG. All of the coating layer (coating) can be peeled off from the surface of the heat-treated material such as the camshaft 5, so a coating layer (film) of the quenching agent component is formed on the surface of the heat-treated material such as the camshaft 5. It can be prevented from being held in this state.

Further, after the driving of the second coolant control mechanism 22 and the second rotational drive mechanism 21 is stopped, a drive signal is subsequently output to the second transport mechanism 7. The second transport mechanism 7 transports the heat-treated material such as the camshaft 5 from the second processing section 2 to the third processing section 3.
is set on the third support mechanism. When the material to be heat treated, such as the camshaft 5, is set on the third support mechanism of the third processing section 3, the third rotation drive mechanism 23 of the third processing section 3 is activated by the tempering heating means 17. The camshaft 5 is driven to rotate, and the second heating coil 24.
... is energized, and the material to be heat-treated, such as the camshaft 5, is high-frequency heated by the second heating coil 24 to an appropriate tempering temperature, and tempering is performed.

Furthermore, after the tempering process is finished, the tempering heating means 17 turns the second heating coil 24 of the third processing section 3 on.
... is cut off and the driving of the third rotational drive mechanism 23 is stopped, and then the third transport mechanism 8 is driven. The second transport mechanism 7 transports the heat-treated material, such as the camshaft 5, from the third processing section 3 to the annealing section 4, where it is annealed.

Therefore, according to the above method, during induction hardening, the camshaft 5
The material to be heat-treated, such as the camshaft 5, etc., is subjected to high-frequency heating to a high temperature state where it becomes austenite, and then the material to be heat-treated, such as the camshaft 5, which has been radio-frequency heated, is heated to a predetermined temperature lower than the Ms point at which the material to be heat-treated transforms into a martensitic structure. Heat treatment of the camshaft 5, etc. is carried out by spraying at a predetermined flow rate a coolant containing a quenching agent that is uniformly mixed into the base liquid at a temperature below the state change temperature and separated from the base liquid at a high temperature above the state change temperature. The material is firstly cooled relatively slowly to below the Ms point at which the heat-treated material transforms into a martensitic structure, and after this first cooling, the appropriate cooling liquid spraying is stopped and then the second spraying is performed. In this method, the cooling liquid is again sprayed from the nozzle onto the heat-treated material such as the camshaft 5 at a flow rate lower than that during the first cooling, thereby cooling the heat-treated material such as the camshaft 5. It is possible to adjust the cooling rate of the material to be heat treated to be relatively slow (in the direction of slowing down). Therefore, it stabilizes the hardening quality of heat-treated materials that are prone to quenching cracks when induction hardened, such as cast iron camshafts 5, and increases the mass productivity of induction-hardened cast iron products. be able to.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] According to the present invention, a heating step of high-frequency heating to a high temperature state to austenite the material to be heat treated, and after this heating step,
A quenching agent that is uniformly mixed into the base liquid at a temperature below a predetermined state change temperature, which is lower than the Ms point at which the heat-treated material transforms into a martensitic structure, and is separated from the base liquid at a high temperature higher than this state change temperature. A first cooling step in which a cooling liquid added with is sprayed onto the heat-treated material to cool the heat-treated material below the Ms point; A second cooling step is provided in which the cooling liquid is sprayed onto the heat-treated material again to cool the heat-treated material to below the state change temperature of the cooling fluid. Quench cracking occurs during induction hardening, and the quality of the heat-treated material can be stabilized and the mass productivity of induction-hardened cast iron products can be increased.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, and FIG. 1 is a characteristic diagram showing the state of temperature change of a material to be heat-treated during induction hardening treatment, FIG. 2 is a schematic configuration diagram of the entire induction hardening apparatus, and FIG.
4 is a front view showing how the camshaft is mounted in the first processing section, and FIG. 5 is a side view of the same. 5... Camshaft (heat treated material), 9... First support mechanism, 10... First rotational drive mechanism, 11... First heating coil, 13... Control unit, 14... Heating control means, 15... Primary cooling control means, 16... Secondary cooling control means.

Claims (1)

[Claims] A heating step of high-frequency heating to a high temperature state that transforms the heat-treated material into austenite, and after this heating step, heating in the base liquid at a temperature below a predetermined state change temperature lower than the Ms point at which the heat-treated material transforms into a martensitic structure. A first step of cooling the heat-treated material to below the Ms point by spraying onto the heat-treated material a cooling liquid to which a quenching agent is added that is uniformly mixed and is separated from the base liquid at a high temperature higher than the state change temperature. a cooling step, and after this first cooling step, the cooling liquid is again sprayed onto the heat-treated material through an appropriate coolant spraying stop time to bring the heat-treated material below the state change temperature of the cooling fluid; An induction hardening method characterized by comprising a secondary cooling step.