JP2023094650A - Manufacturing method of forging heat-treated article - Google Patents

Abstract

To provide a manufacturing method of a forging heat-treated article, in which recovery of a composition and improvement of crystallization are enhanced, by energy saving, in order to obtain a composition suited for cutting, and which obtains a forging heat-treated article of rigidity equivalent to that of quenching and tempering.SOLUTION: A manufacturing method of a forging heat-treated article includes: (1) a step for heating a steel material to 550-650°C; (2) a step for performing forging such that an equivalent strain is 0.05-7.00 with respect to the heated steel material in order to obtain a forging molding raw material; and (3) a cooling step for cooling the raw material immediately after molding while being 400°C at an average cooling speed of 100°C/minute or lower.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing heat-treated forged products used as structural members for automobiles.

In the case of hot forging, forged members used as structural members of automobiles are formed by heating the material to 1050 to 1300° C. to lower the deformation resistance.
After forming, in order to improve the structure, the steel is heated to about 900° C. to form an austenite structure, and then the cooling rate is adjusted to adjust the structure after transformation and obtain the required properties.

As an example of this hot forging, for example, in Patent Document 1,
(1) a step of heating steel having predetermined components to a heating temperature of 1050 to 1300° C.;
(2) a step of forging at a reduction rate of 10 to 90% in the range of 900 ° C. to heating temperature, and immediately quenching at a cooling rate of 20 ° C./sec or more;
(3) Then, a hot forged product manufacturing method is disclosed, comprising a step of tempering in a temperature range of 400° C. to Ac1 point.

However, the structure adjustment using this transformation has the problem of requiring heating energy and dedicated furnace equipment for controlling the cooling rate.

Also, a method is applied in which the material is heated to 1100 to 1300° C. and hot forged to obtain an intermediate product, and then the cooling rate is controlled to obtain the structure and strength.

As an example of this hot forging, for example, in Patent Document 2,
containing specific proportions of C, Mn, P and N plus one of V, Ti and Nb or specific proportions of C, Mn, Cr, V and B plus Ni, Cu and Mo After hot-rolling a steel slab containing one or more of Disclosed is a method for manufacturing a toughness hot forged part of a non-heat treated high strength steel having a structure mainly composed of ferrite and pearlite by performing hot forging.

However, this method also has the problem that it requires energy to heat the material to a high temperature.

JP-A-6-212347 JP-A-8-120342

In view of the problems of the conventional hot forging described above, the present invention saves energy and promotes recovery of the structure and improvement of the crystal structure, thereby obtaining a structure suitable for cutting and quenching. - It aims at providing the manufacturing method of the forging heat treatment product which can obtain the forging heat treatment product of hardness equivalent to a tempering process.

In order to achieve the above object, the method for producing a heat-treated forged product of the present invention comprises:
(1) a step of heating a steel material to 500 to 650°C;
(2) a step of forging the heated steel material with an equivalent strain of 0.05 to 7.00 to obtain a forged material;
(3) A cooling step of cooling the material at an average cooling rate of 100°C/min or less from immediately after molding to 400°C.

In this case, the cooling step can be carried out by leaving the container in a container closed with a heat-dissipating or heat-insulating material.

Moreover, any one of structural tool steel (SC material), chromium steel (SCR material), chromium molybdenum steel, and nickel chromium molybdenum steel (SNCM material) can be used as the steel material.

Further, as the heat-treated forged product, a material for a rotor shaft used in a rotating electric machine can be manufactured.

According to the method for producing a heat-treated forged product of the present invention, a standard steel material specified by JIS is used, and without adding additional alloying ingredients, it is heated to a temperature of 723 ° C. or less at the A1 transformation point, and formed. After completion of grain refining, by utilizing the thermal energy of the material, it is energy-saving and promotes recovery of the structure and improvement of the crystal structure, making it suitable for machining such as cutting. A ferrite/pearlite structure can be obtained, and a forged heat-treated product having a hardness equivalent to that of quenching/tempering can be obtained.
Thereby, the forged member can be manufactured at low cost.

FIG. 3 is an explanatory diagram showing an example of a manufacturing process of a rotor shaft to which the method for manufacturing a heat-treated forged product of the present invention is applied; It is a graph which shows the relationship between the temperature of the manufacturing method of the heat-treated forging product of the present invention and time. FIG. 3 is an explanatory diagram of a method for manufacturing a heat-treated forged product (rotor shaft material) of the present invention; (a1) is a longitudinal sectional view of a rotor shaft material, (a2) is a plan view of the same, (b1) is a longitudinal sectional view of a rotor shaft (final product), and (b2) is a plan view of the same. (a) is a vertical cross-sectional view of a modification of the rotor shaft material, and (b) is a plan view of the same. FIG. 5 is an explanatory diagram of a method for manufacturing a heat-treated forged product (a modified example of a rotor shaft material) according to the present invention; FIG. 4 is an explanatory view showing analysis positions of a rotor shaft material; FIG. 4 is an explanatory view showing analysis results of hardness and microstructure of each part of the rotor shaft material;

An embodiment of the method for manufacturing a heat-treated forged product according to the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 show an example of manufacturing a material for a rotor shaft used in a rotating electric machine, as an example of a process to which the molding method of the present invention is applied.

(1) Heating Step In the heating step, a billet (columnar material) 1 made of structural tool steel (SC material (S45C)) is heated to 550 to 650°C.

(2) Forging process In the forging process, a heated billet (cylindrical material) 1 is forged with an equivalent strain of 0.05 to 7.00, and a hollow shaft material (rotor shaft material) is forged. get 3.
Here, "equivalent strain" is a quantity that defines the magnitude of strain for an arbitrary deformation state, and is obtained by converting strain in three-dimensional deformation into uniaxial deformation.
In this embodiment, as shown in FIG. 3, a billet (columnar material) 1 is formed into a forging die (a rotor shaft material 3 corresponding to deep holes 32a and 32b, a flange portion 33 and a key groove 34 formed in the center of the rotor shaft material 3). Using a forging die formed into a shape that is formed into a shape), by forging (temperature during forging: 550 to 650 ° C.), in one process, through a blank 2 having holes 22a and 22b in the center, with a total length of about 150 to 300 mm, Axle portion 31 (diameter about 40 to 80 mm), deep holes 32a, 32b, flange portion 33 (diameter about 60 to 100 mm) and key groove 34 (length about 100 to 250 mm) length), width of about 5 to 10 mm, and depth of about 1 to 10 mm).
Here, the forging process does not necessarily have to be performed in one process, and may be performed in multiple processes so that the equivalent strain due to forging is 0.05 to 7.00.
Also, two key grooves 34 are formed at 180° symmetrical positions on the shaft portion 31, but one or three or more may be formed.
Moreover, the key groove 34 does not necessarily have to be formed during forging. As in the modification shown in FIG. It can also be formed by cutting using.
Also, the shape of the rotor shaft material 3 is not limited to the shape shown in FIG.

(3) Cooling step Next, in the cooling step, the rotor shaft material 3 is cooled at an average cooling rate of 100°C/min or less, preferably 90°C/min or less, more preferably from immediately after molding to 400°C. Cool at no more than 80°C/min.
This cooling process is carried out by leaving the rotor shaft material 3 in a container closed with a heat insulating material, or by allowing it to cool if the average cooling rate can maintain the above numerical value. be able to.

In this way, the steel material is heated to a temperature of 550 to 650° C., which is lower than the A1 transformation point of 723° C., and grain refinement is performed in parallel with forming in the forging process. At the same time as the molding is finished, grain refining is also finished. After that, by utilizing the thermal energy of the material, the recovery of the structure and the improvement of the crystal structure are promoted in an energy-saving manner, thereby obtaining a ferrite/pearlite structure suitable for machining such as cutting, which will be described later. In addition, it is possible to obtain a forged heat-treated product having a hardness equivalent to that of quenching and tempering.

(4) Intermediate processing The inner peripheral surface of the shaft portion 31 on the side of the deep hole 32b of the rotor shaft material 3 is machined.

(5) Cold Spline Forming Cold spline forming is performed on the inner peripheral surface of the shaft portion 31 on the deep hole 32b side of the rotor shaft blank 3 .

(6) Machining The outer peripheral surface on both sides of the shaft portion 31 of the rotor shaft material 3 is machined (finishing the rotor core mounting portion and the bearing mounting portion, and forming the male thread portion to which the nut is screwed), and the deep hole 32a is formed. , 32b are passed through each other to obtain a rotor shaft (final product) 4 having a keyway 44 shown in FIG. 4(b).

Here, the steel materials used in the method for manufacturing the heat-treated forged product of the present invention include standard steel materials specified by JIS, for example, structural tool steel (SC material) used in this example, chromium steel ( SCR material), chromium molybdenum steel, nickel chromium molybdenum steel (SNCM material) can be used.

Table 1 and FIG. 8 show the analysis results of each part shown in FIG. 7 of the manufactured rotor shaft material 3 (modification shown in FIG. 6).

From the hardness and equivalent strain of each portion of the rotor shaft material 3 shown in Table 1 and the hardness and microstructure of each portion of the rotor shaft material 3 shown in FIG. 8, the following was found. [Example]
Heating temperature in heating step: 600°C
・About hardness Part A: The deformation of the structure is large, and the hardness is high overall. The structure is crushed more on the outer diameter side and the hardness is high. There is no transformation and the effect of work hardening is large.
Part B: Similar to Part A, the outer diameter side has a higher hardness due to work hardening. There is little deformation inside. On the inner diameter side, the structure is deformed, but the hardness is reduced due to heat generated during processing.
Part C: The outer diameter side, the inner part is not transformed and has a high hardness due to work hardening. The inner diameter side has a fine structure.
Part D: Same as C Part E: Same as C Part F: Same as C Microstructure Overall: Coarse ferrite + pearlite structure.
Part A: The tissue is totally crushed over the inner and outer diameters.
Part B: The deformation of the structure is large at the inner and outer diameters, and the inner deformation is small.
Part C to F: It is assumed that the inner diameter part received stronger deformation than parts A and B, and the structure became finer. The inner and outer diameter parts have little deformation, and are slightly deformed from the structure at the time of steel material.

As described above, the method for manufacturing a heat-treated forged product according to the present invention has been described based on the examples. It is configurable.

The method for producing a heat-treated forged product of the present invention saves energy, promotes recovery of the structure and improvement of the crystal structure, thereby obtaining a structure suitable for cutting, and is equivalent to quenching and tempering. Since it is possible to obtain a heat-treated forged product with a hardness of , it can be widely used for manufacturing heat-treated forged products used for structural members for automobiles, etc., in addition to rotor shafts used in rotating electric machines.

1 billet (columnar material)
2 blank 3 raw material for rotor shaft 32a deep hole 32b deep hole 33 flange 34 keyway 4 rotor shaft (final product)
44 keyway

Claims (4)

(1) a step of heating a steel material to 550 to 650°C;
(2) a step of forging the heated steel material with an equivalent strain of 0.05 to 7.00 to obtain a forged material;
(3) A method for manufacturing a heat-treated forged product, comprising: a cooling step of cooling the material at an average cooling rate of 100°C/min or less from immediately after molding to 400°C. 2. The method for manufacturing a heat-treated forged product according to claim 1, wherein the cooling step is performed by allowing the product to cool or leaving it in a container closed with a heat insulating material. 3. The steel material according to claim 1 or 2, wherein the steel material is any one of structural tool steel (SC material), chromium steel (SCR material), chromium molybdenum steel, and nickel chromium molybdenum steel (SNCM material). A method for manufacturing a forged heat-treated product. 4. The method for manufacturing a heat-treated forged product according to claim 1, wherein the heat-treated forged product is a material for a rotor shaft used in a rotating electric machine.

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