Manufacturing method for forged heat-treated products

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]

[0001] The present invention relates to a method for producing a forged heat-treated product used for structural members of automobiles and the like. [Background technology]

[0002] In the case of hot forging, forged members used in structural components of automobiles and the like are formed by heating the material to 1050 to 1300°C to reduce deformation resistance. After forming, in order to improve the structure, the material is heated to around 900°C to create an austenitic structure, and then the cooling rate is adjusted to adjust the structure after transformation and obtain the required properties.

[0003] As an example of this hot forging, for example, Patent Document 1 describes: (1) a step of heating steel having a predetermined composition to a heating temperature of 1050 to 1300°C; (2) Forging at a reduction rate of 10 to 90% in the range of 900 ° C. or higher heating temperature, and immediately quenching at a cooling rate of 20 ° C. / second or more; (3) Then, tempering is performed in the temperature range of 400°C to Ac1 point. A method for manufacturing a hot forged product is disclosed.

[0004] However, this structural adjustment utilizing transformation has the drawback of requiring heating energy and special furnace equipment for controlling the cooling rate.

[0005] 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 desired structure and strength.

[0006] As an example of this hot forging, for example, Patent Document 2 describes: A method for producing a non-tempered, high-strength, tough hot-forged steel part is disclosed, in which a steel billet containing specific proportions of C, Mn, P, and N and one of V, Ti, and Nb, or specific proportions of C, Mn, Cr, V, and B and one or more of Ni, Cu, and Mo is hot-rolled to produce steel with an austenite grain size number adjusted to a specific range, and then this steel is hot-forged with regulated heating temperature, heating rate, and heating holding time to produce a structure mainly composed of ferrite and pearlite.

[0007] However, this method also has the problem of requiring energy to heat the material to a high temperature. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 6-212347 [Patent Document 2] Japanese Patent Application Publication No. 8-120342 Summary of the Invention [Problem to be solved by the invention]

[0009] In view of the problems associated with conventional hot forging, the present invention aims to provide a method for producing forged heat-treated products that is energy-efficient, promotes structural recovery and crystallization improvement, and thereby enables the production of forged heat-treated products with a hardness equivalent to that of products produced through quenching and tempering, while also enabling the production of structures suitable for cutting. [Means for solving the problem]

[0010] In order to achieve the above object, the method for manufacturing a forged heat-treated product of the present invention comprises: (1) a step of heating the steel material to 500 to 650°C; (2) forging the heated steel material so that the equivalent strain is 0.05 to 7.00 to obtain a forged material; (3) a cooling step in which the material is cooled at an average cooling rate of 100°C / min or less from immediately after molding to 400°C; The present invention is characterized by comprising:

[0011] In this case, the cooling step can be carried out by leaving the product in a container closed with a heat radiating or insulating material.

[0012] The steel material may be any one of structural tool steel (SC material), chrome steel (SCR material), chrome molybdenum steel, and nickel chrome molybdenum steel (SNCM material).

[0013] Furthermore, the forged heat-treated product can be a material for a rotor shaft used in a rotating electrical machine. [Effects of the Invention]

[0014] According to the method for manufacturing forged heat-treated products of the present invention, standard steel material specified by JIS is used, and without adding any additional alloying elements, it is heated to a temperature below the A1 transformation point of 723°C. After forming and grain refinement are completed, the thermal energy contained in the material is utilized to promote structural recovery and improvement of the crystalline structure in an energy-saving manner, thereby obtaining a ferrite-pearlite structure suitable for machining such as cutting, and a forged heat-treated product with a hardness equivalent to that of a quenched and tempered product. This allows forged parts to be manufactured at low cost. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is an explanatory diagram showing an example of a rotor shaft manufacturing process to which the method for manufacturing a heat-treated forged product of the present invention is applied. FIG. [Figure 2] 1 is a graph showing the relationship between temperature and time in the method for producing a heat-treated forged product of the present invention. [Figure 3] 1 is an explanatory diagram of a method for manufacturing a forged heat-treated product (a material for a rotor shaft) according to the present invention. [Figure 4](a1) is a longitudinal cross-sectional view of a rotor shaft material, (a2) is a plan view of the same, (b1) is a longitudinal cross-sectional view of a rotor shaft (final product), and (b2) is a plan view of the same. [Figure 5] 1A is a longitudinal sectional view of a modified rotor shaft material, and FIG. 1B is a plan view of the same. [Figure 6] 1 is an explanatory diagram of a method for manufacturing a forged heat-treated product (a modified example of a rotor shaft material) according to the present invention. [Figure 7] FIG. 2 is an explanatory diagram showing analysis positions of a rotor shaft material. [Figure 8] FIG. 2 is an explanatory diagram showing the analysis results of the hardness and microstructure of each portion of a rotor shaft material. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the method for manufacturing a heat-treated forged product of the present invention will be described with reference to the drawings.

[0017] 1 and 2 show an example of a process to which the molding method of the present invention is applied, in which a material for a rotor shaft used in a rotating electrical machine is manufactured.

[0018] (1)Heating process In the heating step, a billet (cylindrical material) 1 made of structural tool steel (SC material (S45C)) as a steel material is heated to 550 to 650°C.

[0019] (2)Forging process In the forging process, a heated billet (cylindrical material) 1 is forged to an equivalent strain of 0.05 to 7.00 to obtain a hollow shaft material (material for rotor shaft) 3, which is a forged material. Here, "equivalent strain" is a quantity that defines the magnitude of strain for an arbitrary deformation state, and is the strain in three-dimensional deformation converted into uniaxial deformation. In this embodiment, as shown in Figure 3, a billet (cylindrical material) 1 is forged (forging temperature: 550 to 650°C) using a forging die (a forging die formed in a shape corresponding to the deep holes 32a and 32b, flange portion 33, and keyway 34 to be formed in the center of the rotor shaft material 3) to form a blank 2 having holes 22a and 22b in its center in one process, and then formed into a rotor shaft material 3 having a total length of approximately 150 to 300 mm, a shaft portion 31 (diameter approximately 40 to 80 mm), deep holes 32a and 32b, a flange portion 33 (diameter approximately 60 to 100 mm), and a keyway 34 (length approximately 100 to 250 mm (length from the flange portion to the tip on the rotor core mounting portion side), width approximately 5 to 10 mm, and depth approximately 1 to 10 mm). Here, the forging step does not necessarily have to be performed in one step, but can be performed in multiple steps so that the equivalent strain due to forging is 0.05 to 7.00. Furthermore, two key grooves 34 are formed at 180° symmetrical positions on the shaft portion 31, but one or three or more key grooves may also be formed. Furthermore, the key groove 34 does not necessarily have to be formed during forging. As shown in a modified example in FIG. 5, the key groove may not be formed during the forging process, but may be formed by cutting using a side cutter, end mill cutter, or the like in the machining process described below. Furthermore, the shape of the rotor shaft material 3 is not limited to the shape shown in FIG. 3, and it may also be a shape like the modified example shown in FIG.

[0020] (3) Cooling process Next, in the cooling process, the rotor shaft material 3 is cooled at an average cooling rate of 100°C / min or less, preferably 90°C / min or less, and more preferably 80°C / min or less from immediately after forming to 400°C. This cooling process can be carried out by leaving the rotor shaft material 3 in a container closed with heat insulating material, or by allowing it to cool naturally if the average cooling rate can be maintained at the above-mentioned value.

[0021] In this way, the steel is heated to a temperature of 550-650°C, below the A1 transformation point of 723°C, and grain refinement is carried out in parallel with the forging process. Grain refinement ends at the same time as forming. By utilizing the thermal energy contained in the material, it is possible to conserve energy and promote structural recovery and improvement of the crystalline structure, resulting in a ferrite-pearlite structure suitable for machining processes such as cutting, as described below, and a forged heat-treated product with a hardness equivalent to that of a quenched and tempered product.

[0022] (4) Intermediate processing The inner peripheral surface of the shaft portion 31 of the rotor shaft material 3 on the deep hole 32b side is machined.

[0023] (5) Cold spline forming The inner peripheral surface of the shaft portion 31 of the rotor shaft material 3 on the deep hole 32b side is subjected to cold spline forming.

[0024] (6) Machining The outer surfaces of both sides of the shaft portion 31 of the rotor shaft material 3 are machined (finishing the rotor core mounting portion and bearing mounting portion and forming the male thread portion into which the nut screws), and the deep holes 32a, 32b are penetrated to obtain the rotor shaft (final product) 4 with a key groove 44 as shown in Figure 4(b).

[0025] Here, the steel material used in the manufacturing method of the forged heat-treated product of the present invention may be a standard steel material specified by JIS, such as the structural tool steel (SC material) used in this example, as well as chromium steel (SCR material), chromium-molybdenum steel, or nickel-chromium-molybdenum steel (SNCM material).

[0026] Here, the analysis results of each portion shown in FIG. 7 of the manufactured rotor shaft blank 3 (the modified example shown in FIG. 6) are shown in Table 1 and FIG.

[0027] [Table 1]

[0028] 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 Figure 8 revealed the following. [Example] Heating temperature during heating process: 600℃ About hardness Part A: The structure is significantly deformed, resulting in high hardness overall. The structure is more crushed on the outer diameter side, resulting in high hardness. There is no transformation, and the effects of work hardening are significant. Part B: Like 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 has decreased due to heat generated by work. Part C: The outer diameter side and the inside are not transformed and have high hardness due to work hardening. The inner diameter side has a fine structure. Part D: Same as C Part E: Same as C F section: same as C About the microstructure Overall: Coarse ferrite + pearlite structure is present. Part A: The tissue is crushed throughout the entire inner and outer diameters. Part B: The tissue deformation is large at the inner and outer diameters, but small at the inside. Parts C to F: The inner diameter part is assumed to have undergone more severe deformation than parts A and B, resulting in a finer structure. The inner and outer diameter parts are less deformed, and are slightly deformed from the structure of the steel material.

[0029] The above describes the manufacturing method of the forged heat-treated product of the present invention based on its examples, but the present invention is not limited to the configurations described in the above examples, and the configuration can be changed as appropriate within the scope of the invention. [Industrial Applicability]

[0030] The method for producing forged heat-treated products of the present invention is energy-efficient and promotes structural recovery and crystallographic improvement, thereby obtaining a structure suitable for cutting, and can produce forged heat-treated products with hardness equivalent to that of products subjected to quenching and tempering. Therefore, the method can be widely used to produce forged heat-treated products used in automotive structural components, as well as rotor shafts used in rotating electrical machines. [Explanation of symbols]

[0031] 1 Billet (cylindrical material) 2 blank 3 Rotor shaft materials 32a deep hole 32b deep hole 33 Flange 34 Keyway 4 Rotor shaft (final product) 44 keyway

Claims

1. (1) a step of heating the steel material from room temperature to 550 to 650 ° C, which is lower than the A1 transformation point of 723 ° C; (2) forging the heated steel material to 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; A method for manufacturing a heat-treated forged product, comprising:

2. 2. The method for manufacturing a heat-treated forged product according to claim 1, wherein the cooling step comprises leaving the forged product to cool naturally or in a container closed with a heat insulating material.

3. 3. The method for manufacturing a forged heat-treated product according to claim 1, wherein the steel material is any one of structural tool steel (SC material), chrome steel (SCR material), chrome-molybdenum steel, and nickel-chrome-molybdenum steel (SNCM material).

4. 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 electrical machine.

Images