JP2001089810A - Treating method of billet for cold-forging and continuous cold forging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a treating method of a billet, capable of cold forging a crank shaft, and the like, continuously without executing a process of an intermediate softening treatment. SOLUTION: A blank 2 taken out from a heating furnace 1 is rapidly cooled after rolling to make the surface layer a fine martensitic structure, and successively, the blank 2 is annealed to change the martenstic structure into a fine spheroidal structure composed of ferrite and cementite.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a processing method for obtaining a billet for cold forging capable of continuously performing cold forging with a high deformation rate without requiring intermediate annealing, and a billet obtained by the processing method. The present invention relates to a cold continuous forging method used.

[0002]

2. Description of the Related Art Conventionally, hot forging is mainly used for forming a crankshaft or a connecting rod of an engine of a motorcycle or the like, and the material is generally forged by heating the material to a recrystallization temperature or higher. However, molding by hot forging tends to wear the mold surface, resulting in poor precision of the forged product,
The machining allowance after forging increases the machining allowance and reduces the machining efficiency. Since the cost of lace processing is large, the number of machines increases, and the initial investment becomes enormous. In the case of hot forging, scale is generated due to forging after heating, and it is necessary to apply a release agent or the like. Therefore, it is difficult to keep the working environment optimal.

[0003] Therefore, cold forging has been attempted. FIG. 16 shows a conventional cold forging process for manufacturing a crankshaft. In conventional cold forging, billets that have been softened by slow cooling after rolling are subjected to draw forming and upset forming in the cold, and then strain generated by draw forming and upset forming. In order to cancel this, a softening treatment is performed, and then rough forming, finish forming, outer periphery punching and pin hole punching are performed again in the cold state, and thereafter, finishing processing such as shaft polishing and induction hardening is performed.

In the above-described conventional cold forging, cracks are more likely to occur during upset forming than in hot forging.
Therefore, in order to prevent this cracking, a softening treatment is performed during the forming to temporarily cancel the strain generated by the cold forging. When the deformation ratio becomes large, it is necessary to further increase the intermediate softening treatment.

[0005] As described above, since the softening process is interposed in the middle, the cold forging that has been performed continuously (the mold is changed) is interrupted, and the heat treatment apparatus must be arranged in the middle. Although not as good as forging, there are similar problems.

Therefore, the present inventors, as shown in FIG. 17, pickled the rolled billet, performed the first spheroidizing annealing, and then performed pickling and bonding, It has been proposed to perform a second spheroidizing annealing after drawing and cutting.

That is, in the first spheroidizing annealing, the workability of the whole material is improved so that distortion can be given to the inside, the pearlite is miniaturized, and the deformation energy is formed inside the material in the drawing step. Partly accumulates to increase the spheroidization rate by miniaturizing the austenite grains generated during the second annealing, and to disperse carbides in the second spheroidizing annealing to further increase the spheroidization rate. In order to obtain a billet with an increased height.

[0008] Then, by cold forging using the spheroidized billet, as shown in FIG. 18, a series of cold forming including drawing forming, upsetting forming, rough forming, finish forming, outer periphery punching and pin hole punching is performed. Forging can now be performed without an intermediate softening treatment.

[0009]

The billet can be spheroidized by the method shown in FIG. 17 to continuously perform cold forging. However, the step of spheroidizing the billet is further simplified. Is desired. That is, by performing spheroidizing annealing (two times in total) before and after drawing, the billet structure can be made into a fine spheroidized structure, but it is desired to omit further steps in terms of cost.

[0010]

In order to solve the above-mentioned problems, a method for processing a billet for cold forging according to the present invention is characterized in that a material drawn out of a heating furnace is rapidly cooled after rolling to form a fine martensite structure on a surface layer. Then, the material is annealed to make the surface martensite into a fine spheroidized structure composed of ferrite and cementite.

Due to the above annealing, the inside of the material was a mixed phase of ferrite and pearlite, but the pearlite was divided and spheroidization progressed. Therefore, both the inside and the surface layer become spherical, and the deformability becomes extremely large.

The conditions for the annealing include, for example, holding the material at about 740 ° C. for 6 hours, and then increasing the temperature to about 680 ° C. by 20 ° C.
At a cooling rate of / hr, the furnace is cooled after cooling down, or the material is held at about 750 ° C for 4 hours, then at about 735 ° C for 3.5 hours, and then to about 680 ° C at 15 ° C / hr. It is conceivable to perform cooling in a cooling furnace at a cooling rate of.

[0013] Further, as the material, C (carbon) is 0.46 to 0.48 wt%, and Si (silicon) is 0.14 wt%.
Hereinafter, Mn (manganese) is 0.55 to 0.65 wt%, P
(Phosphorus) 0.015 wt% or less, S (sulfur) 0.01
5 wt% or less, Cu (copper) 0.15 wt% or less, Ni (nickel) 0.20 wt% or less, Cr (chromium) 0.3
Carbon steel containing 5 wt% or less, the balance being Fe (iron) and impurities is suitable.

Further, the cold continuous forging method according to the present invention comprises:
The billet obtained by the above-described processing method was continuously subjected to cold forging such as drawing, upsetting, and finishing without performing an intermediate softening step. still,
The cold continuous forging method according to the present invention is most suitable for manufacturing a crankshaft.

[0015]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a view for explaining a method of processing a billet for cold forging according to the present invention. In the present invention, first, a raw material 2 derived from a heating furnace 1 is rolled by a rolling mill 3, and a cutting shear 4 is used. After being cut to a predetermined size and rapidly cooled through a cooling device 5, a billet (bar material) 7 is formed.
The billet 7 is sent to the cooling floor 6 and the wire 8 is wound.

The surface layer of the billet 7 has a high hardness martensite structure due to rapid cooling. After the billet 7 whose surface layer has a martensite structure is cut and pickled, spheroidizing annealing is performed to obtain a billet for cold forging.

In the above, the billet 7 having the above-mentioned component ratio is used. The annealing conditions are as shown in FIG. 2 (a). After the billet 7 is held at about 740 ° C. for 6 hours, the billet 7 is heated to about 680 ° C. At the cooling rate of ° C./hr, the pattern 1 in which the furnace was cooled after the temperature was lowered and the billet 7 shown in
After holding at 0 ° C. for 4 hours, holding at about 735 ° C. for 3.5 hours, and then cooling to about 680 ° C. at a cooling rate of 15 ° C./hr,
Pattern 2 in which the furnace was cooled after the temperature was lowered was tried.

As another method for obtaining a billet for cold forging from the billet 7, as shown in FIG. 19A, a billet 7 is cut into a predetermined size by a cutting shear to form a billet for cold forging. There is. The billet for cold forging inevitably has "sink" and "burr" on the end face during cutting, and if drawn and upset as it is, it will break and forging defects such as underfill will occur. After cutting with a shear, both ends of the cold forging billet are subjected to imposition molding to finish the flatness, and then spheroidizing annealing is performed.

Further, if the surface is rapidly cooled by the cooling device 5 of FIG. 1, it has been difficult to wind the wire as a wire in the past. However, by optimizing the cooling conditions, the surface is cooled as shown in FIG. 1. By quenching, the wire 8 having a martensite structure on the surface layer can be obtained. In order to obtain a billet for cold forging from the billet 7, as shown in FIG. 19 (a), a "cutting process" using a cutting shear and "imposition molding" for flattening an end face must be performed using separate facilities. In order to obtain a billet for cold forging from the wire 8, FIG.
As shown in (b), by using the parts former, the "cutting process" and the "imposition molding" can be performed in the same facility.

Next, a description will be given based on a micrograph showing an actual metal structure. First, FIG. 3 to FIG. 7 are micrographs showing a metal structure before annealing, of which FIG. 3 (a) is a cross-sectional photograph of a billet having a martensite surface layer, and FIG.
3A is a diagram created based on the cross-sectional photograph of FIG. 3A, and is a diagram showing a portion of the metal structure shown in FIGS. 4 to 7, and FIG.
Micrograph (× 100) showing the metal structure of the portion of FIG. 5, FIG.
Is a micrograph (200) showing the metal structure of the portion B in FIG.
FIG. 6 is a micrograph (× 400) showing the metal structure of the portion C in FIG. 3, and FIG. 7 is a micrograph (× 400) showing the metal structure of the portion D in FIG. In a), the resin provided outside the billet is a holding resin.

4 and 5, a fine martensite phase is formed in the surface layer portion, and an intermediate layer exists radially inward from the micrographs. FIG. 6 shows that the intermediate layer is composed of martensite. From FIG. 7, it can be seen that martensite disappears at the center and a mixed phase of ferrite and pearlite is formed.

After the billet is washed with an acid,
The microstructure of the billet subjected to the spheroidizing annealing of Pattern 1 and Pattern 2 is shown in the micrographs of FIGS. Here, FIG. 8A is a cross-sectional photograph of a billet in which martensite of a surface layer is made spherical by annealing pattern 1, and FIG. 8B is a diagram prepared based on the cross-sectional photograph of FIG. A diagram showing a portion of the metal structure shown in,
FIG. 9 is a micrograph (1) showing the metal structure of the portion A in FIG.
FIG. 10 is a photomicrograph (× 400) showing the metal structure of the portion B in FIG. 8, FIG. 11 is a photomicrograph (× 400) showing the metal structure of the portion C in FIG. 8, and FIG. 13) is a cross-sectional photograph of a billet in which martensite in the surface layer is made spherical by annealing pattern 2, and (b) is a diagram created based on the cross-sectional photograph of (a). The portion of the metal structure shown in FIGS. FIG. 13 is a micrograph (× 100) showing the metal structure of the portion A in FIG. 12, FIG. 14 is a micrograph (× 400) showing the metal structure of the portion B in FIG. 12, and FIG. It is a microscope photograph (400 times) which shows the metal structure of the C part of No. 12.

From these figures, the annealing pattern is shown in FIG.
In any of the patterns shown in (a) and (b), there is no difference in the metallographic structure, and it can be seen that the surface layer has a fine spheroidized structure in which the martensite phase is a mixed phase of ferrite and cementite. The central part is at a level at which pearlite is being divided into spheres in the mixed phase of ferrite and pearlite, and slightly acicular carbide is present.

[0024]

The following (Table) shows the results of the upsetting test and the crank forming test performed while changing the materials and the conditions of the spheroidizing treatment step. In the upsetting test, only the upsetting test was performed with a billet size of φ34.67 × 60, and the compression ratio was set to 87.5%. Crank forming test is φ34.67 × 73
With a billet size of 93%, the upsetting rate is 93% and the drawing rate is 93%
And The denominator of the confirmation test result is the number of test pieces subjected to the test, and the numerator is the number of test pieces having cracks.

[0025]

[Table 1]

From Table 1, it was confirmed that the billet treated by the method of the present invention did not crack before and after drawing, as in the case where spheroidizing annealing was performed. Here, in Table 1, the R material is a material that is air-cooled on a cooling floor without quenching, and the controlled rolled material has a fine α grain structure by strictly controlling hot rolling conditions. is there. Even if the R material is annealed, it is easily cracked at the time of forming. Therefore, conventionally, a controlled rolled material is used, but it can be seen that cracking occurs by one annealing. In addition, if annealing is performed before and after the drawing step, no crack is generated, and furthermore, it is understood that no crack is generated even by one annealing using the surface hardened steel according to the present invention.

As described above, according to the present invention, the surface layer is made into a fine martensite structure by rapidly cooling the material derived from the heating furnace after rolling, and then the material is annealed to reduce the martensite to ferrite and cementite. Since the microstructure is changed to a fine spheroidized microstructure, it is possible to obtain a billet having low hardness and excellent deformability in both the surface layer and the inside.

Then, by cold forging using a billet having low hardness and excellent deformability, cold forging can be continuously performed to the end without performing a softening treatment in the middle.
The cost of equipment can be greatly reduced and the working environment can be improved.

In particular, using the billet obtained in the present invention,
It is preferable to manufacture an engine part with a shaft such as a crankshaft because it is not necessary to perform a plurality of setup changes such as in a conventional hot forging, and a post-processing cutting step can be omitted.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a method for processing a billet for cold forging according to the present invention.

FIGS. 2A and 2B are graphs showing patterns 1 and 2 of annealing.

3A is a cross-sectional photograph of a billet having a martensitic surface layer, and FIG. 3B is a diagram prepared based on the cross-sectional photograph of FIG. 3A. FIG. FIG.

FIG. 4 is a micrograph (× 100) showing a metal structure of a portion A in FIG. 3;

FIG. 5 is a photomicrograph (× 200) showing a metal structure of a portion B in FIG. 3;

FIG. 6 is a micrograph (× 400) showing a metal structure of a portion C in FIG. 3;

FIG. 7 is a micrograph (× 400) showing a metal structure of a portion D in FIG. 3;

8A is a cross-sectional photograph of a billet obtained by spheroidizing martensite of a surface layer by annealing pattern 1, and FIG. 8B is a diagram prepared based on the cross-sectional photograph of FIG. The figure which shows the part of the shown metal structure.

FIG. 9 is a micrograph (× 100) showing a metal structure of a portion A in FIG. 8;

FIG. 10 is a micrograph (× 400) showing a metal structure of a portion B in FIG. 8;

FIG. 11 is a micrograph (× 400) showing a metal structure of a portion C in FIG. 8;

FIG. 12 (a) is a cross-sectional photograph of a billet in which martensite in a surface layer is made spherical by annealing pattern 2;
FIG. 16 is a diagram created based on the cross-sectional photograph of (a), showing a portion of the metal structure shown in FIGS.

FIG. 13 is a micrograph (× 100) showing the metal structure of the portion A in FIG. 12;

FIG. 14 is a micrograph (× 400) showing a metal structure of a portion B in FIG. 12;

FIG. 15 is a micrograph (× 400) showing a metal structure of a portion C in FIG. 12;

FIG. 16 is a diagram illustrating a conventional cold forging process.

FIG. 17 is a diagram illustrating a spheroidizing process proposed by the present applicant.

FIG. 18 is a view in which an intermediate softening step is omitted from the conventional cold forging step, and a step which can be performed by using a method according to the present invention and a billet obtained by a method previously proposed by the present applicant. .

FIG. 19 (a) is an explanatory diagram when a billet for cold forging is obtained from a bar, and FIG. 19 (b) is an explanatory diagram when a billet for cold forging is obtained from a wire.

[Explanation of symbols]

1 ... heating furnace, 2 ... material, 3 ... rolling mill, 4 ... cutting shear,
5: cooling device, 6: cooling floor, 7: billet, 8: wire rod.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22C 38/00 301 C22C 38/00 301A 38/42 38/42 (72) Inventor Hiroshi Ono Sayama, Saitama 1-10-1 Shinsayama 1 Honda Engineering Co., Ltd. (72) Inventor Mitsuru Kamikawa 1-10-1 Shinsayama 1 Sayama City, Saitama Prefecture Honda Engineering Co., Ltd. F term (reference) 4E087 AA10 BA02 BA14 CA11 CA22 CA31 CB03 DB17 DB22 HA32 4K032 AA05 AA11 AA14 AA16 AA23 AA27 AA29 AA31 BA02 CF02 4K043 AA02 AB04 AB13 AB15 AB22 AB25 AB26 AB27 BA04 BA06 DA01 EA01 EA02 FA03 FA12 FA13

Claims (7)

[Claims] 1. A material obtained from a heating furnace is rapidly cooled after rolling to form a fine martensite structure on the surface layer, and then the material is annealed to convert the surface martensite to a fine spheroidized structure comprising ferrite and cementite. A method for processing a billet for cold forging, comprising: 2. The method for processing a billet for cold forging according to claim 1, wherein the annealing is performed at about 740 ° C. for 6 hours.
A method for processing a billet for cold forging, which comprises holding for a time, lowering the temperature to about 680 ° C. at a cooling rate of 20 ° C./hr, and thereafter cooling the furnace. 3. The method for processing a billet for cold forging according to claim 1, wherein the annealing is performed at a temperature of about 750 ° C. for 4 hours.
A method for processing a billet for cold forging, comprising: holding at a temperature of about 735 ° C. for 3.5 hours after holding for about 3.5 hours; and thereafter cooling the furnace to about 680 ° C. at a cooling rate of 15 ° C./hr. 4. The method for processing a billet for cold forging according to claim 1, wherein the material derived from the heating furnace is rapidly cooled after rolling to obtain a wire having a fine martensitic structure on the surface layer, and the wire is subjected to a predetermined process. A method for processing a billet for cold forging, characterized in that the wire is cut into dimensions and imposed and then the cut wire is annealed to convert the surface martensite into a fine spheroidized structure composed of ferrite and cementite. 5. The processing method according to claim 1, wherein the material has C (carbon) of 0.46 to 0.4.
8 wt%, Si (silicon) is 0.14 wt% or less, Mn (manganese) is 0.55 to 0.65 wt%, and P (phosphorus) is 0.0
15 wt% or less, S (sulfur) is 0.015 wt% or less, Cu
(Copper) 0.15 wt% or less, Ni (nickel) 0.2
A method for processing a billet for cold forging, characterized by being carbon steel containing 0 wt% or less, Cr (chromium) of 0.35 wt% or less, and the balance being Fe (iron) and impurities. 6. The billet obtained by the processing method according to claim 1 is continuously cooled without performing a softening process in the middle, such as drawing, upsetting, and finishing. A cold continuous forging method characterized by performing cold forging. 7. The continuous cold forging method according to claim 6, wherein the method is applied to manufacture of a crankshaft.