JP4471134B2 - Manufacturing method for seamless pipes for automobile parts - Google Patents

Description

The present invention relates to a method of manufacturing a seamless pipe for automobile parts .

  A seamless pipe manufacturing method includes a Mannesmann process in which a heated round steel slab is pierced and rolled with a piercer, then stretched and rolled with a mandrel mill, a plug mill, and the like, and further rolled with a constant diameter with a sizer or the like to obtain a seamless pipe. Are known.

  The piercer is usually a rolling roll consisting of a pair of barrel-type or cone-type main rolls (also referred to as “inclined rolls”), guide means such as guide shoes, disk rolls, roller-type guides, and an inner surface regulating tool called a plug. Is a drilling machine.

  FIG. 1 is a schematic view showing an example of an inclined punching machine using a cone type inclined roll, and FIG. 2 is a schematic view showing an AA arrow view of FIG. FIG. 3 is a diagram schematically showing the plug shape.

  As shown in FIG. 1, in the piercer, for example, the pair of main rolls 1 are such that the roll axis center line forms a crossing angle γ with respect to the pass line XX of the round steel piece B that is a material to be rolled. Are arranged opposite to each other. Moreover, as shown in FIG. 2, the main roll 1 is arrange | positioned so that it may become the inclination | tilt angle (beta) with respect to the pass line XX. The other main roll 1 that is not shown in FIG. 2 is opposed to each other while being inclined in opposite directions at an inclination angle β across the pass line XX. The main roll 1 that applies a screwing motion to the round steel piece B is directly connected to each driving device 4, and can thereby rotate about the roll axis.

  Further, as shown in FIG. 2, a pair of disk rolls 2 arranged so that the phase is shifted by 90 ° from the main roll 1 around the pass line. The pair of disc rolls 2 is rotated at a predetermined speed in the same direction as the direction of travel of the material to be rolled, and plays an important role in suppressing the bulge of the outer peripheral length of the material to be rolled at the time of wall thickness processing. I am doing.

  The plug 3 has a bullet shape, and its base end is supported by the tip of the mandrel bar M, and is disposed on the pass line XX. As a material for the plug 3, Cr—Ni-based low alloy steel is usually used, and an oxide scale film is formed by heat treatment before use in order to enhance durability.

  For example, as shown in FIG. 3, the plug 3 mainly includes a rolling part 31, a reeling part 32, and a relief part 33, and the boundary between the reeling part 32 and the relief part 33 is a maximum diameter Pd. Become. The rolling part 31 mainly plays a role of making a hole in the solid steel material, and the reeling part plays a role of uniformizing the thickness of the hollow shell and smoothing the inner surface of the hollow shell. And the reeling part 32 has an angle of half angle (theta) p with respect to a plug shaft center, ie, the pass line of a round steel piece (refer FIG. 5).

  In the piercer configured in this way, the heated round steel piece B is supplied on the pass line XX in the right direction of the drawing and is passed by the main roll 1 and the plug 3 while passing through the gap between the inclined rolls. Rolled while being thickened. At this time, the round steel piece B is screw-moved on the pass line XX, and a hole is opened by the plug 3 in the axial center portion to become a hollow shell.

  Concavities and convexities formed on the inner surface of the hollow shell during piercing and rolling by a piercer are crushed by an inner surface regulating tool such as a plug of an elongator in the next process and a bar of a mandrel mill or a plug mill, and become wrinkles. And progress. That is, it can be said that the cause of the occurrence of minute internal flaws in the final product is due to the surface property (roughness) in the raw tube after piercing.

  In particular, in seamless steel pipes, such as fuel injection pipes, where there is high pressure on the inner surface, if there are fine rice-grained wrinkles, there is a risk that the pipe will burst starting from the wrinkles and lead to a major accident. When the pipe inner diameter is large, the inner surface flaws can be removed mechanically using a grinder or the like, but when the pipe inner diameter is small, it is difficult to remove completely. Even if it can be removed, not only will the number of maintenance steps increase, but the thickness of the removed part may become thin, which may cause problems as a product.

  In order to solve such a problem, the present applicant discloses in Patent Document 1 a method of manufacturing a seamless steel pipe using a plug in which the scale film of the plug reeling part is thinner than the scale film of the rolled part. ing.

JP-A-10-249412

  According to the invention described in Patent Document 1, the occurrence of rice grain rash can be prevented. However, the removal amount of the scale film must be strictly adjusted. If the film thickness is neglected and the film thickness is made too thin, problems such as seizure of the reeling part and shortened plug life may occur. is there.

The present invention improves the inner surface properties of the hollow shell after piercing-rolling, and to provide a method for manufacturing automobile parts seamless pipe can be suppressed wrinkle flaw auto parts for seamless pipe .

  As a result of intensive studies to solve such problems, the present inventor has found the following knowledge.

  FIG. 4 is a schematic diagram showing an example of a piercing and rolling process in a cross section perpendicular to the pass line. As shown in FIG. 4, in piercing and rolling, for example, the material to be rolled 5 is pressed into a space formed by a pair of main rolls 1 and plugs 3, so that thickening is performed. After that, the bulge of the outer diameter is suppressed by the disc roll 2 at the half-rotated position, and the wall thickness processing by the pair of main rolls 1 and plugs 3 is performed again. By repeating this, a hole is made in the material to be rolled 5, and its thickness is regulated.

  Here, on the inner surface of the material 5 to be rolled that has reached the region indicated by “a” in FIG. 4, a compressive force acts in the circumferential direction, and wrinkles may occur. Thereafter, the material to be rolled 5 is screwed and moved, and when the material 5 reaches the region indicated by “b” in FIG. 4, the outer surface thereof contacts the main roll 1. At this time, the material to be rolled 5 is subjected to outer diameter processing, so that the wrinkles of the inner surface formed in the region indicated by “a” become deeper. Thereafter, when the region indicated by “c” in FIG. 4 is reached, the inner surface of the material to be rolled 5 contacts the plug 3. At this time, wrinkles are stretched in the circumferential direction to develop into fine wrinkles.

  The present inventor investigated the factors that deteriorate the inner surface properties of the material to be rolled. The following findings were obtained regarding the occurrence of poor perforation such as:

(A) When the number of times of plug reeling R _n increases, the propulsive force in the forward direction of the material to be rolled decreases. As a result, the speed at the end of piercing and rolling is reduced, and piercing defects such as clogging are likely to occur. However, Δθ (= θ _p −θ _r , where θ _r is the half angle formed by the pass line and the main roll surface when the main roll tilt angle is zero, and θ _{p is the} pass line and the plug reeling portion. The larger the half-width made), the greater the reduction on the gorge exit side, and the higher the surface pressure, the less likely to perforate. As a result, the degree of freedom of the reeling number of times R _n of the plug (mainly, the degree of freedom of the upper limit) is increased.

(B) When the number of times of plug reeling R _n increases, the number of times of rolling on the material to be rolled increases accordingly, and it becomes easy to reduce the roughness of the inner surface of the pierced shell. The roughness reduction effect increases as Δθ (= θ _p −θ _r ) increases. As a result, the degree of freedom of the reeling number of times R _n of the plug (mainly, the degree of freedom of the lower limit) is increased.

(C) Since the roll peripheral speed on the gorge exit side increases as D ₂ / D ₁ increases, the bulge of the outer diameter in the region indicated by “b” in FIG. 4 can be suppressed. As a result, even if the number of times of plug reeling R _n is reduced, the generation of wrinkles can be suppressed, and the degree of freedom (mainly the lower limit degree of freedom) of the number of times of plug reeling R _n is increased.

The above θ _r is a half angle formed by the pass line and the main roll surface when the main roll tilt angle is zero (see “θ _r ” in FIG. 5), and θ _p is the pass line and the plug reeling portion. Means a half-angle (see “θ _p ” in FIG. 5). Further, the number of times of plug reeling Rn is obtained by the following equation.
_{Rn = L p / (π ×} d a × tanβ / 2)

However, L _p is the length of the reeling section (mm), d _a is a value obtained by the following equation, beta is meant inclination angle of the main roll (°), respectively.
d _a = (d ₁ + d ₂ ) / 2
In the above formula, d ₁ means the outer diameter (mm) of the round steel piece, and d ₂ means the outer diameter of the hollow shell.

This invention is made | formed based on such knowledge, and makes the summary the manufacturing method of the seamless pipe for motor vehicle parts shown to following [1]-[4].

[1] A plug (outer diameter d (mm) has an equal diameter or an outer diameter d in the axial direction along the pass line) between a pair of inclined rolls and a pair of guide means that are arranged opposite to each other around the pass line. The half angle of the taper angle increasing toward the rear end in the direction is a columnar shape with an axial length L2 (mm) of 2 ° or less, and the tip surface has a curvature radius r (mm) and an axial length L1 (mm). A method of manufacturing a seamless pipe by piercing and rolling a round steel piece heated to 1300 ° C. or less by a piercer provided with a tip-shaped rolling part formed in a spherical shape. ) To (3) A method for producing a seamless pipe for automobile parts , characterized by piercing and rolling under conditions satisfying the expressions (3).
−1.0 <Δθ (1)
Δθ = θ _p −θ _r (2)
−0.37 × Δθ + 1.47 ≦ R _n ≦ 0.37 × Δθ + 2.67 (3)
However, the meaning of each symbol in the above formula is as follows.
θ _r : Half angle (°) formed by the pass line and the main roll surface when the main roll tilt angle is zero
θ _p : Half angle (°) between pass line and plug reeling
R _n : Plug reeling frequency (times)

[2] A plug (with an outer diameter d (mm) having an equal diameter or an outer diameter d extending in the axial direction along the pass line) between a pair of inclined rolls and a pair of guide means disposed opposite to each other around the pass line. The half angle of the taper angle increasing toward the rear end in the direction is a columnar shape with an axial length L2 (mm) of 2 ° or less, and the tip surface has a curvature radius r (mm) and an axial length L1 (mm). A method of manufacturing a seamless pipe by piercing and rolling a round steel piece heated to 1300 ° C. or less by a piercer provided with a tip-shaped rolling part formed in a spherical shape. ), (2) and (4) the method of producing automotive parts for seamless pipes, characterized in that the piercing-rolling under the condition satisfying the equation.
−1.0 <Δθ (1)
Δθ = θ _p −θ _r (2)
−0.24 × Δθ + 1.73 ≦ R _n ≦ 0.37 × Δθ + 2.67 (4)
However, the meaning of each symbol in the above formula is as follows.
θ _r : Half angle (°) formed by the pass line and the main roll surface when the main roll tilt angle is zero
θ _p : Half angle (°) between pass line and plug reeling
R _n : Plug reeling frequency (times)

[3] The method for producing a seamless pipe for automobile parts according to [1] or [2], further comprising piercing and rolling under conditions satisfying the following expression (5).
−1.37 × D ₂ / D ₁ + 2.74 ≦ R _n (5)
However, the meaning of each symbol in the above formula is as follows.
D ₁ : Roll diameter (mm) of main roll gorge
D ₂ : Main roll outer diameter (mm) at the position of the maximum plug diameter
R _n : Plug reeling frequency (times)

[4] The method for manufacturing a seamless pipe for automobile parts as described in [1] or [2] above, further comprising piercing and rolling under conditions satisfying the following expression (6).
−1.25 × D ₂ / D ₁ + 2.88 ≦ R _n (6)
However, the meaning of each symbol in the above formula is as follows.
D ₁ : Roll diameter (mm) of main roll gorge
D ₂ : Main roll outer diameter (mm) at the position of the maximum plug diameter
R _n : Plug reeling frequency (times)

In addition, in this invention, a reeling part means the site | part which satisfy | fills any one of following (A)-(B).
(A) Site where thickness processing degree calculated from the following formula is 5% or less Thickness processing level = (G ₁ −G ₂ ) / G ₁ × 100 (%)
However, the meaning of each symbol in the formula is as follows.
G ₁ : distance between the plug and the roll at the start position of the corresponding part of the plug (mm)
G ₂ : distance between the plug and the roll at the end position of the corresponding part of the plug (mm)
(B) The part near the entrance side of the maximum diameter part of the plug (C) If the part corresponding to the reeling part has no curvature, the part where the difference in the surface angle obtained from the following formula is 2 ° or less Difference = Face angle of applicable part of plug-Roll exit side angle (°)
However, “the start position of the corresponding part of the plug” is, for example, the position of the boundary line of reference numerals 31 and 32 in FIG. 3, and “end position of the corresponding part of the plug” is, for example, the reference numerals 32 and 33 of FIG. This means the position of the boundary line.

  ADVANTAGE OF THE INVENTION According to this invention, the inner surface property of the hollow shell after piercing-rolling can be improved, and the wrinkle of the seamless pipe obtained by implementing extending | stretching rolling and constant diameter rolling after piercing-rolling can be suppressed.

Schematic diagram showing an example of an inclined drilling machine using a cone type inclined roll The schematic diagram which shows the AA arrow line view of FIG. Diagram showing plug shape schematically Schematic showing an example of piercing and rolling process in a cross section perpendicular to the pass line Schematic diagram showing main roll and plug in a state where the inclination angle β is zero Diagram showing the relationship between Δθ and R _n Diagram showing the relation between D ₂ / D ₁ and R _n

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Main roll 2 Disc roll 3 Plug 31 Rolling part 32 Reeling part 33 Escape part 4 Drive device 5 Rolled material B Round steel piece (billet)

  As the piercing and rolling machine used in the method for producing a seamless steel pipe according to the present invention, a conventionally used piercer can be used. That is, a plug is disposed along a pass line between a pair of inclined rolls and a pair of guide means arranged opposite to each other around the pass line, and normal guide means such as a guide shoe, a disk roll, and a roller type guide are provided. The piercer you have can be used. Also, the shape of the plug is not particularly limited. For example, as shown in FIG. 3 described above, the plug has a rolling part 31, a reeling part 32, and a relief part 33. The thing of the structure from which the boundary of becomes the maximum diameter can be used.

  As the guide means, it is desirable to use a disk roll because the material speed can be increased in the axial direction. Further, it is desirable to use a cone-shaped roll as the main roll.

  The round steel piece to be subjected to piercing and rolling needs to be heated to 1300 ° C. or less. If the temperature exceeds 1300 ° C., inner surface flaws occur due to melting of the inner surface of the round steel piece, and the inner surface properties of the pipe deteriorate. If the temperature of the round steel slab is too low, the deformation resistance becomes too large to carry out piercing and rolling, or the life of the plug or other manufacturing equipment is significantly reduced. Therefore, it is desirable that the temperature of the round bar is 1150 ° C. or higher.

Here, Δθ defined by the following equation (a) needs to be −1.0 or more.
Δθ = θ _p −θ _r (a)
However, the meaning of each symbol in the above formula is as follows.
θ _r : Half angle (°) formed by the pass line and the main roll surface when the main roll tilt angle is zero
θ _p : Half angle (°) between pass line and plug reeling

That is, the inner surface of the hollow shell after piercing and rolling is smoothed by increasing the number of plug reeling R _n , but depending on the combination of the plug surface angle θ _p with respect to the outlet surface angle θ _r of the main roll, When the smoothness is insufficient, there are cases where defects such as clogging and uneven thickness occur. This tendency becomes stronger as Δθ becomes smaller. When Δθ is less than −1.0, the inner surface of the hollow shell after piercing and rolling can be smoothed even if the number of times of plug reeling R _n is increased. Disappear. Therefore, Δθ is set to −1.0 or more.

On the other hand, the plug reeling number R _n is the surface roughness of the inner surface of the hollow shell after piercing-rolling too small becomes rough, too large butt clogging problem is likely to occur. However, both problems are less likely to occur as Δθ increases. This is because, if Δθ is increased, the reduction on the gorge exit side increases, so that the surface pressure increases and it becomes difficult for poor drilling to occur. That is, the processing in the reeling portion can be concentrated in the second half, and a hollow shell with good inner surface properties can be obtained even with the same number of plug reeling times. Therefore, the number of plug reeling R _n needs to satisfy the relationship of the following equation (b) in relation to Δθ. It is more desirable that the relationship of the following formula (b1) is satisfied.
−0.37 × Δθ + 1.47 ≦ R _n ≦ 0.37 × Δθ + 2.67 (b)
−0.24 × Δθ + 1.73 ≦ R _n ≦ 0.37 × Δθ + 2.67 (b1)

It is desirable that the plug reeling number of times R _n further satisfies the following expression (c). It is more desirable that the following expression (d) is satisfied.
−1.37 × D ₂ / D ₁ + 2.74 ≦ R _n (c)
−1.25 × D ₂ / D ₁ + 2.88 ≦ R _n (d)
However, the meaning of each symbol in the above formula is as follows.
D ₁ : Roll diameter (mm) of main roll gorge
D ₂ : Main roll outer diameter (mm) at the position of the maximum plug diameter

The inner surface roughness of the hollow shell after piercing and rolling is easily affected by the roll diameter at the main roll outlet side position. If set to be larger than the roll diameter D ₂ of the gorge portion of a main roll main roll outer diameter D ₁ of the plug maximum diameter position, easily relaxed circumferential compressive strain acting on the inner surface of the material to be rolled As a result, it becomes easy to suppress wrinkles on the inner surface of the tube. As described above, if Δθ is reduced, it becomes difficult to smooth the inner surface of the tube, but the relationship between D ₂ / D ₁ and R _n should be set so as to satisfy the condition expressed by the above equation (c). This can improve the surface roughness of the tube inner surface. The surface roughness of the inner surface of the tube is further improved by setting the relationship between D ₂ / D ₁ and R _n so as to satisfy the condition expressed by the above equation (d).

  The method for producing a seamless pipe according to the present invention can be applied to the production of any pipe such as a metal pipe, a normal steel pipe, a low alloy steel pipe, and a high alloy steel pipe. Suitable for manufacturing steel pipes for automobile parts.

  With respect to the steel types having the chemical composition shown in Table 1, a 70 丸 round steel piece was cut out from the center of a round steel piece obtained by continuous rolling and finished to 225 φ by partial rolling, and used as a test material. A disk roll is used as a guide means, the main roll shape and the plug shape are changed, piercing and rolling is performed under the manufacturing conditions shown in Table 2 or Table 3, and the roughness of the hollow shell inner surface is set to the maximum defined in JIS-0601. Height Rz) was measured.

FIG. 6 shows the relationship between Δθ and R _n when the hollow shell is manufactured under the manufacturing conditions shown in Table 2, and D ₂ / D when the hollow shell is manufactured under the manufacturing conditions shown in Table 3. The relationship between ₁ and R _n and the tube inner surface properties is shown in FIG.

  6 and 7, “▲” indicates that the roughness of the inner surface of the hollow shell is Rz> 150 μmm, and “Δ” indicates that the roughness of the inner surface of the hollow shell is 100 μm ≦ Rz ≦ 150 μmm, “◯” indicates that the roughness of the inner surface of the hollow shell is Rz <100 μm. In addition, “X” in FIG. 6 indicates that a perforation failure such as clogging of the tail has occurred.

As shown in FIG. 6, in a region where Δθ is less than −1.0, the roughness Rz of the inner surface of the hollow shell exceeds 150 μmm, or poor perforation occurs. Even in the region where Δθ is −1.0, poor perforation occurs in the region where R _n exceeds “0.37 × Δθ + 2.67”, and in the region where R _n is less than “−0.37 × Δθ + 1.47”, the surface roughness Rz increased. Further, the surface roughness Rz could be further reduced by adjusting the manufacturing conditions so that R _n is in the region of “−0.24 × Δθ + 1.73” or more.

As shown in FIG. 7, the surface roughness is large in the region where Rn is less than “−1.37 × D ₂ / D ₁ +2.74”, and the surface roughness is good in the region larger than this. It becomes a range. In the region where Rn is “−1.25 × D ₂ / D ₁ +2.88” or more, the surface roughness can be further reduced.

  A continuous cast material having the chemical composition shown in Table 1 is made into a round steel piece of φ191 by split rolling, and then the above-mentioned round steel pieces are pierced and rolled by 100 pieces under the production conditions shown in Table 4 to obtain an outer diameter. A seamless steel pipe having a diameter of 73 and a wall thickness of 5.51 was manufactured, and the inner surface properties were investigated. The results are shown in Table 5.

  As shown in Table 5, the example of the present invention was able to significantly reduce the internal flaw occurrence rate compared to the comparative example.

ADVANTAGE OF THE INVENTION According to this invention, the inner surface property of the hollow shell after piercing-rolling can be improved, and the wrinkle of the seamless pipe for automobile parts obtained by carrying out extending | stretching rolling and constant diameter rolling after piercing-rolling can be suppressed. Can do.

Claims (4)

A plug (outer diameter d (mm) is the same diameter over the axial direction or the outer diameter d is the rear end in the axial direction) along the pass line between a pair of inclined rolls and a pair of guide means arranged opposite to each other around the pass line. The half angle of the taper angle that increases as it goes to is a cylindrical shape with an axial length L2 (mm) of 2 ° or less, and its tip surface is a spherical shape with a radius of curvature r (mm) and an axial length L1 (mm). A method of manufacturing a seamless pipe by piercing and rolling a round steel piece heated to 1300 ° C. or less with a piercer provided with a tip rolling portion formed), comprising the following (1) to ( 3) A method for producing a seamless pipe for automobile parts , characterized by piercing and rolling under conditions satisfying the formula.
−1.0 <Δθ (1)
Δθ = θ _p −θ _r (2)
−0.37 × Δθ + 1.47 ≦ R _n ≦ 0.37 × Δθ + 2.67 (3)
However, the meaning of each symbol in the above formula is as follows.
θ _r : Half angle (°) formed by the pass line and the main roll surface when the main roll tilt angle is zero
θ _p : Half angle (°) between pass line and plug reeling
R _n : Plug reeling frequency (times) A plug (outer diameter d (mm) is the same diameter in the axial direction or the outer diameter d is the rear end in the axial direction) along the pass line between a pair of inclined rolls and a pair of guide means arranged opposite to each other around the pass line. The half angle of the taper angle that increases as it goes to is a cylindrical shape with an axial length L2 (mm) of 2 ° or less, and its tip surface is a spherical shape with a radius of curvature r (mm) and an axial length L1 (mm). A method for producing a seamless pipe by piercing and rolling a round steel piece heated to 1300 ° C. or less by a piercer provided with a tip rolling portion formed), comprising the following (1), ( A method of manufacturing a seamless pipe for automobile parts , characterized by piercing and rolling under conditions that satisfy the expressions (2) and (4).
−1.0 <Δθ (1)
Δθ = θ _p −θ _r (2)
−0.24 × Δθ + 1.73 ≦ R _n ≦ 0.37 × Δθ + 2.67 (4)
However, the meaning of each symbol in the above formula is as follows.
θ _r : Half angle (°) formed by the pass line and the main roll surface when the main roll tilt angle is zero
θ _p : Half angle (°) between pass line and plug reeling
R _n : Plug reeling frequency (times) Furthermore, piercing-rolling is carried out on the conditions which satisfy | fill following (5) Formula, The manufacturing method of the seamless pipe for motor vehicle parts of Claim 1 or 2 characterized by the above-mentioned.
−1.37 × D ₂ / D ₁ + 2.74 ≦ R _n (5)
However, the meaning of each symbol in the above formula is as follows.
D ₁ : Roll diameter (mm) of main roll gorge
D ₂ : Main roll outer diameter (mm) at the position of the maximum plug diameter
R _n : Plug reeling frequency (times) Furthermore, piercing-rolling is carried out on the conditions which satisfy | fill following (6) Formula, The manufacturing method of the seamless pipe for motor vehicle parts of Claim 1 or 2 characterized by the above-mentioned.
−1.25 × D ₂ / D ₁ + 2.88 ≦ R _n (6)
However, the meaning of each symbol in the above formula is as follows.
D ₁ : Roll diameter (mm) of main roll gorge
D ₂ : Main roll outer diameter (mm) at the position of the maximum plug diameter
R _n : Plug reeling frequency (times)

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