JP3305604B2 - Manufacturing method of seamless steel pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a seamless steel pipe which is pierced and rolled by the Mannesmann method using a material for rolling a seamless steel pipe manufactured to satisfy specific conditions. The invention also charged continuously cast bloom in a heating furnace, after holding at a constant temperature, blooming rolling, followed by a high-carbon chromium bearing round bar steel seamless tube manufactured by the planetary inclined rolling It relates to a rolling method .

[0002]

[Problems to be Solved by the Invention] Under severe circumstances, such as a sharp decrease in the relative international competitiveness of the industry due to a strong yen and a shift of overseas production bases of the automobile industry, which is a major customer of the material manufacturer, The side is making various efforts to reduce the production cost, such as improving the yield rate.

Under such circumstances, for example,
, C: 0.15 to 1.10%, Si: 0.15 to 0.1%
70%, Mn: ≤ 1.10%, Cr: 0.50 to 1.6
0%, Mo: ≦ 1.00%, O: 8ppm or less, balance F
e and round bars manufactured from continuous cast blooms made of unavoidable impurity elements have small cracks at the center and near the center. Racks may occur. In particular, chrome bearing round bar steel occurs more frequently than other steel grades, and when tubing is manufactured from the billet by the piercing and rolling according to the Mannesmann method, blistering scratches will occur. It can occur and is a problem.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to prevent the occurrence of blistering of a steel pipe at the time of manufacturing a seamless steel pipe by the Mannesmann method and to manufacture a seamless steel pipe having a good inner skin. Aim.

[0005]

Means for Solving the Problems The present inventors have conducted various studies to solve the above problems. First, the inventors conducted various tests in order to clarify the causal relationship between the location of the microcracks generated in the billet and the occurrence of blistering scratches. As a result of piercing and rolling test of tiscin billet, FIG.
As shown in the figure, the eccentric distance (that is, the distance from the central axis to the hole) is in all cases where the diameter of the hole is 0.1 to 2.0 mm.
It has been found that when r1) is 4 mm or more, blistering scratches occur. The present invention has been completed based on such knowledge, and the gist of the present invention is as described in the claims.

[0006] That is, the gist is as follows. Man-made for seamless steel tube rolling material made of round bar steel
By performing piercing and rolling by the Nesman method, seamless steel
A method for manufacturing a pipe, comprising: a material for rolling a seamless steel pipe.
As for those that meet the condition of formula (1) shown below
A method for producing a seamless steel pipe, wherein the piercing and rolling is performed . r1 ≦ r0 · {(6.4 × 10 ⁻³ + 0.16r) / (R ² −r ² )} ^0.5 ... (1) where r1 is a minute distance from the center of the seamless steel tube rolling material.
Tsu distance to click r0: the radius of a seamless steel pipe rolling material for R: the radius r of the seamless steel pipe after piercing: inside diameter of the seamless steel pipe after piercing

[0007] 2. The material for seamless steel tube rolling is weight%,
C: 0.15 to 1.10%, Si: 0.15 to 0.70
%, Mn: ≤ 1.10%, Cr: 0.50 to 1.60
%, Mo: ≦ 1.00%, O: 8 ppm or less, balance Fe
And a manufacturing method, a seamless steel pipe according to the item 1, characterized in that those produced from a continuous cast material of chromium bearing steel consisting of unavoidable impurity elements.

Hereinafter, the operation of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a radial cross-sectional view of a seamless steel pipe rolling material before piercing and rolling, and FIG. 2 is a radial cross-sectional view of the pipe after piercing and rolling. The radius of the material before piercing and rolling is r
0, the length is l, the distance from the center where the microcracks are present is r1, the radius of the product after drilling is R, the inner diameter is r, the length is L, and the distance from the center where the blister is present is r '. Then, since the change in volume is not before and after ^{piercing, π · r0 2 · l =} π · (R 2 -r 2) · L ····· (2)

From equation (2), l / L = (R^Two -R^Two ) / R0^Two ..... (3) The distance from the center exists at r1Micro crackIs manne
By piercing and rolling by the Sman method,
Assuming that it moves, π · r1^Two L = π · (r ′^Two -R^Two ) · L (4) From equation (4),  r ’^Two = R1^Two ・ (L / L) + r^Two ・ ・ ・ ・ ・ (5)

From the equations (3) and (5) , r ′ ² = r1 ² · (R ² −r ² ) / r0 ² + r ² ··· (6) From FIG. Assuming that the shortest distance to the existing position is t, t = r′−r (7)

[0012] Equation (6), the equation (7), t = {r1 2 · (R 2 -r 2) / r0 2 + r 2} with ^0.5 -r · · · · · (8) Equation (8) It was derived Te, small class from billet center
Tsu FIG. 4 shows a relationship between the shortest distance t from tube inner surface of the distance r1 and after piercing to click to blistering flaw portion. From this result, r1 is 4mm or less, in other words t is 0.22mm or less
If it is below , it does not exist as a blister .

The above result and φ5 having an eccentric hole closed at one end
The results were compared with the results of a piercing and rolling test of 0 mm plasticine billet. For example, r1 is 4 mm or less,
In other words, if t is 0.22 mm or less , the fu
After the cracks are exposed on the inner surface of the tube or the blisters are broken on the inner surface, the inner surface is flattened by the piercing and rolling plugs, and it is confirmed by collation with the experimental results that it cannot exist as a scratch. Was. Based on the results of this study, the following formula (1) was derived in consideration of the relationship between the plasticity and the extensibility of actual steel. r1 ≦ r0 · {(6.4 × 10 -3 + 0.16r) / (R 2 -r 2)} 0.5 ·· ··· (1)

[0014] From the results of the above research, the seamless steel pipe
When the radius of the rolling material is r0, the distance from the center to the minute crack is r1, the radius of the product after piercing and rolling is R, and the inner diameter is r, a seamless steel tube rolling material satisfying the following equation (1) is used. According to the method for producing a seamless steel pipe by piercing and rolling the material for seamless steel pipe rolling by the Mannesmann method, to prevent blistering of the steel pipe during the production of the seamless steel pipe by the Mannesmann method, which is the object of the present invention, It has been found that the objective of producing a seamless steel pipe having a good inner skin can be achieved.

Next, in claim 2 according to the present invention, C: 0.15 to 1.10% and Si: 0.15 to 0.1% by weight.
0.70%, Mn: ≤ 1.10%, Cr: 0.50
1.60%, Mo: ≦ 1.00%, O: 8 ppm or less,
The reason for limiting the component range of the material for rolling a seamless steel pipe manufactured from a continuous cast material of chromium bearing steel comprising the balance of Fe and unavoidable impurity elements will be described in detail.

C is dissolved in the matrix, strengthens martensite, is added for the purpose of increasing the amount of carbides, and improving the hardness and rolling life after tempering. In order to impart strength to steel, at least 0.15% or more is required. On the other hand, when the content exceeds 1.10%, giant carbides are formed and the rolling contact fatigue characteristics are reduced, and a long time diffusion annealing is required for the diffusion, and the productivity is reduced. Therefore, C
The lower limit of the amount was 0.15% and the upper limit was 1.10%.

Si is an element effective for improving the solid solution strengthening and the tempering softening resistance to improve the life of the bearing. However, if it is less than 0.15%, such an effect is small. However, if the content exceeds 0.70%, the mechanical strength, machinability, and the carburized abnormal layer increase, leading to an increase in the content of 0.15 to 0.70%. Range.

Mn is an element necessary for improving the hardenability, and the upper limit is set to 1.10% because, when Mn is increased, the amount of retained austenite is significantly increased and the rolling fatigue life is reduced.

Cr is an element effective for improving hardenability and tempering softening resistance. In addition, the hard and fine Cr carbide functions to improve the wear resistance. However,
If the content is less than 0.50%, this effect is small,
If it exceeds 1.60%, giant carbides may be generated and the life may be shortened, and the fatigue strength may be deteriorated due to excessive carburization. Therefore, the content is 0.50 to 1.60.
%.

Mo is an element effective for improving hardenability and improving toughness. However,
Even if it is added in excess of 1.00%, the effect is saturated and the economy is impaired, so 1.00% was made the upper limit.

O combines with Al and Si to form hard oxide-based inclusions and deteriorate the fatigue life. Therefore, the content of O must be reduced as much as possible. 8 ppm or less is preferable. Therefore, the upper limit of the amount of O was set to 8 ppm.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION A high carbon chromium bearing steel round bar steel having a closed hole at one end was pierced and rolled by an actual machine. The presence or absence of blistering scratches was confirmed, and as a result, the validity of the present invention was confirmed.

[0023]

EXAMPLES Table 1 shows examples of the present invention, comparative examples, and actual test results of each example. In weight%, C: 0.95-1.10
%, Si: 0.15 to 0.35%, Mn: ≦ 0.50
%, Cr: 1.30 to 1.60%, O: 8 ppm or less,
A round bar made of high carbon chromium bearing steel (SUJ2) having a diameter of 90 mm and a diameter of 1 mm, a length of 40 mm, a diameter of 2 mm, and a length of 40 made of high carbon chromium bearing steel (SUJ2) composed of the balance of Fe and unavoidable impurities.
mm is artificially created by a drill to produce a high carbon chromium bearing steel round bar having a closed hole at one end.
Inventive Example No. No. 1 to 6 for seamless steel tube rolling and Comparative Example No. Seven to ten seamless steel tube rolling materials were manufactured. Each example was pierced and rolled with an actual machine, and the presence or absence of blister scratches was confirmed. As for the bulging scratches, as shown in FIG. 5, the shortest distance t from the inner surface of the tube material to the bulging scratches was measured and compared with the calculated value obtained by using equation (8).

[0024]

[Table 1]

Table 2 shows the results of measurement of the position of the blister flaw by the actual machine test of the embodiment of the present invention and the comparative example. As shown in Table 2, there is almost no difference between the actually measured value and the calculated value obtained by the equation (8).

Further, as is apparent from the results of actual machine tests of the examples of the present invention and comparative examples shown in Table 2, the effect of the present invention is remarkable. It is extremely effective for preventing blistering of steel pipes during the production of seamless steel pipes by the Mannesmann method. In the actual machine tests of the present invention examples and comparative examples shown in Table 2, round bars having r0 of 45 mm and 74 mm were used, but similar results were obtained in actual machine test results using other dimensions. It should be noted that the present invention is not limited by the above embodiments.

[0027]

[Table 2]

[0028]

EFFECT OF THE INVENTION By using the present invention, it is possible to prevent the occurrence of blistering of the steel pipe during the production of the seamless steel pipe by the Mannesmann method, and to produce a seamless steel pipe having a good inner skin. Non-conforming products due to defects can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view in the radial direction of a pipe material before piercing and rolling.

FIG. 2 is a cross-sectional view in the radial direction of a pipe material after piercing and rolling.

FIG. 3 is a view showing the results of a piercing-rolling test using a plastic thin billet having a closed hole at one end.

FIG. 4 is a diagram showing the relationship between the distance r1 from the center of the plastic billet to the defect determined by equation (8) and the shortest distance t from the inner surface of the tube after drilling to the blister.

FIG. 5 is a longitudinal sectional view showing a state of a pipe material after piercing and rolling;
.

──────────────────────────────────────────────────の Continuing on the front page (72) Katsuhiko Ozaki, 3007 character, Nakajima character in Shima, Himeji, Hyogo Prefecture Inside Sanyo Special Steel Co., Ltd. No. Sanyo Special Steel Co., Ltd. (72) Inventor Hiroshi Nakamura 3007 Nakajima character, Shima, Ward, Himeji City, Hyogo Prefecture No. 3007 Sanyo Special Steel Co., Ltd. (56) References JP-A-5-7990 (JP, A) JP-A-4-135001 (JP, A) JP-A-7-164020 (JP, A) JP-A-9-59718 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21B 19 / 04

Claims (2)

(57) [Claims] 1. A material for rolling a seamless steel pipe made of a round steel bar.
Piercing and rolling by the Mannesmann method
A method of manufacturing a seamless steel pipe, the method comprising:
As a material for tube rolling, it satisfies the condition of the following formula (1)
A method for producing a seamless steel pipe , wherein the piercing and rolling is performed on a pipe. r1 ≦ r0 · {(6.4 × 10 ⁻³ + 0.16r) / (R ² −r ² )} ^0.5 ... (1) where r1 is a minute distance from the center of the seamless steel tube rolling material.
Tsu distance to click r0: the radius of a seamless steel pipe rolling material for R: the radius r of the seamless steel pipe after piercing: inside diameter of the seamless steel pipe after piercing 2. The material for rolling a seamless steel pipe, in weight%,
C: 0.15 to 1.10%, Si: 0.15 to 0.70
%, Mn: ≤ 1.10%, Cr: 0.50 to 1.60
%, Mo: ≦ 1.00%, O: 8 ppm or less, balance Fe
And a chromium bearing steel made of a continuous cast material comprising unavoidable impurity elements.
2. The method for producing a seamless steel pipe according to item 1.