JPH04319006A - Skew rolling method of seamless steel tube - Google Patents

Abstract

PURPOSE:To prevent the generation of the outside surface flaw and inside surface flaw of rolled stock by reducing slip between rolls and a material to be rolled in a Mannesmann type inclined piercer. CONSTITUTION:Rolling is executed by controlling so that the surface roughness in the circumferential direction of rolls of the inclined piercer is maintained between 5-40mum in the arithmetic mean deviation Ra of profile and also the average peak interval DHS of ruggedness is in the range of 30-850mum.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for piercing and rolling seamless steel pipes using inclined rolls.

0002

2. Description of the Related Art A Mannesmann type punching machine has a pair of barrel type rolls 10, 10a as shown in FIG. The pair of rolls 10, 10a are provided with a surface angle of several degrees and are arranged at an angle with respect to the pass line. The heated billet 20 moves forward while being rotated by the rolls 10 and 10a, and due to the rotary forging effect received during this process, a hole is easily formed in the center of the billet 20, and the plug 30
perforated by the tip of the With such conventional drilling methods, if high alloy steel such as 9% Cr steel and 13% Cr steel is continuously drilled, slippage between the rolls and the material to be rolled increases and the forward speed of the material to be rolled decreases. A hole is formed in the center by rotary forging before being drilled at the tip of the plug of the rolled material, and this tends to remain as an inner surface flaw after the hole is drilled.

As a measure to prevent such problems, there is a method of imparting a concave shape to the roll surface in advance by knurling or knurling when modifying the roll. The concave shape on the roll surface imparted by these methods is suitable for the purpose of improving the biting property of the rolled material into the roll, but it is not suitable for the purpose of improving the forward speed of the rolled material after biting. Achieving this requires a very deep concave shape, which leaves traces on the surface of the rolled material after rolling, which poses a problem.

[0004] In addition, as shown in Japanese Patent Application Laid-Open No. 61-180603, there is a method of specifying the opening amount of the rolls within a certain range with respect to the entrance diameter of the material to be rolled, or Japanese Patent Application Laid-Open No. 63-49308. As shown in the publication, there is a method of rolling by changing not only the roll opening amount but also the plug lead, roll inclination angle, roll intersection angle, etc., but when these rolling condition settings are changed, the material to be rolled during rolling There is a problem in that it is not possible to give a predetermined dimension to.

[0005]

SUMMARY OF THE INVENTION Therefore, the present invention aims to prevent slippage between the rolled material and the rolls without impairing the surface properties of the outer surface of the rolled material and without changing the settings of the rolling conditions. This is intended to prevent internal surface flaws.

[0006]

[Means for Solving the Problems] The present inventors investigated the surface of the rolled material every several thousand rolls after changing the rolls. In addition, during and after rolling of high-alloy steel, the roll surface was inspected every few dozen rolls. As a result, the following became clear. Regarding the roll surface roughness, the roughness in the circumferential direction is easily influenced by the number of rolled rolls and the type of rolled steel, but the roughness in the axial direction is not so affected by these factors. The surface roughness of the roll in the circumferential direction has a large influence on the slip between the rolled material and the roll. However, the center line average roughness and maximum roughness alone cannot be used for evaluation.

[0007] In order to solve the above-mentioned problems, the present invention was developed based on the results of repeated investigations as described above. The present invention provides an inclined perforation machine in which the surface roughness of the inclined roll in the circumferential direction is set to 5 μm or more and 40 μm in center line average roughness Ra.
30 μm or more in DHS and average peak spacing of unevenness 8
This is a method for inclined rolling of seamless steel pipes, which is characterized by performing rolling while controlling the thickness to be within a range of 50 μm or less.

[0008]

[Operation] The perforation efficiency was used as an index for evaluating the slippage between the rolled material and the rolls. The perforation efficiency η is a value defined as in equation (1) using the component VR-x of the circumferential speed of the inclined roll in the forward direction of the rolled material VR-x and the forward speed VM-x of the rolled material, It can be determined that the smaller η is, the greater the slippage between the rolled material and the rolls is.

[0009] η = {(VM-x)/(V
R-x)}×100 (1) The operation of the present invention will be explained in detail below using the drawings. The surface of the inclined roll is ground and finished, and the rolled material 14 has a diameter of 110 mm.
000 rolls were subjected to rolling chances. Most of the actual rolling chances were rolling of general carbon steel, but only 150 pieces, from 8001st to 8150th, were rolled with 13% Cr steel.

As shown in Table 1, rolling was interrupted at the 1000th roll, 2000th roll after the start of rolling, and every 2000 rolls thereafter, and the roll surface was examined. In addition, for the 8001st to 8350th lines, each 50th line was investigated.

[0011]

[Table 1] ──────────────────────────
───── Roll observation (time) Number of rolled rolls (
This) Rolled steel type 1
0
Before rolling 2
1000 General carbon steel 3
2000 General carbon steel
4 4
000 General carbon steel 5
6000
General carbon steel 6
8000 General carbon steel 7
8050 13%Cr steel
8
8100 13%Cr steel
9 8150
13%Cr steel 10
8200
General carbon steel 11
8250 General carbon steel 12
8300 General carbon steel 1
3 8350
General carbon steel 14
10000 General carbon steel 15
12000 General carbon steel
16 14000
General carbon steel──────────────
────────────────── Roll surface quality is evaluated by roughness. As an index of roughness, there are two methods: one using the magnitude of roughness and the other using the interval between protrusions and recesses. In the present invention, the centerline average roughness Ra is an index using the size of roughness, and the average peak spacing D is an index using the spacing between concavities and convexities.
The roll surface properties were quantified by HS.

As shown in FIG. 2(a), Ra is obtained by extracting a portion of reference length L from the roughness curve in the direction of its center line, and using the center line of this sampled portion as the x-axis and the vertical magnification direction as When the roughness curve is expressed as y=f(x) on the y axis, (
2) The value Ra determined by the formula is expressed in μm.

[0013]

[Math 1]

[0014] Next, DHS is the number of peaks protruding above the center line as shown in FIG. The value obtained by dividing the measured total length L* by a value called high spot count HSC, which is given by the number of peaks protruding above a line passing through the line, is expressed in μm. To explain specifically using FIG. 2(b) as an example, in the case of this profile, the HSC is 7 for the measured total length L*. Therefore DH
S is calculated as in equation (3).

DHS = (L*)/(HSC)
= (L*)/7...(3) Figure 3 shows the influence of the number of rolling rolls on the perforation efficiency η from the roll change to the end of the target rolling chance. Especially from 8000 to 8350
Figure 4 shows an excerpt of the main points. 30 from the start of rolling
When about 000 pieces are rolled, η becomes stable and becomes around 80%, but when the number of rolled pieces exceeds 10000 pieces, η begins to decrease14
At the time of 000 copies, it will be about 40%. Furthermore, due to this decrease in η, internal flaws were found with a high probability on the internal surface of the rolled material after rolling from around 13,000 rolled sheets to the end of the main rolling chance.

[0016] Also, from the 8001st roll after the start of rolling, 81
The 50th 150 pieces were rolled with 13% Cr steel, but as the number of pieces rolled increased, η decreased rapidly, and 13% Cr steel was rolled.
When approximately 100 pieces of r-steel were rolled continuously, η was less than 50%, and internal defects were likely to occur. After that, when the material to be rolled was changed to general carbon steel, η started to increase and became 100 to 150.
After rolling, η returned to the level before rolling the 13% Cr steel.

FIG. 5 shows the influence of the number of rolling rolls from roll change to the end of the target rolling chance on the center line average roughness Ra of the roll surface in the circumferential direction. Especially from 8000 to 8
An excerpt of the 350th line is shown in Figure 6. The increasing/decreasing tendency of η shown in FIG. 3 matches well with the increasing/decreasing tendency of Ra shown in FIG. 5. However, the decreasing tendency of η influenced by the rolling steel type shown in FIG. 4 does not completely match the decreasing tendency of Ra shown in FIG. 6. Therefore, the increase or decrease in η cannot be explained only by the increase or decrease in Ra.

FIG. 7 shows the influence of the number of rolling rolls from the change of rolls until the end of the target rolling chance on the average pitch interval DHS of irregularities in the circumferential direction of the roll surface. Particularly, the 8000th to 8350th lines are excerpted and shown in FIG. The increasing/decreasing tendency of η shown in FIG. 3 does not completely match the decreasing/increasing tendency of DHS shown in FIG. 7 . However, the decreasing tendency of η affected by the type of rolled steel shown in Fig. 4 is different from the tendency of DH shown in Fig. 8.
This agrees well with the increase/decrease trend of S.

From these results, it was found that the increase/decrease in η can be explained by a combination of the increase/decrease in Ra and the decrease/increase in DHS. FIG. 9 shows the influence of the number of rolling rolls and the steel type of the rolled material on the roll surface roughness and the occurrence of internal flaws. From Fig. 9, in order to prevent inner surface flaws, Ra≧5μm, DHS≦850μm
m is a necessary condition.

Next, in order to determine the upper limit value of Ra and the lower limit value of DHS, various roughnesses were mechanically imparted to the inclined rolls and the rolls were actually rolled. Table 2 shows the surface roughness conditions and rolling results for the rolls.

[0021]

[Table 2] ──────────────────────────
────────── Surface roughness in the circumferential direction of the roll Internal flaws External flaws Due to slip Ra (μm) DHS (μm)
Unable to roll
11 32
〇 〇
〇 15 21
× ×
× 15
26 × 〇 〇 16
30 〇
〇 〇 2
2 33
〇 〇 〇
39 223
〇 〇
〇 40 383
〇 〇
〇 40 6
18 〇 〇
〇 46
388 〇
× 〇 49
392 〇
× 〇────────
──────────────────────────
───DHS is 3 to prevent inner surface defects of rolled material.
It was found that Ra is required to be 0 μm or more, and that Ra is required to be 40 μm or less in order to prevent external flaws.

[0022]

[Example] The roll surface management provisions according to the present invention are
It was applied to rolling billets of 0 mm or less. Table 3 shows the surface roughness Ra and DHS managed by the present invention in comparison with the conventional surface roughness. The results of an investigation into the effect of reducing rolling defects by implementing the method of the present invention in which the roll surface roughness is controlled in this manner are shown in FIGS. 10 to 12. FIG. 10 is a comparison diagram of the occurrence rate of internal defects, FIG. 11 is a comparison diagram of the occurrence rate of failure to roll due to slip, and FIG. 12 is a comparison diagram of the occurrence rate of external defects. By controlling the surface roughness during roll modification within the appropriate roughness range specified in the present invention, the occurrence of inner surface flaws immediately after roll change and the occurrence of inability to roll due to slip were almost eliminated. Also, when rolling high-alloy steel, we stop rolling every few dozen rolls and measure the roll surface roughness, and perform light maintenance to restore the roughness before the roll surface roughness deviates from the appropriate range. By operating with the roll surface roughness within the appropriate roughness range defined by the present invention, the incidence of internal defects is reduced to less than 1/4 of the conventional rate, as shown in Figure 10, and the incidence of unrolling due to slips is reduced. As shown in FIG. 11, it decreased to 1/10 or less. Furthermore, even after the number of rolled rolls exceeds 10,000, 500~
After every 1,000 rolls are rolled, the rolling is stopped and the roll surface roughness is measured, and the roll surface roughness is lightly maintained as described above, or the rolls are changed early to reduce the incidence of internal flaws and the possibility of rolling failure due to slipping. We were able to reduce the incidence to an extremely low level.

Furthermore, by carrying out the present invention, it was possible to extremely reduce the incidence of defects on the outer surface of the rolled material after rolling.

[0024]

[Table 3]

[0025]

[Effects of the Invention] According to the present invention, it has become possible to prevent deterioration of the surface properties of the inner and outer surfaces of a seamless steel pipe.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a Mannesmann drilling machine.

FIG. 2 is a diagram related to the definition of roughness used in the present invention.

FIG. 3 is a diagram showing the influence of the number of rolled steel and the type of rolled steel on drilling efficiency.

FIG. 4 is a diagram showing the influence of the number of rolled steel and the type of rolled steel on drilling efficiency.

FIG. 5 is a diagram showing the influence of the rolling number and rolling steel type on roll surface roughness Ra.

FIG. 6 is a diagram showing the influence of the rolling number and rolling steel type on roll surface roughness Ra.

FIG. 7 is a diagram showing the influence of the rolling number and rolling steel type on the peak interval of roll surface roughness.

FIG. 8 is a diagram showing the influence of the rolling number and rolling steel type on the peak interval of roll surface roughness.

FIG. 9 is a diagram related to limit determination of the roughness index of the present invention.

FIG. 10 is a comparison diagram of the incidence of internal defects showing the effects of implementing the present invention.

FIG. 11 is a comparison diagram of the occurrence rate of failure to roll due to slip, showing the effects of implementing the present invention.

FIG. 12 is a comparison diagram of the incidence of external defects showing the effect of implementing the present invention.

[Explanation of symbols]

10,10a Inclined roll 20 billet 30 Plug

Claims (1)

[Claims] Claim 1: The surface roughness in the circumferential direction of the inclined roll of the inclined punching machine is 5 μm or more and 40 μm in terms of center line average roughness Ra.
30 μm or more in DHS and average peak spacing of unevenness 8
A method for inclined rolling of seamless steel pipes, characterized in that the rolling is controlled within a range of 50 μm or less.