JP6015269B2 - Manufacturing method of high Cr seamless steel pipe - Google Patents

Description

  The present invention relates to a method for producing a high Cr seamless steel pipe, and more particularly to a method for producing a high Cr seamless steel pipe which is a seamless steel pipe containing 12 mass% or more of Cr.

  A seamless steel pipe is generally a billet having a round cross section, which is obtained by casting a bloom slab having a large cross section with a continuous caster, hot rolling with a lump mill, blooming mill, billeting mill, etc. Without or without round billets, or round billets are cast with a continuous casting machine, and these round billets are used as workpieces, and the workpieces are pierced and rolled, followed by this It is manufactured by subjecting it to stretching rolling and constant diameter rolling.

As a general rolling equipment line for seamless steel pipes in a pipe factory, a conventional example shown in FIG.
As shown in FIG. 2, the conventional rolling equipment row includes a first heating furnace such as a rotary furnace 1 that performs the first heating for heating the round billet 10 to a high temperature (about 1100 to 1300 ° C.), and then the heating. The rear round billet 10 is drilled with a drilling bar to form a tubular body 11, and then the perforated piercer 2 and then the perforated tubular body 11 are subjected to a one-stage operation under the restraint of the inner surface of the pipe by a mandrel bar. A mandrel mill 3 composed of a group of rolling mills for drawing and rolling, then a reheating furnace 4 for reheating (about 900 to 1100 ° C.) the tube 11 after the drawing and rolling, and then the tube 11 after the reheating. And a reducer mill 5 composed of a group of rolling mills for constant diameter rolling.

The tubular body 11 after the constant diameter rolling is cut into a predetermined length as necessary, and then conveyed to the cooling bed 6 and cooled.
Regarding the quality improvement of the seamless steel pipe, Patent Document 1 discloses that the material temperature (processing temperature) when the inner surface of the hollow shell (corresponding to the tubular body 11) is stretched and rolled while being constrained with a plug is not uniform in the longitudinal direction. Therefore, in order to suppress an increase in the longitudinal quality variation of the product, a workpiece whose raw form is a round billet is heated, then pierced and rolled to form a hollow shell, and then the hollow shell In the method for producing a seamless steel pipe, the inner surface of the workpiece is stretch-rolled while being constrained with a plug, then reheated, then subjected to constant diameter rolling, and then cooled to become a seamless steel pipe. Heat (by induction heating) so that the front end in the longitudinal direction of the workpiece immediately before the stretch rolling (longer rolling → plug mill rolling → reeler rolling) is 30 to 400 ° C. higher than the rear end. Stated That.

JP 2011-098354 A

  However, in the above-described prior art, when a round billet of high Cr steel (Cr: steel containing 12% by mass or more) is used as a starting material, the heating temperature in the rotary furnace heating process is too high (over 1250 ° C.). Then, δ ferrite appears, and material cracks, lashes and fogging occur in the piercer drilling process. Therefore, if the heating temperature is lowered (1250 ° C. or lower) in order to prevent the formation of δ ferrite, the rolling temperature in the mandrel mill rolling process is too low, and a roll and a pipe guide tool (guide, shoe, etc.) There are many seizure potatoes.

  That is, in the prior art, when the work material (round billet before drilling and tube after drilling) is high Cr steel, material cracks, scabs and burrs are generated in the piercer drilling process and mandrel mill There was a problem that it was difficult to prevent both the occurrence of seizure in the rolling process.

The inventors have intensively studied to solve the above problems, and as a result, an induction heating device for induction heating the entire length of the tube passing through the entry side is installed on the entry side of the mandrel mill, The present invention has been made by obtaining the knowledge that the above-mentioned problems can be solved by operating under specific conditions.
That is, the present invention is as follows.
(1) A first heating furnace such as a rotary furnace that performs first heating for heating a round billet, a piercer that drills the round billet after heating to form a tubular body, and then a tubular body that is drilled. It consists of a mandrel mill consisting of a group of rolling mills for drawing and rolling, then a reheating furnace for reheating the tube after the drawing and rolling, and then a group of rolling mills for constant diameter rolling of the tube after the reheating. A rolling mill line for seamless steel pipes, further comprising an induction heating device installed on the inlet side of the mandrel mill for induction heating of the tube passing through the inlet side over the entire length. A method for producing a high Cr seamless steel pipe, which is a seamless steel pipe containing 12% by mass or more of Cr,
Wherein the whole round billet heated to a range of 1,100-12 4 0 ° C. by the first heating, then after said tube by puncturing the round billet, 30 the temperature of the pipe body by the induction heating device to 180 ° C. is raised, high Cr seamless steel pipe production method, which comprises initiating the elongation rolling the tube body as above 1030 ° C. over the entire length.

  According to the present invention, even if the workpiece (round billet before drilling and tube after drilling) is high Cr steel, material cracks and scabs and burrs are generated in the piercer drilling process and mandrels Both seizure generation in the mill rolling process can be easily prevented.

It is the schematic which shows the rolling equipment row | line | column used for the example of this invention. It is the schematic which shows the rolling equipment row | line | column of a prior art example.

FIG. 1 is a schematic view showing a rolling equipment line used in the example of the present invention. In FIG. 1, 8 is an induction heating apparatus, and the same code | symbol is attached | subjected to the same or equivalent member as the prior art example of FIG. 2, and description is abbreviate | omitted.
The induction heating device 8 in the example of the present invention is a tunnel type, and is installed on the entry side of the mandrel mill 3 and induction-heats the tubular body 11 passing through the entry side over the entire length. By this induction heating, the temperature of the tube body on the inlet side of the mandrel mill can be made higher than before. Therefore, with respect to the material to be rolled of high Cr steel, in the mandrel mill 3, the scale amount of the tube surface can be increased by increasing the tube temperature on the entry side, and the rolling load can be reduced. It is possible to prevent seizure due to metal touch between a tube and a tool such as a roll or guide peculiar to high Cr steel, thereby reducing the occurrence of product surface flaws.

In addition, since the tube temperature can be increased on the mandrel mill entry side as described above by installing the induction heating device 8, the heating temperature in the rotary furnace heating process is set to 12 40 for the material to be rolled of high Cr steel. By lowering the temperature to below ℃, the formation of δ-ferrite can be suppressed, thereby reducing the occurrence of material cracking, shave and fogging in the piercer drilling process.
Accordingly, it is possible to easily prevent both material cracks, swells and fogging in the piercer drilling process and seizure in the mandrel mill rolling process.

According to the inventors research, the heating temperature of the high Cr steel round billet by rotating furnace 1 is required the temperature range of from 1,100 to 12 4 0 ° C. for δ ferrite suppression, when heated in a temperature range, Conventionally, the tube temperature on the inlet side of the mandrel mill 3 is often 30 ° C. or more lower than the lower limit of the temperature range in which seizure does not occur (denoted as Tc, Tc≈1030 ° C.). Therefore, in order to compensate for such a temperature drop, the induction heating device 8 needs to have an induction heating capability in which the temperature rise amount (denoted as ΔT) of the tube body 11 by the induction heating becomes 30 ° C. or more. It is. However, ΔT related to the induction heating capacity is more preferably 30 ° C. or more and 180 ° C. or less because the effect of preventing seizure is saturated even if this is over 180 ° C., and the equipment cost and power cost only increase. .

Using the rolling equipment row of FIG. 1, work material = Cr: steel containing 12.0% by mass, rotary furnace heating temperature = 1240 ° C., tube temperature increase ΔT = 30 ° C. by induction heating device, start of stretching rolling 240 seamless steel pipes were manufactured at a temperature = 1030 ° C. and a reheating furnace temperature = 1000 ° C. to obtain Case A (Example of the present invention).
In addition, using the rolling equipment row of FIG. 2, 200 pieces of seamless steel pipes were manufactured with the work material = same as above, rotary furnace heating temperature = same as above, stretch rolling start temperature = 1000 ° C., reheating furnace temperature = same as above, B (comparative example).

  In case A and case B, the rate of occurrence of material cracks, scabs and fogging and the number of seizures were compared. However, the rate of occurrence of seizure was 2.2, which is a relative value with respect to case B as 100, which was much lower than that of case B.

1 Rotary furnace (first heating furnace)
2 Piercer (Bar perforated type)
3 Mandrel mill 4 Reheating furnace 5 Reducer mill 8 Induction heating device 10 Round billet (work material before drilling)
11 Tube (work material after drilling)

Claims (1)

Stretch rolling the first heating furnace such as a rotary furnace that performs the first heating for heating the round billet, the piercer that drills the round billet after the heating to form a tubular body, and then the tubular body that is drilled. A mandrel mill comprising a group of rolling mills, a reheating furnace for reheating the tube after the drawing and rolling, and a reducer mill comprising a group of rolling mills for constant-diameter rolling of the tube after the reheating. And using a rolling equipment line for seamless steel pipes, in which an induction heating device is installed on the inlet side of the mandrel mill for induction heating over the entire length of the tube passing through the inlet side. A high Cr seamless steel pipe that is a seamless steel pipe containing 12% by mass or more,
Wherein the whole round billet heated to a range of 1,100-12 4 0 ° C. by the first heating, then after said tube by puncturing the round billet, 30 the temperature of the pipe body by the induction heating device to 180 ° C. is raised, high Cr seamless steel pipe production method, which comprises initiating the elongation rolling the tube body as above 1030 ° C. over the entire length.

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