JP2013099781A - METHOD FOR PRODUCING HIGH-Cr SEAMLESS STEEL TUBE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a high-Cr seamless steel tube, capable of preventing both of occurrence of material crack, scabs or rash flaw in a piercer boring process and occurrence of burn-in in a plug mill rolling process in a conventional technique when a workpiece is a high-Cr steel.SOLUTION: An induction heating device 8 is installed at the inlet side of a plug mill 3B to induction-heat a tube body 11 passing through the inlet side over the whole length. A first heating step is performed within the temperature range of 1,100 to 1,250°C and after stretch-rolling of a first step following the boring, the temperature of the tube body 11 is elevated by 30-180°C by the induction heating device 8 to start the stretch-rolling of a second step.

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 later round billet 10 is drilled with a drilling plug to form a tube body 11, and a plug-piercing type piercer 2A is formed. Then, the tubular body 11 formed by the drilling is stretched and rolled in three stages under the restraint of the tube inner surface by the plug. As the means for sequentially applying, the first stage elongator 3A, the second stage plug mill 3B, the third stage reeler 3C, and then the tube 11 after the third stage drawing and rolling are reheated ( A reheating furnace 4 that is approximately 900 to 1100 ° C., and then a sizer 5A that includes a group of rolling mills that perform constant diameter rolling of the tube 11 after the reheating.

The tube 11 after the constant-diameter rolling is cut to a predetermined length as necessary, and then is transferred to a cooling bed (not shown) 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 less) so as not to generate δ ferrite, the rolling temperature in the plug mill rolling process is excessively lowered, and the rolls and tube guide tools (guides, shoes, etc.) Many seizure glazes occur.

  That is, in the prior art, when the work material (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 plug mill rolling. There was a problem that it was difficult to prevent both occurrence of seizure in the process.

The inventors have intensively studied to solve the above-mentioned problems, and as a result, an induction heating device is installed on the inlet side of the plug mill to inductively heat the tube passing through the inlet side over the entire length. The present invention has been achieved by obtaining the knowledge that the above-mentioned problems can be solved by operating under the above 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. As means for sequentially performing all three stages of drawing and rolling, the first stage elongator, the second stage plug mill, the third stage reeler, and then the pipe after the third stage drawing and rolling are re-used. A reheating furnace for heating, and then a sizer comprising a group of rolling mills for rolling the reheated tube body at a constant diameter, and a tube body passing through the inlet side on the inlet side of the plug mill. This is a method for producing a high Cr seamless steel pipe, which is a seamless steel pipe containing 12 mass% or more of Cr, using a rolling equipment line for a seamless steel pipe provided with an induction heating device for induction heating over the entire length. And
The temperature of the first heating is set to a range of 1100 to 1250 ° C., and after the first stage of drawing and rolling following the piercing, the temperature of the tubular body is increased by 30 to 180 ° C. with the induction heating device, and 1030 A method for producing a high Cr seamless steel pipe, characterized in that the second stage of drawing and rolling is started at a tube temperature of at least ° C.

  According to the present invention, even when the work material (round billet before drilling and tube after drilling) is high Cr steel, material cracks, scabs, and fogging occur in the piercer drilling process, and the plug mill. It becomes possible to easily prevent both seizures in the rolling process.

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 present invention example. 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 plug mill 3B and induction-heats the tubular body 11 passing through the entry side over the entire length. By this induction heating, the tube temperature on the plug mill entry side can be made higher than before. Therefore, with respect to the material to be rolled of high Cr steel, in the plug mill 3B, the scale amount on 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 Cr steel, thereby reducing the occurrence of product surface flaws.

In addition, since the tube temperature can be increased on the plug 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 1250 ° C. or less for the high Cr steel material to be rolled. By lowering it, it is possible to suppress the formation of δ ferrite, thereby reducing the occurrence of material cracks, shave and fogging in the piercer drilling process.
Therefore, it is possible to easily prevent both material cracks, swells and fogging in the piercer drilling process and seizure in the plug mill rolling process.

  According to the inventors' investigation, the heating temperature of the high Cr steel round billet by the rotary furnace 1 needs a temperature range of 1100 to 1250 ° C. in order to suppress the formation of δ ferrite. The tube temperature on the plug mill 3B entry side is often lower by 30 ° C. or more 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 in FIG. 1, work material = Cr: steel containing 12.0% by mass, rotary furnace heating temperature = 1180 ° C., tube temperature increase ΔT = 100 ° C. by induction heating device, second stage The drawing and rolling start temperature was 1030 ° C., the reheating furnace temperature was 1000 ° C., 160 seamless steel pipes were produced, and Case A (invention example) was obtained.
In addition, using the rolling equipment row in FIG. 2, work piece = same as above, rotary furnace heating temperature = same as above, second stage drawing and rolling start temperature = 1000 ° C., reheating furnace temperature = same as above, 210 seamless steel pipes This was manufactured as Case 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 1.8, which is a relative value with the case B as 100, which is much lower than the case B.

1 Rotary furnace (first heating furnace)
2A Piercer (plug perforated type)
3A Elongator 3B Plug mill 3C Reeler 4 Reheating furnace 5A Sizer 8 Induction heating device 10 Round billet (work material before drilling)
11 Tube (work material after drilling)

Claims (1)

A first heating furnace such as a rotary furnace that performs the first heating for heating the round billet, then a piercer that drills the round billet after heating into a tubular body, and then the perforated tubular body in all three stages. As the means for sequentially performing the drawing and rolling, the first stage elongator, the second stage plug mill, the third stage reeler, and the second stage after the third stage drawing and rolling are reheated. A heating furnace and a sizer comprising a group of rolling mills for rolling the reheated pipe body at a constant diameter, and further, the pipe body passing through the inlet side is provided over the entire length on the inlet side of the plug mill. A method of manufacturing a high Cr seamless steel pipe, which is a seamless steel pipe containing 12 mass% or more of Cr using a rolling equipment row for a seamless steel pipe provided with an induction heating device for induction heating,
The temperature of the first heating is set to a range of 1100 to 1250 ° C., and after the first stage of drawing and rolling following the piercing, the temperature of the tubular body is increased by 30 to 180 ° C. with the induction heating device, and 1030 A method for producing a high Cr seamless steel pipe, characterized in that the second stage of drawing and rolling is started at a tube temperature of at least ° C.

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