JPH04138808A - Manufacture of seamless steel tube - Google Patents

Abstract

PURPOSE:To prevent the generation of the surface flaw of tube due to grain boundary oxidation when heating a billet by preheating the billet on the preceding stage of heating the billet and making the billet into a tube and applying antioxidants on the whole of the surface of a preheated billet. CONSTITUTION:The billet which consists of an austenitic stainless steel is cut and transported with a crane to store temporarily. Further, after it is rolled on a skid which is transported with the crane and transported with a conveyer to charge into a heating furnace, it is preheated in a preheating furnace or the like which is on-line installed. Then, the preheated billet 1 is applied with antioxidants on the whole of its surface with an automatic spraying device 12 which is provided on a billet transporting truck 11. That is, the billet 1, in a preheated state, is transported just under a manipulator 14 to charge into the heating furnace, while it is revolved on the turning rollers 13 of the billet transporting truck 11 and automatically sprayed with antioxidants with the automatic spraying device 12.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing seamless steel pipes made of austenitic stainless steel.

[Prior Art] When manufacturing seamless austenitic stainless steel pipes, a billet made of austenitic stainless steel is heated to about 1210°C in a rotary heating furnace, and the Mannesmann mandrel mill method or the Mannesmann plug mill method is used. It is pierced and rolled.

Here, in austenitic stainless steel, grain boundary oxidation tends to occur during billet heating, and linear scratches due to this grain boundary oxidation occur on the surface of the product tube. To prevent this defect, it is necessary to heat the billet at a low temperature and for a short time.
There is a limit to short-term heating, so an antioxidant is applied to the billet surface before heating. FIG. 7 is a schematic diagram showing a conventional seamless steel pipe manufacturing line.

[Problems to be Solved by the Invention] However, the antioxidants according to the prior art are applied off-line using a spatula or spray gun, which takes a long time to dry and has low productivity. It may peel off due to friction or impact during transportation by a crane.

An object of the present invention is to prevent the occurrence of defects on the pipe surface due to grain boundary oxidation during billet heating, without reducing productivity, during the manufacture of seamless steel pipes made of austenitic stainless steel.

[Means for Solving the Problems] The present invention as set forth in claim 1 provides a seamless steel pipe manufacturing method in which an austenitic stainless steel billet is pierced and rolled using a Mannesmann mill method. In this step, the billet is preheated, and a fermentation inhibitor is applied to the entire surface of the preheated billet.

According to a second aspect of the present invention, the antioxidant is applied by an automatic spraying device provided on a billet transport vehicle.

[Function] According to the present invention as set forth in claim 1, there are the following effects (1) to (4).

■Since the antioxidant is applied to the preheated billet surface, the antioxidant can dry instantly and adhere firmly.

(2) Since the antioxidant can be dried instantly in (2) above, there is no reduction in productivity.

■Since the antioxidant is firmly attached in the above ■, it is possible to prevent the antioxidant from peeling off during the process until the end of heating. During manufacturing, it is possible to prevent the occurrence of tube surface flaws due to grain boundary oxidation during billet heating without reducing productivity.

According to the present invention as set forth in claim 2, there is the following effect (2).

■The antioxidant is automatically applied to a uniform film thickness using an automatic spray device during the billet transportation process, which improves productivity and prevents the antioxidant from peeling off during the process until the end of heating. This can be prevented more reliably.

[Example] Figure 1 is a schematic diagram showing a production line for seamless steel pipes employing the present invention, Figure 2 is a schematic diagram showing an automatic spray device on a billet transfer cart, and Figure 3 is a diagram showing a line before applying an antioxidant. Figure 4 is a micrograph showing the metal structure on the surface of the product tube when no antioxidant is used. Figure 5 is the metal structure of the cross section of the product tube in Figure 4. Figure 6 is a *m mirror photograph showing the metal structure of the cross section of the product pipe when an antioxidant is used.
FIG. 7 is a schematic diagram showing a conventional seamless steel pipe production line.

As shown in Figure 1, a billet made of austenitic stainless steel is cut and transported by crane for temporary storage, then transported by crane to be loaded into a heating furnace, rolled on a skid, and transported by a conveyor. After that, it is preheated to 180 to 240°C in an online preheating furnace or the like.

Then, the preheated billet 1 is as shown in FIG.
Automatic spray device 12 installed on billet transfer trolley 11
As a result, the entire surface is coated with an antioxidant.

That is, the billet 1 is rotated on the turning roller 13 of the billet transfer cart 11 in a preheated state, and transferred directly below the manipulator 14 for charging into the heating furnace while being automatically sprayed with antioxidant by the automatic spray device 12. Ru. Therefore, when the manipulator 14 performs the charging operation, the antioxidant has already been completely dried.

According to the above embodiment, the following effects (1) to (4) are achieved.

■Since the antioxidant is applied to the preheated billet surface, the antioxidant can dry instantly and adhere firmly.

(2) Since the antioxidant can be dried instantly in (2) above, there is no reduction in productivity.

(2) Since the antioxidant can be firmly attached in step (2) above, it is possible to prevent the antioxidant from peeling off during the subsequent process until the end of heating.

■Since the antioxidant is automatically applied to a uniform film thickness by the automatic spray device 12 during the billet transportation process, productivity can be improved, and the antioxidant can be peeled off during the process until the end of heating. can be more reliably prevented.

■With the above ■~■, when manufacturing seamless steel pipes made of austenitic stainless steel, it is possible to prevent the occurrence of tube surface defects due to grain boundary oxidation during billet heating without reducing productivity. .

In addition, it is possible to reduce the maintenance rate of product pipes and improve the inspection yield of product pipes.

In addition, Fig. 3 is a microscopic photograph showing the metal structure of the billet surface before applying the antioxidant, Fig. 4 is a microscopic photo showing the metal structure of the product tube surface when no antioxidant is used, and Fig. 5 is a micrograph showing the metallographic structure of the cross-section of the product tube shown in FIG. 4, and FIG. 6 is a photomicrograph showing the metallographic structure of the cross-section of the product tube when an antioxidant is used. Defects due to grain boundary oxidation can be seen in Figures 4 and 5 where no antioxidant is used, while in Figure 6 where an antioxidant is used, it can be seen that defects due to grain boundary oxidation can be significantly reduced. .

[Effects of the Invention] As described above, according to the present invention, when manufacturing seamless steel pipes made of austenitic stainless steel, it is possible to eliminate pipe surface flaws caused by grain boundary oxidation during billet heating without reducing productivity. Occurrence can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing a seamless steel pipe manufacturing line employing the present invention, Fig. 2 is a schematic diagram showing an automatic spray device on a billet transfer trolley, and Fig. 3 is a schematic diagram showing the billet surface before applying antioxidant. A microscopic photograph showing the metallographic structure, Figure 4 is a microscopic photograph showing the metallographic structure on the surface of the product tube when no antioxidant is used, and Figure 5 is a microscopic photograph showing the metallographic structure of the cross section of the product tube in Figure 4. , Figure 6 is a micrograph showing the metal structure of a cross section of a product pipe when an antioxidant is used.
FIG. 7 is a schematic diagram showing a conventional seamless steel pipe production line. 1... Billet, 11... Billet transfer trolley, 2... Automatic spray device.

Claims (2)

[Claims] (1) In a method for manufacturing a seamless steel pipe in which an austenitic stainless steel billet is perforated and rolled using a Mannesmann mill method, the billet is preheated before heating and pipe forming, and the surface of the preheated billet is A method for manufacturing a seamless steel pipe, characterized by applying an antioxidant to the entire surface of the pipe. (2) The method for manufacturing a seamless steel pipe according to claim 1, wherein the antioxidant is applied by an automatic spray device installed on a billet transfer truck.