JPH0516925B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for hot rolling seamless steel pipes, and in particular, when manufacturing seamless steel pipes by the Mannesmann mandrel mill system and the Mannesmann plug mill system, the present invention relates to a method for hot rolling seamless steel pipes, and in particular, when manufacturing seamless steel pipes using the Mannesmann mandrel mill system and the Mannesmann plug mill system, the invention relates to a method for hot rolling seamless steel pipes. Effectively prevents flaws on the outer surface of the pipe material and shortened roll life, which are feared to occur due to seizure and surface roughness between rolling rolls and/or various rolling rolls such as barrel rolls and slotted rolls. The aim is to advantageously improve the productivity and quality of seamless steel pipes. (Prior Art) There are two typical methods for producing seamless steel pipes: the Mannesmann mandrel mill method and the Mannesmann plug mill method, the steps of which are shown in FIGS. 1a and 1b, respectively. These manufacturing methods are
They are used depending on the outer diameter of the product, and the mandrel mill method is generally used for diameters of 7" or less, while the plug mill method is used for diameters of 7" or more. To explain these manufacturing processes in detail below, in both manufacturing methods, after the round bit material 1 is heated to a predetermined temperature in the rotary heating furnace 2, as the first pass of making holes, a hollow shell is formed by a piercer mill 3. I got 4. Thereafter, in the mandrel mill method, a mandrel bar 5 is inserted into the hollow tube 4, and a mandrel mill 6 serving as an elongation rolling mill applies elongation rolling. After being stretched and rolled by this mandrel mill 6 to a length of 2 to 4 times, it is reduced and rolled by a stretch reducer 9 serving as a finishing mill to form a finished tube 10. On the other hand, in the plug mill method, the hollow tube 4 that has been pierced and rolled by the piercer mill 3 is further elongated by an elongator mill 11 of the same type as the piercer mill 3 to reduce the wall thickness and extend the length. Next, it is drawn with a plug mill 12 to reduce its thickness, and then the inner and outer surfaces are smoothed with a reeler 13 of a polishing machine to obtain a raw tube for a sizer mill. After being reheated in a walking beam heating furnace, it is finally passed through a sizer 14. The finished tube 15 is precisely finished to a predetermined outer diameter. (Problems to be Solved by the Invention) However, in the above-described rolling process, there are three problems that can be broadly classified as follows. That is, the first problem is scratch marks (hereinafter referred to as scratch marks) that occur on the outer surface of the pipe material during rolling with a piercer and an elongator mill as shown in FIG. Here, the manner of rolling by the piercer and elongator mill will be explained based on FIG. 2. Now, in inclined rolling, the rolled material 1 is pierced and rolled by a pair of obliquely opposing barrel-shaped rolling rolls 3A, 3B and a plug 3C, but the outer diameter of the rolled material 1 is expanded by the pierced thinning rolling. is regulated by a pair of plate-shaped guide shoes 3D. During such rolling, since the rolled material 1 and the guide shoe 3D are rolled in a state of sliding friction over the entire surface, shoe marks are likely to occur on the outer surface of the rolled material 1. Therefore, this type of rolling not only causes deterioration of the quality of the pipe materials, but also increases the downtime of the rolling mill required for maintenance and replacement of the shaft, leading to a decrease in productivity, which is a serious problem for actual operations. cause inconvenience. As a solution to such problems, Japanese Patent Application Laid-Open No. 1986-
Publication No. 253105 proposes improving the material of the guide shoe, but this has not yet achieved sufficient results. In addition, JP-A-60-56406 proposes a method of piercing and rolling while applying a lubricant containing fine graphite particles and fine solid asphalt particles dispersed between the guide shaft and the rolled material. However, this method has serious disadvantages in that the lubricant is transferred to the main roll, which significantly reduces the forward speed of the rolled material, resulting in increased slip and reduced perforation efficiency, and cannot be put to practical use. The second problem is seizure flaws (hereinafter referred to as edge flaws) on the outer surface of the rolled material in mandrel mills, stretch reducer mills, sizer mills, etc., as shown in Figure 3 a, b, c, d, and e, respectively. It is. The rolling mode in each mill will be explained below. The mandrel mill (Fig. 3a, b) is a roll stand that incorporates a pair of hole-shaped rolls 6A and 6B.
Arrange 7 to 9 units in a row, changing the arrangement by 90 degrees,
With the mandrel bar 5 inserted into the raw pipe 4A, the raw pipe 4A is passed through the above-mentioned continuous roll stands to continuously reduce the thickness and stretch the raw pipe 4A to obtain the outlet pipe 4B. be. In addition, the stretch reducer mill (Fig. 3 c, d) uses a large number of rows of roll stands with oval holes to reduce and roll the hollow blank tube 4B to a predetermined outer diameter, without inserting a mandrel bar. The finished tube 10 is formed into a thick wall. Here, each roll hole shape 9 in the continuous roll stand row of the stretch reducer 9 is
The diameters of A, 9B, and 9C are set so that the later the stage, the smaller the diameter, and the roll hole shape of the final roll stand is dimensioned to correspond to the outer diameter of the predetermined finished tube.
This allows the outer surface of the finished tube 10 to be finished molded. In addition, sizer mill (Fig. 3 e)
In this method, a plurality of roll stands, each consisting of a pair of grooved rolls 14A and 14B, are arranged 5 to 8 in succession, with the arrangement changed by 90 degrees from each other, and reduction rolling is performed without inserting a mandrel bar into the raw pipe. , and is formed into a finished tube 15 having a predetermined outer diameter. By the way, when rolling these seamless steel pipes, the circumferential speed of the rolls is significantly different between the bottom of the central groove of each groove roll and the shallow part of the groove on both sides of the groove, that is, near the flange. Due to the relative speed difference between the parts (especially near the flange part),
Seizure occurs between the tubing and the slotted roll, which leaves flaws on the external surface of the final product. Therefore, such rolling requires subsequent care, which causes serious inconveniences such as increased manufacturing costs. In order to solve such problems, for example, in Japanese Patent Application Laid-Open No. 119409/1983, the raw pipe is continuously stretched and rolled using a set of three rolls in a mandrel mill, thereby reducing the difference in the circumferential speed of the rolls in the hole-shaped portion. A method has been proposed in which the number of seizure defects is reduced by making the roll smaller than the conventional case of two rolls, but this method has the drawback of requiring a huge investment in equipment. Furthermore, in stretch reducers and sizers, lubricants such as mineral oil containing natural oils and fats and other additives have been used in the vicinity of the flange portions of slotted rolls. However, such lubricants tend to solidify at room temperature, making maintenance of the lubrication system troublesome and having poor wastewater treatment properties, as well as problems in terms of workability and environmental hygiene, such as smoke generation. The third problem is seizure of the surface of the rolls used in each mill. Such seizure of the roll skin is particularly likely when there is little scale on the surface of the rolled material or when rolling high-alloy steels with high hot deformation resistance, such as 13% Cr steel, 22% Cr steel, and austenitic stainless steel. Significantly. If this seizure is severe, the following problems will occur in each mill. In piercer rolling, seizure is significant from the entrance side of the barrel roll to the wall thickness determination area, which slows down the forward speed of the tube and causes slippage, resulting in a significant drop in piercing efficiency. When the drilling efficiency decreases in this way, various negative effects such as an increase in the Mannesmann effect, an increase in processing heat, and damage to the plug occur, resulting in frequent occurrence of internal defects and a significant decrease in yield. . In order to solve this problem, conventionally, before rolling high alloy steel, 1000 to 3000 ordinary steels with significant scale formation were punch-rolled, and after the seizing was improved, high alloy steel was rolled. Ta. However, this method has the disadvantage that the rolling chances are limited and high efficiency piercing rolling of high alloy steel cannot be performed. In addition, in mandrel mills, stretch reducer mills, and sizer mills, the rough surface of the rolls causes indentation scratches on the outer surface of the pipe, which significantly impairs the quality of the pipe. Furthermore, wear increased, resulting in an increase in roll change time and a deterioration in roll consumption. In order to solve these drawbacks, various roll materials and cooling methods have been investigated, but so far no sufficient effect has been obtained. (Means for Solving the Problems) Therefore, the inventors proposed that when manufacturing a seamless steel pipe using a multi-stage rolling mill having an inclined rolling mill and a slotted roll, a guide shaft and/or a barrel shape that comes into contact with the rolled material. In addition to preventing seizure between rolls and grooved rolls, it also suppresses slip between them as much as possible.For example, when there is little scale on the surface of the rolled material or for high-alloy steel with high hot deformation resistance. We have begun to develop an anti-seize agent that can effectively prevent roll seizure without causing guide dust marks on the outer surface of rolls. Based on the recognition of the above-mentioned problems, the inventors searched for anti-seize agents other than mineral oil-based, oil-based, synthetic oil-based, and mixed oil-based ones in order to reliably prevent not only the occurrence of slip but also seizure. did. As a result, it was found that a water-soluble borate compound containing no film forming agent causes no slippage, reliably suppresses seizure, and exhibits excellent performance in reducing roll surface roughness. That is, the present invention provides a method for manufacturing a seamless steel pipe using a multi-stage rolling mill having an inclined rolling mill and/or slotted rolls, in which the guide shoe surface and/or rolling roll surface that comes into contact with the material to be rolled during perforation and elongation rolling is provided. , a water-soluble borate compound: 0.5 to 30 wt% (hereinafter simply indicated as %), and the remainder consists of water. This is an inter-rolling method. The experimental results that led to this invention will be explained below. Table 2 shows the results of investigating the seizure status, the snow marks on the outer surface of the raw tube, and the drilling efficiency when drilling was performed under the following conditions using anti-seize agents having various compositions shown in Table 1. Drilling conditions Drilling machine type: Model piercer with fixed guide shaft Material of rolled material: 22% Cr steel Dimensions of rolled material: 58φ x 250l (mm) Rolling temperature: 1250℃ Hollow size after rolling: 62φ x 4.0 t (mm) How to supply anti-seize agent: Spray at 0.7/min above and below the entry side

【table】

[Table] As is clear from Table 2, significant seizure occurs with water cooling alone without an anti-seize agent, and the outer surface of the tube
A shoe mark flaw of approximately 0.7 mm occurred. On the other hand, when an anti-seize agent was used, the occurrence of seizures and burn marks was significantly improved. Among them, A using a water-soluble borate compound was the best, and was able to reliably prevent seizure and completely eliminate the occurrence of burn marks. Incidentally, no matter which anti-seize agent is used, the drilling efficiency is at the same level as in the case of water cooling without an anti-seize agent, so there is no problem. The reason why water-soluble borate compounds are superior to anti-seize agents with other compositions is that they
Because it becomes amorphous and glass-like under high surface pressure,
This is thought to be the reason why metal contact between the rolled material and the guide shoe is prevented, and seizure is completely eliminated. Next, using the anti-seizing agent consisting of a borate compound with symbol A, which was the most favorable in the above experiment, the influence of its concentration was investigated. The results are shown in Table 3. The concentrations are 0.2, 0.5, 1, 4, 7, 10,
Nine levels of 20, 30 and 35% were tested. The drilling conditions were the same as in the experiment described above.

【table】

[Table] As is clear from the table, the content of borate compounds must be at least
Although 0.5% is necessary, if it exceeds 30%, the stability of the liquid deteriorates, so it is necessary to set it to 0.5 to 30%. Suitable water-soluble borate compounds used in this invention include alkali salts of boric acid (sodium borate, potassium borate), ammonium borate salts,
Examples include boric acid alkanolamine salts, salts of boric acid and water-soluble amines, such as tetraethylenepentamine, cyclohexylamine, diethylenetriamine, alkylamine, and the like. The anti-seize agent of the present invention is an aqueous treatment liquid containing the borate compound as described above, and a small amount (0.1 to 1 %), and similar effects can be expected even when such a spreading agent is added. As described above, when rolling was carried out while supplying an anti-seize agent consisting of an aqueous treatment solution of a water-soluble borate compound to the guide shoe, no seizure occurred even in rolled materials that conventionally could not avoid seizure occurrence. Moreover, the coefficient of friction at this time was as high as about 0.2 to 0.3, and good rolling was possible without deterioration of biting properties or occurrence of slips. The anti-seizure effect in the case of fixed-shape piercing rolling has been described above, but it has been confirmed that the same effect can be obtained in inclined rolling having a rotary disc rolling stock or multi-stage rolling having slotted rolls. Further, the anti-seize agent of the present invention can also be used as an anti-seize agent in hot plastic processing other than the manufacture of seamless steel pipes, such as forging, plate rolling, bar steel, extrusion, etc. As an anti-seize agent using a boron compound, Japanese Patent Publication No. 57-57118 discloses a lubricant made of an organic boron compound. It could not be used for hot rolling seamless steel pipes. (i) Since an organic solvent is used as the solvent, 800
Easily flammable at high temperatures of ~1250℃. (ii) Since a large amount of cooling water is applied, hydrolysis easily occurs and the lubricant does not form as a film on the surface of the rolled material. On the other hand, the anti-seize agent according to the present invention is a liquid dissolved in water, so it not only has excellent liquid stability, but also has no flash point, so there are no storage regulations under the Fire Service Act. In addition, the lubrication system is simple and convenient, and maintenance-free and stable continuous supply is possible at all times. (Example) Examples of the present invention will be described below. The composition of the anti-seize agent used here is as follows. Water-soluble borate compound: 15% Water: 85.0% Example 1 The outer diameter was 110 mm and the length was
1036 pieces of 3000mm 22% Cr steel with an outer diameter of 115mm and wall thickness
During rolling into a 12.5 mm hollow tube, the above-mentioned anti-seizure agent was continuously supplied at a rate of 1/min between the upper and lower guide shafts and the rolled material from the direction of material rotation. Note that the cooling water for the main roll was reduced to about 1/3 of the normal amount. As a result, while conventional roll cooling water alone resulted in about 10% of scum marks and required cleaning of the outer surface, the method of this invention was able to reduce the incidence of scum marks to 0.05%. The number of holes that can be drilled per set of guides is approximately 20.
The number of books increased from 250 books to 250 books. Example 2 A piercer mill, which is the first pass of the Mannesmann mandrel mill method, was used to produce an outer diameter of 110 mm and a length of
300 pieces of 3000mm 13% Cr steel with outer diameter 115mm and wall thickness 14.45
When rolling into a hollow blank tube of mm, the anti-seize agent according to the present invention is applied to the contact area between the main roll and the rolled material after draining the roll cooling water from the rotational direction of the main roll.
It was continuously supplied at a rate of 1.0/min. As a result, even when 300 pieces were continuously punched and rolled, no seizure products were observed, and there was no decrease in perforation efficiency.
The incidence of internal defects has also been drastically reduced from 12% to 0.5%. In addition, abnormal wear of the rolls has decreased, and as a result, the incidence of external defects has drastically decreased from 0.01% to 0.002%.
Furthermore, the life of the rolls was improved by 30%, and roll consumption and changeover time were significantly shortened. In addition, with conventional roll cooling water alone without anti-seizure agent, the perforation efficiency is 60% after rolling about 150 rolls.
As it significantly decreased from 13% Cr to 45%,
After stopping the rolling of steel, rolling of 13% Cr steel could only be resumed after about 1,000 rolls of ordinary steel had been rolled. Example 3 For the four stands of a mandrel mill that thins and draws the hollow tube after piercer rolling, which is the second pass of the Mannesmann mandrel mill method, roll cooling was applied from the rolling direction to the area where the rolls and the material to be rolled came into contact. After draining the water, apply the anti-seize agent according to this invention.
It was continuously supplied at a rate of 1.5/min. In this way, ordinary steel: 29,000 pieces, high alloy steel (13Cr,
22Cr, SUS304): As a result of rolling 1500 pieces,
With conventional water cooling alone without an anti-seizure agent, it was necessary to change the rolls four times a month due to rough skin, but with the rolling method according to the present invention, this was reduced to two times a month. In addition, the incidence of external surface flaws due to abnormal wear is also reduced.
It decreased from 0.03% to 0.01%. Example 4 After draining the roll cooling water from the rolling direction, the anti-seizure agent according to the present invention was applied to the contact area between the roll and the rolled material of a stretch reducer mill as a finishing rolling machine for the Mannesmann mandrel mill method. 1.5
It was continuously supplied at a rate of /min. The material to be rolled and the number of rolled pieces were the same as in Example 1. As a result, almost all of the edge mark defects on the flange portion caused by the circumferential speed difference occurred in the conventional case of only water cooling without an anti-seize agent, but in the rolling method according to the present invention, such occurrence did not occur. There were none. Example 5 A sizer, which is the final mill of the Mannesmann plug mill process, was used to produce a 22mm mill with an outer diameter of 337 mm and a wall thickness of 18.26 mm
When finish rolling 100 pieces of %Cr steel to an outer diameter of 324.8 mm,
After draining the roll cooling water from the rolling direction, the anti-seize agent according to the present invention was continuously supplied at a rate of 1.5/min to the area where the roll and the material to be rolled were in contact with each other in the three stands. As a result, in contrast to the conventional rolling method using only roll cooling water without an anti-seize agent, which caused all edge marks and required subsequent cleaning, the rolling method according to the present invention did not produce any edge marks.
Maintenance is no longer required. (Effects of the Invention) Thus, according to the present invention, in rolling a seamless steel pipe by a multi-stage rolling mill having an inclined rolling mill and a grooved roll, the distance between the rolled material and the guide shoe and/or grooved roll in contact with the rolled material is reduced. It is possible to effectively prevent flaws on the outer surface of the tube material and seizure of the rolls, which are caused by seizure occurrence, and therefore drastically reduce rolling mill downtime required for cleaning and replacing guide shoes, as well as repeated process maintenance. decrease in wood,
It is possible to achieve reductions in roll change time and roll consumption, and in particular, it is possible to manufacture high-quality seamless steel pipes with high efficiency even with high Cr alloy steel, which is of great industrial significance.

[Brief explanation of the drawing]

Figures 1a and b are manufacturing process diagrams of seamless steel pipes according to the Mannesmann mandrel mill method and Mannesmann plug mill method, respectively, and Figure 2 is a
Figures 3a, b, c, d, and e are diagrams illustrating the procedure for piercing and rolling using a piercer mill, respectively, showing rolling modes using a mandrel mill, a stretch reducer mill, and a sizer mill.

Claims (1)

[Claims] 1. A method for manufacturing a seamless steel pipe using an inclined rolling mill and/or a multi-stage rolling mill having slotted rolls, comprising: a guide shoe surface and/or rolling roll that comes into contact with the rolled material during perforation and elongation rolling; Contains a water-soluble borate compound: 0.5 to 30 wt% on the surface,
A method for hot rolling a seamless steel pipe, characterized in that rolling is carried out while supplying an anti-seize agent, the remainder of which consists essentially of water.