JPH0230312A - Hot rolling method for seamless steel pipe and seizure preventing agent - Google Patents

Abstract

PURPOSE:To prevent a flaw on the outside surface of a tube stock and a drop of a service life of a roller by executing the rolling, while supplying a seizure preventing agent whose main component is a water soluble borate compound and which does not contain a film forming agent to the surface of a guide shoe for abutting on a rolled stock and/or the surface of a rolling roller. CONSTITUTION:A seamless steel tube is manufactured by a skew rolling mill such as a piercer mill 3, etc., and/or a multi-stage rolling mill having a caliber roller. In this case, at the time of piercing, drawing and rolling, hot rolling is executed, while supplying a seizure preventing agent whose main component is a water soluble borate compound and which does not contain a film forming agent to a guide shoe 3D for abutting a rolled stock 4 or the surface of a rolling roller. The seizure preventing agent to be used contains 0.-30weight% water soluble borate compound. In such a way, the seamless steel tube having a good quality can be manufactured with high efficiency.

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, and the guide shoes and/or various rolling rolls such as barrel-shaped rolls and hole-shaped rolls that come into contact with the rollers. The objective is to effectively prevent such problems and 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 used depending on the outer diameter of the product; the mandrel mill method has a diameter of 7 or less, and the plug mill method has a diameter of 7 or less.
It is common to use more than ``.

Hereinafter, to explain these manufacturing processes in detail, in both manufacturing methods, after heating the round material I to a predetermined temperature in the rotary heating furnace 2, as the first pass of making a hole, a hollow hole is formed by a piercer mill 3. I'm getting tube 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, the plug mill method
The hollow tube 4 which has been pierced and rolled by the mill 3 is further subjected to elongation rolling by an elongator mill 11 of the same type as the piercer mill 3 to reduce its wall thickness and extend its length. Next, it is drawn with a plug mill 12 to reduce its thickness, and then finished with a polishing machine gluer 13 to smooth the inner and outer surfaces to become a raw tube for a sizer mill.After being reheated in a walking beam heating furnace, it is finally cut into a specified outer diameter with a sizer 14. The finished pipe 15 is finished with high precision in 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 shoe mark marks) that occur on the outer surface of the tube 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, shoe marks are likely to occur on the outer surface of the rolled material 1 because the rolled material 1 and the guide shoe 3D are rolled in a state of sliding friction over the entire surface.

Therefore, this kind of rolling not only causes deterioration of the quality of the pipe materials, but also increases the downtime of the rolling mill required for shoe maintenance and shoe replacement, resulting in a decrease in productivity, which is a serious problem for actual operations. cause inconvenience.

As a solution to such problems, Japanese Patent Laid-Open No. 61-2531
Although the No. 05 publication proposes improving the material of the guide shoe, sufficient effects have not yet been achieved. In addition, JP-A-60-56406 proposes a method in which a lubricant containing fine graphite particles and fine solid asphalt particles is applied between the guide shoe and the rolled material while piercing and rolling is carried out. However, in this method, the lubricant is transferred to the main roll, and the forward speed of the rolled material is significantly reduced. As a result, the slip is increased and the perforation efficiency is reduced, which is a serious drawback and cannot be put to practical use.

The second problem is seizure flaws on the outer surface of the rolled material in mandrel mills, stretch reducer mills, sizer mills, etc., as shown in Figures 3a, bSc, d, and e, respectively.
Hereinafter referred to as edge flaws).

The rolling mode in each mill will be explained below. The mandrel mill (Fig. 3a, b) has a pair of grooved rolls 6A, 6.
7 to 9 roll stands incorporating B are arranged in succession by changing their arrangement by 90 degrees from each other, and while the mandrel bar 5 is inserted into the raw tube 4A, the roll stands are placed in the above-mentioned continuous roll stands. By passing through the tube, the raw tube 4A is continuously thinned and stretched to obtain a drawn tube 4B. In addition, the stretch reducer mill (Fig. 3 c, d) reduces and rolls the hollow blank tube 4B without inserting a mandrel bar using a large number of rows of roll stands with oval holes.
It is formed into a finished tube 10 with a predetermined outer diameter and wall thickness. Here, the diameter of each roll hole shape 9A, 98.9C in the continuous row of roll stands of the stretch reducer 9 is set so that the diameter becomes smaller toward the later stage, and the roll hole shape of the final roll stand is set to a predetermined finish. The size corresponds to the outer diameter of the tube, thereby allowing the outer surface of the finished tube 10 to be finished molded. Furthermore, the sizer mill (Fig. 3e) has a plurality of roll stands each consisting of a pair of hole-shaped rolls 14A and 14B arranged 5 to 8 consecutively in a 90'' increments, and a mandrel bar is attached to the raw pipe. The pipe is subjected to reduction rolling without inserting the pipe, and is formed into a finished pipe 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. The difference in relative speed between the tube and the grooved roll (particularly near the flange) causes seizure between the tube and the slotted roll, which leaves scratches on the outer surface of the final product. Therefore, such rolling requires subsequent care, which causes serious inconveniences such as an increase in manufacturing costs.

In order to solve such problems, for example,
-119409, in a mandrel mill, 3
A method has been proposed in which the raw pipe is continuously stretched and rolled using a set of individual rolls, thereby reducing the difference in roll circumferential speed in the hole-shaped portion compared to the conventional case of using two rolls, thereby reducing seizure defects. However, this method has the disadvantage of requiring huge capital investment. Also stretch reducer
And in sizers, lubricants such as mineral oil containing natural oils and fats and other additives have been used in the vicinity of the flange of the slotted roll. However, such lubricants tend to harden at room temperature, which makes maintenance of the lubrication system troublesome, has poor wastewater treatment properties, and has 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 occurs particularly 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 in the vicinity of the entrance side of the barrel roll and in the vicinity of the wall thickness determination, which slows down the forward speed of the tube material 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 these problems, conventionally, before rolling high-alloy steel, ordinary steel with significant scale formation was rolled to a
After piercing and rolling 3000 pieces and improving seizure, high alloy steel was rolled. However, this method has the disadvantage that the rolling opportunities are limited and high-efficiency piercing rolling of high alloy steel cannot be performed. Furthermore, in mandrel mills, trench reducer mills, and sizer mills, indentation flaws occur on the outer surface of the tube due to the rough surface of the roll, which significantly impairs the quality of the tube. 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 Problem) Therefore, the inventors have developed a guide shoe and/or barrel shape that comes into contact with the rolled material when manufacturing a seamless steel pipe using a multi-stage rolling mill having an inclined rolling mill and a slotted roll. In addition to preventing seizure between rolls and slotted rolls, it also suppresses slip between the two as much as possible, even when there is little scale on the surface of the rolled material or high alloy steel with high hot deformation resistance. We have begun developing an anti-seize agent that can effectively prevent roll seizure without causing guide shoe marks on the outer surface of rolls.

Based on the recognition of the above-mentioned problems, the inventors explored anti-seize agents other than mineral oil-based, oil-based, synthetic oil-based, and mixed oil-based agents 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.

This invention is based on the above knowledge.

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 surface of the guide shoe and the surface of the rolling roll 7 or the surface of the rolling roll are in contact with the material to be rolled during perforation and elongation rolling. This is a hot rolling method for seamless steel pipes, which comprises rolling while supplying an anti-seize agent containing a water-soluble borate compound as a main component and not containing a film-forming agent.

In addition, this invention uses a water-soluble borate compound of 0.5 to 3
It is an anti-seizure agent having a composition containing 0 wt% (hereinafter simply expressed as %) and no film forming agent.

The experimental results that led to this invention will be explained below.

Table 2 shows the results of investigating the seizure status, shoe mark flaws on the outer surface of the tube, and 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 model: Model piercer with fixed guide shoe Material of rolled material: 22% Cr steel Dimensions of rolled material: 58φ x 2501! (Cylinder) Rolling temperature: 1250°C Hollow dimensions after rolling: 62φx4. ot (+nn+) How to supply anti-seize agent: 0.7 to the shoes above and below the entry side
11.7 m1n injection Table 1 (%) As is clear from Table 2, significant seizure occurred with only water cooling without an anti-seize agent, and shoe marks of about 0.7 mm were generated on the outer surface of the tube.

On the other hand, when an anti-seize agent was used, the occurrence of seizure and shoe mark defects 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 shoe 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-seizure agents with other compositions is that they become amorphous glass-like at high temperatures and under high surface pressure. This is thought to be because it prevents metal contact between the parts and completely eliminates the occurrence of seizure.

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 experiment was conducted at nine levels of concentration: 0.2, 0.5, 1.4, 7 and 35%.

The drilling conditions were the same as in the experiment described above.

10.20.30 *Liquid stability evaluation O: No separation after being left at room temperature for 30 days. ×: Separation after being left at room temperature for 30 days. The content needs to be at least 0.5% in order to reliably prevent seizure, but if it exceeds 30%, the stability of the liquid will deteriorate, so it should be in the range of 0.5 to 30%.

Suitable water-soluble borate compounds for use in this invention include alkaline salts of oxalic acid (sodium oxalate, potassium oxalate), ammonium oxalate salts, alkanolamine salts of oxalic acid, and oxalic acid alkanolamine salts. and salts of water-soluble amines, such as salts of tetraethylenepentamine, cyclohexylamine, diethylenetriamine, alkylamines, etc. Also, boric acid dispersed in water or dissolved in water exhibits similar effects and is effective.

The anti-seize agent of the present invention is an aqueous treatment liquid containing the above-mentioned borate compound as a main component, 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 mainly composed of a water-soluble borate compound to the guide shoe, no seizure occurred even in the rolled material, which was unavoidable in the past. Moreover, the coefficient of friction at this time was as high as about 0.2 to 0.3, and there was no deterioration in biting property or occurrence of slip, and good rolling was possible.

The anti-seizure effect in the case of a fixed shoe in piercing rolling has been described above, but it has been confirmed that the same effect can be obtained in inclined rolling having a rotary disk shoe or multi-stage rolling having grooved 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, but such a lubricant is not applicable to the present invention for the following reasons. It could not be used for hot rolling such seamless steel pipes.

i) Since an organic solvent is used as the solvent, 800 to 1
Easily flammable at high temperatures of 250°C.

ii) Since a large amount of cooling water is applied, hydrolysis easily occurs and the lubricant is not formed 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 balate compound: 15% Water: 85.0% Example 1 A piercer mill, which is the first pass of the Mannesmann mandrel mill method, was used to produce two milled grains with an outer diameter of 110 mm and a length of 3000 mm.
When rolling 2% Crt1ii11036 pieces into a hollow tube with an outer diameter of 115 mm and a wall thickness of 12.5 mm, apply the above anti-seize agent between the upper and lower guide shoes and the rolled material from the direction of rotation of the material. It was continuously supplied at a rate of /min. Note that the cooling water for the main roll was reduced to the usual level of about 3 liters.

As a result, while the conventional method using only roll cooling water caused about 10% shoe mark defects and required cleaning of the outer surface, the method according to the present invention was able to reduce the occurrence rate of shoe mark defects to 0.05%. Also, the number of holes that can be drilled per set of guide shoes has increased from about 20 to 250.

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 3000 mm.
Sono's 13% crmaoo book has an outer diameter of 1150 mm and a wall thickness of 14 mm.
When rolling into a 45m+a hollow tube, after draining the roll cooling water from the rotational direction of the main roll, 1. Ofl/
It was continuously supplied at a rate of sin.

As a result, even when 300 pieces were continuously punched and rolled, no seizure products were observed, there was no decrease in perforation efficiency, and the incidence of internal flaws was drastically reduced from 12% to 0.5%. In addition, abnormal wear of the rolls is reduced, and the incidence of external defects is reduced to 0.0.
It decreased sharply from 1% 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-seize agent, 1
The perforation efficiency is 60% to 45% after about 50 rolls are rolled.
Because of this, rolling of the 13% Cr steel was stopped for a while, and rolling of the 13% Cr steel could only be restarted after about 1000 ordinary steel sheets had been rolled.

Example 3 For four stands of a mandrel mill for thinning and drawing the hollow tube after piercer rolling, which is the second pass of the Mannesmann mandrel mill method, rolls were applied from the rolling direction to the area where the rolls and the material to be rolled came into contact. After draining the cooling water, apply the anti-seize agent according to this invention at 1.51! ,/min. In this way, ordinary steel: 29,000 pieces,
High alloy steel (13Cr, 22Cr.

5US304) : As a result of rolling 1500 pieces,
With conventional water cooling alone without an anti-seize 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.

Furthermore, the incidence of external surface flaws due to abnormal wear decreased from 0.03% to 0.01%.

Example 4 After draining the roll cooling water from the rolling direction, one portion of the anti-seizure agent according to the present invention was applied to the contact area between the roll of a stretch reducer mill and the rolled material for finishing rolling of 4 m in the Mannesmann mandrel mill method. It was fed continuously at a rate of .527 fflin. The material to be rolled and the number of rolled pieces are as in Example 1.
The same is true.

As a result, almost all of the edge mark defects on the flange portion caused by the difference in circumferential speed occurred in the case of conventional water cooling without an anti-seize agent, but they did not occur in the rolling method according to the present invention. There were none.

Example 5 Using a sizer, which is the final mill of the Mannesmann plug mill method, a 22% of the outer diameter of 337 mm and wall thickness of 18.26 mm was produced.
When finish rolling 100 pieces of Cr steel to an outer diameter of 324.8 mm, 1 coat of the anti-seizure agent according to the present invention was applied to the areas where the rolls and the rolled material contact each other in the rolling direction after draining the roll cooling water from the rolling direction. It was continuously supplied at a rate of .51/llin.

As a result, while the conventional rolling method using only roll cooling water without an anti-seize agent caused edge marks and required subsequent cleaning, the rolling method according to the present invention did not generate any edge marks and did not require any cleaning. became.

(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 shoes and/or grooved rolls in contact with the rolled material is reduced. Effectively prevents piping external surface defects and roll seizures caused by seizure, resulting in a drastic reduction in rolling mill downtime required for guide shoe maintenance and guide shoe replacement, as well as a reduction in the number of manpower required to repeat the process. ,
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 extremely 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 the Mannesmann plug mill method, respectively. Figure 2 is an explanatory diagram of the procedure for piercing and rolling using a piercer mill. Figures 3 a, b, c, d, and e are diagrams showing rolling modes using a mandrel mill, a stretch reducer mill, and a sizer mill, respectively. Figure 2 <a) Figure 3 (e)

Claims (1)

[Claims] 1. In a method for manufacturing a seamless steel pipe using an inclined rolling mill and/or a multi-stage rolling mill having slotted rolls, the guide shoe surface and/or the guide shoe that comes into contact with the rolled material during perforation and elongation rolling is provided. 1. A method for hot rolling a seamless steel pipe, which comprises performing rolling while supplying an anti-seize agent containing a water-soluble borate compound as a main component and not containing a film forming agent to the surface of a rolling roll. 2. An anti-seize agent characterized by containing a water-soluble borate compound: 0.5 to 30 wt%.