JPH01278902A - Method for rolling seamless steel tube stock such as alloy steel and others generating high working heat and device used for rolling - Google Patents

Abstract

PURPOSE:To improve both the rolling workability and rolled product quality by installing a cooling medium injection tube in a tube stock before rolling after piercing the stock and totally and uniformly cooling the inside surface of the stock in combination with peripheral air cooling effect. CONSTITUTION:A cooling tube body 1 whose peripheral surface has air injection holes 2 is prepared and cooling tube supporting plates 3 are fixed to the periphery of the body 1 at plural positions. The body 1 is inserted into a tube stock 5 pierced by a piercing mill and is placed by fixing a tube end heat insulator 4. Before rolling of the stock 5, cooling air is fed from an air supply source through a tube 6 and the body 1 and an end of the stock 5 is heat insulated by the insulator 4. The cooling air is injected from the injection holes 2 into the stock 5 inside and flows toward the top side and discharges from a discharge hole 7. Thus, temps. of the stock 5 are maintained not higher than the brittle zone temp. even for temp. rising time in rolling. Therefore, brittle zone rolling is avoidable and both the rolling workability and rolled product quality are improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to rolling a steel pipe material that generates high processing heat during rolling, such as high alloy steel, in which the temperature of the raw pipe reaches the embrittlement range during rolling. The present invention relates to a method of rolling without causing damage and a cooling device used therefor.

[Conventional technology] In recent years, in the field of oil country tubular goods, plant steel pipes, etc., high corrosion resistance,
Demand for high-strength seamless steel pipes is increasing.

To meet this demand, the addition of alloying components such as Ni and Cr
The production ratio of so-called high-alloy steel pipes, in which l is higher than usual, is increasing.

When manufacturing these high-alloy steel pipes by rolling, rolling characteristics such as workability and rolling mill load are different from those of forged steel types.
There is a wide variety depending on the steel type (alloy component addition amount). One of these is the difference in the degree of processing heat generation. Certain alloy steels, such as high Ni-based alloy steels with SO5316 or higher ((:r≧2H)
, Ni≧20t), the processing heat generated during rolling is
−・Since it is considerably larger than forged steel, the temperature of the rolled material increases significantly.

[Problems to be Solved by the Invention] Therefore, if the steel is rolled in the same way as forged steel, it will be processed in an embrittled region, and the workability will be extremely poor, for example, sludge marks will be generated on the inner surface of the steel pipe. Furthermore, since the processing heat is large, rolling tools are susceptible to deterioration (e.g., melting and damage), and their lifespan is significantly shorter than that of general steel. These problems can be solved by reducing processing heat generation, but this is difficult in actual operation.

Normally, in the production of seamless steel pipes, a heated material is first processed with a punching machine to form a blank tube, and then the blank tube is guided to a rolling mill such as an elongator, a plug mill, or a mandrel mill, where it is rolled. In fact, the embrittlement region becomes a problem in the rolling process, and the drilling process requires a lower limit temperature that is sufficiently higher than the lower limit temperature in the rolling process.

Therefore, it has been proposed, for example, to take into account the embrittlement temperature range during rolling and to specify a particularly upper limit temperature for the heating furnace extraction temperature to control it within an extremely narrow temperature range. In many cases, the temperature necessary for proper rolling and processing cannot be obtained (reheating). ■As a result of relatively low-temperature rolling, the rolling resistance is large, and the temperature at the end of the tube in particular is lower than other parts, resulting in poor rolling performance, poor biting into the rolling mill, over-rated rolling mill load, and tool failure. Problems such as abnormal deterioration occur. (2) Furthermore, it is practically difficult to perform such heating control for each type of steel.

These things make seamless rolling of high alloy steel difficult.

Note that as a technique for injecting cooling water into the raw pipe during or before rolling, Japanese Patent Application Laid-Open No. 151106/1982 or Japanese Patent Application Laid-Open No. 1987-10406 is known. The purpose of these inventions is to prevent rolling scratches from occurring on the inner surface of the raw tube due to scale present in the raw tube during rolling. For this reason, in the invention disclosed in the above-mentioned publication, the scale is cooled by cooling water supplied into the raw tube, thereby modifying the scale so that it becomes brittle and does not cause rolling scratches. Therefore, the present invention differs in object, purpose, and configuration.

An object of the present invention is to solve the problem of heat generation during processing while ensuring sufficient drilling and rolling temperatures.

[Means for Solving the Problems] The rolling method according to the present invention is characterized in that a heated material is perforated and then rolled by a rolling mill such as an elongator, a plug mill, or a mandrel mill. In the rolling process, the inside of the raw tube that is to be rolled after the piercing is cooled with a cooling medium such as gas to the extent that the temperature of the raw tube during rolling does not reach the embrittlement region due to heat generated by processing. It's about doing.

In addition, in the present invention, in order to cool the vehicle surface described above, a cooling medium jetting insertion tube is inserted into the raw tube of 1) which enters the rolling after the piercing, so that the inside of the raw tube is cooled while cooling the outer periphery of the raw tube. It is preferable that the entire tube be cooled almost uniformly.

Furthermore, the cooling device used in the above method of the present invention is
In a row of seamless steel pipe rolling equipment that perforates the heated material and then rolls it with a rolling mill such as an elongator, a plug mill, or a mandrel mill, in the vicinity of the rolling equipment,
It is characterized by a heat insulating device that surrounds the tube end of the raw pipe and a cooling medium jetting insertion tube installed inside the raw pipe.

[Example] The present invention will be specifically described below based on an example shown in the drawings. FIG. 1 shows the relationship between steps and material temperature for explaining the present invention.

In Figure 1, the material extracted from the heating furnace is heated to a predetermined temperature (θ(l), taking into account the temperature drop from drilling to rolling.
IJT). In the drilling process, a blank tube of 01 is obtained, and then a blank tube of θ is obtained. Start rolling. At this time, the temperature of the raw tube reaches the embrittlement region where it rises to θ1 due to heat generation during processing. (Solid line A) The lower limit 71- of rolling is as shown in the figure, and the lower limit temperature of perforation is much higher in the latter as shown in the figure. Therefore, the heating furnace extraction temperature was lowered (θ・.1
．． 1) If this happens, the lower limit of 7M degrees during perforation will be cut (θ·P) as shown by the chain line B in the figure, and a case will occur where smooth rolling cannot be continued.

Therefore, in the present invention, as shown by the solid line C, the extraction temperature of the material is sufficiently ensured as the minimum drilling temperature as shown by the solid line A, but the amount of rolling work determined according to the steel type before rolling and the temperature rise are In addition, the temperature of the raw tube before the start of rolling, especially the inner surface temperature, is actually measured and the entire tube is cooled so that the temperature of the raw tube 711 degrees does not exceed the embrittlement range (of course, above the rolling lower limit temperature) during rolling. As a means for this, the present invention supplies a cooling medium such as air or, in some cases, atomized mist, to the inside of the blank tube. The reason for this is that natural cooling is the simplest cooling method.

However, natural cooling has the following problems.

This will be explained using FIG. 5. That is, in natural cooling, there is a significant difference in the cooling effect between the outer surface and the inner surface of the raw tube. In other words, the outer surface is exposed to the atmosphere in an open state (sufficiently wide space), so the cooling effect (heat removal by radiation and convection) is fully utilized, but the surface on one side is completely surrounded by high-temperature steel. Since it is a closed space, there is almost no cooling. In this state, it takes a long time to cool the entire tube (inner surface side is rate-limiting), and by the time the entire tube has cooled down, the outer surface temperature has already fallen too low to satisfy the rolling lower limit temperature constraint determined by the rolling mill load, etc. The problem arises that it cannot be done.

Moreover, during natural cooling, the temperature drops the most at the end of the tube, which is cooled from both the circumferential and longitudinal directions. In particular, the end temperature on the rolling top side is one of the important factors related to the quality of rolling properties. That is, if the tube end temperature is low, problems such as poor rolling properties and poor biting into the rolling mill, and abnormal deterioration of the tool due to over-rated rolling mill loads occur. Therefore, rolling must be carried out before the temperature at the outer surface and end of the tube falls below the minimum rolling temperature (although the inner temperature reduction is insufficient), which is not a fundamental solution to the above problem. You can't get it.

For this reason, the present invention uses internal forced cooling as the cooling means. This refrigerant is supplied inside the tube,
In combination with natural cooling of the outer periphery of the raw tube, the entire rolled surface of the raw tube is brought to a predetermined target temperature approximately evenly. For this purpose, the amount and time of refrigerant supply to the inside must be adjusted to match the natural cooling of the outer periphery.

FIG. 2 shows an internal cooling device used in this method (in this example, air is used as the refrigerant), and FIG. 3 shows the inside cooling device inserted into the blank pipe. In the figure, numeral 1 is the cooling pipe body, 2 is the air outlet hole drilled on the outer periphery, and 3 is the cooling pipe body.
4 is a cooling pipe main body support plate provided on the outer periphery of the cooling pipe main body 1;
is a tube end heat insulating device attached to the tube end of the blank tube, and during cooling of the blank tube, the tube end is surrounded and kept warm. 6 is an air supply pipe, and 7 is an air outlet. Note! 15
-5 indicates a blank pipe.

If cooling air is supplied in the state shown in Fig. 3, the air will be ejected from the air jet hole 2 of the cooling pipe body into the raw tube, collide with the inner surface of the raw tube, flow inside the raw tube 5 to the top side, and exit the discharge lower. It is then released into the atmosphere.

(Concrete example) Figure 4 shows the results of cooling the raw tube using this device.

Figure 4 shows a cooling device in which air jet holes are provided only at the tips of the cooling tubes (8), and a cooling device in which the support plate 3 has a swirling function to give a swirling flow to the air flowing through the tube (8). (b) and (C) in which air jet holes were arranged in a spiral around the outer periphery of the cooling tube were used, and the cooling effect due to (C) was plotted in the figure.

Furthermore, the present invention is applied to seamless steel pipe manufacturing equipment using a press-piercing mill that uses square-section bloom as a material, and is cooled immediately before the rolling mill, so that the bottom part of the raw pipe to be cooled is in a closed state. It has become. Cooling was done using "natural cooling on the outside surface + forced air cooling on the inside surface" with the aim of ensuring cooling capacity between the inside and outside surfaces and preventing overcooling of the tube end (rolling top side).

■Applicable steel type composition (t) ■Material extraction temperature 1250℃ ■Material tube temperature before rolling 1037℃ (actual value) ■Predicted temperature of this material for the above total amount of processing -F temperature rise 150℃ ■Cooling conditions/target rolling temperature 1140 °C (Output temperature)/Cooling time
The present invention was applied under the above conditions: 100 seconds/temperature of the raw tube after cooling: 990°C.

As is clear from FIG. 4, (1) the amount of temperature drop on the outer surface side and the amount of temperature drop on the inner surface side are approximately equal, that is, the effects of the inner and outer surfaces are balanced. ■The amount of temperature drop is the same over the entire length of the raw pipe. ■It can be seen that the amount of temperature drop in the raw pipe tootsub section is smaller than in other parts due to the effect of the heat insulating device. These things mean that the entire tube is cooled uniformly while ensuring heat retention in the rolled top part of the tube.

In addition, the temperature of each part of the raw pipe due to the cooling before rolling as described above is 97
As a result, even if the temperature of the raw pipe increases due to processing heat during rolling, the temperature can be kept below the embrittlement range, and it has been confirmed that the number of internal defects has been drastically reduced.

[Effects of the Invention] As described above, according to the present invention, it is possible to avoid rolling in the embrittlement region while ensuring a sufficient processing temperature for materials such as alloy steel that generate a large amount of heat during processing, thereby improving rolling workability and quality. It is possible to roll seamless steel pipes with both surfaces, and the effect is extremely large.

In the embodiments of the present invention, a cooling method using air has been described, but of course, a mixture of water and air in a mist state or cooling using water may be used. However, in the case of water, the cooling capacity is greater than that of other types of cooling, and water may flow at the bottom of the tube and generate uneven heat, so make sure to stop cooling at the target temperature. In addition, for the latter, consideration must be given to supplying cooling water while rotating the raw tube.

[Brief explanation of the drawing]

FIG. 1 shows a rolling process and temperature changes (internal and external surfaces) of a raw material (pipe) for explaining the present invention. FIG. 2 shows the cooling device used in the present invention, and FIG. 3 shows the cooling device inserted into the blank pipe. FIG. 4 shows the relationship between the position of the raw tube and the temperature effect amount according to the embodiment of the present invention. FIG. 5 is a diagram for explaining the problem when cooling naturally.

Claims (1)

[Claims] 1. In a seamless steel pipe rolling method in which a heated material is perforated and then rolled by a rolling mill such as an elongator, a plug mill, or a mandrel mill, the raw pipe temperature during rolling in the rolling step is A method for rolling a seamless steel pipe material such as alloy steel with high processing heat generation, characterized in that the inside of the raw pipe is cooled in advance before rolling after the piercing to prevent the heat generation from reaching the embrittlement region. 2. In a seamless steel pipe rolling method in which a heated material is perforated and then rolled by a rolling mill such as an elongator, a plug mill, or a mandrel mill, the temperature of the raw pipe during rolling may reach the embrittlement range due to heat generated during the rolling process. In order to prevent this from occurring, a cooling medium jet insertion tube is inserted into the raw tube after the above-mentioned drilling and before it starts rolling, so that the inside of the raw tube is cooled by cooling the outer periphery of the raw tube, and the entire raw tube is cooled almost uniformly. A method for rolling alloy steel seamless steel pipe material with high processing heat generation characterized by cooling. 3. In a line of rolling equipment for seamless steel pipes that perforates the heated material and then rolls it using a rolling mill such as an elongator, plug mill, or mandrel mill, a heat-retaining device that surrounds the end of the raw pipe is installed near the rolling equipment. A cooling device for seamless steel pipe materials such as alloy steel that generates high processing heat and is characterized by having an insertion tube for discharging cooling medium into the base pipe.