JPH0266115A - Method and device for improving cooling power and preventing temperature fluctuation after hot rolling of metallic material - Google Patents

Abstract

PURPOSE:To improve the cooling power by a cooling medium and to suppress the generation of a temp. deviation in a cooling stage by subjecting the fresh surface of a metallic material after not working to accelerated oxidation and improving the wettability of a heat transfer surface. CONSTITUTION:The oxidation of the surface of a hot strip is accelerated by a method such as pure oxygen blowing in the period of time shorter than by the oxidation in the atm. air from the outlet of the final stand to the inlet of ROT cooling, i.e., the accelerated oxidation is executed. The wettability of the heat transfer surface, particularly recess of the above-mentioned strip is improved by this accelerated oxidation. Film boiling is generated with the recess as a starting point by which the generation of a temp. deviation is prevented. Since the generation of the temp. deviation in various parts of the hot strip is obviated, the shape of the hot strip is greatly improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is applicable to online controlled cooling heat treatment, online direct quenching, or processing heat treatment (collectively referred to as TMCP) of metal materials, particularly steel materials. The present invention relates to a method and apparatus for realizing a method of improving cooling capacity and a method of preventing temperature deviation from occurring during the cooling process.

[Conventional technology] This will be explained using online heat treatment of steel materials as an example.

In a hot strip mill, the material is water-cooled on a run-out table (hereinafter abbreviated as ROT) 1 to 5 seconds after exiting the final rolling mill. In addition, in the accelerated cooling heat treatment method for thick plates, the time from the final rolling of the thick plate until the controlled cooling is performed is about 20 to 40 seconds.

During this time, the steel material is simply oxidized in the atmosphere due to natural cooling, and in the past, no measures were taken to improve the chemical properties of the surface of the steel material or accelerate cooling between the final rolling mill and the cooling device.

As disclosed in Japanese Patent Application No. 63-112381, the present inventor has discovered that by improving the physical or chemical properties of the heat transfer surface of steel materials before cooling, the cooling capacity can be dramatically improved, and the cooling process can be improved. It was discovered that the temperature deviation of

In a hot strip mill, since the rolling speed is high, the oxidation of the new surface after rolling is insufficient, and the wettability of the new surface, which becomes the heat transfer surface, with water is extremely poor. As a result, the cooling capacity is low, especially for thick-walled materials, and improvements have been desired. It is also desired to reduce variations in winding temperature.

[Problems to be Solved by the Invention] As disclosed by the present inventor in Japanese Patent Application No. 63-112381, roughening and oxidation of the heat transfer surface are effective in improving the cooling ability of metal materials. .

However, especially in the case of hot strips, there are times when a smooth surface is required depending on the application. In addition, there are manufacturing processes where online grinding is almost impossible, such as the rolls of a sizer rolling mill for seamless steel pipes. Furthermore, for example, when the atmospheric oxidation time after rolling until the start of cooling is short, such as in a hot strip mill, the cooling capacity is generally low.

Further, the lower the winding temperature (lower temperature winding), the more likely the winding temperature is to vary, and as a result, material variations and shape defects occur frequently. The same applies to high-temperature winding of 700° C. or higher.

An object of the present invention is to provide a method and means for improving and stabilizing the cooling capacity in such a case.

[Means for Solving the Problems] In order to achieve the object, the present invention improves the wettability of the heat transfer surface by accelerating oxidation of the new surface of the metal material after hot working, and then cools it with a cooling medium. A method for improving the cooling capacity of a metal material after hot rolling, which is characterized by improving the cooling capacity of a metal material by improving the wettability of the heat transfer surface by accelerating oxidation of the new surface of the metal material after hot working. , A method for preventing temperature variations after hot rolling of metal materials, which is characterized by preventing the occurrence of temperature deviations in the cooling process and uniformly cooling by cooling with a cooling medium, and a final stand of a hot rolling mill and metals. This is an apparatus for improving cooling capacity and preventing temperature variations after hot rolling of a metal material, characterized in that a means for accelerating oxidation of the surface of the metal material is provided between the material cooling apparatus. Furthermore, when a metal material is subjected to online heat treatment and cooling after hot processing, at least a portion of the metal material is heated to improve the wettability of the heat transfer surface by accelerating oxidation of the newly formed surface of the metal material after hot processing, and then treated with a cooling medium. A method for increasing the cooling capacity after hot rolling of metal materials and a method for preventing temperature variations, which are characterized by improving the cooling capacity by cooling, preventing the occurrence of temperature deviations in the cooling process, and uniformly cooling the metal material. be.

The present invention will be explained in detail below.

As disclosed by the present inventor in Japanese Patent Application No. 63-112381, the most effective way to improve the cooling capacity of metal materials is to utilize the combined effect of appropriate roughening of the heat transfer surface and oxidation. It is. However, if it is not possible to roughen the heat transfer surface, the independent effect of oxidation is utilized.

Since the new surface immediately after rolling is not oxidized, when it becomes a heat transfer surface, its wettability with water is extremely poor, as is clear from the fact that roll cooling water does not wet the hot strip between the stands of a hot strip mill. . In order to improve the cooling capacity, it is essential to improve the wettability of the heat transfer surface, and the industrial means for achieving this is to promote oxidation.

Conventionally, oxidation was carried out in the atmosphere by natural cooling (zero weight concentration of 21.6%), but an effective method is to spray pure oxygen or oxygen-enriched gas to strongly accelerate oxidation on the heat transfer surface in a short period of time. be.

Figure 2 shows the oxidation time varied from 5 to 35 seconds after the steel pipe was extracted from the heating furnace and placed in the atmosphere until the start of cooling.
This figure shows how temperature deviation occurs when uniform water cooling is applied from the outside surface.

The steel pipe used in the experiment had an outer diameter of 219.1 + nm and a wall thickness of 1
It is a 2.7mm real tube.

Figure 3 shows an example of a cooling curve in which a temperature deviation occurred during the cooling process with an atmospheric oxidation time of 6.6 seconds, and Figure 4 shows an example in which no temperature deviation occurred with an atmospheric oxidation time of 25 seconds. Ta.

In the case of a cooling start temperature of 900°C, it was confirmed that no temperature deviation occurs if oxidation is performed in the air for about 20 seconds or more and then water cooling, and the oxidation of the heat transfer surface before cooling prevents the occurrence of temperature deviation. It was confirmed that the overall cooling capacity was improved.

The cooling curve was measured by attaching eight thermocouples at equal intervals on the inner circumferential surface of the steel pipe (same cross section).

The oxygen concentration in the atmosphere is approximately 21.6%, but as the oxygen concentration increases, oxidation progresses rapidly and the required oxidation time decreases exponentially. In particular, this method is effective when the time required for the new rolling surface to start cooling is extremely short.

The wettability of the heat transfer surface may be improved by a method other than spraying oxygen gas including air, such as spraying an oxidizing agent (liquid).

[Function] The main reason why temperature deviations occur during the cooling process of metal materials is the currently unavoidable surface roughness (indentations) caused by wear and roughening of the rolling rolls (processing tools). By oxidizing these depressions and making them easier to wet, the cooling curve is aligned to the high speed side and the effect of preventing temperature fluctuations is achieved.

In order to improve the productivity of heat treatment of metal materials, especially steel materials, high-speed continuous processing has been implemented, and as the heat transfer surface is cooled without being sufficiently oxidized in the atmosphere, the occurrence of temperature deviation increases. ing. For this reason, the overall cooling rate has become slower, and efforts have been made to improve cooling methods, mainly spray methods, and to develop materials with good hardenability.

However, in recent years, the requirements for preventing material variations and defects in shape and dimensional accuracy of heat-treated products have become increasingly strict.

The present invention has made it possible to meet these demands.

Below, how the technology of the present invention works will be specifically explained in detail using a steel hot strip mill as an example.

The maximum rolling speed of the hot strip mill is approximately 20m/sec.
It is e. The steel material is rolled in each stand, and a new surface is exposed each time.
ROT) and water cooled. As mentioned above, this new surface has inevitable surface roughness (indentations). Local film boiling occurs starting from this depression, resulting in a group of cooling curves as illustrated in FIG. 3, and temperature deviation occurs.

Therefore, oxidation is promoted in a shorter time than in the atmosphere (accelerated oxidation) by, for example, blowing pure oxygen onto the hot strip surface between the exit of the final stand and the ROT cooling population. This accelerated oxidation improves the water wettability of the heat transfer surface, especially the depressions, and prevents film boiling from occurring starting from the depressions and temperature deviations. The shape of the hot strip is also greatly improved since there is no temperature deviation in different parts of the hot strip.

[Example] The method of the present invention was carried out using the example apparatus shown in FIG. Heating furnace 4 in the figure is an electric resistance heating furnace, which is capable of heating in a non-oxidizing atmosphere, and almost no oxidized scale was generated. The heating temperature of the rolled material 3 was approximately 900°C. The rolling mill is a double rolling mill, and rolling roll 1 has a body diameter of 900 na and a body length of 700 m.
, and the rolling speed was largely variable. An accelerated oxidation device 2 is installed on the diameter of the rolling mill, and a water spray cooling device 5 is installed on the rear surface, and the material to be rolled can be cooled for a certain period of time while being moved back and forth inside this device. After cooling, the rolled material 3' was taken out of the cooling device 5, and its surface temperature was measured with a thermotracer 7 in the longitudinal and width directions.

The dimensions of the rolled material 3 were width 450 nn x length 610 nn x plate thickness 30 mm, and mill scale on the surface was removed by grinding with a whetstone. During rolling, a reduction of 15% was applied. The conditions of the rolling mill were adjusted so that the material after rolling was flat.

A 51-Mn medium carbon steel heated to 900'C in a heating furnace 4 is used as the material to be rolled, and after one pass rolling (reduction ratio 15%), oxygen gas is blown for about 3 seconds to perform accelerated oxidation, and then cooled. Approximately 870℃ with device 5, average water density 1 resistance /
The mixture was cooled with water for 25 seconds using m1n-i. In addition, an experiment was also conducted under similar conditions without spraying oxygen gas. The atmospheric oxidation time in this latter case was about 3 seconds.

Table 1 summarizes the temperature measurement data.

Table 1 From Table 1, it was confirmed that the cooling capacity was improved and the temperature deviation was significantly reduced by oxygen gas spraying.

As an example of the present invention, an example using the apparatus shown in FIG. Of course, it can be applied.

That is, the heating furnace 4 can be an electric heating furnace, a gas heating furnace, an induction heating furnace, etc., the rolling rolls can be a double rolling mill, a quadruple rolling mill, a manual rolling mill, etc., and the arrangement of rolling mills is also possible. In addition to a single stand, a tandem mill such as a hot strip mill may be used, and an accelerated oxidation device 2 may be installed between the final stand of the rolling mill and the metal material cooling device to achieve the same effect as shown in this example. can be obtained stably.

Furthermore, when metal materials are subjected to online heat treatment and cooling after hot working, the method of the present invention does not necessarily require continuous heat treatment and cooling of the entire lot of rolled materials, such as hot strips and thick plates. Of course, the method of the present invention can be applied to at least some selected steel plates.

[Effects of the Invention] The present invention has long been desired in heat treatment cooling of metal materials. It has become possible to significantly improve cooling capacity and suppress the occurrence of temperature deviations during the cooling process. Along with this, material variations have been eliminated, and dimensional accuracy and shape defects of metal materials have been significantly reduced.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example apparatus used in an example of the method of the present invention, Fig. 2 is a diagram showing the relationship between atmospheric oxidation time and temperature deviation using a steel pipe as an example, and Fig. 3 is a diagram showing the relationship between the atmospheric oxidation time and temperature deviation, and Fig. 3 is a diagram showing the relationship between the atmospheric oxidation time and temperature deviation, and Fig. 3 A diagram showing an example of temperature deviation. FIG. 4 is a diagram showing an example in which temperature deviation is prevented in the cooling process according to the present invention. 1... Rolling roll 2... Accelerated oxidation device 3...
・Rolled material 4...Heating furnace 5...Cooling device
6... Draining device 7... Thermo tracer Fig. 1 Fig. 2 Oxidation period in the atmosphere (before cooling) sec Two rolling rolls: Accelerated oxidation device Two-liquid rolling material: Heating furnace Two cooling devices: Draining device: Thermo Tracer Figure 3 ime (Sec) Procedural Amendment Figure 4 ]' i me (Sec) 8゜1o. 8. Details of the amendments The following matters in the main application IB will be amended as shown in the attached sheet. Note 1: The scope of the patent request is corrected as shown in the attached sheet. 2. On the 1st and 2nd lines of page 3, the word "hot strip car" is corrected to "hot strip ga." 3. On the 5th line of page 3, the word "via" is corrected to "start." 4. On page 7, line 6, the phrase "oxidation time in the atmosphere" is corrected to "oxidation time in the atmosphere." 5. In the first line of page 11, the word "diameter" is corrected to "immediately after". 6, page 13, lines 1 to 4, claim 1 is characterized by the following: [In addition to rolling mills, cooling bags for metal materials] Accelerated oxidation of new surfaces of metal materials after hot working A method for improving the cooling capacity of a metal material after hot rolling, the method comprising: improving the wettability of a heat transfer surface, and then cooling with a cooling medium to improve the cooling capacity. 2 After accelerating the oxidation of the new surface of the metal material after hot processing to improve the wettability of the heat transfer surface, cooling with a cooling medium prevents temperature deviations during the cooling process and ensures uniform cooling. A method for preventing temperature variations after hot rolling of metal materials. 3. Improving the cooling capacity and preventing temperature variations after hot rolling of metal materials, characterized by providing means for accelerating oxidation of the surface of the metal materials between the final stand of the hot rolling mill and the cooling device for the metal materials. 4. A metal material characterized in that when the metal material is subjected to online heat treatment and cooling after hot working, at least a part of the metal material is heat treated and cooled by the method of claim 1 or claim 2. A method for improving cooling capacity after hot rolling and a method for preventing temperature variations.

Claims (1)

[Scope of Claims] 1. A metal characterized by improving the wettability of the heat transfer surface by accelerating the oxidation of the new surface of the metal material after hot working, and then cooling it with a cooling medium to improve the cooling ability. A method for improving cooling capacity after hot rolling of materials. 2 After accelerating the oxidation of the new surface of the metal material after hot processing to improve the wettability of the heat transfer surface, cooling with a cooling medium prevents temperature deviations during the cooling process and ensures uniform cooling. A method for preventing temperature variations after hot rolling of metal materials. 3. Improving the cooling capacity and preventing temperature variations after hot rolling of metal materials, characterized by providing means for accelerating oxidation of the surface of the metal materials between the final stand of the hot rolling mill and the cooling device for the metal materials. Method. 4. Hot rolling of a metal material, characterized in that when the metal material is subjected to online heat treatment and cooling after hot working, at least a part of the metal material is heat treated and cooled by the method of claim 1 or claim 2. A method for improving cooling capacity and a method for preventing temperature variations.