JPH0692009B2 - Shaped steel manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention, after finishing rolling by cooling control of rolled steel,
The present invention relates to a method for manufacturing a shaped steel capable of being straightened directly without going through a cooling bed.

(Prior Art) A general means for producing a section steel having a flange such as an H-section steel sheet pile or a sheet pile by hot rolling is a heated mill piece 1 and a breakdown mill 2, as shown in FIG. The rolling mill train is composed of a first intermediate universal mill 3 including the universal mill 3a and the edger 3b, a second intermediate universal mill 31 including the universal mill 31a and the edger 31b, and a finishing universal mill 4.

The shaped steel finished and rolled by the finish universal mill 4 is once cooled to a normal temperature that can be straightened by the cooling floor 5, and then straightened by the roller straightening machine 6a or the press straightening machine 6b.

By the way, since the cooling floor 5 has a function of storing the shaped steel until the temperature of the shaped steel falls to a temperature at which it can be straightened, and also has a role of a so-called buffer that absorbs a difference in process capability between the rolling mill and the straightening machine. , Requires an extremely large area of equipment. Further, the operation of the cooling bed requires an operator for operation and maintenance, and there is a problem that the process management of shaped steel products becomes complicated in a factory having a plurality of cooling beds. However, according to the conventional wisdom, it is considered that a cooling bed is an indispensable facility in a rolling mill manufacturing factory, and there is no example of a rolling mill without a cooling floor. It can be inferred that a simple cooling bed can be used if it is forcibly cooled to a low temperature, but it was never put to practical use because there was concern about the material and shape when cooling from a high temperature in the conventional recognition. In order to reduce residual stress, Japanese Patent Publication No. 51-5607 discloses a means for cooling the H-section steel after finishing rolling so that the temperature difference between the central portion of the web and the central portion of the outer surface of the flange falls within a predetermined temperature range. Has been done. However, this technique is different from the object of the present invention in that it does not mention correction of material or shape such as tensile strength and elongation. Further, there are many well-known techniques for thick plates for the purpose of controlling the material related to water cooling after rolling. Examples are JP-A-55-11104 and JP-A-55-11384, but because of the fundamental difference in the cross-sectional shape between thick plate and shaped steel, the control technology for thick plate remains unchanged. Not applicable to. That is, for example, in the case of H-section steel, since the flange and the web have different plate thicknesses, the degree of temperature drop during rolling differs from site to site, and since the same cross section is rolled at the same time, the flange part with a thick plate has a high temperature range. In the case of rolling with a thin plate, the web is rolled at a low temperature range. In this respect, there is a big difference from the cooling after the rolling of the thick plate in which the temperature distribution in the cross section is continuous.

As described above, regarding the cooling of the shaped steel, it is necessary to secure the same material as the non-water-cooled material in all the sections orthogonal to the length direction, that is, the entire section, assuming different rolling histories and cooling start conditions in each part. There is a problem that must be solved, and the means of directly correcting by cooling after rolling has never been practically used in the art.

(Problems to be solved by the present invention) The present invention controls the shape steel having the flange after hot finish rolling by cooling, so that straightening is directly performed without passing through a cooling floor after finish rolling, This is a method for manufacturing a shaped steel that enables the manufacture of long products without causing problems in material and shape.

(Means for Solving Problems and Actions Thereof) The present invention advantageously solves the above-mentioned problems, and its gist is for a shaped steel having a flange immediately after completion of hot finish rolling. Steel composition, flange and web plate thickness in a cross section orthogonal to the length direction, rolling finishing temperature and cooling start temperature, the average cooling rate that satisfies the desired tensile strength and elongation is determined in advance, and the average cooling rate is determined. Cooling control of the flange and the web by speed, after cooling until the average temperature in the cross section is 150 ℃ or less, is a method of manufacturing a shaped steel characterized by performing straightening directly without passing through a cooling bed .

The present invention will be described in detail below.

FIG. 5 shows a cross section of a generally manufactured rolled H-section steel 7. In the figure, the thickness tF of the flange 7a is formed thicker than the thickness tW of the web 7b, and the temperature distribution of the cross section after finish rolling is such that the temperature of the flange 7a is higher than that of the web 7b. Further, the properties of each part in the cross section differ depending on the rolling history such as rolling temperature, reduction ratio, cooling conditions during rolling, etc., and thus such H-section steel cannot be uniformly cooled. The present inventors examined what kind of cooling can be performed to directly correct the material after rolling without causing deterioration in material and shape.

First, the relationship between material and cooling conditions will be described. Figure 1 shows the average cooling rate at each rolling finishing temperature and the tensile strength (TS) and elongation (representative indicators of the material) when cooling is started after the temperature has dropped by 50 ° C after finishing rolling and cooling. The relationship of (El) is shown in Fig. 1 (a), (b),
(C) shows the case where the plate thickness is 34 mm, 18 mm, and 12 mm.

The average cooling rate was obtained by averaging the average cooling rate from the start of water cooling to 300 ° C in the plate thickness direction, and cooling was performed to 150 ° C. The reason for setting the cooling end temperature to 150 ° C. or less in the present invention is empirically found from the relationship between the temperature of the material to be straightened and the straightening effect. This is because during bending, re-bending may occur after correction due to non-uniform temperature change in each part of the cross section. FIG. 2 is an example of the experiment and shows the relationship between the straightening start temperature and the bending at room temperature after straightening. When the straightening start temperature is 150 ° C. or less, almost no bending occurs. The relationship between the rolling finish temperature and the water cooling start temperature should be determined according to the actual equipment sequence.
The figure shows the start of water cooling from a temperature as low as 0 ° C. In addition,
The composition of the target shaped steel is C; 0.12, Si; 0.20, Mn; 1.08, P;
0.021, S; 0.08, balance iron and unavoidable impurities, and general structural rolled steel contained in the respective weight% ranges.

Next, based on the results shown in FIG. 1, a method of setting cooling conditions in which TS after cooling of H-section steel is uniform in all cross sections and El is also satisfied will be described. For example, for H-section steel with a flange thickness of 34 mm and a web thickness of 12 mm, if the rolling finish temperature is 850 ° C at the flange portion and 750 ° C at the web portion, the flange will be about 6 ° C / El at an average cooling rate of seconds
It can be seen that a TS of 55 kg / mm ² can be obtained after satisfying 21% or more. Similarly, for the web, based on Fig. 1 (c), a TS of 55 kg / mm ² can be obtained at an average cooling rate of about 10 ° C / sec. In other words, if the shaped steel is cooled and controlled for each part in the above procedure,
It is possible to obtain a shaped steel satisfying El and having a uniform TS throughout the cross section. That is, if the relational graph of FIG. 1 is created in advance from conditions such as the steel material composition, shaped steel plate thickness, rolling finish temperature, cooling start temperature, etc., it is possible to easily set the cooling rate with no problems with the material. it can. It should be noted that, when alloy components other than the above components or other alloy components are added, it is needless to say that a relational graph for each component condition may be used. In addition,
To measure the rolling finish temperature and the cooling start temperature, a thermometer may be provided on the rear surface of the finish universal mill 4 shown in FIG.

Subsequently, in order to reduce the shape deformation due to water cooling as much as possible, the following cooling was performed in the present invention. Fig. 3 shows the cooling water density on one side of 300 / m ² mi assuming a flange of shaped steel.
n, the amount of deformation that occurs when water cooling the other surface at 0.100, 200 and 300 / m ² min (bending amount per 350 mm)
Is calculated by the finite element method. Thin plate
In the case of 9 mm, large deformation will occur if cooled from only one side.Therefore, in order to eliminate the amount of bending, it is necessary to cool the other side with a lower surface water density of 200 / m ² min or more. Is shown.

Further, FIGS. 4 (a) and 4 (b) show the relationship between the cooling amount and the camber of the cooling portion of the H-section steel. The vertical axis of FIG. 4 (a) shows that the longitudinal end 71 warps with respect to the mounting surface G when the H-section steel 7 after cooling shown in FIG. 6 is placed on the horizontal mounting surface G. The amount S (camber) is shown, and the horizontal axis shows the length from the portion without camber to the end 71. FIG. 4 (b) corresponds to FIG. 4 (a) and shows the flange cooling rate difference of the H-section steel 7 on the horizontal axis. Cooling rate difference (ΔCR) is 4th
It is the cooling rate difference between the point A and the point B at the 1/4 part of the flange width for the one side flange of the H-shaped steel 7 shown in FIG. As is clear from these drawings, the smaller the cooling rate difference, the less the occurrence of camber. Therefore, in cooling, the above-mentioned shape deformation is taken into consideration and the water cooling conditions in the actual operation are set by combining the above-mentioned material control.

(Effects of the Invention) Based on the above-mentioned constitution, even after passing through cooling after rolling, even if it is directly passed through a straightening machine, no bending occurs at room temperature, and there is no material problem and a good product can be obtained. Further, according to the present invention, since a cooling floor is not required, the number of steps and energy can be saved, the number of workers can be reduced, and the industrial effect is extremely large.

[Brief description of drawings]

FIGS. 1 (a), (b), and (c) are graphs showing the relationship between the finishing temperature and the water cooling start temperature and the cooling rate, and FIG. 2 shows the relationship between the straightening temperature and the bending amount, which explain the structure of the present invention. Graph, FIG. 3 is a graph showing the relationship between the water amount density and bending, FIG. 4 (a) is a graph showing the relationship between the end position of the section steel and the camber, and FIG. 4 (b) is against the temperature difference of the cooling part. A graph showing the relationship of the camber, FIG. 4 (c) is an explanatory view showing the water cooling conditions of the cooling portion, FIG. 5 is an explanatory view showing the cross section of the H-section steel, FIG. 6 is a schematic diagram illustrating the camber, and FIG.
The drawing is a schematic diagram showing a conventional row of rolling steel rolling apparatus. 1 …… Bill, 2 …… Breakdown mill 3 …… First intermediate universal mill 31 …… Second intermediate universal mill 4 …… Finishing universal mill 5 …… Cooling floor, 6a …… Roller straightening machine 6b …… Press Straightening machine, 7 ... H section steel

Claims (1)

[Claims] 1. For a shaped steel having a flange immediately after completion of hot finish rolling, the composition of the shaped steel, the thickness of the flange and the web in the cross section orthogonal to the length direction, the rolling finishing temperature and the cooling start temperature. In advance, an average cooling rate that satisfies the desired tensile strength and elongation is determined in advance, the flange and the web are controlled to be cooled by the average cooling rate, and the average temperature in the cross section is cooled to 150 ° C or lower, and then cooled. A method for manufacturing a shaped steel, characterized in that straightening is performed directly without going through the floor.