JPS61284524A - Production of irregular shaped unnormalized high tensile steel plate having excellent weldability - Google Patents

Abstract

PURPOSE:To produce an irregular shaped unnormalized high tensile steel plate having uniform material quality and excellent weldability by hot rolling the irregular shaped steel plate then cooling the steel plate at the cooling rate adjusted according to the desired strength distribution of the steel plate by an accelerated cooling installation. CONSTITUTION:The cooling rate is adjusted by the continuation of accelerated cooling, the adjustment of the water flow density, the control of a passing speed. etc. according to the desired strength distribution of the irregular shaped steel plate of a low carbon equiv. such as different thickness steel plate or tapered steel plate in the stage of cooling the above-mentioned steel plate by the accelerated cooling installation after hot rolling. The desired intensity distribution is thereby formed over the entire part of the above-mentioned steel plate and the irregular shaped unnormalized high tensile steel plate having excellent weldability, low-temp. toughness, etc., is obtd.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to the production of deformed non-heat treated high tensile strength steel sheets with excellent weldability, and more specifically, to improve the rolling efficiency and material homogeneity of deformed steel sheets. This invention relates to a method of manufacturing steel sheets that is optimal for improving the degree of freedom of design for consumers and rationalizing the number of man-hours.

(Prior Art) As is well known, the material and shape of thick steel plates are generally uniform in both the width and length directions.
When manufacturing structures such as tanks and water gates (penstocks) that are subject to static pressure in the length and height direction, thick or high-strength steel plates were arranged at the bottom and welded in sequence. .

In addition, within the same strength range, Japanese Patent Publication No. 50-24898, Japanese Patent Publication No. 36826, 1982, and Japanese Patent Publication No. 52-49
As shown in Japanese Patent No. 781, a method for manufacturing a steel plate with a different thickness (stepped) has been proposed. In addition, Japanese Patent Publication No. 46-37086, Japanese Patent Publication No. 37333-1983, and Japanese Patent Publication No. 1988-60-
As shown in Japanese Patent Application No. 124, a method for manufacturing a steel sheet is proposed.

(Problems to be solved by the invention) However, with the pursuit of economic rationality in recent years, the quality requirements for steel materials have become stricter due to the adoption of large heat input welding and medium hydrogen welding rods, especially carbon equivalent ( Although significant progress has been made in reducing Oeq (Oeq), manufacturing of differential thickness or Tenozoichi steel plates by controlled rolling makes temperature control extremely difficult, resulting in large variations in material quality. had its limits.

As structures become larger, there is a need for steel plates with a large difference in thickness or a steel plate with a large taper, but controlled rolling has not been possible at all since the thickness of the steel plates varies greatly.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides that, after the deformed steel sheet is fully hot-rolled, when the steel sheet is cooled by an accelerated cooling facility, the steel sheet is A method for manufacturing a deformed non-temperature high tensile strength steel plate with excellent weldability is provided, which is characterized by adjusting the cooling rate.

(Function) The present invention advantageously solves the problems of the prior art, further rationalizes the overall design and manufacturing of structures, and makes it possible to provide an optimal manufacturing process that meets customers' demands for lower Oeq. shall be. This will be explained below based on the material properties of the deformed thick steel plate obtained from experiments and studies conducted by the inventors.

According to the results of experiments and studies conducted by the present inventors, according to the present invention, even if a steel having the necessary allowance for weldability is used, the desired temperature of the steel plate can be achieved after rolling with a pass schedule within an allowable range of temperature deviation. The strength distribution can be adjusted by adjusting the cooling rate of the steel plate according to the strength distribution, and low Oeq deformed steel sheets can be used without material changes due to controlled rolling. It becomes possible to manufacture high-quality high-tensile steel sheets.

The desired strength can be imparted to the deformed steel plate by applying accelerated cooling of ON10 F F in consideration of plate thickness, or by intermittent or continuous application of different accelerated cooling. The cooling rate can also be controlled by controlling the amount of water, that is, the density of water.
If limited to the longitudinal direction, the same effect can be achieved by controlling the threading speed even under a constant water flow.

Furthermore, if this technology is used to make the large thickness part of a differential thickness steel plate higher in strength than the small thickness part, or if the strength Chi A- is superimposed on the Chi or E copper plate, it is possible to produce a material that cannot be produced by controlled rolling. It becomes possible to manufacture a steel plate with a function equivalent to that of a steel plate with a large difference in thickness or a large taper.

(Example) Examples of the present invention will be described below along with comparative examples. Table 1
The components of Example Work 4 are shown as #1, and the components of Comparative Example 1.2 are shown as Steel 2.

Table 1 Steel 2 is a deformed steel plate manufactured using conventional technology (normal rolling or controlled rolling), so it has a high Oeq and poor weldability. Although steel 1 has a low ceq due to weldability, by the method of the present invention, it can be made to have the same strength as the comparative example by accelerated cooling after manufacturing the deformed steel plate.

Different thickness steel plates (implemented number of layers, 2 and comparative example 1
) and tapered steel plates (Example 3.4 and Comparative Example 2) are shown in Table 2. The rolling and accelerated cooling conditions are shown in Table 2.

Table 3 shows the results of measuring the tensile strength, etc. of each part of the manufactured steel plate. It can be seen that Example 1, which was manufactured from Steel 1 by accelerated cooling, was a differential thickness steel plate with superior strength, toughness, and weldability.

Furthermore, in Example 2, in which the cooling conditions in the large thick part were changed, high strength was obtained while maintaining the same toughness and weldability as in Example 1, and the large thick part was substantially reduced compared to the small thick part of 25 mm. 35 r
It has become possible to manufacture steel plates with different thicknesses that have a strength equivalent to nanometers.

On the other hand, results similar to those of the differential thickness steel plate were obtained for a tapered steel plate with a length of 20 m, making it possible to manufacture a tapered steel plate with excellent weldability and a tapered steel plate with a strength taper substantially equivalent to a large taper steel plate. became.

(Effects of the Invention) According to the present invention, it is possible to form a desired strength distribution in thick steel plates with different plate thicknesses, and it is possible to improve weldability and low-temperature toughness by lowering the Oeq. The degree of freedom in manufacturing is greatly increased, making it possible to omit the welding process or use high-efficiency welding.

Representative Kato Patent Attorney Masaaki Aki Sawa 2 others

Claims (1)

[Claims] (1) After hot pressing the deformed steel plate, when cooling the steel plate using accelerated cooling equipment, the cooling rate of the steel plate is adjusted according to the desired strength distribution of the steel plate. A method for manufacturing tempered high-tensile steel sheets.