JPS58199817A - Production of high tensile shape steel having excellent toughness - Google Patents

Abstract

PURPOSE:To obtain high tensile shape steel which has excellent toughness and is free from distortion and bending without adding any alloy element having high hardenability by heating the shape steel to be treated to an austenite region in a continuous heat treatment furnace then cooling the same acceleratively while controlling the amt. of cooling media according to respective sections. CONSTITUTION:The shape steel to be heated after hot rolling is heated in a continuous heat treatment furnace in the above-mentioned way; thereafter, the shape steel 6 on a table roll 5 is cooled with a large amt. of cooling media discharged from upper, lower, right and left headers 1-4 to the thick walled parts of the steel 6. Since the continuous heat treatment furnace is used here, the feed speed of the material is variable and the rate of heating is controllable with the size and thickness of the product so that quality is stabilized. The rate of heating is high and smaller crystal grains of austenite are formed; therefore, high toughness and strength are obtainable. The problems of the limitation in the size of the product and the variation in the quality occuring in stacked treatment can be solved. If the rate of cooling is high in an adequate range in the accelerated cooling after the heating, fine ferrite particles are obtained, whereby the high toughness and strength are obtained. Distortion and bending are prevented even with the asymmetrical shape steel by controlling the amt. of the cooling media.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a high-tensile steel section with excellent toughness, and more particularly to a method for producing a heat-treated steel section 11.

In recent years, since the energy crisis, high-tensile steel sections with excellent toughness have been used as containers for transporting and storing liquefied petroleum gas (LPG) and liquefied natural gas (LNG), as well as as structural steel for low temperatures in cold weather. is on the rise.

In general, methods using controlled trawling and heat treatment are known as methods for obtaining products with high toughness and high tensile strength. However, in the case of section steel O, since hole pressing is the main method, there are restrictions such as roll strength. It is difficult to apply a controlled drawing method such as that seen in thick steel plates.

On the other hand, in the case of shaped steel, normalizing treatment in a batch furnace is usually used for thermal steel, and good results have been obtained in terms of toughness in the case of so-called thin products of size S or smaller. , the anti'iI strength (yield point, tensile strength) decreases significantly (sufficient effects cannot be expected). In addition, for thick products with a thickness of 21 m or more, the strength decreases even more significantly and toughness cannot be expected to improve with this thin product.

Furthermore, since the batch process is applied to the ripening process itself, the length of the product is reduced when the unit weight (#/%) is small and the length is relatively long, and the product has a complex shape, such as shaped steel products. There was a problem that the product length was limited, and when stacking was performed, there was a large variation in mechanical properties between the products on the upper stage and those on the lower stage. There were problems such as difficulty in controlling the heating rate and cooling rate, and difficulty in controlling product distortion. Therefore, in the case of shaped steel, in order to obtain higher toughness and strength, K can be replaced with C, Mn, Nl, M, , which has high hardenability.
It was necessary to add alloying elements such as Cr and V. However, the addition of these elements not only increases manufacturing costs, but also increases the value of bulking amount, which is a parameter that indicates the superiority or inferiority of weldability, and has the disadvantage of causing deterioration of the mechanical properties of the layer joint. .

The present invention has been made to improve the above-mentioned drawbacks of the prior art, and uses a continuous heat treatment furnace as the heat treatment furnace after hot-pressing the section steel to be treated. It is recommended to heat the material to the austenite region and then perform accelerated cooling. In this accelerated cooling, the entire shaped steel is cooled while adjusting the amount of cold and #& body according to each part of the shaped steel.

The reason for using a continuous heat treatment furnace in the present invention is that
Continuous heat treatment furnaces have a variable material feed rate, and the temperature increase rate can be controlled according to the product dimensions and thickness, so compared to batch furnaces, there is less variation in quality and stable quality can be obtained. be. In addition, if the heating rate is high, the austenite crystal grains become smaller, so the ferrite grains after heat treatment become smaller9, and as a result, high toughness and high strength are obtained. Furthermore, by adopting a continuous processing furnace, it is possible to solve problems such as limitations on the size of rolled products and variations in quality due to stacking processing.

After applying 1 lkJ to the austenite region, accelerated cooling is performed in the present invention. As in the case of temperature rise, if the Ivgl rate is appropriately high and high, fine ferrite grains can be obtained, and high toughness and strength can be obtained. Moreover, in the present invention, this accelerated cooling is performed while controlling the amount of cooling medium depending on the location to be cooled. This makes it possible to appropriately prevent distortion and bending in the asymmetrical steel section.

FIG. 1 shows a specific embodiment of a cooling device for performing accelerated cooling according to the present invention.

In this example, there are headers (1), (2), (3), (
4), and the KJ11 is arranged so that the amount of cooling medium discharged from each header can be individually controlled. With such a device, it is possible to uniformly cool the entire section by discharging a large amount of cooling medium into the thick section of the heat-treated type* (6) and a small amount into the thin section. can. Note that (5) in the figure is a table roller. In addition, the cooling medium may be air, water (depending on the thickness of the product), or both
Just use it.

Next, write down the % example.

Example 50#/■8 steel (0,1! 澾C-QJ5 澾si-L4
A 3'1Mn-(), 0201Nb) H-section steel was heat treated by the method of the present invention and normalized by the conventional method, and the mechanical properties of the product were examined.

The results are shown in the table below.

From this table, it can be seen that excellent 411 properties can be obtained by the method of the present invention.

[Brief explanation of the drawing]

Figure m1 schematically shows one embodiment of a cooling device for carrying out the method of the invention. In the figure, (1), (2), (3), (4)...
* is a header, (5) is a table roller, and (6) is a section steel. Patent applicant Nippon Kokan Co., Ltd.

Claims (1)

[Claims] In a method for manufacturing high-strength steel sections with excellent toughness, which involves hot-rolling followed by hot rolling, the steel section is heated to austenite in a continuous heat treatment furnace, and then heated to form austenite, and then porcelain while adjusting the amount of cooling medium depending on the location of the section. - A method for manufacturing high-strength shaped steel with excellent toughness due to accelerated cooling.