JP2006233323A - Method for manufacturing square column - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a square column having a tensile strength of a 50 kilogram-force grade and a yield ratio of 80% or lower, more inexpensively than ever. <P>SOLUTION: The manufacturing method is an improved method on a process having the steps of: unwinding a steel strip which has been manufactured by hot-rolling a steel slab and winding it up into a coil form; forming it in a cylindrical shape; jointing the side ends to form a pipe with a circular cross section; and then forming it into a square column having a square cross section through such a roll provided with a square hole die. The steel slab comprises, 0.12-0.18% C, 0.30-0.45% Si, 1.25-1.50% Mn, not more than 0.030% P, not more than 0.015% S, not more than 0.005-0.011% Ti, by mass% and the balance Fe with unavoidable impurity elements. The manufacturing method comprises the steps of: hot-rolling the steel slab with a rolling reduction of 50 to 60% and at a winding up temperature of 570 to 620°C; subsequently, forming the pipe with the circular cross section; then corner-forming it into a square column; heating the square column; and cooling it in a furnace during a temperature between 600 and 300°C so as to precipitate dissolved C. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a rectangular column, and more particularly to a technique for manufacturing a rectangular column having a tensile strength of 50 kilo (K) class and a yield ratio of 80% or less by roll forming.

  Steel pipes having a square cross-sectional shape (hereinafter referred to as square columns) are not only used as general structural materials, but have recently been actively used as building / building materials (see Table 1).

  Some of these square columns are called roll columns and are manufactured using a manufacturing process of a so-called “electrically welded steel pipe”. That is, as shown in FIG. 5, a steel plate (or steel strip 1) as a raw material is formed into a cylindrical shape with a forming roll 3, and both ends in the width direction of the butted steel plates are heated with an induction coil 4 and pressed with a squeeze roll 5 to join them. And it heat-processes (annealing etc.) as needed, and makes the tubular body 8 with a circular cross section. An ERW steel pipe having a circular cross section is used as a product by squeezing the pipe body 8 to a target size (outer diameter, wall thickness, etc.) with a drawing mill 10 as it is. Is rolled with a drawing mill 9 equipped with a square hole roll to make the cross section square.

  Also, it is called a press column separately from the roll column, and the width direction of the steel plate that is the material is processed by a press machine so that the cross section becomes a square shape, and the corners that are manufactured by welding the width direction both ends of the abutted steel plates. There is also a column.

  By the way, as is apparent from Table 1, there is currently no roll column having a tensile strength of 50 kg and a yield ratio of 80% or less, and there is no standard. For this reason, press columns are currently used for applications that require a tensile strength of 50 kg and a yield ratio of 80% or less.

  However, the roll column manufacturing method is manufactured by continuous molding as is apparent from FIG. 5, whereas the press column requires a long time for processing, so the productivity is low, and the manufacturing cost is lower than that of the roll column. It is expensive and the selling price becomes expensive.

  In view of such circumstances, an object of the present invention is to provide a method for manufacturing a square column that can manufacture a square column having a tensile strength of 50 kg and a yield ratio of 80% or less by roll forming at a lower cost than conventional ones. .

  The inventor has intensively studied to achieve the above object, and the results have been embodied in the present invention.

  That is, the present invention comprises a steel tube obtained by hot rolling a steel slab and coiling it into a coil shape, rewinding it into a cylindrical shape, joining it into a tubular body having a circular cross section, and then providing a square hole type. In the manufacturing method of the square column formed into a square cross section with a roll, the components of the steel slab are as follows: C: 0.12-0.18 mass%, Si: 0.30-0.45 mass%, Mn: 1 .25 to 1.50 mass%, P: 0.030 mass% or less, S: 0.015 mass% or less, Ti: 0.005 to 0.011 mass% or less, the balance being Fe and inevitable impurity elements, the steel The slab is subjected to the hot rolling at a reduction ratio of 50 to 60% and the coil winding temperature of the obtained steel strip at 570 to 620 ° C., and subsequently formed into a tubular body having a circular cross section, and then formed into a square column. Then, after heating the square column, between 600-300 ° C. so that solid solution C is precipitated. Is a manufacturing method of the corner column, characterized in that the cold.

  According to the present invention, a rectangular column having a tensile strength of 50 kg and a yield ratio of 80% or less can be stably manufactured by roll forming. As a result, a press column having a tensile strength of 50 kg and a yield ratio of 80% or less can be replaced with a cheaper roll column, and the manufacturing cost of buildings and structures can be reduced.

  Hereinafter, the best embodiment of the present invention will be described based on the background of the invention.

  The inventor decided to manufacture the square column not by press molding but by roll molding. In other words, the present invention includes a square hole mold after a steel strip obtained by hot rolling a steel slab and winding it into a coil shape is rewound into a cylindrical shape and joined to form a tubular body having a circular cross section. The manufacturing method of a square column formed into a square cross section with a roll is improved.

First, the inventors diligently studied what kind of steel strip is suitable for the material, assuming that the target characteristics of the square column are the tensile strength of 50 kg and the yield ratio of 80% or less. As a result, it was judged that it was difficult to achieve a tensile strength of 50 kg only by cold roll forming, and it was decided to heat-treat the square column after roll forming. Based on this judgment, the chemical composition of the raw material (steel slab), including the relationship with the heat treatment conditions of the square column and the resulting metal structure, is established as shown in FIG. Based on the following decision.
C: 0.12-0.18 mass%
C is an element effective for ensuring strength economically. However, if the content is too large, the ductility and impact properties of the steel pipe are deteriorated, so the upper limit was made 0.18% by mass. Moreover, since weldability will be impaired when it is going to ensure intensity | strength only by C, C is restrict | limited to 0.18 mass% and elongation and impact property are supplemented by addition of the following Si and Mn.
Si: 0.30 to 0.45 mass% and Mn: 1.25 to 1.50 mass%
In the present invention, the achievement of tensile strength (TS): 490 MPa is adjusted by the contents of Si and Mn of the material, and these components are set in the above range. The reason is that if Si is less than 0.30% by mass, the strength of the steel pipe is ensured, and if it exceeds 0.45% by mass, the impact property is deteriorated and the target cannot be achieved. Further, if Mn is less than 1.25% by mass, the strength of the steel pipe is ensured, and if it exceeds 1.50% by mass, the characteristic change of the steel may increase during welding. In addition, suitable content of Si and Mn is 0.35 mass% and 1.35 mass%, respectively.
P: 0.030% by mass or less P is an element that easily causes segregation in a steel material when molten steel is solidified by continuous casting or the like, and causes cracking during processing or welding. From this viewpoint, in the present invention, the content is 0.030% by mass or less.
S: 0.015 mass% or less S forms S inclusions in the steel and affects the anisotropy of the steel material. That is, since there is an influence on the drawability and impact property of the steel pipe, the content is set to 0.015 mass% or less from that viewpoint.
Ti: 0.005-0.011 mass%
Ti is added in order to improve the toughness and crack resistance of a portion (also referred to as a seam portion) in which steel strips are formed into a cylindrical shape and both end portions in the width direction are joined by welding or the like. If it is less than 0.005% by mass, there is no effect of addition, and if it exceeds 0.011% by mass, the effect is saturated, so it is limited to the above range.

  As an inevitable impurity element, it is desirable that Nb and V are hardly contained in particular so that it does not precipitate as a secondary precipitation element in the metal structure after the heat treatment of the square column.

  In the present invention, the method for producing a steel slab having such a component is not limited at all, and a steel slab produced by a normal steel making process is sufficient.

  Next, the inventor examined the process of hot-rolling the steel slab of the said component into a steel strip. And in order to make the yield ratio of the square column to be 0.8 or less, it has been found that it is sufficient to pay attention to the hot rolling as long as the crystal grains of the obtained steel strip are coarse so as not to deteriorate the impact characteristics. . Further, by examining specific measures for doing so and rolling a steel slab heated to a normal heating temperature of 1150 to 1250 ° C. at a relatively low reduction of about 50 to 60%, it is obtained. It was found that the yield ratio of the obtained steel strip could be 0.65 or less, and the yield ratio of the square column as the final product was 0.8 or less (see FIG. 2). In addition, it is known that the steel strip temperature (called coil coiling temperature) when winding the steel strip obtained by hot rolling in a coil shape should be as high as possible within the range of 570 to 620 ° C. (See FIG. 3). This is because no influence on the yield ratio of temperature was observed at the coil winding temperature in this range.

  Subsequently, the inventor studied the process of forming the steel strip 1 into a pipe by using the manufacturing process of the electric resistance steel pipe shown in FIG. As a result, until the tubular body 8 has a circular cross section, the conventional pipe forming conditions are sufficient, but it is necessary to suppress the occurrence of processing strain as much as possible during corner forming and to prevent the yield ratio from increasing. It was.

As described above, the tubular body formed into the square cross section is subsequently heat-treated. As a result of examining the heat treatment, as shown in FIG. 1, it was found that the yield ratio of the square column is minimized when the heating temperature during the heat treatment is close to the coil winding temperature (for example, 570 to 610 ° C.). . This is because, within this temperature range, the yield ratio of the steel strip when it is wound into a coil shape can be obtained simply by recovering the processing strain at the time of square forming.
However, in this case, the cooling after heating is preferably performed in the furnace at 600 to 300 ° C. so that solute C is precipitated. This is to suppress an increase in the upper yield point of the corner column.

  As described above, the present invention includes the development of a steel slab as a raw material, the hot rolling process of the steel slab, and the improvement of the processing conditions of the pipe forming process using the obtained steel strip. By subjecting the formed tube to heat treatment under a certain condition, a roll column having a tensile strength of 50 kg and a yield ratio of 80% or less is manufactured. As a result, a square column that can replace the conventional expensive press column can be supplied inexpensively and stably.

  In the steelmaking and continuous casting processes, steel slabs shown in Table 2 were produced under normal operating conditions. By applying the method according to the present invention to this steel slab, a square column called a “roll column” was manufactured. As for the size of the square column, the wall thickness is 12 mm and 19 mm for both the outer diameter of 300 mm and 350 mm.

  First, the steel slab was heated to 1100 ° C. in a heating furnace, rolled into a steel strip at a roll reduction rate of 55% in a hot rolling process, and wound at a coil winding temperature of 570 ° C. The coiled steel strip 1 is rewound by an uncoiler 2 and then continuously supplied to a forming roll 3 and formed into a cylindrical shape. Then, both ends in the width direction of the abutted steel strip are heated by an induction coil 4 and squeezed by a squeeze roll 5. Pressed and joined. Then, heat treatment (using the post annealer 6 and the water injection nozzle 11) was performed under normal conditions (for example, 950 ° C.) to obtain a tubular body 8 having a circular cross section. Subsequently, the tubular body 8 was supplied to a roll 9 having a square hole shape arranged in multiple stages, and rolled with a drawing amount of 3.1% to make the cross section square. Thereafter, the obtained tube (square column) having a square cross section was sent to a heat treatment furnace (not shown), heated to 600 ° C., cooled to 300 ° C. in the furnace, and then air-cooled.

  In the manufactured square column, a sample representing each lot was extracted, and a tensile test was performed on the sample. The results are collectively shown in Table 3. From Table 3, it is clear that all the square columns manufactured by the method according to the present invention have a target tensile strength of 50 kg and a yield ratio of 80%.

It is a figure which shows the relationship between the heat processing temperature of a square column manufactured by roll forming, a yield point (YS), tensile strength (TS), and a yield ratio (YR). It is a figure which shows the relationship between the coil winding temperature of the steel strip obtained by hot rolling, and the yield point (YS), tensile strength (TS), and yield ratio (YR) of this steel strip. It is a figure which shows the relationship between the rolling reduction of the steel slab in hot rolling, and the yield point (YS), tensile strength (TS), and yield ratio (YR) of the obtained steel strip. It is a figure which shows the thought process which determines the component of the steel slab utilized by this invention. It is a schematic diagram which shows the manufacturing process of an electric resistance steel pipe and a square column.

Explanation of symbols

1 Steel strip (coiled steel strip)
DESCRIPTION OF SYMBOLS 2 Uncoiler 3 Forming roll 4 Inductive coil 5 Squeeze roll 6 Post-anilar 7 Bite 8 Tubing 9 Drawing rolling machine with square hole type 10 Drawing rolling machine 11 Water injection nozzle 12 Cutting machine

Claims (1)

A steel strip that has been rolled into a coil by hot-rolling a steel slab is unwound and formed into a cylindrical shape and joined to form a tubular body having a circular cross section. In the manufacturing method of the square column to be molded,
Components of the steel slab are as follows: C: 0.12-0.18 mass%, Si: 0.30-0.45 mass%, Mn: 1.25-1.50 mass%, P: 0.030 mass% % Or less, S: 0.015% by mass or less, Ti: 0.005 to 0.011% by mass or less, the balance being Fe and inevitable impurity elements, and a steel strip obtained by reducing the steel slab by 50 to 60% The coiled coiling temperature of 570 to 620 ° C. is then hot-rolled. Subsequently, the tube is formed into a circular cross-section tube, formed into a square column, heated, then solidified. A method for producing a square column, characterized in that the furnace is cooled between 600 and 300 ° C. so that molten C is deposited.

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