JP2000008124A - Production of electric resistance welded tube low in yield ratio - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for reducing the yield ratio of an electric resistance welded tube produced from a hot coil as the stock by controlling the metallic structure of the hot coil and reducing the yield ratio of the stock. SOLUTION: Using steel contg. 0.05 to 0.25% C, 0.05 to 0.40% Si and 0.50 to 2.00% Mn as fundamental components, and the balance Fe with inevitable impurities, at the time of hot rolling, the total draft at the time of finish rolling at 750 to 1000 deg.C is adjusted to 0.65< (the thickness before the finish rolling -the thickness of a product coil)÷ the thickness before the finish rolling < 0.85, and, successively, by using a hot coil in which the cooling rate on a hot run table is adjusted to 10 to 50 deg.C/sec, and the coiling temp. is adjusted to <=700 deg.C to >=400 deg.C to produce an electric resistance welded tube.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electric resistance welded steel pipe having a low yield ratio.

[0002]

2. Description of the Related Art The present invention controls the metallographic structure of a hot coil used as a material for an ERW steel pipe, thereby reducing the yield ratio of the material. It is intended to provide a method of reducing the amount.

[0003] In recent years, in line pipes for transporting gas and oil, there is an increasing demand for steel pipes having a low yield ratio in order to improve safety and reliability. In addition, some oil well pipes have an upper limit on the yield strength, and in this case, it is necessary to lower the yield ratio. For steel pipes requiring such a low yield ratio, in particular, in an electric resistance welded steel pipe manufactured by cold forming using a hot coil as a material, the yield ratio is increased by this processing. In some cases, heat treatment of the tubular body is performed. On the other hand, also in steel pipes used in the construction field, demands for steel pipes having a low yield ratio are increasing, mainly from the viewpoint of earthquake resistance.

As a method of manufacturing a steel pipe having a low yield ratio, there is Japanese Patent Application Laid-Open No. 5-1055952, entitled "Method of Manufacturing a Low Yield Ratio ERW Steel Pipe". This method is characterized by lowering the yield ratio by combining and controlling cooling during hot rolling and low-temperature winding (300 ° C. or lower) to generate and retain island martensite and retained austenite. In the method of performing low-temperature winding such as the present method, there is a possibility that a size that can be manufactured is restricted due to the capability of hot rolling equipment, particularly cooling and winding equipment. In other words, an increase in the thickness may result in something that cannot be manufactured.

[0005]

An object of the present invention is to limit the total rolling reduction during finish rolling in hot rolling, and to make the metal structure of the hot coil an Ashkiller ferrite structure in combination with the subsequent cooling rate. In this case, the present invention relates to a manufacturing method for reducing the yield ratio. In this case, low-temperature winding or the like is not required, and unnecessarily being restricted by the size of the hot rolling equipment, the electric resistance having a low yield ratio can be obtained. It can supply steel pipe material.

[0006]

The gist of the present invention is as follows: (1) C = 0.05 to 0.25% Si = 0.05 to 0.40% Mn = 0.50 to 2.00% In the hot rolling, a steel consisting of Fe and unavoidable impurities as a component is subjected to a total rolling reduction in finish rolling at 750 ° C. to 1000 ° C .: 0.65 <(thickness before finish rolling−thickness of product coil) ÷ The thickness before finish rolling was set to <0.85, and then the cooling rate on the hot run table was set to 1
0 ° C / sec or more and 50 ° C / sec or less, and the winding temperature is 700
A method for producing an electric resistance welded steel pipe having a low yield ratio, comprising producing an electric resistance welded steel pipe using a hot coil at a temperature of 400 ° C. or less and 400 ° C. or more. And (2) C = 0.05 to 0.25% Si = 0.05 to 0.40% Mn = 0.50 to 2.00% as a basic component, and Nb = 0.01 to 0.10% V = 0.01 to 0.10% Mo = 0.10 to 1.00% Ti = 0.01 to 0.05% Cu = 0.10 to 0.50% Ni = 0.10 to 1.00% In hot rolling, a steel containing one or two or more of the following, and the balance consisting of Fe and unavoidable impurities, is subjected to a total reduction of 0.65 <(before finish rolling) Thickness-product coil thickness) ÷ Thickness before finish rolling <0.85, and then the cooling rate on the hot run table is set to 1
0 ° C / sec or more and 50 ° C / sec or less, and the winding temperature is 700
A method for producing an electric resistance welded steel pipe having a low yield ratio, comprising producing an electric resistance welded steel pipe using a hot coil at a temperature of 400 ° C. or less and 400 ° C. or more.

In the present invention, the total rolling reduction in finish rolling in hot rolling is increased (the thickness ratio before finishing is 0.65 or more,
0.85 or less), and by combining a cooling rate and a winding temperature, an Ashkiller ferrite structure having a low yield ratio is generated, thereby reducing the yield ratio of an electric resistance welded steel pipe made of this material. .

[0008]

Next, the present invention will be described in detail. First, the components of the material will be described. C is an element necessary for securing necessary strength, and is set to 0.05% or more. However, if the C content exceeds 0.25%, the toughness, ductility and weldability are significantly reduced, so the upper limit was made 0.25%. In addition to the element necessary for deoxidation, Si is an important element for securing the strength of steel, and is set to 0.05% or more. Defects easily occur, and the upper limit is set to 0.40%. Mn is also important as an element for securing necessary strength similarly to C, and the lower limit is 0.50%. The upper limit was set to 2.00% from the viewpoint of workability. The above components are used as basic elements, but if necessary, that is, necessary strength, toughness,
It may be effective to add one or more of the following components from the viewpoint of corrosion resistance and the like.

Nb has the effect of strengthening the material itself and improving the toughness by making the structure finer. To obtain the effect, it is necessary to add 0.01% or more, and even if it exceeds 0.10%, improvement of the effect cannot be expected. V is also an element effective for strengthening, and its effect is exhibited in the range of 0.01% to 0.10%. Mo is effective not only for strengthening, but also for suppressing softening of the heat-affected zone when welding a steel pipe, and is set to 0.10% or more. On the other hand, if it exceeds 1.00%, cracks and the like in the slab are liable to occur, and the upper limit is 1.
00%. Ti is an element effective in refining the metal structure of the material, and is effective at 0.01% or more. Also, 0.0
If it exceeds 5%, the ductility of the material is reduced, so the upper limit is made 0.05%. Cu is effective in improving the corrosion resistance of the steel pipe, and is set to 0.10% or more and 0.50% or less.
Ni is effective in improving the toughness of the steel pipe at 0.10% or more, but the upper limit is 1.00% because Ni is an expensive element. In addition, elements such as Al, Ca, and Zr do not adversely affect the object of the present invention, and there is no problem in adding them.

Next, the conditions for the hot rolling will be described.
First, the finish rolling temperature is 750 ° C. or more, 100
0 ° C. or less. The reason for this is that if the temperature is lower than 750 ° C., a two-phase region is formed, and toughness and ductility deteriorate. On the other hand, 10
Even when the temperature exceeds 00 ° C., the toughness and ductility similarly deteriorate significantly. As an important condition of the present invention, the total rolling reduction in finish rolling is "the thickness ratio before finish rolling".
, So that it is not less than 0.65 and not more than 0.85. By setting the rolling reduction of the finish rolling to “0.65 or more of the thickness ratio before finishing rolling”, a large number of strains are given in the austenite region in the rolling stage, and the subsequent cooling and winding produce Ash Killer ferrite. Condition. On the other hand, 0.
If it exceeds 85%, there is a high possibility that problems such as cracks in rolling will occur, and the upper limit is the “thickness ratio before finish rolling”.
0.85 or less. However, in order to stably reduce the yield ratio, 0.75 to 0.80 is preferable. In the subsequent cooling, a cooling rate of 10 ° C./sec or more is required in order to prevent the ferrite structure from being coarsened to increase the yield ratio, and if it exceeds 50 ° C./sec, the strength becomes too high.
The upper limit was set to 50 ° C./sec because toughness and ductility deteriorated. In addition, the winding temperature is required to be 700 ° C. or less in order to prevent the generated ferrite structure from being coarsened. When cooled to less than 400 ° C., the strength becomes too high, and the toughness and ductility are deteriorated. did.

An electric resistance welded steel pipe is manufactured using the hot coil manufactured under the above hot rolling conditions as a raw material.
It depends on the target yield ratio, and it is desirable that the cold forming distortion during the production of the ERW steel pipe be as small as possible in order to minimize work hardening. For example, in the sizing performed at the final stage of molding, the minimum processing amount that can secure the required outer diameter accuracy is preferably 1.0% or less in terms of the outer diameter ratio before and after molding.

[0012]

EXAMPLES Table 1 shows examples of the present invention, and Table 2 shows comparative examples. The components of the steel and the hot rolling conditions include the finish rolling temperature, the total finish reduction, the cooling rate, the winding temperature, and the yield ratio (yield point / yield point /
In each case, the yield ratio is lower than that of the comparative example described as the prior art, and good results are obtained.

[0013]

[Table 1]

[0014]

[Table 2]

[0015]

According to the present invention, in producing an ERW steel pipe having a low yield ratio, the production of the material is performed by focusing on the total rolling reduction in finish rolling, and combining the subsequent cooling and winding conditions. A material having a low yield ratio is provided without performing low-temperature winding as described above, whereby an ERW steel pipe having a low yield ratio is less likely to be subjected to size restrictions and the like. That made it possible to
The effect is extremely large.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22C 38/04 C22C 38/04 38/14 38/14 (72) Inventor Yoji Yamamoto Tokai-cho, Tokai City, Aichi Prefecture 5-3 Nippon Steel Corporation Nagoya Works (72) Inventor Motofumi Koyaba 5-3 Tokai-cho, Tokai City, Aichi Prefecture F-term in Nagoya Works, Nippon Steel Corporation 4E002 AA07 AD04 BC07 BD03 BD07 CB01 4K032 AA04 AA05 AA14 AA16 AA19 AA22 AA23 AA31 AA35 AA36 BA03 CB02 CC03 CC04 CD03 CE01 CE02

Claims (2)

[Claims] 1. A steel comprising C = 0.05 to 0.25% Si = 0.05 to 0.40% Mn = 0.50 to 2.00% as a basic component, with the balance being Fe and unavoidable impurities In hot rolling, the total reduction during finish rolling at 750 ° C. to 1000 ° C. is 0.65 <(thickness before finish rolling−thickness of product coil) ÷ thickness before finish rolling <0.85. Set the cooling rate on the hot run table to 1
0 ° C / sec or more and 50 ° C / sec or less, and the winding temperature is 700
A method for producing an electric resistance welded steel pipe having a low yield ratio, comprising producing an electric resistance welded steel pipe using a hot coil at a temperature of 400 ° C. or less and 400 ° C. or more. 2. C = 0.05 to 0.25% Si = 0.05 to 0.40% Mn = 0.50 to 2.00% as a basic component, Nb = 0.01 to 0.10% V = 0.01 to 0.10% Mo = 0.10 to 1.00% Ti = 0.01 to 0.05% Cu = 0.10 to 0.50% Ni = 0.10 to 1.00% At the time of hot rolling at a temperature of 750 ° C., containing one or two or more kinds, and the balance consisting of Fe and unavoidable impurities.
The total reduction during finish rolling at ~ 1000 ° C is 0.65 <(thickness before finish rolling-thickness of product coil) ÷ thickness before finish rolling <0.85, and then the cooling rate on the hot run table is 1
0 ° C / sec or more and 50 ° C / sec or less, and the winding temperature is 700
A method for producing an electric resistance welded steel pipe having a low yield ratio, comprising producing an electric resistance welded steel pipe using a hot coil at a temperature of 400 ° C. or less and 400 ° C. or more.