JPH0835012A - High strength, high toughness and method of manufacturing ERW steel pipe excellent in corrosion resistance - Google Patents

Abstract

(57) [Summary] [Purpose] To obtain an electric resistance welded steel pipe having high strength and excellent low temperature toughness and corrosion resistance. [Constitution] C: 0.04 to 0.09%, Si: 0.10.
.About.0.30%, Mn: 1.00 to 1.50%, P: 0.
025% or less, S: 0.005% or less, Cu: 0.20
.About.0.50%, Ni: 0.10 to 0.50% as a basic component, Ti: 0.010 to 0.060%, Nb: 0.0
10 to 0.080%, Mo: 0.050 to 0.350%
1 to 1300 ° C. of a steel slab containing one or more of the above and the balance consisting of Fe and unavoidable impurities.
After hot-rolling, after hot rolling at 750 to 800 ° C. or lower, until the coiling is performed at a cooling rate of 5 to 20 ° C./sec, and the cooling ratio of the upper surface to the lower surface of the steel strip is 0.8 to
After water cooling at a ratio of 1.3, the film is wound at 400 to 500 ° C., and after pipe manufacturing, no heat treatment is applied to parts other than the electric resistance welded portion. [Effect] It is possible to stably manufacture an electric resistance welded steel pipe having high strength and excellent low temperature toughness and corrosion resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an electric resistance welded steel pipe having high strength and excellent low temperature toughness and corrosion resistance.

[0002]

2. Description of the Related Art In recent years, crude oil wells and natural gas wells are deep oil fields that have not been neglected in the past due to the surge in crude oil prices and the depletion of oil resources expected in the near future. The development of the sour gas field, which had been abandoned once, is being actively conducted on a global scale. Such oil wells and gas wells are generally extremely deep, and the atmosphere thereof is at a low temperature or an extremely harsh environment containing carbon dioxide, hydrogen sulfide, chlorine ions and the like.
Oil well pipes used for mining such oil and gas wells
A material having high strength and having both corrosion resistance and low temperature toughness is required. Oil well pipes used for the above-mentioned applications are produced by heat-treating the entire pipe after producing hot coils conventionally produced by hot rolling. There were drawbacks such as not being expected to be effective.

C: 0.07% or less, Mn: 1.0
0 to 1.70%, Si: 0.3% or less, P: 0.03%
Hereinafter, S: 0.005% or less, Ti: 0.01 to 0.0
3%, Mn / C ≧ 12, Nb: 0.15% or less, V:
0.07% or less, so that remains by adjusting deoxidation
l. Steel consisting of Al, balance Fe and unavoidable impurities is hot-rolled, wound at 600 ° C. or lower, and then electric resistance welded (JP-A-59-197519), C: 0.
01-0.14%, Si: 0.5% or less, Mn: 1.6
~ 2.0%, V: 0.001 to 0.050%, Ti:
0.04% or less, Nb: 0.001 to 0.050%,
P: 0.03% or less, S: 0.008% or less, N: 0.
ERW welding was performed using a material steel plate of 010% or less and the balance Fe and unavoidable impurities.
A method of performing stress relief treatment by heating at 0 to 1050 ° C. for 5 seconds or more, quenching at a temperature of 750 to 950 ° C. at 30 ° C./sec and 150 ° C./sec, and then heating at 400 to 730 ° C. for less than 1 minute (JP-A-60). Japanese Patent Laid-Open No. -100628) has been proposed.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The method disclosed in Japanese Patent No. 7519 limits the coiling temperature after hot rolling to 600 ° C or lower, but the grain refining effect due to coiling at a relatively low temperature of 400 to 500 ° C cannot be expected. In addition, it is disadvantageous in terms of the cost of the alloy component to be added, and no consideration has been given to the water-cooling cooling rate until hot rolling and subsequent winding, and deterioration of corrosion resistance due to the formation of structure such as martensite, coil There is a problem that the corrosion resistance in the plate thickness direction becomes unstable due to uneven cooling of the upper and lower surfaces. In addition, JP-A-60-10062
In the method disclosed in Japanese Patent Publication No. 8, since the definition of C that deteriorates toughness is 0.01 to 0.14 wt%, 0.10 wt%.
If it exceeds 1.0, the low temperature toughness may deteriorate, and since the coiling temperature of the coil after hot rolling has not been examined, 400-500 ° C is used in the production of high strength electric resistance welded steel pipe.
In addition to the fact that the effect of refining the crystal grains by winding at a relatively low temperature cannot be expected, the heat treatment cost increases.

In order to solve the above-mentioned drawbacks, an object of the present invention is to perform hot rolling by control rolling of a steel slab consisting of components having low C, high Mn, Cu, and Ni as base materials, and after tube making, electric It is an object of the present invention to provide a method for producing an electric resistance welded steel pipe having high strength, excellent low temperature toughness and excellent corrosion resistance, without heat treatment except for the sewn welded portion.

[0006]

[Means for Solving the Problems] The present inventors have conducted various test studies in order to achieve the above object. As a result, low C,
When a steel slab composed of high Mn, Cu, and Ni-based components is hot-rolled and then water-cooled, the upper and lower surfaces of the steel strip are cooled substantially uniformly to stabilize the corrosion resistance in each part in the plate thickness direction. No heat treatment is applied to the parts other than the electric resistance welded part after the pipe.
By suppressing the formation of structures such as martensite by limiting the Rockwell hardness C scale (hereinafter referred to as HRC) specified in Z2245 to 23 or less, an electric resistance welded steel pipe having high strength and excellent low temperature toughness and corrosion resistance can be obtained. The present invention has been reached through the investigation.

That is, according to the present invention, C: 0.04 to 0.
09%, Si: 0.10 to 0.30%, Mn: 1.00
~ 1.50%, P: 0.025% or less, S: 0.005
% Or less, Cu: 0.20 to 0.50%, Ni: 0.10.
.About.0.50% as a basic component, and Ti: 0.010 to 0.
060%, Nb: 0.010 to 0.080%, Mo:
A steel slab containing one or more of 0.050 to 0.350% and the balance consisting of Fe and unavoidable impurities is heated to 1150 to 1300 ° C, and then 750 to 800 ° C.
After performing hot rolling below, the time until winding is 5 to 2
After cooling with water at a cooling rate of 0 ° C./sec and a cooling ratio of the upper surface to the lower surface of the steel strip of 0.8 to 1.3, 4
A method for producing an electric resistance welded steel pipe excellent in high strength, high toughness and corrosion resistance, which is characterized in that after the pipe is wound at 00 to 500 ° C and the pipe is manufactured, no heat treatment is applied to parts other than the electric resistance welded portion.

[0008]

The reason for limiting the chemical composition of the raw material in the present invention will be described in detail. C is an element necessary to obtain the required tensile strength, and if it is less than 0.04, its effect is not sufficient, and if it exceeds 0.09%, the corrosion resistance and low temperature toughness deteriorate with the increase in hardness. Therefore, 0.04 to 0.0
It was set to 9%. Si is an important element for ensuring the necessary tensile strength, and if it is less than 0.10%, its effect is not sufficient,
If it exceeds 0.30%, a penetrator, which is a welding defect, is likely to occur, so the content was made 0.10 to 0.30%. M
n must be 1.00% or more to obtain a high tensile strength and a fine ferrite structure of crystal grains, but if it exceeds 1.50%, a penetrator, which is a welding defect, is likely to occur. ˜1.50%. Since P has a negative effect on toughness due to segregation, it was set to 0.025% or less. S is also set to 0.005% or less because MnS is elongated by rolling and acts in the direction of deterioration of toughness.

Cu is an element necessary for improving the corrosion resistance,
If it is less than 0.20%, the effect is not sufficient, and 0.5
If it exceeds 0%, Cu is concentrated in the surface layer of the slab to cause cracking during heating, so the content was set to 0.20 to 0.50%.
Ni has the effect of preventing cracks from occurring during heating due to Cu concentrated in the surface layer of the steel slab, but if it is less than 0.10%, the effect is not sufficient, and if it exceeds 0.50%, the effect is Not only will it saturate, but it will also increase costs,
It was set to 0.10 to 0.50%. Nb, Ti, and Mo are indispensable for obtaining high tensile strength, but Nb is 0.
Less than 010%, Ti less than 0.010%, Mo 0.0
If it is less than 5%, the effect is not sufficient, and the Nb content is 0.
If the content exceeds 080%, 0.060% for Ti and 0.35% for Mo, the hardness increases more than necessary, so Nb is 0.01
0 to 0.080%, Ti is 0.010 to 0.060%,
Mo was set to 0.05 to 0.35%, and one or more of these elements were included.

Next, the limitation of conditions for producing hot coils from steel slabs will be described. The heating temperature of the billet is 1150
The temperature of 1300 ° C to 1300 ° C is required to be heated to 1150 ° C or higher from the viewpoint of sufficient solid solution of the additional element.
This is because if the temperature exceeds 300 ° C., the crystal grains become coarse and the toughness deteriorates. More preferably, 1200-12
The area is 80 ° C. If the temperature of hot rolling is less than 700 ° C., the temperature is too low to make rolling difficult, and at a relatively low temperature (depending on the component system, a two-phase region of ferrite and austenite) from the viewpoint of improving toughness due to grain refinement. The temperature was set to 800 ° C or lower. Regarding the cooling conditions from the end of rolling to the winding, water cooling is usually performed, but if the cooling rates of the upper and lower surfaces of the steel strip are different, hardness difference occurs in the plate thickness direction. It was set to 1.3. If the cooling rate is less than 5 ° C / sec, the crystal grains become coarse and high strength cannot be obtained. On the contrary, if the cooling rate exceeds 20 ° C / sec, a bainite structure or a partial martensite structure occurs,
It is not preferable from the viewpoint of corrosion resistance. Therefore 5 ~ 20 ℃ / s
It is necessary to uniformly cool the front and back surfaces of the coil at a cooling rate of ec.

The coiling temperature is set to 500 ° C. or less from the viewpoint of producing hot ferrite having high strength and excellent low temperature toughness by producing fine ferrite by controlled cooling after completion of hot rolling. However, since the hardness increases as the coiling temperature is lowered, the temperature is limited to 400 ° C or higher. The cooling ratio of the upper surface to the lower surface of the steel strip is 0.8 to
If it deviates from the range of 1.3, the hardness of the surface with large cooling increases.

In the present invention, as described above, by limiting the chemical composition of the material, the conditions of hot rolling, the cooling conditions from the end of rolling to the winding and the winding temperature, the electric resistance welding after pipe making by electric resistance welding is performed. It is possible to stably manufacture an electric resistance welded steel pipe excellent in high strength, low temperature toughness, and corrosion resistance without performing heat treatment on a portion other than the welded portion.

[0013]

【Example】

Example 1 The chemical composition shown in Table 1 has a thickness of 210 mm and a width of 700 to 19
A test piece was cut out from a hot coil obtained by hot rolling a 50 mm steel piece under the conditions shown in Table 2 to a plate thickness of 11 mm.
The yield point (YS) and tensile strength (TS) were measured according to JIS Z2241 in accordance with the tensile test method for metallic materials.
The absorbed energy in the Charpy impact test was measured according to the metal material impact test method specified in 242. Also, 0.5
H ₂ S to a 5% NaCl aqueous solution added with ₃ % CH ₃ COOH
The Sc value (critical stress) in a shell type SSCC (sulfide stress corrosion cracking) test in which a test piece is immersed in a saturated solution (NACE bath) for 200 hours was measured. The results are shown in Table 2. The toughness is the test temperature of -20 ° C.
The evaluation was made by the absorbed energy in the Charpy impact test in (Test piece: 2 mm V notch 10 mm × 10 mm).
The relationship between the hardness and the tensile strength (TS) of the test result is shown in FIG. Further, the hardness and Sc value (corrosion resistance) in Table 2 above
The relationship of is shown in FIG.

[0014]

[Table 1]

[0015]

[Table 2]

As shown in Table 2, in the case of the examples of the present invention satisfying the conditions of the present invention, an electric resistance welded steel pipe having high strength and excellent in low temperature toughness and corrosion resistance can be obtained. On the other hand, in the comparative example in which any of the conditions of the present invention is deviated, any of the characteristic values is deviated. Further, as shown in FIG. 1, TS = L80 class of American Petroleum Institute (API) standard =
When the HRC is set to 23 or less from the viewpoint of corrosion resistance and 655 N / mm ² (95 KSI) or more, it shows that the management range of TS is 655 to 750 N / mm ² . Further, as shown in FIG. 2, the Sc value decreases as the hardness increases, and the corrosion resistance deteriorates.

Example 2 Winding after water-cooling by changing the cooling ratio of the upper surface to the lower surface of the steel strip in the range of 0.3 to 3.0 between the hot rolling and the winding up in Example 1. The relationship between the water cooling ratio of the upper and lower surfaces and Rockwell hardness (HRC) was investigated. The result is shown in FIG. As shown in FIG. 3, in the example of the present invention in which the cooling ratio of the upper surface to the lower surface is 0.8 to 1.3, which is almost uniform, the hardness difference in the plate thickness direction is small and a uniform structure is obtained in the plate thickness direction. Instability of corrosion resistance can be avoided. On the other hand, in the comparative example in which the cooling ratio of the upper surface to the lower surface is less than 0.8 or exceeds 1.3, even if the hardness difference between the upper and lower surfaces and the central portion of the plate thickness is large and the hardness of the upper and lower one surfaces is HRC23 or less, The hardness of the other surface exceeds HRC23 and has a non-uniform structure in the plate thickness direction.

[0018]

As described above, according to the method of the present invention, an electric resistance welded steel pipe having high strength, excellent low temperature toughness and corrosion resistance can be stably produced.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between tensile strength (TS) and Rockwell hardness (HRC) in Example 1.

FIG. 2 Rockwell hardness (HRC) in Example 1
It is a graph which shows the relationship between Sc value (corrosion resistance) and.

FIG. 3 is a graph showing the relationship between water cooling ratio of upper and lower surfaces and Rockwell hardness (HRC) in Example 2.

Claims (1)

[Claims] 1. C: 0.04 to 0.09%, Si: 0.
10 to 0.30%, Mn: 1.00 to 1.50%, P:
0.025% or less, S: 0.005% or less, Cu: 0.
20 to 0.50%, Ni: 0.10 to 0.50% as a basic component, Ti: 0.010 to 0.060%, Nb:
0.010 to 0.080%, Mo: 0.050 to 0.3
One or more of 50% is contained, and the balance is Fe
And a steel slab consisting of inevitable impurities, 1150 to 13
After heating to 00 ° C., hot rolling is performed at 750 to 800 ° C. or lower, and then a winding rate of 5 to 20 ° C./sec is used until winding, and a cooling ratio of the upper surface to the lower surface of the steel strip is 0.
ERW with high strength, high toughness and excellent corrosion resistance, characterized in that it is water-cooled at a rate of 8 to 1.3, wound at 400 to 500 ° C., and after pipe making, no heat treatment is applied to parts other than the electric resistance welded portion. Steel pipe manufacturing method.