JP2002155345A - Highly corrosion resistant steel tube having excellent formability and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly corrosion resistant steel tube which has excellent formability in hydroforming or the like by limiting the characteristic value of the material, and to provide its production method. SOLUTION: This highly corrosion resistant steel tube which has excellent formability has a composition containing, by mass, 0.001 to 0.3% C, 0.001 to 0.2% N, 0.01 to 2% Si, 0.01 to 5% Mn and 5 to 30% Cr, and the balance iron with inevitable impurities. Either or both of that the average of the X-ray random intensity ratios in the 110}<110> to 111}<110> orientation groups in the sheet face at a sheet thickness of 1/2 in the steel sheet is >=2.0 and that the X-ray random intensity ratio in 110}<110> in the sheet face at a sheet thickness of 1/2 in the steel sheet is >=3.0 are satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-corrosion-resistant steel pipe which is used for, for example, undercarriage of automobiles, members, and the like, and particularly to a highly corrosion-resistant steel pipe excellent in formability, such as hydroform, and a method for producing the same.

[0002]

2. Description of the Related Art With the need to reduce the weight of automobiles, steel sheets are required to have higher strength and higher corrosion resistance. It is possible to reduce the thickness of the sheet by achieving high strength and high corrosion resistance. Recently, attempts have been made to form a complex-shaped portion from a raw steel plate or a steel pipe by using a hydroforming method. This is aimed at reducing the number of parts and reducing the number of welding flanges in response to the need for lighter and lower cost automobiles. As described above, if a new molding method such as hydroform (see Japanese Patent Application Laid-Open No. H10-175026) is actually adopted, great merits such as cost reduction and design flexibility are expected. .

In order to fully utilize the merits of such hydroform molding, materials suitable for these new molding methods are required. For example, as shown in the 50th Lecture Meeting on Plastic Working (1999, p. 447), the influence of the r value on hydroform molding is shown. However, the analysis here is mainly performed by simulation and does not uniquely correspond to actual materials.

[0004]

As described above, the development of materials suitable for hydroform forming has hardly been carried out on a practical level, and existing high workability steel sheets are being used for hydroform forming. An object of the present invention is to provide a highly corrosion-resistant steel pipe excellent in formability such as a hydroform by limiting the characteristic value of a material, and a method for producing the same.

[0005]

Means for Solving the Problems The present inventors have found a texture of a material excellent in formability such as hydroform and a method for controlling the texture, and by limiting this, the moldability of hydroform and the like is excellent. An object of the present invention is to provide a highly corrosion resistant steel pipe and a method for manufacturing the same.

That is, the gist of the present invention is as follows: (1) In mass%, C: 0.001 to 0.3%, N: 0.
001-0.2%, Si: 0.01-2%, Mn: 0.
It contains 0.1 to 5% and Cr: 5 to 30%, with the balance being iron and unavoidable impurities, of {110} <110> to {111} <110> Average of X-ray random intensity ratio of orientation group is 2.0 or more, steel sheet 1/2
A highly corrosion-resistant steel pipe excellent in formability, characterized in that the X-ray random intensity ratio of {110} <110> on the plate surface at the plate thickness is one or both of 3.0 or more. (2) In mass%, P: 0.005 to 0.1%, S: 0.
The highly corrosion-resistant steel pipe excellent in formability according to the above (1), further comprising 0001 to 0.05%. (3) In mass%, Ni: 0.01 to 2%, Mo: 0.0
1-3%, Cu: 0.01-2%, W: 0.01-2
%, Co: 0.01 to 2%, and further contains one or more kinds of the highly corrosion-resistant steel pipes having excellent formability according to the above (1) or (2).

(4) In mass%, Ti: 0.005 to 1
%, Zr: 0.005 to 1%, Nb: 0.005 to 1
%, V: 0.005 to 1% of one or more of the above-mentioned (1) to (3). (5) In mass%, Al: 0.001 to 0.5%, Mg:
0.001-0.5%, Ca: 0.001-0.5%,
REM: The highly corrosion-resistant steel pipe excellent in formability according to any one of the above (1) to (4), further comprising one or more of 0.001 to 0.5%. (6) The highly corrosion-resistant steel pipe excellent in formability according to any one of the above (1) to (5), further comprising, by mass%, B: 0.0005 to 0.01. (7) 50% or more of the area ratio of the metal structure is made of ferrite, and the crystal grain size of the ferrite grains is 0.1 μm to 200 μm.
m, and {110} of the sheet surface at a steel sheet 1/2 sheet thickness
The average of the X-ray random intensity ratio of the orientation group of <110> to {111} <110> is 2.0 or more, and the {110} <110> X-ray random intensity ratio of the plate surface at a half thickness of the steel plate Is 3.
The highly corrosion-resistant steel pipe excellent in formability according to any one of the above (1) to (6), which is one or both of 0 or more.

(8) In mass%, C: 0.001 to 0.3
%, N: 0.001 to 0.2%, Si: 0.01 to 2
%, Mn: 0.01 to 5%, Cr: 5 to 30%, with the balance being iron and unavoidable impurities. As the characteristics of the steel pipe, (1) n value in the pipe longitudinal direction is 0.12 or more. (2) a high corrosion-resistant steel pipe excellent in formability, which satisfies one or both of n in the circumferential direction of the pipe being 0.12 or more. (9) In mass%, C: 0.001 to 0.3%, N: 0.
001-0.2%, Si: 0.01-2%, Mn: 0.
(8) The steel pipe according to the above (8), wherein the steel pipe contains 5 to 30% of Cr and 5 to 30% of Cr, and the balance consists of iron and unavoidable impurities. A highly corrosion-resistant steel pipe excellent in formability according to (1).

(10) In mass%, C: 0.001-0.
3%, N: 0.001 to 0.2%, Si: 0.01 to 2
%, Mn: 0.01 to 5%, Cr: 5 to 30%, with the balance being iron and unavoidable impurities. The texture of the steel pipe is as follows: (1) Sheet surface at 1/2 sheet thickness $ 11
X-ray random intensity ratio of 1｝ <110>, {110} <110> to {332} <110
The average of the X-ray random intensity ratios of the group of orientations>, and at least one of the X-ray random intensity ratios of {110} <110> of the sheet surface at 1/2 steel sheet thickness is 3.0 or more. (2) {100} <11
The average of the X-ray random intensity ratios of the orientation groups of 0> to {223} <110>, {100} <1 of the sheet surface at a steel sheet 1/2 sheet thickness
10> Any one or both of the X-ray random intensity ratios is 3.0 or less; (3) {111} <110> to {111} <112> and {554} <225> have an average X-ray random intensity ratio of 2.0 or more, and {11}
1｝ <110> that one or both of the X-ray random intensity ratios is 3.0 or more, and that one or more of the above items (1) to (3) is satisfied Highly corrosion resistant steel pipe with excellent formability characterized by:

(11) P: 0.005 to 0.5% by mass.
The highly corrosion-resistant steel pipe excellent in formability according to any one of the above (8) to (10), further containing 1% and S: 0.0001 to 0.05%. (12) Ni: 0.01 to 2%, Mo: 0.
01 to 3%, Cu: 0.01 to 2%, W: 0.01 to 2
(8) to (11), wherein one or more of Co: 0.01 to 2% are further contained.
A highly corrosion-resistant steel pipe excellent in formability according to any one of the above. (13) In mass%, Ti: 0.005 to 1%, Zr:
0.005 to 1%, Nb: 0.005 to 1%, V: 0.
The highly corrosion-resistant steel pipe excellent in formability according to any one of the above (8) to (12), further comprising one or more kinds of 005 to 1%. (14) In mass%, Al: 0.001 to 0.5%, M
g: 0.001 to 0.5%, Ca: 0.001 to 0.5
%, REM: 0.001 to 0.5%, and one or more of them, further containing high corrosion resistance excellent in moldability according to any one of the above (8) to (13). Steel pipe. (15) The above (8) to (14), further containing B: 0.0005 to 0.01 in mass%.
A highly corrosion-resistant steel pipe excellent in formability according to any one of the above.

(16) At least 50% of the area ratio of the metal structure is made of ferrite, and the grain size of the ferrite grains is 0.1%.
The highly corrosion-resistant steel pipe excellent in formability according to any one of the above (8) to (15), which is in the range of μm to 200 μm. (17) 50% or more of the area ratio of the metal structure is made of ferrite, and the crystal grain size of the ferrite grains is 1 μm to 200 μm.
And the standard deviation in the particle size distribution of the ferrite particles is within ± 40% of the average particle size, the moldability according to any one of the above (8) to (15), Excellent high corrosion resistance steel pipe. (18) The molding according to (16) or (17), wherein the ferrite grains have an average aspect ratio (grain length in the longitudinal direction / grain length in the thickness direction) of 0.5 to 10.0. High corrosion resistance steel pipe with excellent resistance.

(19) In producing the highly corrosion-resistant steel pipe excellent in formability according to any one of the above (1) to (18), C: 0.001 to 0.3%, N: 0 by mass%. .001-
0.2%, Si: 0.01 to 2%, Mn: 0.01 to 5
%, Cr: 5 to 30%, with the balance being iron and unavoidable impurities.
{110} <110> to {111}
The average of the X-ray random intensity ratio of the <110> orientation group is 2.
0 or more, {110} <110
The X-ray random intensity ratio is> 3.0 or more, and (2) the 面 11 of the sheet surface at a steel sheet 板 thickness
X-ray random intensity ratio of 1｝ <110>, {110} <110> to {332} <110
The average of the X-ray random intensity ratios of the group of orientations>, and at least one of the X-ray random intensity ratios of {110} <110> of the sheet surface at 1/2 steel sheet thickness is 3.0 or more. (3) {100} <11
The average of the X-ray random intensity ratios of the orientation groups of 0> to {223} <110>, {100} <1 of the sheet surface at a steel sheet 1/2 sheet thickness
10> Any one or both of the X-ray random intensity ratios are 3.0 or less. (4) {111} <110> to {111} <112> and {554} <225> in an orientation group having an average X-ray random intensity ratio of 2.0 or more, and {11}
(1) that the X-ray random intensity ratio of 1｝ <110> is one or both of 3.0 or more.
From (4) to the hot rolled steel sheet or cold-rolled steel sheet that satisfies any one or more of the items, and heat the pipe after forming the mother pipe,
A method for producing a highly corrosion-resistant steel pipe excellent in formability, characterized in that diameter reduction is performed at 600 to 1000 ° C.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. First, the invention (1) will be described. Reasons for limiting the basic components of steel are as follows. C: C is effective in increasing the strength and is added in an amount of 0.001% by mass or more. However, if added in a large amount, it is not preferable in controlling the texture, and deterioration of corrosion resistance and cracking during molding are likely to occur. , And the upper limit was 0.3% by mass.

N: Like N, N is effective in increasing the strength, and is added in an amount of 0.001% by mass or more. However, if added in a large amount, it is not preferable in controlling the texture, deterioration of corrosion resistance, The upper limit is set to 0.
It was 2% by mass.

Si: Since Si is also a strengthening element and a deoxidizing element, the lower limit is set to 0.01% by mass. However, the excessive addition causes a decrease in ductility, so the upper limit is set to 2% by mass.

Mn: Mn is also effective in increasing strength and is 0.01%.
The upper limit is set to 5% by mass because excessive addition causes a decrease in ductility.

Cr: Cr is an important element for imparting corrosion resistance with increasing strength, and is added in an amount of 5% by mass or more. However, excessive addition causes a decrease in ductility, so the upper limit is 30% by mass.

{110} <1 of the plate surface at a steel plate 1/2 plate thickness
Orientation groups of 10> to {111} <110> and {11}
0｝ <110> X-ray random intensity ratio: This is the most necessary characteristic value for performing hydroform molding. {110} <110> to when the X-ray diffraction of the plate surface at the plate thickness center position is performed and the intensity ratio of each direction to the random crystal is obtained.
The average in the {111} <110> orientation group was 2.0 or more. The main orientations included in this orientation group are {110} <
110>, {661} <110>, {441} <110
>, {331} <110>, {221} <110>,
{332} <110>, {443} <110>, $ 55
4} <110> and {111} <110>.

The X-ray random intensity ratio in each of these directions can be calculated from a three-dimensional texture calculated by the vector method from the {110} pole figure, {110}, {100}, {211}, and {3}.
What is necessary is just to obtain | require from the three-dimensional texture calculated by the series expansion method based on several pole figures among 10 degree pole figures. For example, to obtain the X-ray random intensity ratio of each crystal orientation by the latter method, (11) in the φ2 = 45 degree section of the three-dimensional texture
0) [1-10], (661) [1-10], (44
1) [1-10], (331) [1-10], (22)
1) [1-10], (332) [1-10], (44)
3) [1-10], (554) [1-10] and (1)
11) It is represented by the intensity of [1-10].

{110} <110> to {111} <11
The average X-ray random intensity ratio of the group of 0> azimuths is an arithmetic mean of the above-mentioned respective directions. If all the intensities in the above directions cannot be obtained, {110} <110>, {441} <11
0> and {221} <110> may be substituted by the arithmetic mean. Among them, {110} <110> is important,
It is particularly desirable that the X-ray random intensity ratio in this direction be 3.0 or more.

{110} <110> to {111} <11
0> The average intensity ratio of the orientation group is 2.0 or more, and # 11
Needless to say, if the strength ratio of 0｝ <110> is 3.0 or more, it is particularly suitable as a steel pipe for hydroforming. When molding is difficult, the average intensity ratio of the orientation group is 3.5 or more, {110} <11.
It is desirable that at least one of the intensity ratios of 0> 5.0 or more be satisfied.

In the invention of the above (10), the texture of the highly corrosion-resistant steel pipe is as follows: (1) the X-ray random strength ratio of {111} <110> on the steel sheet surface at a steel sheet 1/2 thickness; /
{110} <110> to {332} <
110> Average of X-ray random intensity ratio of orientation group, steel sheet 1
At least one or more of the X-ray random intensity ratios of {110} <110> on the plate surface at a plate thickness of / 2 is not less than 3.0; {100} of the board
The average of the X-ray random intensity ratios of the orientation groups of <110> to {223} <110>, {10}
One or both of the X-ray random intensity ratios of 0｝ <110> are not more than 3.0, and (3) {111} <110>-｛of the sheet surface at a steel sheet 1/2 sheet thickness. 111｝ <11
The average of the X-ray random intensity ratios of the orientation groups of 2> and {554} <225> is 2.0 or more, and the {111} <110> X-ray random intensity ratio of 3.0 or more, either or both of the above,
(1) Regarding the orientation limitation, {110} <110> ~
{111} <11 in the orientation group {111} <110>
Regarding 0>, the effect of the present invention is not lost even if it is deleted from its arithmetic mean.

That is, if the random intensity ratio of the orientation group of {110} <110> or {110} <110> to {332} <110> is 3.0 or more, the high formability (each of which means the present invention) (Expansion ratio of 1.25 or more under hydroforming conditions) can be achieved. Thus, the steel sheet 1
{110} <110> to {332}
The orientation group of <110> and the X-ray random intensity ratio of {110} <110> are the most important characteristic values in performing hydroform molding.

Further, regarding the orientation limitation in the above (2),
{110} <110> to {2} of the plate surface at 1/2 steel plate thickness
If the X-ray random intensity ratio of any one of the orientation group of 23 ° <110> and the {100} <110> exceeds 3.0, the object of the present invention, in particular, the expansion ratio etc. in the hydroform is about 1.2. It goes down below.

Further, regarding the orientation limitation in the above (3),
{111} <110> to {1} of the plate surface at 1/2 steel plate thickness
The average of the X-ray random intensity ratios of the orientation groups of 11} <112> and {554} <225> is less than 2.0, and the {111} <110> When the X-ray random intensity ratio is less than 3.0, the expansion rate of the hydroform also becomes low. Therefore, by satisfying any of the conditions of 2.0 or more and 3.0 or more of the degree of integration, respectively, Workability during foam molding was ensured. In each of the above directions, X-ray diffraction is performed on the plate surface at the center position of the plate thickness to determine the intensity ratio of each direction with respect to the random crystal.

The main orientations included in the orientation group will be described. {110} <110> to {332} <110>
The main directions included in the group of directions are {110} <110
>, {661} <110>, {441} <110>,
{331} <110>, {221} <110>, $ 33
2 {110>, {443} <110>, {554} <
110>. Also, {100} <110> to $ 22
3 The main direction included in the direction group of <110> is $ 10.
0 {<110>, {116} <110>, {114} <
110>, {113} <110>, {112} <110
>, {335} <110> and {223} <110>
It is. Also, {111} <110> to {111} <1
The main orientations included in the orientation group of <12> are {111} <1
10> and {111} <112>.

The X-ray random intensity ratio in each of these directions can be calculated from a three-dimensional texture calculated by the vector method from the {110} pole figure, {110}, {111}, {211}, and {3}.
What is necessary is just to obtain | require from three-dimensional texture calculated by the series expansion method based on several pole figures among 10 degree pole figures. For example,
For {110} <110> to {332} <110>, to determine the X-ray random intensity ratio of each crystal orientation from the latter method, the (110) [1- 10], (661) [1-10],
(441) [1-10], (331) [1-10],
(221) [1-10], (332) [1-10],
(443) [1-10], (554) [1-10]
In the orientation group {100} <110> to {223} <110>, (001) [1-10], (116) [1-1
0], (114) [1-10], (113) [1-1
0], (112) [1-10], (335) [1-1
0] and (223) [1-10], {111} <1
(111) in the direction group of 10> to {111} <112>
[1-10] and (111) [-1-12] can be represented respectively.

Particularly important {110} <110>-
For the orientation group of {332} <110>, if all the intensities in the above orientation cannot be obtained, (110) [1-
10], (441) [1-10], (221) [1-1]
0] may be substituted.

Incidentally, the texture of the present invention usually has φ
2 = 45 degree cross section has the highest intensity within the range of the above orientation group, and the intensity level gradually decreases as the distance from this orientation group increases. Taking into account the problem of twisting, the problem of the accuracy of the preparation of X-ray samples, and the like, the orientation showing the highest intensity may deviate from these orientation groups by about ± 5 ° to 10 °.

When performing X-ray diffraction on a steel pipe, an arc-shaped test piece is cut out from the steel pipe and pressed to form a flat plate for X-ray diffraction. Also, when making a flat plate from an arc-shaped test piece,
In order to avoid the influence of crystal rotation due to the processing of the test piece, the strain was performed as low as possible, and the upper limit of the applied strain was set to 10% or less. The plate-like sample thus obtained is reduced in thickness to a predetermined thickness by mechanical polishing, and thereafter, the distortion is removed by chemical polishing or the like, and at the same time, adjustment is performed so that the central layer of the thickness becomes the measurement surface.

When a segregation zone is observed in the thickness center layer of the steel sheet, the measurement may be performed at a place where there is no segregation zone in the range of ／ to ／ of the thickness. In addition, even when the segregation zone is not recognized, a plate surface other than the plate surface having a plate thickness of 、,
For example, in 3/8 to 5/8, the texture described in the claims may be obtained. If X-ray measurement is more difficult, EBS
It can be measured by the P method or the ECP method.

As described above, the texture of the present invention is defined by the results of X-ray measurement at the center of the sheet thickness or at the surface near the center of the sheet thickness. desirable. However, from the outer surface of the steel pipe to a thickness of about 1/4, the texture changes due to the shear deformation due to the diameter reduction described below, and the above-mentioned requirements for the texture may not be satisfied. In addition, {hkl}
<Uvw> means that when a sample for X-ray is collected by the above-described method, the crystal orientation perpendicular to the plate surface is {hkl} and the longitudinal direction of the steel pipe is <uvw>.

Although the features relating to the texture of the present invention cannot be represented only by a normal inverse pole figure or a positive pole figure, for example, an inverse pole figure representing the radial direction of a steel pipe was measured in the vicinity of the center of the sheet thickness. In this case, the X-ray random intensity ratio in each direction is preferably as follows. <100>: 2
Hereinafter, <411>: 2 or less, <211>: 4 or less, <1
11>: 15 or less, <332>: 15 or less, <221
>: 20.0 or less, <110>: 30.0 or less. Also,
In the reverse pole figure showing the axial direction, <110>: 10 or more, and all directions other than the above <110>: 3 or less.

Next, the invention (8) will be described. n value: Hydroform may be processed to some extent isotropically, and it is necessary to secure n value in the longitudinal direction and / or circumferential direction of the pipe.
Was set as the lower limit. The effect of the present invention can be obtained without particularly setting the upper limit of the n value. The n value is a value obtained when the strain amount in the JIS tensile test method is 5 to 10% or 3 to 8%.

Next, the invention (9) will be described. r value: In the hydroform, there is also a process of flowing the material by axial pressing, and the lower limit of the r value in the longitudinal direction of the tube was set to 1.1 in order to secure the workability of such a portion. The effect of the present invention can be obtained without particularly setting the upper limit of the r value. The r value is defined as a value obtained at a strain amount of 10 or 5% in a tensile test according to JIS.

The reasons for limiting the steel components other than the basic components in the present invention will be described below. P and S are unavoidable impurity elements contained in steel. Both are not only harmful to the moldability, but also rust easily and reduce the corrosion resistance. However, even if they are extremely reduced, only the cost is increased and the effect is small.
0.1% by mass, 0.0001 to 0.05% by mass.

Ni, Mo, Cu, W, and Co are all elements that increase the strength and improve the corrosion resistance, and one or more of them can be added, if necessary, in an amount of 0.01% or more by mass%. . However, since excessive addition causes a decrease in ductility, the upper limit is set to 3% for Mo and 2% for other elements.

Each of Ti, Zr, Nb and V is an element for increasing the strength and improving the corrosion resistance, particularly the corrosion resistance of the welded portion.
At 0.005% or more. However, since excessive addition causes a decrease in ductility, 1% for all elements
Was set as the upper limit.

Al, Mg, Ca, and REM are deoxidizing elements, which reduce oxide-based inclusions and improve formability. However, excessive addition degrades formability and weldability. Therefore, if necessary, one or more of these are added in an amount of 0.001 to 0.5% by mass, respectively.

B has the effect of strengthening the grain boundaries with a small amount and suppressing cracking during molding or secondary processing. However, excessive addition degrades formability and weldability. Therefore, 0.0005 to 0.01% by mass is added as necessary.

Crystal grain size: In controlling the texture, it is important to control the crystal grain size. In particular, in the inventions of (7) and (16), in order to further increase the strength of {110} <110>, it is necessary to control the grain size of ferrite as a main phase to 0.1 to 200 μm. It is. Further, even if the particles are mixed to some extent, for example, 0.1 to 1
Even in a metal structure in which a region of 0 μm ferrite grains and a region of 10 to 100 μm ferrite particles coexist,
If the strength of {110} <110>, which is the most important for improving the formability in the orientation group of 0 <110> to {332} <110>, cannot be increased, the effect of the present invention is not lost. Here, the ferrite grain size was determined by a cutting method based on JIS.

Further, as a metal structure other than ferrite, a structure such as martensite, austenite phase and carbonitride may be included. In addition, it is difficult to industrially produce recrystallized grains of less than 0.1 μm,
Since the strength of {110} <110> is reduced when excessive grains are mixed, the upper limit is set.

Further, in the inventions of (17) and (18),
By increasing the intensity ratio of the orientation group of {110} <110> to {332} <110>, {100} <110> to {223}
In order to lower the strength ratio of <110>, the standard deviation of the ferrite grain size or the aspect ratio of the ferrite grain was further limited. These values were obtained by observing at least 20 visual fields with a 100- to 1000-fold optical microscope, and for each particle size, the circle equivalent diameter was determined by image analysis to calculate the standard deviation. The aspect ratio was determined from the ratio of the number of ferrite grain boundaries crossing a line segment parallel to the rolling direction and a line segment in the vertical direction having the same length. Standard deviation is ± 40% of average particle size
, Or when the aspect ratio is less than 0.5 or more than 3, the moldability tends to deteriorate, so these were set as the upper and lower limits.

In the invention of the above (17),
{111} <110> and / or {110} <110
> To {332} <110>, the lower limit of the ferrite grain size was set to 1 µm.

Further, in manufacturing the steel pipe of the present invention, ingot casting or continuous casting is performed by performing various secondary refining following melting in a blast furnace or an electric furnace, and in the case of continuous casting, hot rolling is performed as it is. Even if they are manufactured by combining the above-mentioned manufacturing methods, the effects of the present invention are not impaired at all.

Further, the steel ingot is heated to 1050 ° C. to 1300 ° C., rough rolling is performed at 950 ° C. or more and less than 1150 ° C., and finish rolling is performed at 750 ° C. or more and less than 1050 ° C.
Hot rolling is performed by lubricating rolling, and hot rolled
Steel sheets before pipe making, such as performing at 0 ° C. or less, annealing a hot-rolled sheet by box annealing or continuous annealing, and further performing cold rolling, and then performing box annealing or continuous annealing. Even if they are manufactured by combining the above-mentioned manufacturing methods, the effects of the present invention are not impaired at all. That is, a hot-rolled sheet, a hot-rolled annealed sheet, a cold-rolled sheet or a cold-rolled annealed sheet can be used as the steel sheet for pipe making.

Further, O, Sn, Zn, As, Sb, P
The effect of the present invention is not lost by mixing elements of 0.01 mass% or less such as b and Bi. Further, in producing steel pipes, welding and pipe forming techniques such as electric resistance welding, TIG, MIG, laser welding, UO, and forging can be used.

The manufacturing method defined in the invention (19) will be described. Texture of hot rolled steel sheet or cold rolled steel sheet:
Satisfying any one or more of (1) to (4)
This is a condition for improving the formability of the steel pipe. (1) {110} <110> ~ of the plate surface at 1/2 steel plate thickness
The average of the X-ray random intensity ratio of the {111} <110> orientation group is 2.0 or more, and the {11}
(2) X-ray random intensity of {111} <110> on the surface of the steel plate at 1/2 steel plate thickness Strength ratio, {110} <110> to {33}
2｝ Average of X-ray random intensity ratio of <110> orientation group,
2. One or two or more of the X-ray random intensity ratios of {110} <110> on the plate surface at 1/2 steel plate thickness
0 or more, (3) ｛1 of the plate surface at 1/2 steel plate thickness
X of the orientation group of 00 の <110> to {223} <110>
(4) the average of the line random intensity ratios, and / or one or both of the X-ray random intensity ratios of {100} <110> of the sheet surface at 1/2 sheet thickness of the steel sheet are not more than 3.0; Steel plate 1
{111} <110> to {111}
The average of the X-ray random intensity ratios of the orientation groups of <112> and {554} <225> is 2.0 or more, and the {111} <110> X-ray random intensity ratio of the sheet surface at a steel sheet 1/2 thickness. Is at least one of 3.0 or more,

Diameter processing temperature: The processing temperature at the time of diameter reduction is set to 600 ° C. or higher in order to recover strain hardening after diameter reduction. However, the temperature is limited to 1000 ° C. or less in order to prevent coarsening of the grains. If the recovery after diameter reduction is insufficient or there is precipitation of carbides, etc.
Even if the heat treatment is performed at a temperature of 00 ° C. or less, the effect of the present invention is not impaired.

The heating temperature is 700 ° C. or higher for improving the formability of the welded portion and the like, and 10 ° C. for preventing the grains from becoming coarse.
It is desirable that the temperature be not higher than 00 ° C. In the production of these welded steel pipes, the heat affected zone of the weld may be subjected to local solution heat treatment alone or in combination depending on the required properties, and may be repeated several times in some cases. Further enhance. The purpose of this heat treatment is to add only to the welded portion and the weld heat affected zone, and the heat treatment can be applied online or offline during manufacturing. Further, it is desirable to provide lubrication at the time of diameter reduction in view of improvement of formability. In particular, the texture near the surface layer is set as described in the claims, and {111} <110> and / or {110} is applied to the entire plate thickness. <11
0> to {332} <110>, and a steel pipe excellent in formability with an increased degree of integration can be manufactured, which promotes the effects of the present invention.

[0051]

EXAMPLES Example 1 A hot-rolled steel sheet having a thickness of 2.5 mm and a cold-rolled steel sheet having a thickness of 2.0 mm having the components shown in Tables 1 and 2 were used as base plates for pipe making. The steel plates are cooled to an outside diameter of 1
After forming a pipe to a thickness of 08 to 49 mm using TIG, laser or electric resistance welding, the pipe is heated to 700 to 1000 ° C.
The outer diameter was reduced to 75 to 25 mm at ９950 ° C. to produce a highly corrosion-resistant steel pipe. Hydroform molding has a shaft pushing amount of 1 mm, 1
The test was performed under the condition of 00 bar / mm until the burst. A 10 mmφ scribed circle was transferred to a steel pipe in advance, and the longitudinal strain: εφ and circumferential strain: εθ of the pipe near the fractured portion or in the portion where the maximum thickness was reduced were measured.
The expansion ratio at which the ratio ρ = εφ / εθ of the two strains becomes −0.5 (becomes negative because the plate thickness decreases) was obtained, and this was evaluated as one index of hydroform moldability.

The X-ray analysis was performed by cutting out an arc-shaped test piece from a steel pipe and pressing it as a flat plate. Further, the relative intensity of X-rays was determined by comparing with a random crystal. For the n value and r value in the longitudinal and circumferential directions, an arc-shaped test piece was sampled, and the n value was a strain amount of 5% -10% or 3% -8%.
The r value was determined at 10% or 5%, respectively.

Tables 1 and 2 show that {110} <11
0> and {110} <110> to {111} <110
> Shows the X-ray random intensity ratio of the group of orientations> and the tube expansion ratio up to the burst in hydroform molding (= diameter of portion where ρ = εφ / εθ = −0.5 at the time of burst / diameter of original tube). In the steels A to R of the present invention, {110} <110
> All X-ray relative intensities are 3.0 or more and {110}
The average X-ray random intensity ratio of the orientation group of <110> to {111} <110> is 2.0 or more, and the expansion ratio is 1.25.
Good value exceeding. On the other hand, S to U of comparative component steels
Are {110} <110> and {110} <110>
The X-ray random intensity ratio of the orientation group of {111} <110> is low, and the expansion ratio is also low.

[0054]

[Table 1]

[0055]

[Table 2]

Example 2 A hot-rolled steel sheet having a thickness of 3.0 mm and a cold-rolled steel sheet having a thickness of 1.8 mm having the components shown in Table 3 were used as base plates for pipe making. The steel plates are cold-rolled with an outside diameter of 108-49.
After TIG, laser or ERW welding, the tube is heated to 650 ° C. to 1100 ° C.
The outer diameter was reduced to 75 mm to 25 mm at ℃ to produce a high corrosion resistant steel pipe. Hydroform molding was performed up to the burst. By controlling the internal pressure and the amount of axial pushing, the hydroforming is performed with various pushing amounts and internal pressures until buckling or bursting occurs, and the maximum expansion ratio (expansion ratio = maximum perimeter after molding / perimeter of the mother pipe) And the strain in the longitudinal direction: εφ and the strain in the circumferential direction: εθ near the fractured portion or the portion where the maximum thickness was reduced were measured. Ratio of these two strains ρ = εφ / εθ
And the maximum expansion ratio were plotted, and the expansion ratio at which εφ / εθ becomes −0.5 (becomes negative because the plate thickness decreases) was obtained, and this was also evaluated as one index of hydroform moldability.

Table 4 shows the characteristics of each steel. Those in which the strength, n value, and r value of the orientation group of each texture satisfy the range of the present invention have a high pipe expansion rate. As for the volume fraction and particle size distribution of ferrite, most steels have ferrite as a main phase and the average particle size is 100 μm or less.

On the other hand, if the heating temperature during the diameter reduction and / or the temperature for the diameter reduction processing are too high (NA +, ND +), the ferrite grain size grows coarsely, and the expansion ratio decreases. Also,
If the heating temperature during the diameter reduction and / or the diameter reduction processing temperature is too low (NF +, NJ +), the accumulation of the texture is insufficient and the expansion ratio is low. Further, CAN and CNC have a low pipe expansion ratio due to a ferrite structure composed of coarse expanded grains, and CNB has a low pipe expansion rate because the austenite phase remains at 50% or more.

[0059]

[Table 3]

[0060]

[Table 4]

[0061]

According to the present invention, a texture of a material excellent in formability such as a hydroform and a method for controlling the texture are found, and this is limited. It is intended to provide a highly corrosion-resistant steel pipe having excellent formability such as hydroform, and its industrial value is extremely high.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Nobuhiro Fujita 20-1 Shintomi, Futtsu City Nippon Steel Corporation Technology Development Division (72) Inventor Naoki Yoshinaga 20-1 Shintomi, Futtsu City Nippon Steel Corporation Within the Technology Development Division (72) Inventor Akira Ito 20-1 Shintomi, Futtsu City Nippon Steel Corporation Technology Development Division F-term (reference) 4K032 AA01 AA02 AA04 AA05 AA08 AA09 AA10 AA12 AA13 AA14 AA15 AA16 AA17 AA19 AA20 AA21 AA22 AA23 AA24 AA27 AA29 AA31 AA32 AA35 AA36 AA37 AA39 AA40 BA03 CA01 CB01

Claims (19)

[Claims] 1. mass%, C: 0.001 to 0.3%, N: 0.001 to 0.2%, Si: 0.01 to 2%, Mn: 0.01 to 5%, Cr : 5 to 30%, the balance being iron and unavoidable impurities, {110} <110> to {11}
The average of the X-ray random intensity ratio of the 1｝ <110> orientation group is 2.0 or more, and the {110} <1
A highly corrosion-resistant steel pipe excellent in formability, characterized in that the ratio of X-ray random intensity of 10> is one or both of 3.0 or more. 2. The excellent moldability according to claim 1, further comprising P: 0.005 to 0.1% and S: 0.0001 to 0.05% by mass%. High corrosion resistant steel pipe. 3. Mass%: Ni: 0.01 to 2%, Mo: 0.01 to 3%, Cu: 0.01 to 2%, W: 0.01 to 2%, Co: 0.01 The highly corrosion-resistant steel pipe excellent in formability according to claim 1 or 2, further comprising at least one of 2% or more. 4. One or two types of Ti: 0.005 to 1%, Zr: 0.005 to 1%, Nb: 0.005 to 1%, and V: 0.005 to 1% by mass%. The highly corrosion-resistant steel pipe excellent in formability according to any one of claims 1 to 3, further comprising: 5. A mass% of Al: 0.001 to 0.5%, Mg: 0.001 to 0.5%, Ca: 0.001 to 0.5%, REM: 0.001 to 0. The highly corrosion-resistant steel pipe excellent in formability according to any one of claims 1 to 4, further comprising 5% of one or more kinds. 6. The highly corrosion-resistant steel pipe excellent in formability according to claim 1, further comprising, by mass%, B: 0.0005 to 0.01%. . 7. An area ratio of a metal structure of 50% or more of ferrite, and a crystal grain size of ferrite grains is 0.1 μm or more.
In the range of 200 μm, the average of the X-ray random intensity ratios of the {110} <110> to {111} <110> orientation groups on the sheet surface at a steel sheet 1/2 sheet thickness is 2.0 or more. 2
7. The X-ray random intensity ratio of {110} <110> of the plate surface at the plate thickness is one or both of 3.0 or more, 7. High corrosion resistant steel pipe with excellent formability. 8. Mass%, C: 0.001 to 0.3%, N: 0.001 to 0.2%, Si: 0.01 to 2%, Mn: 0.01 to 5%, Cr : 5 to 30%, the balance being iron and unavoidable impurities, and the properties of the steel pipe are as follows: (1) n value in the pipe longitudinal direction is 0.12 or more; (2) pipe circumferential direction A highly corrosion-resistant steel pipe excellent in formability, characterized by satisfying one or both of n value of 0.12 or more. 9. Mass%: C: 0.001 to 0.3%, N: 0.001 to 0.2%, Si: 0.01 to 2%, Mn: 0.01 to 5%, Cr , And the balance is iron and inevitable impurities, and as a characteristic of the steel pipe, the r value in the longitudinal direction of the pipe is 1.1 or more. Excellent corrosion resistant steel pipe. 10. In mass%, C: 0.001 to 0.3%, N: 0.001 to 0.2% Si: 0.01 to 2%, Mn: 0.01 to 5%, Cr: 5-30%, with the balance being iron and unavoidable impurities, as the texture of the steel pipe: (1) {111} <110>
X-ray random intensity ratio of the steel sheet, ｛1
X of the orientation group of 10｝ <110> to {332｝ <110>
The average of the line random intensity ratio, and at least one or more of the X-ray random intensity ratios of {110} <110> of the sheet surface at a steel sheet 1/2 sheet thickness is 3.0 or more; 2) {100} <110> of the plate surface at 1/2 steel plate thickness
Average of the X-ray random intensity ratios in the group of orientations of ~ {223} <110>, {100} <110 of the sheet surface at 1/2 sheet thickness
> One or both of the X-ray random intensity ratios are 3.0 or less; (3) {111} <110>
The average of the X-ray random intensity ratio of the orientation groups of {111} <112> and {554} <225> is 2.0 or more, and the steel sheet 1
(1) to (3) that the X-ray random intensity ratio of {111} <110> on the plate surface at a plate thickness of 1/2 is at least one or both. A highly corrosion-resistant steel pipe excellent in formability, characterized by satisfying any one or more of the above items. 11. The composition according to claim 8, further comprising P: 0.005 to 0.1% and S: 0.0001 to 0.05% by mass%.
The highly corrosion-resistant steel pipe excellent in formability according to any one of the above. 12. In mass%, Ni: 0.01 to 2%, Mo: 0.01 to 3%, Cu: 0.01 to 2%, W: 0.01 to 2%, Co: 0.01 The highly corrosion-resistant steel pipe excellent in formability according to any one of claims 8 to 11, further comprising 1 to 2% of 2% or more. 13. One or two kinds of Ti: 0.005 to 1%, Zr: 0.005 to 1%, Nb: 0.005 to 1%, and V: 0.005 to 1% by mass%. The highly corrosion-resistant steel pipe excellent in formability according to any one of claims 8 to 12, further comprising: 14. Al: 0.001 to 0.5%, Mg: 0.001 to 0.5%, Ca: 0.001 to 0.5%, REM: 0.001 to 0. The highly corrosion-resistant steel pipe excellent in formability according to any one of claims 8 to 13, further comprising 5% or more of one or more kinds. 15. The composition according to claim 8, further comprising B: 0.0005 to 0.01% by mass%.
The highly corrosion-resistant steel pipe excellent in formability according to any one of the above. 16. An area ratio of the metal structure is 50% or more of ferrite, and the crystal grain size of the ferrite grains is 0.1 μm.
The highly corrosion-resistant steel pipe excellent in formability according to any one of claims 8 to 15, wherein the pipe is in a range of from about 200 µm to about 200 µm. 17. Ferrite has an area ratio of metal structure of 50% or more, and the ferrite grains have a grain size of 1 μm to 2 μm.
The moldability according to any one of claims 8 to 15, wherein the ferrite grains have a standard deviation within ± 40% of the average grain size in the grain size distribution of the ferrite grains. Excellent high corrosion resistance steel pipe. 18. The ferrite grains having an average aspect ratio (grain length in the longitudinal direction / grain length in the thickness direction) of 0.5 to 10.
The highly corrosion-resistant steel pipe excellent in formability according to claim 16 or 17, wherein the value is 0. 19. In producing the highly corrosion-resistant steel pipe excellent in formability according to claim 1, C: 0.001 to 0.3%, and N: 0.001 by mass%. -0.2%, Si: 0.01-2%, Mn: 0.01-5%, Cr: 5-30%, with the balance being iron and unavoidable impurities. (1) {110} <110> of the plate surface at 1/2 steel plate thickness
The average of the X-ray random intensity ratios in the group of orientations of {111} <110> is 2.0 or more, and {11}
0｝ <110> has one or both of X-ray random intensity ratios of 3.0 or more; (2) {111} <110>
X-ray random intensity ratio of the steel sheet, ｛1
X of the orientation group of 10｝ <110> to {332｝ <110>
The average of the line random intensity ratio, and at least one or more of the X-ray random intensity ratios of {110} <110> of the sheet surface at a steel sheet 1/2 sheet thickness is 3.0 or more; 3) {100} <110> of the plate surface at 1/2 steel plate thickness
Average of the X-ray random intensity ratios in the group of orientations of ~ {223} <110>, {100} <110 of the sheet surface at 1/2 sheet thickness
> One or both of the X-ray random intensity ratios are 3.0 or less; (4) {111} <110>
The average of the X-ray random intensity ratio of the orientation groups of {111} <112> and {554} <225> is 2.0 or more, and the steel sheet 1
(1) to (4), wherein the X-ray random intensity ratio of {111} <110> on the plate surface at a plate thickness of / 2 is not less than 3.0 or both. A hot rolled steel plate or a cold rolled steel plate satisfying any one or more of the above items is used as a substrate, and then the mother pipe is heated and then subjected to diameter reduction at 600 to 1000 ° C. Manufacturing method of corrosion resistant steel pipe.