JP2002339044A - High strength martensite stainless steel strip and production method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high strength martensite stainless steel strip, and a production method therefor. SOLUTION: Steel having a composition containing <=0.02% C, 0.1 to 0.3% Si, 0.1 to 0.3% Mn, 11 to 15% Cr, 1 to 7% Ni, <=0.06% Al, 0.008 to 0.03% N and <=0.002% S, by mass, and to which one or more kinds selected from Nb, V, Ti, Ca, Zr, Mg, Cu and Mo are added in accordance with desired characteristics, and the balance substantially Fe with inevitable impurities is hot-rolled, and is thereafter heat-treated to control an effective N content to >=60 ppm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a martensitic stainless steel strip formed by winding a hot-rolled steel strip into a coil and a method of manufacturing the same, and more particularly, to various positions of a coil such as a central portion and an outer peripheral portion of the coil. And a method for producing the same with excellent and uniform strength characteristics.

[0002]

2. Description of the Related Art Steel materials used for line pipes for transporting oil and natural gas are required to be excellent in corrosion resistance and on-site weldability according to the use environment. In recent years, the use of stainless steel has been considered from the viewpoint of corrosion resistance. However, existing stainless steel does not always have sufficient performance for line pipes, and new development has been desired.

[0003] For example, 0.2C-13Cr type is for oil country tubular goods which does not require welding, and is suitable for line pipes which require high preheating and post-heating temperatures to prevent welding cracks and where on-site weldability is important. Not. Further, duplex stainless steel such as 22Cr does not require heat treatment after preheating, but is expensive as a raw material and is difficult to use in pipelines requiring a large amount of steel.

Accordingly, Japanese Patent Laid-Open No. 6-100943 discloses
JP-A-4-268018, JP-A-8-10026
No. 6 proposes a 13Cr-based alloy having a reduced C content and improved weldability, and its application to line pipes has been studied.

[0005] Particularly, recently, with the practical use of laser welded ERW steel pipes using a combination of ERW and laser welding, a coiled 13Cr stainless steel strip is uncoiled and continuously formed by a multi-stage forming roll. After forming an open pipe into a pipe, the application to an electric resistance welded steel pipe manufactured by welding opposite edges of the open pipe is increasing.

In the application of 13Cr stainless steel,
Since the material itself has high quenchability and becomes a martensitic structure by air cooling after hot rolling, it is wound into a coil and then subjected to a heat treatment to obtain desired material properties, and then to various steel pipes.

[0007]

However, when an ERW steel pipe is manufactured by the above-described manufacturing method, the desired strength is often not obtained, and a heat treatment needs to be performed again.

[0008] In the re-heat treatment, a long time of 10 to 50 hours is required to uniformly heat the coil-shaped material of several to several tens of tons, and the burden is large and trial and error is limited. Appropriate manufacturing guidelines were desired.

Accordingly, an object of the present invention is to provide a high-strength martensitic stainless steel strip capable of obtaining a desired strength stably after hot rolling, coiling, and heat treatment, and a method for producing the same. And

[0010]

Means for Solving the Problems The inventors of the present invention have studied the material, especially the strength, of a hot-rolled 13Cr martensitic stainless steel strip which has been subjected to two-phase heating and tempering after hot rolling. The effects of the composition of the components and the manufacturing conditions on the quality were investigated.

As a result, in the case of long-time heating required for heat treatment of the coil-shaped material, AlN precipitates, and the precipitation of AlN reduces the effective N amount acting as tempering softening resistance, resulting in a decrease in strength. I found it. The present invention has been further studied based on the above findings, that is, the present invention provides: A high-strength martensitic stainless steel strip, wherein the effective N content (X) in the steel is 60 ppm or more.

Here, the effective N amount (X) = totalN−N
asTiN-NasAlN2. Steel composition, in mass%, C: 0.02% or less, Si:
0.1-0.3%, Mn: 0.1-0.3%, Cr: 1
1 to 15%, Ni: 1 to 7%, sol. Al: 0.06
% Or less, N: 0.008 to 0.03%, S: 0.002
%, With the balance substantially consisting of Fe and unavoidable impurities.

3. In mass%, Nb: 0.01 to 0.2
%, V: the high-strength martensitic stainless steel strip according to 2, containing one or two kinds of 0.01 to 0.2%.

4. By mass%, Ca: 0.005% or less,
4. The high-strength martensitic stainless steel strip according to 2 or 3 containing one or more of Zr: 0.005% or less and Mg: 0.005% or less.

[0015] 5. The high-strength martensitic stainless steel strip according to any one of 2 to 4, which contains 0.1 to 3% of Cu by mass%.

6. The high-strength martensitic stainless steel strip according to any one of 2 to 5, which contains 0.3 to 3% of Mo by mass%.

[7] 7. The high-strength martensitic stainless steel strip according to any one of 2 to 6, containing, by mass%, Ti: 0.07% or less.

[0018] A laser electric resistance welded steel pipe made of the high-strength martensitic stainless steel strip according to any one of 8.1 to 7 above.

9. Effective N in steel depending on desired strength
A method for producing a high-strength martensitic steel strip, characterized by adjusting the amount.

[10] 10. The method for producing a high-strength martensitic steel strip according to 9, wherein the effective N content in the steel is adjusted by a heating rate during reheating and / or tempering in the two-phase region of the steel strip after hot rolling. .

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The reasons for limiting the components of the present invention will be described.

C is important for obtaining a martensite structure, and C in steel is important.
It is added to form a carbide with a carbide-forming element such as r and improve the strength. On the other hand, if added excessively, the amount of Cr effective for corrosion resistance is reduced, the hardness of the heat affected zone is increased, and heat treatment after welding is required, so the content is made 0.02% or less.

Si Si is added as a deoxidizing agent. If it is less than 0.1%, the effect is not obtained. On the other hand, if it exceeds 0.3%, the effect is saturated, and delta ferrite crystallizes, and it is necessary to increase the amount of Ni to maintain phase balance. 0.1-0.3
% (0.1% or more, 0.3% or less).

Mn Mn is added as a desulfurizing agent on steelmaking. If it is less than 0.1%, there is no effect and the hot workability also decreases. On the other hand, 0.3%
If added in excess of, the corrosion resistance under carbon dioxide deteriorates, so the content is made 0.1 to 0.3%.

Cr Cr is added because it is effective in improving corrosion resistance in an environment containing wet carbon dioxide gas. Less than 11% has no effect, while 1
If it exceeds 5%, a martensite structure cannot be obtained even when other component elements are adjusted, so that the content is set to 11 to 15%.

Ni Ni is added in an appropriate amount according to the amount of Cr in order to form an austenite phase and obtain a martensite structure. If it is less than 1%, phase stability is insufficient, and the material of the welded part is impaired.
On the other hand, if it exceeds 7%, the effect is saturated and the material cost also increases.

Sol. Al Al is added for deoxidizing elements and for making the structure finer. s
ol. If Al exceeds 0.06%, alumina-based inclusions and nitrides increase, and manufacturability and toughness decrease.

NN is made 0.008% or more in order to secure the strength and suppress the dependence of the strength on the heat treatment. On the other hand, if it is added in excess of 0.03%, it forms a compound with Cr in the steel and decreases Cr effective for corrosion resistance.
%.

AlN AlN is a precipitate that affects the amount of Cr2N deposited. If the amount is more than 60 ppm, the final strength of the product is reduced. Therefore, the amount of AlN is preferably less than 60 ppm. If the precipitation amount of AlN is large, it is presumed that the amount of solid solution N decreases, and during tempering, the precipitation amount of Cr2N, other carbonitrides and nitrides decreases, and the softening resistance is impaired, but the details are unknown.

The precipitation amount of AlN can be controlled by heat treatment after hot rolling, but by increasing the temperature at the time of tempering for strength adjustment, particularly at 50 ° C./h above 400 ° C. It is preferable to control.

The amount of AlN precipitation is measured at the center of the thickness in the product region of the steel strip.

Effective N content Effective N is determined by solid solution or fine C
r2N also forms fine precipitates that cannot be measured by conventional extraction analysis methods, and prevents softening. In the present invention, APIX8
In order to satisfy the strength and toughness characteristics of 0, the content is set to 60 ppm or more.

The effective N content is determined by checking the total N content in the steel by a check analysis, quantifying Al and Ti extracted by the 10% bromine-methanol method using ICP, and then determining them as AlN and TiN. The existing N amount is calculated, and the effective N amount (X) = totalN−NasTiN−
Determined as NasAlN.

The basic composition of the present invention and the definition of precipitates in steel are as described above. Depending on the desired properties, one or more of the following elements can be selectively added. is there.

Nb and V Nb and V are all carbides and nitrides of C and N in steel.
Form carbonitride and improve the strength of steel by grain refinement and precipitation strengthening. When these elements are added, 0.1.
If it is less than 01%, the effect is not sufficient. On the other hand, if it exceeds 0.2%, carbon and nitrogen which form carbonitrides are insufficient, and the reinforcing function is saturated. And

Ca, Zr, Mg Ca, Zr, Mg tend to delay the precipitation of AlN in steel. However, these elements are 0.005%
If more than 0.005%, oxide-based inclusions are formed and the toughness is degraded.

Cu Cu stabilizes the austenite phase and also improves toughness.
If it is less than 0.1%, the effect cannot be obtained. On the other hand, excessive addition exceeding 3% lowers the toughness.
And

Mo Mo improves corrosion resistance. If it is less than 0.3%, the effect cannot be obtained. On the other hand, if it exceeds 3%, the effect is saturated, the strength increases, and it becomes difficult to perform cold plastic deformation. %.

Ti Ti is added when forming carbides, nitrides, and carbonitrides with C and N in the steel to improve the strength of the steel by grain refinement and precipitation strengthening. In order to impair the property, 0.07% is added as an upper limit.

The steel strip according to the present invention is melted in a converter, an electric furnace, or a combination of them, turned into a slab by a continuous casting machine or a mold, worked into a predetermined shape by hot rolling, and then effectively treated by heat treatment. The amount of N deposited is controlled to achieve the target strength.

As the heat treatment after the hot rolling, it is desirable to perform tempering after reheating in the two-phase region for refining the crystal grain size, and it is desirable to adjust the effective N amount by adjusting the amount of AlN precipitated.

Using the steel strip of the present invention as a raw material, ie, uncoiling a coiled 13Cr stainless steel strip, forming an open pipe continuously by a multi-stage forming roll, and then opposing both edges of the open pipe. It is possible to manufacture a laser ERW steel pipe manufactured by combining ERW and laser welding.

[0043]

EXAMPLES (Example 1) Steels having the chemical components shown in Table 1 were melted using a vacuum melting furnace, and hot-rolled at a heating temperature of 1200 ° C and a finish rolling temperature of 900 ° C to obtain a steel sheet having a thickness of 12 mm. After that, normalizing and tempering were performed. Assuming actual operation,
After heating the hot-rolled steel plate to 780 ° C and 750 ° C,
Tempering was performed at any one of 20 ° C, 650 ° C, and 680 ° C.

After the heat treatment, a tensile test (JISZ2203)
YS and TS were determined as mechanical properties. The effective N amount was measured from a part of the remaining material in the tensile test.

Table 2 shows the test results. Effective N amount is 60p
In the case of the steel of the present invention having a temperature of not less than pm, YS was 570 Mpa or more at any two-phase region temperature or tempering temperature, and high strength was obtained stably irrespective of changes in heat treatment conditions.

[0046]

[Table 1]

[0047]

[Table 2]

Example 2 A steel having a chemical composition shown in Table 3 was melted using a vacuum melting furnace, and hot-rolled at a heating temperature of 1200 ° C. and a finish rolling temperature of 900 ° C. to form a steel sheet having a thickness of 12 mm. After the two-phase region heating, tempering was performed. Assuming actual operation, the steel sheet after hot rolling was heated in a two-phase region at 750 ° C,
Tempering was performed at any one of a temperature of 650 ° C and 650 ° C.

After the heat treatment, a tensile test (JISZ2203)
YS and TS were determined as mechanical properties. The effective N amount was measured from a part of the remaining material in the tensile test.

Table 4 shows the test results. Effective N amount is 60p
In the case of the steel of the present invention having a pm or more, YS was 570 Mpa or more at any two-phase region temperature or tempering temperature, and high strength was obtained stably irrespective of changes in heat treatment conditions.

[0051]

[Table 3]

[0052]

[Table 4]

[0053]

According to the present invention, a high-strength martensitic stainless steel strip having high strength and high material stability and a method for producing the same can be obtained, and are extremely useful in industry.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // B23K 26/00 310 B23K 26/00 310J (72) Inventor Yusuke Minami 1-1-1, Marunouchi, Chiyoda-ku, Tokyo No. 2 Inside Nippon Kokan Co., Ltd. (72) Inventor Yukio Maho 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan No. 2 Nippon Kokan Co., Ltd. (72) Toshihiko Fukui, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan No.Nihon Kokan Co., Ltd. F-term (reference) 4E028 CA01 CA13 4E068 BG00 DA15 DB01 4K032 AA01 AA04 AA08 AA13 AA14 AA15 AA16 AA19 AA20 AA21 AA22 AA24 AA31 AA35 AA36 AA39 BA01 CA02 CA03 CC04 CF02

Claims (10)

[Claims] 1. A high-strength martensitic stainless steel strip, wherein the effective N content (X) in steel is 60 ppm or more. However, effective N amount (X) = totalN−NasTiN−
NasAlN 2. The steel composition is, in mass%, C: 0.02% or less, Si: 0.1 to 0.3%, Mn: 0.1 to 0.3.
%, Cr: 11 to 15%, Ni: 1 to 7%, sol. A
l: 0.06% or less, N: 0.008 to 0.03%,
The high-strength martensitic stainless steel strip according to claim 1, wherein S: 0.002% or less, and the balance substantially consists of Fe and unavoidable impurities. 3. Nb: 0.01 to 0.2% by mass%,
The high-strength martensitic stainless steel strip according to claim 2, which contains one or two kinds of V: 0.01 to 0.2%. 4. Ca in a mass% of 0.005% or less, Z
The high-strength martensitic stainless steel strip according to claim 2 or 3, containing one or more of r: 0.005% or less and Mg: 0.005% or less. 5. The high-strength martensitic stainless steel strip according to claim 2, which contains, by mass%, Cu: 0.1 to 3%. 6. The high-strength martensitic stainless steel strip according to claim 2, which contains 0.3 to 3% of Mo by mass%. 7. The high-strength martensitic stainless steel strip according to claim 2, which contains, by mass%, Ti: 0.07% or less. 8. A laser electric resistance welded steel pipe made of the high-strength martensitic stainless steel strip according to any one of 1 to 7. 9. A method for producing a high-strength martensitic stainless steel strip, characterized by adjusting the amount of effective N deposited in steel according to the desired strength. 10. The method according to claim 9, wherein the precipitation amount of the effective N content in the steel is adjusted by a heating rate during two-phase zone heating and / or tempering of the steel strip after hot rolling. Method for producing high-strength martensitic stainless steel strip.