JPH0499128A - Production of martensitic stainless steel line pipe - Google Patents

Abstract

PURPOSE:To produce the martensitic stainless steel line pipe having excellent corrosion resistance and weldability by subjecting a martensitic stainless steel pipe having a specific compsn. to austenitization, temper treatment and cooling treatment under specific conditions. CONSTITUTION:The martensitic stainless steel pipe which is decreased in C to <0.02%, contains, by weight%, 11 to 14% Cr, 1.2 to 4.5% Cu, 4h1% Si, <=2% Mn, and 0.005 to 0.2% Al, decreased in the content of N to <=0.015% an the residue thereof consisted of the balance Fe and unavoidable impurities is made into a steel pipe, and thereafter, the steel pipe is austenitized at 920 to 1100 deg.C and is then cooled at a cooling rate above water cooling. After this steel pipe is subjected to the temper treatment at the temp. above 600 deg.C and below Ac1 temp., the steel pipe is cooled at the cooling rate above the air cooling, by which the martensitic stainless steel line pipe is produced.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a method for manufacturing a martensitic stainless steel line pipe with excellent weldability, and more specifically, it is suitable for use in the transportation of oil and natural gas, for example. High pzll in environments containing wet carbon dioxide or wet hydrogen sulfide.

The present invention relates to a method for manufacturing with high productivity a line pipe tube that has corrosion resistance, excellent impact toughness of a welded heat affected zone, and reduced hardness of the welded heat affected zone.

(Prior Art) In recent years, petroleum and natural gas produced in Japan increasingly contain a large amount of wet carbon dioxide. It is well known that carbon steel and low alloy steel corrode significantly in such environments. For this reason, corrosion inhibitors have traditionally been added as a corrosion prevention measure for line pipes used for transportation. However, corrosion inhibitors often lose their effectiveness at high temperatures, and the cost of adding and recovering corrosion inhibitors to submarine pipelines is enormous, so they are often not applicable. Recently, there has been a growing need for corrosion-resistant materials that do not require the addition of corrosion inhibitors. In addition to corrosion resistance, materials used for line pipes are required to have high strength to withstand the pressure of the transport fluid flowing inside them, and to have excellent weldability. As a typical characteristic of weldability, it is necessary that the welded part has excellent impact toughness. Furthermore, when transporting a fluid containing hydrogen sulfide, it is also required that the hardness of the welded part be low. Of course, it is necessary that the base material also has excellent impact toughness.

Stainless steel, which has good corrosion resistance, was first considered as a corrosion-resistant material for petroleum and natural gas containing a large amount of carbon dioxide. For example, Corr, J., Klein, Corr.
As shown in vapor number 211, Al5I (American Iron and Steel Institute) 410 is used as a high-strength and relatively low-cost rope for oil country tubular goods without welded structures.
Steel or 420 steel, with 0.1% or 0 C
．． Martensitic stainless steel containing 2% Cr and 12-13% Cr is beginning to be widely used. However, the high content of C in these steels makes the welds very hard and the impact toughness of the welds poor, making it difficult to use them as line pipes. Al
Line pipe using 5I410 It has recently become an API.
Although it has been standardized by the American Petroleum Institute (American Petroleum Institute), for example, Masataka Suga et al., NKK Technical Report, published in 1989, No. 129
No., pp. 15-22, the problem is that the impact toughness of the on-site welded part is poor. This is because, as reported by them, the weld heat affected zone becomes a coarse ferrite-based structure.

When conventional martensitic stainless steel pipes are heat treated after pipe making, cooling during quenching is usually done by air cooling. This is because cooling at a faster cooling rate than air cooling, for example water cooling, will cause quenching cracks, so cooling must be done slowly at a cooling rate that does not cause quenching cracks. If air cooling is used for cooling during quenching, it takes a long time to cool down to room temperature, so it also has the disadvantage that productivity is significantly lower than, for example, water cooling.

Therefore, it would be of great significance in terms of productivity if it could be produced by water cooling during quenching.

As steel for line pipes, JP-A-61-119654
In the publication, C and N are reduced, and AI or Ca
Furthermore, steels containing (1) as well as Ni and Mo have been proposed. However, since this steel contains a large amount of Ni, which is an expensive alloying element, it is expensive and its properties are not satisfactory.

(Problems to be Solved by the Invention) In view of the current situation, the present invention has developed a martensitic stainless steel that has sufficient corrosion resistance even in a carbon dioxide environment, has excellent impact toughness and weldability of the base material, and has excellent productivity. The purpose is to provide a method for manufacturing line pipes.

(Means for Solving the Problems) In order to achieve the above object, the present inventors have conducted various studies on the components and heat treatment conditions of martensitic stainless steel line pipes, and as a result, they have finally discovered the following knowledge. Ta.

First, the amount of C in steel containing 11 to 14% Cr is 0.02
% and after reducing N to 0.015% or less, the steel is made into a steel pipe and then cooled at a faster cooling rate than water cooling during quenching, and the quenching and tempering conditions are appropriately selected. If this is done, the strength and excellent toughness necessary for a line pipe can be obtained, and if C and N are reduced as described above, problems such as quench cracking will not occur even when cooling at a faster cooling rate than water cooling. In particular, it has been found that by reducing C and N, the hardness of the weld heat-affected zone can be significantly lowered, and the corrosion resistance in carbon dioxide-containing saline solution can be significantly improved. And Cu is added to the steel.
Adding 1.2 to 4.5% of It was found that the impact toughness of steel can be improved.

Furthermore, the inventors of the present invention further investigated the composition of a line pipe made of martensitic stainless steel to be subjected to the heat treatment as described above, containing 11 to 14% Cr, reduced C and N, and 1.0% Cu. N in steel containing 2-4.5%
that the addition of i is effective in further improving the impact toughness of the weld heat affected zone; that the addition of one or more of Mo and W is effective in improving the corrosion resistance in a wet carbon dioxide environment; Ti.

Adding one or more of Nb, Ta, Zr, and If is effective in further improving corrosion resistance, and adding one or more of Ca and rare earth elements is effective in improving hot workability and corrosion resistance. It has been found that even when these elements are added, if C and N are controlled within the above ranges, quench cracking will not occur even if rapid cooling such as water cooling is performed during quenching.

The present invention has been made based on the above findings, and the gist of the first invention is that C is 0.0% by weight.
Reduced to less than 2%, Cr11-14%, Cu1,2-4
．． 5%, Si 1% or less, Mn 2% or less, AIo, 005
~0.2%, reducing N to 0.015% or less,
After producing a steel pipe from martensitic stainless steel consisting of the balance Fe and unavoidable impurities, 920-11
A martensitic stainless steel that is austenitized at 00°C, then cooled at a cooling rate higher than water cooling, then tempered at a temperature of 600°C or higher and lower than Ac+ temperature, and then cooled at a cooling rate higher than air cooling. The gist of the second invention is a method for manufacturing a line pipe, and the second invention is a martensitic stainless steel line using a steel that further contains 4% or less Ni by weight in addition to the steel covered by the first invention. The gist of the third invention resides in a method for manufacturing a pipe, in which the steel covered by the first and second inventions is further coated with No. 2% or less in weight%.
The gist of the fourth invention is a method for manufacturing a martensitic stainless steel line pipe using sea bream containing one of W4% or less or 2N. In addition to the name to which the invention is directed,
In weight%, V 0.5% or less, Ti 0.2% or less, N
A method for manufacturing a martensitic stainless steel line pipe using a steel containing one or more of the following: b0.5% or less, Ta0.2% or less, ZrO, 2% or less, and HfO, 2% or less. Yes, the gist of the fifth invention is the first invention, the second invention,
In addition to the characteristics targeted by the third and fourth inventions, in weight%, CaO, 0.08% or less, rare earth elements 0.02
% or less of martensitic stainless steel line pipe.

Further, the gist of each of the sixth to tenth inventions is that in each of the first to fifth inventions, the method of manufacturing a steel pipe is a press pipe manufacturing method, a hot rolling method, a hot rolling method,
There are methods for manufacturing martensitic stainless steel line pipes, which are the UOE steel pipe method, the ERW steel pipe method, and the spiral steel pipe method.

(Function) The reasons for limiting the components and heat treatment conditions in the present invention will be described below.

C: When present in a large amount, C reduces corrosion resistance in an acid gas environment and increases the hardness of the weld heat affected zone. If the amount of C is less than 0.02%, the effect of improving corrosion resistance and reducing the hardness of the weld heat affected zone is particularly significant.
The amount of C is limited to less than 0.02%.

St: Si is an element necessary for deoxidation, but 1
If added in excess of 1%, the toughness will be significantly reduced, so the upper limit content is 1%.

Mn: Mn is an effective element for deoxidizing and ensuring strength, but its effect becomes saturated when added in excess of 2%, so the upper limit content is set to 2%.

Cr: Cr is the most basic and essential element constituting martensitic stainless steel, and is necessary to impart corrosion resistance, but if the content is less than 11%, the corrosion resistance is insufficient; %, no matter how you adjust the other alloying elements, it will be difficult to form a single austenite phase when heated to a high temperature, making it difficult to ensure strength, so the upper limit content should be 14%.

Cu: Cu improves impact toughness and improves corrosion resistance in a humid carbon dioxide environment by changing the microstructure of the weld heat-affected zone into a martensitic structure, as well as the base metal of steel with reduced C and N contents. However, if the content is less than 1.2%, these effects are insufficient, and even if 4.5% is added, the effects not only become saturated but also reduce hot workability. It is limited to a range of 1.2 to 4.5% because it significantly reduces the

Al: Aj is an element necessary for deoxidation, and its effect is not sufficient if the content is less than 0.005% (,0
If it is added in excess of 2%, coarse oxide inclusions will remain in the steel and reduce cracking resistance in hydrogen sulfide.
The content range was o, oos to 0.2%.

N: If N exceeds 0.015%, it increases the hardness of the weld heat affected zone and reduces the impact toughness of the base metal and the weld heat affected zone, so the upper limit content is 0.015%.
Should be. More preferably, in order to improve the impact toughness of the weld heat affected zone, it is desirable that N be less than 0.01%.

The above are the basic components of martensitic stainless steel, which is the material for line pipes targeted by the present invention, but in the present invention, the following elements are further added as necessary to further improve the characteristics. is also targeted.

Ni: Ni coexists with 1.2% or more of Cu and is effective in further improving the impact toughness of the weld heat affected zone.
Even if it is added in excess of 4%, the effect will not only be saturated, but also
The upper limit content is set at 4% because it unnecessarily increases costs and increases the hardness of the weld heat affected zone.

Mo: Mo coexists with 1.2% or more of Cu and is effective in improving corrosion resistance in a wet carbon dioxide environment, but 2%
Even if added in excess of 2%, the effect not only becomes saturated, but also other properties such as toughness deteriorate, so the upper limit content is set at 2%.

WOW is also effective in coexisting with 1.2% or more Cu to improve corrosion resistance in a wet carbon dioxide environment, but adding more than 4% not only saturates the effect but also improves other properties such as toughness. The upper limit content is set at 4% since it degrades the properties.

V, Ti, Nb, Dina, Zr+ H
f: V, ri, Nb, Ta,
Zr.

If is an effective element to further improve corrosion resistance, but in the case of Tin Zr, Ta, If, 0.2%, V,
When Nb is added in excess of 0.5%, coarse precipitates and inclusions are formed, resulting in poor SS in hydrogen sulfide-containing environments.
The upper limit content is Tl because it lowers the C resistance.
lZr+ Ta and Hf were set at 0.2%, and V and Nb were set at 0.5%.

Ca, rare earth elements: Ca and rare earth elements (REM) are elements that are effective in improving hot workability and corrosion resistance, but Ca exceeds 0.008%, and rare earth elements exceed 0.02%. If added in excess, coarse non-metallic inclusions will be formed and the hot workability and corrosion resistance will deteriorate, so the upper limit content was set to o, oos% for Ca and 0.02% for rare earth elements. In addition, in the present invention, rare earth elements include those having atomic numbers of 57 to 71 and 89 to 103.
Refers to the number element and Y.

The reason why the austenitizing temperature was set at 920 to 1100°C when stainless steel having the above components was made into a pipe and then heat-treated to give it a specified strength was because at temperatures lower than 920°C, austenitization was not sufficient. This is because it is difficult to obtain the necessary strength, and if the austenitizing temperature force exceeds 1100°C, the crystal grains will become significantly coarser and the impact toughness of the base material will decrease, so the austenitizing temperature is 920 to 1100°C. And so.

The reason why the cooling rate in the cooling after austenitization is set to be higher than water cooling is because if the cooling rate is slower than water cooling, it becomes difficult to secure the desired strength and toughness, and the corrosion resistance decreases.

The reason why the tempering temperature is set to be above 600°C and below the A c H temperature is because if the tempering temperature is less than 600°C, sufficient tempering will not occur, and if the tempering temperature exceeds the A c H temperature, part of the material will become austenite, and then it will be cooled. This is because fresh martensite is sometimes produced, and martensite that has not been sufficiently tempered remains, reducing impact toughness and increasing SSC susceptibility in an environment containing hydrogen sulfide.

The reason why the cooling rate in cooling after tempering was set to be higher than air cooling is because toughness decreases at a cooling rate slower than air cooling.

In the present invention, a martensitic stainless steel having a predetermined composition is made into a steel pipe, and the pipe making method is to use a press pipe manufacturing method or a hot rolling method to make a seamless steel pipe. UOE steel pipe, t&! The present invention is applicable to both steel pipes and welded steel pipes as spiral steel pipes. Here, the press tube manufacturing method refers to a normal press tube manufacturing method such as a hot extrusion method or a bush bench method. The hot rolling method refers to a normal hot rolling method such as a plug mill method or a mandrel mill method. UOEil pipe, ERW steel pipe or spiral steel pipe refer to ordinary UOE steel pipe, ERW steel pipe or spiral steel pipe, respectively.

(Example) Examples of the present invention will be described below.

Stainless steel with the components shown in Table 1 is melted and made into steel pipes with a wall thickness of 12.7 m through the steps shown in Table 1, and then quenched and tempered under the conditions shown in Table 1. High-strength martensitic stainless steel with a 0.2% offset yield strength of 42 kg/IIm" or more
It was made into a tube. The cooling during quenching was water-cooled, and the cooling during tempering was air-cooled. These steel pipes were circumferentially welded by hand to produce joints. The welding heat input was 17 kJ/c+e.

JIS No. 4 impact test pieces (full size) were taken from the base metal and the weld heat affected zone of the circumferential weld, and an impact test was conducted. Further, the maximum hardness of the weld heat affected zone was determined by micro-Vickers measurement with a load of 100 g.

In addition, test pieces were taken from the base metal and subjected to corrosion tests in a humid carbon dioxide environment. For the corrosion test in an infiltrated carbon dioxide environment, a test piece with a thickness of 3-1, a width of 15 strips, and a length of 50 cm was used, and a 5% NaCl aqueous solution was used in an autoclave at a test temperature of 150°C at a carbon dioxide gas partial pressure of 40 atm. 30 inside
The corrosion rate was calculated from the weight change before and after the test after immersion for one day. The unit of corrosion rate is 1/y, but if the corrosion rate of a material in the boat fishing environment is less than 0.1/y, the material is considered to be sufficiently corrosion resistant and usable. ing.

The test results are also shown in Table 1. In Table 1, in the impact test results, O indicates a fracture surface transition temperature of 130°C or less, ×
indicates that the fracture surface transition temperature exceeds 130℃ and is below 0℃, XX indicates that the fracture surface transition temperature was 0℃, and 0 indicates the maximum hardness of the weld heat affected zone. 300
Less than or equal to 0.05 mm, × means that the maximum hardness was 300 or more and less than 450, and XX means that the maximum hardness was 450 or more. In the corrosion test results, O means that the corrosion rate is less than 0.05 min/y, O The corrosion rate is 0.05 wa/y or more.
．． Less than 10 cm/y, × represents a corrosion rate of 0.10 cm/y or more and less than 0.5 cm/y, and XX represents a corrosion rate of 0.5 cm/y or more. In Table 1, the comparison steel N[L29 is Al5I 420 steel, and Na30 is 9Cr-IMo sea bream, both of which are conventional steels conventionally used in a humid carbon dioxide environment.

As is clear from Table 1, line pipes Nos. 1 to 28 manufactured according to the method of the present invention have significantly superior impact toughness of the base metal and weld heat affected zone, and sufficiently low hardness of the weld heat affected zone. Even at extremely high temperatures of 150"C for a line pipe in an acid gas environment, the corrosion rate is lower than the practically usable corrosion rate of 0.1/y, and it has excellent corrosion resistance. It can be seen that the line pipes manufactured according to the method of the present invention can be water-cooled during quenching, and have excellent productivity. 29
- No. 31 showed quench cracking during quenching by water cooling. Comparative Examples 32 to 34 also have a corrosion rate well above 0.1°/y at 150°C in a humid carbon dioxide environment, and the impact toughness of the base metal and weld heat affected zone is poor, and the welding heat The hardness of the affected area is high.

(Effects of the Invention) As described above, the present invention provides a method for manufacturing a high-strength martensitic stainless steel line pipe that has excellent corrosion resistance and weldability in a humid carbon dioxide environment, and also has excellent productivity. This makes it possible to provide this technology, and it will greatly contribute to the development of industry.

Claims (10)

[Claims] (1) In weight%, C is reduced to less than 0.02%, Si: 1% or less, Mn: 2% or less, Cr: 11-14%, Cu: 1.2-4.5%, Al: 0.005 to 0.2%, N is reduced to 0.015% or less, and the balance is Fe and unavoidable impurities.
A martensitic stainless steel that is austenitized at 00°C, then cooled at a cooling rate higher than water cooling, then tempered at a temperature of 600°C or higher and lower than Ac_1 temperature, and then cooled at a cooling rate higher than air cooling. Method of manufacturing line pipes. (2) The method for manufacturing a martensitic stainless steel line pipe according to claim 1, wherein the martensitic stainless steel further contains 4% or less Ni by weight as an additional component. (3) The martensitic stainless steel further contains one or two of Mo: 2% or less and W: 4% or less as additional components by weight. A method for manufacturing martensitic stainless steel line pipe. (4) Martensitic stainless steel further contains additional components by weight of V: 0.5% or less, Ti: 0.2% or less, Nb: 0.5% or less, Zr: 0.2% or less, and Ta. The method for producing a martensitic stainless steel line pipe according to claim 1, 2 or 3, characterized in that the method contains one or more of Hf: 0.2% or less and Hf: 0.2% or less. . (5) A claim characterized in that the martensitic stainless steel further contains one or two of Ca: 0.008% or less and rare earth elements: 0.02% or less as additional components. The method for manufacturing a martensitic stainless steel line pipe according to 1, 2, 3 or 4. (6) The method for manufacturing a martensitic stainless steel line pipe according to claim 1, 2, 3, 4, or 5, wherein the method for manufacturing the steel pipe is a press pipe manufacturing method. (7) Claim 1, wherein the method of forming the steel pipe is a hot rolling method.
, 2, 3, 4, or 5. The method for manufacturing a martensitic stainless steel line pipe according to . (8) The martensitic stainless steel according to claim 1, 2, 3, 4, or 5, wherein the method for forming a steel pipe is to manufacture a martensitic stainless steel plate and then form a UOE steel pipe. Method of manufacturing line pipes. (9) The martensitic stainless steel according to claim 1, 2, 3, 4, or 5, wherein the method for forming a steel pipe is to manufacture a martensitic stainless steel plate and then form an ERW steel pipe. Method of manufacturing steel line pipe. (10) Claim 1, 2, 3, 4, or 5, wherein the method for forming a steel pipe comprises manufacturing a martensitic stainless steel plate and then forming a spiral steel pipe.
A method for manufacturing a martensitic stainless steel line pipe described in .