JPH07246481A - High strength clad steel sheet manufacturing method - Google Patents

Abstract

(57) [Summary] [Purpose] A method for producing a high-strength clad steel sheet by TMCP having high efficiency and low-temperature toughness of a low-alloy base material and excellent sour resistance. [Structure] A sandwich slab is assembled by seal-welding an extremely low S-Ca treated low C-Ni-Cu-high Nb-trace Ti steel base material and a stainless steel or nickel-based alloy composite material, and this is assembled into a specific TMCP. A clad steel plate is manufactured by rolling under the conditions. [Effect] TMCP has enabled the production of high-quality clad steel plates. As a result, energy saving and process saving have become possible, and the safety of the pipeline has been significantly improved by improving various characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is a clad steel plate (a UOE steel pipe, a bending roll steel pipe, etc.) made of a high alloy composite material having excellent corrosion resistance such as stainless steel or nickel base alloy and a base material of low alloy steel. The present invention relates to a high quality and highly efficient manufacturing method of.

[0002]

2. Description of the Related Art From the viewpoint of safety and economy, a crude oil / natural gas transportation line pipe containing a large amount of corrosive substances (H ₂ S, CO ₂ , Cl ⁻ ) is used as a combination material of stainless steel and nickel base alloy. The demand for high alloy clad steel pipes tends to increase more and more. Conventionally, such a steel pipe was manufactured by forming a clad steel plate manufactured by rolling, seam welding, and then reheating and water cooling (solution treatment) the entire steel pipe, but this method had extremely low productivity. . Therefore, recently, a technique capable of omitting the solution treatment in a steel pipe and achieving various properties without rolling (for example, JP-A-60-2169).
84, 62-16892, 63-130283, JP-A-4-197588, and JP-A-4-319081) have been invented, and the technology for producing a clad steel plate has made a dramatic progress. However, the low temperature toughness and sour resistance (hydrogen-induced cracking: HIC and sulfide stress corrosion cracking: resistance to SSC) of the base material that can be achieved by these techniques are not always satisfactory.

[0003]

DISCLOSURE OF THE INVENTION The present invention provides a clad steel plate which can simultaneously achieve excellent corrosion resistance of a laminated material (including weld metal) and strength of base metal, low temperature toughness, and sour resistance without solution treatment of steel pipe. It provides manufacturing technology, and is characterized by high productivity in addition to high quality (excellent characteristics and soundness).

[0004]

SUMMARY OF THE INVENTION The gist of the present invention is a composite material of stainless steel or a nickel-based alloy, and in weight%, C: 0.02 to 0.06 Si: 0.6 or less Mn: 0.8 To 1.5 P: 0.015 or less S: 0.0010 or less Ni: 0.2 to 0.5 Cu: 0.1 to 0.5 Nb: 0.08 to 0.12 Ti: 0.005 to 0 0.03 or less Al: 0.01 to 0.005 Ca: 0.001 to 0.005 N: 0.001 to 0.006 further containing V: 0 to 0.10 (including the case of no addition), and X = Mn + Ni + Cu (%), 1.5 ≦ X ≦
A low alloy steel base material, the balance of which satisfies 2.3, is composed of iron and unavoidable impurities is overlapped and seal welded on four circumferences to assemble a slab, which is reheated to a temperature of 1100 to 1250 ° C. and then fully reduced. Ratio 5 or more, rolling end temperature 850 to 1
After rolling at 000 ° C and air cooling for 60 to 200 seconds,
6 at a cooling rate of 5-40 ° C / sec from a temperature of 800 ° C or higher
Cooling to a temperature of 00 ° C. or lower.

The stainless steel of the present invention means austenite and austenite-ferrite two-phase system, and nickel-based alloy is a corrosion resistant material such as Incoloy 825 and Inconel 625. Further, the base material has high strength and high strength in the direction perpendicular to the rolling direction such that the strength is X52 or more (API standard), the low temperature toughness is the absorbed energy at -30 ° C. in the Charpy test ≧ 250 J, and the fracture surface transition temperature ≦ −70. It is a tough low alloy steel.

The method for producing the clad steel sheet of the present invention will be described in detail below. Its features are (1) rolling of the assembled slab at high temperature, air cooling for an appropriate time, and then water cooling, and (2) low C-Ni-Cu-high treatment of the base metal component system with extremely low S-Ca. As the Nb-trace Ti system, excellent corrosion resistance of the laminated material and excellent strength, low temperature toughness and sour resistance of the base material are simultaneously achieved. As a result of the research conducted by the present inventors, in order to obtain excellent corrosion resistance (pitting corrosion resistance) in a laminated material, the alloying elements are sufficiently solution-treated at the time of reheating, this is rolled at a high temperature, and air-cooled for an appropriate time to austenite. The structure is recrystallized and rapidly cooled to obtain the σ phase and α'phase (C
It has been clarified that the precipitation of (r-carbide) must be suppressed. However, when rolling is performed at a high temperature such that the austenite structure of the laminated material is recrystallized, the crystal grains of the base material are not sufficiently refined, and the low temperature toughness and sour resistance required for the line pipe cannot be obtained. For this reason, a composition system having good strength / toughness balance and sour resistance even after rolling at high temperature was examined. As a result, low C-Ni- treated with extremely low S-Ca as a base material component.
It was found that the Cu-high Nb-trace Ti system is effective,
We invented a new clad steel plate manufacturing method to which this is applied.

In the present invention, the slab is assembled by the following method. First, superimpose the mating material on the surface of the low alloy steel base material,
Assemble the slab by seal welding the four laps. At this time, the adhered surfaces of the base material and the laminated material are machined (or polished) to be smooth in advance, and cleaning / degreasing and deaeration with a vacuum pump are performed. Further, the mating material surfaces of the two slabs thus assembled are brought into close contact with each other via a separating agent, and four laps are welded to assemble a so-called sandwich slab. In this method, two clad steel plates can be manufactured by rolling once by cutting and separating the four circumferences of the rolled steel plate.

Next, the reheating, rolling and cooling conditions of the present invention will be described. In the present invention, the sandwich slab 110
Reheat to a range of 0 to 1250 ° C. This is necessary to secure the corrosion resistance of the laminated material and the various properties of the base material. In order to obtain excellent corrosion resistance in the laminated material, the alloying elements must be sufficiently solution-treated and the austenite structure must be recrystallized after rolling at a rolling end temperature of 850 ° C. or higher. For this purpose, it is necessary to reheat at least at 1100 ° C or higher. However, if the reheating temperature exceeds 1250 ° C., the austenite grains of the base material become coarse and the crystal grains after rolling also become large, and the low temperature toughness and sour resistance deteriorate. Therefore, the upper limit of the reheating temperature is 1250 ° C.

The reheated slab must be rolled at a total reduction ratio of 5 or more, and the rolling end temperature must be 850 to 1000 ° C. The reason why the reduction ratio is 5 or more is that (1) the bonding material and the base material are completely metallurgically bonded, and (2)
This is for refining the crystal grains of the base material. In terms of the performance of use of the line pipe, it is preferable that the mating material and the base material are metallurgically bonded, and for this purpose, a larger reduction ratio is more desirable. The minimum reduction ratio depends on the type of the laminated material, the reheating temperature and the rolling temperature, but is 5 or more when the rolling temperature is high as in the present invention. In the present invention, rolling is performed at 850 to 10
Finish at 00 ° C. If the rolling end temperature is 850 ° C. or lower, the structure of the laminated material is not sufficiently recrystallized, and corrosion resistance (for example, pitting corrosion resistance, test conditions 10% FaCl ₃ .6H ₂ O solution immersion for 48 hours, ASTM G48 standard) is obtained. Remarkably deteriorates. From the viewpoint of the corrosion resistance of the laminated material, the higher the rolling finish temperature is, the more desirable. However, if the rolling end temperature is too high, the crystal grains of the base material do not become fine and the low temperature toughness and sour resistance are deteriorated. Therefore, the rolling end temperature is limited to 1000 ° C or lower.

Further, in the present invention, 60 to 20 after the completion of rolling.
Air cooling for 0 seconds, cooling from a temperature of 800 ° C. or higher to an arbitrary temperature of 600 ° C. or lower at a cooling rate of 5 to 40 ° C./second, and then air cooling (cooling). The reason for providing air cooling time after rolling is
This is for promoting the recrystallization of the austenite structure of the laminated material and improving the corrosion resistance. If it is rapidly cooled immediately after rolling, good corrosion resistance cannot be obtained unless the rolling end temperature is considerably high. When the rolling end temperature is 850 ° C. or higher, an air cooling time of at least 60 seconds is required (desirably 100 seconds or longer). However, the extension of the air cooling time causes the temperature of the rolled steel sheet to decrease, and the σ phase,
Not only does it cause the precipitation of α'phase (Cr carbide), but it also hinders the strengthening of the base metal by accelerated cooling. For this reason, although depending on the thickness of the steel sheet, the air cooling time must be 200 seconds or less and water cooling must be performed at 800 ° C or higher. At this time, in order to suppress precipitation of the σ phase and α ′ phase and to strengthen the base material by accelerated cooling, it is necessary to cool to 600 ° C. or less at a cooling rate of 5 to 40 ° C./second as a cooling condition.

Reheating (tempering) the clad steel sheet after rolling to a temperature below the Ac ₁ point for the purpose of improving low temperature toughness, dehydrogenation treatment, etc. does not impair the characteristics of the present invention. .

The reasons for limiting the base material components of the present invention will be described below. C, Mn, Ni, C to secure the strength and ductility of the base material, sour resistance and corrosion resistance of the laminated material
u, Nb and Ti contents are 0.02 to 0.06, respectively.
%, 0.8-1.5%, 0.2-0.5%, 0.1
0.5%, 0.08-0.12%, 0.005-0.0
Limited to 3%.

The lower limits of the amounts of C and Mn are the target base metal
It is the minimum amount for sufficiently exerting the effects of weld strength, low temperature toughness, precipitation hardening due to addition of Nb, and refinement of crystal grains.
Further, the upper limit value is a limit value for improving the center segregation of the cast slab, reducing the hardened structure detrimental to sour resistance, achieving fine dispersion, excellent low temperature toughness of the base material, and field weldability.
If the C content of the base metal is too high, C diffuses into the extremely low C composite material when reheating the slab and deteriorates the corrosion resistance. Therefore, from the viewpoint of the corrosion resistance of the composite material, the upper limit of the C content is 0.06%. Must be limited to:

Ni and Cu are added, and X = Mn + Ni
The purpose of setting + Cu to 1.5 ≦ X ≦ 2.3 is low C and low Mn.
This is to improve the strength of the steel of the present invention without deteriorating the low temperature toughness and the sour resistance. Ni, Cu addition is Mn
In comparison with the addition of Cr, Mo, and B, the strength of the steel of the present invention, which has been rolled at a high temperature, is increased without forming a hardened structure detrimental to low temperature toughness and sour resistance in the rolled structure (especially the central segregation zone of the slab). It turned out to let me. However, in order to obtain such an effect, it is necessary to limit the X = Mn + Ni + Cu (%) value in relation to the individual Ni and Cu addition amounts and Mn. When the amounts of Ni and Cu are 0.2, 0.1% or less or the X value is less than 1.5%, the effect of substantially improving the strength is small, and the Ni and Cu amounts are 0.5% or more or the X value is 2 or less. If it exceeds 0.3%, the increase in strength is large, but since a hardened structure is generated and the low temperature toughness and sour resistance are deteriorated, the Ni and Cu contents and the X value are 0.2 to 0.5% and 0. 1 to 0.5%, 1.5 ≦ X ≦
It was limited to 2.3 (%).

In the steel of the present invention, N is an essential element.
b: 0.08 to 0.15%, Ti: 0.005 to 0.0
Contains 3%. Nb contributes to grain refinement and precipitation hardening in controlled rolling, and has a toughening action for steel. In the steel of the present invention in which the rolling must be finished at a high temperature of 850 ° C. or higher in order to improve the corrosion resistance of the laminated material, it is necessary to add at least 0.08% or more of Nb. As a result, the refinement of crystal grains and the precipitation hardening proceed even under special manufacturing conditions based on high-temperature rolling as in the present invention, and a strength / toughness balance superior to that of conventional clad steel sheets can be achieved. However, if Nb is added in an amount of 0.12% or more, the on-site weldability and the toughness of the welded portion deteriorate, so the upper limit value is set to 0.
It was set to 12%. Also, addition of Ti forms fine TiN,
It is effective in improving the low temperature toughness of the base metal and the weld heat affected zone (HAZ) by refining the microstructure by suppressing coarsening of austenite grains during slab reheating and welding. Suppression of coarsening of austenite grains during slab reheating is particularly important in the steel of the present invention which finishes rolling at high temperature. In order to fully bring out the effect of such TiN, at least 0.0
05% Ti addition is required. However, if the amount of Ti is too large, coarsening of TiN and precipitation hardening due to TiC occur,
Since the low temperature toughness deteriorates, the upper limit value must be limited to 0.03%.

Further, in the present invention, the impurity element P,
S is 0.015 or 0.0010% or less, respectively, and C
0.001 to 0.005% of a is added. The main reason for this is to improve sour resistance (HIC resistance, SSC resistance) and further improve the low temperature toughness of the base material and the welded portion. Reducing the amount of P reduces center segregation of the cast slab and improves sour resistance, as well as prevents grain boundary fracture and improves low temperature toughness. Further, the reduction of the amount of S has the effect of reducing the stretched MnS and improving the sour resistance and ductility. C
a controls morphology of sulfide (MnS) and improves low temperature toughness (increased absorbed energy in Charpy test, etc.)
In addition to that, it also exerts a remarkable effect in improving the resistance to HIC and SSC. However, when the amount of Ca is 0.001% or less, there is no practical effect, and when added in excess of 0.005%, CaO-CaS is produced in a large amount and clusters,
Not only does it impair the cleanliness of the steel and becomes a large inclusion, it also adversely affects the field weldability. Therefore, the amount of Ca added is limited to 0.001 to 0.005%. HIC resistant
In order to improve the resistance and the SSC resistance, the S and O contents are set to 0.
001%, 0.002% or less, ESSP = (C
a) [1-124 (O)] / 1.25 (S) 0.5 ≦
It is particularly effective to set ESSP ≦ 10.0.

Next, the reasons for limiting the other elements will be described. Si is generally an element added for deoxidation and strength improvement, but if added in large amounts, the weldability and HAZ toughness deteriorate, so the upper limit value was made 0.6%. Deoxidation of steel is Ti
Alternatively, Al alone is sufficient, and Si does not necessarily have to be added.

Al is an element usually contained in steel as a deoxidizing agent and also effective in refining the structure. However, the amount of Al is 0.
If it exceeds 06%, Al-based non-metallic inclusions increase and impair the cleanliness of steel, so the upper limit value was made 0.06%. Deoxidation is also possible with Ti or Si, and it is not always necessary to add it.

N forms TiN and suppresses coarsening of austenite grains during slab reheating and welding, and improves base material toughness and HAZ toughness. The minimum amount required for this is 0.001%. However, if it is too large, it may cause deterioration of the HAZ toughness due to slab surface flaws and solute N, so the upper limit must be suppressed to 0.006%.

Next, the reason for adding V will be described.
The main purpose of adding V as necessary to the basic component is to increase the manufacturable plate thickness and improve the properties such as strength and toughness of the base metal without impairing the excellent characteristics of the steel of the present invention. Is. Therefore, the amount added is of a nature that should be limited by itself.

V has almost the same effect as Nb, but the result is much weaker than Nb. The upper limit value is 0.10% from the viewpoint of local weldability and HAZ toughness. The lower limit of the effect of the amount of V is 0.01%.

[0022]

EXAMPLES Next, examples of the present invention will be described. Converter-
Base metal slab of various steel components (thickness: 240
mm) was manufactured. After rolling this slab to a specified thickness, machine one surface and superimpose it with a specified thickness of SUS316L or Incoloy 825 laminated material (adjusted so that the laminated material thickness of the clad steel plate after rolling is 3 mm), and make four turns. Was vacuum-evacuated and seal-welded. Further, two slabs manufactured in this manner were superposed on the surface of the laminated material with the separating material interposed therebetween, and four laps were welded to assemble a sandwich slab. The low-alloy steel and the bonded surface of the laminated material were all machined to be smooth, washed and degreased.

The sandwich slab was reheated, rolled and cooled under various conditions to produce a clad steel plate, and various properties were investigated. The adhesion between the base material and the laminated material was investigated by ultrasonic flaw detection,
The mechanical properties of the base metal were investigated in the direction perpendicular to rolling. The sour resistance of the low alloy steel base material is the NAC test piece with the laminated material removed.
9 in E solution (5% NaCl + 0.5% CH ₃ COOH)
After immersion for 6 hours, ultrasonic flaw detection was performed on the surface of the test piece, and the crack area ratio (%) of the test piece was evaluated. Further, the corrosion resistance of the laminated material was evaluated by a pitting corrosion test (test condition: SUS316L was immersed in a 10% FeCl ₃ .6H ₂ O solution at 15 ° C. for 48 hours, and Incoloy 825 was immersed at 30 ° C. for 48 hours).

Examples are shown in Table 1. The clad steel sheet produced according to the present invention has excellent strength, low temperature toughness and sour resistance in the low alloy steel base material, and excellent corrosion resistance in the laminated material. On the other hand, in the comparative steel, the chemical composition of the base material or the clad steel plate manufacturing conditions is not appropriate,
Either characteristic is inferior. Since Steel 7 has a high C content, the low temperature toughness of the base material, the HIC resistance and the corrosion resistance of the laminated material are poor. Since Steel 8 has a high Mn content, the HIC resistance of the base material is poor. In Steel 9, since the addition of Ni and Cu is not included and the X value is small, the strength, low temperature toughness and HIC resistance of the base material are inferior. Steel 10 has a small amount of Nb, so the strength, low temperature toughness and HIC resistance of the base material are poor. Since Steel 11 does not contain Ti, it is inferior in low temperature toughness and HIC resistance. Steel 11,12
In each case, Ca is not added or the S content is high, so that the HIC resistance of the base material is poor. Steel 14 has a too low slab reheating temperature, so the strength of the base material and the corrosion resistance of the laminated material are poor. Since Steel 15 has a small rolling reduction ratio, the adhesion between the base material and the laminated material and the low temperature toughness of the base material are poor. Since steel 16 has a short air-cooling time after rolling, the corrosion resistance of the laminated material is poor. Steel 17 has a water cooling start temperature that is too low, resulting in poor strength / low temperature toughness of the base metal, HIC resistance, and corrosion resistance of the laminated material. Since steel 18 is air-cooled after rolling, the strength of the base material, the HIC resistance, and the corrosion resistance of the laminated material are poor.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

[Table 3]

[0028]

EFFECTS OF THE INVENTION By using the clad steel plate of the present invention, a high quality large diameter clad steel pipe can be manufactured without subjecting the entire steel pipe to solution treatment. As a result, energy saving and process saving have become possible, and the safety of the pipeline has been significantly improved by improving various characteristics.

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location C22C 19/05 E 38/00 301 F 302 H 38/58 // B21B 3/00 A 3/02

Claims (1)

[Claims] 1. A composite material of stainless steel or a nickel-based alloy, and in% by weight, C: 0.02-0.06 Si: 0.6 or less Mn: 0.8-1.5 P: 0.015 or less. S: 0.0010 or less Ni: 0.2 to 0.5 Cu: 0.1 to 0.5 Nb: 0.08 to 0.12 Ti: 0.005 to 0.03 Al: 0.06 or less Ca: 0.001 to 0.005 N: 0.001 to 0.006, further containing V: 0 to 0.10 (including no addition), and X = Mn + Ni + Cu (%), 1.5 ≦ X
Assemble a slab by superposing a low-alloy steel base material, the balance of which satisfies ≦ 2.3, consisting of iron and unavoidable impurities, and seal-welding the four circumferences, and reheating the slab to a temperature of 1100 to 1250 ° C. Rolling ratio 5 or more, rolling end temperature 850-
Production of a high-strength clad steel sheet, which comprises rolling at 1000 ° C., air-cooling for 60 to 200 seconds, and then cooling from a temperature of 800 ° C. or more to a temperature of 600 ° C. or less at a cooling rate of 5 to 40 ° C./sec. Method.