JP2914138B2 - Manufacturing method of steel for high corrosion resistance ERW steel pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an American Petroleum (American Petroleum).
X-4 of the standard)
The present invention relates to a method for producing high corrosion-resistant steel for electric resistance welded steel pipe excellent in hydrogen-induced cracking resistance (hereinafter referred to as HIC resistance) mainly used in line pipes of class 2 to X-80.

[0002]

2. Description of the Related Art In recent years, oil wells and gas wells of natural gas have been developed in deep oil fields which have not been neglected in the past due to soaring crude oil prices and depletion of petroleum resources expected in the near future. excavation and of the development is to develop for, such as single Dan abandoned sour gas field has been actively conducted on a global scale.
Such oil and gas wells are generally extremely deep,
Further, the atmosphere is an extremely severe corrosive environment containing CO ₂ , H ₂ S, Cl ⁻ and the like. When petroleum or natural gas containing a large amount of H ₂ S coexists with seawater or freshwater, not only corrosion of the steel surface, but also hydrogen generated by the corrosion penetrates into the steel to cause internal cracking, which is a problem.

[0003] The cracks generated by the penetration of hydrogen into steel are caused by HI.
C, called hydrogen blister cracks. If such a crack occurs in a line pipe for transporting oil and natural gas and penetrates in the plate thickness direction, there is a possibility that the pipeline may be broken due to oil leakage, gas leakage, or the like. In recent years, an electric resistance welded steel pipe is often used as a line pipe, and prevention of HIC has been an important issue.

Conventionally, as a method for preventing HIC, C
The method of preventing corrosion of hydrogen by adding u to form a corrosion-resistant coating and the inclusion of Ca, Zr, R
Methods for controlling the form of inclusions that are spheroidized by EM or the like have been proposed (for example, Japanese Patent Application Laid-Open Nos. 50-97515 and 5
4-382214, JP-A-54-31020, etc.). Further, in order to prevent the generation of cracks due to the formation of bainite or martensite, which is a low-temperature transformation structure due to segregation of Mn and P, and A-based inclusions such as MnS in the central segregation part generally observed in continuous cast materials, And reduction of P have been proposed (for example, JP-A-52-111815, JP-A-62-227067, etc.). Furthermore, it has been pointed out that Nb carbonitride also becomes a starting point of HIC generation.
A method of limiting the amounts of C and N has also been proposed (for example, JP-A-56-119759). The above-mentioned technique makes it possible to produce a steel pipe that can withstand a severe environment from a continuous cast material by an electric resistance welded pipe method.

[0005]

However, the electric resistance welded steel pipe manufactured by the method disclosed in the above publication is used in an environment (pH: 4.8 to 5.0) used in Alaska, Canada and the like.
4 so-called BP environment) or more severe pH:
In an environment of 4.5 or less (so-called NACE environment), HIC resistance cannot be maintained for a long period of time.

[0006] An object of the present invention is to solve the above problems,
An object of the present invention is to provide a method for producing ERW steel pipe excellent in hydrogen-induced cracking resistance capable of maintaining HIC resistance for a long period of time even in a BP environment or a NACE environment.

[0007]

Means for Solving the Problems The present inventors have proposed the BP
As a result of investigating and examining the cracks generated in the HIC test under the environment and NACE environment, as a result, the Ar gas blown for the purpose of closing the immersion nozzle during the continuous casting is captured in the continuous cast slab, and hot rolled In the ERW steel pipe manufactured using the hot-rolled coil, non-metallic inclusions existing around the uncompressed bubbles and Mn, P It was found that due to the local segregation of the steel, the steel could not exhibit the corrosion resistance that the steel originally had, and cracking occurred.

[0008] As a result of further testing and research, steel having excellent HIC resistance under BP environment, for example, C: 0.01 to
0.20%, Si: 0.01 to 0.50%, Mn: 0.
5 to 1.8%, P: 0.020% or less, S: 0.010
% Or less, Al: 0.1% or less, Cu: 0.2 to 0.8
%, Ni: 0.6% or less, and Cr: 1.
0% or less, Mo: 1.0% or less, Ti: 0.01-0.
HIC in steel containing one or more of 10%, Nb: 0.01 to 0.10%, and V: 0.1% or less, with the balance being Fe and unavoidable impurities, This was caused by plate-like sulfides such as Mn and MnS existing in the P segregation zone generated along the uncompressed bubbles. The segregation of Mn and P along the uncompressed bubbles is caused by Ar gas bubbles blown into the molten steel during solidification in continuous casting, which are trapped by the dendrites during solidification during the ascent, and are concentrated due to solidification delay due to the adiabatic effect. It was considered that segregation occurred. The low-temperature transformation structure such as bainite and martensite due to the segregation of Mn and P has an extremely large number of dislocations, and it has been conventionally known that HIC is easily generated.

Further, steel having excellent HIC resistance in a NACE environment, for example, C: 0.01 to 0.20%, Si:
0.01 to 0.50%, Mn: 0.5 to 1.8%, P:
0.020% or less, S: 0.010% or less, Al: 0.
1% or less, Ti: 0.001 to 0.1%, Nb: 0.0
0.5 to 0.1%, Ca: 0.0001 to 0.005%, Cu: 0.2 to 0.8%, Ni: 0.
6% or less, Cr: 1.0% or less, Mo: 1.0% or less,
V: HIC generation in steel containing one or more of 0.1% or less and the balance consisting of Fe and inevitable impurities is caused by Ti-based inclusions (mainly This was due to TiN) or Ca-based inclusion clusters.

[0010] It is well known that Ar gas bubbles blown into molten steel capture inclusions crystallized in the molten steel and float and separate them. It is also well known that inclusions are liable to precipitate in the solidification-delayed portion. It has been found that when uncompressed bubbles due to the residual Ar gas are present in the steel, the HIC resistance is not improved even with the above-mentioned various conventional techniques. Furthermore, the present inventors investigated continuous cast slabs and steel sheets hot-rolled using the slabs, and found that the number of bubbles in the steel changed depending on the amount of Ar gas blown into the molten steel during continuous casting. MnS, Ca-A which causes HIC by reducing the amount of Ar gas blown into molten steel to a predetermined value or less to prevent clogging of the immersion nozzle during continuous casting.
The present inventors have found that it is possible to accumulate l-based / Ca-based inclusion clusters, Ti / Nb-based inclusions, etc., and to reduce uncompressed bubbles of Ar gas in steel materials that cause the generation of Mn and P segregation zones, and reached the present invention. did.

That is, according to the present invention, C: 0.01-0.
20%, Si: 0.01 to 0.50%, Mn: 0.5 to
1.8%, P: 0.020% or less, S: 0.010% or less, Al: 0.1% or less, Cu: 0.2 to 0.8%, N
i: 0.6% or less, Cr: 1.0% or less, Mo: 1.0% or less, Ti: 0.01 to 0.10
%, Nb: 0.01 to 0.10%, V: 0.1% or less of HIC resistance in a BP environment containing at least one of Fe and inevitable impurities . Excellent
In continuous casting of extruded steel, the amount of Ar gas blown into the molten steel to prevent clogging of the immersion nozzle was reduced by 4
It is a method for producing high corrosion resistance steel for electric resistance welded steel pipe, characterized in that the volume is not more than 1 liter.

C: 0.01 to 0.20%, Si:
0.01 to 0.50%, Mn: 0.5 to 1.8%, P:
0.020% or less, S: 0.010% or less, Al: 0.
1% or less, Ti: 0.001 to 0.1%, Nb: 0.0
0.5 to 0.1%, Ca: 0.0001 to 0.005%, Cu: 0.2 to 0.8%, Ni: 0.
6% or less, Cr: 1.0% or less, Mo: 1.0% or less,
V: NACE containing one or more of 0.1% or less, with the balance being Fe and unavoidable impurities
In continuous casting of steel with excellent HIC resistance under the environment ,
A method for producing highly corrosion resistant steel for electric resistance welded steel pipe, characterized in that the amount of Ar gas blown into molten steel to prevent clogging of a submerged nozzle is 3 liters or less per molten molten steel Ton.

[0013]

The reasons for limiting the chemical composition of the steel for high corrosion resistance ERW steel pipes, which is the subject of the present invention, are as follows. C is a basic element for improving the strength of steel, and is required to be 0.01% or more to secure the strength. However, if it exceeds 0.20%, it is not desirable for toughness and weldability, and affects use. Not only that, but also unfavorable to prevent the generation of an abnormal structure (bainite or martensite) in the center segregation zone in the continuous cast material, the content was set to 0.01 to 0.20%. Si is an element necessary as a deoxidizing agent in the steelmaking process, and is required to be 0.01% or more in order to improve the strength of steel. 50%.
Mn is an element necessary for imparting the strength and toughness of steel. To secure the strength, 0.5% or more is required. However, if it exceeds 1.8%, the weldability and toughness are reduced. 5-1.8
%.

Since P is an element that promotes the abnormal structure of the central segregation zone, it is set to 0.020% or less. S generates sulfide-based inclusions and has a large adverse effect on HIC.
0.010% or less. Al is an element necessary as a deoxidizing agent in the steelmaking process, but if it exceeds 0.1%, inclusions increase and the corrosion resistance is impaired. Cu is an element effective for improving the strength of steel and reducing HIC, but if it is less than 0.2%, its effect is not sufficient, and if it exceeds 0.8%, weldability is deteriorated and hot workability is deteriorated. In order to invite, it was set to 0.2 to 0.8%. But,
The corrosion resistance effect of Cu is large when the pH is 5 or more,
If it is less than 10, the corrosion resistance effect cannot be expected, so that it is not always necessary to add it to steel in a use environment where the pH is less than 5. N
i is an element that has an effect on improving the toughness of steel, but it is harmful to the prevention of hydrogen permeation into steel, and it is better to use less.
In the case where 0.30% or more of u is added, Cu embrittlement occurs unless Ni is added, and adversely affects surface quality and the like.
When the Cu of the steel of the present invention is 0.8% or less, it is set to 0.6% or less, which does not significantly affect HIC. When Cu is not added depending on the use environment, it is not always necessary to add Ni for the above reason.

[0015] Ti and Nb are elements having an effect of improving strength, but if the content is less than 0.01%, the effect is not sufficient.
If it exceeds 0.10%, the toughness is impaired.
0.10%. In the NACE environment, it is not necessary to add Cu because Cu has no corrosion resistance effect. However, in order to secure strength when Cu is not added, 0.0% of Ti and Nb is added.
Addition of 1% or more is required. Cr and Mo are elements having an effect of improving the strength. However, if the content exceeds 1.0%, the effect is saturated, which is economically disadvantageous.
V is an element having a strength improving effect similarly to Cr and Mo, but if it exceeds 0.1%, the effect is saturated and it is economically disadvantageous, so V is set to 0.1% or less. Ca is used for controlling the morphology of inclusions, but if added over 0.005%, there is no further effect, and if less than 0.0001%, Ca-based inclusion clusters increase and HIC resistance increases. Therefore, the content is set to 0.0001 to 0.005% or less in order to lower the property.

According to the present invention, the amount of Ar gas blown into molten steel for the purpose of cleaning the deposits such as inclusions in the immersion nozzle during continuous casting is determined by controlling the HIC resistance under the BP environment.
4 liters or less per discharge molten steel Ton is an excellent steel,
Discharged molten steel for steel with excellent HIC resistance under NACE environment
By controlling the volume to 3 liters or less per Ton , Ar gas bubbles remain in the continuously cast slab, thereby reducing the HIC.
, And the segregation bands of Mn and P are greatly reduced, and the HIC resistance can be greatly improved. In the present invention, the amount of Ar gas blown into the molten steel for the purpose of cleaning the deposits such as inclusions in the immersion nozzle at the time of continuous casting is reduced by the HIC resistance under the BP environment.
For excellent steel, less than 4 liters per molten molten steel Ton , N
For steel with excellent HIC resistance under ACE environment, discharge molten steel T
The reason for setting it to 3 liters or less per on is that the number of bubbles in the continuously cast slab is reduced when the amount of Ar gas to be blown is reduced, but sharply decreases at around 4 liters per molten steel Ton. This phenomenon is remarkable when the width of the cast slab is 1500 mm or more. However, since the reduction of the bubbles remaining in the steel slab with the decrease in the amount of Ar gas injected is obvious, the width of the cast slab is not particularly limited. The reduction of the bubbles remaining in the steel slab reduces the inclusions adhering and accumulating around the bubbles, and also suppresses the low-temperature transformation structure (bainite, martensite) due to Mn and P generated along the bubbles. It will be.

[0017]

【Example】

Example 1 The amount of Ar gas blown into molten steel for the purpose of cleaning deposits such as inclusions that adhere to the immersion nozzle during continuous casting was changed in the range of 0 to 12 liters per molten discharge Ton.
Cast slab width 1200mm, 1500mm, 1800
mm, three types of continuously cast slabs were manufactured, and the number of cells per 100 cm ^{2 of} the slab cross section was investigated. The result is shown in FIG. As shown in FIG. 1, the number of bubbles in the continuous casting slab decreases as the amount of the injected Ar gas decreases,
It decreases sharply at around 4 liters per discharged molten steel Ton. In particular, when the casting slab width is 1500 mm or more, the decrease in the amount of the injected Ar gas at around 4 liters per discharged molten steel Ton is remarkable.

Example 2 As shown in Table 1, A to E steels having excellent HIC resistance in a BP environment and F to F steels having an excellent HIC resistance in a NACE environment.
J steel was melted, continuously cast into slabs under the continuous casting conditions shown in Table 2, hot rolled into a hot rolled coil, and then subjected to ERW welding to obtain an ERW steel pipe. The HIC test in the BP environment or the NACE environment of each obtained electric resistance welded steel pipe was performed. Table 2 shows the results. FIG. 2 shows the relationship between the amount of Ar gas blown into molten steel during continuous casting and the crack area ratio (CAR), which is one of the evaluations of HIC resistance. In addition, in the Ar gas injection amount column in Table 2, the amount per molten molten steel Ton, and in the crack occurrence column, ○ indicates no cracking, Δ indicates blister-like minute cracking, and X indicates large cracking. HIC test is NACE
The measurement was performed according to standard TM-02-84.
However, the BP environment in the test result column in Table 2 was a test solution at 25 ± 3 ° C. and an immersion time of 96 using artificial seawater (so-called BP solution) having a pH of 4.9 to 5.3 saturated with H ₂ S as a solution. Time. Also, the NACE environment uses p
Using a 5% NaCl + 0.5% acetic acid solution (so-called NACE solution) of H3.1 to 3.5, the test temperature was 25 ± 3.
C., immersion time 96 hours. In the test, a test piece collected from each of the ERW steel tubes was immersed in the above solution for 96 hours under no load, and then the presence or absence of HIC was determined by a cross-sectional microscope. The test piece was 3 pcs per test solution from each test ERW steel pipe.
Individual test pieces were collected, and it was determined that no HIC was generated only when no HIC was generated in any of the test pieces.

[0019]

[Table 1]

[0020]

[Table 2]

As shown in Table 2 and FIG. 2, the amount of Ar gas blown into the molten steel during continuous casting of steel having excellent HIC resistance under the BP environment or the NACE environment was determined under the BP environment.
Steel with excellent HIC resistance of 4 liters or less per molten molten steel Ton , excellent in HIC resistance under NACE environment
In this case, the HIC, which is frequently generated in the past, is eliminated by setting the discharge molten steel Ton to 3 liters or less . On the other hand, in the comparative examples in which the amount of Ar gas blown into the molten steel was 5 liters or more per molten molten steel Ton, HIC was generated and the crack area ratio exceeded 1% in all cases.

[0022]

As described above, according to the method of the present invention, the amount of Ar gas blown into molten steel during continuous casting of steel having excellent HIC resistance in a BP environment or a NACE environment is reduced by the BP environment. 4 liters or less per molten Ton for HIC in HACE under NACE environment
3 liters per molten Ton for steel with excellent IC properties
By a simple operation that follows, BP environment or NAC
It is possible to manufacture steel for an electric resistance welded steel pipe having excellent HIC resistance in an E environment.

[Brief description of the drawings]

FIG. 1 shows Ar per molten molten steel Ton in Example 1.
It is a graph which shows the relationship between the gas amount and the number of air bubbles in a slab cross section.

FIG. 2 shows Ar per discharged molten steel Ton in Example 2.
It is a graph which shows the relationship between gas amount and crack area ratio.

Continuation of the front page (56) References JP-A-50-97515 (JP, A) JP-A-54-38214 (JP, A) JP-A-62-227067 (JP, A) JP-A-56-119759 (JP, A) , A) JP-A-62-38747 (JP, A) JP-A-2-247052 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B22D 11/00 360 B22D 11/00

Claims (2)

(57) [Claims] C: 0.01 to 0.20%, Si: 0.1%
01-0.50%, Mn: 0.5-1.8%, P: 0.
020% or less, S: 0.010% or less, Al: 0.1%
Hereinafter, Cu: 0.2 to 0.8%, Ni: 0.6% or less, Cr: 1.0% or less, Mo: 1.0%
Hereinafter, Ti: 0.01 to 0.10%, Nb: 0.01 to
0.10%, V: Continuation of steel containing one or more of 0.1% or less and excellent in resistance to hydrogen-induced cracking in a BP environment consisting of Fe and unavoidable impurities. In the casting, a method for producing high corrosion resistant steel for electric resistance welded steel pipe, wherein an amount of Ar gas blown into molten steel to prevent clogging of a submerged nozzle is 4 liters or less per molten molten steel Ton. 2. C: 0.01 to 0.20%, Si: 0.
01-0.50%, Mn: 0.5-1.8%, P: 0.
020% or less, S: 0.010% or less, Al: 0.1%
Hereinafter, Ti: 0.001 to 0.1%, Nb: 0.005
0.1%, Ca: 0.0001-0.005%, Cu: 0.2-0.8%, Ni: 0.6%
Hereinafter, Cr: 1.0% or less, Mo: 1.0% or less, V:
Under NACE environment containing one or more of 0.1% or less, with the balance being Fe and unavoidable impurities
In continuous casting of steel excellent in hydrogen-induced cracking resistance at
A method for producing highly corrosion resistant steel for electric resistance welded steel pipe, characterized in that the amount of Ar gas blown into molten steel to prevent clogging of a submerged nozzle is 3 liters or less per molten molten steel Ton.