KR20120044120A - Api steel sheet with excellent heat treatment properties for oil tubular country goods and method of manufacturing the api steel sheet - Google Patents

Abstract

PURPOSE: An API(American Petroleum Institute) steel sheet with high heat treatment characteristic for an oil well and a manufacturing method thereof are provided to achieve a steel pipe for an oil well by securing a tensile strength of 1100 MPa(Mega Pascal) or greater and a yield strength of 890MPa or greater after heat treatment. CONSTITUTION: A method for manufacturing an API steel sheet for an oil well comprises a step of finish-rolling a slab to an FDT(Finishing Delivery Temperature) of 800-900°C(S105) and a step of cooling and coiling the hot-rolled sheet at a CT(Coiling Temperature) of 650-550°C(S120). The slab comprises C(Carbon) of 0.22-0.27wt.%, Si(Silicon) of 0.1-0.3wt.%, Mn(Manganese) of 1.2-1.5wt.%, Al(Aluminum) of 0.02-0.04wt.%, Nb(Niobium) of 0.01-0.03wt.%, Ti(Titanium) of 0.01-0.03wt.%, Ni(Nickel) of 0.05-0.2wt.%, Cu(Copper) of 0.01-0.2wt.%, Ca(Calcium) of 0.001-0.004wt.%, B(Boron) of 0.001-0.0025wt.%, and Fe(Iron) and inevitable impurities of the remaining amount.

Description

API steel sheet with excellent heat treatment characteristics and manufacturing method {API STEEL SHEET WITH EXCELLENT HEAT TREATMENT PROPERTIES FOR OIL TUBULAR COUNTRY GOODS AND METHOD OF MANUFACTURING THE API STEEL SHEET}

The present invention relates to an oil tubular country goods (API) American Petroleum Institute (API) steel sheet manufacturing technology used for drilling of oil or gas, and more particularly, an API steel sheet for oil wells having excellent heat treatment properties after piping and a method of manufacturing the same. It is about.

Oil well steel pipes are steel pipes used for drilling oil or gas. Such oil well steel pipes are usually upgraded by hot-rolled steel sheets and then subjected to QT (Quenching & Tempering) heat treatment according to the purpose of use.

In general, it is manufactured through a slab reheating process, a hot-rolling process and a cooling / coiling process.

The slab reheating process reheats slab plates that are semifinished.

In the hot rolling process, the slab sheet is rolled to a final thickness at a high temperature using a rolling roll.

In the cooling / winding process, the rolled sheet is cooled by cooling to a specific coiling temperature (CT).

An object of the present invention is to provide an API steel sheet for oil wells having excellent heat treatment properties having mechanical properties of API-5CT J55 standard (tensile strength of 517 MPa or more and yield strength of 379 MPa or more) that are widely used as steel pipe materials for oil wells by controlling alloy components and controlling the conditions of hot rolling processes. It is to provide a manufacturing method.

It is another object of the present invention to provide an API steel sheet for oil wells having a tensile strength (TS) of 590 MPa or more and a yield strength (YS) of 420 MPa or more and an elongation (EL) of 30% or more, and at the same time, excellent heat treatment characteristics.

API steel sheet manufacturing method excellent in the heat treatment property according to an embodiment of the present invention for achieving the above one object by weight, carbon (C): 0.22 ~ 0.27%, silicon (Si): 0.1 ~ 0.3%, manganese (Mn): 1.2 to 1.5%, aluminum (Al): 0.02 to 0.04%, niobium (Nb): 0.01 to 0.03%, titanium (Ti): 0.01 to 0.03%, nickel (Ni): 0.05 to 0.2%, copper (Cu): 0.01 ~ 0.2%, Calcium (Ca): 0.001 ~ 0.004%, Boron (B): 0.001 ~ 0.0025% and slab plate consisting of remaining iron (Fe) and unavoidable impurities FDT (Finishing Delivery Temperature): 800 Hot rolling step of finish rolling to ℃ ~ 900 ℃; And a cooling / winding step of winding the hot rolled plate to CT (Coiling Temperature): 650 ° C to 550 ° C.

At this time, before the hot rolling step, the slab plate re-heating Slab (Slab Reheating Temperature): 1150 ~ 1200 ℃ reheating step; may further include a.

API steel sheet for oil wells excellent in the heat treatment characteristics according to the embodiment of the present invention for achieving the other object by weight, carbon (C): 0.22 ~ 0.27%, silicon (Si): 0.1 ~ 0.3%, manganese (Mn) : 1.2 ~ 1.5%, Aluminum (Al): 0.02 ~ 0.04%, Niobium (Nb): 0.01 ~ 0.03%, Titanium (Ti): 0.01 ~ 0.03%, Nickel (Ni): 0.05 ~ 0.2%, Copper (Cu) : 0.01 ~ 0.2%, calcium (Ca): 0.001 ~ 0.004%, boron (B): 0.001 ~ 0.0025% and the remaining iron (Fe) and inevitable impurities, characterized by having a complex structure containing ferrite and pearlite It is done. The steel sheet may include phosphorus (P): 0.018% or less and sulfur (S): 0.005% or less.

In this case, the steel sheet preferably includes silicon (Si) and manganese (Mn) in a range satisfying Equation 1 below, and the steel sheet is sulfur (S) and calcium in a range satisfying Equation 2 below. It is preferable to include (Ca).

Equation 1: 6 ≤ [Mn] / [Si] ≤ 9

Equation 2: 2.0 ≤ [Ca] / [S] ≤ 2.5

Where [] is the weight percent of each element

Oil well API steel sheet excellent in heat treatment properties according to the present invention to increase the carbon (C) content to 0.22 ~ 0.27% by weight, hardenable elements such as titanium (Ti), boron (B), nickel (Ni), copper (Cu) There is an advantage that can have excellent heat treatment properties by adding.

Therefore, the API steel sheet manufactured by the method according to the present invention can secure a tensile strength of 1100 MPa or more and a yield strength of 890 MPa or more after heat treatment, and has an advantage of upgrading to an oil well steel pipe having various mechanical properties.

Figure 1 is a flow chart schematically showing a method for producing a well API API steel sheet excellent heat treatment according to an embodiment of the present invention.
2 is a microstructure photograph of a hot rolled specimen prepared by the method according to Example 1 of the present invention.
FIG. 3 is a microstructure photograph after QT heat treatment of the hot rolled specimen shown in FIG. 2.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various different forms, and only the embodiments make the disclosure of the present invention complete, and those skilled in the art to which the present invention pertains. It is provided to fully inform the person having the scope of the invention, which is defined only by the scope of the claims. Like reference numerals refer to like elements throughout.

Hereinafter, with reference to the accompanying drawings will be described in detail with respect to an oil well API steel sheet and a manufacturing method excellent in heat treatment properties according to a preferred embodiment of the present invention.

Oil Well API Steel Plate

The API steel sheet for oil wells having excellent heat treatment characteristics according to the present invention can be upgraded to various steel grades through QT (Quenching and Tempering) heat treatment after the tubing, and the API-5CT J55 defined by the American Petroleum Institute (API) It aims to secure mechanical properties of tensile strength (TS) of 517 MPa or more and yield strength of 379 MPa or more.

To this end, the API steel sheet for oil wells according to the present invention in weight%, carbon (C): 0.22 ~ 0.27%, silicon (Si): 0.1 ~ 0.3%, manganese (Mn): 1.2 ~ 1.5%, aluminum (Al): 0.02 ~ 0.04%, Niobium (Nb): 0.01 ~ 0.03%, Titanium (Ti): 0.01 ~ 0.03%, Nickel (Ni): 0.05 ~ 0.2%, Copper (Cu): 0.01 ~ 0.2%, Calcium (Ca): 0.001% to 0.004%, boron (B): 0.001% to 0.0025%, and has a composite structure containing ferrite and pearlite. In addition, the API steel sheet for oil wells according to the present invention may include phosphorus (P): 0.018% or less and sulfur (S): 0.005% or less. The rest of the alloy components are made of iron (Fe) and impurities which are inevitably included in steelmaking.

Hereinafter, the role and content of each component included in the oil well API steel plate according to the present invention will be described.

Carbon (C)

Carbon (C) is added to secure the strength, considering the characteristics of the present invention to secure the strength after the heat treatment, it is preferable to be added to less than heavy carbon.

The carbon is preferably added in 0.22 to 0.27% by weight of the total weight of the API steel sheet according to the present invention, more preferably 0.23% by weight can be presented. When the carbon content is less than 0.22% by weight, it is difficult to secure sufficient strength, and when the carbon content exceeds 0.27% by weight, there is a problem that the toughness is lowered and the weldability is decreased during electric resistance welding.

Silicon (Si)

In the case of silicon (Si), when it is added in excess of 0.3% by weight, the weldability of the steel may be degraded, and re-heating during the hot rolling process and red scale during the hot rolling may cause problems on the surface quality. After the plating can be inhibited.

On the other hand, Al-Si complex deoxidation is required to control the properties of Mn-oxide and Si-oxide due to the characteristics of the API steel plate according to the present invention in which manganese (Mn) is added in an amount of 1% by weight or more. do. This is because when the resistance resistance welding (ERW) for manufacturing steel pipes within the range of 6 ~ 9 Mn / Si ratio within a certain range will significantly reduce the occurrence of weld cracks.

Therefore, the content of the silicon is preferably 0.1 to 0.3% by weight of the total weight of the API steel sheet according to the present invention.

Manganese (Mn)

Manganese (Mn) is very effective as a solid solution strengthening element, and is an effective element for securing strength by improving the hardenability of steel. In addition, manganese is an austenite stabilizing element, which contributes to the refinement of ferrite grains by retarding ferrite and pearlite transformation.

The manganese is preferably added in an amount ratio of 1.2 to 1.5% by weight of the total weight of the API steel sheet according to the present invention in consideration of the strength improving effect and the central segregation. If the added amount of manganese is less than 1.2% by weight, the effect of strengthening the solid solution is insignificant.On the contrary, if the added amount of manganese exceeds 1.5% by weight, the weldability is greatly reduced. There is a problem that greatly reduces.

Phosphorus (P)

Phosphorus (P) is added to inhibit cementite formation and increase strength.

However, since phosphorus deteriorates weldability and causes final material deviation by slab center segregation, the phosphorus (P) is in the range of 0.018% by weight or less of the total weight of the API steel sheet according to the present invention. It is preferred to add in a limited manner.

Sulfur (S)

Sulfur (S) is an element that inhibits the toughness and weldability of steel, and combines with manganese to form MnS non-metallic inclusions to generate cracks during processing of steel.

Therefore, the content of sulfur (S) is preferably limited to 0.005% by weight or less of the total weight of the API steel sheet according to the present invention.

Aluminum (Al)

Aluminum (Al) is added for deoxidation during steelmaking.

The aluminum is preferably added in 0.02 to 0.04% by weight of the total weight of the API steel sheet according to the present invention, more preferably 0.03% by weight can be presented. If the content of aluminum is less than 0.02% by weight, sufficient deoxidation effect cannot be obtained. On the contrary, when the content of aluminum exceeds 0.04% by weight, there is a problem of inhibiting weldability.

Niobium (Nb)

Niobium (Nb) is one of the elements that have the greatest influence on the strength of steel as a precipitate forming element. It is an element that improves the strength of steel by precipitating carbonitride in steel or strengthening solid solution in Fe. In particular, niobium-based precipitates are solid-solution precipitated during hot rolling after solid solution in a heating furnace of 1150 ℃ or more when reheating the slab effectively increases the strength of the steel.

The niobium is preferably added in a content ratio of 0.01 to 0.03% by weight of the total weight of the API steel sheet according to the present invention, more preferably 0.015% by weight can be presented. It has a sufficient niobium addition effect when the content of niobium is 0.01% by weight or more. On the other hand, when the content of niobium exceeds 0.03% by weight, due to excessive precipitation it can reduce the playability, rolling properties and elongation.

Titanium (Ti)

In the present invention, titanium (Ti) is a TiN precipitate forming element, and forms TiN during slab reheating, thereby suppressing austenite grain growth and increasing strength. In particular, TiN precipitates are not easily dissolved at high temperatures due to the high dissolution temperature, and thus serve to refine the grains in the weld heat affected zone (HAZ).

In addition, as in the present invention, in the case of boron (B) -added steel, the precipitation of BN is prevented by remarkably reducing the dissolved nitrogen through TiN precipitation, thereby effectively improving the hardenability by the addition of boron.

The titanium is preferably added in 0.01 ~ 0.03% by weight of the total weight of the API steel sheet according to the present invention, more preferably can present 0.02% by weight. If the content of titanium is less than 0.01% by weight, the effect of adding titanium is insignificant, and if the content of titanium is more than 0.03% by weight, the TiN precipitate is coarsened to reduce the effect of inhibiting grain growth, and the surface defects of the manufactured API steel sheet May cause.

Nickel (Ni)

Nickel (Ni) refines grains and is dissolved in austenite and ferrite to strengthen the matrix. In particular, nickel is an effective element for improving low temperature impact toughness.

The nickel is preferably added at 0.05 to 0.2% by weight of the total weight of the API steel sheet according to the present invention, more preferably 0.1% by weight can be presented. When nickel (Ni) is added at less than 0.05% by weight, the effect of improving the strength and the low temperature impact toughness due to the addition of nickel cannot be properly exhibited. On the contrary, when the content of nickel (Ni) exceeds 0.2% by weight, there is a problem of causing red brittleness and raising the manufacturing cost.

Copper (Cu)

Copper (Cu) is added as nickel (Ni) as an element to improve the hardenability and corrosion resistance of the steel.

The copper is preferably added in 0.01 to 0.2% by weight of the total weight of the API steel sheet according to the present invention. When the content of copper is less than 0.01% by weight, the addition effect may not be sufficiently exhibited. On the contrary, when the content of copper exceeds 0.2% by weight, there is a problem of lowering the surface properties of the steel.

Calcium (Ca)

Calcium lowers the sulfur content in the steel by forming CaS, and also reduces MnS segregation, thereby reducing steel cleanliness and grain boundary segregation of sulfur, thereby increasing resistance to reheat cracking.

The calcium is preferably added in 0.001 to 0.004% by weight of the total weight of the API steel sheet according to the present invention, more preferably 0.0025% by weight can be presented. When the content of calcium is less than 0.001% by weight, there is a problem in that the content of sulfur is minimized so as to satisfy Equation 2, that is, 2 ≦ [Ca] / [S] ≦ 2.5. On the contrary, when the content of calcium exceeds 0.004% by weight, there is a problem of forming inclusions such as CaO.

Boron (B)

Boron (B) is an element that segregates in austenite grains and stabilizes austenite by lowering grain boundary energy, thereby improving hardenability of steel.

The boron is preferably added in 0.001 to 0.0025% by weight of the total weight of the API steel sheet according to the present invention, more preferably 0.002% by weight can be presented. When the content of boron is less than 0.001% by weight, the effect of improving hardenability is insufficient. On the other hand, when the content of boron exceeds 0.0025% by weight, there is a problem of rapidly increasing the brittleness of the steel.

On the other hand, the API steel sheet for oil wells according to the present invention preferably comprises silicon (Si), manganese (Mn), sulfur (S) and calcium (Ca) in a range that satisfies the following formula (1).

Equation 1: 6 ≤ [Mn] / [Si] ≤ 9

Equation 2: 2.0 ≤ [Ca] / [S] ≤ 2.5

Where [] is the weight percent of each element

Equation 1 shows the best weldability when the ratio of the content of silicon (Si) to the content of manganese (Mn) is 6 to 9, and the ratio of the content of manganese (Mn) to the content of silicon (Si) is less than 6 Or, if it exceeds 9, MnO and SiO ₂ oxides that are stable at high temperature may be generated to cause hook cracks during electric resistance welding, thereby greatly deteriorating weld quality.

In addition, when the ratio of the content of calcium (Ca) to the content of sulfur (S) in the formula (2) is less than 2.0, CaS is insufficient to cause central segregation, and the content of calcium to sulfur is more than 2.5. In the case of the excessive addition of calcium, inclusions such as CaO are formed or the amount of sulfur has to be controlled to a minimum, there is a problem that the manufacturing cost of steel increases.

Manufacturing method of API steel plate for oil well

Figure 1 is a flow chart schematically showing a method for producing a well API API steel sheet excellent heat treatment according to an embodiment of the present invention.

Referring to Figure 1, the API steel sheet manufacturing method according to the present invention shown includes a hot rolling step (S110) and cooling / winding step (S120). In addition, the API steel sheet manufacturing method according to the present invention may further include a slab reheating step (S105) before the hot rolling step (S110).

In the manufacturing method of the API steel sheet for oil wells according to the present invention, the slab sheet material of the semi-finished state, which is the target of the hot rolling process, in weight%, carbon (C): 0.22 to 0.27%, silicon (Si): 0.1 to 0.3%, manganese (Mn) : 1.2 ~ 1.5%, Aluminum (Al): 0.02 ~ 0.04%, Niobium (Nb): 0.01 ~ 0.03%, Titanium (Ti): 0.01 ~ 0.03%, Nickel (Ni): 0.05 ~ 0.2%, Copper (Cu) : 0.01 ~ 0.2%, calcium (Ca): 0.001 ~ 0.004%, boron (B): 0.001 ~ 0.0025% and the remaining iron (Fe) and inevitable impurities.

At this time, the slab plate may include phosphorus (P): 0.018% or less and sulfur (S): 0.005% or less.

On the other hand, the slab plate material, as described above, preferably contains silicon (Si), manganese (Mn), sulfur (S) and calcium (Ca) in a range satisfying the following formula (1) -2.

Equation 1: 6 ≤ [Mn] / [Si] ≤ 9

Equation 2: 2.0 ≤ [Ca] / [S] ≤ 2.5

Where [] is the weight percent of each element

The slab plate having the composition can be obtained through a continuous casting process after obtaining a molten steel of the desired composition through a steelmaking process.

Reheat slab

When the slab reheating step (S105) is included in the method for manufacturing an oil well API steel plate according to the present invention, in the slab reheating step (S105), the slab plate material having the composition is reheated to SRT (Slab Reheating Temperature): 1150 to 1200 ° C.

Through the reheating of slab plates, restocking of segregated components and reclaims of precipitates may occur during casting.

The reheating temperature (SRT) of the slab plate is preferably 1150 to 1200 ° C. If the slab reheating temperature (SRT) is less than 1150 ° C., the segregated components during casting may not be sufficiently reusable, and precipitate dissolution such as niobium (Nb) may not be sufficient. On the contrary, when the slab reheating temperature (SRT) exceeds 1200 ° C, the austenite grain size may increase, resulting in coarsening of the ferrite of the final microstructure, which may make it difficult to secure the strength. .

Hot rolling

In the hot rolling step (S110), the slab plate is finish-rolled to FDT (Finishing Delivery Temperature): 800 ~ 900 ℃. When the slab reheating step S105 is included, the rolling target is a reheated slab plate.

Finish rolling temperature (FDT) in the hot rolling step (S110) is preferably 800 ~ 900 ℃. When the finish rolling temperature (FDT) exceeds 900 ℃ austenite grains are coarse, the ferrite grains are not sufficiently refined after the transformation, it may be difficult to secure the strength. In addition, when the finishing temperature is too low below 800 ° C, problems such as generation of a mixed structure due to abnormal reverse rolling may occur.

Cooling / winding

In the cooling / winding step (S120), the hot rolled sheet is coiled by cooling to CT (Coiling Temperature): 650 ° C to 550 ° C.

In the present invention, the cooling process is to cool the rolled plate to 650 ℃ ~ 550 ℃ corresponding to the pearlite temperature region through a method such as water cooling, thereby suppressing the grain growth of the steel sheet to form a matrix structure having fine ferrite grains, It is carried out to form a pearlite structure to ensure high strength and high toughness. Cooling rate may be about 1 ~ 100 ℃ / sec, but is not limited thereto.

In the present invention, if the coiling temperature (CT) exceeds 650 ℃, the strength is insufficient, on the contrary, if the coiling temperature (CT) is less than 550 ℃, the manufacturing cost of the steel increases, it is possible to secure sufficient strength, but high toughness There is a problem that is difficult to secure.

The API steel sheet prepared through the above process may have a ferrite and pearlite composite structure, and may have an average grain size of 10 to 20 μm.

In addition, the prepared API steel sheet for oil wells may have high strength of tensile strength (TS): 590 MPa or more and yield strength (YS): 420 MPa or more, and may also secure high elongation of 30% or more.

The API steel sheet for oil wells according to the present invention can secure characteristics of various oil well steel types through QT (Quenching and Tempering) heat treatment.

Example

Hereinafter, the configuration and operation of the present invention through the preferred embodiment of the present invention will be described in more detail. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.

Details that are not described herein will be omitted since those skilled in the art can sufficiently infer technically.

1. Preparation of Hot Rolled Specimens

Hot-rolled specimens were prepared in Example 1 and Comparative Example 1 using the compositions shown in Table 1 and the process conditions described in Table 2.

In the case of hot-rolled specimens according to Example 1 and Comparative Example 1, ingots having respective compositions were prepared, and the rolled simulation test machine was used to simulate hot-rolling processes such as heating, hot rolling, cooling (water cooling), and the like. Charged.

[Table 1] (unit:% by weight)

TABLE 2

2. Evaluation of mechanical properties

Tensile tests were conducted to evaluate the materials of the hot rolled specimens prepared according to Example 1 and Comparative Example 1.

Referring to Table 2, in the hot-rolled specimen prepared according to Example 1, the tensile strength (TS) was 590 MPa or more, the yield strength (YS) was 420 MPa, and the elongation was 33% or more.

On the other hand, in the hot-rolled specimen prepared according to Comparative Example 1, the tensile strength (TS) and the yield strength was somewhat lower than in Example 1, particularly in the case of the elongation (EL) was significantly lower than in Example 1.

2 is a microstructure photograph of a hot rolled specimen prepared by the method according to Example 1 of the present invention.

Referring to FIG. 2, it can be seen that the microstructure of the hot rolled specimen prepared by the method according to Example 1 is composed of a fine ferrite and pearlite composite structure having an average grain size of 10 to 20 μm.

FIG. 3 is a microstructure photograph after QT heat treatment of the hot rolled specimen shown in FIG. 2.

For QT (Quenching and Tempering) heat treatment, the hot-rolled specimen prepared according to Example 1 was heated to 1000 ° C. and then quenched by water cooling, and then tempered at 550 ° C.

After QT heat treatment, the specimen showed tensile strength (TS) 1100 MPa, yield strength (YS) 890 MPa, and elongation (EL) 16%. This corresponds to mechanical properties that satisfy the API 5CT P110 specification (tensile strength of 862 MPa or more, yield strength of 750 MPa or more) that requires the highest strength.

Therefore, the API steel sheet for oil wells according to the present invention can be upgraded to various steel grades such as API 5CT L80, API 5CT N80, and API 5CT P110, which are used as oil well steel pipes, depending on the QT heat treatment conditions.

Meanwhile, referring to FIG. 3, it can be seen that the hot rolled specimen after the heat treatment is made of martensite structure. This corresponds to the effect of adding a hardenable element such as titanium (Ti), boron (B), copper (Cu), nickel (Ni) to the composition of the API steel sheet for oil wells according to the present invention.

As described above, the oil-based API steel sheet manufactured by the manufacturing method according to the present invention satisfies the API-5CT J55 characteristics before heat treatment, and is required by API-5CT N80, API-5CT L80, API-5CT P110, etc. by excellent heat treatment characteristics. There is an advantage to secure the strength.

In the above description, the embodiment of the present invention has been described, but various changes and modifications can be made at the level of those skilled in the art. Such changes and modifications may belong to the present invention without departing from the scope of the present invention. Accordingly, the scope of the present invention should be determined by the following claims.

S105: Slavic Reheating Step
S110: hot rolling stage
S120: Cooling / Coiling Step

Claims (11)

By weight%, carbon (C): 0.22 to 0.27%, silicon (Si): 0.1 to 0.3%, manganese (Mn): 1.2 to 1.5%, aluminum (Al): 0.02 to 0.04%, niobium (Nb): 0.01 ~ 0.03%, Titanium (Ti): 0.01 ~ 0.03%, Nickel (Ni): 0.05 ~ 0.2%, Copper (Cu): 0.01 ~ 0.2%, Calcium (Ca): 0.001 ~ 0.004%, Boron (B): 0.001 A hot rolling step of finishing and rolling the slab plate composed of ˜0.0025% and the remaining iron (Fe) and unavoidable impurities to FDT (Finishing Delivery Temperature): 800 ° C. to 900 ° C .; And
The hot rolled plate CT (Coiling Temperature): cooling / winding step of winding by cooling to 650 ℃ ~ 550 ℃; API (American Petroleum Institute) steel sheet manufacturing method comprising a.
The method of claim 1,
Before the hot rolling step, the slab plate material SRT (Slab Reheating Temperature): Slave reheating step of reheating to 1150 ~ 1200 ℃; API API steel sheet manufacturing method further comprising a.
The method according to claim 1 or 2,
The slab plate is
A method for producing an API steel sheet for oil wells, comprising silicon (Si) and manganese (Mn) in a range satisfying Equation 1 below.
Equation 1: 6 ≤ [Mn] / [Si] ≤ 9
Where [] is the weight percent of each element
The method according to claim 1 or 2,
The slab plate is
Phosphorus (P): 0.018% or less and sulfur (S): 0.005% or less comprising a method for producing an API steel sheet for oil wells.
The method of claim 4, wherein
The slab plate is
API steel sheet for oil wells, characterized in that it comprises sulfur (S) and calcium (Ca) in a range satisfying the following equation (2).
Equation 2: 2.0 ≤ [Ca] / [S] ≤ 2.5
Where [] is the weight percent of each element
By weight%, carbon (C): 0.22 to 0.27%, silicon (Si): 0.1 to 0.3%, manganese (Mn): 1.2 to 1.5%, aluminum (Al): 0.02 to 0.04%, niobium (Nb): 0.01 ~ 0.03%, Titanium (Ti): 0.01 ~ 0.03%, Nickel (Ni): 0.05 ~ 0.2%, Copper (Cu): 0.01 ~ 0.2%, Calcium (Ca): 0.001 ~ 0.004%, Boron (B): 0.001 ~ 0.0025% and the remaining iron (Fe) and inevitable impurities,
API steel sheet for oil wells, characterized in that it has a composite structure containing ferrite and pearlite.
The method of claim 6,
The steel sheet
An API steel sheet for oil wells comprising silicon (Si) and manganese (Mn) in a range satisfying Equation 1 below.
Equation 1: 6 ≤ [Mn] / [Si] ≤ 9
Where [] is the weight percent of each element
The method of claim 6,
The steel sheet
Phosphorus (P): 0.018% or less and sulfur (S): 0.005% or less comprising an API steel sheet for oil wells.
The method of claim 8,
The steel sheet
API steel sheet for oil wells, characterized in that it comprises sulfur (S) and calcium (Ca) in a range satisfying the following equation (2).
Equation 2: 2.0 ≤ [Ca] / [S] ≤ 2.5
Where [] is the weight percent of each element
The method of claim 6,
The ferrite is
API steel sheet for oil wells, characterized in that the average grain size is 10 ~ 20㎛.
The method of claim 6,
The steel sheet
An API steel sheet for oil wells having a tensile strength (TS) of 590 MPa or more, a yield strength (YS) of 420 MPa or more, and an elongation (EL) of 33% or more.

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