KR20030053757A - Line pipe steel with excellent sulfide stress corrosion cracking resistance and method for manufacturing the steel - Google Patents

Abstract

PURPOSE: Provided is a method for manufacturing a line pipe steel with excellent sulfide stress corrosion cracking resistance by suppressing the formation of MnS inclusion. CONSTITUTION: The method includes the steps of reheating a steel slab comprising C 0.01 to 0.10 wt.%, 0.05 wt.% or less of Si, 0.20 wt.% or less of Mn, 0.015 wt.% or less of P, 0.01 wt.% or less of S, Al 0.01 to 0.1 wt.%, Ca 0.001 to 0.005 wt.%, a balance of Fe and incidental impurities to the temperature range of 1100 to 1300 deg.C, wherein the steel slab further comprises at least one element selected from 0.09 wt.% or less of Nb, 0.09 wt.% or less of V, 0.05 wt.% or less of Ti; hot rolling the reheated steel slab, wherein finish hot rolling temperature is 950 to 800°C; and coiling the hot rolled steel sheet at 500 to 700°C.

Description

Line Pipe Steel with Excellent Sulfide Stress Corrosion Cracking Resistance and Method for Manufacturing the Steel}

The present invention relates to a line pipe steel excellent in emulsion stress corrosion cracking resistance used as a raw material of the crude oil or natural gas transport line pipes, and to a method of manufacturing the same, and more specifically to the emulsion stress corrosion cracking resistance without intentionally adding Mn A superior Mn non-added linepipe steel and a method of manufacturing the same.

In recent years, corrosion of line pipes due to H ₂ S gas contained in crude oil or natural gas has become a big problem in accordance with high pressure transportation to improve the development and transportation efficiency of oil or gas fields with high H ₂ S content. Corrosion cracking resistance is required.

Numerous patents have been filed / registered for emulsion stress corrosion cracking resistance at present.

For example, in Japanese Patent Laid-Open No. 7-278659, a method for improving emulsion stress corrosion cracking resistance by adding Cr is disclosed. Suggesting.

However, the sources of the above methods basically contain Mn, and elements such as Cr and Cu are added to prevent the damage of the emulsion stress corrosion cracking resistance caused by the formation of MnS.

Therefore, a number of studies have been conducted on the method for improving the emulsion stress corrosion cracking resistance, and one of the results is the method described in the 171.172 Seosan Commemorative Technical Lecture held by the Japan Iron and Steel Association in 1999. (See 'Overview of Major Products and Manufacturing Methods of Steel Pipes', 1999, Juwoo Metal Industry Steel Pipe Division, p. 8)

In this course, in order to improve emulsion stress corrosion cracking resistance, the formation of MnS should be prevented. For this purpose, the amount of Mn added should be reduced and the amount of S present as an impure element should be reduced as much as possible (10 ppm or less). Controlled execution, clean steel production by vacuum treatment, P content reduction (150 ppm or less) for suppressing central segregation during ingot production, Cu addition for hydrogen intrusion prevention, and the like are proposed.

Of these, the role of the MnS inclusions in the elongated phase, which act as a starting point of the emulsion stress corrosion cracking, is particularly important.

However, even if all of the above treatments are actually performed, the emulsion stress corrosion cracking resistance of the material is greatly changed depending on the method of manufacturing the material and the heat treatment technology.

An object of the present invention is to provide a line pipe steel having excellent emulsion stress corrosion cracking resistance by appropriately controlling other chemical components and manufacturing processes without adding Mn.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

In the present invention, C: 0.01 to 0.10%, Si: 0.50% or less, Mn: 0.0 (no addition) or 0.20% or less, P: 0.015% or less, S: 0.01% or less, Al: 0.01 to 0.1%, Ca : 0.001% to 0.005% based on Nb: 0.09% or less, V: 0.09% or less, and Ti: 0.05% or less, or a combination thereof alone, Cu: 0.50% or less, Ni: 0.50% or less and Cr : Relates to a linepipe steel containing 0.50% or less of a single or combination, and excellent in emulsion stress corrosion cracking resistance composed of residual Fe and unavoidable impurities.

The present invention also relates to a method for producing line pipe steel excellent in the above-mentioned emulsion stress corrosion cracking resistance of the present invention.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The reason for limiting the chemical composition of the steel of the present invention is explained.

The C is the most economical and effective alloying element for strengthening the steel, but the weldability, emulsion stress corrosion cracking resistance, etc. are reduced when added in a large amount is limited to 0.01 to 0.10% in the present invention.

The reason for setting the lower limit of the content of C in the present invention to 0.01% is because it is a minimum amount that combines with Nb, V or Ti added to strengthen the steel to exert the effect.

On the other hand, the addition of a large amount of C causes brittleness problems, and lowers the emulsion stress corrosion cracking resistance by the formation of the target pearlite, the upper limit of the content of C is preferably limited to 0.10%.

The Si is generally an element having the effect of deoxidation and solid solution strengthening of molten steel. If the content is 0.50% or more, the weldability and the like deteriorate, so it is preferable to limit it to 0.5% or less.

The Mn is generally added to about 0.5% -2.0% as an essential element for securing strength and toughness.

However, in the present invention, when a large amount of Mn is added, it promotes central segregation during play and reduces impact toughness and emulsion stress corrosion cracking resistance due to MnS formation.

That is, in the present invention, Mn is not intentionally added, but inevitably contained up to 0.2% depending on the Mn content present in the ferroalloy when using ferroalloy to add other components, the content of which is as small as possible Preferably, the upper limit of the content is limited to 0.2%.

However, as described below, since Mn is present at 0.2% or less, the target emulsion stress corrosion cracking resistance is deteriorated. Thus, by adding an appropriate amount of Cu, Ni, Cr, etc. alone or in combination, the emulsion stress corrosion cracking resistance is increased. We can greatly improve

P promotes central segregation with Mn during play, thereby lowering impact toughness and emulsion stress corrosion cracking resistance, and also lowering weldability, so that the content thereof is preferably limited to 0.015% or less.

S forms MnS together with Mn in the steel to greatly reduce brittleness, and in particular, greatly reduces emulsion stress corrosion cracking resistance, but may be limited to 0.01% or less because Mn is hardly added in the present invention.

Al is generally an element contained in the deoxidized steel, and at least 0.01% or more must be added to exhibit the effect of deoxidation.

In addition, in the present invention, since deoxidation by addition of Si was suppressed, up to 0.1% was added in order to enhance the deoxidation effect by Al addition, and when a large amount of Al was added, it shows a side effect accompanied by the effect of increasing the strength.

The Ca is an element that improves the odor resistance by controlling the MnS shape of steel inclusions, and in order to obtain the effect of addition, more than 0.001% should be added. It causes a decrease in weldability.

Therefore, the content of is preferably set to 0.001 to 0.005%.

The Nb and V show a precipitation strengthening effect by the addition of a small amount, and the upper limit is preferably limited to 0.09% because the strength increase due to precipitation strengthening is not large at 0.09% or more, respectively.

The Ti is precipitated with TiN in the steel to suppress the grain growth of the austenite when reheated to obtain a high strength and excellent impact toughness, and also precipitated by TiC, etc. serves to strengthen the steel.

However, since the effect is not large when the content of Ti is 0.05% or more, the upper limit is preferably limited to 0.05%.

The Cu, Ni, and Cr are useful elements for preventing emulsion stress corrosion cracking, and at the same time, in the present invention, Mn is added because it is effective in increasing the strength of steel and miniaturizing grains.

The upper limit of each of Cu, Ni, and Cr is set at 0.5% or less because the economical efficiency is lost as the amount of the added element is increased.

By hot rolling and winding the steel formed as described above under ordinary conditions, in the present invention, high strength line pipe steel excellent in emulsion stress corrosion cracking resistance can be produced.

In the present invention, hot rolling and winding are performed under ordinary conditions, and are not particularly limited. Preferably, the heating temperature is about 1100 to 1300 ° C, the rolling end temperature is 950 to 800 ° C, and the winding temperature is 500 to 700. ℃.

Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE

Ingots were manufactured by hot-rolling the inventive steel and the comparative steel having the chemical composition as shown in Table 1 using a vacuum induction melting furnace.

Hot rolling conditions were made into the conditions which are commercially applied in order to manufacture a board | plate material.

That is, after heating for a sufficient time (1 to 3 hours) in the temperature range of 1100 ~ 1300 ℃, the rolling finish temperature was rolled up to 12mm thick under the conditions of Table 2 and cooled to the winding temperature of Table 2 by water cooling In order to impart a coiling effect, the resultant was cooled in a furnace after 1 hour at that temperature.

Tensile properties and emulsion stress corrosion cracking resistance were investigated using the hot rolled steel thus obtained, and the results are shown in Table 2 below.

The evaluation of the emulsion stress corrosion cracking resistance in Table 2 was performed in a solution containing 5% NaCl and 0.5% acetic acid at room temperature saturated with 1 atm of H ₂ S gas.

In the state in which the annular tensile test piece was immersed in the above-mentioned solution, a stress corresponding to 72% of the yield stress of each material obtained through the tensile test was applied, and then the fracture was determined.

In the following Table 2, SSCC resistance ^A represents the break time at 72% stress addition state of the sulfide stress corrosion cracking (Sulfide Stress Corrosion Cracking) yield stress.

As shown in Table 2, when forming a steel component according to the present invention (invention steel 5-8), it can be seen that the emulsion stress corrosion resistance is superior to the comparative steel (1-4) outside the scope of the present invention. have.

In the case of comparative steel (1-4), even though there is no Mn addition, the resistance of emulsion stress corrosion is small is due to the decrease in toughness of the steel due to no Mn addition and grain coarsening.

That is, even if it is manufactured under the same rolling conditions without adding Mn, crystal grains are coarsened and emulsion stress corrosion cracking resistance is remarkably lowered. However, when Cu, Ni, Cr, etc. are added, excellent emulsion stress corrosion cracking is not caused. It's showing resistance.

The above results show that the inventive steel has excellent emulsion stress corrosion cracking resistance in an H ₂ S containing atmosphere.

As described above, the present invention is excellent in emulsion stress corrosion cracking resistance by not containing Mn or containing a very small amount, and in particular, it is possible to alleviate efforts to reduce S combined with Mn in the steelmaking process. ₂ S-containing crude oil and natural gas can be applied more effectively in the field of pipe steels.

Claims (2)

By weight%, based on C: 0.01 to 0.10%, Si: 0.50% or less, Mn: 0.20% or less, P: 0.015% or less, S: 0.01% or less, Al: 0.01 to 0.1%, and Ca: 0.001 to 0.005% Here, Nb: 0.09% or less, V: 0.09% or less, and Ti: 0.05% or less are mixed or contained alone, Cu: 0.50% or less, Ni: 0.50% or less and Cr: 0.50% or less Linepipe steel with excellent emulsion stress corrosion cracking resistance, which is contained in a composite and composed of residual Fe and unavoidable impurities. By weight%, based on C: 0.01 to 0.10%, Si: 0.50% or less, Mn: 0.20% or less, P: 0.015% or less, S: 0.01% or less, Al: 0.01 to 0.1%, and Ca: 0.001 to 0.005% Here, Nb: 0.09% or less, V: 0.09% or less, and Ti: 0.05% or less are mixed or contained alone, Cu: 0.50% or less, Ni: 0.50% or less and Cr: 0.50% or less It is characterized in that the steel contained in the composite, the remainder Fe and the inevitable impurities are heated to a temperature range of 1100 ~ 1300 ℃, the hot rolling end temperature to 950 ~ 800 ℃, then wound at 500 ~ 700 ℃ Method for manufacturing line pipe steel with excellent emulsion stress corrosion cracking resistance