JPS59177350A - Steel with superior resistance to sulfide corrosion cracking - Google Patents

Abstract

PURPOSE:To improve the resistance of a steel contg. prescribed percentages of C, Si, Mn and Co to sulfide corrosion cracking by forming a sulfide film on the surface of the steel. CONSTITUTION:The titled steel is obtd. by forming a sulfide film on the surface of a steel consisting of 0.05-0.5% C, 0.05-1% Si, 0.1-2% Mn, 0.03-1% Co and the balance Fe. The resulting steel has superior resistance to sulfide corrosion cracking in a wet environment contg. hydrogen sulfide.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a low alloy steel having excellent LTJ sulfide corrosion cracking properties in a humid environment containing hydrogen sulfide (H2S).

BACKGROUND OF THE INVENTION During the drilling, transportation, refining, and storage processes of petroleum, corrosion cracking of preparations caused by H2S contained in crude oil often becomes a problem. For example, drilling for oil.

Oil country tubular goods, line pipes and LI used for transportation
Sulfide corrosion is always a concern in tanks.

What steel materials are used for these 1flj pipes, tanks, etc.?

There is a tendency for steel with high mechanical strength to be required.

Sulfide corrosion cracking is more likely to occur in materials with higher mechanical strength (4). Sulfide corrosion cracking occurs when stressed steel is
It is said that hydrogen generated during corrosion in a wet environment containing 2S penetrates into the steel, causing hydrogen embrittlement of the steel.

As a countermeasure against this sulfide corrosion cracking, the steel structure 1
Painting the surface of strength-regulated 2 steel and injecting inhibitors into the corrosive environment are being done. However, this measure has not been able to provide stable corrosion cracking resistance over a long period of time.

The present invention provides copper with improved sulfide corrosion cracking resistance, and includes Co in the steel components.1. By forming a sulfide film on the steel surface, hydrogen penetration into the steel is suppressed, and sulfide corrosion cracking resistance is improved.This effect is independent of the structure and material of the steel. It is something that we have. The summary is C: 0.05~0.50%, Si
: 0.05~1.0%, Mn: 0, 1-0~2
．． 00%, Co: 0.03~]00%, with the balance consisting of iron and inevitable impurities, with a sulfide film formed on the surface of the steel. It is.

The present invention will be explained in detail below.

The C contained in the steel composition of the present invention is added in an amount of 0.05% or more as a reinforcing component for structural materials such as steel pipes and steel plates used in humid environments containing H2S.

However, excessive wrinkling increases sulfide corrosion cracking and reduces toughness, so the upper limit was set to 05.

Sl is a residual component in the copper manufacturing process, and like C, 0.05% or more is required as a reinforcing component for steel, and containing it in excess will embrittle the grain boundaries of the steel structure. The limit was set at 1.00, which deteriorates the tetrasulfide corrosion cracking property and the workability of steel.

Mn is a component that improves strength and hardenability, or O
The effect cannot be obtained if the number is less than J. Excessive content exceeding 20 modulus will form significant segregation zones during agglomeration, and will have an adverse effect on toughness and sulfide corrosion cracking. From the viewpoint of sulfide corrosion cracking resistance, the Mn content of the needles is preferably 12 or less.

COIre-<+1i Contain 0.03-1.0% in NI. When steel containing CO is immersed and corroded in an acidic solution (particularly in the amount of solution relative to the surface area of the steel), a sulfide film is formed on the steel surface.
When used in a practical environment, the sulfide film acts as a protective film, suppressing hydrogen penetration into the steel,
Improves sulfide corrosion cracking resistance. Such an effect of cobalt on the formation of a protective film cannot be obtained when the content is less than 0.03%, and when the content exceeds -1.0%, it reaches a saturated state and the hardenability also deteriorates.

P is included as another unavoidable impurity component.

S and the like should be reduced as much as possible because they deteriorate the mechanical properties and sulfide corrosion cracking resistance of steel. Preferably, -P<0.020 and S<0.015%.

Furthermore, the effect of co as mentioned above is the strength of steel.

Cu: 0 to improve mechanical properties such as toughness, weldability, etc.
．． 10-0.50%, N1: O1-03, cr: 0.
20~2.00chi, Mo:0.05~], 00φ, W
: 0.05~1.00%, Nb: 0.01~0.15%, y: 0.01~0.15%, Ti: O○1~01
,5%, B:0, OOO:”-・0.0 0 5 0
%, Co:O,OO1~00'' 0 It does not disappear even in a plow that selectively contains 2 p1 or more of 1 type of candy.

In the present invention, molten steel having the composition described above is continuously cast in a melting furnace such as a converter or an electric furnace, or after ingot formation.

Steel plates, steel pipes, steel bars, and shaped steel products manufactured through hot working or further quenching of these products.

A sulfide film is formed on the surface of steel that has been subjected to arbitrary heat treatment such as tempering and standardization.

The formation of this sulfide film occurs when the steel in an unloaded state) (2S
The lower the specific liquid ratio of this solution and the higher the Oo content in the steel, the more stable the sulfide film (e.g. cos,
(co-Fe)s'4) is formed on the surface of the handle material.

Once formed, this sulfide film has a higher specific liquid volume.
Even in a corrosive liquid containing I28, the effect as a retaining film is not lost, and the 11A corrosion resistance is improved, and by suppressing hydrogen penetration into the steel, the sulfide corrosion cracking resistance is improved.

-1- The steel product of the present invention as described above can be used for a long period of time in a humid environment containing )]2S.

Next, examples of the present invention will be described.

Example 1 Steels with four types of chemical compositions as shown in Table 1 were melted and
A hot-tempered steel plate was quenched and tempered to give a yield strength of 73 to 7/-, which was used as a test sample.

The sulfide corrosion cracking resistance of these steels is DCB (Doul) 1
It was evaluated by the K15cc value obtained by the eCant, ileveY13eam) test. In addition, the corrosive liquid has a typical NA (1!E) used in sulfide corrosion cracking tests.
Standard solution (05% CH3CO0H, 5% N.C1 at 25℃
(an aqueous solution saturated with H2S).

Table 2 shows the experimental conditions. Experimental condition 1 corresponds to the evaluation of the sulfide corrosion cracking property of conventional steel, and experimental condition 11 corresponds to the evaluation of the sulfide corrosion cracking property of the steel of the present invention. It is a test to

The preliminary immersion in Table 2, Experimental Condition 1, is a treatment to form a stable sulfide film on the steel surface in NACE liquid with a small specific liquid volume of 3 cc/crIf for the unstressed DCB specimen. This corresponds to The right column of Table 1 shows the stress for the specimens subjected to this pre-soaking (Experiment 2) and those not subjected to this pre-soaking (Experiment 1).
14 in NAOE solution under the condition of specific liquid volume of c, /era.
This is the result of measuring KISCC after immersing the steel for one day and measuring the amount of hydrogen in the steel using the 45°C glycerin replacement method.

This shows that the amount of hydrogen reserve in the culm steel with a large Ki scc value decreases greatly.

In Experiment 2, pre-soaking was performed according to Table 1.

Except for steel A, which does not contain CO, Kjr,
CC has improved significantly. Also compared to A steel.

It can be seen that the amount of hydrogen in the B, C, and D steels containing Co is greatly reduced by pre-soaking.

The figure shows the relationship between the amount of hydrogen in steel and Kjsca for both Experiment] and Experiment 20.
When it becomes less than m, K15cc suddenly becomes a high value. The stable sulfide film formed on the steel surface by pre-soaking and pre-soaking acts as an effective post-preservation film against hydrogen intrusion into the steel, resulting in improved sulfide corrosion cracking resistance of the steel. It will be done.

Embodiment Table 4 shows the results of investigating the effect of pre-soaking on steels E to J having the compositions shown in Table 3.

These steels also contain CO, such as E, F, 0. H and I steels can be pre-soaked to +K15ec
Height: Approximately 20-50 K9-mln Although it is a high value, -C
In J steel that does not contain O, almost no effect of H+ immersion is observed compared to K15c'c.

* Experimental Conditions I (See Table 1) ** Experimental Conditions ■ (See Table 1) In this way, steel containing CO was prepared with a stable sulfide film formed on its surface under no-load conditions. is H2S
The resistance to sulfide corrosion cracking is improved in a humid environment containing high loads under practical conditions.

[Brief explanation of drawings]

FIG. 1 is a chart showing the relationship between the amount of hydrogen in steel and KISCC.

Claims (1)

[Claims] C: 0.05 to 0.50 qb, si', 0.
Section 05-1.0. Mn', 0.10-2.00%, Cn: 0.0
A steel having excellent sulfide corrosion cracking resistance, characterized in that a sulfide film is formed on the surface of the steel, which contains 3 to 100% iron and the remainder consists of iron and inevitable impurities.