JPS62243737A - Steel sheet having superior resistance to hydrogen induced cracking - Google Patents

Abstract

PURPOSE:To manufacture a steel sheet having superior resistance to hydrogen induced cracking by specifying the relation between the hardness of the segregated part of a steel sheet contg. specified percentages of C, Si, Mn, P, S and Al and the total length of inclusions in the part whose hardness has been measured. CONSTITUTION:A steel sheet consisting of, by weight, 0.01-0.30% C, 0.02-0.60% Si, 0.50-2.50% Mn, <=0.020% P, <=0.010% S, 0.005-0.060% Al and the balance Fe with inevitable impurities is manufactured. When the Vickers hardness Hv of the segregated part of the steel sheet is <=230, the relation among the hardness Hv, the total length A(mum) of A type inclusions of >=10mum length in 10mm<2> area of the part whose hardness has been measured and the total length B(mum) of B type inclusions is specified so as to satisfy a formula Hv<=230-4/10X(A+B/2). Thus, a steel sheet causing no hydrogen induced cracking in an environment of about 3pH is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application 1] The present invention relates to a steel plate with excellent hydrogen-induced cracking resistance, and more specifically, a steel plate with a tensile strength of 40 to 100 mm for use in line pipes, pressure vessels, tanks, etc. The present invention relates to a steel plate with excellent hydrogen-induced cracking resistance of Qkgf/am''.

[Prior Art 1 In recent years, equipment used in a humid hydrogen sulfide atmosphere, for example,
BACKGROUND ART There are many accidents caused by so-called hydrogen-induced cracking in line pipes, oil refineries, etc. that transport crude oil and natural gas containing hydrogen sulfide, and there is a strong need for steel sheets with excellent resistance to hydrogen-induced cracking.

This hydrogen-induced cracking occurs due to the pressure of hydrogen generated by corrosion of the steel, which penetrates and diffuses into the steel in an atomic state, accumulates and becomes molecules at the interface between inclusions and the base steel. This is said to propagate along band-like hardened structures that occur in segregated areas in the steel.

Therefore, the current measures to prevent hydrogen-induced cracking are (1) suppression of hydrogen intrusion and diffusion into steel;

(2) Reduction and shape control of inclusions, especially A-based inclusions that have a large notch effect at the tip.

(3) Reducing segregation and suppressing the formation of hardened structures.

The following methods have been adopted.

Regarding (1), for example, JP-A-50-09
As described in Japanese Patent No. 7515, there is a method of forming a corrosion-resistant film by adding Cu, but it is not effective in a harsh environment such as pH = 3, and it is difficult to suppress the occurrence of hydrogen-induced cracking. Regarding (2),
Method for regulating the shape and number of sulfides disclosed in JP-A-51-114318, JP-A-55-128536
Ca, R of JP-A No. 54-031020, etc.
There is a method of controlling the morphology of AM inclusions by EM, but as the strength level of steel sheets increases and the environment becomes harsher, it is difficult to completely prevent the occurrence of hydrogen-induced cracking (3
), there is a method of drastically lowering the P content to 0.006 wt% or less, as described in JP-A-52-111815, but there is a problem in terms of cost, and There is a method of setting the hardness of the hardened tissue portion to Hv≦350, as described in Japanese Patent No. 57-073162.
It is difficult to completely eliminate hydrogen-induced cracking in high-strength steel under harsh environments with low pH.

Of course, these methods are often used in combination, but p
It is difficult to completely suppress the occurrence of hydrogen-induced cracking in a harsh environment such as H = 3, and even if it is possible, it is not sufficient in terms of productivity and manufacturing cost of industrial products. This is the actual situation.

[Problem to be Solved by the Invention 1] The present invention is based on the above-mentioned various problems of conventional steel sheets with respect to hydrogen-induced cracking, and as a result of intensive research by the present inventor, We have developed a steel sheet with excellent hydrogen-induced cracking resistance that does not occur in harsh environments.

[Means for solving the problems] The steel sheet having excellent hydrogen-induced cracking resistance according to the present invention has (1)
C0001~0.30wt%, S i 0.02~0
．． 60wt%, Mn 0.50-2.50wt%, P
0.020wt% or less, S 00010wt% or less, A
l Contains 0.005 to 0.060 wt%, the balance being Fe
and unavoidable impurities, and the Vickers hardness of the segregated part, the total length A (μ) of A-based inclusions with a length of 10 μ or more in the area 10u+2 in the hardness measurement part, and the total length B of B-based inclusions. A steel plate with excellent hydrogen-induced cracking resistance, characterized in that the relationship with (μ) satisfies the following formula.

The first invention is Hv≦230-4/10X (A+B/2), (2) C0.01-0.30u+t%, Si0.02
~0.60u+t%, Mn 0.50-2.50wt%
, P 0.020wt% or less, S 0.010wt% or less, AI 0.005-0.060u+t%, Nb 0.005-0.150ut%, V 0.005
~0.150wt%, Ti 0.005~0.150w
t%, Cu 0005-0.50wt%, Cr 0.0
5-0.50wt%, Mo 0.05-0.50wt%
, Ni 0.05 to 1.00 wt%, and B 0.0003 to 0.0030 wt%, the balance being Fe and unavoidable impurities, and the segregated portion Vickers hardness and the total length A (
A steel sheet with excellent hydrogen-induced cracking resistance, characterized in that the relationship between B (μ) and the total length B (μ) of B-based inclusions satisfies the following formula.

Hv≦230-4/10X (A+B/2) as the second invention, (3) C0.01-0.30wt%, S i 0.0
2-0.80wt%, Mn 0.50-2.50wt%
, P 00020 wt% or less, S 0.010 wt% or less, Al 0.005 to 0.060 wt%, and Ca 0.0005 to 0.0050 wt%, REM 0
．． 001 to 0.030 wt%, the remainder consists of Fe and unavoidable impurities, and the Vickers hardness of the segregated part and the length in the area 10III12 in the hardness measurement part are 10μ or more. A steel plate having excellent hydrogen-induced cracking resistance, characterized in that the relationship between the total length A (μ) of A-based inclusions and the total length B (μ) of B-based inclusions satisfies the following formula.

Hv≦230-4/10X (A+B/2) as the third invention, (4) C0.01-0.30wt%, S i 000
2-0.60wt%, Mn 0.50-2.50wt%
, P 0.020 wt% or less, S 0.010 wt% or less, Al 0.005 to 0.060 wt%, and Nb 0.005 to 0.150 wt%, V 0.005
~0.150wt%Ti 0.005~0.150wt
%, Cu 0.05-0.50wt%, Cr 0.05
~0.50wt%, Mo 0.05~0.50wt%,
Contains one or more selected from Ni 0.05 to 1,00 wt%, B 000003 to 0.0030 wt%, and further Ca 0.0005 = 0.0050 wt%, REM 0
．． 001 to 0.030 wt% of one or two types, the remainder consisting of Fe and unavoidable impurities, and the Vickers hardness of the segregated part and the A-based intervention having a length of 10 μ or more in an area of 10 mm in the hardness measurement part. total length of a thing A
A steel sheet with excellent hydrogen-induced cracking resistance, characterized in that the relationship between B (μ) and the total length B (μ) of B-based inclusions satisfies the following formula.

This invention consists of four inventions, with the fourth invention being Hv≦230-4/10x (A+B/2).

The steel sheet with excellent hydrogen-induced cracking resistance according to the present invention will be described in detail below.

First, the relationships among the components, component ratios, hardness, and inclusions of the steel sheet with excellent hydrogen-induced cracking resistance according to the present invention will be explained.

In order to ensure strength, the content of C must be 0.01 wt% or more, and if the content exceeds 0.30 u+t%, the susceptibility to weld cracking increases. Therefore, the C content is set to 0.01 to 0.30 wt%.

Si is an element necessary for deoxidation, and for this purpose, the content needs to be 0.02 wt% or more, and if it is contained in a large amount, the toughness will deteriorate. Therefore, the Si content is 0.02
~0.60wt%.

Mn is an element necessary to ensure strength, and the content is 0.
．． This effect is small at less than 50 wt%, and 2.5 wt%
If the content exceeds 0 wt%, weldability will be impaired. Therefore, the Mn content is set to 0.50 to 2.50 wt%.

P is inherently undesirable because it increases the hardness of the segregated part of the steel and deteriorates the hydrogen-induced cracking resistance, but as long as the relationship between the hardness of the segregated part and the length of inclusions satisfies the predetermined conditions, it is especially , P are not required to be regulated. However, from the viewpoint of the toughness of the weld, the P content is only 0.020 wt%.

S is an element that forms A-based inclusions and impairs hydrogen-induced cracking resistance, and is therefore undesirable.As long as the relationship between the hardness of the segregated part and the length of inclusions satisfies the specified conditions, it is particularly important to avoid the use of S and regulations. is not necessary, but from the viewpoint of toughness, the S content is 0.010.
It should be less than wt%.

The content of A1 as a deoxidizing element must be 0.005 wt% or more, and since a large amount of content causes deterioration of toughness, the upper limit is regulated to 0.060 wt%. Therefore, the A1 content is set to 0.005 to 0.060 wt%.

If the content of Nb5V and Ti is less than 0.005 wt%, it will have little effect on improving strength, and if the content exceeds 0.150 wt%, the toughness of the weld will deteriorate. Therefore, N
b, ■, Ti content is 0.005 to 0.150 wt%
shall be.

If the Cu content is less than 0.05 wt%, it will have little effect on improving strength, and if the content exceeds 0.50 wt%, it will deteriorate hot workability. Therefore, the Cu content is 0.0
5 to 0.50 wt%.

When the content of Cr and Mo is less than 0.05 wt%, the effect of improving the strength is small, and when the content exceeds 0.50 wt%, weldability is deteriorated. Therefore, the content of Cr and Mo is set to 0.05 to 0.50 wt%.

If the Ni content is less than 0.05 wt%, it will have little effect on increasing strength, and if it is contained in more than 1.00 wt%, the effect will be saturated and the economy will be impaired.

Therefore, the Ni content is set to 0.05 to 1.00 wt%.

B is 0.0003Il to increase the strength! L%
It is necessary to have a content of 0.0030wt% or more.
If the content exceeds this amount, the toughness will deteriorate. Therefore, the S content is set to 0.0003-0.0030 wt%.

Ca is an element that is effective in spheroidizing sulfurized I&I inclusions, and if the content is less than 0.0005 wt%, this effect is small, and if the content is more than 0.0050 wt%, it deteriorates the toughness. . Therefore, the Ca content is 0.00
05 to 0.0050 wt%.

Like Ca, REM is an element that is effective in spheroidizing sulfide-based inclusions, and its content must be 0.001wt% or more, and if it is contained in excess of 0.030wt%, it deteriorates toughness. let Therefore, the REM content is 0.001~
It is set to 0.030wt%.

The occurrence of hydrogen-induced cracking is determined by the Vickers hardness of the segregation part and the A of 10μ or more in length in a 10mm2 area at the hardness measurement part.
It is limited by the total length A (μ) of B-type inclusions and the total length B (μ) of B-type inclusions, that is, as shown in Figure 1, the hardness of the segregated part and the inclusion length As a result of conducting a hydrogen-induced cracking test for 96 hours under the condition of pH = 3 using steel plates with different
Hydrogen-induced cracking occurs even if there are no A-based and B-based inclusions with a length of 10° C. or more. In addition, the hardness of the segregated part is Hv≦23
0, the relationship between the total lengths A and B of A-based and B-based inclusions with a length of 10μ or more and the Vickers hardness Hv of the segregated part satisfies HV≦230-4/10 (A+B/2). , hydrogen-induced cracking does not occur, but if this condition is not satisfied, hydrogen-induced cracking will occur.

In this case, inclusions with a length of less than 10 μm were omitted because such small inclusions have a small interface area with the base steel, and the peeling of the tip of the inclusion is also small, which increases the risk of hydrogen-induced cracking. This is because it has no effect. In addition, the coefficient of the total length of B-type inclusions is 17 of the total length coefficient of A-type inclusions.
The reason why this coefficient was set to 2 is because if it were set to the same coefficient as for hemi-based inclusions, it would not be possible to clearly determine the presence or absence of hydrogen-induced cracking due to the relationship between the hardness of the segregated part and the length of the inclusions. This is because, as shown in FIG. 1, the occurrence of hydrogen-induced cracking can be controlled by the relationship between the two.

Moreover, the segregation part refers to a part where components are segregated during solidification, which is located at or near the center of the steel sheet.

The reason why the occurrence of hydrogen-induced cracking is limited by the hardness of the segregated part and the total length of the inclusion at that location has not yet been elucidated, but the area of the interface between the inclusion and the base steel,
This is thought to be related to the sharpness of the tip of the interface, the extreme pressure of hydrogen gas, and the degree of hydrogen embrittlement in the base metal surrounding the inclusion.

[Example 1] An example of a steel plate having excellent hydrogen-induced cracking resistance according to the present invention will be described.

Examples Steels having the components and proportions shown in Table 1 were melted, cast by a continuous casting method or an ingot-forming method, and then hot rolled to produce test steel plates.

The hardness of the segregated part of each test steel plate was measured using a Vickers hardness tester (load 1
00g), and the area at that part is 10
The total length of A-type inclusions and B-type inclusions with a length of 10 μ or more in 11I2 was measured using an optical microscope at a magnification of 400 times.

The test steel plate used for this measurement was sampled from the same location as the test steel plate for the hydrogen-induced cracking test described below.

The measurement results are shown in Table 2.

The evaluation of hydrogen-induced cracking resistance is N A C E S La
It was carried out according to ndard TM-02-84. However, the solutions used in the test were artificial seawater saturated with H2S (so-called BP solution 1.H: s > 5% NaCl + 0
．． There are two types: 5% acetic acid solution (so-called NACE solution, pH=3).

A test piece taken from each test steel plate was immersed in the above solution for 96 hours under no load, and then the presence or absence of hydrogen-induced cracking was determined using a cross-sectional microscope.

The test piece subjected to the above hydrogen-induced cracking test was taken from the position where the segregation was considered to be the largest, as shown in FIG. 2. The shape of the test piece and the position of the cross-sectional microscope are shown in FIG. 3, and the size of the test piece is tX20wX1001sei. Further, the thickness of the test piece was determined by cutting each law on both the front and rear surfaces of the steel plate.

Three test pieces were taken for each test solution from each test steel plate,
Only when no hydrogen-induced cracking was observed in any of the test pieces, it was determined that no hydrogen-induced cracking occurred.

The test results are shown in Table 2.

As is clear from Table 2, in the steel sheet with excellent hydrogen-induced cracking resistance according to the present invention, hydrogen can be used not only in the BP solution of pH; 5 but also in the NACE solution of pH'::'3. No induced cracking occurred.

In addition, hydrogen-induced cracking occurs in all steel sheets that do not satisfy the requirements for a steel sheet with excellent hydrogen-induced cracking resistance according to the present invention.

)I[1...230-4/10X(A+B/2)○:
No hydrogen-induced cracking, ×: Hydrogen-induced cracking occurred.

[Effects of the Invention] As explained above, since the steel sheet with excellent hydrogen-induced cracking resistance according to the present invention has an overlay structure, no hydrogen-induced cracking occurs even in a harsh environment such as pH=3. It has the effect of having excellent hydrogen-induced cracking resistance without causing any damage.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between the hardness of the segregated part of a steel sheet and the length of inclusions that affect the occurrence of hydrogen-induced cracking, Figure 2 is a perspective view showing the sampling position of hydrogen-induced cracking test pieces, and Figure 3 is a diagram showing the relationship between hydrogen-induced cracking test pieces. FIG. 2 is a perspective view showing the shape of a test piece and the position of a cross-sectional microscope. Fuku 9'y name"L@(Hv) -i?2 Figure?3!i!1

Claims (4)

[Claims] (1) C0.01-0.30wt%, Si0.02-0
．． 60wt%, Mn0.50-2.50wt%, P0.
020wt% or less, S0.010wt% or less, Al0.
005 to 0.060 wt%, the remainder consists of Fe and unavoidable impurities, and the Vickers hardness of the segregated part and the length of 10 μ in an area of 10 mm^2 at the hardness measurement part.
A steel plate with excellent hydrogen-induced cracking resistance, characterized in that the relationship between the total length A (μ) of the above A-based inclusions and the total length B (μ) of the B-based inclusions satisfies the following formula: . Hv≦230-4/10×(A+B/2) (2) C0.01-0.30wt%, Si0.02-0
．． 60wt%, Mn0.50-2.50wt%, P0.
020wt% or less, S0.010wt% or less, Al0.
005-0.060wt%, and Nb0.005-0.150wt%, V0.005-0
．． 150wt%, Ti0.005-0.150wt%,
Cu0.05-0.50wt%, Cr0.05-0.5
0wt%, Mo0.05-0.50wt%, Ni0.0
5-1.00wt%, B0.0003-0.0030w
Contains one or more selected from t%, and the remainder is F.
e and unavoidable impurities, and the Vickers hardness of the segregated part, the total length A (μ) of A-based inclusions with a length of 10 μ or more in an area of 10 mm^2 in the hardness measurement part, and the same as that of B-based inclusions. A steel plate with excellent hydrogen-induced cracking resistance, characterized in that the relationship with the total length B (μ) satisfies the following formula. Hv≦230-4/10×(A+B/2) (3) C0.01-0.30wt%, Si0.02-0
．． 60wt%, Mn0.50-2.50wt%, P0.
020wt% or less, S0.010wt% or less, Al0.
005 to 0.060 wt%, and Ca0.0005 to 0.0050 wt%, REM0.0
01 to 0.030 wt%, the remainder consists of Fe and unavoidable impurities, and the Vickers hardness of the segregated part,
The relationship between the total length A (μ) of A-based inclusions with a length of 10 μ or more in an area of 10 mm^2 in the hardness measurement part and the total length B (μ) of B-based inclusions satisfies the following formula. A steel plate with excellent hydrogen-induced cracking resistance. Hv≦230-4/10×(A+B/2) (4) C0.01-0.30wt%, Si0.02-0
．． 60wt%, Mn0.50-2.50wt%, P0.
020wt% or less, S0.010wt% or less, Al0.
005-0.060wt%, and Nb0.005-0.150wt%, V0.005-0
．． 150wt%, Ti0.005-0.150wt%,
Cu0.05-0.50wt%, Cr0.05-0.5
0wt%, Mo0.05-0.50wt%, Ni0.0
5-1.00wt%, B0.0003-0.0030w
t%, and further contains Ca0.0005-0.0050wt%, REM0.0
01 to 0.030wt%, the balance consists of Fe and unavoidable impurities, and the Vickers hardness of the segregated part and the length of A of 10μ or more in an area of 10mm^2 in the hardness measurement part
A steel sheet with excellent hydrogen-induced cracking resistance, characterized in that the relationship between the total length A (μ) of B-based inclusions and the total length B (μ) of B-based inclusions satisfies the following formula. Hv≦230-4/10×(A+B/2)