JPS6347352A - Steel sheet having excellent resistance to hydrogen induced crack - Google Patents

Abstract

PURPOSE:To provided a titled steel sheet which is entirely free from hydrogen induced crack in environment of >=5pH by forming said steel sheet of a specific component compsn. and specifying the relations among the Vickers hardness of a segregated part, Cu content, the length of an A-inclusion in a specific area in the hardness measuring part and likewise the total length of a B- inclusion. CONSTITUTION:This steel sheet contains, 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 0.10-0.50% Cu, has the excellent resistance to hydrogen induced crack and has the following characteristics. The generation of the hydrogen induced crack of said steel sheet is limited by the Vickers hardness Hv in the segregated part, the length A (mu) of the A-inclusion having >=10mu length in 10mm<2> area in the hardness measuring part and likewise the total length (mu) of the B-inclusion. The above- mentioned steel sheet is the steel sheet which satisfies the conditions expressed by the equation in the relations between the total lengths A and B of the A- and B-inclusions having >=10mu length and the Vickers hardness Hv of the segregated part, and obviates the generation of the hydrogen induced crack.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a steel plate with excellent hydrogen-induced cracking resistance. The present invention relates to a steel plate with excellent hydrogen-induced cracking resistance of kgf/mm2.

[Prior Art] 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 hydrogen-induced cracking resistance.

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

Therefore, as a countermeasure against hydrogen-induced cracking, currently, (1) R
Suppresses hydrogen intrusion and diffusion.

(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.

It is said that the method is as follows.

Regarding (1), for example, JP-A-50-09
As described in Publication No. 7515, there is a method of forming a corrosion-resistant coating by adding Cu, but when the strength level of the steel plate is high or the amount of inclusions is large, it is difficult to completely suppress the occurrence of hydrogen-induced cracking. Regarding (2), a method for regulating the shape and number of sulfides is disclosed in JP-A-55-128-536.
Ca, R of JP-A No. 54-031020, etc.
There is a method of controlling the shape of A-based inclusions by EM, but as the strength level of the steel sheet increases, it is difficult to completely prevent hydrogen-induced cracking. As described in Japanese Patent Laid-open No. 111815, there is a method of extremely lowering the P content to 0.006 wt% or less, but there is a problem in terms of cost, and
As described in Japanese Patent Application No. 3162, there is a method of adjusting the hardness of the hardened composite part to Hv≦350, but it is difficult to completely eliminate hydrogen-induced cracking when the amount of inclusions in the steel sheet is large. be.

Of course, the reality is that these methods are often used in combination, or are not sufficient in terms of productivity and manufacturing costs for industrial products to completely suppress the occurrence of hydrogen-induced cracking.

[Problems to be Solved by the Invention] In view of the various problems of conventional steel plates with respect to resistance to hydrogen-induced cracking as explained above, the present inventor has conducted extensive research, and as a result, the present invention has been developed to solve the problem of hydrogen-induced cracking. To prevent the occurrence of
There is no need to unnecessarily restrict the shape and number of chemical components or inclusions, and it is necessary to restrict the length of inclusions to be short and/or
If the content is increased, the hardness of the segregated part will not become unnecessarily low, and if the hardness of the segregated part is low and/or the Cu content is high, the length of the inclusions will be shortened. Furthermore, it has been found that the Cu content can be reduced if the inclusion length is regulated short and/or the hardness of the segregated part is regulated low, that is, the hardness of the segregated part and Cu By combining the control of content and length of inclusions, we have developed a steel sheet with excellent hydrogen-induced cracking resistance that does not cause hydrogen-induced cracking even in an environment of pH-5.

[Means for solving the problems] The steel sheet having excellent hydrogen-induced cracking resistance according to the present invention has (1)
G 0.01~0.3ht%, Si 0.02~Q
, 60wt%, Mn 0.50-2.50wt%, P
0. Q20wt% or less, S 0.010wt% or less, A
I 0.005-0.060wt%, Cu 0.10
~0.50wt%, with the balance consisting of Fe and unavoidable impurities,
Vickers hardness Hv of segregated part and Cu content (wt%)
and length 10 in area 10mm' at hardness measurement part
Excellent hydrogen-induced cracking resistance, characterized in that the relationship between the total length A (μ) of A-based inclusions of μ or more and the total length B (μ) of B-based inclusions satisfies the following formula: The first invention is a steel plate, Hv≦250+200×Cu-1/2x (A+B/2)
(2) C0.01-0.30wt%, Si 0.0
2-0.6ht%, Mn 0.50-2.50wt%,
P 0.020wt% or less, S 0.010wt% or less, AI 0.005-0.060wt%Cu 0.1
0 to 0.50 wt%, and Nb 0.005 to 0.150 wt%, V 0.005
~0,15111wt%, Ti 0.005~0.15
0wt%, Cr 0.05-0.50wt%, Ni
0.05-0.40wt%, B 0.0003-0.0
A steel containing one or more selected from 0.030twt%, further satisfying Ni/Cu≦0.8, and the balance being Fe and unavoidable impurities, is determined by the Vickers hardness Hv of the segregated part and the Cu content. (wt%), the total length A (μ) of A-based inclusions with a length of 10 μ or more in the area of 10 mm in the hardness measurement part, and the total length B (μ) of B-based inclusions as shown below. A second invention provides a steel plate with excellent hydrogen-induced cracking resistance that satisfies the following formula: Hv≦250+200×Cu-1/2x(A-+-B/
2)(3) C0.01-0.30wt%, Si0.0
2-0.6ht%, Mn 0.50-2.50wt%,
P 0.02ht% or less, S 0.010wt% or less,
A10.005~0.060wt%Cu Q, 10~0
．． 50 wt%, and Ca 0.0005 to 0.0050 wt%, REM 0
．． Steel containing one or two of 001 to 0.030 wt%, the balance consisting of Fe and unavoidable impurities,
The Vickers hardness of the segregated part I4v and the CLI content m (wt
%) and the total length A (μ) of A-based inclusions with a length of 10 μ or more in an area of 10 mm2 in the hardness measurement part, and the relationship between the total length B (μ) of B-based inclusions or the following formula is satisfied. The third steel plate with excellent hydrogen-induced cracking resistance is
As an invention, Hv≦250+200×Cu-1/2x (A+B/2)
(4) C0.01-0. aOwt%, S i 0.0
2-0.60wt%, Mn 0.50-2.50wt%
, P 0.020wt% or less, S Q, 010wt% or less, Al 0.005-0.060wt% Cu 0.1
0 to 0.50 wt%, and Nb 0.005 to 0.150 wt%, V 0.005
~0.150wt%Ti 0.005~0.150wt
%, Cr 0.05-0.5ht%, Ni 0.05
~0.40wt%, B 0.0003~0.0030w
t%, contains one or more selected from t%, further satisfies Ni/Cu≦0.8, and contains Ca 0.0005-0. OQ50wt%, REM 0
．． 001 to 0.030 wt% of one or two types, with the remainder consisting of Fe and unavoidable impurities,
Vickers hardness Hv of segregated part and Cu content (wt%)
and length 10 in area 10mm' at hardness measurement part
Excellent hydrogen-induced cracking resistance, characterized in that the relationship between the total length A (μ) of A-based inclusions of μ or more and the total length B (μ) of B-based inclusions satisfies the following formula. Hv≦250+200XCLl-1/2X (A+B/2
) This invention consists of four inventions.

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 needs to be 0.01 wt% or more, and if the content exceeds 0.3 ht%, the susceptibility to weld cracking increases. Therefore, the C content is 0.
01-0.30 guest t%.

Si is an element necessary for deoxidation, and for this purpose, the content m needs to be 0.02 wt% or more, and if it is contained in a large amount, the toughness will deteriorate. Therefore, Si-containing fi is 0.0
2 to 0.60 wt%.

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 condition, In particular, regulation of P is unnecessary. However, from the viewpoint of the toughness of the welded part, the P content is set to 0.02ht%.

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 Al 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 0.06 Qwt%.

Cu is an element that is effective in improving hydrogen-induced cracking resistance in an environment where pH≧5, and the content is 0 and 10 wt.
If the content is less than 0.50 wt %, this effect will be small, and if the content exceeds 0.50 wt %, the effect will be saturated, and furthermore, hot workability will be deteriorated. Therefore, the Cu content is 0.10 to 0.5
It is set to 0wt%.

If the content of Nb, V, and Ti is less than 0.005 wt%, it will have little effect on improving the strength, and if the content exceeds 0.150 wt%, the toughness of the weld will deteriorate. Therefore, N
b5V, Ti') content is 0.005-0.150wt
%.

If the content of Cr is less than 0.05 wt%, it will have little effect on improving the strength, and if the content exceeds 0.5 ht%, it will deteriorate weldability. Therefore, the Cr content is 0.05~
It is set to 0.5 ht%.

If the Ni content is less than 0.05 wt%, it will have little effect on increasing the strength, and if the Ni content exceeds 0.40 wt%, the effect will be saturated and the economy will be impaired.

Therefore, the Ni content is set to 0.05 to 0.40 wt%. Since excessive Ni content inhibits the hydrogen-induced cracking improvement effect of Cu, the range of Ni/Cu≦0.8 is set.

B content needs to be 0.0003 wt% or more in order to increase strength, and if it is contained in excess of 0.0030 wt%, toughness deteriorates. Therefore, the B content is set to 0.0003 to 0.0030 wt%.

Ca is an element that is effective in spheroidizing sulfide inclusions, and if the m content is less than 0.0005 wt%, this effect is small, and if it is contained in more than 0.0050 wt%, it deteriorates the toughness. Therefore, the Ca content is 0.0005~
It is set to 0.0050wt%.

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 REV content is 0.0111
~0.030wt%.

Next, in the steel sheet having excellent hydrogen-induced cracking resistance according to the present invention, the relationship between the hardness of the segregated portion, the C and u content, and the length of inclusions will be explained.

In an environment where p11≧5, hydrogen-induced cracking occurs due to the Vickers stool in the segregation area and the total length A of A-based inclusions with a length of 10μ or more in an area of 10mm2 in the hardness measurement area.
(μ) is also limited by the total length B (μ) of B-based inclusions. That is, as shown in Fig. As a result of a 96-hour hydrogen-induced cracking test under the conditions of
), hydrogen-induced cracking will occur even if there are no A-based and B-based inclusions with a length of 10 μ or more. In addition, if the hardness of the segregated part is Hv≦250+200x Cu (wt%),
The relationship between the total lengths A and B of A-type and B-type inclusions with a length of 10μ or more and the Vickers density Hv of the segregated part is as follows: (v ≤ 250 + 200 x Cu (w
t%)-1/2(A+B/22), no hydrogen-induced cracking will occur, but if this condition is not satisfied, only hydrogen-induced cracking will occur.

In this case, inclusions with a length of less than 10μ were omitted because such small inclusions have a small interface area with the base steel, and the sharpness of the tips of the inclusions is small, making them highly susceptible to hydrogen-induced cracking. This is because it has no effect. In addition, the coefficient of the total length of B-based inclusions is set to 1/1 of the coefficient of the total length of A-based inclusions.
The reason why this coefficient was set to 2 is because if the coefficient is the same as that for A-based inclusions, the presence or absence of hydrogen-induced cracking cannot be clearly determined due to the relationship between the hardness of the segregated part and the length of the inclusion. 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. In Figure 1,
Cu: 0.45wt%, O: no cracks, ・: cracks,
At Cu 0330wt%, △ means no cracks, MU means cracks,
At 0.15 wt% Cu, no cracks were observed, and ■ indicates cracks.

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 position has not yet been elucidated, or the area of the interface between the inclusion and the base steel,
It is thought that this is related to the sharpness of the tip of the interface, the magnitude of the hydrogen gas pressure, and the degree of hydrogen embrittlement of the steel base surrounding the inclusion.

[Example] 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 10μ or more in mm'' was measured using an optical microscope at a magnification of 400x.

Specimen 162 used in this measurement was taken from the same location as the steel sheet sample for the hydrogen-induced cracking test described below.

The measurement results are shown in Table 2.

The evaluation of hydrogen-induced cracking resistance was conducted by NA CE Sta.
It was conducted on ndard TM-02-84. Therefore, the solution used in the test was artificial seawater saturated with H and S (so-called BP solution, pH=5).

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 specimens subjected to the hydrogen-induced cracking test were taken from the position where the segregation was considered to be the greatest, as shown in FIG. 2. Figure 3 shows the shape of the test piece and the position of the cross-sectional microscope.

The size of the test piece is t×20wXl001+nm. In addition, the thickness of the test piece was cut by cutting 1 mm on both 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 having excellent hydrogen-induced cracking resistance according to the present invention, no hydrogen-induced cracking occurred in the BP solution at pH=5.

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.

Table 2 *l ・-250+200Cu-1/2x (A+B/2
)Mi2...Hydrogen-induced cracking test result O: No hydrogen-induced cracking. ×: Hydrogen-induced cracking photogenesis.

[Effects of the Invention] As explained above, since the steel sheet with hydrogen-induced cracking resistance according to the present invention satisfies the above 1+, hydrogen-induced cracking does not occur at all in an environment with pH≧5. It has the effect of having excellent hydrogen-induced cracking resistance.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between the hardness of the deflected portion of a steel plate, the Cu content, 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 The figure is a perspective view showing the shape and cross-sectional microscope position of a hydrogen-induced crack test piece. fl Zusuke Kai n Beni (Aki 8, 6) Spear 2 Figure

Claims (4)

[Claims] (1) C0.01-0.30wt%, Si0.02-0
．． 60wt%, Mn0.50-2.50wt%, P0.020wt% or less, S0.010wt% or less, Al0.005-0.060
wt%, Cu 0.10 to 0.50 wt%, and the balance consists of Fe and unavoidable impurities.
Vickers hardness Hv of segregated part and Cu content (wt%)
and the length 1 in the area 10mm^2 at the hardness measurement part
Excellent hydrogen-induced cracking resistance, characterized in that the relationship between the total length A (μ) of A-based inclusions of 0μ or more and the total length B (μ) of B-based inclusions satisfies the following formula: steel plate. Hv≦250+200×Cu-1/2×(A+B/2) (2) C0.01-0.30wt%, Si0.02-0
．． 60wt%, Mn0.50-2.50wt%, P0.020wt% or less, S0.010wt% or less, Al0.005-0.060
Contains wt% Cu0.10-0.50wt%, and Nb0.005-0.150wt%, V0.005-0
．． 150wt%, Ti0.005~0.150wt%, Cr0.05~0
．． 50wt%, Ni0.05-0.40wt%, B0.0003-0.
Steel containing one or more selected from 0.0030wt%, Ni/Cu≦0.8, and the balance being Fe and unavoidable impurities is determined by the Vickers hardness Hv of the segregated part and the Cu content. (wt%) and length 10μ in area 10mm^2 at 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≦250+200×Cu-1/2×(A+B/2) (3) C0.01-0.30wt%, Si0.02-0
．． 60wt%, Mn0.50-2.50wt%, P0.020wt% or less, S0.010wt% or less, Al0.005-0.060
Contains 0.10 to 0.50 wt% of Cu, and 1 or 2 of 0.0005 to 0.0050 wt% of Ca, 0.001 to 0.030 wt% of REM, and the balance is Fe and unavoidable impurities. Steel made of
Vickers hardness Hv of segregated part and Cu content (wt%)
and the length 1 in the area 10mm^2 at the hardness measurement part
Excellent hydrogen-induced cracking resistance, characterized in that the relationship between the total length A (μ) of A-based inclusions of 0μ or more and the total length B (μ) of B-based inclusions satisfies the following formula: steel plate. Hv≦250+200×Cu-1/2×(A+B/2) (4) C0.01-0.30wt%, Si0.02-0
．． 60wt%, Mn0.50-2.50wt%, P0.020wt% or less, S0.010wt% or less, Al0.005-0.060
Contains wt% Cu0.10-0.50wt%, and Nb0.005-0.150wt%, V0.005-0
．． 150wt% Ti0.005~0.150wt%, Cr0.05~0
．． 50wt%, Ni0.05-0.40wt%, B0.0003-0.
0.0030 wt%, Ni/Cu≦0.8, and 0.0005 to 0.0050 wt% of Ca and 0.001 to 0.030 wt% of REM. steel containing one or two species, with the balance consisting of Fe and unavoidable impurities,
Vickers hardness Hv of segregated part and Cu content (wt%)
and the length 1 in the area 10mm^2 at the hardness measurement part
Excellent hydrogen-induced cracking resistance, characterized in that the relationship between the total length A (μ) of A-based inclusions of 0μ or more and the total length B (μ) of B-based inclusions satisfies the following formula: steel plate. Hv≦250+200×Cu-1/2×(A+B/2)