JPS63134647A - High-strength steel plate excellent in hydrogen-induced cracking resistance - Google Patents

Abstract

PURPOSE:To improve hydrogen-induced cracking resistance by specifying respective contents of C, Si, Mn, P, S, Nb, Al, and Fe, forming an acicular ferritic structure, and further controlling the relationship between hardness and inclusions. CONSTITUTION:This high-strength steel plate has a composition containing, by weight, 0.01-0.06% C, 0.02-0.6% Si, 1.3-2.5% Mn, <=0.02% P, <=0.01% S, 0.01-0.15% Nb, and 0.005-0.06% Al and also has a uniform acicular ferritic structure. Moreover, an inequality (Vickers hardness Hv in a segregation zone) <=300-4/10X(A+B/2) [where A(mu) means the total length of A-type inclusions of >=10mu length in 10mm<2> area in a hardness-measuring section and B(mu) also means the total length of B-type inclusions] is satisfied in this steel plate.

Description

[Detailed Description of the Invention] [Industrial Application Field] Does the present invention have excellent hydrogen-induced cracking resistance? :rJ strength ropes and plates, more specifically, tensile strength of 50 to 80 kgr/n+a used for line pipes, pressure vessels, tanks, etc.
Regarding steel plates with excellent resistance to hydrogen-induced cracking.

[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 infiltrates and diffuses into the steel in an atomic state, accumulates and becomes molecules at the interface between the inclusions and the base steel. It is said that this propagates along band-like hardened structures that occur in the uneven Ft portion of the steel.

Therefore, as a countermeasure against hydrogen-induced cracking, currently (+)M
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.

The following methods have been adopted.

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 it is not effective in a harsh environment such as plf = 3, and it is difficult to suppress the occurrence of hydrogen-induced cracking. Regarding (2), the shape of sulfide and the method for controlling the loss are disclosed in JP-A-51-1-4318, and JP-A-55-12853.
6, JP-A No. 54-031020, etc.

There is a method to control the morphology of Δ-based inclusions using ItEM, but as the strength of steel sheets increases and the environment becomes harsher, it is difficult to completely prevent hydrogen-induced cracking. ), as described in Japanese Unexamined Patent Application Publication No. 1815, Type 1), the content n is 0.006wt.
There is a method of extremely lowering the hardness to less than %, but there is an interlayer in terms of dust, and there is also a method of making the hardness of the hardened tissue part Hv≦350 as described in Japanese Patent Application Laid-open No. 57-0731G2. There is, but I)! It is difficult to completely eliminate hydrogen-induced cracking in high-strength steel under harsh environments with low -1.

[Problems to be Solved by the Invention] In view of the various problems of conventional steel plates with respect to hydrogen-induced cracking as explained above, the present inventor has conducted extensive research, and as a result, the present invention solves the conventional method independently. It is difficult to completely suppress the occurrence of hydrogen-induced:l;+1 in the harsh environment of pII = 3, or by simply using them in combination. The reality is that it cannot be said to be sufficient in terms of manufacturing cost, and furthermore, the present inventor has developed a combination of chemical composition, inclusion length, and segregation hardness control in order to solve the problem of hydrogen-induced cracking. As a result of this research, we have developed a steel sheet with excellent hydrogen-induced cracking resistance and are currently applying for the application. In other words, by changing the steel structure to an acicular ferrite structure and controlling the GFr part hardness and the inclusion length, even in an environment where pl-1 = 3, We have developed a high-strength steel sheet with excellent hydrogen-induced cracking resistance that never causes hydrogen-induced cracking.

[Means for Solving the Problems] The high-strength steel sheet with excellent hydrogen-induced cracking resistance according to the present invention has: (1) G 0.01 to 0.06 wt%, S I 0.
02-0.60wt%, Mn 1.30-2.50wt
%, P 01020wt% or less, S 09010wt%
Below, Nb 0.010-0.150wt%, A1
0.005 to o, containing t% of oao (rL), consisting of the remainder Fa and unavoidable impurities, and having a substantially uniform acicular ferrite structure, and furthermore, the Vickers hardness of the segregated part and the hardness Area at measurement part: 10mm
Hydrogen-induced cracking resistant, characterized in that the relationship between the total length A (μ) of Δ-based inclusions with a length of 10 μ or more and the total length B (μ) of B-based inclusions satisfies the following formula: High-strength steel plate with excellent properties.

Bv≦300-4/I 0X (A-1/2) as the first invention, (2) G 0.01 to 0.06 wt%, Si 0.
02-0.60wt%, Mn 1.30-2.50wt
%, P 0.020wt% or less, S 0.010wt%
Below, Nb 0.010-0.150wt%, A10.
005 to 0.150 wt%, and V 0.005 to 0.150 wt%, 'I''i 0.005 to 0.15 ht%, Cu 0.0
5-0.50wt%, Cr 0.05-0.50wt
%, Mo 0.05-0.50wt%, Ni 0.0
5-1. oowt%, B0.0003~0.0030w
t %, the remainder consists of FCj and unavoidable impurities, and has a substantially uniform acicular ferrite structure, and further has a Vickers hardness of the segregated part, The total length Δ (μ) of Δ-based inclusions with an area Ion of 10 μ or more in the hardness measurement part, and the total length B (μ) of B-based inclusions
A high-strength steel plate with excellent resistance to hydrogen-induced cracking, characterized in that the relationship between

1st type v≦300-4/I OX (Δ+B/2) as 2nd
(3) C0.01-0.0hL%, S i 0.02
~0.60wt%, Mn 1.30~2.50wt%,
P 0.02ht% or less, S 0.01ht% or less, N
b 0.010-0.150wt%, AI 0.00
Contains 5 to 0.060 WL%, and Ca 0.0005 to 0.0050 wt%, ILEM
0.001 to 0.030 wt% of one or two types (T), the remainder consists of Fa and unavoidable impurities, and the acicular ferrite structure is approximately uniform. Vickers hardness of the part, total length Δ (μ) of hemi-based inclusions with length lOμ or more in surface type 1 '1 type 0 mm2 at the hardness measurement part, and total length B (μ) of 'B-based inclusions A high-strength M temporary with excellent hydrogen-induced cracking resistance, characterized in that the relationship between

Type 1 v≦300-4/l0X (Δ+B/2) is the third invention, (4) C0.01-0.06wt%, S i 0.0
2-0.60wt%, Mn 1.30-2.50wt%
, P 0.02ht% or less, S Q, 010wt% or less, Nb 0.010-0.15 (1wt%, A1 0.
005-0.0601t%, and V 0.005-0.150wt%, Ti 0.005-0.150wt%, Cu 0.0
5-0.50wt%, Cr 0.05-0.5hL
%, Mo 0.05-0.50wt%, N! 0.05
~1.0ht%, [30.0003~0.0030wt
%, and further contains Ca 0.0005 to 0.0050 wt%, REM 0
．． 001 to 0.030 wt% of one or two types, the remainder consists of I2e and unavoidable impurities, and the structure has a substantially uniform acicular ferrite structure, and furthermore, the Vickers hardness of the segregated part and the hardness The total length Δ (μ) of A-based inclusions with a length of 10 μ or more in the surface clearness of 10 Il + m” at the measurement part, and the total length B of B-based inclusions
A high-strength steel plate with excellent hydrogen-induced cracking resistance, characterized in that the relationship with (μ) satisfies the following formula.

This invention consists of four inventions, with type 1 v≦300-4/l0x (A+B/2) as the fourth invention.

The high-strength steel plate 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 high-strength steel sheet with excellent hydrogen-induced cracking resistance according to the present invention will be explained.

In order to ensure strength, the C content must be 0.01 wt% or more, and if it is contained in excess of 0.06 wt%, an acicular ferrite structure with zero content cannot be obtained. Therefore, the C content is set to 0.01 to 0.06 t%.

Sl is an element necessary for deoxidation, and for this purpose, the content must 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 to 0.60 wt%.

Mn is an element necessary to ensure strength and obtain an acicular ferrite structure, and the content is mm21.30wt%.
If the content is less than 2.50 wt%, this effect will be small, and if the content exceeds 2.50 wt%, weldability will be impaired.

Therefore, the Mn content is set to 1.30 to 2.50 wt%.

P is inherently undesirable because it increases the hardness of the segregating part of the steel by 1 and deteriorates the hydrogen-induced cracking resistance, but as long as the relationship between the ease of the segregating part and the length of inclusions satisfies the predetermined conditions. In particular, regulation of P is not necessary. However, from the viewpoint of the toughness of the weld zone, the P content is set to 0.0201 wt.

S is an element that forms Δ-based inclusions and impairs water resistance to X-induced cracking, and is therefore undesirable.As long as the relationship between the hardness of the segregated part and the length of cE inclusions satisfies a predetermined condition, S
Although it is not necessary to regulate S, from the viewpoint of toughness,
l is 0.010 wt% or less.

Nb is an element necessary to ensure strength and obtain an acicular ferrite structure, and the content is 0.0IOwt%.
If the content is less than 0.150 wt%, this effect will be poor, and if the content exceeds 0.150 wt%, the toughness of the weld will deteriorate. Yotte, Nb content mli 0.010-0.150wt%
shall be.

As a deoxidizing element, Al needs to be contained at 0.005 wt% or more, and since the inclusion of a large amount of In will lead to deterioration of toughness, the limit is regulated to 0.080 wt%. Therefore, Al
Including? Ti'tt is 0.005 to 0.060 wt%.

V% 'l' 1% Cu, Cr, MOINiSll are selectively contained in order to improve strength.

If the content of V and i'l is less than 0.1% by weight, it will have little effect on improving strength, and if the content exceeds 100wt% of Q, it will deteriorate the toughness of welding + MS. Therefore,
The YT content of V and i'i is 0.005 to 0.150WL%
shall be.

If the content of Cu is less than 20.05 wt%, it will have little effect on improving strength, and if it is contained in more than 0.50 wt%, it will deteriorate hot workability. Therefore, the Cu content is 0.
05 to 0.50 wt%.

If the content of Cr or MO is less than 20.05 wt%, it will have little effect on improving strength, and if the content exceeds 0.50 wt%, it will deteriorate weldability. Therefore, Cr.

The MoC content is set to 0.05 to 0.50 wt%.

If the Ni content is less than 0.05 wt%, it has little effect on the upper limit of strength, and 1. If the content exceeds oowt%, the effect will be saturated and the economy will be impaired.

Contains Ni (ffn) at 0.05 to 1.00 wt%.

B content must be 0.0003 wt% or more in order to increase the strength, and if it is contained in excess of 0.0030 wt%, the toughness will deteriorate. Therefore, B includes T
rJ1 is set to 0.0003 to 0°0030 wt%.

Ca is an element that is effective in spheroidizing sulfide-based inclusions, and this effect is small when the content of T"J is less than 0.0005 t%, and it should not be contained in amounts exceeding 0.0050vr%. The toughness is deteriorated.Therefore, the Ca content ('T amount is 0.
0005 to 0.0050 wt%.

[EM, like Ca, is an element that is effective in spheroidizing sulfide-based inclusions;
When subjected to T, the toughness deteriorates. Therefore, IT including rtEM
m is 0.001 to 0.030 t%.

As mentioned above, the nearly uniform acicular ferrite structure is caused by hydrogen-induced cracking, which occurs when hydrogen generated by corrosion of the steel in a humid hydrogen atmosphere penetrates into the steel, and molecules form at the interface between the inclusions and the base steel. It is said that this occurs when the sub-steel cannot withstand the pressure of hydrogen gas caused by hydrogen. Normally, the cracking resistance that exists in steel sheets is small, and hydrogen-induced cracking is likely to occur. However, they discovered that hydrogen-induced cracking could be completely prevented by controlling the hardness of the segregated part to below a critical value, which is determined by the relationship between the hardness of the segregation part and the length of the inclusion. They have discovered that by creating a substantially uniform acicular ferrite structure, the critical hardness for preventing hydrogen-induced cracking in the segregated portion can be significantly increased. The reason for this is thought to be related to the high toughness of the acicular ferrite structure.

Next, to explain the relationship between the hardness of the segregated part and the length of inclusions, in acicular ferritic steel, hydrogen-induced cracking occurs when the Vickers hardness of the segregated part and the area Ion at the hardness measurement part are medium lengths. It is limited by the total length A (μ) of Δ-based inclusions of 10μ or more and the total length B (μ) of B-based inclusions, that is, as shown in Figure 1, the hardness of the segregated part and Using steel plates with different inclusion lengths, pI! =
As a result of a 96-hour hydrogen-induced cracking test under the conditions of 3, if the hardness of the segregated part is try > 300, the length is 10
Without Δ-based and B-based inclusions larger than μ, hydrogen-induced cracking will occur. In addition, when the hardness of the segregated part is Irv≦300, the total length Δ of Δ-based and B-based inclusions with a length of IOμ or more
If the relationship between B and Vickers hardness Ilv of the segregated part satisfies Hv≦300-4/10 (Δ→・r3/2), hydrogen-induced cracking will not occur, but if this condition is not satisfied, Hydrogen-induced cracking occurs.

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 tip of the inclusion is small, making them highly susceptible to hydrogen-induced cracking. format! This is because it does not give In addition, the coefficient of the total length of B-based inclusions is set to 1 of the coefficient of the total length of Δ-related inclusions.
/2 was chosen because if the coefficient was the same as that for Δ-based inclusions, it would not be possible to clearly determine whether or not hydrogen-induced cracking occurred due to the relationship between the hardness of the segregated part and the length of the inclusions. This is because, as shown in FIG. 2, the occurrence of hydrogen-induced cracking can be controlled by the relationship between these numbers.

(In Fig. 2, l indicates the hydrogen-induced cracking limit line of the acicular ferrite of the high-strength steel sheet with excellent hydrogen-induced cracking resistance according to the present invention, and 2 indicates the hydrogen-induced cracking limit line of the conventional ferrite pearlite. ) Also, what is a segregated part?
l! I refers to the component segregation area during solidification located at or near the temporary center.

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.The reason for this is still unknown, but 'l, sharpness of the interface tip, magnitude of hydrogen gas pressure,
This is thought to be related to the degree of hydrogen embrittlement in the base steel surrounding the inclusion.

[Example] An example of a high-strength steel plate having excellent water resistance '+' and induced cracking resistance according to the present invention will be described.

EXAMPLES Steel having the components and proportions not shown in Table 1 was melted, cast by a continuous casting method or an ingot-forming method, and then hot rolled (a test sample was manufactured).

Vickers rB for the segregation j1≦ of the valley test steel plate! When measured by courage (i::7fff I OOg),
In that part, there was a △ extra order and a B extra order with a length of 10 μ or more in a space of 10 mm' (the total length of the object was measured using an optical microscope at a magnification of 400 times).

The 1 sample steel plate used for this measurement is of the same type as the hydrogen-induced cracking test sample 1 steel plate explained below! Collected from.

The measurement results are shown in Table 2.

The evaluation of hydrogen-induced cracking resistance is N A C E S La
This was done earlier than ndard TM-02-84. However, the solution used in the test was artificial seawater saturated with ITtS (so-called np solution I) II = 5) and 5% Na
C++ 0.5% acetic acid solution (so-called NACE solution, l) I
・■=3).

After immersing a test piece taken from a test steel plate in the above solution for 9C in an unloaded state, the presence or absence of hydrogen-induced cracking was determined by cross-sectional microscopy.

The test pieces used in the hydrogen-induced cracking test were taken from the position where the segregation was considered to be the largest, as shown in FIG. Figure 4 shows the shape of the test piece and the position of the cross-sectional microscope.

The size of the test piece is tX20wXl00 1mm. In addition, the thickness of the test piece is 1 m each on both surfaces of MF<
It was cut by m.

Three test pieces per three test solutions were taken 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, the steel sheet according to the present invention with enhanced resistance to hydrogen-induced cracking is susceptible to hydrogen-induced cracking not only in the 13P solution at pH=5 but also in the MACE solution at ptl=3. has not occurred at all.

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

In addition, FIG. 1(a) shows the high-strength Ii' steel plate (steel 1 in Table 1) with excellent hydrogen-induced cracking resistance according to the present invention and the steel sheet shown in FIG.
b) shows a micrograph showing the metallographic structure of Comparative M (jll 8 in Table 1).

[Effects of the Invention] As explained above, the high-strength steel plate with excellent hydrogen-induced cracking resistance according to the present invention has a structure of plr=3.
It has the effect of having excellent hydrogen-induced cracking resistance, with no hydrogen-induced cracking occurring even under such harsh environments.

[Brief explanation of the drawing]

Figure 1 is a microscopic photograph of the metallographic structure of a high-strength steel sheet according to the present invention with 1U of hydrogen-induced cracking resistance and a comparative steel. Intermediate (
Figure 3 is a perspective view showing the sampling position of the hydrogen-induced cracking test piece, and Figure 4 is a perspective view showing the shape and cross-sectional position of the hydrogen-induced cracking test piece. . 3 Figure 4 Figure 5, Date of amendment order Procedural amendment (method) % formula % ■, Small case indication 1988 Patent Application No. 281495 2, Title of invention High strength steel plate with excellent resistance to hydrogen-induced cracking 3. Relationship with the case of the person making the amendment Patent applicant Address 1-3-18 Wakihama-cho, Chuo-ku, Kobe Name (Class 1 9) Kobe Steel, Ltd. Representative Fuyu Maki
Hiko 4, Agent address: 901 Fujiwa Toyocho Co-op, 2-2-15 Minamisuna, Koto-ku, Tokyo (1) nn 2400 lines 7-14 amended as follows 6
, Subject of amendment (1) Brief explanation of drawings in the specification (2) Figure 1 7, content of amendment as attached: 4. Brief explanation of drawings Figure 1 (a) relates to the present invention A high-strength steel sheet with excellent hydrogen-induced cracking resistance shows no metallographic structure.
b) is a micrograph showing the metallographic structure of the comparison steel, Figure 2 is a diagram showing the relationship between the hardness of the segregated part of the steel plate and the length of inclusions, which does not lead to hydrogen-induced cracking, and Figure 3 is a hydrogen-induced cracking test piece. FIG. 4 is a perspective view showing the collected image 1 type 1, and FIG. 4 is a perspective view showing the shape and cross-sectional microscope position of the hydrogen-induced crack test piece. ”

Claims (4)

[Claims] (1) C0.01-0.06wt%, 510.02-0
．． 60wt%, Mn1.30-2.50wt%, P0.
0201wt or less, S0.010wt% or less, Nb0.
010~0.150wt%, Al0.005~0.06
0wt%, the balance consists of F℃ and unavoidable impurities, and the structure has a substantially uniform acicular ferrite structure, and furthermore, the Vickers hardness of the segregated part and the area of 10mm^2 in the hardness measurement part The total length A (μ) of A-based inclusions with a length of 10 μ or more, and the total length B (μ) of B-based inclusions
) A high-strength steel plate with excellent hydrogen-induced cracking resistance, characterized in that the relationship between Hv≦300-4/10×(A+B/2) (2) C0.01-0.06wt%, Si0.02-0
．． 60wt%, Mn1.30-2.50wt%, P0.
020wt% or less, S0.010wt% or less, Nb0.
010~0.150wt%, Al0.005~0.06
0wt%, and V0.005-0.150wt%, Tl0.005-0.150wt%, Cu0.05-0.50wt%, Cr0.05-0.5
0wt%, M00.05-0.50wt%, Ni0.0
5-1.00wt%, B0.0003-0.0030w
t%, the balance consists of Fe and unavoidable impurities, and the structure has a substantially uniform acicular ferrite structure, and furthermore, 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 total length B (μ) of B-based inclusions
) A high-strength steel plate with excellent hydrogen-induced cracking resistance, characterized in that the relationship between Hv≦300-4/10×(A+B/2) (3) C0.01~0.06wt%, Si10.02~
0.60wt%, Mn1.30-2.50wt%, P0
．． 20wt% or less, S0.010wt% or less, Nb0.
010~0.150wt%, Al0.005~0.06
0wt%, and one or two of Ca0.0005~0.0050wt% and REM0.001~0.030wt%, the remainder being Fe and inevitable impurities, and the structure is It has a substantially uniform acicular ferrite structure, and furthermore, 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 B Total length B (μ
) A high-strength steel plate with excellent hydrogen-induced cracking resistance, characterized in that the relationship between Hv≦300-4/10×(A+B/2) (4) C0.01-0.06wt%, Si0.02-0
．． 60wt%, Mn1.30-2.50wt%, P0.
020wt% or less, S0.010wt% or less, Nb0.
010~0.150wt%, Al0.005~0.06
0wt%, and 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 one or two selected from Ca0.0005~0.0050wt%, REM0.001~0.030wt%, and the balance is Fe and unavoidable The structure is composed of impurities and has a substantially uniform acicular ferrite structure, and furthermore, the Vickers hardness of the segregated part and the A-based inclusions with a length of 10 μ or more in an area of 10 mm^2 in the hardness measuring part. The total length A (μ), and the total length B (μ) of B-based inclusions
) A high-strength steel plate with excellent hydrogen-induced cracking resistance, characterized in that the relationship between Hv≦300-4/10×(A+B/2)