JPH0535209B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a high-strength steel plate with excellent hydrogen-induced cracking resistance, and more specifically, a high-strength steel plate with a tensile strength of 50 to 80 Kgf/
Concerning a steel plate with excellent hydrogen-induced cracking resistance of mm ² . [Prior art] In recent years, equipment used in a humid hydrogen sulfide atmosphere,
For example, there are many accidents caused by so-called hydrogen-induced cracking in line pipes and oil refinery equipment that transport crude oil and natural gas containing hydrogen sulfide.
Steel sheets with excellent hydrogen-induced cracking resistance are desperately needed. This hydrogen-induced cracking is caused by the pressure of hydrogen gas generated when hydrogen generated by corrosion of the steel enters and diffuses into the steel in an atomic state, accumulates and becomes molecules at the interface between inclusions and the base steel. However, 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 the steel; (2) Reduction and morphology 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,
As described in Publication No. 097515, there is a method of forming a corrosion-resistant film by adding Cu, but PH
It has no effect under harsh environments such as =3, and the occurrence of hydrogen-induced cracking cannot be suppressed. There are methods to control the number of A-based inclusions, and methods to control the form of A-based inclusions using Ca and REM, such as those disclosed in JP-A-55-128536 and JP-A-54-031020. , it is difficult to completely prevent the occurrence of hydrogen-induced cracking when the environment becomes harsh, and regarding (3),
As described in Publication No. 52-111815, there is a method to extremely reduce the P content to 0.006wt% or less,
There was a problem in terms of cost, and
As described in Publication No. 073162, there is a method to make the hardness of the hardened structure Hv≦350, but it is difficult to completely eliminate the occurrence of hydrogen-induced cracking in high-strength steel in harsh environments with low pH. It is. [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 solves the conventional method. It is difficult to completely suppress the occurrence of hydrogen-induced cracking in the harsh environment of PH = 3 when used alone or in combination, and if possible, it is difficult to completely suppress the occurrence of hydrogen-induced cracking in the harsh environment of PH = 3. However, in order to solve the problem of hydrogen-induced cracking, the present inventors have developed hydrogen-induced cracking resistance by combining chemical composition, inclusion length, and segregation hardness control. As a result of this research, the hydrogen-induced cracking resistance of the steel will be further improved by creating a nearly uniform axial ferrite structure. Find out that, that is,
By combining the steel structure with an axial ferrite structure and controlling the hardness of the segregated part and the length of inclusions, it has excellent hydrogen-induced cracking resistance, with no hydrogen-induced cracking occurring even in an environment of PH = 3. The company developed a high-strength steel plate. [Means for solving the problems] The high-strength steel sheet with excellent hydrogen-induced cracking resistance according to the present invention has the following properties: 1 C0.01-0.06wt%, Si0.02-0.60wt%, Mn1.30-2.50wt% %, P0.020wt% or less, S0.010wt% or less, Nb0.010~0.150wt%, Al0.005~0.060wt%, the balance consists of Fe and unavoidable impurities, and the structure is almost uniform. It has a cyular 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 at the hardness measurement part, and the B-based inclusions as well. A high-strength steel plate with excellent hydrogen-induced cracking resistance, characterized in that the relationship with the total length B (μ) satisfies the following formula. Hv≦300−4/10×(A+B/2) as the first invention, 2 C0.01~0.06wt%, Si0.02~0.60wt%, Mn1.30~2.50wt%, P0.020wt% or less , Contains S0.010wt% or less, Nb0.010~0.150wt%, Al0.005~0.060wt%, and V0.005~0.150wt%, Ti0.005~0.150wt%, Cu0.05~0.50wt %, Cr0.05~0.50wt%, Mo0.05~0.50wt%, Ni0.05~1.00wt%, B0.0003~0.0030wt%, and the balance is Fe. and unavoidable impurities, and has a substantially uniform axial ferrite structure, and furthermore, has a Vickers hardness of the segregated part and an A-based intervention with a length of 10 μ or more in an area of 10 mm ² in the hardness measurement part. A high-strength steel sheet with excellent hydrogen-induced cracking resistance, characterized in that the relationship between the total length A (μ) of objects and the total length B (μ) of B-based inclusions satisfies the following formula. Hv≦300−4/10×(A+B/2) as the second invention, 3 C0.01~0.06wt%, Si0.02~0.60wt%, Mn1.30~2.50wt%, P0.020wt% or less , S0.010wt% or less, Nb0.010~0.150wt%, Al0.005~0.060wt%, and one or two of Ca0.0005~0.0050wt%, REM0.001~0.030wt%. It contains seeds, the remainder is Fe and unavoidable impurities, and has an ^almost uniform acyl ferrite structure. Excellent hydrogen-induced cracking resistance characterized by the relationship between the total length A (μ) of A-based inclusions having a diameter of 10 μ or more and the total length B (μ) of B-based inclusions satisfying the following formula. High strength steel plate. Hv≦300−4/10×(A+B/2) as the third invention, 4 C0.01~0.06wt%, Si0.02~0.60wt%, Mn1.30~2.50wt%, P0.020wt% or less , Contains S0.010wt% or less, Nb0.010~0.150wt%, Al0.005~0.060wt%, and V0.005~0.150wt%, Ti0.005~0.150wt%, Cu0.05~0.50wt %, Cr0.05~0.50wt%, Mo0.05~0.50wt%, Ni0.05~1.00wt%, B0.0003~0.0030wt%, and further, Containing one or two of Ca0.0005~0.0050wt% and REM0.001~0.030wt%, the balance consisting of Fe and unavoidable impurities, and having a substantially uniform ashkyular ferrite structure, Furthermore, the Vickers hardness of the segregated area, the total length A (μ) of A-based inclusions with a length of 10 μ or more in the area of 10 mm ² in the hardness measurement area, and the total length B (μ) of B-based inclusions are also calculated. A high-strength steel plate with excellent resistance to hydrogen-induced cracking, characterized in that the relationship satisfies the following formula. This invention consists of four inventions, with Hv≦300−4/10×(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. The content of C is 0.01wt% to ensure strength.
If the content exceeds 0.06 wt%, the desired axial ferrite structure cannot be obtained. Therefore, the C content is 0.01~0.06wt%
shall be. 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 set to 0.02 to 0.60 wt%. Mn is an element necessary to ensure strength and obtain an axial ferrite structure, and the content is
This effect is small below 1.30wt%, and
If the content exceeds 2.50wt%, 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 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 zone, the P content is
The content shall be 0.020wt%. 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 the inclusion satisfies a predetermined condition, S should be regulated in particular. Although it is not necessary, the S content should be 0.010wt% or less from the viewpoint of toughness. Nb is an element necessary to ensure strength and obtain an axial ferrite structure, and the content is
If it is less than 0.010wt%, this effect will be poor, and
If the content exceeds 0.150wt%, the toughness of the weld will deteriorate. Therefore, the Nb content is 0.010~
The content shall be 0.150wt%. The content of Al as a deoxidizing element must be 0.005wt% or more, and since a large amount of content causes deterioration of toughness, the upper limit is regulated to 0.060wt%. Therefore, the Al content is set to 0.005 to 0.060 wt%. V, Ti, Cu, Cr, Mo, Ni, and B are selectively included to improve strength. If the content of V 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. Then,
The content of V and Ti is 0.005 to 0.150 wt%. 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 set to 0.05 to 0.50 wt%. When the content of Cr and Mo is less than 0.05 wt%, the effect on strength improvement is small, and when the content exceeds 0.50 wt%, weldability deteriorates. So, Cr, Mo
The content is 0.05 to 0.50wt%. 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 economic efficiency will be impaired. Therefore, the Ni content is set to 0.05 to 1.00 wt%. In order to increase the strength, B content must be 0.0003 wt% or more, and if the B content exceeds 0.0030 wt%, the toughness will deteriorate. 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 content is less than 0.0005 wt%, this effect will be small, and if the content is more than 0.0050 wt%, the toughness will deteriorate. Therefore, the Ca content is 0.0005
~0.0050wt%. Like Ca, REM is an element that is effective in spheroidizing sulfide-based inclusions, and its content needs to be 0.001 wt% or more, and if it is contained in an amount exceeding 0.030 wt%, it deteriorates toughness. Therefore, the REM content is
The content should be 0.001 to 0.030wt%. As mentioned above, hydrogen-induced cracking occurs when hydrogen generated by corrosion of steel in a humid hydrogen sulfide atmosphere penetrates into the steel, causing molecules to form at the interface between inclusions and base steel. It is said that this occurs when the base steel cannot withstand the pressure of hydrogen gas caused by hydrogen. Normally, the segregated portions present in a steel plate have a small resistance to cracking, 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 axial 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 acyl ferrite structure. Next, to explain the relationship between the hardness of the segregated part and the length of inclusions, in axial ferrite steel, the occurrence of hydrogen-induced cracking is determined by the Vickers hardness of the segregated part and the length of the 10 ^mm2 area at the hardness measurement part. 10μ
It is limited by the total length A (μ) of the A-based inclusions and the total length B (μ) of the B-based inclusions, as shown in Figure 1. Using steel plates of different lengths, under PH3 conditions.
As a result of a 96-hour hydrogen-induced cracking test, if the hardness of the segregated part is Hv > 300, A with a length of 10μ or more
Hydrogen-induced cracking occurs even in the absence of B-type and B-type inclusions. In addition, if the hardness of the segregated part is Hv≦300,
Total length A of A-type and B-type inclusions with a length of 10μ or more
If the relationship between B and the Vickers hardness Hv of the segregated part satisfies Hv≦300-4/10 (A+B/2), hydrogen-induced cracking will not occur, but
If this condition is not satisfied, 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 tip of the inclusion is also small, making them susceptible to hydrogen-induced cracking. This is because it has no effect. In addition, the coefficient of the total length of B-based inclusions was set to 1/2 of the coefficient of the total length of A-related inclusions.
If the coefficient is the same as that for system 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 inclusions, whereas if this coefficient is set to 1/2, as shown in Figure 2. Second, the relationship between the two makes it possible to control the occurrence of hydrogen-induced cracking.
(In Figure 2, 1 is the limit line for hydrogen-induced cracking of acyl ferrite, which is a high-strength steel plate with excellent hydrogen-induced cracking resistance according to the present invention, and 2 is the limit line for hydrogen-induced cracking of conventional ferrite pearlite. In addition, the segregated area refers to the area where the components are segregated during solidification, 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 segregation zone 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, the tip of the interface This is thought to be related to the sharpness of the inclusion, 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 high-strength steel plate having excellent hydrogen-induced cracking resistance according to the present invention will be described. Examples Steels having the components and ratios shown in Table 1 were melted, cast by continuous casting method or ingot forming method, and then hot rolled to produce test steel plates. The hardness of the segregated portion of each test steel plate was measured using a Bitkers hardness tester (load: 100 g), and the total length of A-based inclusions and B-based inclusions with a length of 10 μ or more in the area of 10 mm ² was measured optically. magnification using a microscope
Measured at 400x magnification. 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. Hydrogen-induced cracking resistance evaluation is based on NACE Standard
It was carried out according to TM-02-84. However, the solution used in the test was artificial seawater saturated with H ₂ S (so-called
There are two types: BP solution, PH=5) and 5% NaCl + 0.5% acetic acid aqueous 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 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 t×
It is 20w x 100lmm. In addition, the thickness of the test piece was obtained by cutting 1 mm each on both surfaces of the steel plate. Three test pieces were taken for each test solution from each test steel sheet, and only when no hydrogen-induced cracking was observed in any of the test pieces, it was determined that no hydrogen-induced cracking had 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, PH=
Of course, in the BP solution of PH=3,
No hydrogen-induced cracking occurred in the MACE solution either. 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. In addition, FIG. 1a shows the metal structure of the high-strength steel sheet with excellent hydrogen-induced cracking resistance according to the present invention (Steel 1 in Table 1), and FIG. 1B shows the metallographic structure of the comparative steel (Steel 8 in Table 1). A micrograph shown is shown.

【table】

[Table] ○: No hydrogen-induced cracking. ×: Hydrogen-induced cracking occurred.
[Effects of the Invention] As explained above, since the high-strength steel sheet with excellent hydrogen-induced cracking resistance according to the present invention has a superior composition, hydrogen-induced cracking does not occur at all even under harsh environments such as PH3. It has the effect of having excellent hydrogen-induced cracking resistance without causing any damage.

[Brief explanation of drawings]

Figure 1a is a photomicrograph showing the metallographic structure of a high-strength steel sheet with excellent hydrogen-induced cracking resistance according to the present invention, Fig.1b is a photomicrograph showing the metallographic structure of a comparative steel, and Fig.2 is a photomicrograph showing the metallographic structure of a comparative steel. A diagram showing the relationship between the hardness of the segregated part of the steel plate and the length of inclusions that affect the occurrence of the cracking. Figure 3 is a perspective view showing the sampling position of the hydrogen-induced crack test piece. Figure 4 shows the shape and cross-sectional examination of the hydrogen-induced crack test piece. It is a perspective view showing a mirror position.

Claims (1)

[Claims] 1 C0.01~0.06wt%, Si0.02~0.60wt%, Mn1.30~2.50wt%, P0.020wt% or less, S0.010wt% or less, Nb0.010~0.150wt% , contains 0.005 to 0.060wt% Al, with the balance consisting of Fe and unavoidable impurities,
In addition, the structure has a substantially uniform axial ferrite structure, and furthermore, the Vickers hardness of the segregated part and the total length A of A-based inclusions with a length of 10 μ or more in an area of 10 mm ² in the hardness measurement part A high-strength steel sheet with excellent resistance to hydrogen-induced cracking, characterized in that the relationship between B (μ) and the total length B (μ) of B-based inclusions satisfies the following formula. 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, Contains Nb0.010~0.150wt%, Al0.005~0.060wt%, and V0.005~0.150wt%, Ti0.005~0.150wt%, Cu0.05~0.50wt%, Cr0.05~0.50 wt%, Mo0.05-0.50wt%, Ni0.05-1.00wt%, B0.0003-0.0030wt%, and the remainder consists of Fe and inevitable impurities.
In addition, the structure has a substantially uniform axial ferrite structure, and furthermore, the Vickers hardness of the segregated part and the total length A of A-based inclusions with a length of 10 μ or more in an area of 10 mm ² in the hardness measurement part A high-strength steel sheet with excellent resistance to hydrogen-induced cracking, characterized in that the relationship between B (μ) and the total length B (μ) of B-based inclusions satisfies the following formula. Hv≦300−4/10×(A+B/2) 3 C0.01~0.06wt%, Si0.02~0.60wt%, Mn1.30~2.50wt%, P0.020wt% or less, S0.010wt% or less, Contains Nb0.010~0.150wt%, Al0.005~0.060wt%, and one or two of Ca0.0005~0.0050wt%, REM0.001~0.030wt%, and the balance is Fe. and unavoidable impurities,
In addition, the structure has a substantially uniform axial ferrite structure, and furthermore, the Vickers hardness of the segregated part and the total length A of A-based inclusions with a length of 10 μ or more in an area of 10 mm ² in the hardness measurement part A high-strength steel sheet with excellent resistance to hydrogen-induced cracking, characterized in that the relationship between B (μ) and the total length B (μ) of B-based inclusions satisfies the following formula. 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, Contains Nb0.010~0.150wt%, Al0.005~0.060wt%, and V0.005~0.150wt%, Ti0.005~0.150wt%, Cu0.05~0.50wt%, Cr0.05~0.50 wt%, Mo0.05-0.50wt%, Ni0.05-1.00wt%, B0.0003-0.0030wt%, and further contains Ca0.0005-0.0050wt%. , contains one or two of REM0.001~0.030wt%, with the balance consisting of Fe and unavoidable impurities,
In addition, the structure has a substantially uniform axial ferrite structure, and furthermore, the Vickers hardness of the segregated ^part and the total length A ( A high-strength steel sheet with excellent resistance to hydrogen-induced cracking, characterized in that the relationship between B (μ) and the total length B (μ) of B-based inclusions satisfies the following formula. Hv≦300−4/10×(A+B/2)