JPH0530898B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a steel plate with excellent hydrogen-induced cracking resistance, and more specifically, to line pipes, pressure vessels,
The present invention relates to a steel plate having a tensile strength of 40 to 70 Kgf/mm ² and excellent resistance to hydrogen-induced cracking for use in tanks and the like. [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 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 coating by adding Cu, but when the strength level of the steel plate is high or the amount of inclusions is large, hydrogen-induced cracking cannot be completely suppressed. Regarding (2), the method of regulating the shape and number of sulfides disclosed in Japanese Patent Application Laid-Open No. 114318/1983
There are methods for controlling the shape of A-based inclusions using Ca and REM, such as those disclosed in JP-A-55-128536 and JP-A-54-031020, but as the strength level of the steel sheet increases,
It is difficult to completely prevent the occurrence of hydrogen-induced cracking, and for (3), there is a method to extremely reduce the P content to 0.006 wt% or less, as described in JP-A-52-111815. However, there is a problem in terms of cost, and there is a method of making the hardness of the hardened structure Hv≦350 as described in JP-A-57-073162, but the amount of inclusions in the steel sheet If there are many hydrogen-induced cracks, it is difficult to completely eliminate hydrogen-induced cracking. Of course, these methods are often used in combination, but the reality is that these methods 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 water resistance-induced cracking as explained above, the present invention solves the following problems:
As a result of intensive research conducted by the present inventor, we have found that in order to prevent the occurrence of hydrogen-induced cracking, it is not necessary to unnecessarily restrict the chemical components or the shape and number of inclusions, but rather to restrict the length of inclusions to be short and/or Alternatively, increasing the Cu content will not unnecessarily lower the hardness of the segregated area, and if the hardness of the segregated area is low and/or the Cu content is high, the inclusion length will be reduced. There is no need to shorten the length of the inclusion, and the length of the inclusion can be regulated short.
and/or that the Cu content can be reduced if the hardness of the segregated area is controlled to be low; that is, by combining the hardness of the segregated area with control of the Cu content and inclusion length, the PH =5
We have developed a steel sheet with excellent hydrogen-induced cracking resistance that does not cause hydrogen-induced cracking even under these conditions. [Means for solving the problems] The steel plate having excellent hydrogen-induced cracking resistance according to the present invention contains (1) 0.01 to 0.30 wt% of C, 0.02 to 0.60 wt% of Si,
Mn 0.50-2.50wt%, P 0.020wt% or less, S
0.010wt% or less, Al 0.005~0.060wt%, Cu
The Vickers hardness Hv of the segregated part, the Cu content (wt%), and the area in the hardness measurement part of steel containing 0.10 to 0.50 wt% with the balance Fe and unavoidable impurities
Total length A of A-based inclusions with a length of 10μ or more in ^10mm2
The first invention is a steel plate 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: ×Cu−1/2×(A+B/2) (2) C 0.01 to 0.30wt%, Si 0.02 to 0.60wt%,
Mn 0.50-2.50wt%, P 0.020wt% or less, S
0.010wt% or less, Al 0.005~0.060wt%Cu
Contains 0.10-0.50wt%, and Nb 0.005-0.150wt%, V 0.005-0.150wt
%, Ti 0.005~0.150wt%, Cr 0.05~0.50wt
%, Ni 0.05~0.40wt%, B 0.0003~
A steel containing one or more selected from 0.0030wt%, with Ni/Cu≦0.8, and with the balance Fe and unavoidable impurities, is determined by the Vickers hardness Hv of the segregated part and the Cu content ( wt%) and 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,
Similarly, the second invention is a steel plate with excellent hydrogen-induced cracking resistance, characterized in that the relationship with the total length B (μ) of B-based inclusions satisfies the following formula: Hv≦250+200×Cu−1 /2×(A+B/2) (3) C 0.01~0.30wt%, Si 0.02~0.60wt%,
Mn 0.50-2.50wt%, P 0.020wt% or less, S
0.010wt% or less, Al 0.005~0.060wt%Cu
A steel containing 0.10 to 0.50 wt%, and one or two of Ca 0.0005 to 0.0050 wt%, REM 0.001 to 0.030 wt%, and the balance consisting of Fe and unavoidable impurities is heated to Hardness Hv, Cu content (wt%) and area at hardness measurement part
Total length A of A-based inclusions with a length of 10μ or more in ^10mm2
(μ) and the total length B (μ) of B-based inclusions satisfies the following formula. ×Cu−1/2×(A+B/2) (4) C 0.01 to 0.30wt%, Si 0.02 to 0.60wt%,
Mn 0.50-2.50wt%, P 0.020wt% or less, S
0.010wt% or less, Al 0.005~0.060wt%Cu
Contains 0.10-0.50wt%, and Nb 0.005-0.150wt%, V 0.005-0.150wt
%Ti 0.005~0.150wt%, Cr 0.05~0.50wt%,
Ni 0.05~0.40wt%, B 0.0003~0.0030wt%
Ni/Cu≦0.8, and contains one or two of Ca 0.0005~0.0050wt% and REM 0.001~0.030wt%, The Vickers hardness Hv of the segregated part, the Cu content (wt%), and the area in the hardness measurement part of the steel consisting of the balance Fe and unavoidable impurities were measured.
Total length A of A-based inclusions with a length of 10μ or more in ^10mm2
The fourth invention is a steel plate 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≦250+200 ×Cu−1/2×(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. The content of C is 0.01wt% to ensure strength.
Moreover, if the content exceeds 0.30wt%, 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 set to 0.02 to 0.60 wt%. Mn is an element necessary to ensure strength, and if the content is less than 0.50 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 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
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 inclusions satisfies the specified conditions, it is particularly important to avoid the use of S and regulations. However, from the viewpoint of toughness, the S content should be 0.010wt% or less. As a deoxidizing element, the content of Al needs to 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%. Cu is an element that is effective in improving hydrogen-induced cracking resistance in an environment where PH≧5.
This effect is small below 0.10wt%, and
If the content exceeds 0.50wt%, the effect will be saturated and hot workability will further deteriorate. Therefore, the Cu content is set to 0.10 to 0.50 wt%. If the content of Nb, V, and Ti is less than 0.005 wt%, there is little effect on improving strength, and if the content exceeds 0.150 wt%, the toughness of the weld will deteriorate. Therefore, the content of Nb, V, and Ti is set to 0.005 to 0.15 wt%. If the Cr 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 weldability. Therefore, the Cr content is
The content should be 0.05-0.50wt%. 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 0.40 wt%, the effect will be saturated and the economic efficiency 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 is set to Ni/Cu≦0.8. In order to increase the strength, B content must be 0.0003 wt% or more, and if it is contained in excess of 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 0.005 wt%, this effect will be small, and if the content is more than 0.0050 wt%, it will deteriorate the toughness. 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%. 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 Cu content, and the length of inclusions will be explained. The occurrence of hydrogen-induced cracking is caused by 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 Vickers hardness of the segregated part and the hardness measurement part in an environment with pH ≥ 5. Total length B (μ) of B-based inclusions
As shown in Figure 1, a hydrogen-induced cracking test was conducted for 96 hours at pH = 5 using steel plates with different hardnesses of segregated parts and different lengths of inclusions. As a result, the hardness of the segregated part is Hv>250+
If it is 200×Cu (wt%), 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, the hardness of the segregated part is Hv≦250＋200×Cu
(wt%), 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 is Hv≦250+200×Cu(wt%)−1/2 (A+B/
If 22 is satisfied, 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 tips of the inclusions 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-type inclusions was set to 1/2 of the total length coefficient of A-type inclusions.
If the coefficient is the same as that for system inclusions, it is not 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, whereas if this coefficient is set to 1/2, as shown in Figure 1. Second, the relationship between the two makes it possible to control the occurrence of hydrogen-induced cracking. 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, at Cu0.45wt%, ○ indicates no cracking, ● indicates cracking, Cu 0.30wt%, △ indicates no cracking, ▲ indicates cracking, and Cu 0.15wt%, □ indicates no cracking, and ■ indicates cracking. show. 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 is not yet clear, but the area of the interface between the inclusion and the base steel, the interface This is thought to be related to the sharpness of the tip, 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 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. For evaluation of hydrogen-induced cracking resistance, use NACE Stand
and TM-02-84. Therefore, the solution used in the test was artificial seawater saturated with H ₂ 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 test pieces subjected to the hydrogen-induced cracking test were taken from the position where the segregation was considered to be the largest, 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×
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=
No hydrogen-induced cracking occurred in the BP solution No. 5 at all. 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】

【table】

【table】

[Table] [Effects of the Invention] As explained above, the steel sheet having excellent hydrogen-induced cracking resistance according to the present invention has the above structure, so the PH
It has the effect of having excellent hydrogen-induced cracking resistance in which hydrogen-induced cracking does not occur at all under an environment of ≧5.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the hardness of the segregated part of a steel sheet, Cu content, and inclusion length on 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 FIG. 2 is a perspective view showing the shape and cross-sectional microscope position of a hydrogen-induced cracking test piece.

Claims (1)

[Claims] 1 C 0.01-0.30wt%, Si 0.02-0.60wt%,
Mn 0.50-2.50wt%, P 0.020wt% or less, S
0.010wt% or less, Al 0.005~0.060wt%, Cu 0.10
~0.50wt%, with the remainder being ^Fe and unavoidable impurities. 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≦250+200×Cu-1/2×(A+B/2) 2C 0.01-0.30wt%, Si 0.02-0.60wt%,
Mn 0.50-2.50wt%, P 0.020wt% or less, S
0.010wt% or less, Al 0.005~0.060wt%Cu 0.10~
Contains 0.50wt%, and Nb 0.005-0.150wt%, V 0.005-0.150wt%,
Ti 0.005~0.150wt%, Cr 0.05~0.50wt%, Ni
A steel containing one or more selected from 0.05 to 0.40wt% and B 0.0003 to 0.0030wt%, further satisfying Ni/Cu≦0.8, and the balance being Fe and unavoidable impurities,
The Vickers hardness Hv of the segregated area and the Cu content (wt
%) and length in area 10mm ² at hardness measuring part
Total length A (μ) of A-based inclusions of 10μ or more, also B
A steel sheet with excellent hydrogen-induced cracking resistance, characterized in that the relationship with the total length B (μ) of system inclusions satisfies the following formula. Hv≦250＋200×Cu−1/2×(A+B/2) 3 C 0.01 to 0.30wt%, Si 0.02 to 0.60wt%,
Mn 0.50-2.50wt%, P 0.020wt% or less, S
0.010wt% or less, Al 0.005~0.060wt%Cu 0.10~
The Vickers hardness of the segregated part is Hv, Cu content (wt%), total length A (μ) of A-based inclusions with a length of 10 μ or more in an area of 10 mm ² , and total length B (μ) of B-based inclusions in the hardness measuring part. A steel plate with excellent hydrogen-induced cracking resistance, characterized in that the relationship between the two satisfies the following formula: Hv≦250＋200×Cu−1/2×(A+B/2) 4 C 0.01 to 0.30wt%, Si 0.02 to 0.60wt%,
Mn 0.50-2.50wt%, P 0.020wt% or less, S
0.010wt% or less, Al 0.005~0.060wt%Cu 0.10~
Contains 0.50wt%, and Nb 0.005-0.150wt%, V 0.005-0.150wt%
Ti 0.005~0.150wt%, Cr 0.05~0.50wt%, Ni
Contains one or more selected from 0.05 to 0.40wt%, B 0.0003 to 0.0030wt%, furthermore, Ni/Cu≦0.8, and Ca 0.0005 to 0.0050wt%, REM 0.001 to 0.030. The Vickers hardness Hv of the segregated part, the Cu content (wt%), and the length of the area in the hardness measurement part of 10 mm ² were measured. 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. steel plate. Hv≦250＋200×Cu−1/2×(A+B/2)