JPH0625394B2 - Hydrogen resistant low alloy steel for high temperature and high pressure - Google Patents

Description

TECHNICAL FIELD The present invention relates to a steel material as a constituent material of chemical devices used under high temperature and high pressure, and particularly has excellent resistance to high temperature and high pressure hydrogen. The present invention relates to hydrogen-resistant low-alloy steel for high-temperature and high-pressure, which is suitable as a constituent material for chemical plant equipment.

(Prior arts and problems) In recent years, the chemical industry has made remarkable progress, and a wide range of equipment is used in high-temperature high-pressure hydrogen atmospheres such as petrochemical refining and heavy oil cracking processes. There is a tendency, and the usage conditions are becoming severe. Therefore, it is necessary to fully consider hydrogen resistance when selecting the constituent materials.

In particular, the hydrogen resistance of the weld is inferior to that of the base metal, and sufficient measures are required. Under these circumstances, there has recently been a particular demand for the development of low-alloy steel that is resistant to embrittlement in a high-temperature high-pressure hydrogen atmosphere and has high hydrogen resistance.

Therefore, some proposals have already been made in order to meet such a demand, for example, Japanese Patent Publication No. 50-7528.
The technique described in Japanese Patent Publication No. 57-10947 is known. That is, all of these techniques measure the fixation of C by adding a carbide-forming element to steel. Hydrogen embrittlement is considered to be due to the fact that C in steel reacts with hydrogen that has entered and diffused from the outside hydrogen atmosphere to generate methane gas, and cracks occur because the pressure of this methane gas is extremely high. Therefore, it can be said that if C is fixed as a carbide, the gas generation reaction by the methane reaction can be suppressed.

However, this means does not use W, T to fix C.
There is a problem that it is necessary to add a large amount of strong carbide forming elements such as i, Zr and Nb.

Further, in order to reduce the reaction in which C in steel reacts with hydrogen diffused from the outside hydrogen atmosphere to generate methane gas, it is conceivable to reduce C in steel, but there is a drawback that strength is lowered. .

Therefore, some of the inventors of the present invention previously investigated a new means for imparting hydrogen resistance to steel in addition to the means for low carbonization or carbide formation. As a result, since the methanogenic reaction is a reaction of solid solution C and carbide C with hydrogen, the methanogenic reaction is activated when the activity of C becomes large,
We have reached the conclusion that it is sufficient to reduce the amount of elements that increase the activity of C or add the elements that decrease the activity of C, and proposed a new proposal to reduce Si as one of such elements. 59-6357.

However, even in such a technique, the point of positively adding an element that reduces the activity of C has not been studied, and it is necessary to further study in this respect.

Therefore, the inventors of the present invention continued to study elements that reduce the activity of C, that is, elements that have a large effect of imparting hydrogen resistance, and as a result, particularly in the Mo-based low alloy steel, the Si content was not reduced. We have obtained a completely new finding that REM and Ca show the most remarkable effect for such purpose. Also, by containing an appropriate amount of V,
The high temperature strength, which is one of the essential properties in high temperature and high pressure materials, is increased, and the brittleness after hydrogen treatment is 10 to 2
It was confirmed that the effect of 0% reduction was also obtained.

That is, the inventors of the present invention melted various test trial steels in the composition range shown in Table 1 in order to carry out an experiment of hydrogen resistance and high temperature strength characteristics, cut out a test piece of 12 mmφ × 65 mm in size from this, and reproduced the thermal cycle. Accelerated tests were performed in high-temperature high-pressure hydrogen using a sample in which the heat-affected zone of welding was reproduced by an apparatus. The test conditions and the results are shown in Table 1.

Further, FIG. 5 shows the relationship between the embrittlement degree (%) and REM and Ca from the result of the accelerated test. In this case, REM and Ca
For the simultaneously added steel, the one with the higher REM% or Ca% in the figure is shown. What is the degree of brittleness? Where ψ _O is the aperture value before hydrogen treatment and ψ is the aperture value after hydrogen treatment. Thus, this equation shows that the larger the degree of embrittlement, the smaller the resistance to hydrogen.

As is clear from the experimental results, in the Mo-based low alloy steel, by adding the REM and Ca, which are C activity suppressing elements, alone or in combination without reducing the Si content that is a C activity increasing element. As a result of the decrease in the activity of C and the suppression of the methane production reaction by this, hydrogen embrittlement of the steel material in a high temperature and high pressure hydrogen atmosphere can be prevented, and the addition of V further increases the high temperature strength. And, the knowledge that a conventional example that the suppression effect of hydrogen embrittlement is obtained was considered was obtained. The present invention has been made based on such findings.

(Means and Actions for Solving Problems) The gist of the present invention is C: 0.05 to 0.25% by weight and Si: 0.01
5 to 0.70%, Mn: 0.2 to 1.5%, Mo: 0.3 to 1.5%, V: 0.0
Contains 5 to 0.40%, REM: 0.01 to 0.10% and Ca: 0.0
01-0.010% One or both, and Si and REM
Fig. 1 shows the range surrounded by ABCDE, Fig. 2 shows the relationship between Si and Ca the range surrounded by Fig. 2 ABCDE, and Si, RE.
The relationship between M and Ca satisfies each of the ranges surrounded by ABCDEFGHIJ in Fig. 3, and further in Fig. 4 ABCD.
It contains SolAl and N in the range surrounded by E and contains the balance Fe.
And a hydrogen-resistant low alloy steel for high temperature and high pressure, which is characterized by comprising unavoidable impurities.

However, in Fig. 1, Si% and REM% are A (0.015, 0.01), B (0.10, 0.01), C (0.70, 0.0)
3), D (0.70, 0.10), E (0.015, 0.10), Si% and Ca% in Fig. 2 are A (0.015, 0.001), B (0.10, 0.001), C (0.70,
0.007), D (0.70, 0.010), E (0.015, 0.010), Si%, REM%, Ca% in Fig. 3 are A (0.015, 0.01, 0.001), B (0.015, 0.01, 0.01)
0), C (0.015, 0.10, 0.010), D (0.015, 0.10, 0.
001), E (0.70, 0.10, 0.001), F (0.70, 0.10, 0.
010), G (0.70, 0.01, 0.010), H (0.70, 0.01, 0.
007), I (0.70, 0.03, 0.001), J (0.10, 0.01, 0.
001), SolAl% and N% in Fig. 4 are A (0.010, 0.003), B (0.010, 0.005), C (0.01
6, 0.008), D (0.06, 0.008), E (0.06, 0.003).

Hereinafter, the present invention will be described in detail.

First, C is at least to improve hardenability and strength.
The upper limit is set to 0.25% in consideration of the need for 0.05% or more, and the adverse effects on hydrogen resistance and toughness and weldability when a large amount is used.

Next, Si needs to be at least 0.015% as a deoxidizing agent and has an effect of increasing the tensile strength, but if contained in a large amount, it impairs toughness, so the upper limit was set to 0.70%.

Mn, which is used as a deoxidizing element, is an element that enhances hardenability and strength and toughness. But,
If it is less than 0.2%, the effect is not sufficient, and if it exceeds 1.5%, the hydrogen resistance is reduced, so that the range is 0.2 to 1.5%.

Further, Mo is required to be 0.3% or more in order to increase high temperature strength and hydrogen resistance. However, addition of more than 1.5% lowers toughness, so the range is 0.3-1.5%.
And

Further, V is required to be at least 0.05% or more in order to increase the high temperature strength and suppress hydrogen embrittlement, but if it exceeds 0.40%, the hardenability, hot workability or toughness is impaired. It was set to 0.05 to 0.40%.

Further, in the present invention, since the activity of C is decreased,
That is, one or both of REM and Ca are added to enhance the hydrogen resistance imparting effect.

REM is one or two of the rare earth elements with atomic numbers 57 to 71.
However, if the content is more than 0.1%, the toughness after stress relieving annealing will be reduced, so the range was made 0.01 to 0.10%.

Further, Ca has an effect of suppressing the activity of C similarly to REM, but if it is less than 0.001%, it does not have the effect, and if it exceeds 0.010%, the toughness after stress relief annealing decreases and at the same time it becomes solid in Mo-based low alloy steel. Since it becomes difficult to dissolve it, the range is set to 0.00
It was set to 1 to 0.010%.

Further, in the present invention, in containing one or both of REM and Ca, the content of REM and Ca in relation to Si is decreased in order to reduce the activity of C, that is, to enhance the hydrogen resistance imparting effect. There is an important skeleton in the prescribed place. That is, when either REM or Ca is contained, the relationship between Si and REM or Si and Ca satisfies the range surrounded by ABCDE in each of FIG. 1 and FIG. In the case of containing Si, the relationship among Si, REM and Ca is shown in Fig. 3 ABCD
The range surrounded by EFGHIJ must be satisfied. However, in FIG. 1, the coordinate points A, B, C, D, and E are Si% and REM% are A (0.015, 0.01), B (0.10,
0.01), C (0.70, 0.03), D (0.70, 0.10), E (0.
015, 0.10), and in FIG. 2, A, B, C,
At each coordinate point of D and E, Si% and Ca% are A (0.015, 0.001),
B (0.10, 0.001), C (0.70, 0.007), D (0.70, 0.
010), E (0.015, 0.010), and the coordinate points A, B, C, D, E, F, G, H, I, and J in FIG.
Si%, REM%, Ca% are A (0.015, 0.01, 0.001), B
(0.015, 0.01, 0.010), C (0.015, 0.10, 0.010),
D (0.015, 0.10, 0.001), E (0.70, 0.10, 0.00)
1), F (0.70, 0.10, 0.010), G (0.70, 0.01, 0.01)
0), H (0.70, 0.01, 0.007), I (0.70, 0.03, 0.00)
1) and J (0.10, 0.01, 0.001).

First, regarding the relationship between Si and REM, it was found that the relationship as shown in FIG. 1 is necessary in order to reduce the activity of C, that is, to enhance the hydrogen resistance imparting effect. Line AB in the figure is the lower limit of 0.01% for REM, and line ED is REM.
Shows the upper limit of 0.10% for each, and line AE shows the lower limit of Si of 0.
The line CD shows the upper limit of 0.70% for Si and the line CD shows 0.70%. The shaded line BC is necessary to increase the activity of C, that is, to reduce the activity of C by REM, that is, to increase the effect of imparting hydrogen resistance, with respect to the Si content that reduces the effect of imparting hydrogen resistance. The equilibrium relationship of content is shown.

Next, regarding the relationship between Si and Ca, it was found that the relationship as shown in FIG. 2 is necessary in order to reduce the activity of C, that is, to enhance the hydrogen resistance imparting effect.
In the figure, the line AB indicates the lower limit of Ca of 0.001%, and the line ED indicates the upper limit of Ca.
0.010% is shown for each, and line AE is the lower limit of Si 0.015
%, And the line CD shows the upper limit of 0.70% for Si. Diagonal line B
C is a content necessary to increase the activity of C, that is, to reduce the activity of C due to Ca, that is, to increase the effect of imparting hydrogen resistance to the content of Si that reduces the effect of imparting hydrogen resistance. The equilibrium relationship of quantity is shown.

Furthermore, in the case of adding both REM and Ca in combination, the relationship with Si must be within the range ABCDEFGHIJ in FIG. The plane ABGHJ in the figure is
The lower limit of REM is 0.01%, and the upper limit of REM is 0.10% for planar CDEF.
, And the plane ADEIJ is the lower limit of Ca of 0.001.
%, The plane BCFG shows the upper limit of 0.010% for Ca, and the plane ABCD shows the lower limit of 0.015% for Si.
FGHI shows the upper limit of Si of 0.70%. Plane HIJ
Is necessary to increase the activity of C, that is, to reduce the activity of C by REM and Ca, that is, to increase the effect of imparting hydrogen resistance to the content of Si that reduces the effect of imparting hydrogen resistance. The equilibrium relationship of content is shown.

In the present invention, in addition to the definition of the relationship between Si and one or both of REM and Ca as described above, the relationship between SolAl and N is defined within the range surrounded by ABCDE in FIG. It is attempted to control the grain size of γ grains in the steel of the above component system, and thereby improve hydrogen resistance and toughness. That is, the relationship of FIG. 4 is as follows: C: 0.05-0.25%, Si: 0.015
~ 0.70%, Mn: 0.2 ~ 1.5%, Mo: 0.3 ~ 1.5%, V: 0.05
~ 0.40, REM: 0.01 ~ 0.10%, Ca: 0.001 ~ 0.010
% Of steels containing one or both of them are obtained as a result of studying by adding various SolAl and N while changing them.

The line AB in the figure indicates the lower limit of 0.01% for SolAl, and the line DE indicates the upper limit of 0.06% for SolAl. If the content of SolAl is less than 0.01%, the γ grains become coarse, so that tempering tends to cause embrittlement, and the degree of embrittlement tends to increase, resulting in lower toughness. On the other hand, if it exceeds 0.06%, the γ grains become mixed grains, and the toughness decreases. Also, line A
E indicates a lower limit of N of 0.003%, and line CD indicates an upper limit of N of 0.008%. If N is less than 0.003%, the γ grains become coarse, so that temper embrittlement easily occurs, the degree of embrittlement increases, and the toughness further decreases. On the other hand, if it exceeds 0.008%, the γ grains become finer, and the toughness, hardenability and strength deteriorate.

Furthermore, the line BC shows that the amount of SolAl and N is stoichiometrically 1: 1.
Shows the relationship. Regarding the relationship between SolAl and N, the γ grains become finer above this line and the toughness, hardenability and strength decrease.

Next, the effects of the present invention will be described in more detail by way of examples.

(Example) Table 2 shows the chemical composition of the test material. NO.1, 3, 5,
7, 9, 10, 12, 13, 14 are steels according to the present invention, NO.2,
4, 6, 8, 11, and 15 are comparative steels.

In order to compare the hydrogen resistance of the test materials, the tensile properties after heating for 100 hours in a high-temperature high-pressure hydrogen atmosphere using a sample in which the weld heat affected zone was reproduced are also shown in Table 2. As a result, the steel of the present invention does not undergo hydrogen embrittlement in this high-temperature and high-pressure hydrogen treatment and exhibits significantly higher properties than the comparative steel, but the comparative steel has a reduced tensile strength due to the high-temperature and high-pressure hydrogen treatment, and has a reduced drawing strength. It can be seen that is significantly reduced.

(Effects of the invention) As described above, the Mo-based low alloy steel of the present invention has excellent properties that hydrogen embrittlement can be advantageously prevented in a hydrogen atmosphere under high temperature and high pressure, and the strength does not decrease, and its industrial value. Is extremely large.

[Brief description of drawings]

FIG. 1 is a diagram showing a proper range of the relationship between Si and REM in the present invention, FIG. 2 is a diagram showing a proper range of the relationship between Si and Ca in the present invention, and FIG. 3 is a diagram showing Si and REM in the present invention. FIG. 4 is a diagram showing an appropriate range of the relationship between Ca and Ca, and FIG.
FIG. 5 is a diagram showing an appropriate range of the relation between lAl and N, and FIG. 5 is a diagram showing the relation between REM and Ca and the degree of embrittlement.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsukuni Hashimoto 5-10-1 Fuchinobe, Sagamihara-shi, Kanagawa Nippon Steel Corporation Second Technical Research Institute (56) Reference JP-A-58-1059 (JP , A) JP-A-57-73162 (JP, A) JP-A-56-3655 (JP, A) JP-A-55-38901 (JP, A) JP-A-54-31020 (JP, A) JP-B 57-10947 (JP, B2) Japanese Patent Publication Sho-50-7528 (JP, B2)

Claims (1)

[Claims] 1. C: 0.05 to 0.25%, Si: 0.015 to 0.70%, Mn: 0.2 to 1.5%, Mo: 0.3 to 1.5% by weight. %, V: 0.05 to 0.40%, REM: 0.01 to 0.10% and Ca: 0.001 to 0.010
%, And the relationship between Si and REM is the range surrounded by ABCDE in FIG. 1, the relationship between Si and Ca is the range surrounded by ABCDE in FIG. 2, and Si, REM and Ca.
The relationship between the three parties satisfies each of the ranges surrounded by ABCDEFGHIJ in Fig. 3, and further contains SolAl and N in the range surrounded by ABCDE in Fig. 4, and the balance is Fe and inevitable impurities at high temperature. Hydrogen resistant low alloy steel for high pressure. However, in Fig. 1, Si% and REM% are A (0.015, 0.01), B (0.10, 0.01), C (0.70, 0.0).
3), D (0.70, 0.10), E (0.015, 0.10), Si% and Ca% in Fig. 2 are A (0.015, 0.001), B (0.10, 0.001), C (0.70,
0.007), D (0.70, 0.010), E (0.015, 0.010), Si%, REM%, Ca% in Fig. 3 are A (0.015, 0.01, 0.001), B (0.015, 0.01, 0.01)
0), C (0.015, 0.10, 0.010), D (0.015, 0.10, 0.
001), E (0.70, 0.10, 0.001), F (0.70, 0.10, 0.
010), G (0.70, 0.01, 0.010), H (0.70, 0.01, 0.
007), I (0.70, 0.03, 0.001), J (0.10, 0.01, 0.
001), SolAl% and N% in Fig. 4 are A (0.010, 0.003), B (0.010, 0.005), C (0.01
6, 0.008), D (0.06, 0.008), E (0.06, 0.003).