JP2546071B2 - Rolled clad steel sheet with excellent resistance to hydrogen delamination cracking - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolled clad steel sheet, and an object thereof is to provide a rolled clad steel sheet having excellent resistance to hydrogen delamination cracking by controlling the thicknesses of base material components and intermediate materials.

[0002]

2. Description of the Related Art Clad steel obtained by overlay welding austenitic stainless steel on Cr-Mo steel is used for equipment such as high-temperature high-pressure hydrogen reactor used in petroleum refining plants. However, in these devices, peeling cracks due to hydrogen accumulation occur in the vicinity of the boundary between the base metal and the weld metal when the operation is stopped. To prevent this, Japanese Patent Publication No. 54-107453 discloses.
What was examined from the viewpoint of welding materials as typified by JP-B-54-71746, JP-B-61-379.
As typified by Japanese Patent Laid-Open No. 51, there are some which have been improved from the viewpoint of the base material component. That is, all of these materials improve the hydrogen delamination cracking resistance of the solidification structure formed in the boundary layer between the base metal and stainless steel, which is peculiar to the cladding metal, from the viewpoint of the phases formed and the diffusion of carbon. This is what we are trying to measure.

In addition to the above-mentioned build-up welding method, there are a hot rolling method, a bombardment method, and a cast-girth method as a method for producing a clad steel sheet. The hot rolling method is the best.

[0004] Therefore, if a clad steel having a hydrogen delamination cracking resistance equal to or higher than that of the conventional build-up welded clad steel can be obtained as this hot-rolled material, there is a great economical advantage. Studies on steel have not yet been fully conducted.

[0005]

In the above-mentioned hot rolled clad steel, unlike the overlay welding clad steel, there is no solidification structure formation due to the melting of the boundary phase, and therefore the martensitic phase which lowers the hydrogen exfoliation resistance is reduced. It is not necessary to pay attention to the formation and the formation of coarse crystal grains, but on the other hand, there is a problem that hydrogen peeling cracking resistance is deteriorated due to hydrogen accumulation at the bonding interface. Since such problems are not effectively solved, it is not possible to appropriately obtain this hot-rolled clad steel material, which has great economic merit.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been studied so as to solve the above-mentioned problems in the conventional one, and the hot rolling clad can be obtained by appropriately selecting the base material component and the thickness of the Ni material as the intermediate material. It has succeeded in securing excellent hydrogen delamination cracking resistance in steel materials and is as follows.

(1) C: 0.05 to 0.30 wt%, Si: 0.03 to 1.00
wt%, Mn: 0.20 to 1.60 wt%, Cr: 0.80 to 3.50 wt%, Mo:
0.30 to 1.50 wt%, Al: 0.005 to 0.10 wt%, V: 0.05 to 0.40 wt%, Nb: 0.10 to 0.40 wt%, and the balance is Fe and Cr-Mo steel consisting of unavoidable impurities is a base material, austenitic stainless steel is a composite material, and Ni is an intermediate material. Later Ni phase thickness is 0.05-0.
A rolled clad steel sheet with excellent resistance to hydrogen delamination cracking characterized by a thickness of 30 mm.

(2) In addition to containing the component described in the item (1), Ni: 0.01 to 0.50 wt%, Ti: 0.005 to 0.10 wt%,
B: 0.0002 to 0.0050% of any one kind or two kinds or more, and the balance is Cr-Mo steel consisting of Fe and inevitable impurities as a base material, austenitic stainless steel as a composite material, and Ni. It is a laminated hot-rolled clad steel sheet as an intermediate material, and moreover, the thickness of the Ni phase after hot rolling in the clad steel sheet is 0.05 to 0.30 mm, which is excellent in hydrogen delamination cracking resistance. Rolled clad steel plate.

[0009]

The reason for limiting the component composition of the base material as described above will be described below in terms of wt% (hereinafter simply referred to as "%").

C is required to be 0.05% or more in order to secure tensile strength and creep strength, but if it exceeds 0.30%, weldability,
Impact properties are reduced.

Si is required to be 0.03% or more from the viewpoint of deoxidation and securing of strength, but if it exceeds 1.0%, the impact characteristics are deteriorated.

Mn needs to be 0.20% or more from the viewpoint of deoxidizing and securing strength, but if it exceeds 1.60%, weldability is deteriorated.

Cr is for improving oxidation resistance and creep strength.
0.80% or more is required, but if it exceeds 3.50%, the weldability is deteriorated, so this is made the upper limit.

Mo is required to be 0.30% or more in order to secure the strength, especially the creep strength, but the upper limit was set to 1.50% in consideration of the expensive element and weldability.

V is a particularly important element in the present invention. As shown in FIG. 1, V is required to be 0.05% or more to improve the hydrogen peeling crack resistance, whereas if it exceeds 0.40%, S is added.
R cracking sensitivity is significantly increased.

Nb is an element as important as V in the present invention, and as shown in FIG. 1, 0.10% or more is required from the viewpoint of hydrogen delamination cracking resistance, but if it exceeds 0.40%, impact resistance is obtained. This is the upper limit because it will decrease.

From the viewpoint of deoxidation, Al is required to be 0.005% or more, but if it exceeds 0.10%, the ductility and impact properties deteriorate.

From the viewpoint of refining the crystal grains and effectively utilizing B, Ti is required to be 0.005% or more, but if 0.10% or more is added, the impact properties deteriorate.

B is required to be 0.0002% or more for improving the hardenability, but if it exceeds 0.0050%, SR cracking susceptibility becomes high, so this is made the upper limit.

Ni is required to be 0.01% or more from the viewpoint of improving the hardenability, but since it is an expensive element, the upper limit was 0.50%.

To further explain the present invention as described above, in order to solve the above problems, the present inventor reproduced the delamination cracking phenomenon when the hydrogen reactor was shut down by using a hydrogen autoclave. The hydrogen delamination cracking resistance of rolled clad steel was examined.

[0022] In other words, as shown in the following Table ¹ 2 _1/4 Cr-1Mo
Steel was used as a base material, SUS347 was used as a composite material, and Ni foil was used as an intermediate material. After heating to 1200 ° C, a reduction ratio of 4 (5
0 + 4) t was hot-rolled.

[0023]

[Table 1]

The thickness of the Ni phase after hot rolling was 0.07 mm, and thereafter, heat treatment such as normalizing (900 ° C.), tempering (720 ° C.) and SR (690 ° C.) was performed.

From these clad steels, (46 + 4) t ×
A 70 w × 100 l sample was taken and soaked in a hydrogen autoclave under the conditions of 450 ° C. and a hydrogen partial pressure of 200 kgf / cm ² for 24 hours and then cooled to room temperature at 4 ° C./min.
Considering that the peeling occurs several hours to several days after reaching the room temperature, the peeled area ratio was obtained using an ultrasonic flaw detector after 7 days.

FIG. 1 shows these results, including the results of the clad steel obtained by overlay welding the first phase SUS309L and the second phase SUS347L to the sample steel 1. Rolled clad steel is more excellent in peel crack resistance than overlay clad steel, and hydrogen peel crack does not occur at all when V is added by 0.05% or more or Nb is added by 0.10% or more. Therefore, from the viewpoint of the base material component system, addition of V of 0.05% or more or Nb of 0.10% or more is desirable.

FIG. 2 shows a test steel 4 satisfying the above composition conditions.
Using as a base material, SUS347 as a composite material, and including the case where Ni foil is not inserted, hot rolled and heat treated rolled clad steel with different thickness of the intermediate material after rolling under the same conditions as in Fig. 1. About 450 ℃, hydrogen partial pressure 200kgf /
The peeled area ratio after hydrogen charging under the condition of cm ² is shown.

When the Ni phase thickness after rolling is less than 0.05 mm,
The peeled area ratio increases as the thickness decreases. On the other hand, in the region where the Ni phase thickness exceeds 0.30 mm, the delamination area ratio increases as the thickness increases. Therefore, in order to improve the hydrogen peeling crack resistance, the Ni phase thickness after rolling needs to be 0.05 to 0.30 mm. In general, in case of clad steel, Ni foil may be charged from the viewpoint of preventing carburization from the base metal to the base metal and suppressing the propagation of stress corrosion cracking from the base metal to the base metal. In this case, it is only necessary to secure a certain thickness or more,
The present invention is fundamentally different from the conventional one in that there is an optimum range for the Ni phase thickness after rolling.

FIG. 3 shows the results of using the test steel 9 of Table 1 satisfying the composition requirements of the present invention, and considering that the thickness of the Ni phase after rolling is 0.15 mm satisfying the above range. The reduction ratio is changed from 1.5 to 4.0 by heating at ℃ (60 + 4)
The hydrogen peeling resistance when the clad steel rolled to t is subjected to the same heat treatment as in FIG. Sample size is (46+
4) t, the hydrogen charging conditions are 400 ° C. and the hydrogen partial pressure is 200 kgf / cm ² .

Although the heating temperature and the composition of components are also related, in general, when the reduction ratio during hot rolling is less than 2.0, the peeled area ratio increases as the reduction ratio decreases, but the reduction ratio is 2.0 or more. No peeling occurred at all.

From the above results, in rolled clad steel,
To obtain hydrogen delamination cracking resistance equivalent to or better than that of conventional build-up welded clad steel, the base material is Cr-Mo steel with a V content of 0.05% or more.
Or, using steel containing 0.10% or more of Nb, either one or two, Ni is used as an intermediate material and the thickness after rolling is 0.
By setting the reduction ratio during hot rolling to 2.0 or more so as to be 05 to 0.30 mm, it is possible to appropriately obtain a rolled clad steel sheet with excellent hydrogen delamination cracking resistance.

Hydrogen peeling cracks at the interface of the clad steel are Cr
-It is caused by the accumulation of hydrogen at the joint interface due to the difference in the solubility and diffusion coefficient of hydrogen between Mo steel and stainless steel.This is caused by (1) Suppression of void formation at the joint interface, which is the hydrogen accumulation site, and (2) ) It is suppressed by suppressing the accumulation of hydrogen at the interface.

As shown in FIG. 1, V, 0.10 or more of 0.05% or more.
% By adding more than Nb, these elements become C,
It bonds with N to form a precipitate, and the interface between the precipitate and the matrix serves as a trap site for hydrogen, suppressing hydrogen accumulation at the clad junction interface.

As shown in FIG. 2, by setting the thickness of the Ni phase after rolling within the optimum state range, it is possible to suppress an increase in the hydrogen accumulation location and the amount of hydrogen accumulated at the interface.

That is, when the thickness of the Ni phase after rolling is 0.05 mm or more, carburization from the base material to the laminated material occurs in the cooling process after rolling and the subsequent heat treatment process, and as a result, Cr, Nb, This prevents Ti carbide from being formed and becoming a hydrogen accumulation site.

By setting the thickness of the Ni phase after rolling to 0.30 mm or less, the solubility of hydrogen in Ni is larger than that of the stainless steel which is the composite material and the Cr-Mo steel which is the base material. It is avoided that hydrogen accumulates during steady-state operation (or hydrogen autoclave experiment corresponding to it), diffuses and accumulates at the interface during cooling, and reduces hydrogen peel crack resistance. In other words, Ni needs to be 0.05 mm or more from the viewpoint of suppressing the diffusion of C from the base material to the laminated material, but if it exceeds 0.30 mm, hydrogen accumulates in the steady state and the amount of hydrogen accumulated on the interface during cooling increases, so it is in the optimum There is a thickness of.

The reduction ratio during hot rolling depends on the temperature and other conditions, but is generally 2.0 or more as shown in FIG. 3 so that unbonded voids do not remain at the bonding interface. To do. That is, since hydrogen accumulates in the unbonded voids that remain when the reduction ratio is insufficient, a hot rolling reduction ratio that does not leave such unbonded voids is adopted.

[0038]

EXAMPLES Specific examples of the present invention will be described below.

Example 1 As shown in Table 2 below, the composition of the components within the scope of the present invention was 2.
30Cr-1.10Mo-0.15V steel was used as a base material, SUS321 was used as a composite material, and Ni was used as an intermediate material.

[0040]

[Table 2]

In heating at 1200 ° C., the reduction ratio was changed,
The thickness of the Ni phase after rolling was changed to 80 mm and 120
rolled to mm.

After performing the same heat treatment as in FIG. 1 described above, a sample of (46 + 4) t × 70 w × 100 l was taken and hydrogen-charged at 450 ° C. under the condition of hydrogen partial pressure of 200 kgf / cm ^{2 to} remove hydrogen. The results of evaluation of crackability are shown in Table 3 below.

[0043]

[Table 3]

Among the conditions A to D rolled to 120 mm, C
The thickness of the Ni phase after rolling, which is the condition of the present invention, is 0.05 mm or more.
Since it did not satisfy 0.30 mm or less, hydrogen peeling cracking occurred. On the other hand, A, B, and D satisfy the conditions of the present invention, so that hydrogen peeling cracks have not occurred. Also, rolled E to 80 mm
Also in G, hydrogen peeling cracks occurred in F and G that did not satisfy the reduction ratio and the Ni phase thickness after rolling, which are the conditions of the present invention, but cracks were not observed in E that satisfied the conditions of the present invention.

1.23Cr-0.70Mo-0.20Nb steel as shown in Table 4 below, which is a steel within the composition range of the present invention, was used as a base material, and SU was used.
S304L was used as a composite material and Ni was used as an intermediate material.

[0046]

[Table 4]

After heating at 1250 ° C., after changing the reduction ratio, after rolling
The thickness of the Ni phase was changed and rolled to 60 mm and 150 mm. After performing the same heat treatment as in FIG. 1, a sample similar to that in Example 1 was sampled, and the hydrogen peel crack resistance was evaluated under the same conditions.

That is, the results of such evaluation are as shown in Table 5 below.

[0049]

[Table 5]

That is, no matter whether the plate thickness is 60 mm or 150 mm, hydrogen peeling cracks do not occur at all in the J, K and N materials having the Ni phase thickness of the conditions of the present invention. On the other hand, the thickness of the Ni phase after rolling does not reach the conditions of the present invention I
In the H and N materials in which the Ni phase and the Ni phase do not exist at all, or in the L material in which the Ni phase is thicker than the conditions of the present invention, hydrogen delamination cracking occurs.

Example 3 The composition of the Cr-Mo steel as the base material was changed as shown in Table 6 below, and SUS347 was used as a composite material and Ni was an intermediate material.
When heated at ℃, the reduction ratio is 4.0 and the Ni phase thickness after rolling is 0.
It was rolled to 50 mm to be 15 mm.

[0052]

[Table 6]

After performing the same heat treatment as in FIG.
Table 6 also shows the results of evaluating the hydrogen peeling cracking resistance under the same conditions as the above samples. 2.25 shown from Q to T
Among Cr-1.05Mo steels, hydrogen peeling cracks have occurred in Q and R which do not satisfy the conditions Nb and V addition amount of the present invention. On the other hand, in S and T satisfying the conditions of the present invention, no cracking is observed. Even in the 1.03Cr-0.45Mo steels indicated by U to W, hydrogen peeling cracks are generated in U containing no Nb and V, whereas cracks are not recognized in V and W satisfying the conditions of the present invention. This steel contains T and B, but as long as the conditions of the present invention for Nb and V are satisfied, the effect can be recognized even if added alone or in combination. 3.45Cr- shown in X-Z
In 2.32 Mo steel, hydrogen peeling cracks did not occur in Y and Z satisfying the Nb and V addition amounts of the present invention, whereas cracks occurred in X which did not satisfy the conditions of the present invention.

[0054]

As described above, according to the present invention, compared with the conventional build-up clad steel, the base material composition of the rolled clad steel and the thickness of the intermediate material after rolling are selected as the optimum state in a specific range. Clad steel with significantly improved hydrogen delamination cracking resistance can be economically obtained by the hot rolling method to provide products suitable for various pressure vessel steels, etc. It is an invention.

[Brief description of drawings]

FIG. 1 is a chart showing changes in the peeled area ratio with the addition amounts of Nb and V.

FIG. 2 is a table showing changes in the peeled area ratio with changes in the Ni phase thickness after rolling.

FIG. 3 shows the Ni phase thickness after rolling for the test steel 9 in Table 1.
Flat steel rolled by changing the reduction ratio from 1.5 to 4.0 so as to be 0.15mm is 400 ℃, hydrogen partial pressure is 200kgf /
It is a chart about the result of having evaluated hydrogen delamination cracking resistance characteristic by charging with hydrogen at cm ² .

Claims (2)

(57) [Claims] 1. C: 0.05 to 0.30 wt%, Si: 0.03 to 1.00 wt%
%, Mn: 0.20 to 1.60 wt%, Cr: 0.80 to 3.50 wt%, Mo: 0.
30 to 1.50 wt%, Al: 0.005 to 0.10 wt%, and
V: 0.05 to 0.40 wt%, Nb: 0.10 to 0.40 wt%, one or two, with the balance being Fe and inevitable impurities of Cr-Mo steel as the base material, and austenitic stainless steel. Is a clad steel sheet that is hot rolled together with Ni as an intermediate material and Ni as an intermediate material, and the thickness of the Ni phase after hot rolling in the clad steel sheet is 0.05 to 0.30 mm.
A rolled clad steel sheet having excellent hydrogen delamination cracking resistance, which is characterized by 2. The composition according to claim 1, containing Ni: 0.01 to 0.50 wt%, Ti: 0.005 to 0.10 wt%, and B:
It contains any one or more of 0.0002 to 0.0050%, and the balance is Cr-Mo steel consisting of Fe and unavoidable impurities as a base material, austenitic stainless steel as a composite material, and Ni as an intermediate material. Is a clad steel sheet that has been hot rolled by superposition as a rolling clad steel sheet, and that the thickness of the Ni phase after hot rolling in the clad steel sheet is 0.05 to 0.30 mm, which is excellent in hydrogen delamination cracking resistance. steel sheet.