JP2889022B2 - Steel for pressure vessels with excellent electron beam welding properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure vessel steel having excellent electron beam welding characteristics.

[0002]

2. Description of the Related Art Sufficient consideration is given to the safety of boiler / pressure vessel equipment, especially to safety during a hydraulic test, and steel for pressure vessels is required to have a certain toughness. The request is of course also made for the welds forming part of the structure. Conventional welding of pressure vessel steel is latent welding (SAW)
Is the subject. In these weldings, the number of layers increases at an accelerating rate as the plate thickness increases. For example, plate thickness 1
With a material of 00 mm, lamination of 20 passes or more is required in SAW welding even if a narrow groove is formed. The resulting construction time is enormous. The application of electron beam welding has come to be considered in order to improve the welding work efficiency and meet the toughness requirements. Compared to conventional arc welding (SAW welding), electron beam welding is a cost-effective area in a range exceeding a plate thickness of 50 mm, and its effect increases as the plate thickness increases. However, unlike conventional welding methods, electron beam welding melts and joins the steel sheets themselves, and therefore, in the manufacture of steel sheets, it is necessary to design components in consideration of the welds, especially the toughness.
Until now, as known literatures on steel for pressure vessels, there are JP-A-2-77557, JP-A-2-77561, JP-A-2-77562 and JP-A-2-277743, but furthermore, electron beam welding. There is a demand for pressure vessel steel having excellent toughness.

[0003]

SUMMARY OF THE INVENTION In view of the above, the object of the present invention is to provide a pressure vessel having a good low-temperature toughness of a weld portion and excellent electron beam welding characteristics even when welding is performed by electron beam welding. It is to provide steel for use.

[0004]

SUMMARY OF THE INVENTION The present invention provides, in weight percent, C:
0.13% or more and less than 0.16%, Si: 0.05-0.
30%, Mn: 0.6% or more and less than 1.15%, P: 0.
005% or less, S: 0.010% or less, Al: 0.00
5% to 0.040%, N: 0.004% to 0.008%, balance Fe and unavoidable impurities, characterized by excellent pressure vessel steel with excellent electron beam welding characteristics, and weight%.
And C: 0.13% or more and less than 0.16%, Si: 0.0
5 to 0.30%, Mn: 0.6% or more and less than 1.15%,
P: 0.005% or less, S: 0.010% or less, Al:
0.005 to 0.040%, N: 0.004 to 0.00
8% as a basic component, Cu ≦ 2.0%, Ni ≦
4.0%, Cr ≦ 1.0%, Mo ≦ 1.0%, Nb ≦
Excellent in electron beam welding characteristics, characterized by containing one or more of the strength improving element group consisting of 0.1% and V ≦ 0.1%, the balance being Fe and unavoidable impurities. Pressure vessel steel.

[0005]

In the electron beam welding, instead of supplying a different material to the welded portion and improving the characteristics of the welded portion as in the conventional welding method, the steel plate itself is melted and welded. For this reason, when manufacturing a steel sheet, a steel sheet having high toughness is adjusted by a method such as grain refinement. However, the steel sheet is melted at a high temperature, resulting in low toughness. JP-A-2-77
557, JP-A-2-77561, JP-A-2-775
No. 62 and Japanese Patent Application Laid-Open No. 2-277743 disclose that coarse carbides and nitrides precipitated in grains and at grain boundaries in an electron beam weld reduce the toughness of the electron beam weld. is there. The present inventors have conducted various studies to develop a steel material having even better toughness in an electron beam welded part. Microcracks occur along with solidification segregation. This greatly reduces toughness. In other words, it has been found that it is important to eliminate microcracks in order to improve the toughness of the electron beam welded part, and that it is necessary to reduce solidification segregation. To reduce this solidification segregation, P,
It has been found that the contents of Mn and N are kept within a certain range, that is, the toughness of an electron beam weld is remarkably improved due to the superposition of these effects.

As shown in FIGS. 1A to 1C, M
n amount is 0.60% or more and less than 1.15%, P amount is 0.00
5%, good toughness of vE_ ₂₀ ≧ 10kgf · m is obtained by putting N amount in the range of 40 or more 80ppm or less. The reasons for limiting the components are described below. C is an element harmful to toughness, and as described above, if it is 0.16% or more, the base material toughness is reduced, so that C is set to less than 0.16%. However, if it is less than 0.13%, it is difficult to secure strength. Since Si is an element that lowers low-temperature toughness and weldability, it is reduced as much as possible and the upper limit is 0.30%. However, 0.05% is necessary for steelmaking. Since Mn causes microcracks due to solidification segregation due to the superposition of P, the content of Mn is set to less than 1.15%. However, if it is less than 0.6%, it is difficult to secure the strength.
Was set as the lower limit. As described above, P generates microcracks due to solidification segregation due to the superposition of Mn, and therefore it is necessary to reduce P to 0.005% or less. S is an element harmful to toughness, and is limited to 0.010% or less. Al is required to be 0.005% or more for deoxidation. However, if it exceeds 0.040%, the ratio with N becomes too small, so that AlN precipitates become coarse and the toughness is rather lowered. And As described above, N makes the inside and the grain boundaries embrittle by the superposition of Mn and P, so that N is made 0.008% or less. However, if it is too low, it will not be possible to refine the grains with AlN, so the lower limit is set to 0.0.
04%. Cu, Ni, Cr, Mo, Nb and V have a uniform effect of increasing the strength of steel,
One or more of these may be contained as necessary, but Cu: 2.0%, Ni: 4.0%, Cr: 1.0%,
Mo: 1.0%, Nb: 0.1%, and V: 0.1% exceeding the upper limit of the content do not become economical because the effect of the action is saturated or the cost is increased. The content of each component of the above-mentioned strength improving element group was determined as described above. In melting this steel, either an electric furnace or a converter may be used. In making steel sheet, forging,
Any of rolling may be used. In the heat treatment of the steel sheet, it is also possible to use normalizing, normalizing-tempering, or accelerated cooling in the case of a thick material.

[0007]

EXAMPLES Of the chemical components shown in Table 1, 1 to 5 are steels of the present invention, and 6 to 14 are comparative steels. The smelting of the steel was carried out by a converter, made into a slab by a conventional method, and then rolled to a plate thickness shown in Table 1. The heat treatment conditions for the steel sheet are quenching: 910 ° C., water cooling, and tempering: 650 ° C. Table 1 shows a tensile test, a Charpy impact test, and a Charpy impact test of an electron beam weld of the base metals of these steels. However, the electron beam welding conditions were as follows: voltage 150 kV, current 180 mA, speed 20 cm /
min. The notch position in the Charpy test of the electron beam weld is at the center of the weld metal.

[0008]

[Table 1A]

[0009]

[Table 1B]

The steels 1 to 5 of the present invention have good low-temperature toughness of the electron beam weld due to the superposition effect of Mn, P and N in an appropriate range. The base material toughness is also good. Next, steel 6 has a high C, base metal and
Particularly, the toughness of the electron beam weld is low. Steel 7 has low C and low base metal strength. Steels 8 and 9 have high P, steel 10 has high N, and the toughness of the electron beam weld is low. Steel 11 has high Si, and has low toughness in both the base material and the electron beam weld. Steel 12 has low Mn, steel 13 has high S, steel 14 has high Al,
The toughness of each electron beam weld is low.

[0011]

As described above, according to the present invention, M
By limiting the components to appropriate ranges for n, P and N,
It is intended to reduce the solidification segregation of the welded portion, economically provide a steel for a pressure vessel having a high toughness of an electron beam welded portion, and has a great industrial effect.

[Brief description of the drawings]

FIG. 1 is a diagram showing the influence of the amount of Mn, the amount of P and the amount of N on the Charpy impact test value of an electron beam weld.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-15321 (JP, A) JP-A-5-39538 (JP, A) JP-A-5-39539 (JP, A) JP-A-5-39539 39540 (JP, A) JP-A-5-39541 (JP, A) JP-A-5-39542 (JP, A) JP-A 5-39543 (JP, A) Patent 2688067 (JP, B2) Patent 2803839 (JP) , B2) JP 5-83625 (JP, B2) JP 5-83626 (JP, B2) JP 5-88297 (JP, B2) JP 5-34415 (JP, B2) JP, B 5-34416 (JP, B2) JP 6-25392 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) C22C 38/00-38/60

Claims (2)

(57) [Claims] C: 0.13% to less than 0.16% Si: 0.05 to 0.30% Mn: 0.6% to less than 1.15% P: 0.005% or less S: 0.010% or less Al: 0.005 to 0.040% N: 0.004 to 0.008% A pressure vessel excellent in electron beam welding characteristics, comprising a balance of Fe and inevitable impurities. For steel. 2. In% by weight, C: 0.13% or more and less than 0.16% Si: 0.05-0.30% Mn: 0.6% or more and less than 1.15% P: 0.005% or less S: 0.010% or less Al: 0.005 to 0.040% N: 0.004 to 0.008% as a basic component, and further, Cu ≦ 2.0% Ni ≦ 4.0% Cr ≦ 1. 0% Mo ≦ 1.0% Nb ≦ 0.1% V ≦ 0.1% It contains one or more of the strength improving elements, and the balance consists of Fe and unavoidable impurities. Excellent pressure vessel steel with excellent electron beam welding characteristics.