JPH0277561A - Nuclear reactor steel plate excellent in electron beam welding characteristic - Google Patents

Abstract

PURPOSE:To prevent the precipitation of coarse carbide and nitride, to form the structure of the title steel plate into a structure composed principally of lower bainite, and to improve toughness in an electron beam weld zone by specifying respective contents of C, Si, Mn, P, S, Cu, Ni, Cr, etc. CONSTITUTION:The title nuclear reactor steel plate has a composition consisting of, by weight, 0.13-0.16% C, 0.05-0.03% Si, 1.3-1.5% Mn, <=0.005% P, <=0.01% S, <=0.1% Cu, 0.7-1% Ni, 0.1-0.6% Cr, 0.5-0.6% Mo, 0.005-0.04% Al, 0.003-0.006% N, and the balance Fe. By using the above steel plate, the precipitates of coarse carbide and nitride can be reduced, and further, the base structure can be changed from upper bainite practically to lower bainite and toughness in an electron beam weld zone can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a nuclear reactor steel plate with excellent electron beam welding properties.

[Prior Art] Interest in the safety of nuclear power generation equipment has been increasing in recent years, and requirements for toughness values for steel plates for nuclear reactors have become extremely strict. Naturally, this requirement is also made for welded parts that constitute part of the structure.

Conventional welding of steel plates for nuclear reactors is mainly performed by submerged arc welding (SAW) or MIG welding. In these welding processes, the number of laminated layers increases at an accelerating rate as the plate thickness increases. For example, with a material with a thickness of about 100 mm, it is difficult to perform construction with a narrow gap.
Both AW and MIG require a stack of 20 or more buses. The construction time associated with this will be enormous. In order to improve welding efficiency and meet strict toughness requirements, the application of electron beam welding has begun to be considered.

Electron beam welding is conventional arc welding (SAW).

Compared to MIC welding), it is advantageous in terms of cost in a range of plate thicknesses exceeding 50 mm, and the thicker the plate thickness, the greater the effect.

However, unlike conventional welding methods, electron beam welding involves melting and joining the steel plates themselves, so when manufacturing steel plates, it is necessary to design the components of the welded part, especially considering the toughness. It is no exaggeration to say that this point has not been considered at all in conventional steel plates for nuclear reactors.

Publicly known documents related to improving the toughness of steel sheets for nuclear reactors include Japanese Patent Publication No. 5B-33449, Japanese Patent Publication No. 59-9
No. 619 is available, but since it is based on the assumption that welding will be performed using a conventional welding method, there is no consideration given to the welded portion by electron beam welding.

[Problems to be Solved by the Invention] The object of the present invention was to provide a nuclear reactor with excellent electron beam welding characteristics, which provides good low-temperature toughness of the welded part even when welding is performed by electron beam welding. Our objective is to provide steel plates for industrial use.

[Means for Solving the Problems] The present invention is based on mm%, C: 0.13% or more and less than 0.16%, S L: 0.05-0.03%, Mn: 1.30-
1.50%, P≦0.005%, S≦0.010%, C
u≦0.10%, Ni≦more than 0.70%, 00% or less, Cr:0. lO~0. (i0%, Mo: 0.50~
0.60%, Aρ: 0.005-0.040%, N.

0.003 to 0.00 [i%, the basic component, the remainder F
This is a nuclear reactor steel sheet with excellent electron beam welding characteristics, characterized by comprising c and unavoidable impurities.

[Operations] Electron beam welding does not supply another material for the weld zone to improve the properties of the weld zone, as in conventional welding methods, but instead melts and welds the steel plates themselves. Therefore,
When manufacturing steel plates, steel plates with high toughness are prepared by methods such as grain refinement, but because they are melted at high temperatures, they end up with low toughness.

As a result of examining various steel materials that have good toughness for electron beam welding, the inventors found that coarse carbides and nitrides precipitated within grains and at grain boundaries significantly reduce the toughness of electron beam welding. This is what I found. The absolute amount of these coarse carbides and nitrides increases when the C content and N content are high1, causing embrittlement of grain interiors and grain boundaries. Also, P is these C,
It was discovered that the effect of H.

It has been found that in order to prevent this, the contents of C, P, and N should be kept within a certain range; in other words, the toughness of the electron beam welded part is significantly improved by the superposition of these effects.

Furthermore, in order to improve the toughness of electron beam welds, we found that it is important to reduce these harmful precipitates and at the same time change the base structure from upper bainite to almost lower bainite.

FIG. 1 is a diagram showing the influence of Pi and Nm on the Charpy impact test value of an electron beam welded part using the C parameter.

Cff1 is 0.13% or more and less than 0.16%, pm is 0.
0.005% or less, and by setting the N amount in the range of 30 to 130 ppm, good toughness of V E ao≧lOkgf-m can be obtained. Furthermore, the influence of individual components is not linear.

For example, C: 0.15%, N: 90p1) III
If P decreases from 0.010 to 0.005%,
vE-30 is 2.5 to 3. When P decreases from 0.010 to 0.005% with N: 60 p1) In, V E-3o significantly improves from 35 to 12.3 kg f-m. , the superposition effect of P and N is obvious. In addition, the superposition effects of C and N, and C and P are also clear from this figure.

Standards specify a narrow range of components for steel sheets for nuclear reactors. Therefore, Mn increases hardenability.

Ni, Cr, Mo based on component standards (JIS 5QV3A
, 5QV3B), it is necessary to change the base structure from upper bainite to almost lower bainite.

The reasons for limiting the ingredients are described below.

C is an element harmful to toughness, and as mentioned earlier, if it exceeds 0.16%, coarse carbides will precipitate due to the superimposed action with P and N, significantly reducing the toughness of electron beam welded parts. Since it becomes difficult to satisfy the specifications of steel plates for nuclear reactors, the upper limit is set at less than 0.1896. However, 0,1
If it is less than 3%, it will be difficult to ensure strength.

Since Si is an element that deteriorates low-temperature toughness and weldability, it should be reduced as much as possible and the upper limit should be 0.30%. However, due to steel manufacturing, 0.
05% is necessary.

Mn is an element that increases hardenability, and must be added in an amount of 1.30% or more to make the structure almost lower bainite, but the upper limit is set to 1.50% based on the standard component range.

As mentioned above, P embrittles the grain interior and grain boundaries due to the superimposed action with C and N, so it is necessary to reduce it to 0.005% or less.

S is an element harmful to toughness and needs to be reduced to 0.01% or less.

Since Cu is an element that promotes neutron irradiation embrittlement, the upper limit is set to 0.1096.

N1 is an element that increases hardenability, and needs to be added in an amount exceeding 0.70% in order to make the structure almost lower bainite, but the upper limit was set at 1.00% based on the standard component range.

Cr is an element that increases hardenability, and it is necessary to add 0.10% or more to make the structure almost lower bainite, or 0.
．． The upper limit was set at 60%.

MO is an element that increases hardenability, and it is necessary to add 0.50% or more to make the structure almost lower bainite, but the upper limit is set to 0.60% from the standard component range.

Al is an element that refines the structure and improves toughness.
It is effective at 0.005% or more. However, if it exceeds 0.040%, the ratio with N becomes too small and the AgN precipitates become coarser, reducing the toughness, so the upper limit is set to 0.0209%.
Set it to 6.

As mentioned above, N embrittles the grain interior and grain boundaries due to its superimposed action with C1P, so it is set to less than 0.00%. However, if it is too low, grain refinement by AgN will not be possible, so the lower limit is set to 0.003%.

In melting this steel, either an electric furnace or a converter may be used. In making a steel plate, either forging or rolling may be used. In addition, the heat treatment of the steel plate includes quenching and tempering.

[Example] Among the chemical components shown in Table 1, 1 to 5 are the steels of the present invention, and 6 to 5 are the inventive steels.
No. 17 is comparative steel.

The steel was melted in a converter, made into slabs by a conventional method, and then rolled into slabs to the thickness shown in Table 1.

The heat treatment conditions for the steel plate are standard: 800℃ air cooling, quenching 288℃
0℃ water cooling, tempering; 670℃ air cooling, stress relief annealing: 825
℃ air cooling.

Table 2 shows the results of the tensile test, Charpy impact test of the base material of these steel plates, and the Charpy impact test of the electron beam welded parts.

However, the electron beam welding conditions are voltage 150kV, current 1
80mA, speed 20cm/win.

The notch position for the Charpy test of the electron beam weld was placed at the center of the weld metal.

Steels 1 to 5 of the present invention have good low-temperature toughness of electron beam welded parts due to the superimposed effect of C1P and Nff1 within appropriate ranges.

The base material properties are also good. Next, m6 has low C and low base material strength.

m7 has a high C content, and the toughness of the base metal and especially the electron beam welded part is low. Steel 8 has a high P content, and the toughness of the electron beam welded part is low. Steel 9 has a high N content and has low toughness in the electron beam welded part.

n410 has a high S+ and low toughness in both the base metal and the electron beam welded part. Steel 11 has low Mn, and steel I2 has S or high <,n
413 has low N1, steel 14 has low cr, steel 15 has M
o is low, and the toughness of the electron beam welded part is low. m
1B has a low AJ, and Steel 17 has a high AJ), and the toughness of the base metal and the electron beam weld are low, respectively.

[Effects of the Invention] As described above, according to the present invention, the components of C1P and N can be limited to appropriate ranges, and Mn, Cr, and Ni.

By limiting the content of Mo to near the upper limit of the specification, coarse carbides and nitrides do not precipitate, and the structure becomes almost lower bainite, making it possible to significantly improve the toughness of electron beam welds, which is a great tool in industry. It is effective.

[Brief explanation of the drawing]

Figures 1a, 1b, and 1c are charts showing the influence of the amount of P and the amount of N on the Charpy impact test value of an electron beam welded part, with C as a parameter. Agent Patent attorney Tatsuo Chanoki (phantom Figure 1 C; θ) 3 people 2 5 no OP amount (X) θ-3 force (b) C=0゜noj, Z βt (xtozu2) (V) C=0. /9X 2 5 no 0 Pi (x/□-ya)

Claims (1)

[Claims] In weight%, C: 0.13% or more and less than 0.16% Si: 0.05-0.03% Mn: 1.30-1.50% P≦0.005% S≦ 0.010% Cu≦0.10% Ni≦more than 0.70% and less than 1.00% Cr: 0.10 to 0.60% Mo: 0.50 to 0.60% Al: 0.005 to 0 .040% N: 0.003 to 0.006% A steel plate for nuclear reactors with excellent electron beam welding characteristics, characterized by comprising the remainder Fe and unavoidable impurities.