JP2668541B2 - Austenitic stainless steel for fusion reactor first wall member with excellent smoothing and flattening characteristics of melt surface during plasma disruption - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an austenitic stainless steel for a first wall member of a fusion reactor, which is excellent in smoothing and flattening characteristics of a molten surface during plasma disruption. It is.

In the present invention, plasma disruption refers to a phenomenon in which plasma is extinguished instantaneously.

[Conventional technology]

Since the first wall of a fusion reactor is used in a harsh environment that is not found in conventional structures, extremely high reliability and soundness are required for its constituent materials. The reason is that the α particles generated by the fusion reaction constantly apply a high heat load to the first wall, but the plasma disruption also applies a transient or local ultrahigh heat load. In particular, the heat load during plasma disruption is tens to hundreds of times the normal heat load, and the accompanying melting / evaporation / solidification behavior of members and the cracking behavior associated with excessive thermal stress, etc. A great deal of attention has been paid from the standpoint of ensuring the soundness of research, and research and analysis have been promoted. The first wall member of a fusion reactor includes the Atomic Energy Society of Japan, Vol. 29, No. 10 (19
87), various materials such as stainless steel such as SUS304 and SUS316, ceramics such as graphite, Mo, W, Ta, Al or silicon carbide as shown in P855 have been studied. From the viewpoint of availability, stainless steel is one of the promising material candidates.

[Problems to be solved by the invention]

However, recent plasma disruption heat load simulation tests using stainless steel indicate that there is a difference in the resolidification surface state after melting between materials even with the same standard steel grade, and depending on the material, the surface Becomes uneven with many craters. In the case of the first wall, this uneven melting / resolidification behavior causes a selective reduction in the thickness of the plate due to repeated plasma disruptions. Make it difficult. This is extremely undesirable from the viewpoint of the reliability of the structure. From the viewpoint of design based on life expectancy, the surface after melting by plasma disruption is desired to be smooth and flat. However, there has been almost no study on the properties of these materials on the melting / solidification behavior under high energy.

The present invention has been made from such a background, and is characterized by using a material that does not concavo-convexly solidify due to surface melting during plasma disruption, and uses it to predict life
An austenitic stainless steel for a first wall member of a fusion reactor that can be designed and has high reliability is provided.

[Means and actions to solve the problem]

That is, the present inventors conducted a plasma disruption heat load simulation test using various SUS304-based and SUS316-based stainless steels, and examined the surface melting behavior.

As a result, the surface condition after melting remarkably changes due to the difference in the trace elements in the steel, but the unevenness of the surface after melting especially due to the increase in the content of unavoidable impurity elements sulfur (S) and oxygen (O). (Unevenization) was found to be significantly promoted. As an example, FIG. 1 (a) shows a schematic diagram of the melting / solidifying surface of a SUS304 type stainless steel containing 0.0195 wt% S after a plasma disruption simulation test. Once these irregularities are formed on the surface after melting, the surface becomes smooth and flat by repeated melting and solidification (ev
en), and it was also confirmed that the irregularities progressed more and more unilaterally.

On the other hand, on the other hand, as a result of systematically examining the effect of the trace amount component, it was found that the surface after melting is less likely to be roughened by containing a trace amount of Al, Ti, REM, and Ca alone or in combination, and In order to stabilize this effect, it has been found that reduction of harmful impurity elements S and O is effective. FIG. 1 (b) is a schematic view of a molten and solidified surface of a SUS304 type stainless steel containing 0.071 wt% of Al and 0.005 wt% of Ca after a simulation test of plasma disruption. It is extremely smooth and flat as compared with that of (a).

That is, the gist of the present invention is as follows: C: 0.15 wt%
Hereinafter, Si: 1.0 wt% or less, Mn: 2.0 wt% or less, Cr: 16.0 to 20.
0 wt%, Ni: 8.0 to 15.0 wt%, Mo: 3.0 wt% or less, Ti: 0.02 to 0.1 wt%, Al: 0.02 to 0.1 wt%, REM: 0.01 to
Melting during plasma disruption characterized by containing one or more of 0.1 wt% and Ca: 0.003 to 0.02 wt%, and S: 0.005 wt% or less, O: 0.007 wt% or less An austenitic stainless steel for a first wall member of a fusion reactor having excellent surface smoothness and flattening characteristics.

 Next, the reasons for limiting the components of the present invention will be described.

The composition of C, Si, Mn, Cr, Ni and Mo almost conformed to the component range of SUS300 series austenitic stainless steel centering on SUS304 and SUS316 from the viewpoint of manufacturability, cost, material properties and the like.

S is one of the unavoidable impurities, and significantly affects the surface melting behavior at the time of plasma disruption. In order to reduce the tendency of the molten surface to be uneven, the content needs to be at least 0.005 wt% or less.

O also has a significant adverse effect on the surface melting behavior during plasma disruption. In order to reduce the tendency of the molten surface to be uneven, the content needs to be at least 0.007 wt% or less.

Ti promotes smoothing by reducing the unevenness tendency of the molten surface during plasma disruption by containing at least 0.02 wt% or more, but if the content exceeds 0.1 wt%, its effect is not recognized, 0.02 wt% or more and 0.1 wt% or less.

Al is used as a deoxidizing agent in the steelmaking reaction, and at the same time, the content of 0.02 wt% or more has the effect of reducing the uneven surface tendency of the molten surface during plasma disruption and promoting smoothing. On the other hand, if the content exceeds 0.1 wt%, the effect is not recognized and the weldability of the steel sheet is also deteriorated, so the range was made 0.02 wt% or more and 0.1 wt% or less.

REM refers to so-called rare earth elements such as La and Ce and their mixtures. A content of 0.01 wt% or more has the effect of smoothing the molten surface during plasma disruption, but a content of more than 0.1 wt% reduces the steel sheet. Manufacturability is reduced, so the upper limit is 0.1w
t%.

Ca is used as a deoxidizing agent and a desulfurizing agent in the steelmaking reaction, but at the same time, if it is contained in an amount of 0.003 wt% or more, it is effective in smoothing the molten surface during plasma disruption. But,
If the content exceeds 0.02 wt%, the productivity of the steel sheet is reduced, so the upper limit is made 0.02 wt%.

The balance is inevitable impurities other than Fe, S, and O, and P and N may be 0.04 wt% and 0.08 wt% or less, respectively.

〔Example〕

 The present invention will be described in detail below with reference to examples.

Various stainless steels were prepared based on SUS304 and SUS316 with different trace elements. These were melted in vacuum and then hot-rolled into a steel plate having a thickness of 5 mm. Table 1 shows these chemical compositions and the chemical compositions of commercially available SUS304 and 316 which were also subjected to the experiment. In the table, Nos. 1 to 14 are steels of the present invention, and Nos. 15 to 26 are comparative steels.

A test piece of 4 mm t × 50 mm × 20 mm was cut out from these steel sheets, and the surface was polished with # 400 to prepare a test piece. In the experiment, a plasma disruption simulation test was performed using a hydrogen ion beam with a beam energy of 120 KeV. The beam irradiation time was 20-250 ms, during which the heat flux was 80 MW / m ² . Observe the molten surface properties of the test specimen after irradiation, and
It was classified into three stages: even, partially uneven, and uneven. As already mentioned, the surface after irradiation is completely smooth and flat (even)
Is desirable as a material. The results of the experiment are shown in Table 1 together with the chemical components. From this, S: 0.005wt% or O: 0.007wt
%, The surface quality after plasma irradiation is from even to un
The transition to even is clear. In addition, there are cases in which only a slight amount of these impurity elements is suppressed, for example, as shown in No. 21, there is a case where it becomes partially uneven.Therefore, addition of Ti, Al, REM, and Ca to stabilize even conversion of the surface. The effect is clear. On the other hand, excess Al, as seen in Nos. 24 and 25,
The inclusion of Ti is rather harmful to the surface properties after melting and solidification. Therefore, the amount of S, O is kept low and Ti, Al, REM, Ca
It has been clarified that the appropriate content of one or more of the above is effective for smoothing and flattening the melted / solidified surface during plasma disruption.

〔The invention's effect〕

In the stainless steel used for the first wall member of the fusion reactor, the amount of S, O is kept low, and by containing an appropriate amount of one or more of Ti, Al, REM, and Ca, plasma disruption Abnormality of the melting / solidification behavior at the time (surface unevenness) can be suppressed. Also, in a fusion reactor using this, material damage due to plasma disruption of the first wall can be predicted by design, and reliability of the structure,
Increases soundness.

[Brief description of the drawings]

FIG. 1 (a) is a schematic view of a molten / solidified surface of a SUS304 type stainless steel (18.9Cr-9.0Ni, No. 15 in Table 1) containing 0.0195 wt% of S after a plasma disruption simulation test. Fig. 1 (b) shows S: 0.0010wt%, Al: 0.071wt% and C
a: SUS304 type stainless steel containing 0.005wt% (18.
FIG. 4 is a schematic diagram of a melting / solidifying surface of 4Cr-8.5Ni, No. 4 in Table 1) after a simulated plasma disruption test.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideo Sakurai 5-10-1 Fuchinobe, Sagamihara-shi, Kanagawa 2nd Technical Research Laboratory, Nippon Steel Corp. (72) Hiroshi Inoue 5-10 Fuchinobe, Sagamihara-shi, Kanagawa ―1 Inside Nippon Steel Co., Ltd. 2nd Technical Research Laboratory (72) Inventor Haruki 1-16-3 Kohinata, Bunkyo-ku, Tokyo (56) Reference JP-A-59-182956 (JP, A) JP-A- 59-110767 (JP, A) JP-A-57-85956 (JP, A) Actually developed 54-112719 (JP, U)

Claims (1)

(57) [Claims] [Claim 1] C: 0.15 wt% or less, Si: 1.0 wt% or less, Mn: 2.0 wt% or less, Cr: 16.0 to 20.0 wt%, Ni: 8.0 to 15.0 wt%, Mo: 3.0 wt% or less , Further contains one or more of Ti: 0.02 to 0.1 wt%, Al: 0.02 to 0.1 wt%, REM: 0.01 to 0.1 wt%, Ca: 0.003 to 0.02 wt%, and S: 0.005 wt% Below, O: 0.007 wt% or less is an austenitic stainless steel for the first wall member of a fusion reactor, which has excellent smoothing and flattening characteristics of the molten surface during plasma disruption.