JP3457768B2 - Joining method of martensitic stainless steel pipe - Google Patents
Joining method of martensitic stainless steel pipeInfo
- Publication number
- JP3457768B2 JP3457768B2 JP12099695A JP12099695A JP3457768B2 JP 3457768 B2 JP3457768 B2 JP 3457768B2 JP 12099695 A JP12099695 A JP 12099695A JP 12099695 A JP12099695 A JP 12099695A JP 3457768 B2 JP3457768 B2 JP 3457768B2
- Authority
- JP
- Japan
- Prior art keywords
- stainless steel
- martensitic stainless
- melting point
- joining
- joined
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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- Pressure Welding/Diffusion-Bonding (AREA)
- Heat Treatment Of Articles (AREA)
Description
【発明の詳細な説明】
【０００１】
【産業上の利用分野】本発明は化学プラントなどの配管
に用いるに適した高能率なマルテンサイト系ステンレス
鋼管の接合方法に関する。
【０００２】
【従来の技術】ＳＵＳ４１０などのマルテンサイト系ス
テンレス鋼管は耐食性、耐熱性に優れ、オーステナイト
系ステンレス鋼と比較すると安価なことから、硫酸プラ
ントなどの各種化学プラント装置の配管材として多く用
いられている。従って化学プラント装置の製造に当たっ
ては、工場での製造工程並びに現地での組立工程におい
て、マルテンサイト系ステンレス鋼管同士の接合作業は
多数必要となる。従来この接合は溶接により行われてき
た。しかしながらマルテンサイト系ステンレス鋼は自硬
性がある材料であることから、溶接後の冷却過程におい
て溶着金属並びに溶接熱影響部は硬化し、これに伴い靱
性は低下する。靱性が低下したまま使用すると、運転時
の起動停止に伴って繰り返し発生する熱応力によって割
れが発生するなどの問題があるため、従来では溶接後に
おいて熱処理を実施し、溶接部の硬さを低下させ靱性の
向上を図ってきた。また厚肉管になると溶接により残留
応力が発生するため、この残留応力を除去するためにも
溶接後の熱処理は必要であった。
【０００３】従って従来のマルテンサイト系ステンレス
鋼の接合方法である溶接では熱処理の工程が別途必要に
なることから、化学プラント装置の製造において熱処理
の分だけ製造期間が長くなり、また製造費用も余分に必
要であった。特に現地工事では機器全体を熱処理できな
いことから各溶接部位ごとに熱処理する必要があり、工
場で熱処理するよりもはるかに多大な期間並びに費用が
必要であった。
【０００４】
【発明が解決しようとする課題】本発明は以上の事情に
鑑みてなされたものであり、短時間かつ低費用で従来技
術の溶接と同程度の品質の高能率なマルテンサイト系ス
テンレス鋼管の接合方法を提供しようとするものであ
る。
【０００５】
【課題を解決するための手段】本発明者はインサート材
に融点降下元素を含む低融点のシート材を用いる液相拡
散接合法を適用することによって、残留応力の発生を防
止し、また接合後の冷却過程において適正な条件で冷却
することによって、接合部の硬化がなく、靱性低下が防
止できることを見出だし、本発明を完成するに至った。
【０００６】すなわち、本発明は接合面間にインサート
材として被接合材のマルテンサイト系ステンレス鋼管よ
り低融点のシート材を挿入し、そのシート材の融点以上
でかつ被接合材の融点以下の温度域に加熱した後、加圧
することによって液相拡散接合した後、常温までの冷却
過程において被接合材のＡｃｌ点＋２０℃からＡｃｌ点
＋１５０℃までの温度において、被接合材の厚さ１ｃｍ
あたり２０分以上保持した後、３０℃／ｈ以下の冷却速
度で冷却することを特徴とするマルテンサイト系ステン
レス鋼管の接合方法である。
【０００７】なお、本発明でいうシート材とは鉄−クロ
ム合金、鉄−ニッケル−クロム合金またはニッケル−ク
ロム合金を母材とし、融点を降下させる元素としてボロ
ン、シリコン、リン等を１０重量％以下添加した合金で
あり、その厚さが２０〜１００μｍのものを云う。
【０００８】
【作用】以下、図１を用いてこの発明を説明する。図１
（ａ）〜（ｄ）はこの発明の接合方法を示す説明図であ
る。図１において、１及び２は被接合材であるマルテン
サイト系ステンレス鋼管であり、３はインサート材であ
る。
【０００９】（１）インサート材３を接合面間に挿入し
た後、接合するマルテンサイト系ステンレス鋼管１，２
を突き合わせる。（図１（ａ））
【００１０】（２）高周波加熱装置などを用いて接合部
を加熱し、同時に加圧して被接合材１，２を押しつけ液
相拡散接合する（図１（ｂ））。この場合、時間の経過
に伴い、ボロンなどの融点降下元素が液相−固相拡散に
よって被接合材１，２に拡散して行くことに伴い、溶融
部の融点が上昇して行く。所定の時間経過後融点降下元
素であるボロンなどが十分に拡散すると凝固が完了し、
接合が終了する。ここで、加熱温度がインサート材３の
融点より低い場合にはインサート材３の溶融が起こら
ず、また被接合材１、２の融点よりは高い場合には溶接
と同様の溶融接合となるため、残留応力などの観点から
は望ましくないため、インサート材３の融点以上で被接
合材１、２の融点以下の温度で加熱する必要がある。こ
の温度に加熱した場合の溶融部の厚さは数百ミクロン程
度であるから、凝固収縮はほとんどなく、従って残留応
力の発生もほとんどない。
【００１１】（３）被接合管１、２を液相拡散接合した
後、冷却過程において被接合管のＡｃｌ点＋２０℃から
Ａｃｌ点＋１５０℃までの温度において、被接合材の厚
さ１ｃｍあたり２０分以上保持（図１（ｃ））した後、
３０℃／ｈ以下の冷却速度で５００℃程度まで冷却し、
その後は放冷する（図１（ｄ））熱処理を施す。この冷
却過程をとることによって、液相拡散接合終了後、保持
に至るまでの冷却過程で硬化した組織は焼き戻され、靱
性は向上する。この保持温度がＡｃｌ点＋１５０℃以上
の場合、接合部の結晶粒が粗大化し、強度、靱性が低下
するので望ましくない。またＡｃｌ点＋２０℃以下の場
合、焼き戻し効果が不十分であり、靱性が向上しない。
保持時間が被接合材の厚さ１ｃｍあたり２０分以下の場
合では焼き戻し効果が不十分であり、靱性が向上しな
い。また、保持後の冷却速度が３０℃／ｈ以上の場合、
再び硬化し靱性が低下するので望ましくない。なお５０
０℃以下においては冷却過程での特性変化はないため、
作業効率向上のため加熱装置を取り外し、放冷すること
が望ましい。
【００１２】
【実施例】以下、本発明の実施例について説明する。直
径３００ｍｍ、板厚２５ｍｍの鋼管で化学組成は重量％
でＣ：０．０９％、Ｓｉ：０．３％、Ｍｎ：０．５％、
Ｐ：０．００８％、Ｓ：０．００７％、Ｃｒ：１２．３
％、残りＦｅのもの（Ａｃｌ点：８１０℃、融点：１５
１０℃）を突き合わせ、その接合面間に厚さ３０μｍの
シート材で化学組成は重量％でＢ：３％、Ｃｒ：１０．
１％、残りＦｅのもの（融点１２００℃）を挿入し、Ａ
ｒ中において、高周波加熱によって１３００℃に加熱
し、被接合材の熱膨張を利用して面圧：５Ｋｇｆ／ｍｍ
2 となるように被接合材を押しつけ液相拡散接合し、そ
の後引き続きこの高周波加熱装置を用いて表１に示す条
件で熱処理した継手を作製した。ここで冷却速度は５０
０℃までの値であり５００℃以下では放冷とした。
【００１３】また、従来技術の例として同じ鋼管をＪＩ
Ｓ Ｄ４１０の溶接材（重量％で、Ｃ：０．０８、Ｓ
ｉ：０．３７、Ｍｎ：０．２９、Ｐ：０．０２、Ｓ：
０．００３、Ｃｒ：１２．８７）を用いて、被覆アーク
溶接を行った後、熱処理を行わなかったもの、及びこの
鋼管の標準的な熱処理温度である７５０℃で１時間の熱
処理を行ったものの継手を作製した。継手の性能はシャ
ルピー衝撃試験及び引張り試験により評価した。シャル
ピー衝撃試験は接合面に平行に接合部にノッチを入れた
試験片を３本作製し、０℃にて試験を行い、３本の平均
値を求めた。引張り試験は接合面に垂直に平行部の直径
７ｍｍ、ゲージ長さ３０ｍｍの試験片を３本採取し、室
温にて試験を行い、引張り強度及び伸びについて３本の
平均値を求めた。また、各々の接合作業並びに熱処理作
業に要した時間を測定した。これらの評価結果を表１に
示す。
【００１４】
【表１】
【００１５】Ｎｏ．１〜４は本発明の例であるが、Ｎ
ｏ．１１の従来例の溶接及び熱処理を施したものと同様
の継手性能を有することが分かる。また作業時間は従来
例Ｎｏ．１１の約１／２と短時間であった。Ｎｏ．５も
本発明の例であるが、冷却速度が１０℃／ｈと遅いた
め、Ｎｏ．１〜４と較べると作業時間は長くなった。し
かしながら、従来例Ｎｏ．１１と較べると短い。
【００１６】Ｎｏ．６は比較例であり、保持温度が本発
明の範囲以下のものである。この場合熱処理による焼き
戻し効果が不十分なため、本発明例と較べると衝撃値は
低く伸びも小さい。Ｎｏ．７も比較例であり、保持温度
が本発明の範囲以上のものである。この場合結晶粒の粗
大化が起きるため、衝撃値並びに強度が本発明例と較べ
ると小さい。Ｎｏ．８も比較例であり、保持時間が本発
明の範囲以下のものである。この場合熱処理による焼き
戻し効果が不十分なため、本発明例と較べると衝撃値は
低く、伸びも小さい。Ｎｏ．９も比較例であり、冷却速
度が本発明の範囲より速いものである。この場合作業時
間は最も短いが、冷却速度が速く冷却過程で再び硬化す
るため、本発明例と較べると衝撃値は低く伸びも小さ
い。
【００１７】Ｎｏ．１０は従来技術に係わる比較例であ
り、溶接後、熱処理を行わなかったものである。この場
合作業時間は本発明例と同等であるが、焼き戻しがまっ
たく行われていないため、すべての実施例の中で衝撃
値、伸びは最も小さく、強度は最も高かった。Ｎｏ．１
１は従来技術の例であり、溶接後、熱処理を行ったもの
である。この場合、継手性能は本発明例と同様であった
が、作業時間は本発明例の約２倍程度必要であった。
【００１８】なお、表１に示した作業時間は直径３００
ｍｍ、板厚２５ｍｍの鋼管を接合した場合の作業時間で
ある。被接合管の径、板厚が大きくなると溶接の作業時
間はそれに応じて多くなるが、液相拡散接合では作業時
間は被接合管のサイズによらないため、本発明による接
合作業の高効率化はより顕著なものとなる。
【００１９】
【発明の効果】以上詳述したごとく、本発明方法によれ
ば化学プラント装置などの配管に用いられるマルテンサ
イト系ステンレス鋼の高効率な接合方法が提供でき、工
場製造時、及び現地組立時において工期の大幅な短縮が
図れる。また化学プラント装置などの現地補修作業の高
効率化が可能なことから、定期点検期間の短縮化が図れ
プラント運転効率の向上が可能となる。Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining highly efficient martensitic stainless steel pipes suitable for use in piping of chemical plants and the like. 2. Description of the Related Art Martensitic stainless steel pipes such as SUS410 have excellent corrosion resistance and heat resistance, and are inexpensive compared to austenitic stainless steels. Have been. Therefore, in the production of chemical plant equipment, a large number of joining operations between martensitic stainless steel pipes are required in the production process at the factory and the assembly process at the site. Conventionally, this joining has been performed by welding. However, since martensitic stainless steel is a material having self-hardening properties, the deposited metal and the heat affected zone are hardened during the cooling process after welding, and the toughness is reduced accordingly. If used with reduced toughness, cracks may occur due to thermal stress that is repeatedly generated due to startup and shutdown during operation.Therefore, heat treatment is conventionally performed after welding to reduce the hardness of the welded part. To improve toughness. In addition, since a residual stress is generated by welding in a thick-walled pipe, heat treatment after welding is necessary to remove the residual stress. [0003] Therefore, in the conventional welding method of joining martensitic stainless steel, a heat treatment step is required separately, so that the production time is increased by the heat treatment in the production of chemical plant equipment, and the production cost is extra. Was needed. In particular, in the field construction, since the entire equipment cannot be heat-treated, it is necessary to heat-treat each welding part, which requires much more time and cost than heat treatment in a factory. SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is a short-time, low-cost, high-efficiency martensitic stainless steel having a quality comparable to that of conventional welding. An object of the present invention is to provide a method for joining steel pipes. SUMMARY OF THE INVENTION The present inventor has applied a liquid phase diffusion bonding method using a low melting point sheet material containing a melting point lowering element to an insert material, thereby preventing the occurrence of residual stress, In addition, it has been found that by cooling under appropriate conditions in a cooling process after joining, there is no hardening of a joined portion and a decrease in toughness can be prevented, and the present invention has been completed. That is, according to the present invention, a sheet material having a lower melting point than a martensitic stainless steel pipe as a material to be joined is inserted as an insert material between joining surfaces, and a temperature not lower than the melting point of the sheet material and less than the melting point of the material to be joined is used. After heating to the temperature range and performing liquid phase diffusion bonding by applying pressure, the thickness of the material to be joined is 1 cm at a temperature from the Acl point + 20 ° C. to the Acl point + 150 ° C. of the material to be joined in the cooling process to room temperature.
Per minute, and then cooling at a cooling rate of 30 ° C./h or less. In the present invention, the sheet material is made of an iron-chromium alloy, an iron-nickel-chromium alloy or a nickel-chromium alloy as a base material, and contains 10% by weight of boron, silicon, phosphorus or the like as an element for lowering the melting point. The alloy added below has a thickness of 20 to 100 μm. The present invention will be described below with reference to FIG. FIG.
(A)-(d) is explanatory drawing which shows the joining method of this invention. In FIG. 1, reference numerals 1 and 2 denote martensitic stainless steel pipes to be joined, and reference numeral 3 denotes an insert material. (1) After inserting the insert material 3 between the joining surfaces, the martensitic stainless steel tubes 1 and 2 to be joined are joined.
To match. (FIG. 1 (a)) (2) The joint is heated using a high-frequency heating device or the like, and is simultaneously pressed to press the materials 1 and 2 to perform liquid phase diffusion bonding (FIG. 1 (b)). . In this case, as the melting point lowering element such as boron diffuses into the materials 1 and 2 by liquid-solid diffusion over time, the melting point of the molten portion increases. After a predetermined time elapses, solidification is completed when the melting point lowering element such as boron is sufficiently diffused,
Joining ends. Here, when the heating temperature is lower than the melting point of the insert material 3, melting of the insert material 3 does not occur. When the heating temperature is higher than the melting points of the materials 1 and 2, the same fusion bonding as welding is performed. Since it is not desirable from the viewpoint of residual stress and the like, it is necessary to heat at a temperature higher than the melting point of the insert material 3 and lower than the melting point of the workpieces 1 and 2. When heated to this temperature, the thickness of the melted portion is on the order of several hundred microns, so that there is almost no solidification shrinkage, and therefore, there is almost no generation of residual stress. (3) After joining the pipes 1 and 2 by liquid phase diffusion, in the cooling process, at a temperature between the Acl point + 20 ° C. and the Acl point + 150 ° C. of the pipes to be welded, the pipes 1 and 2 have a thickness of 20 cm / cm. After holding for more than a minute (Fig. 1 (c)),
Cool to about 500 ° C at a cooling rate of 30 ° C / h or less,
After that, a heat treatment for cooling (FIG. 1D) is performed. By taking this cooling process, after the liquid phase diffusion bonding is completed, the structure hardened in the cooling process up to the holding is tempered and the toughness is improved. If the holding temperature is equal to or higher than the Acl point + 150 ° C., it is not desirable because the crystal grains at the joint become coarse and the strength and toughness are reduced. If the Acl point is lower than + 20 ° C., the tempering effect is insufficient, and the toughness is not improved.
When the holding time is 20 minutes or less per 1 cm of the thickness of the material to be joined, the tempering effect is insufficient, and the toughness is not improved. When the cooling rate after holding is 30 ° C./h or more,
It is not desirable because it hardens again and the toughness decreases. 50
Below 0 ° C there is no characteristic change during the cooling process,
It is desirable to remove the heating device and allow it to cool to improve work efficiency. Embodiments of the present invention will be described below. Steel composition with a diameter of 300mm and a thickness of 25mm.
And C: 0.09%, Si: 0.3%, Mn: 0.5%,
P: 0.008%, S: 0.007%, Cr: 12.3
%, With the remaining Fe (Acl point: 810 ° C., melting point: 15
10 ° C.), and a sheet material having a thickness of 30 μm between the joining surfaces and having a chemical composition of B: 3% by weight and Cr: 10.
1%, with the remaining Fe (melting point 1200 ° C.)
In r, the material is heated to 1300 ° C. by high-frequency heating, and the surface pressure is 5 kgf / mm using the thermal expansion of the material to be joined.
The material to be joined was pressed to form a liquid-phase diffusion bond so as to obtain a joint material 2, and then a joint was heat-treated under the conditions shown in Table 1 using this high-frequency heating apparatus. Here, the cooling rate is 50
It was a value up to 0 ° C, and was allowed to cool below 500 ° C. Further, as an example of the prior art, the same steel pipe is used in JI.
Welding material of SD410 (% by weight, C: 0.08, S
i: 0.37, Mn: 0.29, P: 0.02, S:
(0.003, Cr: 12.87), and after performing covered arc welding, heat treatment was not performed, and heat treatment was performed at 750 ° C., which is the standard heat treatment temperature of this steel pipe, for 1 hour. The joint of the thing was produced. The performance of the joint was evaluated by a Charpy impact test and a tensile test. In the Charpy impact test, three test pieces having a notch in the joint parallel to the joint surface were prepared and tested at 0 ° C., and an average value of the three pieces was obtained. In the tensile test, three test pieces having a diameter of a parallel part of 7 mm and a gauge length of 30 mm were sampled perpendicularly to the joint surface, tested at room temperature, and the average value of the tensile strength and elongation was determined. The time required for each joining operation and heat treatment operation was measured. Table 1 shows the results of these evaluations. [Table 1] No. 1-4 are examples of the present invention,
o. It can be seen that the joint performance is the same as that of the eleventh conventional example subjected to welding and heat treatment. The working time is the same as that of the conventional example No. This was a short time of about １ ／ of 11 in this example. No. No. 5 is also an example of the present invention, but the cooling rate is as slow as 10 ° C./h. The working time was longer compared to 1-4. However, the conventional example No. Short compared to 11. No. Reference numeral 6 is a comparative example, in which the holding temperature is lower than the range of the present invention. In this case, since the tempering effect by the heat treatment is insufficient, the impact value is low and the elongation is small as compared with the examples of the present invention. No. 7 is also a comparative example, and the holding temperature is higher than the range of the present invention. Since the coarsening of this crystal grains occurs, shock撃値and strength is small Compared with the present invention embodiment. No. 8 is also a comparative example, and the holding time is below the range of the present invention. In this case, since the tempering effect by the heat treatment is insufficient, the impact value is low and the elongation is small as compared with the examples of the present invention. No. 9 is also a comparative example, in which the cooling rate is faster than the range of the present invention. In this case, the working time is the shortest, but the cooling rate is high and the material is hardened again in the cooling process. No. Reference numeral 10 is a comparative example according to the prior art, in which no heat treatment was performed after welding. In this case, the working time was the same as that of the example of the present invention, but since no tempering was performed, the impact value and elongation were the smallest and the strength was the highest among all the examples. No. 1
Reference numeral 1 denotes an example of the prior art, in which heat treatment was performed after welding. In this case, the joint performance was the same as that of the present invention, but the working time was about twice as long as that of the present invention. The working time shown in Table 1 is 300 mm in diameter.
mm, a work time when a steel pipe having a thickness of 25 mm is joined. When the diameter and plate thickness of the pipes to be welded increase, the work time for welding increases accordingly.However, in liquid phase diffusion welding, the work time does not depend on the size of the pipes to be welded. Will be more pronounced. As described in detail above, according to the method of the present invention, it is possible to provide a highly efficient joining method of martensitic stainless steel used for piping of a chemical plant, etc. The time required for construction can be significantly reduced during assembly. In addition, since it is possible to improve the efficiency of on-site repair work for chemical plant equipment and the like, it is possible to shorten the period of periodic inspections and improve plant operation efficiency.
【図面の簡単な説明】
【図１】本発明の接合方法を示す説明図。（ａ）はイン
サート材を挿入した状態、（ｂ）は液相拡散接合時の状
態、（ｃ）は熱処理時の状態、（ｄ）は冷却後の状態を
それぞれ示す。BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view showing a joining method of the present invention. (A) shows a state in which an insert material is inserted, (b) shows a state during liquid phase diffusion bonding, (c) shows a state during heat treatment, and (d) shows a state after cooling.
Claims (1)
のマルテンサイト系ステンレス鋼管より低融点のシート
材を挿入し、そのシート材の融点以上でかつ被接合材の
融点以下の温度域に加熱した後、加圧することによって
液相拡散接合した後、常温までの冷却過程において被接
合材のＡｃｌ点＋２０℃からＡｃｌ点＋１５０℃までの
温度において、被接合材の厚さ１ｃｍあたり２０分以上
保持した後、３０℃／ｈ以下の冷却速度で冷却すること
を特徴とするマルテンサイト系ステンレス鋼管の接合方
法。(57) [Claims] [Claim 1] A sheet material having a lower melting point than a martensitic stainless steel pipe as a material to be joined is inserted as an insert material between joining surfaces, and the material to be joined is at or above the melting point of the sheet material. After being heated to a temperature range equal to or lower than the melting point of the material and then subjected to liquid phase diffusion bonding by applying pressure, the material to be bonded is heated at a temperature from the Acl point + 20 ° C. to the Acl point + 150 ° C. of the material to be bonded in the cooling process to room temperature. A method for joining martensitic stainless steel pipes, wherein the pipe is kept at a cooling rate of 30 ° C./h or less after holding for 20 minutes or more per 1 cm thickness.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP12099695A JP3457768B2 (en) | 1995-05-19 | 1995-05-19 | Joining method of martensitic stainless steel pipe |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP12099695A JP3457768B2 (en) | 1995-05-19 | 1995-05-19 | Joining method of martensitic stainless steel pipe |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH08311563A JPH08311563A (en) | 1996-11-26 |
| JP3457768B2 true JP3457768B2 (en) | 2003-10-20 |
Family
ID=14800209
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP12099695A Expired - Fee Related JP3457768B2 (en) | 1995-05-19 | 1995-05-19 | Joining method of martensitic stainless steel pipe |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3457768B2 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3168927B2 (en) * | 1996-11-19 | 2001-05-21 | 住友金属工業株式会社 | Method for manufacturing duplex stainless steel joint |
| JP2007296568A (en) * | 2006-05-01 | 2007-11-15 | Mazda Motor Corp | Friction joining method |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH01111820A (en) * | 1987-10-27 | 1989-04-28 | Mitsubishi Heavy Ind Ltd | Method for adjusting liquid-phase distributed joining composition |
| JP2687840B2 (en) * | 1993-04-30 | 1997-12-08 | 住友金属工業株式会社 | Diffusion bonding method |
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1995
- 1995-05-19 JP JP12099695A patent/JP3457768B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH08311563A (en) | 1996-11-26 |
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