JP2682109B2 - Surface defect removal method for sintered forged parts - Google Patents
Surface defect removal method for sintered forged partsInfo
- Publication number
- JP2682109B2 JP2682109B2 JP4706289A JP4706289A JP2682109B2 JP 2682109 B2 JP2682109 B2 JP 2682109B2 JP 4706289 A JP4706289 A JP 4706289A JP 4706289 A JP4706289 A JP 4706289A JP 2682109 B2 JP2682109 B2 JP 2682109B2
- Authority
- JP
- Japan
- Prior art keywords
- sintered
- sintered forged
- shot
- fatigue strength
- shot peening
- 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
Links
Landscapes
- Powder Metallurgy (AREA)
Description
【発明の詳細な説明】 ［産業上の利用分野］ 本発明は燃焼鍛造部品に加熱とショットピーニングを
交互に施し表面欠陥を除去し疲労強度の優れた燃焼鍛造
部品を得ることのできる表面欠陥除去方法に関する。DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention removes surface defects by alternately performing heating and shot peening on combustion forged parts to obtain surface forged parts with excellent fatigue strength. Regarding the method.
［従来の技術］ 粉末冶金によって得られる焼結体の機械的強さ、寸法
精度が不十分である場合には焼結体に対し熱間で精密鍛
造が行なわれる。この焼結鍛造により理論密度に近い高
強度、高靭性の焼結鍛造部品が得られるが、表層部に線
状欠陥、異常組織、脱炭層などの欠陥が現れる。これら
欠陥を消滅させる方法として、鍛造後再加熱を施す方法
が提案されており、この方法により引張強さおよび疲労
強度の向上が得られている。[Prior Art] When the mechanical strength and dimensional accuracy of a sintered body obtained by powder metallurgy are insufficient, precision forging is performed on the sintered body by hot working. By this sintering forging, a high-strength and high-toughness sintered forged part close to the theoretical density can be obtained, but defects such as linear defects, abnormal structures, and decarburized layers appear in the surface layer portion. As a method of eliminating these defects, a method of performing reheating after forging has been proposed, and this method has improved tensile strength and fatigue strength.
さらに、高強度焼結コネクティングロッドの製造方法
として、焼結体にショットピーニングを施すことにより
表面部の空孔を圧潰し、然る後表面を高周波加熱などに
より急速加熱して表面部を強固な金属結合状態とする方
法が提案され、この方法によって疲労強度の向上の図る
ことができる。Further, as a method for manufacturing a high-strength sintered connecting rod, shot peening is performed on the sintered body to crush the pores in the surface portion, and then the surface is rapidly heated by high-frequency heating or the like to strengthen the surface portion. A method of forming a metal-bonded state has been proposed, and this method can improve fatigue strength.
［発明が解決しようとする課題］ しかしながら、前者の方法においては鍛造後再加熱す
ることにより表層部の線状欠陥、異状組織、脱炭の欠陥
は消滅するが、鍛造時に焼結体表面が鍛造型に接触して
急冷されるため、表層部に残留空孔が存在するようにな
り、その後の最加熱によっても空孔は依然として残留す
るため、充分な引張強さ、疲労強度が得られないという
欠点がある。単純な形状であれば、空孔は存在しにくい
が、特にコンロッドのような複雑な形状では空孔が発生
する。[Problems to be Solved by the Invention] However, in the former method, although linear defects, abnormal structures, and decarburization defects in the surface layer part disappear by reheating after forging, the surface of the sintered body is forged during forging. Since it contacts the mold and is rapidly cooled, residual pores will exist in the surface layer, and the pores will remain even after the subsequent maximum heating, so sufficient tensile strength and fatigue strength cannot be obtained. There are drawbacks. Voids are unlikely to exist if the shape is simple, but vacancies are generated especially in a complicated shape such as a connecting rod.
焼結体に鍛造を施さずにショットピーニングを施し、
表面部の空孔を機械的に圧潰し、その後最加熱を施す後
者の方法では、圧潰した部分を拡散結合させることによ
り、疲労強度は向上できる。しかしながら、問題にする
疲労強度は曲げを支配的とするような使用環境では、確
かにこの効果がみられるが、コンロッドのように引張お
よび圧縮応力が発生するものについては、空孔が存在す
る内部から疲労破壊が発生するため、疲労強度向上には
限界があった。Shot peening without forging the sintered body,
In the latter method of mechanically crushing the pores in the surface portion and then performing the maximum heating, the fatigue strength can be improved by diffusion-bonding the crushed portions. However, this effect is certainly seen in the use environment where the fatigue strength in question is dominant in bending, but in the case where tensile and compressive stress is generated like connecting rods, the inside where pores exist is present. Therefore, there is a limit to the improvement of fatigue strength.
本発明は焼結鍛造部品のショットピーニングによる強
化方法の前記のごとき問題点に鑑みてなされたものであ
って、表層部の空孔を完全に圧潰するとともに、金属結
合を充分に行い、疲労強度の向上を図ることのできる焼
結鍛造部品の表面欠陥除去方法を提供することを目的と
する。The present invention has been made in view of the above problems of the strengthening method by shot peening of a sintered forged component, in which the holes in the surface layer portion are completely crushed, the metal bonding is sufficiently performed, and the fatigue strength is improved. It is an object of the present invention to provide a method for removing surface defects of a sintered forged part that can improve the above-mentioned.
［課題を解決するための手段］ 本発明の焼結鍛造部品の表面欠陥除去方法は、焼結鍛
造部品に第１のショットピーニングを施し表面部の空孔
を圧潰する工程と、前記焼結鍛造部品のうちＣを含む焼
結鍛造部品の場合は還元性雰囲気または保護雰囲気中で
Ｃを含まない焼結鍛造部品の場合は還元性雰囲気中で加
熱することにより表面部の酸化物を還元するとともに表
面部の粉末同志を金属結合状態にする工程と、前記焼結
鍛造部品に第２のショットピーニングを施し表面部に残
留圧縮応力を付与する工程とからなることを要旨とす
る。[Means for Solving the Problems] A surface defect removing method for a sintered forged component according to the present invention comprises a step of subjecting a sintered forged component to first shot peening to crush holes in a surface portion, and the sintered forging described above. Among the parts, in the case of a sintered forged part containing C, the oxide on the surface is reduced by heating in a reducing atmosphere or a protective atmosphere and in the case of a sintered forged part not containing C in a reducing atmosphere. The gist of the present invention is that it comprises a step of bringing the powders of the surface portion into a metal-bonded state and a step of subjecting the sintered forged part to a second shot peening to give a residual compressive stress to the surface portion.
本発明が適用される焼結鍛造部品は、焼結体をその材
料の再結晶温度以上で鍛造するもの、あるいは単純な形
状の焼結体をその材料の再結晶温度以上で精密鍛造する
ものいずれでも良い。The sintered forged parts to which the present invention is applied are those forging a sintered body at a recrystallization temperature of the material or higher, or precision forging of a sintered body having a simple shape at a recrystallization temperature of the material or higher. But good.
ショットピーニングを行う装置は従来のものを用いる
ことができる。ショットの投射装置としては、回転する
翼車の羽根によって加速する遠心式投射装置、あるいは
圧縮空気がノズルから噴出するときの空気速度を利用す
る空気式吹付投射装置のいずれをも使用することができ
る。A conventional device can be used for the shot peening. As the shot projection device, either a centrifugal projection device that is accelerated by the blades of a rotating impeller or a pneumatic spray projection device that uses the air velocity when compressed air is ejected from a nozzle can be used. .
ショットは、砂、鋳鉄ショット、鋳鋼ショット、鋼線
ショット等のいずれを用いても良い。ショット径、投射
速度、投射時間等のショットピーニングの条件は、部品
の材質、部品の大きさ等により適宜選択されるが、第１
のショットピーニングにおいては、焼結鍛造部品の表面
部の空孔を圧潰するに充分なショット径、投射速度、投
射時間が選択される。The shot may be sand, cast iron shot, cast steel shot, steel wire shot, or the like. Shot peening conditions such as shot diameter, projection speed, and projection time are appropriately selected according to the material of the parts, the size of the parts, etc.
In the shot peening, the shot diameter, the projection speed, and the projection time which are sufficient to crush the holes in the surface portion of the sintered forged part are selected.
第１のショットピーニング後の再加熱に使用される雰
囲気は還元性雰囲気または保護雰囲気である。還元性雰
囲気とは吸熱ガス反応によって得られる還元性の強いガ
スで、たとえばRxガス、Axガスのようなものである。ま
た、保護雰囲気とは主として不活性ガス雰囲気を指し、
たとえばN2ガス、Arガス等である。Ｃを含む焼結鍛造部
品の場合は、Ｃによる自己還元及び還元性雰囲気による
還元を行うため還元性雰囲気及び保護雰囲気が選ばれ、
Ｃを含まない焼結鍛造部品においては還元雰囲気による
還元が必要なため、還元性雰囲気が選ばれる。The atmosphere used for reheating after the first shot peening is a reducing atmosphere or a protective atmosphere. The reducing atmosphere is a highly reducing gas obtained by an endothermic gas reaction, such as Rx gas or Ax gas. The protective atmosphere mainly means an inert gas atmosphere,
Examples include N 2 gas and Ar gas. In the case of a sintered forged part containing C, a reducing atmosphere and a protective atmosphere are selected in order to carry out self-reduction by C and reduction in a reducing atmosphere,
A reducing atmosphere is selected because reduction in a reducing atmosphere is necessary for a sintered forged part that does not contain C.
本発明が適用される焼結鍛造部品には、鉄系のみなら
ず銅系およびアルミ系の焼結鍛造部品にも適用できる。
再加熱の条件は鉄系の場合は900〜1150℃とすることが
好ましい。加熱温度が900℃未満であると、酸化物の還
元および粉末同志の金属結合が十分に行なわれないから
であり、1150℃を超えると結晶粒が粗大化するので好ま
しくない。加熱時間は５〜30分間することが好ましい。
加熱時間が５分間未満では酸化物の還元が充分でなく、
30分を超してもそれ以上に金属結合が進行しないからで
ある。The sintered forged parts to which the present invention is applied can be applied not only to iron-based but also to copper-based and aluminum-based sintered forged parts.
The reheating condition is preferably 900 to 1150 ° C in the case of iron system. This is because if the heating temperature is lower than 900 ° C., the reduction of the oxide and the metal bonding between the powders are not sufficiently performed, and if the heating temperature exceeds 1150 ° C., the crystal grains become coarse, which is not preferable. The heating time is preferably 5 to 30 minutes.
If the heating time is less than 5 minutes, the reduction of the oxide is not sufficient,
This is because even if it exceeds 30 minutes, the metal bond does not proceed further.
第２のショットピーニングにおいては、焼結鍛造部品
にさらに残留圧縮応力を付し面粗度を良くするために、
ショット径は第１のショットピーニングのものと同等ま
たはそれ以下とすることが好ましい。In the second shot peening, in order to further apply residual compressive stress to the sintered forged part to improve the surface roughness,
The shot diameter is preferably equal to or smaller than that of the first shot peening.
［作用］ 焼結鍛造部品は表面部に約５％の空孔率で空孔を有す
る。この焼結鍛造部品に第１のショットピーニングを施
すことにより、焼結鍛造部品の表面部の空孔が圧潰され
るので、表面部は欠陥の少ない機械的結合状態となる。[Operation] The sintered forged part has pores on the surface portion with a porosity of about 5%. By subjecting the sintered forged part to the first shot peening, the pores in the surface part of the sintered forged part are crushed, so that the surface part is in a mechanically bonded state with few defects.
続いて、前記焼結鍛造部品のうちＣを含む焼結鍛造部
品の場合は還元雰囲気または保護雰囲気中でＣを含まな
い焼結鍛造部品の場合は還元性雰囲気中で加熱すること
により表面部の酸化物、すなわち空孔圧着界面および線
状欠陥に介在する酸化物を還元するとともに、表面部の
粉末同志を金属結合状態にし、表面が無欠陥状態とする
ことができる。Subsequently, in the case of a sintered forged part containing C among the above-mentioned sintered forged parts, in the case of a sintered forged part not containing C in a reducing atmosphere or a protective atmosphere, the surface of the surface portion is heated by heating in a reducing atmosphere. It is possible to reduce the oxide, that is, the oxide existing in the pore pressure bonding interface and the linear defect, and to bring the powder particles in the surface portion into a metal-bonded state so that the surface is in a defect-free state.
次いで、第２のショットピーニングにより、焼結鍛造
部品にさらに残留圧縮応力を付与し面粗度が改善される
ので、面粗度等の欠陥により表面から疲労破壊が発生す
るのが防止され、さらに残留圧縮応力の付加により、疲
労強度が向上する。Then, the second shot peening further applies a residual compressive stress to the sintered forged part to improve the surface roughness, which prevents the surface from fatigue fracture due to defects such as surface roughness. Fatigue strength is improved by adding residual compressive stress.
［実施例］ 本発明の実施例を従来例と比較して説明し、本発明の
効果を明らかにする。Example An example of the present invention will be described in comparison with a conventional example to clarify the effect of the present invention.
（実施例１） −80メッシュの純鉄粉に電解銅粉２％、鱗片状黒煙粉
末0.6％、ステアリン酸亜鉛を0.6％添加し20分間混粉し
た。混合粉を面圧5ton/cm2にて加圧成形し、次ぎにRxガ
ス中にて加熱焼結し焼結体を得た。次いで得られた焼結
体は炉から取り出した後、直ちに面圧10ton/cm2で熱間
鍛造後空冷した。得られた焼結鍛造材の引張圧縮疲労強
度を測定したところ14kg/mm2であった。(Example 1) 2% of electrolytic copper powder, 0.6% of scaly black smoke powder and 0.6% of zinc stearate were added to -80 mesh pure iron powder and mixed for 20 minutes. The mixed powder was pressure-molded at a surface pressure of 5 ton / cm 2 , and then heat-sintered in Rx gas to obtain a sintered body. Then, the obtained sintered body was taken out of the furnace and immediately hot forged at a surface pressure of 10 ton / cm 2 and then air-cooled. The tensile compression fatigue strength of the obtained sintered forged material was measured and found to be 14 kg / mm 2 .
得られた焼結鍛造材はショット機（ターンブラスト）
にてショット粒径1.4mmを用いて20分間第１のショット
ブラストを施した。第１のショットピーニング後の焼結
鍛造材の引張圧疲労強度を測定したところ18kg/mm2であ
った。The obtained sintered forged material is a shot machine (turn blast)
The first shot blasting was performed for 20 minutes using a shot grain size of 1.4 mm. The tensile pressure fatigue strength of the sintered forged material after the first shot peening was measured and found to be 18 kg / mm 2 .
続いて1000℃で15分間Rxガス中にて加熱処理後空冷し
た。この再加熱後の焼結鍛造材の引張疲労強度は25kg/m
m2であった。再加熱後の焼結鍛造材はショット機（ター
ンブラスト）にてショット粒径0.5mmにて第２のショッ
トブラストを20分間施した。第２のショットピーニング
を施した後の焼結鍛造材の引張圧縮疲労強度は30kg/mm2
であった。Subsequently, it was heat-treated in Rx gas at 1000 ° C. for 15 minutes and then air-cooled. The tensile fatigue strength of the sintered forged material after this reheating is 25 kg / m.
It was m 2. After the reheating, the sintered forged material was subjected to a second shot blasting for 20 minutes with a shot machine (turn blasting) at a shot grain size of 0.5 mm. The tensile compression fatigue strength of the sintered forged material after the second shot peening is 30kg / mm 2
Met.
（実施例２） −80メッシュの低合金粉末（Fe−１％Cr−0.7％Mn−
0.2％Mo）に鱗片状黒鉛0.6％、MnS0.5％、ステアリン酸
亜鉛を0.6％を20分間混粉し、密度が6.8〜7.2kg/cm3に
なるように加圧成形後、1300℃で20分間N2雰囲気で加熱
して焼結した後炉冷して焼結体を得た。得られた焼結体
の引張圧縮疲労強度を測定したところ12kg/mm2であっ
た。(Example 2) -80 mesh low alloy powder (Fe-1% Cr-0.7% Mn-
0.2% Mo) is mixed with 0.6% scaly graphite, 0.5% MnS, and 0.6% zinc stearate for 20 minutes, and pressure-molded to a density of 6.8 to 7.2 kg / cm 3 , then at 1300 ° C. After heating for 20 minutes in a N 2 atmosphere to sinter, the furnace was cooled to obtain a sintered body. The tensile compression fatigue strength of the obtained sintered body was measured and found to be 12 kg / mm 2 .
得られた焼結体はショット機（ターンブラスト）にて
ショット粒径1.4mmを用いて20分間第１のショットブラ
ストを施した。第１のショットピーニング後の焼結体の
引張疲圧縮労強度を測定したところ18kg/mm2であった。The obtained sintered body was subjected to a first shot blast for 20 minutes using a shot machine (turn blast) with a shot grain size of 1.4 mm. The tensile fatigue compression working strength of the sintered body after the first shot peening was measured and found to be 18 kg / mm 2 .
続いて1000℃で15分間Rxガス中にて加熱処理後空冷し
た。この再加熱後の焼結材の引張疲労強度は22kg/mm2で
あった。再加熱後の焼結鍛造材はショット機（ターンブ
ラスト）にてショット粒径0.5mmにて第２のショットブ
ラストを20分間施した。第２のショットピーニングを施
した後の焼結材の引張疲圧縮労強度は22kg/mm2であっ
た。なお、引張圧縮疲労強度はクランクの往復運動によ
り引張圧縮の応力を与える西原式を用いて測定した。Subsequently, it was heat-treated in Rx gas at 1000 ° C. for 15 minutes and then air-cooled. The tensile fatigue strength of the sintered material after the reheating was 22 kg / mm 2 . After the reheating, the sintered forged material was subjected to a second shot blasting for 20 minutes with a shot machine (turn blasting) at a shot grain size of 0.5 mm. The tensile fatigue compression working strength of the sintered material after the second shot peening was 22 kg / mm 2 . The tensile compression fatigue strength was measured using the Nishihara equation, which gives tensile compression stress by the reciprocating motion of the crank.
以上で得られた結果をまとめて第１表に示す。なお、
第１表において表面、内部は疲労破壊する起点部を示し
た。また、第１図は引張圧縮疲労強度と繰り返し数との
関係を示す図である。The results obtained above are summarized in Table 1. In addition,
In Table 1, the surface and the inside show the starting point portion where fatigue failure occurs. Further, FIG. 1 is a diagram showing the relationship between tensile compression fatigue strength and the number of repetitions.
第１表および第１図に示したように、焼結体のままの
ものについては、第１のショットピーニング処理後再加
熱後の引張圧縮疲労強度は22kg/mm2と低く、さらに第２
のショットピーニング処理を施しても引張圧縮疲労強度
が22kg/mm2のままで、引張圧縮疲労強度の向上が見られ
ず、本発明方法を焼結体に適用しても効果の無いことが
明らかとなった。 As shown in Table 1 and FIG. 1, as for the sintered body as it is, the tensile compression fatigue strength after reheating after the first shot peening treatment is as low as 22 kg / mm 2, and
Even after the shot peening treatment, the tensile compression fatigue strength remains 22 kg / mm 2 , no improvement in the tensile compression fatigue strength is observed, and it is clear that there is no effect even when the method of the present invention is applied to a sintered body. Became.
また、焼結鍛造材に第１のショットピーニング後に再
加熱しただけの場合は、引張圧縮疲労強度が25kg/mm2と
まだ十分でなく、かつ表面から疲労破壊が発生している
ことが明らかとなった。Also, when the sintered forged material was only reheated after the first shot peening, it was revealed that the tensile compression fatigue strength was still insufficient at 25 kg / mm 2 and that fatigue fracture had occurred from the surface. became.
これに対して、焼結鍛造材に本発明方法、すなわち第
１のショットピーニング→再加熱→第２のショットピー
ニングを施した例では、引張圧縮疲労強度が30kg/mm2で
あって、しかも疲労破壊は内部から発生しており、表面
欠陥が除去されるとともに疲労強度が著しく向上できる
ことが確認された。On the other hand, in the case where the sintered forged material is subjected to the method of the present invention, that is, the first shot peening → reheating → second shot peening, the tensile compression fatigue strength is 30 kg / mm 2 and It was confirmed that the fracture occurred from the inside, and the surface defects were removed and the fatigue strength could be remarkably improved.
［発明の効果］ 本発明の焼結鍛造部品の表面欠陥除去方法は以上説明
したように、焼結鍛造部品に第１のショットピーニング
を施すことにより、焼結鍛造部品の設面部の空孔を圧潰
し、表面部を欠陥の少ない機械的結合状態とし、続いて
焼結鍛造部品のうちＣを含む焼結鍛造部品の場合は還元
性雰囲気または保護雰囲気中で加熱することにより表面
部の酸化物、すなわち空孔圧着界面および線状欠陥に介
在する酸化物を還元するとともに、表面部の粉末同志を
金属結合状態にし、表面が無欠陥状態とし、次いで、第
２のショットピーニングにより、焼結鍛造部品にさらに
残留圧縮応力を付与し、面粗度等の欠陥により表面から
疲労破壊が発生するのが防止され、さらに残留圧縮応力
の付与により、疲労強度が向上するという優れた効果が
ある。[Effects of the Invention] As described above, the method of removing surface defects of a sintered forged component of the present invention removes holes in the installation surface of the sintered forged component by performing the first shot peening on the sintered forged component. The oxide of the surface portion is obtained by crushing to bring the surface portion into a mechanically bonded state with few defects, and subsequently, in the case of a sintered forged component containing C among the sintered forged components, heating in a reducing atmosphere or a protective atmosphere. That is, while reducing oxides existing in the pore pressure bonding interface and linear defects, the surface powder particles are brought into a metal-bonded state to make the surface defect-free, and then by second shot peening, sintering forging is performed. Residual compressive stress is further applied to the parts to prevent fatigue fracture from occurring on the surface due to defects such as surface roughness, and by giving residual compressive stress, fatigue strength is improved. .
第１図は焼結材および焼結鍛造材の引張圧縮疲労強度と
繰り返し数との関係を示す図である。FIG. 1 is a diagram showing the relationship between the tensile compression fatigue strength and the number of repetitions of a sintered material and a sintered forged material.
Claims (1)
を施し表面部の空孔を圧潰する工程と、前記焼結鍛造部
品のうちＣを含む燃焼鍛造部品の場合は還元性雰囲気ま
たは保護雰囲気中でＣを含まない焼結鍛造部品の場合は
還元性雰囲気中で加熱することにより表面部の酸化物を
還元するとともに表面部の粉末同志を金属結合状態にす
る工程と、前記焼結鍛造部品に第２のショットピーニン
グを施し表面部に残留圧縮応力を付与する工程とからな
ることを特徴とする燃焼鍛造部品の表面欠陥除去方法。1. A step of subjecting a sintered forged part to a first shot peening to crush holes in a surface portion, and a reducing atmosphere or a protective atmosphere in the case of a combustion forged part containing C among the sintered forged parts. In the case of a sintered forged part that does not contain C, a step of reducing the oxide on the surface part by heating in a reducing atmosphere and bringing the powders of the surface part into a metal-bonded state, and the sintered forged part And a step of applying a second compressive peening to give a residual compressive stress to the surface portion of the same.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP4706289A JP2682109B2 (en) | 1989-02-28 | 1989-02-28 | Surface defect removal method for sintered forged parts |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP4706289A JP2682109B2 (en) | 1989-02-28 | 1989-02-28 | Surface defect removal method for sintered forged parts |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH02225604A JPH02225604A (en) | 1990-09-07 |
| JP2682109B2 true JP2682109B2 (en) | 1997-11-26 |
Family
ID=12764670
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP4706289A Expired - Fee Related JP2682109B2 (en) | 1989-02-28 | 1989-02-28 | Surface defect removal method for sintered forged parts |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2682109B2 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE9602376D0 (en) * | 1996-06-14 | 1996-06-14 | Hoeganaes Ab | Compact body |
-
1989
- 1989-02-28 JP JP4706289A patent/JP2682109B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH02225604A (en) | 1990-09-07 |
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