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The case of a 42-year-old woman with delusional disorder, somatic type (DDST), with infestation delusion and delusions of body odor and halitosis accompanied by severe secondary depression is presented. These somatic delusions and depressive symptoms responded favorably to treatment with paroxetine 10 to 30 mg/d. Hypoperfusion in the left temporal and parietal lobes observed when she had marked clinical symptoms was improved at near recovery. The present report suggests that paroxetine is effective and a reasonable drug for DDST with secondary depression. It also supports previous observations that DDST is associated with hypoperfusion in the temporal and parietal lobes.

A 54-year-old man with delusional disorder, somatic type (DDST) showed extremely grotesque somatic delusions, i.e., the presence of another lower jaw with teeth and tongue accompanied by annoying sensations. These somatic delusions responded favorably to treatment with risperidone 2-3 mg/day. The single photon emission computed tomography taken when he had marked somatic delusions showed hypoperfusion in the temporal and parietal lobes. The present report suggests that delusion of reduplication of body parts, which has been generally associated with organic brain diseases, is also observed in DDST. This report also supports prior observations on the efficacy of risperidone for DDST and the association between this disorder and hypoperfusion in the temporal and parietal lobes.

Investigations were made on the chemical, mechanical, non-destructive, and corrosive properties of welded joints of 1 mm thick Nb and Ta sheets that were either electronbeam welded in a high vacuum or TIG welded in a controlled welding chamber filled with 1 atm argon gas containing an impurity gas of air, nitrogen, oxygen, or hydrogen. The electron-beam melted Nb specimen showed no porosity with both welding methods. However, sintered Nb specimens showed greater porosities with electron-beam welding. The sintered Ta specimens showed no porosity both with TIG and electron-beam welding. Other properties are also listed. (P.C.H.)

Hot ductility, as revealed the values of reduction in area at the fracture surface tested at high temperatures on the weld thermal cycles, was studied on austenitic stainless steel weld metals by means of a reproducing apparatus of weld thermal cycles.Five weld metals, including type 308L, 347 and 316, were tested in this study. A round bar tensile specimen made from multiple pass weld, was heated rapidly up to the peak temperature of 1350°C and then broken at each temperature of 800, 1000, 1100, 1200 and 1300°C both on heating and cooling along the thermal cycle, respectively.From the tests, hot ductility curves, expressed as percent reduction in area at fracture as a function of the testing temperatures were obtained for each weld metal.From the values of reduction in area as measured both on heating and cooling at 1200°C, hot ductility rating about these weld metals was determined as the following order.On heating-308L [347(A), 347(B), 316] 347(C)On cooling-308L [347(A), 347(B)] 316, 347(C)Among the test weld metals, the hot ductility of type 308L was the most superior, while that of type 347(C) containing no ferrite was the poorest on the contrary.Furthermore, the comparison was made between hot ductility and Fisco cracking test results for the test weld metals. A close relationship was found between the two, then the hot ductility was assured to be effective extensively as a measure of hot cracking susceptivility of austenitic stainless electrodes.

Chemical compositions, porosities and mechanical properties of electron-beam welds were studied of ractive and refractory metals, aluminium alloy, stainless steel and carbon steel by comparing with controlled atmosphere TIG welds and the following conclusions were obtained :(1) The contents of oxygen and nitrogen in titanium and zirconivm were changed neither by electron-beam welding (EBW) nor by TIG.By EBW, contents of carbon and oxygen in sintered niobium sheets, that of carbon in a sintered tantalum sheet and that of nitrogen in a type 304 stainless steel plate were considerably reduced.(2) X-ray radiographs of both EBW and TIG welds in sintered niobium, molybdenum and tungsten sheets showed usually many porosities in weld metal near the fusion line, while porosityfree welds were obtiand in vacuum melted sheets.Repeated electron-beam bead welding in sintered sheets was very effective in eliminating porosities in weld metals.(3) An element of which the partial pressure at melting point of a base metal is higher than about 10-2mmHg is likely to be vaporized during EBW in a vacuum of (1-5) × 10-5mmHg.(4) Subsize V-charpy impact values of commercially pure titanium, zirconium and Zircaloy-2 plates were generally far greater in EBW welds than in TIG welds.(5) Brittle behavior of arc welds of molybdenm sheets was not improved by EBW, probably because of grain coarsening in weld zone.(6) The joint efficiency of EBW, welds of a 1 mm thick 24 S aluminum alloy sheet was about 87% and much greater than 50 to 70% in TIG welds, owing to the very narrow width of weld metal and heat-affected zone.(7) The joint efficiency of EBW weld of a 6 mm thick 17-7 PH plate was 100% and was greater than 95% in TIG weld.

高張力鋼板および溶接棒の有意義な割れ試験方法を求めるために,リーハイ型U開先および鉄研式y開先の2種類の突合せ拘束割れ試験の比較検討を行なった.両試験片とも,標準のものより小型の新しい試験片を用い,引張強さ40～90kg/mm2の鋼材と低水素系および高酸化チタン系溶接棒の組合せについて割れ試験を行なった.溶接割れの重要な諸因子,すなわち溶接入熱,予熱温度,冷却速度,割れの時期,割れ発生温度,開先形状,母材の化学組成,溶接棒の被覆系統および強さ,熱影響部の最高かたさ,溶接直後の後熱,等価炭素量等が割れの様相やルート,断面および表面における割れ率におよぼす影響について研究を行なった。高張力鋼の溶接割れ感受性におよぼす熱的拘束(冷却速度)の影響を示すために,3種類の割れ率の値をボンドの300℃における冷却速度に対して求め,割れを生じない冷却速度から100%の割れをおこす冷却速度までの範囲で割れ率の遷移曲線をえた.そして割れ率が50%になる臨界冷却速度の値を割れ感受性指示数と名付け,割れ感受性判定の尺度として用いた.割れ発生の時期および温度を求めるために溶接部の横収縮の測定も行なった.本研究の結果えられた結論をまとめると次のようになる.(1)高張力鋼溶接部の割れの状態は試験片の開先形状により大きく影響され,特にリーハイ型の対称形をなすU開先と鉄研式の非対称なy開先とにおいて著しい差異がある.(2)供試鋼材および溶接棒でみとめられた溶接割れはほとんど全部が溶接部のルートまたはビード底面から発生し,溶接金属や熱影響部に伝播した.(3)このようなルート割れは25～200℃の予熱温度に無関係に,溶接終了後約3min以上経って,温度が90℃以下,室温近くまで冷却した後に発生した.(4)リーハイ型U開先試験片では母材の強さや溶接棒種に無関係に割れはほとんど溶接金属に生ずる.ただし非常に延性に富む溶接金属では割れは熱影響部か溶接金属のいずれかに生ずる.(5)鉄研式y開先試験片では低水素系溶接棒を用いたときには割れはルート(鈍角をなす側)から母材の熱影響部に沿って進んだ後,溶接金属中へ折れ曲がった.しかし熱影響部より延性の劣る溶接金属の場合には割れは溶接金属か熱影響部のいずれかに生じた、一方,高酸化チタン系溶接棒ではリーハイ型U開先の場合にみられるような溶接金属割れのみを生じた.(6)リーハイ型U開先試験片は溶接棒の相違には非常に敏感であるけれども鋼材の相違に対しては必ずしもそうだとはいえない.鉄研式y開先試験片は鋼材の相違には非常に敏感であるけれども溶接棒の相違に対しては必ずしもそうだとはいえない.(7)リーハイ型U開先試験片は溶接棒の割れ試験用として鉄研式y開先試験片より適している。これに対してy開先試験片は母材の割れ試験用としてU開先試験片より適している.これを誤用すれば高張力鋼板とその溶接棒の割れ感受性を正しく評価することができないであろう.(8)対称形の60°V開先(Y開先)試験片は実用上U開先試験片と等価である.(9)ビード表面まであらわれない割れが多いので,割れ試験ではビード表面のみではなく横断面やルートにおける割れを問題にする必要がある.(10)予熱は割れ防止に非常に有効であり,特に引張張さのレベルが80kg/mm2級の高級高張力鋼についてその効果が著しい.(11)80kg/mm2級高張力鋼を予熱なしで溶接した場合,溶接終了直後(2min以内)に酸素アセチレン焔により溶接部を局部的に600℃に加熱することにより冷間割れを防止することができた.(12)割れは熱影響部の最高のかたさがある限界値以上になると急激に増大する.y開先試験片についてはその限界値が50kg/mm2級高張力鋼に対するHv310(荷重1kg)の値から80kg/mm2級高張力鋼に対するHv400の値まで変化した.U開先試験片では溶接金属のかたさの限界値は50～80kg/mm2級の溶接金属に対してHv210～320であった.(13)鉄研式y開先試験片により求められたルートにおける割れ感受性は母材の等価炭素量と良好な相関関係が求められた。

The effects of exposure at 550°C for times up to 5, 000hr on the notch ductility and the microstructure change of welded joints of Ni-Cr-Mo type HT60 tempered steel were investigated. Test steel, 100 mm thick, was produced experimentally for nuclear pressure vessels and welded joints were made by the electroslag welding and the CO2 arc welding.The results of the study indicated that the base metal, the weld metal and the heat-affected zone (HAZ) of base metal exposed at 550°C for times up to 5, 000 hr tended to embrittle owing to the grain growth of ferrite and the cohering of carbide toward grain boundaries. This process of change in microstructure may be divided into the following three kinds of stage. There are in different combination of the three kind of stage due to the structure before exposure.(I) stage ; Tempering of martensite and spheroidizing of carbide(II) stage ; Formation of fine ferrite(III) stage ; Grain growth of ferrite and, cohering and coasening of carbide toward grain boundariesThe chang in microstructure for the base metal occur with (III) stage only ; the HAZ with electroslag welding (II) → (III) stages ; the HAZ with CO2 are welding (I) → (II) → (III) stages, respecitvely.

This report describes the method of plotting the continuous cooling transformation (CCT) diagram of weld metal, of which columnar structure and transformation on cooling are reproduced, and also describes the CCT diagrams of synthetic weld metals which contain Si and Mn ; Si, Mn and Ni ; and Ni, Cr and Mo. The results are follows.1) The microstructure of actual weld metal can be reproduced by melting the center of the specimen (4.5 mmφ×70 mml) with induction heating. and CCT diagrams of synthetic weld metals can be plotted by this method.2) The microstracture and hardness of synthetic weld metal are coincide with them of actual weld metal.Der UmriB : Der Bericht beschreibt die Methoden des Zeichens des ZTU-Schaubildes fur kontinuierliche Abkuhlung des kunstlichen wiederproduzieren Schwissmetalls, dessen Mikrostruktur and Umwandlung auf der Abkuhlungen wewieder-produziert wird, and ouch beschreibt die ZTU-Schauild fur kontinuierliche Abkuhlung deskustlichen wieder produzieren Schwissmetalls, die enthalten Si and Mn ; Si Mn and Ni ; und auch Ni, Cr and Mo. Die Resultater der Experimentes sind folgend.(1) Die Mikrostruktur des tatsachlichen Schwissmetalls kan mit der Mitten der Pruflings (4.5mmφ ×70mml) zu shmelzen durch die Hochfrequenzinduktionhitzen wiederproduziert werden, and die Umwandlung auf der Ackuhlungen kan mit der Hitzanalysen gemessen werden. Das ZTU-Schaubild fur kontinuierliche Abkuhlung des kunstlichen wiederproduzieren Schweissmetalls kan mit der Methoden gezeicht werden.(2) Und wir konnte tatsachlich gebeweiren, das die Mikrostruktur and Harte des kunstlichen wiederproduzieren Schweissmetalls haben die des tatsachlichen Schweissmetalls ubereinstimmen.

Effects of microstrure on root cracking of high strength steel welds were discussed in this report, mainly with the use of SH-CCT diagrams of test steels. Critical hardness values for root cracking were also discussed.The main conclusions obtained in this study are as follows :(1) A safety cooling process to prevent root cracking in HAZ should be chosen so that the ferrite and intermediate structure may appear more than about 40% for HT 60, intermediate structure more than about 25% for HT 70, and more than about 10% for HT 80 steels, respectively, when a joint of severe restraint is welded with a low hydrogen type electrode.(2) For a weld metal, it is necessary to prevent root cracking in a severe restraint joint that the ferrite and intermediate structure precipitate more than in HAZ.(3) A root crack in HAZ or weld metal is a mixed fracture of transcrystalline and intercrystalline types.(4) There was found no relationship between root cracking tendencies and Mf temperatures.(5) Retained austenite in HAZ was decomposed with the lapse of time above 250°C, but did not affect the root cracking phenomena.(6) Critical hardness, above which a root crack will surely occur in a joint of severe restraint, were found to be as follows :270 VHN (1 kg) for HAZ of mild steel weldment365 VHN (1 kg) for HAZ of HT 50 weldment400 VHN (1 kg) for HAZ of HT 60 weldment405 VHN (1 kg) for HAZ of HT 70 weldment415 VHN (1 kg) for HAZ of HT 80 weldment290 VHN (1 kg) for weld metal of HT 50 and HT 60 weldments330 VHN (1 kg) for weld metal of HT 70 and HT 80 weldments

The effects of anode voltage, welding current, beam diameter, welding speed and thickness of specimen on the characteristics of bead section (such as, penetration, width and penetration-to-width ratio) were studied with the 1.5 kW NRIM electron-beam welding equipment for type 304 stainless steel, low carbon steel, aluminium, brass, zirconium and titanium.The following conclusions were obtained:(1) An increase of anode voltage or welding current increased the penetration greatly and the width slightly. An increase of beam diameter greatly reduced the penetration but increased the width. An increase of welding speed coordinately reduced both the penetration and width.(2) New parameters were introduced to correlate satisfactorily the effects of anode voltage (V), welding current (I), welding speed (ν) and beam diameter (φ) on penetration (ρ) and width (ω) in bead welding; that is:ρ=κa×E1.7×Ι1/ν0.4×1/φ0.8ω=κb×E0.1×Ι0.2/ν0.5×φ0.6 (φ

Stress rupture tests with 40 ton tester were conducted at 500 and 600°C for large welded specimens of stainless clad steel, Mn-Mo-Ni steel ASTM A 302 B claded with AISI 304 L, which is essential to nuclear applications. The large specimen, 38 mm thick and 40 mm wide, showed much inferior property to usual small welded specimen.The results of test at 600°C under a stress of 12 kg/mm2 are : (1) The rupture time of transverse as-welded specimen was 55 % of base metal. (2) The rupture times of transverse welded specimens decreased through heat treatment after welding at 550, 650 and 870°C × 1.5 hr as low as to 40, 60 and 90 %, respectively, of as welded specimen. (3) Machining the reinforcement flush with the surface of base metal increased the rupture time of 550°C × 1.5 hr heat treated specimen by 1.5 times. (4) Longitudinal welded specimen was approximately equivalent to base metal in rupture time. (5) Transverse specimen manually welded showed about 50% longer rupture time than submerged-arc welded specimen.Macroscopic and microscopic examinations showed that cracking in rupture occurred along bond in the graphitized heat-affected zone of base metal. The initiation of cracking occurred mostly at the intersection between the surface of bond of stainless weld metal and the cladding surface, viz., the line along which concentration of strees and local strain were most extreme. Crack initiation in backing steel ocurred frequently at the toe of carbon steel weld metal. If the bottom of stainless weld metal were made smooth with cladding surface, the rupture time of transverse welded specimen would become identical to base metal.The test results at 500°C, however, showed 45 degrees shear type fracture which is different from that at 600°C in which fracture occurred along bond.

The electron-beam diameter and intensity distribution of the NRIM 1.5 kW electron-beam welder, home-made, were measured by interrupting the beam with a water-cooled copper plate. The effects of filament current, anode voltage, welding beam current and focusing voltage on beam focusing were studied experimentally.The following conclusions were obtained:1) The intensity distribution of electron-beam current on the specimen surface showed approximately a normal distribution.2) The electron-beam was of a cone shape with a vertex angle of 7 degrees.3) The minimum diameter of electron-beam on the specimen is affected severely by filament current, anode voltage, welding current and focusing voltage. Greater values of filament current and anode voltage and smaller welding current contributed to making the diameter of electron-beam smaller.4) In electron-beam welding, the beam diameter on the specimen should always be noted besides welding current, anode voltage and welding speed.

The Apparatuses for plotting the continuous cooling transformation diagram (CCT diagram) for welding, purpose using the high frequency type synthetic apparatus for reproducing weld thermal cycle are explaind. The CCT diagram obtained with these apparatuses is compared to it obtained with the traditional appratuses of silicon-carbide heating type for the same high tension steel.It is understood from the result that the CCT diagram for welding obtained with the high frequency type is most useful in the case that the cracking of the weld heat-affected zone is to be discussed with the CCT diagram in detail.For obtaining simply the critical cooling times, however, it is sufficient with silicon-carbide heating type.

In this report, the continuation of authors' first report, various types of austenitic, martensitic and ferritic stainless steels were studied by RPI hot ductility test, the effects of working method upon the hot ductility were investigated about wrought round bars and rolled plates of austenitic stainless steels, and the effects of austenite grain size on the hot ductility were also studied. The following results were obtained.(1) It was found that the hot ductility during the cooling portion of thermal cycle is, in general, higher in rolled plates than in wrought round bars.In the 347 type stainless steels, the effect of working method on the hot ductility is remarkable, and it appears that this is one of the characteristic of these 347 type stainless steels. It was also found that the variation of hot ductility depending on the change is large in this steel.(2) The hot ductility measured at 1200°C to 1300°C during the cooling portion was the best in a 16-8-2 Cr-Ni-Mo alloy among various austenite stainless steels, followed by 316 type, 304L type, 304 type and 347 type in that order, the lowest value being given by 310 type. It was found by metallographic observation that the decrease of hot ductility of these austenitic stainless steels was due to the embrittlement caused by the partial liquation of grain boundary din heating up to 1340°C.(3) The behaviours of ferritic stainless steel 430 type and martensite stainless steel 410 type were quite different from that of austenitic ones.These steels did not show the embrittlement caused by liquation of grain boundary which occurred in austenitic stainless steel, since their melting points were much higher. Therefore, the decrease of hot ductility during cooling portion may be attributable to the growth of grains. In general, these steels showed good hot ductility, and it appears that the weld cracking of these steels may not be hot cracking but low temperature cracking due to martensitic transformation.(4) It was found by the RPI hot ductility test that the weldability of some austenitic stainless steels could be improved by the refinement of grain size and the steels with large grains inclined to suffer from more weld cracking.

High temperature tensile and creep rupture propenties of six low alloy, high strength steels were investigated for base metals and welded joints made with covered electrodes. The high temperature tensile and rupture strengths of welded joints were generally inferior to those of base metals. Tensile strength of both base metals and welded joints began to decrease at 300 deg C for quenched and tempered HT 50 and HT 70 steels, and at 350 deg C for normalized HT 60 steels. The rupture of tensile specimens of welded joints was generally located in base metal at lower temperatures, and in weld metal at higher temperatures. Generally, higher creep rupture strengths were observed for steels with higher tensile strengths at high temperatures. As far as the present test steels are concerned, normalized steels seem to have better high temperature strength than quenched and tempered steels. (auth)

Mechanical and corrosion properties were investigated of welded joints of pure zirconium plates, 1 and 2 mm thick, which were welded in a controlled atmosphere welding chamber filled with either pure argon or impure argon mixed with an impurity gas of air, nitrogen, oxygen or hydrogen.Effects of surface cleaning and impurity in argon atmosphere on mechanical properties and cor-rosion resistance against acids at room temperature and high temperature high pressure water were studied and the following conclusions were obtained :(1) It is necessary to pickle (HF 5%+HNO3 45%+H2O 50%) the zirconium specimen prior to welding.(2) Microstructure of weld metal shows α' (acicular α) and air, N2 and H2 in argon atmosphere increase the amount of α'.(3) Tensile fracture of welded joint occurs at the most softened zone in base metal.(4) The amount of absorbed nitrogen or oxygen in weld metal is proportional to its initial par-tial pressure in argon atmosphere.(5) The effects of impurity gases in argon atmosphere on mechanical and chemical properties of weld metal are as follows :(a) More than 200 ppm (vol.) of air or N2 decreases greatly the corrosion resistance against high temperature high pressure water.(b) More than 700-1, 000 ppm of each gas (air, N2 or O2) embrittles the mechanical properties, and hardens the weld metal. However, H2 does not change the hardness and tensile strength although it embrittles the weld metal.(c) More than 105 ppm of each gas decreases the corrosion resistance against HCl+Iron solution.(d) Up to 104 ppm of each gas does not decrease the corrosion resistance against 81% H2SO4.(6) It is necessary to pickle the weld zone after welding in order to improve high temperature high pressure corrosion resistance.(7) As far as the controlled atmosphere welding is concerned, it seems to be necessary for reactor purposes to use an initial vacuum less than 10-2 mmHg and filling with high pure grade (99.99%) argon to one atm. For chemical industry purposes the chamber should be initially evacuated less than 0.5mmHg and filled with same high pure grade (99.99%) argon.

To study the individual and correlated effects of mechanical and thermal restraints on weld cracking behaviours of steels and electrodes, two types of dynamic cracking testers have been used in the present paper, that is, a Murex type bending cracking tester and a new type tensile cracking tester. In the latter, one piece in a butt weld specimen is tensile and can be displaced at any constant speed against the other stationary piece during or after welding at an arbitrary instant.Dynamic cracking tests of several mild steel coated electrodes showed that these two testers were satisfactory for classifying cracking susceptibility. Among the tested electrodes, the low hyd-rogen type showed the least, the high titania type the greatest and the high cellulose and illmenite types medium. susceptibility to both hot and cold cracking of weld metal.Stainless steel coated electrodes could be satisfactorily evaluated with this dynamic cracking tester concerning the suitability for the first pass welding of a clad steel.Comparing the two cracking test methods, the tensile restraint cracking tester was found to be more sensitive and reproducible than the Murex type bending restraint cracking tester. An instant of weld cracking in the former tester can be determined very successfully by observing a corres-ponding discontinuous change in the tensile load across the test weld. Further studies are being continued with the tensile restraint cracking tester.

The important role of hydrogen in root cracking of high strength steel welds had been already discussed in the previous report. In this report the quantitative effect of hydrogen was clarified with HT 60 welds and the effects of lower cooling process below 300°C on root cracking were discussed. The activation energy necessary for root cracking was measured with slotted cracking specimens which were quenched at various low temperatures. Difference in cracking behavior with a change of groove type or root opening was discussed and the repeating number of specimens necessary for a root cracking test was obtained.The conclusions obtained in the study are as follows:(1) There was ascertained an obvious difference in the iniation of root cracks when diffusible hydrogen contents in HT 60 welds varied from 1 to about 3 cc/100 gr(2) Initiation of a root crack in a weld metal was remarkably affected, by chemical compositions of a weld metal, even with a diffusible hydrogen content of lcc/100gr.(3) Propagation of a root crack in an HT 60 weld metal was little affected, even if the diffuible hydrogen content was increased from 3 to 6cc/100gr.(4) It was the cooling process above 300°C that affected the initiation of root cracks in HT 60 welds. In HT 80 welds, however, the cooling process below 300°C also affected the initiation of root cracks.(5) Through the measurement of incubation time for root cracking in slotted cracking specimens which were quenched at various low temperatures, the activation energy necessary for root cracking was estimated at about 10, 500 cal/g. atom, the value of which was in good agreement with the activation energy for the diffusion of hydrogen in a-Fe.(6) Repeating number of specimens which was necessary and sufficient for estimation of cracking tendency was three or four, so far as the slotted cracking test was regarded as "go or no go test". At least eleven specimens were necessary in order that cracking percentage might be estimated in detail.(7) It was understood with consideration of angles of inclination of fusion lines that a root crack occurred exclusively in HAZ with y-groove specimens and in a weld metal with U-groove specimens.(8) It was also explained by the angle of inclination of a fusion line that cracking behavior was varied with the gap of root.

Following the previous paper, the notch toughness of the weld HAZ microstructures of high strength steels was evaluated by means of the synthetic apparatus. Summalizing the whole results, including previous tests, the effects of steel composition, microstructure and other factors on the notch toughness of weld HAZ specimens have been clarified. From these discussions, the following conclusions were summalized ;(1) The notch toughness of coarsened HAZ microstructures in high strength steels was generally decreased compared that of their unaffected base metals, especially in quenched and tempered steels.(2) The toughness of HAZ microstructures was decreased in accordance with the order of decreasing hardness, namely, martensite, mixed structure (martensite and bainite), coarse bainite and pearlite or ferrite.(3) The critical carbon content at which the martensite toughness in weld HAZ was markedly declined, may be about 0.18%.(4) The superiority of the test steels, when compared to the toughness of reproduced HAZ microstructures, was convinced by the test to agree with that of the tensile ductility which obtained by synthetic HAZ ductility tests in previous studies.

ZrおよびZr-2を空気中でスポット溶接し,その溶接適正条件と溶接継手の機械的ならびに高温水中の腐食試験による性能試験をおこなった.その結果つぎの結論をえた.(1)溶接前の表面処理はペーパ処理または化学酸洗(HF 5%+HNO3 45%+H2O 50%,20秒)がよい.しかし処理精度の均一性,電極の消耗,および原子炉中の腐食の点よりみて化学酸洗のほうがより望ましいと考えられる.(2)本実験の範囲内では適正なスポット溶接条件として近似的に次式のような実験式がえられた.電流(I)=5000+5000T0 (A)圧力(P)=80+220T0 (kg)通電時間(t)=1+5T0 (Cycles)ただしT0=溶接板の板厚(mm)(3)スポット溶接部には気泡,割れその他の欠陥は全く認められなかった.(4)適正溶接条件でおこなったスポット溶接部の機械的性質について次のことがいえる.(i)引張せん断試験では,破断は熱影響部と素材の間でおこり,ボタン状の破断を示す.(ii)引張せん断強さは板厚と共に増加し,実験範囲内では板厚1mmの増加にともないZrでは約700～800kg,Zr-2では1,000～1,500kg程度増加する.またZr-2はZrに比し強さが大である.焼なまし後の強さは焼なまし温度が上昇するにしたがい急速に低下していく.(iii)ナゲット部のかたさはTIG溶接部に比しかなり高い.この原因は空気中の酸素,窒素ガスの吸収によるものではなく冷却速度が速いための焼入硬化に起因する.(iv)ナゲット部の組織は巨大な樹枝状晶を示し,各樹枝状晶内はほとんど完全なα'(acicular α)であり,硬化もこのα'に起因しているものと思われる.(5)適正溶接条件と溶接部の機械的性質を総合してZrおよびZr-2の点溶接の作業基準を求めるとTable 4がえられる.(6)溶接部近傍の熱サイクルの測定結果によれば,空気と接触する部分が400～500℃以上の高温に保たれる時間は数サイクル～10サイクル程度である。したがってこの時間内に空気中の酸素,窒素ガスが素材と反応する程度はごくわずかで,その悪影響は無視できるほどである.(7)溶接継手の高温高圧水(320℃,115～117気圧)に対する耐食性は溶接後の酸洗の有無にかかわらず健全である.以上の実験結果よりZrおよびZr-2を空気中でスポット溶接した継手は化学工業用にはもちろん原子炉用としても何ら懸念することなく使用できる.最後に本研究に対し,高温高圧水の腐食に関して金属材料技術研究所第五部の伊藤博士と清水技官の絶大な御指導,御協力をいただいた.また材料は日本金属工業(株)の御厚意によるものでありここに厚く感謝の意を表する。