Showing papers in "Quarterly Journal of The Japan Welding Society in 1994"

Study of Friction Welding between Titanium/Aluminium System(Report 1). Effects of Post-Weld Heat Treatment on the Properties of Commercially Pure Titanium/Pure Aluminium Friction Welds.

Abstract: In this report, the friction welding conditions for commercially pure titanium/pure aluminium joint were developed, and the effect of post-weld heat treatment (PWHT) on the mechanical and metallurgical properties of the complete friction welds was examined in basic research. The friction welding conditions range, which can produce the complete weld joints having more than 100% joint efficiency as joint tensile property and excellent bend ductility in the as-welded conditions, was clarified. PWHT temperatures including up to 873 K (600°C) for 36 ks (1 H) had no influence on joint mechanical properties, especially, joint tensile and bend ductility. However, they drastically decreased during PWHT at 873 K (600°C) for more than 72 ks (20 H). X-ray diffraction analysis and SEM observation confirmed that those reductions were due to the formation of large contents of Al3Ti intermetallic compound phase at the pure titanium/pure aluminium interface. The critical width of Al3Ti phase (at PWHT of 873K for 72 ks), which steeply reduced the mechanical properties, was around 10 μm. Several atomic percents of silicon concentrated in the Al3Ti phase.

Ge含有アルミニウムろうによるAl-Mg, Al-Mg-Si合金のろう付

Abstract: Vacuum brazing of A5000 (Al-Mg) series and A6000 (Al-Mg-Si) series aluminum alloys are considerably difficult because of their rather high magnesium contents. For the purpose of sound and high strength brazing of these materials, a series of Al-Ge-Si-Mg system based filler metales was developed by the authors. Evaluations of brazed joint strength of A5052 and A6061 base alloys with these filler metals were performed and the relationship between the joint strength and the brazing conditions was investigated.In A6061 base alloy, the brazed joints provided sufficient joint strength which were equal to that of the base alloy. In A5052 alloy, on the other hand, the joint strength was considerably low which was as low as one half of that of the base alloy.The examination of brittle intermetallic compound Mg2Ge through the reaction between Mg in the base alloys and Ge in the filler metals occured at the interfaces of the brazed joints. Accordingly the formation of this intermetallic compound lead the decrease in the joint strength of A5052 alloy, which contains much Mg.

Study on production mechanism of welding residual stress at the juncture of a pipe penetrating a thick plate

Abstract: This paper studies welding residual stresses at the intersection of a small diameter pipe penetrating a thick plate. The pipe is welded to the plate, and Tungsten Innert Gas (TIG) cladding is melted on the inner surface of the pipe to protect it from stress corrosion cracking due to long operation in nuclear power plants.Stresses are calculated by heat conduction analysis and thermal elasto-plastic analysis, and also measured by strain gauges. Welding residual stresses are shown to have no corrosive influence on the inner pipe surface, and the stresses are compressed enough to protect the pipe against stress corrosion cracking on the outer surface.It was also studied to make clear the production mechanism of the residual stresses which were generated by welding processes at the pipe.

Toughness Deterioration and Its Improvement of Weld HAZ with High Heat Inputs in 780 and 980MPa Class HSLA Steels(Report 2). Metallographic Investigation of M-A Constituent.

Abstract: The internal microstructure, chemical composition, and hardness of M-A (Martensite-Austenite constituent) formed in weld CGHAZ (Coarse Grained Heat Affected Zone) of 780-980 MPa class HSLA steels have been investigated in order to reveal metallographic characteristics of the M-A constituent. The martensite was classified into lath and twin type. The massive M-A constituent had higher C contents, and included more twin type martensite and retained austenite than the elongated M-A. The cementite was found to be classified into a coarse rod type and a dendritic or fine needle type. The coarse rod type is considered to be precipitated directly from the austenite. The dendritic or fine needle type is probably precipitated by the self tempering of martensite.The C content of the M-A constituent was increased with Δt8/5 (cooling time from 1073 to 773 K) and reached 1.3-2.2% for Δt8/5=100-1000s.The hardness of the M-A constituent was increased with C content. The hardness of the massive M-A constituent (Hv-950) was generally higher than that of the elongated M-A constituent (Hv-700). The hardness and C content of the M-A constituent can be reduced significantly by a post weld heat treatment at temperatures from 623 to 773 K.

ダイヤモンド-活性金属ろう界面における凝固現象および接合強度 : ダイヤモンドと金属の接合に関する研究(第1報)

Abstract: Natural diamond has been brazed to Fe-42Ni alloy sheet using Ag-Cu eutectic filler including active metal of 4.5 wt% Ti, in order to investigate on the relation between the segregation behavior of the active metal to the brazed interface and the joint strength.The examination of the effects of brazing thermal cycles on the reaction products and titanium segregation behavior at the diamond-filler interface showed that the microstructures at the interface were dendrite and cell structure in case of cooling rate of 12 K/sec and 1.5 K/sec respectively, and that the active metal (Ti) was not detected by EDS in the both structures. This suggests that titanium segregation at the joint interface and the grain boundaries occurs as a result of exclusion of titanium out of Ag-Cu eutectic crystals accompanied by the crystal growth.The joints were fractured at the interface between diamond and brazing filler using a developed tensile shear test method to get the joint strength and the fractured surfaces at the interface. The strength of the joint made by the cooling rate of 1.5 K/sec was higher than that made by the rate of 15 K/sec. The disregistry values were also calculated from the mismatch of surface orientations and lattice constants at the bonded interface. The results showed that the disregistry of diamond and TiC to Ti were remarkably larger than those to Cu and Ag, which corresponded to the joint strengths and the fracture paths.

単層及び多重溶接熱サイクル再現溶接熱影響部の靱性に及ぼす島状マルテンサイトの挙動に関する検討 80及び100キロ級高張力鋼大入熱溶接haz部の靱性劣化とその改善に関する研究(第1報)

Abstract: In this research work, the effect of area fraction of M-A constituent on charpy absorbed energy (vE) of both simulated-CGHAZ (Coarse-Grained HAZ for high heat input welding process) and ICCGHAZ (Intercritically-Reheated CGHAZ for multiple welding process) of either 780 or 980 MPa class HSLA steel has been studied.The M-A constituent is classified into two types such as massive M-A and elongated M-A depending on its form. The form of M-A changes from "elongated M-A" to "elongated M-A+massive M-A" and then to "elongated M-A+massive M-A+carbide" according to the increase of cooling time, Δt8/5. Furthermore, the size of M-A increases.It has been clarified that the vE of ICCGHAZ is rather lower than that of CGHAZ as the result of dual thermal cycle test at the temperature of 1073 K where the peak temperature of second thermal cycle, Tp2 exceeds Ac1 due to the formation of massive M-A of large size. However, the vE at both 873 K and 673 K where the peak temperature of third thermal cycle, Tp3 is lower than Ac1 is improved to be more than the vE at temperature of 1073 K which is equal to Tp3 in the triple thermal cycle test. Since these improvement of vE considerably corresponds with the decrease of area fraction of M-A, the M-A constituent is decomposed by the tempering effect of third thermal cycle so that the vE value of ICCGHAZ seems to have been improved.The increase of area fraction of total M-A in both single and multiple welding thermal cycle tests causes the increase of that of massive M-A seems to be the decisive factor for the deterioration of vE in both CGHAZ and ICCGHAZ of either 780 or 980 MPa class HSLA steel.

Effect of Heat Treatment on Bond Characteristics of Aluminum Clad Steel. Development of Clad Materials by Vacuum Roll Bonding and its Characteristics. (Report 2).

Abstract: An aluminum clad steel was produced using the vacuum roll bonding. The clad steel was heated at 560 to 650°C for 0 to 20 s to study formation of intermetallic phases and bond shear strength in the bond interface between the aluminum and the steel of the aluminum clad steel given weld thermal cycles. Main results obtained are as follows ; (1) Although the clad steel was heated at 650°C without holding, an intermetallic phase was not formed in the bond interface. (2) However, when the clad steel was heated for a certain time, intermetallic phases of FeAl3 and Fe2Al5 were formed in the bond interface and the activation energy for formation of the phases was 41 kcal/mot. (3) When the thickness of the phases was more than around 1.5μm, the bond shear strength of the clad metal was abruptly decreased in comparison with that of the clad steel in as-produced condition.

Neuro-Fuzzy Control of Weld Pool in Pulsed MIG Welding.

Abstract: This paper deals with the problem concerning the sensing and the controlling of weld pool. In order to obtain the high quality of the welding result, it is important to control the weld pool depth in the robotic welding regardless of the external disturbance such as an irregular change of the groove gap. The method of controlling the weld pool depth without mathematical model is discussed.Since it is difficult to directly measure the depth, the depth is estimated from the surface shape of the weld pool, the groove gap, and the welding current. A neural network is used to estimate the depth without mathematical model. The weld pool depth is controlled from the output of the neural network by using the fuzzy controller. The validity of the neural network and of the fuzzy controller was verified by the welding experiments.

チタン/aisi304lステンレス鋼の摩擦圧接で生じる残留応力・ひずみ分布の特徴とそれらの生成機構

Abstract: In order to elucidate the characteristics of residual stress and plastic strain produced by the dissimilar friction welding operation, detailed FEM modelling was carried out. The obtained main results are as follows :(1) During numerical modelling of residual stress and plastic strain formation in dissimilar joints, the distribution of δz (axial component) in the radial direction produced by uniform cooling from 800°C, in material adjacent to the bondline in both substrates, provides an effective means for evaluating the accuracy of the computational procedure in dissimilar materials welds.(2) Heat transfer into a narrow zone, z=±20 mm on either side of the bondline promotes residual stress formation. The peak temperature occurs in the AISI304L substrate.(3) Adjacent to the bondline, σr (radial component) is tensile in the higher thermal expansion substrate (AISI304L), and is compressive in the substrate (titanium) with the lowest thermal expansion value. σz is tensile in the central region of the component (where the stiffness is large) and is compressive at the periphery of the component.(4) The σz distribution in the axial direction, in material far from the bondline, indicates that σz is compressive in the central region of the component and is tensile at the component periphery. Specially, σz is tensile in titanium substrate, except in regions extremely close to the bondline at the periphery of the component.(5) Considerable plastic strain is produced perpendicular to the bondline and in the radial direction. Limited plastic strain occurs in the circumferential direction.(6) Severe plastic strain is produced in titanium substrate close to the bondline. This region in titanium close to the bondline has a hardness 1.5 times higher than in the base metal.

Effect of Welding Parameters on Hot Cracking Susceptibility of Alloy 800

Abstract: The varestraint cracking test was carried out to assess the hot cracking tendency of alloy 800 at different welding conditions and augmented strain levels. The test results revealed that the hot cracking susceptibility of alloy 800 increases with increasing the heat input and augmented strain levels. This emphasizes the role of constraint either internally induced or externally applied to the welded structure.A cracking threshold or the minimum augmented strain (∈min) below which no hot cracking takes place has been found to be 0.25 for alloy 800. Also, the Critical Strain Rate to Time (CSS) required to cause cracking was found to be 6.42×10-3 sec-1 at welding condition of 100 Amp, 13 Volt and 140 mm/min.

Surface Alloying of Aluminum Alloy using Fe Powder by Laser Alloying Process.

Abstract: Laser alloying process has been investigated to make a thick hardened alloyed layer on the surface of commercial aluminum alloy (A5052) plate using the powder mixtures of Al with 20, 50, 70 and 100 mass% Fe. The measured hardeness and wear resistance of alloyed layer have been discussed in relation to the microstructure of alloyed layer. The optimum traveling speed to obtain a smooth surface decreases with the increase in Fe content in the powder mixture. There were four types of the microstructural morphologies in alloyed layer depending on Fe content in the powder mixture and traveling speed, namely cellular dendrite, needle-like FeAl3, fine needle-like FeAl, and lump-like Fe2A15. The hardness of alloyed layer with needle-like FeA13i fine needle-like FeA13 and lump-like Fe2Al5 were HV100-200, HV300-500 and HV700-900, respectively, though cracking occurred in the case of lump-like Fe2A15 structure. The wear resistance of alloyed layer increased with the increase in hardness. The most desirable structure of alloyed layer for wear resistance was that with fine needle-like FeA13 having 29-34 mass% Fe.

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Effect of Friction Welding Parameters on Mechanical Properties of Cast Iron Joints

Abstract: The feasibility of using friction welding was used to join similar kinds of cast irons was studied. This study was carried out to examine influence of welding parameters on tensile properties of friction welded joints by similar materials of spheroidal graphite iron castings and gray iron castings. It was found that cast iron, which is difficult to join by fusion welding, can be joined by friction welding without resorting to special measures such as precheating or postheating. Under proper welding conditions, the friction welds are defect free. This paper describes process parameters during friction welding which governing mechanical properties. Materials were selected two types of cast irons, spheroidal graphite iron castings and gray iron castings with flaky graphites which are called ductile cast iron and gray cast iron hereafter in this paper. The friction welding conditions for similar kinds of cast irons in the same diameter can be defined either by the minimum heat input rate or by the friction upset speed. The tensile strength of the joint increases with decreasing heat input rate or upset speed and it is possible to obtain joint strengths equal to that of the base metals.

A Comparison of the Conventional and Reverse Houldcroft Type Hot Cracking Tests in A5052 Aluminum Alloy Sheet

Abstract: The influence of the heat input on the crack ratio (length of crack versus welded length) has been investigated using both the conventional and reverse Houldcroft type hot cracking tests for A5052 aluminum alloy sheet. In the conventional type test, where the temperature distribution around the molten pool is the main factor, the crack ratio decreased linearly when the heat input increased. In the reverse type test, where restraint is the main factor instead of the temperature distribution, the crack ratio increased when the heat input increased. This is the same tendency which is experienced actually in welding. Hence, the reverse type test is recommended as a better test. The study also showed that the crack would propagate more easily in the case of equiaxed dendrites than in the case of columnar crystals.The rotation angle at the tip of the crack was observed using.a video camera from the back side of the specimen. The rotation angle had a maximum value of about 0.08 rad near the start of the welding, and decreased gradually as the crack propagated. The crack stopped when the rotation angle reached from about 0.01 to 0.03 rad. It was made clear that the rotation angle greatly influences the propagation and arrest of the crack.

すみ肉溶接における固有ひずみの関数表示とその精度 : 固有ひずみ分布の関数表示による残留応力の推定法と測定法(第4報)

Abstract: In this paper, three dimensional residual stresses due to single pass and multipass fillet welding are analysed by thermal elastic-plastic Finite Element Method. Then, inherent strain distributions produced in fillet welds are expressed by series function with good accuracy. Based on the results of series function, a very simple distribution pattern of inherent strains is proposed and described as functions which only has a few unknown parameters. To determine these parameters by experiments, required measurements will be greatly reduced.

Zr添加試作Al-高Mg溶接ワイヤと低周波パルスミグ溶接法の併用によるAl-Zn-Mg3元系合金の溶接凝固割れ感受性の改善

Abstract: Solidification crack susceptibility of GMA weld metal of Al-4.5%Zn-1.2%Mg A7N01 base metal has been successfully improved by combination of low frequency switching pulsed GMAW process and Zr added Al-7%Mg tentative wire. Close relationship between grain size of weld metal and crack susceptibility was observed and remarkable reduction in crack susceptibility was obtained in weld metal with fine equiaxed grains of 20 to 30 μm in diameter. This marked grain refinement can be obtained only by the combination of low frequency switching pulsed GMAW of 2.5 to 50 Hz and Zr added Al-7%Mg tentative wire. No considerable grain refinement was observed with Zr-free wire. Relationship between oscillation behavior of molten pool caused by current pulsation and grain refinement was discussed.

Modeling of Weld Pool Oscillation using Energy Method

Abstract: An analytic model estimating the natural frequency of a weld pool is derived using energy method. The model is applied to the complex weld geometries, penetration conditions and oscillation modes. In addition to partial and full penetration, transition penetration is introduced and analyzed as the intermediate state between partial and full penetration conditions. Results show that the predicted natural frequency of the weld pool is affected by oscillation modes and geometric parameters such as the eccentricity and sidewall slope of the weld pool as well as material properties and pool dimensions.

Toughness Deterioration and Its Improvement of Weld HAZ with High Heat Inputs in 780 and 980 MPa Class HSLA Steels (Report 3). Decomposition Behavior of M-A Constituent and Recovery of Toughness.

Abstract: The decomposition of M-A constituent by PWHT (Post Weld Heat Treatment) and its effects on the toughness have been investigated for the weld CGHAZ (Coarse Grained Heat Affected Zone) of HSLA steels of 780-980 MPa classes.As the PWHT temperature and time were increased, the area of the M-A constituent was decreased for all the steels employed, but dependence of the toughness of the 980 MPa class steels on PWHT parameters was quite different from that of the 780 MPa class steels. For the weld CGHAZ of 780 MPa class steel, the toughness was increased, as the M-A constituent was decomposed into ferrite and cementite by the PWHT. For the weld CGHAZ of 980 MPa class steel, however, embrittlement occurred at PWHT temperatures above 823 K though the toughness was increased with PWHT time at temperature below 623 K.From these results, it can be concluded that the toughness of HSLA steels impaired by the high-heat-input welding can be improved significantly by PWHT at temperature about 623 K.

Fracture Toughness Evaluation of Multipass Weld HAZ with Focus on Mechanical Mis-Matching Effect.

Abstract: HAZ-notched CTOD tests have been conducted for multipass welds of high strength steels with SMYS 420 to 460 MPa for offshore structural use. The weld metal strength overmatch brings about different fracture behaviors depending upon the actual CGHAZ toughness. In the case that the CGHAZ is completely embrittled, the weld metal overmatch leads to lower bound critical CTOD value. This is due to the elevation of the local stress in the CGHAZ caused by the constraint effect by the overmatch weld metal. The fracture surface is generally flat and brittle fracture originates from the CGHAZ sampled by the fatigue crack front. Larger fraction of the CGHAZ along the crack front gives smaller critical CTOD value. On the other hand, in the case that the CGHAZ has moderate toughness, the weld metal overmatch can produce a higher critical CTOD value at brittle fracture initiation. This is attributed to the crack path deviation toward the base metal. The plastic strain accumulates preferably to a larger extent in the softer base metal side, before the critical stress condition for brittle fracture is attained at the CGHAZ. This asymmetrical plastic deformation promotes the deviation of ductile crack growth from the crack tip CGHAZ. In such a case, the critical CTOD value does not always reflect the CGHAZ toughness itself.Notch tip location much closer to weld metal sometimes causes fracture initiation at the weld metal even if the fatigue crack tip samples the CGHAZ. Such test data can not tell the real CGHAZ toughness.The meaning of critical CTOD value obtained in the test must be identified in the fracture toughness eveluation of the weld CGHAZ. This paper presents an evaluation procedure for CTOD test results of HAZ-notched welds taking the mis-matching effect into account.

活性金属法によるAlNと金属の接合部組織 : 窒化アルミニウムと金属の接合に関する研究(第1報)

Abstract: Brazing of AlN to metals was conducted at 1073-1293 K for 0-129.6 ks using active filler metals of Cu-22%Ti, Cu-10%Zr, Cu-15%Hf binary alloys and Ag-27%Cu-2%Ti ternary alloy. The reaction layer which was comprised of TiN, ZrN or HfN was formed at the bonding interface between AlN substrate and the brazing layer, and eutectic phases such as Cu-Cu4Ti were detected in the brazing layer when binary filler metals were used for AlN to copper joining. TiN was identified in the reaction layer of AlN-molybdenum joint brazed using ternary filler metal. The thermodynamic calculation suggested that TiN, ZrN and HfN were produced by the interfacial reaction between AlN and active metals in the melted binary filler metals.

アロイ800の液相拡散接合用インサート金属の開発 : 数理計画法による接合用インサート金属組成の最適化(第1報)

Abstract: This report presents a new alloy-designing technique to develop the insert metal for liquid diffusion bonding. A mathematical programming method was developed by modifying the method in two dimensions proposed by I.P. Schagen into multi dimensions. The main procedure of this method is to obtain the optimum point to maximize some index of an objective performance by calculation from the limited experimental data using interpolation. An interpolating function which yields a curved surface passing on all the specified data points was determined assuming the values of data were normally distributed. If the curved surface is once obtained, its general view will give suggestions for further searches and the optimum point can be efficiently searched. This method has been applied for developing the insert metal for liquid diffusion bonding of Alloy 800. As for the candidate insert metals, alloys which had similar composition to that of Alloy 800, but contained some amounts of silicon, boron and carbon as the depressant elements were chosen. The objective function which was introduced as an index of the performance of insert metals involves the melting point, the strength (hardness) and formability of brittle phases in the bonding interlayer as the evaluating factors. Through calculation based on twenty three experimental date, a composition of Fe-20Cr-30Ni-1.5B-0.75C-4Si which optimized the objective function was determined. Scanning electron microscopic analysis revealed that the joint bonded with the newly developed insert metal (Fe-20Cr-30Ni-1.5B-0.75C-4Si) had a sound microstructure without forming brittle phases in the bonding interlayer. This joint also exhibited good tensile properties, that is, its strength and ductility were comparable to those of the base alloy.

Study on welding of zirconium alloy tubing (report 3). TIG welding phenomenon and properties of welds in welding atmospheres with various oxygen and nitrogen partial pressures (part 1)

Abstract: The purpose of this study is to investigate the influence of extremely low levels of oxygen and nitrogen partial pressure, Po2 and PN2 in TIG welding atmospheres on the welding phenomenon and properties of welds of zirconium alloy tubing.In TIG welding of Zircaloy-2 tubing in welding atmospheres with various Po2 and PN2, the arc voltages were measured and the properties of welds (surface discoloration, oxygen and nitrogen contents) were examined.Although definite arc voltage change is not observed at welding in ≤ 4.1 Pa of Po2, a significant arc voltage drop with increase of PN2 is observed at welding in 0.4-16.9 Pa of PN2, and oxygen appears to inhibit this arc voltage drop.The surface of weld metal and heat affected zone (HAZ) in the atmosphere of 0.1 Pa of Po2 and 0.4 Pa of PN2 remains bright.The surface discoloration is observable slightly on weld metal and HAZ in the atmosphere of 1.1 Pa of Po2, and with increase of Po2 the initial straw color becomes darker until it gets partially blue.No surface discoloration is observable on weld metals and HAZ in the atmospheres of PN2 - 16.9 Pa with 0.1 Pa of Po2.The nitrogen content [N] in the weld metal increases linearly with increase of √PN2 and the increasing rate of [N] in inner part of weld metal is lower than that of [N] in outer part.The oxygen content [O] in the weld metal increases linearly with increase of √Po2 and shows same relations as [N], although the values of [0] in the weld metals fluctuate more than [N].

溶接後熱処理による溶接継手部の靱性改善に関する検討 : 80及び100キロ級高張力鋼大入熱haz部の靱性劣化とその改善に関する研究(第4報)

Abstract: In order to determine optimum parameters of PWHT (Post Weld Heat Treatment) for improving the toughness of HAZ of 780 and 980 MPa class HSLA steels welded with high heat inputs, the effect of PWHT on the toughness of simulated weld HAZ of the steels has been systematically investigated in relation to the decomposition of the M-A (Martensite-Austenite) constituent.The optimum PWHT time and temperature proposed by considering the practical workability are 8 hr's and 623 K for the weld CGHAZ (Coarse Grain HAZ) and ICCGHAZ (Intercritically Reheated CGHAZ) of the employed steels of 780 and 980 MPa classes.The optimum PWHT parameters have been tested on specimens actually welded with a heat input twice as high as the conventional. The toughness of the actually welded specimen, estimated from CTOD value, is also improved significantly by PWHT under the proposed conditions, and satisfies demands for practical application. The tensile strength of the actually specimen welded with a heat input twice as high as the conventional, estimated from wide tensile test pieces, has been presumed to satisfy the specification of weld joint using 780 MPa class HSLA steel.The tensile strength of the actually welded joint, although it includes the HAZ softening zone, is calculated to be a value satisfying the specification of 780 MPa class steels, provided that the width of the test specimen is more than 5 times as large as the thickness.

Development of Stress Relief Method for Weld Joint of Pipe using Ice Plug

Abstract: A stress relief method using ice plug for butt weld joint of piping is described. The method is as follows. Two ice plugs are formed inside piping, and isolate a section which include weld joint. An internal pressure of isolated section increases as ice plugs grow, and it gives tensile strain to pipe wall of the section. After the pressure reaches target level, the pressure is released and the residual stress decreases. The stress relief method is named by authors as Twin Ice Plug (TIP) method. This paper described details of this process, measuring of internal pressure from outside of piping, controlling internal pressure, and the effect of stress relief.The internal pressure of isolated section is estimated by the strain measured by strain gauge on outer surface of the section. A control of a pressure of the section is done by controlling supply rate of refrigerant (LN2) and heating pipe wall. The maximum internal pressure reached in this method is 40 MPa for 4BSch4O (O.D.=114.3 mm, t=6.0 mm) stainless pipe and 22.5 MPa for 6BSch4O (O.D.= 165.2 mm, t=7.1 mm). The residual stress of as GTA weld joint of stainless pipe is measured, its maximum value is more than +300 MPa. The effects of this method are confirmed by measuring residual stress of 4BSch40 6BSch40 joints that are treated by this method. The residual stress of inside surface decreases and changes to compression, and that of outside surface also decreases to under 100 MPa.