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QUARTERLY JOURNAL OF THE JAPAN WELDING SOCIETY Vol. 6 (1988), No. 3

ISIJ International
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ONLINE ISSN:
PRINT ISSN: 0288-4771
Publisher: JAPAN WELDING SOCIETY

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QUARTERLY JOURNAL OF THE JAPAN WELDING SOCIETY Vol. 6 (1988), No. 3

Experimental Study on Restraint Intensities of Fillet Welded Joints

Akio Itoh, Noboru Watanabe

pp. 330-335

DOI:

10.2207/qjjws.6.330

Abstract

This paper presents the results of the following experimental study: the intensity of tensile restraint (RF) of tack-welded joints and the intensity of bending restraint (KB) caused by side fillet welding performed as onesided welding, using I-section girders and hollow cylinders as structures.
In this paper, RF values are defined as the product of the intensity of tensile restraint coefficient (p) and the plate width (h). After tack-welding, p values were measured. Subsequently, welding was conducted: after cooling off, we observed the occurrence with or without cold cracking in the welded joints. The effect of KF on RB values and the relationship with the weldment cracking parameter (Pw), etc. were then determined. The major findings of this investigation are as follows.
1) The coefficient p for girders and cylinders is influenced by the geometrical mean thickness among the vertical and horizontal plates; it is influenced not so much by the number of joints as by the location along the wled line.
2) The effect of KB of girders and cylinders on the coefficient p was determined. In other words, the coefficient p in both kinds of models showed a tendency to decrease under the influence of the bending restraint. However, it was observed that even as KB increases, the p values for the girders and cylinders converge approximately on 8 and 4-5 kN/mm.mm/mm, respectively.
3) The occurrence of cold cracking of girders can be determined by using the relation between Pw and Tcr of butt joints (graph) as RF increases, even in the case of high KB values. On the other hand, for cylindrical models, cracks were sometimes observed in the welded joints with relatively small KB and RF values; thus, making it very difficult to judge cold cracking from relational graph mentioned above.

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Experimental Study on Restraint Intensities of Fillet Welded Joints

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A Proposal of Evaluating Method for Reheat Crack from Mechanical Point of View

You Chul Kim, Teruhisa Yamakita, Han Sur Bang

pp. 335-340

DOI:

10.2207/qjjws.6.335

Abstract

Usually, stress relief annealing (SR) treatment among various PWHT (post weld heat treatment) are widely performed for the purpose of removement of the welding residual stress and softening of the welded joint. However, a crack (namely SR-crack) at the notch of the coarse grained zone in the heat affected zone (HAZ) of the welded joint may be produced anew by SR-treatment although it improves the quality of the welded joint.
In this paper, making a comparison of the mechanical behavior during SR-treatment between with the notch and without one at the coarse grained zone in HAZ of the welded joint, the influences of the existence of the notch on the stress-strain are clarified. Moreover, a mechanical measure for the reheat crack (SR-crack) is proposed and an evaluating method for it is shown from a mechanical point of view.

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A Proposal of Evaluating Method for Reheat Crack from Mechanical Point of View

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Study on Residual Stress Measurement on Plasma Sprayed Coatings

Akira Noutomi, Masaru Kodama, Toyoaki Ono, Yoshiaki Inoue, Masakazu Kawano, Noboru Tani

pp. 341-347

DOI:

10.2207/qjjws.6.341

Abstract

In order to measure residual stresses in plasma sprayed coatings (Ni-Cr alloy, ZrO2-20%Y2O3), the authors measured at first X-ray stress coefficient K and Young's modulus E of the coating material and then investigated the effect of plasma spraying conditions on the residual stresses by X-ray diffraction method.
The stress relaxation method with a strain gauge was used also to measure stress values for comparison with the values measured by X-ray diffraction method.
The results obtained are summarized as follows;
1) X-ray stress coefficient K and Young's modulus E of coatings are very small in comparison with those of bulk materials.
2) The tensile residual stress values on the Ni-Cr coatings measured by the stress relaxation method are about 30% higher than those measured by X-ray diffraction method.
3) The residual stresses on the Ni-Cr coatings are affected neither by coating thickness nor by spraying distance, but are tend to decrease as the temperature of the base metal rises.
4) No residual stresses on the ZrO2-20%Y2O3 coatings are recognized.

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Study on Residual Stress Measurement on Plasma Sprayed Coatings

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Theoretical Determination of the Sizes of Standard Model and Effect of Chages in Heat Input and Kind of Steel on Inherent Strain

Yukio Ueda, Min Gang Yuan

pp. 348-353

DOI:

10.2207/qjjws.6.348

Abstract

This paper proposes a method to determine the sizes of the standard model which is used in the proposed predicting method of welding residual stress, since the model is necessary for estimating the inherent strain (the source of the residual stress) produced in a joint. In this paper, the method is applied to a butt-welded joint.
Based on the distributions of inherent strain in a butt-welded joint that had been obtained before, it is also shown how to modify them in accordance to the changes of heat input and the kind of steel including the effect of phase transformation.

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Theoretical Determination of the Sizes of Standard Model and Effect of Chages in Heat Input and Kind of Steel on Inherent Strain

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Investigation on the Phenomena of High Speed One-side Welding of Thin Sheet Paying Attention to Arc Force

Katsuhiko Yasuda, Teruhiko Hinata, Takashi Jimma, Tadao Onzawa

pp. 362-366

DOI:

10.2207/qjjws.6.362

Abstract

Paying special attention to the arc force, the welding phenomenon of high speed one-side welding of thin sheet was investigated.
In high speed and high current one-side welding method, the arc force becomes very strong. The solid surface is produced at the front part of the molten pool by this strong arc force and others. But the high speed one-side welding of thin sheet is possible using high current TIG and plasma arc welding method because the strong arc force effects to this solid surface. However, in the case of these welding, the face bead becomes undercut bead.
In spite of high welding current, the arc force holding forward torch angle keeps lower level. So this method is more effective for high speed one-side welding. Especially, using the knife-edge electrode with forward torch angle, these tendency becomes more effective.

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Investigation on the Phenomena of High Speed One-side Welding of Thin Sheet Paying Attention to Arc Force

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On the Oxygen and Nitrogen contents of Submerged Arc Welding Stage

Kanichiro Shimizu, Nobuya Iwamoto, Yukio Makino, Taisuke Akamatsu

pp. 367-374

DOI:

10.2207/qjjws.6.367

Abstract

The change of the contents of oxygen and nitrogen in the electrode wire tip, droplet and weld metal of the submerged arc welding was studied by varying the arc voltage and welding speed.
The results obtained are summarized as follows.
(1) The oxygen and nitrogen contents in the electrode wire tip are far higher than the level of the wire by the influence of the partial pressure.
(2) At the electrode wire tip the reactions of the silicon and manganese occur considerably.
(3) The oxygen and nitrogen contents in the droplet metal increase as the welding speed increases.
(4) The estimated oxygen and nitrogen contents of droplet metal with the welding speed 40 cm/min decreases than the level of electrode wire metal.
(5) In the droplet metal deoxidation reaction occur during flight in the arc.
(6) The oxygen and nitrogen contents are remarkably different by the exposure time in the gas phase and flight pass of droplet metal.
(7) The oxygen content of weld metal is lower than the level of droplet metal and the nitrogen content of weld metal is higher than it.

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On the Oxygen and Nitrogen contents of Submerged Arc Welding Stage

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Fatigue Strengths of Solid State Bouded Joints of Spheroidal Graphite Cast Irons

Shizuo Mukae, Kazumasa Nishio, Mitsuaki Katoh, Shintaro Abe

pp. 374-381

DOI:

10.2207/qjjws.6.374

Abstract

Fatigue strengths of diffusion bonded joints of spheroidal graphite cast irons and the spheroidal graphite cast iron to a mild steel have been investigated using the rotating bending fatigue test machine. The results obtained are as follows; (1) When tensile strength of the base metal of the spheroidal graphite cast iron was 500 to 800 MPa, the fatigue limit of these joints was a nearly constant value of 240 to 250 MPa though that of the base metal increased as the tensile strength of the base metal increased. (2) Fa-tigue strength at 105 and 106 cycles in the spheroidal graphite cast iron joint which was annealed to be changed the structure from ferrite+pearlite to all ferrite was almost the same as that of the base metal of the ferritic spheroidal graphite cast iron. However, the fatigue limit of the joint was lower than that of the base metal by 20 MPa. (3) Fatigue strengths at 105 and 106 cycles in the joint of the cast iron to the mild steel and after ferritizing of the joint were almost the same as that of the base metal of the ferritic spheroidal graphite cast iron. (4) When the joint of spheroidal graphite cast iron having the tensile strength of about 500 MPa was heat-treated at 950°C for 21.6 ks, the fatigue limit was improved up to that of the base metal.

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Fatigue Strengths of Solid State Bouded Joints of Spheroidal Graphite Cast Irons

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Study on Ti-6Al-4V Alloy Brazed with Ag-5Al-0.5Mn Filler Metal

Hiroshi Izui, Yoshifumi Suezawa

pp. 381-387

DOI:

10.2207/qjjws.6.381

Abstract

This paper summarized the effect of brazing temperature and time on the joint properties of Ti-6Al-4V alloy brazed with Ag-5Al-0.5Mn filler metal. The brazing was performed in a resistance heating type vacuum furnace. The brazing temperatures and times were ranging from 1143 K to 1203 K and from 0 to 30 minites respectively. Microscopic, EPMA, and X-ray diffraction analysis were carried out to investigate the microstructure of the brazed joints. Tensile tests of brazed joints were performed on each brazing condition.
The obtained results were summarized as follows:
(1) Silver and aluminum diffused into the base metal and some types of intermetallic compounds were formed at the brazing interfaces. The thickness of reaction layer increased with increasing brazing temperature and brazing time.
(2) Brazing at 1173 K for 10 min gave the maximum tensile strength of brazed joint.

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Study on Ti-6Al-4V Alloy Brazed with Ag-5Al-0.5Mn Filler Metal

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The Nitrogen Absorption of Arc-Melted Fe-Cr and Fe-Ni Alloys

Takeshi Kuwana, Hiroyuki Kokawa, Naoki Muramatsu

pp. 388-394

DOI:

10.2207/qjjws.6.388

Abstract

Fe-Cr and Fe-Ni alloys were melted by tungsten arc-melting under argon-nitrogen gas mixture at-mospheres with various melting conditions in order to study effects of chromium and nickel on the nitrogen absorption of arc-melted iron. In Fe-Cr alloys with chromium more than 8%, the nitrogen content decreases with increasing the arc current. In Fe-Cr alloys with chromium less than 5.6% and Fe-Ni alloys, the nitrogen content increases slightly with the arc current. In all alloys, the nitrogen content increases with the arc-melting time and then reaches the saturated value which increases with the nitrogen partial pressure of the atmosphere, but does not obey the Sieverts' law. The nitrogen content of arc-melted iron increases remarkably with the chromium content, while decreases slightly with increasing the nickel content. The nitrogen absorption of the arc-melted alloys was discussed thermodynamically with measured temperatures of the molten alloys during arc-melting.

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The Nitrogen Absorption of Arc-Melted Fe-Cr and Fe-Ni Alloys

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Behaviors of Solidification Front, Initiation and Propagation of Bolidification Crack

Fukuhisa Matsuda, Hiroji Nakagawa, Shogo Tomita, Kazuhiko Sorada

pp. 394-400

DOI:

10.2207/qjjws.6.394

Abstract

A new technique named MISO has been invented by the authors, in which solidification front and/or hot cracking during welding is photographed with camera mounted on optical microscope and analyzed with film analyzer. The MISO technique was applied to welding of stainless steels, Inconel alloy 600 and plain carbon steels. The technique revealed next phenomena: (1) The apparent solidification range where liquid was clearly observed with cellular dendrite growing was only 20 to 35% of the true solidification range measured as brittleness temperature range (BTR). (2) Initiation of solidification crack in a high strain rate with tensile hot cracking test occurred near the solidification front. These were well explained by the calculation of solid fraction vs. temperature relation and fractography. Furthermore, all these suggested that so-called liquid film stage occurs comparatively near the liquidus temperature, and that the about lower half of BTR is liquid droplet stage where the liquid phases locate discontinuously at interdendritic boundary. Based on these, a modification of the "Generalized theory" seems to be necessary in terms of crack susceptibility vs. temperature relation in solid-liquid coexistent region.

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Behaviors of Solidification Front, Initiation and Propagation of Bolidification Crack

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Measuring of Critical Strain for Initiation of Solidification Crack by Rapid Tensile Cracking Test

Fukuhisa Matsuda, Hiroji Nakagawa, Shogo Tomita, Hiroaki Kohomoto, Yoshioki Honda

pp. 401-405

DOI:

10.2207/qjjws.6.401

Abstract

The MISO technique, invented by the authors to observe dynamically the behaviors of solidification front and solidification cracking during welding, has been expanded to measure the critical strain required for initiation and propagation of solidification crack. For this purpose, dotty marks in high speed cine photos resulting from ruggedness on macrostructure on weld metal surface have been utilized as the re-ference points of gauge length to measure the dynamical change of the strain. The optimum gauge length has been shown to be 1 to 2 mm on the basis of feasibility, although the critical strain has been increased with shortening of gauge length. This technique has been applied to a tensile hot cracking test under the condition of high strain rate for carbon steels and stainless steels, and the critical strain measured has been shown to be more precise and reasonable than that measured by the Varestraint cracking test.

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Measuring of Critical Strain for Initiation of Solidification Crack by Rapid Tensile Cracking Test

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Microstructures of Synthetic Weld Heat-Affected Zone of Nodular Graphite Cast Irons and Strength of Cast Iron Welds

Shosuke Itomura, Kenki Heshiki, Fukuhisa Matsuda, Yoneo Kikuta

pp. 406-411

DOI:

10.2207/qjjws.6.406

Abstract

Microstructures and martensite transformation start (Ms) temperatures of the synthetic weld heataffected zone of two types of nodular graphite cast irons, FCD40 and FCD60, are investigated. The thermal cycles of the test pieces, 3 mm in diameter and 10 mm in length, are simulated to those of real arc welding; test pieces are rapidly heated to a temperature about 1100°C in 4 seconds, then cooled to room temperature. Implant cracking tests using smoothed 6 mm in diameter specimens FCD40 are also carried out with and without preheating.
When the peak temperature of the specimens were made higher, the Ms temperature became lower; from about 300°C to below 200°C. Though two types of cast irons had different matrices at room temperature, the Ms temperatures of those were nearly same. This means that, in spite of very short holding time, the minimum carbon content of matrices of both irons become nearly equal, when they are heated to high temperature near melting point. This concept was proved from the results of the implant tests of FCD40 showing same critical strength of welds, about 28OMPa, and martensitic fracture structure as previous work for FCD50 and FCD60.

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Microstructures of Synthetic Weld Heat-Affected Zone of Nodular Graphite Cast Irons and Strength of Cast Iron Welds

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Comparison of Sensitization of Explosively Bonded and of Welded Stainless Steel Plugs

Yoshihiko Mukai, Masato Murata

pp. 411-415

DOI:

10.2207/qjjws.6.411

Abstract

Plug bonding method was often applied to prevent accidents of failure in heat exchangers. In these cases, the plug bonded region would be subjected to low temperature sensitization in the service period.
Then the susceptibility to low temperature sensitization of explosively bonded and welded plugs was compared. The main results are as follows. In case of welded plugs, corriosion attack was concentrated to grain boundaries in HAZ by Strauss test. On the otherhand, the susceptibility to low temperature sensitization of the explosively bonded plugs was comparatively higher than expected, because of carbide precipitation occuring spontaneously with the disappearance of martensite. And corrosion had propagated along prior martensite lath where many carbide particles had precipitated.

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Comparison of Sensitization of Explosively Bonded and of Welded Stainless Steel Plugs

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Sizes of Tensile Specimen for Estimation Strength of Joint without Defect

Toshio Terasaki, Tetsuya Akiyama, Akio Yao, Masanobu Matsuo, Kenji Seo

pp. 415-420

DOI:

10.2207/qjjws.6.415

Abstract

Specimen size for obtaining joint strength of dissimilar materials subjected to tension has been investigated by using numerical method and experiment. Stress distributions along the bond are calculated by the Finite element method with 8-node distorted element. It was shown that both the residual stress produced by changing temperature and the stress produced by load were dominated by similar law. Tensile test of diffusion bonded joint of dissimilar materials of Ti and Cu was done. The following conclusion is obtained; When the length of tensile specimen is longer than 8 times of diameter of round bar, specimen size does not affect the tensile strength.

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Sizes of Tensile Specimen for Estimation Strength of Joint without Defect

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Effect of Laser Remelting of Weld Toe on Fatigue Strength of Aluminum Alloy A5083P-O Welded Joint

Isao Masumoto, Muneharu Kutsuna, Masayoshi Hasegawa

pp. 420-425

DOI:

10.2207/qjjws.6.420

Abstract

The effect of laser remelting of weld toe on fatigue strength of A5083P-O aluminum alloy welded joint (plate thickness: 6 mm) was investigated using 2 kW CO2 laser facility with an intersecting and rotating optical system.
The following experimental results were obtained;
1) The fatigue strength of welded joint was increased by laser remelting of the weld toe, when the travel speed was 500 and 800 mm/min at laser power of 2 kW.
2) The main reasons for the improvement in fatigue strength were the increases in radius of weld toe and hardness of remelted zone by laser remelting.
3) The influence of travel speed on microcracks of remelted zone was significant, and crack sensitivity of remelted zone increased with decrease of travel speed less than 500 mm/min.
4) These cracks were considered to be hot cracking due to significant segregation of magnesium on grain boundary.

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Effect of Laser Remelting of Weld Toe on Fatigue Strength of Aluminum Alloy A5083P-O Welded Joint

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Near Threshold Fatigue Crack Propagation in Welded Joints under Random Loadings

Akihiko Ohta, Yoshio Maeda, Susumu Machida, Hitoshi Yoshinari

pp. 426-430

DOI:

10.2207/qjjws.6.426

Abstract

62 level block fatigue loadings in which waveform were approximating to the Rayleigh distribution of peak (distribution factor=0.25, 0.5 and 1) were applied on center cracked transverse butt welded joints in which tensile residual stresses were always induced at the crack tip. It was revealed that the fatigue crack propagation rate, da/dn*, could be estimated by the result obtained at constant amplitude tests assuming linear cumulative damage law. That is,
da/dn*=C(ΔK*eqm-ΔKmth)whereΔK*eq={(ΣΔKmi ·ni)/ni}1/m,
ni=0 at ΔKi≤ΔKth or ni=ni at ΔKi>ΔKth.

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Near Threshold Fatigue Crack Propagation in Welded Joints under Random Loadings

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Application of one side Welding to Field Girth Joint of Big Scale Penstock

Ryuji Shimoda, Toshihiko Matsuura, Yukiomi Nishigami, Takeshi Sakai

pp. 431-435

DOI:

10.2207/qjjws.6.431

Abstract

Big scale penstock for the hydropower station is mostly an embedded type to be constructed in the underground tunnel. In addition, due to the increase of the penstock capacity, the superior quality of the joint performance is required with the steel materials of heavier thickness and higher strength.
For the construction of such embedded penstock of big scale, it is essential to overcome the severe conditions of the field welding work under high temperature and high humidity in the tunnel for securing superior joint performance, and to minimize the sectional area of the tunnel for expediting the construction periods and costs of civil work.
To fullfil above two requirements for the field welding of penstock, automatic GTA welding method with remote control system and one side URANAMI welding method with backing metal were developed.
The former was developed to enable the excellent joint performance under the severe field conditions, and the latter was developed to enable the field welding only from the inside of penstock in the narrow tunnel.

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Application of one side Welding to Field Girth Joint of Big Scale Penstock

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Effect of Alloying Elements on surface Hardening Behavior of Ni Alloys by means of PIN Process

Fukuhisa Matsuda, Kazuhiro Nakata, Takashi Makishi, Sigeru Kiya

pp. 436-441

DOI:

10.2207/qjjws.6.436

Abstract

Tentative Ni binary alloys containing nitride forming elements such as Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, Mn, Fe, Al and Si were nitrided by PIN process under the conditions of 873K, 10.8 ks, N2+H2 mixed gas atmosphere of 800Pa.
Surface hardening was observed in all Ni alloys used, however surface hardness were much different with depending on the kind of alloying elements and its contents. Maximum surface hardness were approximately Hv 550-800 for Ti, V, Nb and Cr containing alloys with more than 4, 4, 10 and 20wt%, respectively, and Hv 300-400 for Mo, Fe and Mn containing alloys more than 20, 30 and 30wt%, respectively, but Zr, Hf, Ta, Al and Si containing alloys were only slightly hardened as Hv 200-300. By using hardness increasing rate of each alloying elements, an equation to estimate the surface hardness of Ni alloy after PIN treatment was drawn and it was confirmed that there was a good agreement between measured and estimated hardness for various kinds of commercially used Ni alloys.
From results of EPMA and X-ray analyses, it was considered that surface hardening was due mainly to lattice strain of a matrix of nitrided layer caused by dispersive precipitations of fine nitrides of each alloying elements.

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Article Title

Effect of Alloying Elements on surface Hardening Behavior of Ni Alloys by means of PIN Process

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Measurement by Laser Flash Method of Thermal Diffusivity of Two-Layer Composites

Katsunori Inoue, Etsuji Ohmura

pp. 442-446

DOI:

10.2207/qjjws.6.442

Abstract

A flash method of determining the thermal diffusivity of one layer of two-layer composites with the thermal contact resistance at the interface; of the layers is described. A flash pulse is absorbed in the front surface of a thermally insulated specimen, and the resulting temperature history of the rear surface is measured by a radiation thermometer and recorded with a transient memory and a recorder. The time required for the temperature to rise 30 and 70 percents, for example, of the maximum temperature increase is read from the temperature versus time curve. These results are used for the numerical computation based on the theoretical equation of the normalized temperature increase on the rear surface and the method of bisection, and the thermal contact resistance can be obtained easily as well as the thermal diffusivity. The fundamental equation of the temperature increase on the rear surface in the present one-dimensional heat conduction problem is derived by Laplace transform. The present method is applied to some joining specimens whose thermophysical properties have been all measured in advanced by the laser flash halftime method, and the effectivneess of this method is confirmed. The thermal contact resistance is also measured in addition by another method proposed in this study, and these obtained results are in fairly good agreement each other.

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Measurement by Laser Flash Method of Thermal Diffusivity of Two-Layer Composites

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Estimation of Accuracy in Measurement by Flash Method of Thermal Diffusivity of Two-Layer Composites

Katsunori Inoue, Etsuji Ohmura

pp. 446-450

DOI:

10.2207/qjjws.6.446

Abstract

Accuracy in determining by the flash method proposed by the authors of the thermal diffusivity of one layer of two layer composites is estimated theoretically and experimentally. The present method can be applied to the two-layer composites with the thermal contact resistance at the interface of the layers, if the thermal conductivities of two layers and the thermal diffusivity of the other layer are known. Influence of each relative error of thickness of layers, thermal conductivities, the other thermal diffusivity, and thirty and seventy percent time on accuracy of the results obtained by this method of thermal diffusivity and thermal contact resistance is estimated theoretically. The present method is applied to some joining specimens whose thermophysical properties have been all measured in advance by the laser flash half-time method. Influence of the amount of scatter in measured values of thirty and seventy percent time and influence of the combinations of various percent time on the estimated results of thermal diffusivity and thermal contact resistance are investigated. It is confirmed that the most important factor of accuracy in the present method is the measured time in temperature history of the rear surface such as thirty and seventy percent time. Influence of the accuracy of the thermophysical properties used on accuracy of the results is relatively small.

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Estimation of Accuracy in Measurement by Flash Method of Thermal Diffusivity of Two-Layer Composites

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