Multi-layer Welding Research Articles

100キロ高張力鋼多層溶接継手の割れ試験結果

The present study is an application of the NRIM TRC test (Tensile Restraint Cracking test) to cold cracking in multilayer welds of a high-sterngth steel with a strength level of 100 kg/mm2. It was aimed in this study to make clear the cracking behavior and to get practical methods for the prevention of cracking.A TRC specimen was set up in a 1000 tons NRIM TRC tester and pulled after finishing of a test weld. The constant loading at various stress levels was sustained for sufficient time for cracking.There occurred two types of macrocracks in multilayer welds depending on the direction of restraining, that is, transverse and longitudinal cracks in longitudinal and transverse TRC tests, respectively. Those cracks in longitudinal and transverse TRC tests, respectively. Those cracks were considered extensions of microcracks. Cracks, both transverse and longitudinal, were the delayed type due to hydrogen and occurred after an incubation period under a sustained tensile loading which exceeded the critical tensile stress for cracking. The incubation period extended from about 1 to 10 hr, mainly depending on restraining stress and hydrogen content. The critical tensile stress for cracking was raised with an increase of preheating temperature and with a decrease of hydrogen content. The critical tensile stress for longitudinal cracking was slightly lower than that for transverse cracking at the same welding conditions and hydrogen content.Transverse cracks were prevented under the longitudinal tensile stress of 65 kg/mm2 with any of the following methods: (a) preheating at 200°C, (b) 100°C preheating and locally tempering postheating at 500°C, or (c) 150°C preheating and lower temperature postheating for 5 hr at 100°C. The restraining stress of 65 kg/mm2 was a little over the restraining stress in the so-called window restrained test which has been appreciated as fairly reporducible one of actual severe restraint. Very little change of hydrogen content, about 0.2 cc/ 100 g, in deposited metal was decisive to transverse cracking in such high strength steel welds, supposing actual joints with severe restraint.Longitudinal cracks were gradually propagated and then usually caused a brittle fracture throughout the joint. The carck was prevented with preheating at 200°C under the transverse tensile stress of 55 kg/mm2 At the tensile stress of 65 kg/mm2 any crack did not occur with simultaneous use of 150°Cpreheating and lower temperature postheating, 200°C for 1 hr or 100°C for 5 hr.Effectiveness of lower temperature postheating was discussed with an estimation of existing hydrogen content in a weld at the instant of cracking.

高張力鋼厚板溶接部のルート割れ試験結果

A series of root cracking tests were conducted with y-groove restraint cracking specimen of high strength steels with thickness from 30 to 50 mm. Effects of size of specimen, including bead length and plate thickness, and of multi-layer weld on root cracking were mainly studied in the report.The conclusions obtained in the study are as follows:(1) The root cracking tendencies of six high strength steels with their strength levels from 60 to 79 kg/mm2, that is, HT 60 and HT 70 steels, were evaluated and preheating temperatures necessary for the prevention of root cracking were decided.The maximum hardnesses in HAZ of these steels, which were safe to root cracking, ranged from 350 to 400 VHN under the load of 1 kg.Microstructures of HAZ safe to root cracking were decided with an, aid of of CCT diagrams, that is, 5-10% ferrite, 20-30% intermediate structure and 60-70% martensite for HT 60 and 10-25% intermediate structure and 75-90% martensite for HT 70 in their area percentages of constituents.(2) Neither the root crack, which was initiated at the first layer weld, was propagated nor a new crack was initiated with the progress of a multi-layer weld.Cracking tendencies rather decreased in multi-layer welds with a choice of proper interpass temperature.(3) An increase of root cracking was not detected with an increase of bead length and a root crack rather increased with a decrease of bead length at a bead length below 150 mm, because of a rapid cooling of a short bead.Therefore it was suggested that the transverse tensile residual stress in a weld would directly affect the initiation of a root crack and the longitudinal tensile residual stress would indirectly affect the initiation of a root crack.(4) The tendencies of root cracking did not increase with an increase of plate thickness if the welds were cooled by the same cooling process.(5) It was confirmed that the slotted cracking specimen with a size of 200 mm×150 mm was equivalent to one of 300×200 mm. The smaller size is therefore satisfactory for a root cracking test of high strength steel welds.

原子炉用HT70鋼大型溶接継手のクリープラプチャに関する研究(第1報)

In the foregoing reports, comparison in creep rupture strength between large and small size welded specimens, discussion on the mechanism of creep rupture and the influence of heat treatment after welding were made. In this report, the difference in rupture configuration between large and small size welded specimens, and welding methods viewed from creep rupture configuration are discussed.The large size welded specimens are ruptured at the heataffected zone of base metal (HAZ) near the bond, while the small size welded specimens are ruptured at HAZ near the base metal. The plate thickness of the steel used is 30 mm, and the welded joints are made by multi-layer welding. Therefore, it may be considered that the properties at welded joint of specimens of both sizes are different. It is clear from the foregoing report that creep strength may be proportionate to the absorbed energy to rupture in a high temperature tensile test. Therefore, tensile tests at 450°C on synthetic HAZ specimens, with respect to the coarse grain part near bond and the fine grain part near base metal in HAZ of small size welded specimens, are carried out to measure the absorbed energy. The value of absorbed energy in fine grain part is less than that in coarse grain part. Consequently, it may be considered that small size welded specimens are ruptured at fine grain part of HAZ near base metal, while large size welded specimens are ruptured at coarse grain part of HAZ near bond.The creep rupture configurations of large size specimens are discussed in various ways. As a result, it is believed to be desirable for improving the creep rupture strength of welded joint to make the pentration of the final bead as shallow as possible.

A Study on Relations between the Micro Crack Initiation and the Welding Conditions in a Fillet Joint of Thick Steel Plate (Appendix)

In the previous report the authors reported various conditions for the loss of ductility of the toe of the first pass side welding during finishing pass side welding due to thermal strain. But the present paper deals with the investigation carried out in order to clarify the relation between such phenomenon and fracture mechanism seen from the stand point of material mechanics.In other words, the authors sought the effects upon ductility of prestrain, aging, etc. by means of simple testing of round bar, etc. Moreover, concerning the notch at the toe of the first pass side welding, its relation with welding conditions and effects on fracture were studied. Further-more, root cracking conditions of one side multi-layer butt welding were also investigated.The results of these investigations were as follows : 1) The effects of tensile strain and compressive strain upon ductility differ. The former reduces ductility by raising flow stress from the stand point of material quality while the latter causes it by complicated causes such as changes of notch shapes, triaxiality, etc.2) Notch shape changes according to welding position and electrode diameter and, the effects of such notch conditions upon crack initiation have been recognized.3) Similar to the toe of fillet welding, the multi-layer welding root of the butt joint initiates crack in accordance with the strain due to subsequent pass welding and notch conditions.

Cr系不銹鋼板の熔接性(第4報)

V-butt multi-layer welding of a 18Cr steel plate, 7., 5mm thick, has been carried out with three kinds of austenite electrodes (AlSl type 308, 316 and 310) and one kind of ferrite-austenite electrodes (all of them, 4mm diameter). The obtained welds have been subjected to a hardness test, microstructu-re test, V-notch Charpy impact test at -200-+300°C; fractographs of the brittle-fractured surfaces in their impact fractures have been examined and some considerations made on them.Some of the major results are summarized :1) Transition temperature in the non-affected and the heat-affected zone of parent metal is very high. It is higher in the latter than in the former ; in the latter no annealing effect is observable.2) Impact value of welds using ferrite-austenite electrodes are in general lower than those of the ones using austenite electrodes. However, excessive lowering of these values does not take place on low temperature side.3) Fractographs of brittle fractures in the impact fractures of the heat-affected, non-affected zones of parent metal and of welds have been studied to seek the relationship to ductility.

Effect of Welding Sequence on Transverse Shrinkage and Residual Stresses

This report is the second part of serial experiments which are being made to survey the effect of welding sequence on transverse shrinkage and residual stresses. In this report the analysis about the part of transverse shrinkage of 4 th series of experiment of which. main object is the comparison between multilayer and block welding sequence is treated.The size of specimen (slit type) and welding conditions were the same as what were used in the preceding serieses. The welding sequence applied for each specimen is listed. in Table 1.The measurement of transverse shrinkage was performed by a measuring machine after the welding of each layer. The results obtained so for are summarized as follows : 1) Form of ShrinkageThe form of shrinkage for each specimen is shown in Fig. 1.It becomes considerably uneven when the block welding sequence is applied, and on the contrary, far even when the multilayer welding sequence is used.These problems were analysed using the “unfairness index of shrinkage” δ defined by Eq. (4) ** Refer to Appendix of this report concerning with the definition of δ and U. There exist some correspondences between the theory of inherent stress and aerodynamics.As shown in Fig. 2 the value or δ gradually decreases as the progress of welding, especially when the multilayer welding is applied. This phenomenon seems to be attributed to the tendency of approaching to the form of minimum strain energy in manual welding.When the block welding sequence is adopted, the larger value of δ is obtained than the case of multilayer welding. However, the value of mean shrinkage decreases by the use of block welding sequence. The combined effects of these two factors have been.analysed using the “apparent shrinkage energy” U defined by Eq. (4). The value of U decreases by the use of block welding sequence, as shown in Fig. 3. Consequently, the block welding sequence seems to be a suitable sequence from the view point of decreasing total strain energy stored by welding.2) Mean ShrinkageThese also exists a linear relation between mean shrinkage and logarithm of weight of deposited metal in multilayer welding as shown in Fgi. 4. The value of shrinkage may decrease by the application of block welding sequence.

自動熔接施工時に生ずる拘束亀裂について

It has been disturbing experience of those engaged in submarged arc welding of structural steel plates to find cracks in the weld metal. These cracks which frequently take place while the weld is still very hot, and usually while the joint is subjected to high stresses, are associated with weakness between dendrites and it is believed to be probably hot cracking caused by increasing restraint due to the larger thickness of plates.Using large restraint specimens authors have experimented of the development of these cracks quantitatively and compared the various welding procedures with the result obtained.Covering the experimental methods used and the results obtained, this paper presents data whose several phases are as follows :(1) In order to prevent the restrained crack, it is more desirable the deposit of the first layer is made larger. (cf Fig. 5, 6 and 7)Generally, speaking of the performance of joint after welded, a multi-layer weld is said better. However, in view of such fact, it seems to be somewhat dangerous to increase the number of layers too much, which may cause the dwindling of the deposit of the first layer.(2) Among two combinations of rod and flux used in test, the low manganese rod of the combination I whose width of bead is larger is showing much better result (cf Fig. 5, 6, 10 and 11) As for the restraint crack of manual welding, better fusion and higher the deposit top is showing a better result, but a different aspect is presented in the automatic welding.(3) In the restraint crack of manual welding, the cold crack mainly poses a problem, but in the automatic welding it is conceivable the crack develops at a fairly high temperature (cf Fig. 10, 11).

Radial Contraction and Residual Stresses in Circular Patch-Weld, Part I

This research has been conducted for the purpose of investigating the fundamental characteristics in the contraction and residual stresses occured in patch-weld. The following three cases were studied.(i) Circular groove bead weld by multilayer sequence.(ii) Circular patch-weld by multilayer sequence.(iii) Circular patch-weld by block sequence.The size of specimen and welding sequence are shown in Fig. 1 and Table 1.The measurement of radial contraction (by measuring machine, ) and reaction stress occured in the central part of specimen (by electric resistance wire strain gauges) were conducted after the welding of each layer.The results obtained so far are summarized as follows : -1) Form of radial contractionForm of radial contraction is remarkably affected by welding procedures. In order to investigate the effect of welding procedures on the form of contraction, the radial contraction is classified into three components as uniform contraction, relative translation between-welded patch and outer ring, and contraction of higher order as shown in Eq. (1) and Fig. 7. The effect of welding procedures on contraction are analysed using two parameters such as “unfairness index of shrinkage” δ and “apparent shrinkage energy” U defined by Eq. (2) and (2) '. The magnitude of translational motion, the contraction of higher order and therefore the value of δ took the highest values in the specimen patch-welded by block sequence. But in this specimen the lowest values of uniform contraction and U were obtained.2) Relation between radial contraction and weight of deposited metal.Relation between logarithm of weight of electrode consumed per unit weld length log w and mean contraction ur is shown in Fig. 6.The linear relation between log w and ur, . holds good in following cases : -(i) Groove bead weld …all stages of welding (ii) Patch-weld by multilayer sequence …after the completion of 1st layer (iii) Patch-weld by block sequence. …only for the increase of contraction in the welding of each blockThese facts show that the linear relation of this kind generally holds good when the multilayer welding is taken into consideration.3) Change of reaction stress during weldingChange of reaction stress during welding is shown in Fig. 10. The most ununiform distribution of strain was obtained in the specimen welded by block sequence.4) Comparison between block and multilayer sequenceThe block sequence seems to be more suitable than multilayer sequence to reduce, , the residual stress ocured in patch-welding, mainly from the view point of reducing the total strain energy stored in the specimen.The residual stresses after the completion of welding were also measured. These data will be reported soon later.

Radial Contraction and Residual Stresses in Circular Patch-Weld, Part II

This research has been conducted for the purpose of investigating the fundamental characteristics in the contraction and residual stresses occured in patch-weld. The following three cases were studied.(i) Circular groove bead weld by multilayer sequence.(ii) Circular patch-weld by multilayer sequence.(iii) Circular patch-weld by block sequence.The size of specimen and welding sequence are shown in Fig. 1 and Table 1.The measurement of radial contraction (by measuring machine, ) and reaction stress occured in the central part of specimen (by electric resistance wire strain gauges) were conducted after the welding of each layer.The results obtained so far are summarized as follows : -1) Form of radial contractionForm of radial contraction is remarkably affected by welding procedures. In order to investigate the effect of welding procedures on the form of contraction, the radial contraction is classified into three components as uniform contraction, relative translation between-welded patch and outer ring, and contraction of higher order as shown in Eq. (1) and Fig. 7. The effect of welding procedures on contraction are analysed using two parameters such as “unfairness index of shrinkage” δ and “apparent shrinkage energy” U defined by Eq. (2) and (2) '. The magnitude of translational motion, the contraction of higher order and therefore the value of δ took the highest values in the specimen patch-welded by block sequence. But in this specimen the lowest values of uniform contraction and U were obtained.2) Relation between radial contraction and weight of deposited metal.Relation between logarithm of weight of electrode consumed per unit weld length log w and mean contraction ur is shown in Fig. 6.The linear relation between log w and ur, . holds good in following cases : -(i) Groove bead weld …all stages of welding (ii) Patch-weld by multilayer sequence …after the completion of 1st layer (iii) Patch-weld by block sequence. …only for the increase of contraction in the welding of each blockThese facts show that the linear relation of this kind generally holds good when the multilayer welding is taken into consideration.3) Change of reaction stress during weldingChange of reaction stress during welding is shown in Fig. 10. The most ununiform distribution of strain was obtained in the specimen welded by block sequence.4) Comparison between block and multilayer sequenceThe block sequence seems to be more suitable than multilayer sequence to reduce, , the residual stress ocured in patch-welding, mainly from the view point of reducing the total strain energy stored in the specimen.The residual stresses after the completion of welding were also measured. These data will be reported soon later.

Chemotherapy of subacute enterococcus endocarditis: Sirota, J. H., Gerber, I. E., and Baehr, G.: J. Mt. Sinai Hosp. 14:604 (Sept.–Oct.), 1947

During ship design, welding-induced distortions are roughly estimated as a function of the size of the component as well as the welding process and residual stresses are assumed to be locally in the range of the yield stress. Existing welding simulation methods are very complex and time-consuming and therefore not applicable to large structures like ships. Simplified methods for the estimation of welding effects were and still are subject of several research projects, but mostly concerning smaller structures. The main goal of this paper is the application of a multi-layer welding simulation to the block joint of a ship structure. When welding block joints, high constraints occur due to the ship structure which are assumed to result in accordingly high residual stresses. Constraints measured during construction were realized in a test plant for small-scale welding specimens in order to investigate their and other effects on the residual stresses. Associated welding simulations were successfully performed with fine-mesh finite element models. Further analyses showed that a courser mesh was also able to reproduce the welding-induced reaction forces and hence the residual stresses after some calibration. Based on the coarse modeling it was possible to perform the welding simulation at a block joint in order to investigate the influence of the resulting residual stresses on the behavior of the real structure, showing quite interesting stress distributions. Finally it is discussed whether smaller and idealized models of definite areas of the block joint can be used to achieve the same results offering possibilities to consider residual stresses in the design process.