Hiroshi Kihara

Studies on Notch Ductility of Stainless Clad Steel

In order to investigate the ductility of stainless clad steel with various clad ratios and clad arrangements, eight tests for the notch sensitivity of steel were performed, and clad ratios were varied in five stages, zero (mild steel), 1/7, 1/3, 1 and infinite (stainless steel) and clad arrengements were varied in three types, single type, double type and sandwich type. Effect of clad ratio and clad arrangement on various transition temperature can be seen in Table 3 and 4.In all tests performed, clad ratio and clad arrangement affects the ductility of stainless clad steel and higher clad ratio indicated more ductility and sandwich type clad steel had highest ductility in the three clad arrangement.

As to Arc Phenomenon of Multiple Electrode Submerged Arc Welding

In the submerged arc welding to analyze the transfer phenomenon of the metal (1) and the fo mation of the crater by arc in the covered flux (2), the X-ray radio photograph and oscilgraphic photograph tests are applied to the single electrode and multiple electrode welding. In taking the X-ray, the constant potential 280 KVP capacity to be used and the selected shutter speed of the photograph for transfering the metal and formation of the crater by arc to be 1/900 sec. and 1/50 sec. respectively. The A.C. welder and D.C. constant potential welder are to be used.Judging from the X-ray radio and oscilograph tests being practiced it is presumed that the transfering metal of the submerged arc welding is transmitted (dropped) irregularly as the fine grain. And the condition of the crater which is made by arc in other works the shape of the weld puddle and the relative positions between the weld puddles and electrodes differ depending upon the welding current, speed, voltage and electrode distance in the case of the multiple electrode process. It also confirms the relation between the shape of the weld puddle and bead appearance and penetration as well as the distribution of the electric current in the parallel connection welding method.

Explosion Tests on Arc Welded Tubes with Various Welding Procedures

The use of an abundant explosive energy is one of the successful method to investigate the behavior of the brittle fracture of welded structures. Authors have previously conducted the explosive tests on arc welded mild steel tubes. Recently, however, another phase of study have been made carring out series of explosion tests on the arc welded tube specimens made of high tensile strength steel (“50 kg/mm2 Mn-Si steel”, “60 kg/mm2 V-Ti alloy steel” and “quenched and tempered steel”).The purpose of this investigation is the examination of such various effects on the behavior of brittle fracture as that of the quality of steel, welding procedure (manual and submerged welding), stress relieving after welding (600°C, 1 hour heat treatment, the Linde method and peening).Codes and numbers of specimens are listed in table 1, and the chemical and mechanical properties in table 2. The size of specimens were 400 mm diameter, 800 mm height and 20 mm thickness. The explosive (T. N. T.) was set in the center of a specimen filled up with water and detonated.The relation between test temperature and circumferential strain at fracture for different series of steel codes are shown in figs. 5 to 7, respectively. Detailed sketches of the fractured specimens are also shown in fig. 8. Figs. 9 to 11 show the relation between test temperature and averaged thickness of shear lips appeared on the fractured surface in the three kinds of base metal, respectively. Similar relationship was observed in weld metal and heat affected zone as shown in fig. 12. It can be seen from fig. 13 that the former is larger than the latter concerning to the thickness of shear lips.Summarizing the test results the following conclusions are obtained.1. Comparing the as-welded tested specimens with respect to the effect of the quality of steel on the circumferential strain at fracture, it can be concluded that 50 kg/mm2 high tensile steel is the best, and then comes quenched and tempered steel, 60 kg/mm2 high tensile steel. And concerning the thickness of shear lips, quenched and tempered steel comes first and then 50 kg/mm2 high tensile steel, 60 kg/mm2 high tensile steel. In other words 50 kg/mm2 high tensile steel is superior for the initiation of fracture, and the quenched and tempered steel for the propagation of fracture.2. So far as the circumferential strain at fracture the effect of stress relieving heat treatment has not been remarkably observed. But after heat treatment the possibility of crack initiation at circumferential weld can be considered to increase. It may be the effect of the increased brittleness due to heat treatment on weld metal deposited by low hydrogen type electrodes.3. The effect of the low temperature stress relieving by the Lide method was not appreciable. 4. In all the tested specimens peened on every layer of the outer surface, the crack initiated on the outer surface of the circumferential weld, and the strain at fracture was not so large.The peening on the last layer can be considered to produce extremely fine cracks and strain hardning of weld metal consequently crack will start more frequently at low strain level in spite of rich ductility the base metal. From the viewpoint of the brittle fracture peening on the last layer should be positively avoided.5. The difference due to manual and submerged arc welding was no appreciable.6. With the exception of peened specimens cracks were usually initiated from the inner surface of the pipe, especially from the heat affected zone of longitudinal seam joints, or blow holes in circumferential weld.

Investigations of Pull-out Type Fracture of Fillet welds

最近某造船所における大型油槽船の建造に際して一部隅肉熔接部に熔着金属が母材から剥離するという事故が発生しその熔接部およば使用鋼板の安全性を調査する研究が当部に依頼された.本文はその研究報告の概要であって隅肉熔接シャルピー衝撃試験およぶ隅肉熔接疲労試験が行われている.その結果を総括すると以下の各項となる.1)この鋼板の隅肉熔接部に発生した欠陥(剥離性破壊)は通常のアンダービードグラックとは異なり鋼板自体の持つ微小偏析物がその板厚の方向の強度を著しく不足させていることに基くものである.2)低水素系熔接棒の使用や予熱を行うことは剥離性破壊の発生を幾分少なくする程度に止まっている.3)鋼板に焼準を施す事によっても充分な効果は期待できない.4)この鋼板は衝合熔接に対しては全く欠陥を示さなかった.5)この鋼板に対して行われた隅肉熔接部の疲労強度は良好な鋼板と比較して殊んど損色が見られず疲労試験に於いては熔着金属が母材から剥離することは全くなかった.6)隅肉シャルピー衝撃試験の結果では試験温度が上昇するほど剥離性破壊の発生は増加している.

Effect of Chemical Composition and Heat Treatment upon Impact Toughness of High Tensile Mn-Si Steels-Report II

V-notch Charpy impact tests were performed of 30 ship steel plates which were rolled into 12 or 20mm in thickness from the top and bottom of nine production heats of weldable high strength manganesesilicon steels.The results of tests may be summarized as follows :(1) The yield ration was generally 65 percents. However, steels M3 and M6 showed higher ratio of 75% which was comparable to that of German HSB steel.(2) The notch toughness of test steels in as rolled condition was inferior to that of the current killed ship steels and approximately equal to that of rimmed steels. However, the notch toughness was improved remarkably by normalizing the test steels, and was then superior to that of killed steels.(3) The notch toughness was almost constant in a range, 0.3 to 0.6%, of silicon content.(4) The notch toughness of test steels was affected more remarkably by ferrite grain size of distribution of carbide, than by chemical composition.

Effect of Grain Size and Heat Treatment upon Impact Notch Toughness of High Tensile Mn-Si Steels

The effects of ferrite grain sizes and microstructures after various heat treatments on the V-Charpy transition temperatures were investigated with two high tensile Mn-Si steels, of approximately the same chemical comporition, but the one aluminum treated and the other not-treated.The results obtained are summarized as follows ;(1) The austenitic grain-coarsening temperature of the Al treated steel N3B was considerably higher than that of Al non-treated steel K1B.(2) A close relationship was found between the ferrite and the austenite grain sizes after various heat treatments of test steels.(3) Generally, the transition temperature increased with increasing the austenitizing temperature and with lowering cooling rate.(4) The greatest difference in transition temperatures between these steels occured after heat treatment at about 950°C at which the difference of austenitic grain sizes was the most significant.(5) A linear relationship exsisted clearly between the V-Charpy transition temperature and the ferrite grain size.

Effect of Welding on Brittle Fracture of High Tensile Steels

Effect of welding on brittle fracture of two high tensile steels was investigated with notched C-Bead Tear Test Specimens which were side-beaded with six electrodes ; four low hydrogen high tensile electrodes, one ilmenite-type mild steel electrode and one hard-facing electrode.The conclusions may be summarized as follows :(a) The effect of welding was very remarkable in crack initiation, and reduced considerably absorbed energy to maximum load, lateral contraction at root-notch, and nominal tensile strength. With a deposit of low ductility, the reduction was very serious.(b) However, the effect of welding was hardly observed in crack propagation through base metal.(c) Some examples were observed in which a ductile heat affected zone of base metal could arrest and change into a ductile fracture the brittle crack which had been propagated through a brittle weld metal.(d) The nominal strength of notched C-Bead Tear Test Specimen was independent of base metal, but depended on the type of electrodes which were used in bead welding.(e) Home made low hydrogen electrodes which were tested, showed the same quality with an imported electrode of low hydrogen type, as far as notch sensitivity of welded plates was concerned.

Explosion Tests on Arc-Welded Tubes with and without Stress Annealing

Explosion tests were conducted on pipe specimens to determine the effect of stress annealing. Pipe specimens, 400 mm diameter, 800 mm height and 20 mm thickness, were welded in four longitudinal and one circumferential joints.Specimen was filled of water to reduce the detonating effect of explosive shock wave, and then an explosive set in the center of pipe was detonated.Evaluation of the performance of specimen was provided by checking the circumferential strain on circumferential butt joint.Explosion test showed a remarkable difference which could not been examined by longitudinal bend test or V-notch Charpy impact test. Namely, the annealed specimen was fractured by explosion when the circumferential strain reached at 11%, while aswelded one at 6 %.

Studies on Peening Operation (Part 2)

Some experiments were made to determine the effects of peeping on the residual stress relieving and the properties of the peened weld metal for the low-temperature brittleness in the butt weld joints, , which were prepared from two plates of 1200×500×19mm. by manual welds. Details of the specimens and the conditions of welding and peening are shown in Fig. 1, 2 and Table 1-5, respectively.The residual stresses as welded and after peened were mesured by three methods successibly, for the purpose of increasing the reliability of the measured data.Electric resistance strain gauges were fastened on the plates, as shown in Fig. 4, which then was drilled as follows:1. One Hole Relaxation2. Two Hole Relaxation3. Plug Relaxation4. Slit RelaxationAustrian tests were conducted as the extensive experiments to research the effects of peening on the low temperature brittleness of the weld metal.Measured residual stresses are shown in Fig. 5-8, and the results of Austrian Tests conducted at the range of -650°C... -70°C are shown in Table 6, respectively.Summary results of measured longitudinal residual stresses are shown in Table 7.Fig. 8 represents the summary of longitudinal mean stress resulted from the various peeping conditions. Except for the specimen No. 2, in Fig. 8, longitudinal stresses were considerably reduced by peeping compared with the as-welded specimen, namely in the specimen No. 3, peening lowered the longitudinal stress of 28 kg/mm2 tension.The following conclusions appear to be warranted:1. The first laver shall not be peened.2. Peening of the last layer should be considered a dangerous practice which greatly increases the hazard of low temperature brittleness.3. Hot peening confers the undesirable effects on the properties of weld metal.4. The welds shall not be over peened.5. As the stress relieving procedur, peening only the last layer by 2-in. stroke is even effective.6. Transverse stresses were lowerd to some extent by peening.