SRC構造に使用できる鋼材は, 現在のところSM53以下となっている。のSRC構造への適用を推進するため, 3か年計画の実験的研究が行われた。この研究で得られた成果は, (1)を使用したSRC部材の強度は, 鋼材の降伏点またはコンクリートの圧縮強度を調整することによって, 累加強度式を適用して求あることができる, (2)を用いたSRC部材のほうが, 普通鋼を用いた部材より粘り強い, (3)断面欠損のある鉄骨を用いる場合は, 欠損部分を鉄筋で補強することによって耐力低下が補われ, 脆性破壊が避けられる, (4)L形フープで靭性が確保できる, (5)S部分とRC部分の剛性を組み合わせることによって, SRC部材のクリープたわみを推定することができる。本稿では, これらの研究結果により, を用いたSRC構造の設計法と詳細設計の方法とを提案した。

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各種の溶接構造用に, 室温ないし600℃の範囲で引張予歪を与えてから, 残留延性試験と切欠靱性試験を行なってキルド軟鋼の成績と比較した。
3種の50kg/mm²級 [YND (Q&T) ・HT50 (Q&T) ・HT50 (N)] と, 80kg/mm²級1種 [WT80 (Q&T)] とを用いて行なった残留延性試験の結果によると, キルド軟鋼に比べてこれらのでは高温予歪による残留延性の低下は一般に少ないことが認められた。とくに200℃での予歪処理による悪影響は明らかに軽微であった。またキルド軟鋼をも含めて, この高温予歪処理による悪影響はあまり大きなものではなく, 残留延性を室温予歪よりも顕著に損なうようなことはなかった。
以上の鋼種にさらに80kg/mm²級2種 [K-O (Q&T) ・K-O (N)] を加えて, vシャルピー衝撃試験により切欠靱性試験を行なった。その結果によれば悪影響のもっともはなはだしい処理温度は, キルド軟鋼が200℃であったのに対し, 供試鋼ではすべて300℃であった。またこの危険温度での予歪処理によって遷移温度 (Tr₁₅とTr_s) が示す上昇度は, 全供試鋼ともキルド軟鋼の場合の数分の1程度で脆化は遙かに少なかった。したがって高温予歪の悪影響がきわめて著しかったキルド軟鋼に比べて, 供試はすべてかなり安全側にあるものと推定される。高温予歪が切欠靭性に及ぼすその他の影響に関しては, キルド軟鋼のときと同様な結果が得られた。

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This paper describes the effects of compressive pre-strain on susceptibility to liquid zinc induced cracking of 590MPa class steels. It was reported by the authors that liquid zinc induced crackings occurred, in some cases, at the toes of fillet welds between 590MPa class steel tubes and ring-plates during a hot-dip galvanizing. The mechanism could be explained with plastic compressive bending moment due to the temperature difference between the tube and the ring-plate at the initial stage of the galvanizing. As the temperature difference decreased with a time elapsed, the bending moment decreased to convert compressive stress to tensile stress. Zinc induced cracking could occur under tensile stress. There have been neither experimental data nor testing methods so far to refer to the effects of the compressive pre-strain on susceptibility to liquid zinc induced cracking. In this research, critical strains for crack initiation (ε_c) of several 590MPa class steels with some compressive pre-strain were measured by a newly developed testing method. The compressive pre-strain(ε_p) has an effect to lower the value of ε_c. And also, the tensile deformation rate (V) and Carbon Equivalent for Zinc induced cracking (CEZ) correlate well with the value of ε_c respectively. As a result, ε_c can be estimated from the parameters of ε_p, V and CEZ. These results will be useful information to prevent liquid zinc induced cracking in pipe structures.

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A heavy thick (100mm) 100kgf/mm² class high tensile strength steel plate (H-T100) and the submerged-arc welding (SAW) consumables have been developed. The developed HT100 steel plate has uniform mechanical properties in the through-thickness direction, and has good weldability comparable to that of 80kgf/mm² class high tensile strength steel plate (HT80) against hydrogen cracking and bearing rather high heat input of 60kJ/cm. The developed SAW consumables has been certified the weld metal has good resistance for cold cracking due to the ultra low hydrogen content in addition to good toughness and has good workability even in applying a narrow gap welding.
The characteristics of HT100 steel plate and its welded joints obtained are as follows:
(1) The newly developed HT100 steel plate whose chemistry consists of. 13%C-0.12%Si-0.87%Mn-2.97%Ni-Cr-Mo-V-B, has been successfully manufactured by using the low-temperature-quenching and tempering process.
(2) The pre-heat temperature for preventing weld cracking was 100°C, which was evaluated by an oblique Y-groove cracking test. The maximum hardness on HAZ was lower than 400 in Vickers hardness. These results prove that the weldability of the HT100 steel plate is same that of HT80 steel plate.
(3) By the addition of optimum amount of carbonate, fluoride and MgO into agglomerated flux hydrogen content in the weld metal can be decreased in ultra low level and oxygen content can be adjusted in the optimum range. The slag detouchability is also improved so good as to use in a narrow gap welding.
(4) The tensile strength of weld joint was 101kgf/mm² for the weld heat input of
47kJ/cm and 100kgf/mm² for 60kJ/cm, respectively. An absorbed energy of Charpy test at -12°C notched in a fusion line was 11.1kgf m for 47kJ/ cm welding and 7.1kgf·m for 60kJ/cm, respectively. The Charpy test results show that these welded joints are safety enough against brittle fracture in spite of adoption of rather high heat input welding.

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自動車軽量化を目的として，高比強度材料である板の自動車部品への適用が進んでいる．板は軟鋼板と比較して成形性に劣る．板の難加工性を克服し，さらなる適用拡大を図るためには，成形シミュレーションによる不具合減少の予測精度向上が不可欠である．材料変形挙動の予測精度向上に対して，二軸応力下における塑性変形挙動を考慮した材料モデルの適用が必要である． 本研究では，590MPa級板に曲げと溶接を加えた円管試験片を製作し，円管試験片に軸力と内圧を付与し，二軸応力を負荷する試験法（二軸バルジ試験法）を適用し，線形応力経路を負荷した．それによって降伏初期から母材の破断に至るまでの応力－ひずみ曲線の測定に成功した．また本供試材の等塑性仕事面および塑性ひずみ速度の方向の再現精度に優れる降伏関数を決定し，成形限界ひずみや成形限界応力の測定にも成功したので報告する．

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Maximum strength and plastic rotation capacity of square hollow section members made of SN-steel subjected to axial compression and bending are investigated. Square hollow sections include a)fabricated by welding four plates and b)hot finished. The equivalent width-to-thickness ratio of compression side flange of square hollow section members under combined compression and bending are assessed using experimental results. The prediction formulae on maximum strength and plastic rotation capacity are derived by combining the theoretical moment-rotation relationship and the maximum buckling strength of compression side flange defined by the equivalent width-to-thickness ratio. The prediction thus obtained are compared with experimental results to show the satisfactory correlation. The width-to-thickness ratio limitations according to ductility demand levels are suggested.

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This paper describes the load-displacement relationships and the strain distribution of beams. These beams are fabricated from high strength steel with low yield ratio, or high yield ratio. But the nominal tensile strength of these steels are 590N/mm^2, together. The large deformation behavior of these high strength steel beams are obtained by experiments and numerical analysis. The plastic deformation capacity of these beams are evaluated by the difference of their material properties and width-thickness ratio of these plate elements. And the plastic deformation capacity of high strength steel beams are compared with one of the ordinary steel.

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The aim of the application of high strength steel to mammoth structures is to maximize their allowable stress in designing and at the same time reduce their weight as a whole by the use of high strength steel in critical parts of the structures. In accordance with the existing concepts of elastic design, high strength steel has been generally used for the members subject to higher stress or inducing a stress concentration in the structures built up by welding together high strength steel and mild steel. However, the strain behaviors should be considered as one of the most important factors in the application of high strength steel to the structures, because the high strength steel is more sensitive to the strain concentration than mild steel is. In the previous report, the plastic deformation behaviors of the smaller size of composite weldment, in which high strength steel and mild steel are symmetrically arranged about the longitudinal axis, have been investigated under static tension parallel to the weld line. There are still problems of the similarity of the strain behaviors of the larger size of composite weldment to those of the smaller one. In this research, mechanical behaviors of the wide specimens having the heterogeneity are investigated in various combinations of the size of dissimilar steels with different strength.
It is concluded as a result that ultimate tensile strength and yield strength of the wide specimens of composite weldment can be estimated by the strength of each steel and the hybrid ratio of high strength steel, and that their equivalent uniform elongation increases with the rate of mild steel to high strength steel.

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欧米で軟鋼が大量に生産されるようになったのは1860年頃であるが，軟鋼の出現により陸上・海上のあらゆる構造物に使用されるようになった．しかし，産業の進歩発展に伴って各種の鉄鋼構造物は大型化，大容量化の傾向が強まり，軟鋼を用いたのでは部材の断面が課題となり構造上，構築上種々の困難が出てきた．そこで開発されたのが

である．戦前は鋲，ボルトで接合していたが戦後は溶接継手が主力になったので，溶接に適した強度の高い鋼が生産されるようになり，特殊用途用にも各種の鋼が出現した．

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Under fully reversed and pulsating load, the low cycle fatigue tests of notched composite weldment plates were carried out and the plates were composed of high strength steel HT60 and mild steel SM 41, and symmetrically arranged about the axis parallel to the direction of axial load.
Strain behavior near a notch root was analyzed by Moire method at the successive stages of cyclic loading and static strain distribution near a notch root was calculated by FEM.
These strains and their distribution were used to the formulae for the estimation of crack initiation life proposed by the authors.
From these test results and analysis, it was found that the fatigue crack initiation life of the notched composite weldment specimen was equal to the notched single material one when the strain behavior near the notch root was equal, but crack propagation life of the composite specimen was generally different from that of the single material one and was dependent on the arrangement of materials.

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In his study, experiments were performed to make clear the influence of the contentious cooling transformation in heat affected zone (HAZ) of the 1Cr-1/4Mo (SCM4 and SCM22) steels on notch toughness, tensile properties and HAZ cracking by making the SH-CCT diagram, heat cycle simulating tests and slit type cracking tests. The results of these test are summarised as follows.
(1) The impact value falls strikingly when the single heat cycle of 1, 350°C is given, and those values (vE₂₀) are 0.5-1 kg-m/cm² for SCM4 and 2-3 kg-m/cm² for SCM22. However, the influence of the cooling rate in the heat cycle cannot be especially recognized.
(2) The impact value will be remarkably improved when the cooling time of the heat cycle from 800 to 500°C is made less than 20s for SCM4 and 10s for SCM22 (the area percentage of the martensite are in the range 80-100%) and then postheated at 600°C for 2 or 3 hours.
(3) In slit type cracking tests on the tested steels, when the bainite structure of the HAZ was made approximately more than 40-60% by preheating, the HAZ cracking cannot be recognized even though wet coated electrode (12cc H/100g) was used.

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