Low Transformation Temperature Welding Material Research Articles

Development of 16Cr8Ni low transformation temperature welding material for optimal characteristics under various dilutions due to all repair welding positions

A new low transformation temperature (LTT) welding material 16Cr8Ni was developed to satisfy the optimal characteristics in diluted welds due to all repair welding positions. Its good weldability for all welding positions was tested. The measured Ms temperature of weld metals with different dilutions was between 150°C and 250°C which is the optimal range for compressive residual stress generation and fatigue life extension. The in-situ observation of phase evolution by the synchrotron-based X-ray diffraction technique validated the solidification mode of LTT welds for the prevention of solidification cracks. Moreover, the mechanical properties in the diluted LTT welds were measured by miniature uniaxial tensile tests. Large compressive residual stresses at the welded joints due to all welding positions were confirmed numerical analyses.

新低変態温度溶接材料と全姿勢伸長ビード補修法による溶接接手の高疲労寿命化 -第2報：全姿勢伸長ビード補修法による角回し溶接継手の疲労寿命延伸-

新低変態温度溶接材料と全姿勢伸長ビード補修法による溶接接手の高疲労寿命化 -第2報：全姿勢伸長ビード補修法による角回し溶接継手の疲労寿命延伸-

新低変態温度溶接材料と全姿勢伸長ビード補修法による溶接接手の高疲労寿命化 -第１報：新低変態温度溶接材料の成分系設計と全姿勢溶接性の検証-

新低変態温度溶接材料と全姿勢伸長ビード補修法による溶接接手の高疲労寿命化 -第１報：新低変態温度溶接材料の成分系設計と全姿勢溶接性の検証-

A Study on Fatigue Life Improvement of Welded Joints using Elongated Bead Welding with Low Transformation Temperature Welding Material

A Study on Fatigue Life Improvement of Welded Joints using Elongated Bead Welding with Low Transformation Temperature Welding Material

A Study on Fatigue Life Improvement of Welded Joints in All Positions and Fracture Toughness of Weld Metal for CO2 Gas Arc Elongated Bead Welding Method with Low Transformation Temperature Welding Material

A Study on Fatigue Life Improvement of Welded Joints in All Positions and Fracture Toughness of Weld Metal for CO₂ Gas Arc Elongated Bead Welding Method with Low Transformation Temperature Welding Material

ESPIシステムの溶接への適用

Behavior of displacement at welded joints during welding is an important factor for reliability of the joints. But in-situ measurement of the behavior is very difficult because contact method such as strain gauge is inapplicable in high temperature. In this study, ESPI (Electronic speckle pattern interferometry) system is applied to in-situ measurement of displacement increment distribution in SUS304 steel, 9%Ni steel, and low transformation temperature welding (LTTW) material during GTA welding. Qualitative tendency of measured results agrees with numerical simulation. Expansion behavior of phase-transformation is detected in 9%Ni steel and LTTW material during cooling. Moreover ESPI system enabled measurement of displacement increment at uranami bead surface and surrounding area of molten pool. These results show that ESPI system is applicable to measurement of displacement distribution at welded joints during welding process.

Repair of fatigue cracks initiated around box welds using low transformation temperature welding material

In order to improve the fatigue strength of welded structure, compressive residual stress is induced by means of marten site expansion of weld metal using developed low transformation temperature welding wire. Fatigue limit could be improved on repaired box welded joints.

Repair of fatigue cracks initiated around box welds using low transformation temperature welding material

Repair of fatigue cracks initiated around box welds using low transformation temperature welding material

Fatigue strength improvement of box welds using low transformation temperature welding material. Tripled fatigue strength by post weld heat treatment

The fatigue strength of box welds was tripled by using low transformation temperature welding wire and postweld heat treatment (PWHT). The improved fatigue strength was obtained due to the stress ratio effect resulting from compressive residual stress. The low transformation temperature welding material which contains 10 mass % Cr and 10 mass % Ni expands during the final cooling process of welding. This expansion of weld metal induced the compressive residual stress around the welded part. The PWHT at 720°C for 1 hour and subsequent cooling in air induced the transformation from austenite to martensite at the same time for three passes. That is, the volume expansion on three passes by PWHT became large compare with that on final pass in as-welded condition, and the compressive residual stress could be induced efficiently.

疲労 低変態温度溶接材料による自動車用薄鋼板重ね溶接継手の疲労強度向上

The fatigue strength of lap welded joints of thin steel plate for automobile use was improved by using low transformation temperature welding material which induced the compressive residual stress around welded part. The transformation of welding material from austenite to martensite begins around 200°C and finishes around room temperature. The expansion of weld metal due to the transformation was constrained by the surrounding base metal, and the compressive residual stress is induced in the as welded condition. The mean stress effect due to this compressive residual stress improved the fatigue strength.

低変態温度溶接材料を用いた角回溶接継手の疲労強度向上 溶接後熱処理による３倍化

The fatigue strength of box welds was tripled by using low transformation temperature welding wire and postweld heat treatment (PWHT). The improved fatigue strength was obtained due to the stress ratio effect resulting from compressive residual stress. The low transformation temperature welding material which contains 10 mass % Cr and 10 mass % Ni expands during the final cooling process of welding. This expansion of weld metal induced the compressive residual stress around the welded part. The PWHT at 720°C for 1 hour and subsequent cooling in air induced the transformation from austenite to martensite at the same time for three passes. That is, the volume expansion on three passes by PWHT became large compare with that on final pass in as-welded condition, and the compressive residual stress could be induced efficiently.

Fatigue strength improvement of box‐welded joints using low transformation temperature welding material

The fatigue strength of developed box welds was improved about two times of the conventional box welds. The improved welds used the low transformation temperature welding material which contains 10% Cr and 10% Ni. The expansion of the developed welding material was 0.55% due to the transformation from austenite to martensite. This expansion induced the compressive residual stress around welds. On low stress range condition, the stress ratio effect by this compressive residual stress avoids the fatigue crack initiation at the weld toe. On high stress range condition, the fatigue crack initiated from weld toe and the fretting was observed on the fractured surface. While in the conventional welds, no trace of fretting was observed.

Fatigue Strength Improvement of Welded Joints by Low Transformation Temperature Welding Material

Fatigue strength of welded joints were improved by inducing the compressive residual stress around fatigue critical area by mean of low transformation temperature welding material which expands around room temperature due to the transformation from austenite to martensite. In the case of box welds, the fatigue strength at 2×107 cycles was doubled without preheating and PWHT. In the case of box section welded member containing longitudinal weld lines, the fatigue strength at 2×106 cycles was improved about 1.3 times of the usual joints.

低変態温度溶接材料を用いた角回し溶接継手の疲労強度向上

The fatigue strength of developed box welds was improved about two times of the conventional box welds. The improved welds used the low transformation temperature welding material which contains 10% Cr and 10% Ni. The expansion of the developed welding material was 0.55% due to the transformation from austenite to martensite. This expansion induced the compressive residual stress around welds. On low stress range condition, the stress ratio effect by this compressive residual stress avoids the fatigue crack initiation at the weld toe. On high stress range condition, the fatigue crack initiated from weld toe and the fretting was observed on the fractured surface. While in the conventional welds, no trace of fretting was observed.

低変態温度溶接材料を用いた箱型断面溶接部材の疲労強度向上

The box section welded members were made by using low transformation temperature welding material without preheating and postweld heat treatment. The expansion of weld metal due to the transformation from austenite to marensite around room temperature induced the compressive residual stress of-159 MPa along the weld line. The fatigue strength at 2×106 cycles was improved about 1.3 times as large as that of a usual box section welded member. The blowholes of which size was up to 4.5 mm did not induce the fatigue crack in the compressive residual stress field.