• Journal of Welding and Joining
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• v.8 no.4
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• pp.69-75
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• 1990

In this paper, ultimate compressive strength of TMCP 50HT steel plates (yield stress .sigma.$_{o}$=36kg/mm$^{2}$) with HAZ softening is studied. Finite element method formulated by the author is applied to analyze the elasto-plastic large deflection behaviour of the plates. The influence of HAZ softening breadth, welding direction and slenderness ratio on the ultimate compressive strength is investigated. The results obtained are summarized as 1) With the increasing of the HAZ softening breadth, early plasticity on the plates is formed and then the ultimate compressive strength is decreased, in which about 8% of the ultimate strength for the plate with h/t=4(h: HAZ softening breadth, t: plate thickness) was reduced comparing with no HAZ softening. 2) The large decrease of the ultimate strength for the case that the welding direction is normal to the loading direction is occurred than the case that the welding direction is parallel to the loading direction. 3) The influence of HAZ softening on the ultimate compressive strength is serious for thick plates, while it may be negligible for thin plates.s.

• Journal of Welding and Joining
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• v.29 no.1
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• pp.59-64
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• 2011

Al6082-T6 is widely used because of its corrosion resistance and excellent strength. HAZ softening occurs in MIG welding process for this aluminium alloys because this aluminium alloy is heated to higher temperature than its aging temperature during welding. Therefore, low heat input and minimum standard deviation of heat input are required for narrow HAZ width and, for higher strength of welds. In this study, Al6082-T6 was used to examine for HAZ softening with various heat input in aluminium MIG welding. For weldments, micro hardness was measured and tensile test was carried out. Minimum hardness was increased at high speed welding such as 80cm/min and 120cm/min in welding speed comparing with 40cm/min. Also, in case of high speed welding such as 80cm/min and 120cm/min, tensile strength of weldments was increased about 10% comparing with low speed welding(40cm/min).

• Journal of Welding and Joining
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• v.9 no.2
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• pp.44-50
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• 1991

The use of high tensile steel plates is increasing in the fabrication of ship and offshore structures. The softening region which has lower yield stress than base metal is located to prevent cracking in the conventional high tensile steel. Also, thermo mechanical control process(TMCP) steel with low carbon equivalent has the softening region which occurs in the heat affected zone when high heat input weld is carried out. The softening region in the high tensile steel gives rise to serious effect on structural strength such as tensile strength, fatigue strength and ultimate strength. In order to make a reliable structural design using high tensile steel plates, the influence of the softening on plate strength should be evaluated in advance. In the previous paper, the authors discussed the ultimate compressive strength of 50HT steel square plates with softening region. In this paper, the ultimate compressive strength with varying the yield stress of softening region and the aspect ratio of the plate is investigated by using the elasto-plastic large deformation finite element method.

• Journal of Welding and Joining
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• v.6 no.1
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• pp.28-34
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• 1988

The fatigue test was carried out to evaluate the fatigue characteristics of the accelerated cooled (ACC) TMCP steel and its welded joint. From this study, it was confirmed that ACC TMCP steel has higher fatigue strength than conventional steels. After welding, however, the fatigue strength of ACC TMCP steel was deteriorated associated with HAZ softening when weld reinforcement was removed. On the other hand, with weld reinforcement, there is no effect of HAZ softening on the fatigue strength of welded joint because it is strongly dependant on the detail weld geometry i.e., stress concentration factor. Accordingly the fatigue strength of actual welded joint increases with decreasing the stress concentration factor of welded joint, regardless of HAZ softening.

• Corrosion Science and Technology
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• v.3 no.2
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• pp.81-86
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• 2004

The sulfide stress corrosion cracking (SSCC) resistance of API X70 grade steel weldment has been studied using SSCC test in NACE TM-O177 method A. Also, microstructures and hardness distribution of weldment was investigated. The microstructure of SAW joint composed ferrite, pearlite and some MA constituent. Instead of hardening in CGHAZ, softening on the HAZ near base metal occurred. The low carbon TMCP type steel used for SAW showed softening behaviour in the HAZ adjacent to base metal, which was known to be closely related with the SOHIC (stress oriented hydrogen induced cracking). The SSC testing revealed that the API X70 SAW weld was suitable for sour service, satisfying the NACE requirements. By suppressing softening in the ICHAZ region, the SSCC resistance of low carbon TMCP steel welded joints could be more improved.

• Journal of Welding and Joining
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• v.4 no.3
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• pp.43-49
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• 1986

Weldability of the TMCP steel manufactured by controlled rolling followed by accelerated cooling process was investigated. For comparison, two other steel plates produced by different manufacturing processes were selected; normalized and controlled rolled. Tandem submerged arc welding with both side one run technique was carried out. The results of this study can be summarized as follows; TMCP steel having the lowest carbon equivalent shows the best combination of mechanical properties, not only in the base metal but also in the heat affected zone. In the HAZ, the accelerated colling effect imarted on the trengthis releved by the weld thermal cycles, and thus the strength of the welded joint decrease substantially accompanied with the fracture in the HAZ. On the other hand, not only the softening but the fine microstructure can preserve the high toughness of TMCP steel in the HAZ.

• Proceedings of the KWS Conference
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• 2006.05a
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• pp.92-93
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• 2006

In recent time there are vigorous requirement for the use of thick steel plate in various industrial fields including shipbuilding industry. Application of TMCP steel plates, especially, is increase progressively. As a welding process for thick steel plate assembly high heat input welding method is used. However, HAZ softening of TMCP steel plates has a possibility to reduce the strength of welded joint. In this study, therefore, tensile strength of TMCP welds had softened HAZ was examined using numerical calculation and experiment.

• Journal of Ocean Engineering and Technology
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• v.22 no.6
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• pp.41-45
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• 2008

Effectsof carbon content on the weldability of B-containing 620 grade high Cr ferritic cast steels were investigated. Cast steel with lower carbon content of 0.07% showed lower HAZ hardness because of the formation of lower carbon martensite in HAZ. It also showed less solidification cracking susceptibility in weld metal because of the formation of delta ferrite. However, hot ductility showed no difference between cast steels with lower and higher carbon contents. Cast steel with lower carbon content showed greater HAZ softening after PWHT in the region heated between AC1 and AC3 because of its higher base metal hardness.

• Journal of Welding and Joining
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• v.16 no.6
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• pp.44-51
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• 1998

It is well known that the fine bainitic microstructure obtained by TMCP(thermo-mechanical control process) secures the high toughness of base metal. Besides, TMCP steel is very suitable for high heat input in welding as it has low carbon equivalent. In HAZ, however, the accelerated cooling effect imparted on the matrix by the weld thermal cycles is relieved and thus the weldment of TMCP steel has softening zone which shows low fracture toughness compared with base metal. Therefore, PHWT of weldment is carried out to improve the fracture toughness in weldment of TMCP steel which has softening zone. In this study, the effects of PWHT on the weldment of AH36-TMCP steel are investigated by the small punch (SP) test. From the several results such as SP energy and displacement at room temperature, the behavior of transition curves, the fracture strength at -196$^{\circ}C$, distribution of (DBTT)sp and (DBTT)sp, the PWHT condition of A.C. after 85$0^{\circ}C$-1 sec W.C. was suitable condition for recovering a softening zone of HAZ as welded.

• Journal of Welding and Joining
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• v.30 no.2
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• pp.76-80
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• 2012

In this study, the effect of the welding current on the hardness characteristics and microstructure in the resistance spot welding of 1GPa grade cold-rolled DP steel was investigated, Also, correlation between the hardness and microstructure was discussed. In spite of the change in the welding current, the hardness distributions near weld was similar. the hardness in the HAZ and the fusion zone was higher than that of the base metal and the hardness in the fusion zone was variated with the location. Especially, the hardness of HAZ adjacent to the base metal showed maximum value, and softening zone in the base metal adjacent to HAZ was found. With the increasing of welding current, there were no difference in maximum hardness and average hardness in the fusion zone were, but the hardness of the softening zone reduced. The difference in the hardness in each location of weld due to grain size of prior austenite. The softening of the base metal occurred by tempering of the martensite.