• Journal of Welding and Joining
• /
• v.8 no.4
• /
• pp.46-57
• /
• 1990

TMCP steel manufactured by controlled rolling followed by accelerated cooling process is known to have extra-ordinary mechanical properties such as tensile strength and toughness. However, there is much uncertainty about the fatigue fracture characteristics, especially, in the welded state of this steel. In case of this steel, the softening zone by welding is generated in heat affected zone in contrast with the case of conventional normalized high strength steel. This softening zone is considered to play significant roles in low cycle fatigue fracture of the welded part of this steel. In this paper, the low cycle fatigue behaviors of TMCP steel were inspected in as-received and welded state using the smooth specimen. The fatigue life-time was seperately investigated on the basis of failure of the specimen and crack initiation which is detected by differential strain method. Moreover, the low cycle fatigue characteristics of TMCP steel were quantitatively compared with those of the conventional normalized steel of same strength level.

• Progress in Superconductivity and Cryogenics
• /
• v.1 no.2
• /
• pp.1-7
• /
• 1999

we evaluated the effects of joining process such as contact method. shape of joined area and pressure on the electrical and mechanical properties of Bi-2223 superconducting tape, Specifically. the current capacity of the jointed tape was measured as a function of uniaxial pressure. and the thermal shock, bonding strength and the thermal of the tape were evaluated and correlated to the microstructural evolution. It was observed that the current capacity was significanrly dependent on the uniaxial pressure The jointed tape, fabricated with a pressure of 1,000-1,600 Mpa. showed the highest value of current capacity results from improvements in core density, contacting area and grain alignment, ect. In addition, the strength of jointed tape was measured to be 86 Mpa, which is about 88% of the unjoined ape's strength. The irreversible strain($\varepsilon$irrev) for the jointed tape was measured to be 0.1%, smaller than that of unjoined tape ($\varepsilon$irrev= 0.3%). The decrease in the strength and irreversible strain for jointed tape is believed to be due to the irregular geometry/morphology of the transition area of the tape.

• Journal of Welding and Joining
• /
• v.23 no.3
• /
• pp.54-60
• /
• 2005

Tungsten Inert Gas(TIG) welding is today one of the most popular arc welding process because of its high quality welds and low equipment costs. Even if welding productivity increases with welding speed and current, this strategy is limited by the appearance of defects such as undercut and humping bead due to the depressed molten metal. The purpose of this study investigates the effect of He mixing ratio on the characteristics with high current and speed in TIG welding. The conclusions obtained permit to explain the arc start characteristics quantitatively and the maximum welding speed on stable bead formation with He mixing ratio for high current and speed TIG welding observed in experiments. Also through the relation of the maximum arc pressure and surface depression depth at high current and speed TIG welding, it made clear the mechanism of unstable bead formation.

• Journal of Welding and Joining
• /
• v.29 no.1
• /
• pp.59-64
• /
• 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
• /
• v.32 no.5
• /
• pp.65-71
• /
• 2014

Atmospheric plasma spraying (APS) is world-widely used process in the automotive industry as a method to provide wear resistance coatings for engine cylinder bore, using various materials. The weight of engine blocks can be considerably decreased by removing cast iron liners, which can finally result in the improvement of fuel efficiency. In this study, five kinds of powder materials, 1.2C steel powder and 1.2C steel powder mixed with 5, 10, 15, 20 wt.%. molybdenum powder, were deposited by atmospheric plasma spraying in order to investigate the effect of molybdenum on the wear resistance of coatings. Microstructural analysis showed that molybdenum splats were well distributed in 1.2C steel matrix with intimate bonding. The molybdenum added coatings showed better tribological properties than 1.2C steel coating. However, above the 15 wt.%. blending fraction, wear resistance was somewhat degraded with poor roughness of worn surface due to the brittle fracture occurred in molybdenum splats. Consequently, compared to conventional liner material, gray cast iron, 10 wt. pct. molybdenum blended 1.2C steel coating showed much better tribological properties and therefore it looks very feasible to replace gray cast iron liner.

• Journal of Welding and Joining
• /
• v.20 no.5
• /
• pp.87-92
• /
• 2002

Weldability of Friction Stir Welded(FSW) AZ31B-H24 Mg alloy sheet with 4m thick was evaluated by changing welding speed. The sound welding conditions mainly depended on the suffiicient welding heat input during the process. The insufficient heat input resulted in the void like defect in the weld zone. Higher welding speed caused a larger inner void or lack of bonding. The defects were distributed at the stir zone or the transition region between stir zone and thermo-mechanical affected zone (UE). The size of defects slightly increased with increasing welding speed. These defects had a great effect on the joint strength of weld zone. The weld zone was composed of stir zone, TMAZ and heat affected zone. The stir zone was cosisted of fine recrystallized structure with $5-8\mu\textrm{m}$ in the mean grain size. The hardness of weld zone was near the 60HV, which was slightly lower than that of base metal. The maximum joint strength was about 219MPa that was 75% of that of base metal and the yield strength was also lower than that of base metal partly due to the existance of defects.

• Journal of Welding and Joining
• /
• v.15 no.5
• /
• pp.92-103
• /
• 1997

The purpose of this study is to improve the wear resistance and hardness of Al alloy by making a formation of the thick surface hardening layers. The thick surface hardening layers were formed by PTAW(Plasma Transferred Arc Welding), with the addition of metal powders (Cu), ceramics powders (NbC, TiC), and mixture powders (Cu+NbC) in Al alloy (A1050, A5083). Mechanical properties of overlaid layers (wear resistance, hardness) were investigated in relation to the microstructure. The results obtained are summarized as follows: The depth of penetration was increased with increasing powder feeding rate. It is considered that these increase were due to the thermal pinch effect by the addition of powders, especially, for the Cu powders, were due to the heat of reaction with the matrix. The hardness and wear resistance of overlaid layers were improved with increasing powder feeding rate. For the Cu powders, it is considered that these increase were due to the increase of the formation of ${\theta}(CuAl_2)$ phase with increasing feeding rate of Cu powers.

• Journal of Welding and Joining
• /
• v.32 no.1
• /
• pp.22-27
• /
• 2014

In the past, cold crack was commonly observed in the HAZ(heat affected zone) of high-strength steels. Applying to TMCP(thermo-mechanical controlled process) and HSLA(high strength low alloy) steels, cold crack tends to increase the occurrence in the weld metal. It is generally understood that cold crack occurs when the following factors are present simultaneously : diffusible hydrogen in the weld metal, a susceptible microstructure and residual stress. In particular, many studies investigated the microstructural effect on the cold crack in HAZ and the cold crack in weld metals starts to receive the special attendance in modern times. The purpose of the study is to review the effect of weld microstructures (grain boundary ferrite, Widm$\ddot{a}$nstatten ferrite, acicular ferrite, bainite and martensite) on cold crack in the weld metals. Among various microstructures of weld metals, acicular ferrite produced the greatest resistance to the cold crack due to the fine interlocking nature and high-angle grain boundary of the microstructure.

• Journal of Welding and Joining
• /
• v.32 no.2
• /
• pp.54-62
• /
• 2014

Manhole cover, which is usually made of grey cast iron and consists of frame and cover, should have enough strength to support the heavy traffic load. The manhole cover made of cast iron has heavy weight to handle manually and is vulnerable to impact force with its brittle characteristics. Moreover, its production process of casting has been regulated in terms of environmental pollution. In this study, steel manhole cover is proposed to substitute the cast cover with a series of structural analyses to confirm its strength to support the test load for manhole cover. The cover of the proposed steel manhole cover is made of thin circular pate and stiffeners below the plate. Rectangular columns and hollow circular plate were selected for the shape of the stiffener. In order to give enough strength for the cover to behave within elastic range in the loading, strengthening structures of the cover were varied with increasing the number and the size of the stiffeners. The results of the analyses revealed that when both the hollow circular stiffener and cross stiffeners were additionally applied at the same time to the steel cover with longitudinal stiffeners, the maximum stress level in the cover could be reduced to that level presented in the cast cover.

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