• Proceedings of the KWS Conference
• /
• 2009.11a
• /
• pp.64-64
• /
• 2009

The use of ultra high strength steels (UTSS) is a natural result with increasing the demands for the lightweight materials and developing an innovative steel technology. Recently it has been used a 1500MPa grade hot stamping steel as automobile bodies, reinforcement parts, and seat frame parts in the automotive industry. It is a quenchenable steel manufactured by hot stamping process. It is well known that UTSS welding has softening in the heat affected zone(HAZ). Because welding is a sort of process applying heat, it should change the heat treated features and degrade the strength. This study was performed to investigate the influence of the heat input on the softening of the HAZ in the GMAW process. Each experiment was compared with that in the conditions having a different current and voltage at a same heat input. In order to analysis characteristics of the HAZ, optical microscope was used to observe microstructure and vickers hardness tests were carried out across the welds. Applying low heat input means a fast cooling rate. It leads to high hardness in the HAZ. It is found that characteristics of the HAZ are determined by microstructure obtained by different cooling rate.

• Journal of Welding and Joining
• /
• v.26 no.5
• /
• pp.49-59
• /
• 2008

Hastelloy C-276, corrosion resistant alloy at high temperature, is used in chemical plant and power generation industry. In this study, process parameter of laser welding for welding property in Hastelloy C-276 using a continuous wave Nd:YAG laser was studied. As the result of experiment, laser welding did not show segregation or crack at heat affected zone compared to conventional GTWA welding. The melting zone showed cell dendritic structure along with welding line. In addition, planer front solidification is occurred from welding structure, and it was progressed to cellular solidification. Optimal process parameter for butt welding was 1.2kW and 2.0 m/min for laser power and welding speed, respectively. While heat input, output density, tensile stress, and longitudinal strain was $441.98{\times}103$ J/cm2, $29.553{\times}103$ W/cm2, 768 MPa, and 0.689, respectively. Lap welding of the same material showed greater discrepancy in tensile property during 1 line and 2 line welding. For 1 line welding, tensile stress was about 320 MPa, and 2 line showed slightly larger tensile stress. However, strain was decreased by 20%. From this result, lap welding of the same material, Hastelloy C-276, with 2 line welding is considered to be more effective process than 1 line welding with consideration of mechanical property.

• Proceedings of the KWS Conference
• /
• 2002.10a
• /
• pp.330-335
• /
• 2002

Resistance spot welding is one of the most widely used processes in sheet metal fabrication. Quality assurance of welding has been important to increase the productivity. In this study, weld quality estimation using primary circuit dynamic resistance applied to the in-process real-time systems. For quality estimation, factors relating to quality were extracted from the dynamic resistance, measured in the timer. The relationship between these factors and weld quality was determined through a artificial neural network model. This method has the advantage over the conventional one, such as obtaining the quality information without the use of extra devices.

• Proceedings of the KWS Conference
• /
• 2007.11a
• /
• pp.254-256
• /
• 2007

In this paper, the effects of the reflow number in the mechanical reliability of flip chip solder joint was investigated by flip chip shear test and thermal shock test. For evaluation mechanical reliability of flip chip, We experiment that specimens were operated 3-times, 6-times, 9-times, 12-times under reflow Process. After shear test and thermal shock test, We measured max shear strength and coming first crack number of thermal cycle. And We observe fracture surface and cross section by using SEM(Scanning Electron Microscope) and optical scope. In the results, the more specimens were operated reflow process, the more decreased maximum shear strength and number of thermal cycle.

• Journal of Welding and Joining
• /
• v.26 no.1
• /
• pp.69-75
• /
• 2008

Spot welding which use the main process for side block production of stainless steel railway vehicle is legged behind in laser welding about a quality and productivity. Although the laser welding has many potential advantages such as low heat input and aspect ratio of weld bead, its application to a new structural component still is required many engineering data including mechanical properties such as tensile, fatigue strength, etc on. Therefore, experimental analysis was carried out to understand the fatigue phenomena of different thickness stainless steel overlap joining panels by Nd:YAG laser welding. The fatigue life curves were obtained through fatigue tests with the various levels of applied load. The fatigue life is related with the parameters such as gap size and penetration depth through experiment. As the results, tensile strength and fatigue life were proportional in heat input level and gap was identified the major factor for fatigue life. Also we could know that deferent a-ferrite content at HAZ depend on welding heat input was important factor to determine a formation of initial crack and total fatigue life cycle.

• Journal of Welding and Joining
• /
• v.32 no.5
• /
• pp.21-25
• /
• 2014

Oil and gas fields were left unexploited which deemed too deep and sour. New developing markets are emerging in this part and pipe manufacturers need demanding requirements in the combination of sour service requirements with heavier wall thickness required to cope with increasing water depths. Whilst, the strength and fracture toughness needed to meet the strict requirements In order to deliver the optimum sour properties in the final pipe, attention needs to be paid to each stage throughout the process from steel making. The main key during steel making is strengthening, securing mechanical properties and suppression of center segregation by adding proper chemical elements and controlling water cooling and plate rolling. Additionally in welding, it is required to prevent HAZ softening by high heat input during welding of heavy thick pipes and hydrogen assisted cracking in high strength steels with hard phases. In this paper, we introduce markets of sour resistant linepipe steels and in response to this, have a look in the development trend of sour resistant linepipe steels and its sour characteristics in welded joints.

• Journal of Welding and Joining
• /
• v.31 no.6
• /
• pp.65-70
• /
• 2013

In joining Alumina to copper plate by Mo-Mn metallizing process, the effects of the composition of metallizing paste on the bonding strength were investigated. The bonding strength increased with increasing Mn amount in the paste up to 20% but followed by the decrease with addition of Mn. The maximum bonding strength reached 50MPa at 20%Mn when heated to $1550^{\circ}C$ for 60minute. The addition of Si to the metallizing powder increased the bonding strength of the joint by enhancing the mechanical bonding between the Alumina and the metallizing layer due to the decrease of layer viscosity with the addition of $SiO_2$. It is thought that MnO reacted with $Al_2O_3$ to yield $MnAl_2O_4$ spinel, forming a joint.

• Journal of Welding and Joining
• /
• v.33 no.2
• /
• pp.23-31
• /
• 2015

Stainless steel is used in automobile muffler and exhaust systems. However, in comparison with other steels it has a high thermal expansion rate and low thermal conductivity, and undergoes excessive thermal deformation after welding. To address this problem, we evaluated the use of arc brazing in place of welding for the processing of an exhaust system, and investigated the parameters that affect the joint characteristics. Muffler parts STS439 and hot-dipped Al coated steel were used as test specimens, and CuAl brazing wire was used as the filler metal for the cold metal transfer (CMT) welding machine, which is a low heat input arc welder. In addition, a Box-Behnken design of experiment was used, which is a response surface methodology. The main process parameters (current, speed, and torch angle) were used to determine the appropriate welding quality and the mechanical properties of the brazing part was evaluated at the optimal welding condition. The optimal processing condition for arc brazing was 135A current, 51cm/min speed and $74^{\circ}$ torch angle. The process was applied to an actual exhaust system muffler and the prototype was validated by thermal fatigue, thermal shock, and endurance limit tests.

• Journal of Welding and Joining
• /
• v.9 no.4
• /
• pp.28-39
• /
• 1991

The change of microstructure in the bonded interlayer and mechanical properties of the joints were investigated during Transient Liquid Phase Diffusion Bonding(TLP bonding) of STS304/SM17C and STS304/SM45C couples using Ni base amorphous alloys added boron and prepared alloy as insert metal. Main experimental results obtained in this study are as follows: 1) Isothermal solidification process was completed much faster than theoretically expected time, 14ks at 1473K temperature. Its completion times were 3.6ks at 1423K, 2.5ks at 1473K and 1.6ks at 1523K respectively. 2) As the concentration of boron in the insert metal increased, the more borides were precipitated near bonded interlayer and grain boundary of STS304 side during isothermal solidification process, its products were $M_{23}P(C,B)_6}_3)$ The formation of grain boundary during isothermal solidification process was completed at structural carbon steel after starting the solidfication at STS304 stainless steel. 4) The highest value of hardness was obtained at bonded interface of STS304 side. The desirable tensile properties were obtained from STS304/SM17C, STS304/SM45C using MBF50 and experimentally prepared insert metal with low boron concentration.

• Journal of Welding and Joining
• /
• v.27 no.6
• /
• pp.43-48
• /
• 2009

In this study, Cu-based bulk metallic glass (BMG) coatings were deposited by atmospheric plasma spraying (APS) process with different process conditions (with- and without hydrogen gas). As adding the hydrogen gas, thermal energy in the plasma flame increased and induced difference in the melting state of the Cu-based BMG particles. The microstructure and mechanical properties of the coatings were analyzed using a scanning electron microscope (SEM) with an energy dispersive spectroscopy (EDS) and nano-indentation tester in the light of phase analysis. It was elucidated by the nano-indentation tests that un-melted region was a mainly amorphous phase which showed discrete plasticity observed as the flow serrations on the load.displacement (P - h) curves, and the curves of solidified region showed lower flow serrations as amorphous phase mingled with crystalline phase. Oxides produced during the spraying process had the highest hardness value among the phases and were well mixed with other phases resulted from the increase in melting degree.