Kuang-Hung Tseng

Evaluation of TIG flux welding on the characteristics of stainless steel

Abstract The aim of the present study was to investigate the effect of specific oxide fluxes on the surface appearance, weld morphology, retained δ ferrite content, hot cracking susceptibility, angular distortion and mechanical properties obtained with the tungsten inert gas (TIG) process applied to the welding of 5 mm thick austenitic stainless steel plates. An autogenous gas tungsten arc welding process was applied to stainless steels through a thin layer of activating flux to produce a bead on plate welded joint. The MnO2 and ZnO fluxes used were packed in powdered form. The experimental results indicated that the 80% MnO2–20% ZnO mixture can give full penetration and also a satisfactory surface appearance for type 304 stainless steel TIG flux welds. TIG welding with MnO2 and/or ZnO can increase the measured ferrite number in welds, and tends to reduce hot cracking susceptibility in as welded structures. It was also found that TIG flux welding can significantly reduce the angular distortion of stainless steel weldments.

The effect of pulsed GTA welding on the residual stress of a stainless steel weldment

Abstract The objective of this study was to investigate the effect of pulsed GTA welding parameters on the residual stress of the weldment. Autogenous gas tungsten arc welding was applied on SUS 304 and SUS 310 stainless steels to produce a bead-on-plate weld. The residual stress was determined by using the hole-drilling strain-gage method of ASTM standard E837. The experimental results show that a greater pulse frequency, a larger pulse spacing, a greater amplitude ratio, and a greater duration ratio can reduce the magnitude of the residual stress in the austenitic stainless steel weldment. The residual stress of the 310 stainless steel weldment is greater than that of the 304 stainless steel weldment under the same welding conditions because of its lower thermal conductivity and thermal diffusivity. The experimental results also showed that pulsed current welding has a smaller range of the tensile residual stress zone as compared to that of constant current welding because of its lesser amount of heat input.

The study of nitrogen in argon gas on the angular distortion of austenitic stainless steel weldments

Abstract The objective of this study was to investigate the effect of nitrogen added in argon shielding gas on the angular distortion of austenitic stainless steels. An autogenous gas tungsten arc welding was conducted on austenitic stainless steels 304 and 310 to produce a bead-on-plate weld. The delta-ferrite content of welds was measured by using Ferritscope. The angular distortion of weldments was determined by using the mean vertical displacement method (MVDM). The present results indicate that the retained ferrite content in Type 304 stainless steel weld metals was rapidly reduced as the nitrogen addition in argon shielding gas was increased. The welding angular distortion was raised with the increase of the amount of nitrogen added in the shielding gas. This experimental result also found that the existence of retained ferrite microstructure within the austenitic matrix has a beneficial effect in reducing welding distortion tendency of austenitic stainless steel weldment.

Effect of pulsed gas tungsten arc welding on angular distortion in austenitic stainless steel weldments

Abstract The effect of the parameters of the pulsed gas tungsten arc welding (GTAW) process on the angular distortion in austenitic stainless steel weldments was investigated. Autogenous GTAW was conducted on types 304 and 310 stainless steels to produce a bead on plate weld. The weldment thermal cycle was recorded during pulsed GTAW to investigate the influence of thermal stress. Angular distortion was determined by using the mean vertical displacement method. The experimental results indicate that higher pulse frequency, smaller pulse spacing, greater amplitude ratio, and greater duration ratio can reduce the angular distortion. The angular distortion of type 310 stainless steel weldments was greater than that of type 304 weldments under the same welding conditions because of the lower thermal conductivity and thermal diffusivity of type 310.

Effect of Activated TIG Flux on Performance of Dissimilar Welds between Mild Steel and Stainless Steel

The purpose of the present work was to investigate the effect of oxide fluxes on surface appearance, weld morphology, angular distortion, and weld defect obtained with activated tungsten inert gas (TIG) process applied to the welding of 6 mm thick dissimilar metal plates between JIS G3131mild steel and SUS 316L stainless steel. The CaO, Fe2O3, Cr2O3, and SiO2 fluxes used were packed in powdered form. The results indicated that the surface appearance of TIG welds produced with oxide flux formed residual slag. TIG welding with SiO2 powder can increase joint penetration and weld depth-to-width ratio, and therefore the angular distortion of the dissimilar weldment can be reduced. Furthermore, the defects susceptibility of the as-welded can also be reduced.

Effect of nitrogen addition to shielding gas on residual stress of stainless steel weldments

Abstract The objective of the present study was to investigate the effect of nitrogen additions to the shielding gas on the ferrite content and residual stress in austenitic stainless steels. Autogenous gas tungsten arc (GTA) welding was applied on austenitic stainless steels 304 and 310 to produce a bead on plate weld. The delta ferrite content of the weld metals was measured using a Ferritscope. The residual stress in the weldments was determined using the hole drilling strain gauge method. The present results indicated that the retained delta ferrite content in type 304 stainless steel weld metals decreased rapidly as nitrogen addition to the argon shielding gas was increased. The welding residual stress increased with increasing quantity of added nitrogen in the shielding gas. It was also found that the tensile residual stress zone in austenitic stainless steel weldments was extended as the quantity of added nitrogen gas in the argon shielding gas was increased.

UNS S31603 Stainless Steel Tungsten Inert Gas Welds Made with Microparticle and Nanoparticle Oxides

The purpose of this study was to investigate the difference between tungsten inert gas (TIG) welding of austenitic stainless steel assisted by microparticle oxides and that assisted by nanoparticle oxides. SiO2 and Al2O3 were used to investigate the effects of the thermal stability and the particle size of the activated compounds on the surface appearance, geometric shape, angular distortion, delta ferrite content and Vickers hardness of the UNS S31603 stainless steel TIG weld. The results show that the use of SiO2 leads to a satisfactory surface appearance compared to that of the TIG weld made with Al2O3. The surface appearance of the TIG weld made with nanoparticle oxide has less flux slag compared with the one made with microparticle oxide of the same type. Compared with microparticle SiO2, the TIG welding with nanoparticle SiO2 has the potential benefits of high joint penetration and less angular distortion in the resulting weldment. The TIG welding with nanoparticle Al2O3 does not result in a significant increase in the penetration or reduction of distortion. The TIG welding with microparticle or nanoparticle SiO2 uses a heat source with higher power density, resulting in a higher ferrite content and hardness of the stainless steel weld metal. In contrast, microparticle or nanoparticle Al2O3 results in no significant difference in metallurgical properties compared to that of the C-TIG weld metal. Compared with oxide particle size, the thermal stability of the oxide plays a significant role in enhancing the joint penetration capability of the weld, for the UNS S31603 stainless steel TIG welds made with activated oxides.

Effect of process parameters of micro-plasma arc welding on morphology and quality in stainless steel edge joint welds

Abstract The effects of the process parameters of micro-plasma arc welding (micro-PAW) on the morphology and quality of stainless steel edge joint welds were investigated. Micro-PAW was applied on type 304 stainless steels to produce an edge joint weld. Welding experiments were carried out for various combinations of arc current, welding speed, arc length, shielding gas, and clamp distance, with all other operating conditions held constant. The experimental results indicated that the collimated shape of the low current plasma arc was mainly responsible for the low sensitivity of the weld morphology to variations in the nozzle standoff distances. The arc voltage increased with increasing quantity of added hydrogen in the argon shielding gas. It was also found that satisfactory edge joint welds can be formed using a clamp distance of 0.35 mm, and that the edge joint penetration on a 0.1 mm thickness stainless steel is about 60% of the clamp distance.

Small-scale projection lap-joint welding of KOVAR alloy and SPCC steel

The objective of this study was to investigate the effect of projection heights and operating conditions on projection collapse, nugget size, and joint strength of KOVAR alloy and steel plate cold-rolled commercial (SPCC) grade in small-scale projection welding of dissimilar metals. All welds were produced with a capacitor charging power supply. Three projection designs with different heights were used. Harris and Riley-type projection was embossed on the SPCC steel sheets. Nugget size was estimated using a peel test. Joint strength was evaluated using a tensile-shear test. The results indicated that a low-level projection has a positive effect, increasing the load-bearing capacity of projection. The nugget diameter and joint strength increase as the weld current and projection height increase. Increasing the electrode force will produce a small nugget. Nugget size is a good indicator of the strength of the welded joint. This study also found that a cold-collapse ratio of approximately 25% produces the highest tensile-shear strength of small-scale projection lap-joint welds.

Monitoring Nugget Size of Micro Resistance Spot Welding (Micro RSW) Using Electrode Displacement-Time Curve

The objective of this work is to investigate the relationship between nugget development and electrode displacement curves during micro RSW of stainless steel sheets. A DC transistor type micro RSW machine equipped with a real-time monitoring system was employed for this study. A laser displacement sensor was used to detect the displacement signals in the movement of upper electrode. This research can provide references for monitoring and control micro RSW quality using maximum electrode displacement. The results showed that electrode displacement increased rapidly at the initial heating stage of welding, and then at a reducing rate under normal cooling stage. The maximum electrode displacement is proportional to the weld current and is inversely proportional to the electrode force. An electrode displacement curve is an ideal monitoring signal can reflect the formation and growth of a nugget during micro RSW.