Welding Metallurgy of

Effect of grain refinement on fracture toughness in extruded pure magnesium

Microstructure and mechanical properties of friction stir processed AISI 316L stainless steel

Keyhole gas tungsten arc welding of AISI 316L stainless steel

Microstructure, mechanical and corrosion properties of friction stir welded high nitrogen nickel-free austenitic stainless steel

In this study, the friction stir butt welding of 2-mm-thick high nitrogen-containing stainless steel (HNS; Ni-free austenitic stainless steel containing 1 mass% nitrogen) plates was performed using a load-controlled friction stir welding (FSW) machine with a Si 3 N 4 -based tool at various welding speeds, i.e., 50 mm/min, 100 mm/min, 200 mm/min and 300 mm/min, and a constant tool rotating speed of 400 rpm. To determine the optimum welding conditions to create reliable HNS FSW joints, the effect of the heat input on the mechanical properties of the HNS FSW joints was studied. The mechanical properties were evaluated by the Vickers hardness test and the tensile strength test. Full-penetrated and defect-free butt welded joints were successfully produced, under all the applied welding conditions. The stir zones consisted of very fine grained structures and showed an increase in the Vickers hardness. These joints also showed a higher tensile strength and yield strength than the base metal. In particular, the FSW welds obtained at a welding speed of 100 mm/min, which showed the best mechanical properties, had a relatively higher Vickers hardness, which indicates a good relationship between the welding parameter (heat input) and the hardness profile due to the microstructure refinements. It was estimated that these welding conditions were optimal, and under these conditions both grain growth and α-phase formation were prevented.

Mechanical properties of friction stir butt welds of high nitrogen-containing austenitic stainless steel

Study on reduction in wear due to magnetization

Comparison of Ti-5Al-5V-5Mo-3Cr Welds Performed by Laser Beam, Electron Beam and Gas Tungsten Arc Welding

Gas tungsten arc welding experiments were conducted using austenitic stainless steel containing 0.51%N and 0.78%N. Microstructure observation and hardness measurement were made to study the loss of nitrogen. It was found that welding resulted in a considerable loss of hardness in the weld metal for the case of 0.78%N steel, but not for 0.51%N steel. We explain this in terms of a higher nitrogen content enabling a significantly smaller critical pore size and hence N2 porosity formation to be energetically more favourable. The major finding was that, for the case of 0.78%N steel, a band of microporosity was observed along and near the complete fusion boundary of the weld. It was identified that these micropores were present in the parent metal, not in the weld metal. Partial melting in the zone next to the complete fusion boundary resulted in a nitrogen content significantly higher than the solubility of nitrogen in the liquid channels or pockets. Nitrogen gas pores then formed and became trapped in that zone. Supporting this forming mechanism of microporosity band was the fact that hardness decreased in that zone due to the loss of nitrogen in γ phase matrix for solute strengthening and that nitride particles disappeared after welding.

Microporosity formation in partially melted zone during welding of high nitrogen austenitic stainless steels

This article briefly summarises previous reports as well as some recent results on welding of various titanium alloys. Titanium is available in a wide range, hence, their properties and characteristics (including welding characteristics) may also varied significantly. The alloys studied represented three major areas; they are (1): unalloyed or commercially pure titanium (CP Ti), (2): near α and α+β alloys, and (3): β alloys. From our preliminary results, it can be reported that the structure of fusion zone (FZ) and heat affected zone (HAZ) of alloys from area (1) may change but their hardness remained, arguably, the same as the as-received material. Alloys from area (2) showed an increase in hardness in the FZ and HAZ areas due to the formation of α-prime or martensite, while alloys from area (3) experienced a reduction in hardness associated with dissolution of α phase leaving only retained β in the FZ. Further investigations are required to confirm these findings. Such information are very useful so that appropriate post welding heat treatment (PWHT) can be applied to improve their properties and performance.

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Osamu Kamiya

Papers

Mechanical properties of friction stir butt welds of high nitrogen-containing austenitic stainless steel

Study on reduction in wear due to magnetization

Comparison of Ti-5Al-5V-5Mo-3Cr Welds Performed by Laser Beam, Electron Beam and Gas Tungsten Arc Welding

Microporosity formation in partially melted zone during welding of high nitrogen austenitic stainless steels

Welding of titanium alloys