Takeshi Terajima

Micro Flash Welding of Super Duplex Stainless Steels

Super duplex stainless steels were welded using new flash butt welding technology of temperature controlling system. The super duplex stainless steel (329J4L) and conventional duplex stainless steel (329J3L) were used. The samples were mounted in the dies using a Gleeble thermal simulator and flash but welding was made. The specimens were heated up to 1373K for 10sec, 20sec and 30sec. Flash butt welding has consisting of a two stage processes of a flash action and a contact resistance. First stage was a flash welding process and second stage was a solid state bonding process. The cross sectional microstructure of the weld bond region showed two types of a deposited fine particles region and a solid state bonding region. The grain growth was hardly observed in the weld region and the heat-affected zone. For further increasing joining efficiency of solid state bonding at the second stage, the welding time at 1373K was increased from 5 sec to 180sec. The bonding area increased with increasing welding time at 1373K and successfully welded for conventional duplex stainless steel.

Development of Cu-Clad Metallic Glass for Soldering

Soldering is a potential technique for joining metallic glasses. It can be performed at far below the crystallization temperature of various metallic glasses; thus, there is no possibility of crystallization. However, Cu-Zr-based metallic glass displays poor wettability to Pb-free solder, because a strong native oxide film prevents direct contact between the solder and the glass. To overcome this problem, Cu-Zr-based metallic glass clad with a thin film of Cu has been developed. This was produced by casting the melt of a Cu36Zr48Al8Ag8 pre-alloy into a Cu mold cavity, inside which a thin film of Cu with a thickness of 2 μm was placed. Cu36Zr48Al8Ag8 metallic glass was successfully formed and welded to the Cu thin film. From microstructure analysis, it was found that a reaction layer was formed at the interface between the Cu and the Cu36Zr48Al8Ag8 metallic glass. However, no oxide layer was observed in the Cu-clad layer. It was found that the Cu cladding played an important role in preventing the formation of the surface oxide film. Consequently, solderability to the Cu-Zr-based metallic glass was drastically improved.

Resistance Welding by Inserting Wires between Joint Interfaces

Butt resistance welding of super duplex stainless steel by inserting type 316L stainless steel wires was investigated. When the base material temperature was increased from room temperature to 1100 oC at the heating rate of 550 oC /sec, base materials were jointed through the insert wires and HAZ (heat affected zone) of the joint interface were less than 80 μm. In this joining technique, the insert wires played a role of concentrating current on the wires and increasing their temperature up to melting point or near melting point. When the welding was performed at a load of 10 N, the insert wires consisted of ferrite and austenite growing along the ferrite grain boundary. When the welding was performed at a load of 70N, insert wire remained austenite. That is because the contact resistance between insert wire and base materials at 70 N was lower than that of 10 N, and consequently the insert wire were not adequately heated.

Precise Resistance Welding with Wire Insert

Butt resistance welding of super duplex stainless steel type 329J4L with inserting type 316L stainless steel wires was investigated. When the base material temperature was increased from room temperature to 1373 K at the heating rate of 550 K /sec, base materials were jointed through the insert wires. HAZ (heat affected zone) of the joint interface were less than 80 μm. In this jointing technique, the insert wires played an important role of concentrating current on the wires and increasing their temperature up to melting point or near melting point. Thermal analysis using thermography revealed that insert wires were adequately heated just after current started at a load of 10 N. When the welding was performed at a load of 70 N, joint area was increased by plastic deformation of the base material. That led to decrease of current concentration. Consequently insert wires were jointed in the solid state.