Fanyong Zhang

Microstructure Analysis and Weldability Investigation of Stainless Steel Clad Plate

Stainless steel clad plate and pipe have a prevailing applications in nuclear power plants. The microstructure and mechanical properties of 304 austenite stainless steel clad plate by vacuum hot rolling were investigated in detail. Due to the severe diffusion of carbon element from carbon steel substrate to stainless steel clad, the decarburized layer and carburized layer were formed at the interfacial transition zone. The bending test reveals super-high interface strength and toughness, delaying the premature occurrence of interfacial delamination crack. The stainless steel clad pipe were successfully fabricated by elbowing and welding. There are no macroscopic and microscopic defects in the weld zone, fusion zone and heat affected zone. The heat affected zone of carbon steel layer contains widmanstatten, completely crystallized zone, partial crystallized zone and recrystallized zone. The weld zone of carbon steel contains widmanstatten structure and refined ferrite and pearlite. However, the heat affected zone is only comprised of coarse grains. With the increase of distance between weld zone and fusion zone, the small plane grain firstly changes into cellular crystal grain, and finally into columnar crystal in the stainless steel weld zone.

Microstructure and Mechanical Properties of Aluminum Clad Steel Plates by Cold Rolling and Annealing Heat Treatment

Aluminum clad steel plate has been successfully fabricated by cold rolling and annealing heat treatment. The thicknesses of total clad plate and aluminum cladding layer were about 1.5 mm and 50–70 μm, respectively. The grain morphology, mechanical properties revealed a slight anisotropy. Herein, the grains were severe elongated along the cold rolling direction. The clad plates exhibited a superior tensile elongation and slight interfacial delamination, and highest value of multiple bending fracture times was located at the clad plate along the angle of 45°. Moreover, the perfect interfacial brazing bonding presented at the base clad plate and fins, which can be used in the power station.

Plasma Nitriding of 2024 Al Alloy Deposited with Ti Film: Effects of N 2 –H 2 Ratio on Microstructure Evolution and Mechanical Properties

2024 Al alloys were firstly deposited with pure Ti film (~5.0 μm in thickness) using magnetron sputtering, then plasma nitrided for 8 h at 490 °C under N2–H2 gas mixtures with different N2 content (15, 40 and 50%). The Ti–N and Ti–Al diffusion reactions were activated simultaneously on the surface of Al alloy to obtain duplex coatings. The results showed that the duplex coatings were composed of nitride/aluminide layers (TiN0.3/Al3Ti/Al18Ti2Mg3 layers). With increasing the N2 content in the gas mixture, the peak ratio I(002)/I(100) of the outer TiN0.3 phase increased and the nitride particles grew larger. The surface hardness of coatings increased with the increasing N2–H2 ratio, reaching the maximum value of 630 HV under 50%N2 + 50%H2. The coatings obtained under gas mixture with high N content showed larger fluctuation at the initial stage during friction tests. All the obtained coatings showed the similar friction coefficient (~0.30) at the stable stage, much lower than the untreated Al alloy (~0.45). The sample nitrided under 50%N2 + 50%H2 exhibited the lowest wear rate, 60% lower than that of the uncoated one. The nitrided samples exhibited predominant abrasive wear and adhesive wear.