The effect of hydrostatic pressure (HP) on the corrosion behaviour of X80 steel is investigated to assist the development of deep-sea oil and gas resources. The results show that the corrosion current increases as HP increases whereas the charge transfer resistance follows the opposite trend. The corrosion products are composed of γ-FeOOH, α-Fe 2 O 3 and α-FeOOH at atmospheric pressure, while Fe 3 O 4 is only formed at a high HP. Additionally, the inner layer of the corrosion products contains more Fe 3 O 4 compared with the surface corrosion layer. HP accelerates the corrosion rate of X80 steel due to its effect on the chemical and physical properties of the corrosion products, including the promoted reduction of γ-FeOOH and the formation of wider and deeper cracks on the corrosion product layer.

Herein, single-pass laser-cladded 2205 duplex stainless steel is fabricated on the surface of Q235 carbon steel at different laser powers in the range of 1.7À2.7 kW. The relationships between laser powers and geometrical characteristics, microstructure, microhardness, and corrosion resistance of the cladded layers (CLs) are analyzed. The results show that with the increase in laser power, the width and height of the bead increase, and the dilution rate and depth of the molten pool also significantly increase. Furthermore, the shape of ferrite gradually transforms from coarse to slender and eventually turns into a discontinuous vermicular shape. It is found that the CL obtained at a laser power of 2.3 kW has higher average microhardness and exhibits better corrosion resistance than the other samples (%20 times better than that of the carbon steel substrate), with its corrosion potential and corrosion current density of À0.146 V and 0.13 μA cm À2 , respectively.

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By applying 2205 duplex stainless steel powders to repair and improve carbon steel, multi-pass laser-cladding tests were conducted on Q235 carbon steel surfaces with different laser powers in the range of 1.9~2.5 kW in order to evaluate the performance of the laser-cladding layers. The phase composition, macro- and microstructure, electrochemical corrosion resistance, friction, and wear resistance of the laser-cladding layers were investigated. Macroscopic observation identified no obvious cracks. The phases that made up the multi-pass laser-cladding layers were γ-Fe and α-Fe. Owing to the optimal laser power at 2.3 kW, a large number of equiaxed crystals and a small number of cellular crystals made up the microstructure of the prepared laser-cladding layer, which contributed to its good corrosion resistance. The wear resistance of the multi-pass laser-cladding layer and the carbon steel was also studied. A combined action of adhesive wear and abrasive wear, accompanied by oxidative wear, was determined through observation of pits and furrows on the friction surface of the multi-pass laser-cladding layer, while a typical mechanism of abrasive wear was confirmed by checking the friction surface of the carbon steel.

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