| Class R4s mooring chain is a new low-carbon and low alloy high strength steel, with excellent overall performance. In the work process, the floating-body of mooring chain connected with the seawater,the next phase with the seabed anchor leg,henselae basic immersion in sea water by the surrounding environment is primarily seawater corrosion, and along with the role of ocean currents, with the sea water back and forth up and down vibration response. Because of its self-gravity and surface tension floating body to withstand a certain amount of stress and stress response to vibration has caused the change, resulting in alternating stress, and the joint action of sea water corrosion, resulting in corrosion fatigue.Based on the mooring chain welded in a continuous heat treatment furnace in the actual production conditions, choose the temperature insulation 30min at 930℃than water quenching after rapid heating temperature of + 930℃insulation 30min after the rapid heating of the secondary water-cooled quenching quenching tempering temperature + 630℃insulation 30min, At the same time, the use of optical microscope, scanning electron microscopy and other analytical instruments , samples of the above-mentioned microstructure and fracture morphology were analyzed; The use of Rockwell hardness tester, micro hardness tester, universal testing machine and impact testing machine for different heat treatment state of the mechanical properties were tested; The use of electrochemical tests, the sea is hanging patch test, stress corrosion test corrosion of materials were tested,Combination of the previous mechanics, corrosion, corrosion fatigue testing on the use of mooring chain R4s grade steel corrosion fatigue performance of Germany has been tested and objective analysis.Experimental results show that mooring chain steel by corrosion and the common role of the alternating stress, corrosion and fatigue damage while just the surface of the sea water solution of ions and oxygen on the steel surface erosion pitting produced, while the role of the alternating stress makes the steel surface The formation of small, mobile dislocation slip bands resulting in grooves and ridge, both working together, pitting corrosion on the steel surface and the tip of the groove bottom of the slip caused by adsorption of a greater amount of Cl-and OH-, resulted in reduced affinity of metal atoms bond, namely, the metal surface can reduce, in the role of alternating stress, promote the breakdown of metal, micro-cracks in the steel surface. As the alternating stress and the continuing role of the corrosion, cracks along the two are not mutually parallel to the (111) slip plane expansion, crack propagation direction parallel to (111) planes of the cross-lines, namely, (110) direction. Crack caused stress concentration increased gradually, step by step to the material within the crack extension. With the corrosion time increased, the corrosion products also increase, and corrosion products covering the cracks around the corrosion products will be separated between the crack tip in the etching solution and to prevent the corrosion progresses, the crack growth at this time mainly by the alternating stress expansion of metal under the action of sliding, resulting in fresh metal surface. The crack under the action of alternating stress around the crack tip for a one relaxation exercise, relaxation campaign will squeeze out the cracks seam corrosion products, will bring tears of corrosion products, corrosion of the metallic solution contact with the fresh crack surface. As the corrosion products cover the crack surface - corrosion product layer break - to re-cover the process of repeated, crack in the expansion of (110) faces are also ongoing, until the metal can not withstand stress fracture occurred. |
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