摘要
R4s级系泊链钢是新型低碳、低合金高强度钢,具有优良的综合性能。系泊链在工作过程中,上与海面浮体相连,下与海底锚腿相接,通体基本浸入在海水中,受到周围环境主要是海水的腐蚀,而且随着海洋洋流的作用,随着海水的响应上下来回震动。由于其自身重力和海面浮体的拉力,使其承受了一定的应力作用,而响应震动又引起了应力的变化,产生了交变应力,和海水腐蚀的共同作用,产生了腐蚀疲劳。
本文根据系泊链焊接后在连续炉中热处理的实际生产条件,选择在930℃温度保温30min快速加热后水冷淬火+930℃温度保温30min快速加热后水冷淬火的二次淬火+630℃温度回火保温30min,同时,利用金相显微镜、扫描电镜等分析仪器,对上述样品的微观组织和断口形貌进行了分析;利用洛氏硬度计、显微硬度计、万能试验机和冲击试验机等,对不同热处理状态下的力学性能进行了测试;利用电化学试验、海水挂片试验、应力腐蚀试验对材料的腐蚀性能进行了测试,结合前面的力学、腐蚀性能,利用腐蚀疲劳试验对R4s级系泊链钢的腐蚀疲劳性能进行了测试及客观的分析。
实验结果表明:系泊链钢在受到腐蚀和交变应力共同作用时,腐蚀和疲劳作用同时在刚表面进行伤害,海水溶液中的离子和氧对钢表面进行侵蚀产生点蚀,而交变应力作用使得钢表层的位错移动形成小的滑移带从而产生沟槽和隆脊,二者的共同作用下,钢表面上的点蚀尖部和滑移所引起的沟槽底部吸附了较多的Cl-和OH-,致使金属原子键的亲和力减弱,即金属表面能降低,在交变应力的作用下,促进了金属的破裂,微观裂纹在钢表面形成。随着交变应力和腐蚀的继续作用,裂纹沿着两组互不平行的{111}滑移面扩展,裂纹的扩展方向平行于{111}面的交线,即{110}方向。裂纹的扩展引起了应力集中逐渐增大,裂纹逐步向材料内部扩展。随着腐蚀时间的增加,腐蚀产物也随之增多,腐蚀产物覆盖在裂纹的周围,腐蚀产物会阻隔在腐蚀液与裂纹尖端之间,阻止了腐蚀的进行,此时裂纹扩展主要由交变应力作用下的金属滑移扩展,产生新鲜的金属表面。而裂纹在交变应力作用下围绕裂纹尖端作一张一弛运动,张弛运动将腐蚀产物挤压出裂纹缝,也会将腐蚀产物撕裂,腐蚀溶液接触新鲜的金属裂纹表面。随着腐蚀产物覆盖裂纹表面-腐蚀产物层破裂-重新覆盖的过程不断重复,裂纹在{110}面上的扩展也不断进行,直到金属不能承受应力作用时发生断裂。
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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