Study On The Interaction Of Stress And Corrosion Of Mine Steel Wire In Corrosive Environment

As a load bearing member to connect the hoist and lifting container, wire ropefor mine hoisting has the mission of promotion of coal and gangue, decentralization ofmateirals, movement of personnel and equipment. During mine hoisting, the ropes aresubjected to externally applied tensile load, cyclic axial load and cyclic bending load.While the corrosion phenomenon of steel wire is very serious for the harshenvrionment of high humidity and acid erosion. Furthermore, wire rope will enduregreat applied stress in the process of servicethat produce extremelydangerous low-stress damage form under the combined action of stress and corrosion,therefore, constant stress or slow rate of strain conditions will result in stresscorrosion cracking. In the joint action of cyclic tensile stress, steel wire is prone toproduce corrosion fatigue fracture. In view of this situation, the paper focuses onimprove electrochemical corrosion behavior, stress corrosion behavior and corrosionfatigue behavior of steel wire for hoisting under specific mine corrosive environmentas well as systematically investigate the impacts of corrosion-stress interaction onlifetime of steel wire. The main research contents and the resulting conclusions are asfollows:(1) Through analysis of polarization curves of the steel wire in different corrosivesolutions with different surface treatments to obtain the anode and cathode reactionprocess of wire under different conditions. The results showed that corrosion productfilm was generated in the corrosion process of steel wire. The protection of the film tosteel substrate was related to the solution of corrosive and soaking time. The variationof corrosion potential and corrosion current density in different stages was acquiredby the analysis of the polarization curve using Tafel linear extrapolation. The resultssuggest that the corrosion rate of bare wire is the fastest during the whole process ofsoaking in acid solution, and the corrosion resistance of steel wire under differentconditions was associated with immersion time. Electrochemical impedancespectroscopy (EIS) of steel wire under different conditions were measured. Theequivalent circuit of steel wire under different conditions was acquired by usingZsimpwin software to fit the Nyquist diagram, which provided a theoretical basis tostudy the electrochemical corrosion process.(2) Slow strain rate tensile test (SSRT) was conducted with smooth wirewithout gap to investigate the influence of different applied potentials and different corrosion solutions on the sensitivity of stress corrosion crack. The result suggestedthat the steel wires in three different solutions had SCC susceptibility. The steel wirein acid solution under Ecorr+400mV had the minimum tentile strength of about1673MPa, and the minimum average elongation of about14.71%. The fracturemorphologies of steel wires in corrosion solutions were similar to the morphology inair, which were mainly the dimple pattern. The SCC sensitive area was accompaniedby minor brittle fracture characteristics. The tendency of SCC caused by anodicdissolution will decrease with the raise of the anode potential in acid solution. And theSCC sensitivity under the open circuit potential was weaker. However, the tendencyof SCC created by anodic dissolution will increase with the raise of additional anodepotential in neutral and alkaline solution. The steel wire SCC mechanisms arecompletely influenced by hydrogen embrittlement mechanism in these three solutionswhen they are couple with cathode potential. Vigorous hydrogen evolution reactioncontribute to obvious hydrogen content increase and enhancement of SCC sensitivityalong with the negative shift of applied cathode potential.A constant stress corrosion testing machine of steel wire is developed to acquirethe corrosion potential and Nyquist curves over time through stress corrosion test ofthe steel wire in different solutions and different applied constant stress. It turned outthat the applied stress may reduce steel corrosion potential which is influenced bysolution corrosion strength. The influnce of applied stresses on the Nyquist diagram ofsteel wire is violent. The radius of low-frequency capacitive when applied1125MPain acid solution is the biggest after1h.(3) Corrosion fatigue tests of steel wires were conducted to compare the S-Ncurves in the air and different corrosive solutions. The findings showed that the wirehad shortest corrosion fatigue lifetime in acidic solution with alkaline take the secondplace, and then followed by neutral solution. Moreover, stress and corrosion had amutual promotion relationship on reduction of fatigue lifetime. The results of steelcorrosion fatigue test under different stress ratio and different frequency showed thatthe smaller of the stress ratio and higher of the frequency had a shorter corrosionfatigue lifetime of steel wire. The initiation of crack is mainly controlled by anodicdissolution mechanism. The corrosion fatigue behavior of steel wire under differentapplied potential study showed that anode polarization effect could significantlyreduce the corrosion fatigue lifetime of the wire and obvious fracture morphologymay occurred at wire fracture fatigue source. The area of dimple region may increase with the raise of applied anode potential. When applied with cathodic polarizationpotential, the hydrogen produced by cathodic reaction of hydrogen was not able toenter into the steel substrate and the corrosion fatigue lifetime may significantlyprolonged as a result of effective obstruction of anodic dissolution reaction. Therelatively more smooth fracture suggested a clear and definite brittle fracturemechanism.(4) The effect of different pits sizes and different applied stress on internal stressdistribution of pit was investigated through finite element model. And the findingsindicated that the greater of the external tensile stress, the tendency of stressconcentration at the bottom of pits were more obvious with which accompanied byhigher equivalent stress. The stress concentration area was likely to extend out alongby the direction of applied stress vertical line (main crack propagation direction). Thelarger radius of pits and stronger equivalent stress were also visible for the severecorrosion tend when the external stress is the same.The extension tendency was moreobvious for main crack vertical to the applied stress. The effect of complex stress state(including stress ratio and loading frequency) on steel wire pits stress distribution wasanalyzed to find that different conditions may lead to similar equivalent stressdistribution around the pits and equivalent stress of each point was relevant to thedistance from the bottom of the pits. The magnitude of anodic corrosion currentdensity (iσ) at the bottom of the pits of different diameter was calculated underdifferent applied stress by theoretical calculation to find that improved external tensilestress and increased pits radius was able to increase iσ.