| Deformation is a necessary process in the manufacturing,processing,and use of materials in engineering.In recent years,the exploration of how to break through the performance of "Super Steel" and conduct high-performance materials such as higher strength and corrosion resistance has begun.Some domestic scholars have developed carbon steel materials with yield strength of 2200 MPa and ductility of about 25%.From the perspective of corrosion science,materials with high strength and high ductility deformation are more prone to corrosion fracture than materials with low strength and low deformation.However,in current research on the corrosion life of materials,the impact of high ductility strain on the corrosion life is rarely considered.This paper focused on the strain phenomenon that often occur in the use of highly ductile materials,and conducted a study on the relationship between strain and corrosion.316L austenitic stainless steel material,which is often used as rupture disc for safety relief device in high-temperature and high-pressure equipment,was selected as the research object,because of its excellent ductility,which can reach a strain of over 40%;Moreover,because domestic high-end rupture discs are mostly dependent on imports,it is necessary to obtain the relationship between strain and corrosion of rupture disc to propose a prediction method for corrosion life,so this choice also has important engineering significance.Based on the research methods of theoretical analysis,experimental verification and simulation prediction,the quantitative equation for calculating the effect of strain on corrosion resistance of austenitic stainless steel was improved aimed to the issue of the effect of strain on the corrosion resistance of materials.It was applied to explore the corrosion law of rupture disc and predict its corrosion life.(1)The quantitative equation of the effect of strain on the corrosion resistance of austenitic stainless steel is improved,and the validity of the formula is proved by experimental test and finite element simulation.In response to the unclear physical significance and wide range of values of the orientation factor υ(0.4～0.5)and the coeffrcient α(109～1011 cm-2)between shear strain and dislocation de1sity in the current mechanochemical effect formula:φa,eq=φa,eq0-ΔPmVm/zF-TR/zFln(υα/N0εp+1),based on the material theory viewpoint that strain is essentially related to dislocation,the modified Ludwigson hardening model and Taylor formula were involved,combined with the relationship between dislocation density and strain in austenitic stainless steel,a piecewise linear function relationship between the strain and dislocation density of austenitic stainless steel was obtained,and the modified piecewise function equation for calculating the effect of strain on the anode equilibrium potential of austenitic stainless steel was derived:φa,eq=φa,eq0-ΔPmVm/zF-TR/zFln(K/N0εp+1)by ocmbined it with the mechanoelectrochemical effect theory,in which the orientation factor υ and the relation coefficient between shear strain and dislocation density a are replaced by K.It uniformly represented the linear relationship coefficients K1(7×l015 m-2)and K2(5×1015 m-2)between dislocation density and strain in two stages:strain less than 5%and strain greater than or equal to 5%,respectively.It was clarified that the physical meaning of K is that it represented the linear relationship coefficient between dislocation density and strain.Experimental testing and finite element simulation verification were used to demonstrate that the mechanoelectrochemical effect is the main mechanism for reducing material corrosion resistance within the 20%strain range,and the modified mechanochemical effect formula is more accurately to describe the effect of strain on corrosion resistance of austenitic stainless steel.(2)The improved equation for the effect of strain on corrosion resistance is applied to simulate the deformation and corrosion behavior of rupture disc through stamping,and the critical condition for judging the corrosion failure of rupture disc is proposed.In view of the fact that the corrosion law of rupture disc was unknown and the inability to predict the corrosion life of rupture disc,the stamping simulation model of rupture disc was successfully established by using arc top displacement control method with reference to the stamping process of rupture disc.The effects of relief diameter,initial thickness,and clamping radius on the set blasting pressure and rupture disc thickness were explored,and the evolution law of rupture disc deformation was summarized and analyzed.The conclusion was drawn that the thickness of the top of the rupture disc can be used as the critical condition for corrosion failure due to its fastest thinning at the top of the arc position;The experimental results showed that in weakly acidic NaCl solution,the corrosion rate of the rupture disc at the arc top is about 2.82 times that of the undeformed sample.According to the corrosion thinning process and law of the rupture disc arc top position,combined with the corrosion margin evaluation method,a method for predicting the corrosion life of the rupture disc was proposed,which not only solved the problem of the lack of corrosion life prediction method caused by unknown corrosion failure conditions of the rupture disc,but also established a simulation model which can be used to predict the corrosion life of rupture discs of different specifications.(3)The corrosion simulation model of rupture disc in Cl-and H2S environment is established successfully,and the variation rules of corrosion rate and surface profile of rupture disc with time are obtained.H2S is a common factor leading to corrosion failure of equipment in petrochemical industry,and it is also an important reason for the failure of rupture disc in advance.However,due to limitations such as harsh experimental conditions and long experimental cycles,the corrosion law of rupture disc in H2S environment is not convenient to be obtained by traditional experimental methods.This study established corrosion simulation model successfully for rupture discs in Cl-and H2S environment,and systematically studied the effects of factors such as H2S concentration,porosity of the corrosion product layer and geometric shape of rupture disc on the corrosion behavior and surface morphology of rupture discs.The results showed that the corrosion rate and deposition rate of corrosion products at the top of the rupture discs arc were positively correlated with H2S concentration and porosity of the corrosion product layer,and negatively correlated with the initial thickness and relief diameter of the rupture disc.Moreover,the corrosion rate at the contact position between the rupture disc and the fixture may also become the fastest corrosion rate position.For rupture discs with the same set blasting pressure,the thicker the initial thickness,the larger the discharge diameter,and the longer the corrosion life.The research results not only provided data support for the study of the corrosion behavior of rupture discs in environments containing Cl-and H2S,but also provided theoretical basis and model reference for the design and use of rupture discs from the corrosion science perspective... |
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