The Effect Of Different Heat Treatment Processes On The Corrosion Behavior Of X80 Steel In Simulated Acidic Soil Solution

At present, in the oil and gas pipeline construction, the pipeline is often made into pipe, three links and other important components by heat processing combined with the required topography and engineering construction. X80 steel, as the main pipeline of conveying steel for the west-to-east gas transmission project, has a wide application prospect. For this kind of micro alloy pipeline steel like X80 steel, the heat treatment is equivalent to the two heat treatment of a re-austenite, continuous cooling transformation and tempering of the pipeline steel after controlled rolling and cooling. In the different conditions, such heat treatment will make some changes of the structure and properties of pipeline steel. And the external environment of soil corrosion of pipeline steel is very complex, which makes large changes to the components with different structure in the complex soil environment. Therefore, the influence of different heat treatment processes on the corrosion behavior of X80 steel in typical soil environment (such as Ying Tan acid soil) in our country is studied, which will provide data reference and scientific support for the safe use of important components of pipeline steel.In this paper, the process of X80 pipeline steel under the environment of the short period of uniform corrosion behavior in simulated acidic soil, the contrast of stress corrosion cracking (SCC) sensitivity in the elastic deformation stage and the effect of applied potential on the SCC mechanism of original X80 steel and also the X80 steel with different heat treatment process were mainly studied through heat treatment experiment, full immersion corrosion test, electrochemical impedance spectroscopy (EIS), potential speed scanning technology, constant strain four point bending test and slow strain rate tensile test.The results show that:(1) The quality order of corrosion resistance of X80 pipeline steel with four heat treatment process after 28 days of corrosion in Ying Tan soil simulation solution was exhibited as follows:original specimen, water quenching and high temperature tempering, water quenching, air cooling, which was related to the change of the microstructure of X80 steel and the density of the corrosion products on the surface of steel. (2) The pitting phenomenon of X80 steel was the most serious and the SCC tended to be larger in the elastic deformation stage after empty cold treatment; applied stress made the corrosion rate increased significantly with four kinds of heat treatment processes of X80 pipeline steel in Ying Tan simulated soil solution, especially for the air cooling treatment of X80 steel. (3) The SCC sensitivity of X80 steel in Ying Tan soil simulated solution after four kinds of processes was significantly affected by the applied potential:above Eocp was mainly controlled by anodic dissolution (AD) mechanism; below the zero potential Eo of fast scanning polarization curve was mainly controlled by hydrogen embrittlement (HE) mechanism; the potential between two of them was mainly controlled by the mixing mechanism of AD and HE. (4) Under the same external potential, the SCC sensitivity of the original X80 steel and the cold treated X80 steel in Ying Tan soil simulated solution was higher among the four kinds of heat treatment process. (5) With the negative transfer of the applied potential, the fracture characteristics of X80 steel in the four processes were gradually changed from ductile fracture to brittle fracture or ductile brittle mixed fracture.