Study on Tensile Properties of Q235NH After Corrosion

In the process of using, wearthing steel will be affected by temperature, collision, load and other effects, resulting in changes in its mechanical properties. It has been shown that corrosion has a significant effect on the mechanical properties of weathering steel, which can not be ignored. In order to obtain the tensile properties of corroded Q235NH, accelerated corrosion test was carried out on Q235NH specimen with neutral salt spray (salt solution with concentration of (50±5) g/L and pH value between 6.5 to 7.2) at 35 ℃,and the accelerated corrosion time was 6, 24, 48, 72, 96 h respectively. The tensile test was also carried out on the corroded Q235NH specimen. The corrosion surfaces, tensile fracture, stress-strain relationship curve and the change law of mechanical property parameters of Q235NH specimen were investigated. The change law of mechanical property parameters was fitted by formula, the constitutive model of stress-strain relationship was established and the degradation law of reduction coefficient was analyzed. The test results showed that: 1)at the initial stage of corrosion, there was only local corrosion. With the increase of corrosion time, the corrosion became more obvious, and the rust layer fell off. The stress-strain relationship curves of the specimen had an obvious yield plateau, and the stress-strain curve of Q235NH after corrosion was lower than that in the non corroded state, and the yield stage was shortened. With the increase of the corrosion time, the strength of the specimens decreased first, then increased, and then decreased. The reason for these phenomena was that after corrosion of weathering steel, a protective rust layer formed on its surface, which could protect the substrate. With the increase of corrosion time, the adsorption force of the rust layer increased, which slowed down the decline of the mechanical properties of the specimen. 2)The yield strength, tensile strength, yield-to-tensile strength ratio and its reduction factors showed a linear degradation trend with the increase of corrosion time, and then the linear regression relation was established. 3)The secondary plastic flow constitutive model was modified by the parameter of β on the strengthening stage. The modified quadratic plastic flow constitutive model could well simulate the stress-strain relationship of Q235NH before and after corrosion. At the same time, the shape parameters k₁, k₂ and k₃ that affected the stress-strain relationship curve of Q235NH were analyzed, the recommended values of Q235NH shape control parameters k₂ and k₃ were proposed, and the linear degradation law of shape control parameter k₁ with time was established. Through the tensile test of Q235NH under normal conditions, the reduction law of relevant parameters and bonding strength with corrosion time and the modified secondary plastic flow constitutive model could be obtained, and the reduction of mechanical properties of the material after corrosion could be calculated.