Papers by Author: Qiang Liu

Abstract: Titanium alloys have been taken as Oil Country Tubular Goods (OCTG) owing to their higher strength, and better corrosion resistance, but there are some problems in their application process. The corrosion types of titanium alloys were emphatically discussed, and corrosion mechanism was analyzed in this paper. The results showed that the main corrosion type of titanium alloys in hydrochloric acid was pitting, and the surface roughness of titanium alloys could affect it. The critical current density of titanium alloys in phosphoric acid was closely related to temperature and phosphoric acid concentration. The passivation of titanium alloys could be carried out by the growing oxide film at low current density, to achieve the higher stability of passivating film in the concentrated sulfuric acid. Titanium alloys suffered from more serious corrosion in the CO₂-containing completion fluid environment than that in the CO₂-containing formation water environment. H₂S would cause electrochemical corrosion and stress corrosion of titanium alloy pipe, leading to hydrogen embrittlement and even cracking of OCTG. Passivating film was the key to corrosion resistance of titanium alloys, and its composition would change with the depth of the film, presenting N-type. The dynamic corrosion of titanium alloys was mainly controlled by charge transfer.

Abstract: The hot deformation behavior of TiNiFe shape memory alloy were investigated by isothermal single-pass compression on Gleeble-3500 thermal simulator at the temperature range of 800°C to 1050°C and the strain rate range of 0.01s-1 to 10s-1. The results showed that the true stress-strain curves of TiNiFe shape memory alloy increase with decreasing deformation temperature and increasing strain rate, which indicating that the hot deformations of these conditions are dynamic recrystallization. The hot compression deformation of TiNiFe shape memory alloy can be represented by Arrhenius model. The constitutive equation of TiNiFe shape memory alloy under hot compression deformation is calculated by a linear regression analysis. The activation energy for hot deformation of the experimental steel is 202.54kJ/mol.

Abstract: The hot deformation behavior of Fe-25Mn-3Si-3Al TWIP steel were investigated by isothermal single-pass compression on Gleeble-3500 thermal simulator at the temperature range of 900°C to 1100°C and the strain rate range of 0.01s^-1 to 1s^-1. The results showed that the true stress-strain curves of Fe-25Mn-3Si-3Al steel had a typical feature which often appears during the hot deformation process of metals and alloys with high stacking fault energies. In true stress-strain curves, No obvious flow stress peak was observed. With the increase of strain, flow stress reaches the saturation value, indicating that the hot deformations of these conditions are dynamic recovery. The hot compression deformation of Fe-25Mn-3Si-3Al steel can be represented by Arrhenius model. The constitutive equation of Fe-25Mn-3Si-3Al steel under hot compression deformation is calculated by a linear regression analysis. The activation energy for hot deformation of the experimental steel is 422.51kJ/mol.

Abstract: In-situ tensile tests with specially designed SEM were conducted to trace the entire process of crack initiation and propagation till fracture in X80 pipeline steel. The mode of crack initiation induced by inclusions under tensile load was investigated. The results show that: (1) All the inclusions crazed and fracture was the typical tensile fracture, which indicates that the inclusions have little effect on the tensile properties of the X80 material under tensile load. (2) When the size of inclusion is larger than the critical size, crack initiated at inclusion/matrix interface first, and could easily propagate into matrix，but the long crack cannot form. When the size of inclusion is smaller than the critical size, cracks first formed in the inside of inclusions but not propagate into matrix. (3) If the area of cross section of round inclusion is less than 100μm², crack initiated firstly in the inside of inclusion. If the area of cross section of round inclusion is larger than 100μm², crack initiated firstly at the inclusion/matrix interface. For the rectangle inclusion, when its area of cross section is below 150μm², cracks usually initiate in the center of inclusions.