Guanqiao Su

Bio: Guanqiao Su is an academic researcher from Northeastern University (China). The author has contributed to research in topics: Martensite & Microstructure. The author has an hindex of 5, co-authored 9 publications receiving 77 citations.

Influence of extruding temperature and heat treatment process on microstructure and mechanical properties of three structures containing Mg-Li alloy bars

Abstract: The Mg-Li alloy bars with density of 1.38 g/cm3 as well as ultimate tensile strength of 329.2 MPa were fabricated. Simultaneously, an industrial process with convenience and low cost was developed. In the cast alloys, hcp-Mg was transformed gradually into bcc-Li with increasing Li content. During extruding at different temperatures, the dynamic recrystallization (DRX) in Mg-8Li-5Al-2Zn-0.5Y was weaker than Mg-5Li-5Al-2Zn-0.5Y and Mg-11.4Li-5Al-2Zn-0.5Y due to the mutual limitation between hcp-Mg (α) and bcc-Li (β). In the annealing process, abnormal grain growth in Mg-11.4Li-5Al-2Zn-0.5Y was found at 573 K, and a kind of regular dendritic structure was discovered in the coarse grains at 593 K. Additionally, a sort of solid solution strengthening behavior in bcc-Li was observed and enhanced remarkably the alloy strength (increased by ～160 MPa in maximum). Through controlling cooling velocity, a precipitation behavior could be achieved in the alloys. Through mathematical modeling with high accuracy, the relationships among microstructural evolution and alloy properties in the solid solution and precipitation processes were quantitatively analyzed and determined.

Intercritical tempering enables nanoscale austenite/ε-martensite formation in low-C medium-Mn steel: A pathway to control mechanical properties

Abstract: In a 0.05C-5.4Mn-0.2Si-0.8Cr-wt% steel intercritically tempered at 700 °C for 50 min a new hexagonal closed-packed phase (e-martensite) appears on former reversed austenite by an air-cooled process. The tensile strength of the tested steel increased from ~ 840 MPa after intercritical tempering at 650 °C for 50 min to ~ 1002 MPa with the tempering temperature increased to 700 °C, and the product of strength and elongation was improved from 19.9 GPa % to 21.6 GPa %; moreover, the impact energy at − 40 °C was decreased from 143 J to 68 J, and the yield ratio was reduced from 0.84 to 0.50. This result was attributed to the weakening of TRIP effect in existence of e-martensite. The partitioning of alloying elements at different intercritical tempering conditions and the calculation of SFE (stacking faults energy) indicated that e-martensite was produced in the ~ 50–100 °C temperature range while cooling in air after tempering at 700 °C for 50 min e-Martensite affected the stability of the reversed austenite and the fracture mode. The fracture mode was changed with the increased tempering temperature. The results reveal that a multiphase low-C medium-Mn steel can be produced via intercritical tempering accompanied by a unique phase transformation process. A high-temperature and long-time tempering condition will lead to a thermally-induced e-martensite transformation due to lower SFE possibly associated with more homogenized (or less amount of) alloying elements in austenite, and affects the mechanical behaviors of medium Mn steel.

Impact of Reversed Austenite on the Impact Toughness of the High-Strength Steel of Low Carbon Medium Manganese

Abstract: We elucidate the relationship between the volume fraction of austenite and the Charpy impact toughness in a medium-Mn steel in terms of microstructural evolution with impact temperature. Different from retained austenite in the matrix after direct quenching, sub-micron lath-shaped morphology-reversed austenite in medium-Mn steel was produced by intercritical annealing. We found that reversed austenite steadily affected the fracture mode; only ductile fractures and dimples decreased with decreasing impact temperature. After the impact fracture test, the content of reversed austenite in the matrix increased slightly with a decreasing impact temperature due to the stability of the austenite grains caused by recrystallization of α′ martensite. Reversed austenite slightly decreased during the impact process with a decreasing impact temperature.

Effect of microstructure refinement on hydrogen-induced damage behavior of low alloy high strength steel for flexible riser

Abstract: The effect of different microstructures on hydrogen-induced damage behavior of low alloy high strength steel for flexible riser was studied by hydrogen permeation test and electrochemical hydrogen charging test. The mechanism of hydrogen-induced damage behavior in tested steel was elucidated in terms of microstructure characterization, calculation of hydrogen permeation parameters and sensitivity analysis of hydrogen-induced cracking of tested steel. The results indicated that the microstructure of the tested steel was tempered martensite with precipitated phase, and the microstructure was finer and contained more proportions high angle grain boundaries after multi-stage heat treatment. After multi-stage heat treatment, the irreversible hydrogen traps and total number of hydrogen traps in the microstructure increased significantly, resulting in a significant decrease in hydrogen effective diffusion coefficient (Deff). Compared with quenched and tempered heat treatment, the crack sensitivity of hydrogen-induced cracking in microstructure obtained by multi-stage heat treatment decreased greatly, and the crack mainly presented transgranular propagation and more tortuous.

Effect of Tempered Martensite and Ferrite/Bainite on Corrosion Behavior of Low Alloy Steel Used for Flexible Pipe Exposed to High-Temperature Brine Environment

Abstract: Immersion experiments and electrochemical measurements were carried out to study the effect of tempered martensite and ferrite/bainite on corrosion behavior of low alloy steel used for flexible pipe exposed to high-temperature brine environment in terms of microstructure morphology, corrosion rate, corrosion products characteristics, potentiodynamic polarization curves and electrochemical impedance spectroscopy The experimental results indicated that the proportion of high-angle grain boundaries of tempered martensite steel was greater than ferrite/bainite steel The corrosion rate of ferrite/bainite steel was lower than tempered martensite steel With increasing immersion time, the structure of corrosion products formed on the surface of ferrite/bainite steel was more compact and denser than tempered martensite steel In addition, the current density of ferrite/bainite steel was lower than tempered martensite steel The charge transfer resistance and total impedance of ferrite/bainite steel were larger than tempered martensite steel Thus, the corrosion resistance of ferrite/bainite steel exposed to high-temperature brine environment was excellent compared to the tempered martensite steel

Heat-resistant 650°C steels - Design and testing of model alloys

Abstract: In the recent two decades advanced martensitic/ferritic 9-12 % Cr steels are recognized to be the most potential materials for 650°C Ultra Super Critical (USC) Power Plants. The critical issues are the improvement of long-term creep strength and corrosion resistance. The aim of the present research is to design new super heat-resistant 12 % Cr martensitic/ferritic steels using basic principles and concepts of physical metallurgy, to test and optimize model alloys and to investigate and clarify their behavior under long-term creep conditions with emphasis on microstructural stability and corrosion resistance. Fine distributions of stable precipitates, which block the movement of subgrain boundaries (M 23 C 6 carbides, Laves phase) and dislocations (MX carbonitrides) and delay coarsening of microstructure, are the key to high creep strength of this type of steels. Therefore, different carbide, nitride and Laves phase forming elements (Cr, W, Nb, V, Ta, Ti) have been used to provide precipitation hardening. Furthermore, the aim is to produce a sequence of precipitates with different kinetics, i.e. with precipitation of a new phase during coarsening of the prior one. Co has been used for obtaining 100% martensite initially and for slowing down diffusion processes and particle coarsening. The partial replacement of Co by Cu is also investigated to reduce costs. The first results of mechanical tests of the studied model alloys have shown positive effects of the addition of W and Ta as Laves phase and MX forming elements, respectively, as well as of the addition of B. Alloying with Co has also shown beneficial effects on the creep strength.

A comprehensive review of the development of magnesium anodes for primary batteries

Abstract: Mg alloys are important light structural materials and also are promising energy materials, which support Mg-based primary batteries such as Mg–air batteries as the main development direction of next-generation batteries. This rapidly developing field has attracted an increasing number of research investigations. We review the state-of-the-art of Mg-based anodes, including the fundamentals of Mg dissolution for primary batteries, the evaluation systems for the discharge performance of Mg-based anodes, the application of contemporary methods for understanding Mg discharge, and the influence of alloying and production methods. The recent developments, current opportunities and future directions of research are discussed. The main objective of this review is to help guide new studies that will promote the development of Mg-based anodes even further.

Simultaneously improved mechanical properties and corrosion resistance of Mg-Li-Al alloy produced by severe plastic deformation

Abstract: In this study, the mechanical properties and corrosion resistance of LA143 alloy specimens produced by severe plastic deformation (SPD) were investigated. It was found that SPD was an effective way to simultaneously improve the Vickers hardness and corrosion resistance of LA143 alloy specimens in 3.5 mass% NaCl aqueous solution.