Papers by Keyword: Ultra-High Strength

Abstract: By combining the three-point bending beam test with theoretical derivation, the elastic modulus, fracture toughness, surface energy and the maximum defect size permissible under certain working stress of ultra-high strength cement-based materials were obtained. The fracture properties were studied with the water to binder ratios (W/B) from 0.18 to 0.14. Test results showed that the ultra-high strength cement-based materials are quasi-brittle and the net bending strength of specimen decreased substantially when there was a notch. The elastic modulus of ultra-high strength cement-based materials can be up to 74.0 GPa, obviously higher than that of ordinary cement-based materials, showing greater elastic deformation resistance. Moreover, with decrease of W/B ratio, the compressive strength, fracture toughness, critical strain energy release rate as well as the maximum defect size permissible under certain working stress of ultra-high strength cement-based materials increased significantly, indicating that the anti-cracking ability increased with the decrease of W/B ratio.

Abstract: Processing bulk nanoscrystalline materials for structural applications still poses a significant challenge, particularly in achieving an industrially viable process. In this context, recent work has proved that complex nanoscale steel structures can be formed by solid reaction at low temperatures. These nanocrystalline bainitic steels present the highest strength ever recorded, unprecedented ductility, fatigue on par with commercial bearing steels and exceptional rolling-sliding wear performances. A description of the characteristics and significance of these remarkable structures in the context of the atomic mechanism of transformation is provided.

Abstract: The latest R&D of new-type titanium alloys and their aviation applications as well as the newly developed processing technologies in China have been reviewed in this paper. To meet the requirements of high performance and low cost design of aviation-oriented titanium alloys, great efforts and achievements have been made in establishing a system with Chinese characteristics, in which the low-strength-and-high-toughness titanium alloy (such as Ti45Nb alloy used for fasteners and TA18 for tubes & pipes), the medium-strength and high-damage-tolerance titanium alloy (such as TC4-DT used for large-integral airframe structures), the high-strength and high-toughness damage tolerance titanium alloy (such as TC21 used for large-integral airframe structures), and the ultra-high strength titanium alloy (such as TB8) are included. Some new processing technologies such as quasi-β forging and quasi-β heat treatment, integral isothermal forging and electron beam welding, have been demonstrated to be able to markedly enhance the properties of titanium alloys, which is regarded to be very important in increasing the application amount and level of titanium in aviation industry.

Abstract: In the High-rise building construction, the selection, combination and optimization of top-down method have not been systematized to date and rely on experience and appraisal. In this article, four classes of parameters are selected according to the different nature of the factors influencing the design of top-down method so as to conduct systematized reorganization and analysis of the geological situation, structural characteristics, construction quality and term, and economic efficiency of the building. This study proposes several tables classifying the influencing factor, establishes selection criteria and suggests detailed flowchart for the planning of top-down method. Case study confirms the suitability of the resulting top-down method planning, and derives and combines the optimized method to provide fast construction.

Abstract: Overaging after intercritical annealing of ultra-high strength multiphase steel was conducted in a continuous annealing simulator of the laboratory. The effect of overaging temperature on the mechanical properties of multiphase steel has been studied by observing the microstructural evolution during overaging. The results have shown that multiphase microstructures containing ferrite, martensite, bainite and retained austenite were obtained by overaging treatments after intercritical annealing in ultra-high strength steel, and overaging temperatures affected all constituents of the microstructure. UTS and YS dereased with increasing overaging temperature, and TEL decreased after overaging at 350°C. A good combination of ultimate tensile strength (1400MPa), yield strength (795MPa), and total elongation (15%) was exhibited for the specimen overaged at 250°C. This was attributed to synthetic action of all constituents of ultra-high strength steel microstructure.

Abstract: Currently, long period stacking/ordered phases (LPSO phases) are known to reinforceMg97Y2Zn1 type Mg-RE alloys. The LPSO phases are composed of a solid solution of Y and Znatoms placed orderly in long periods along the Mg basal plane. Also, an efficient way to strengthena polycrystalline material is to reduce its grain size. This increases the density of grain boundarieswhich impede the flow of dislocations. In many of the LPSO forming solidification processed Mg-RE alloys, the common practice is to solutionize the ingot, quench in warm water, hot extrude andthermally age. While this practice is suitable for obtaining high strength Mg-RE alloys, itconveniently employs the common idea in conventional metallurgy of fine intermetallicstrengthening while refining the grain size to within the micron regime. In this work, an alternativemethod involving boride nanoparticle addition to obtain a selected solidification processed ultrahighstrength (tensile yield strength > 400 MPa) Mg-RE alloy is discussed. Here, LPSO phaserather than fine intermetallic formation while retaining grain size under the micron regime ishighlighted.

Abstract: Some research results are introduced briefly in this paper. A new kind of titanium alloy was designed based on nine elements system, which belongs to (a+b) type. Bars with diameter of 14 mm were produced via Vacuum Arc Remelting (VAR) melting and conventional forging and rolling facilities. Influence of alloy elements contents and heat treatments on microstructure and mechanical properties of the new alloy were studied. The results show that Ultimate Tensile Strength (UTS) is about 1200~1700MPa and Elongation (EL) is normally less than 5% at R.T., though Electron Beam (EB) welding can be proceeded, but the toughness of the alloy is poor at R.T.High temperature (HT) short-term strength of the alloy is also acceptable up to 600. Based on the above performances, the new material can be applied in the corresponding circumstances.

Abstract: Ultrasonic fatigue testing was conducted for 3000 MPa-class mould steel to investigate the fatigue behavior. The fatigue specimen is designed particularly due to the ultra-high strength. Ultrasonic fatigue tests are conduced using two types of specimen sizes and the test results are compared to investigate the size effect on the fatigue property.

Abstract: To research the key factor that affect on material characteristic of hot stamping, this paper studied the spring-back problem of hot forming of the ultra-high strength steel, "U" shaped part by using the combination method of numerical simulation and experimental verification. By obtaining the data of BR1500 HS isothermal tensile test, it established a "U" shaped part of thermal-mechanical coupled model which is based on ABAQUS to analyze the influences of forming speed and holding time on the forming properties. Simulation analysis showed that: When the forming speed of sheet metal is faster than 35mm/s, the rebound value is small, and further increase has no significant effect on the rebound; after holding 6s, the temperature quenching would become stable. The results verify the reliability of the finite element model. Also the study has provided a theoretical basis for determining the process parameters of the type of steel hot forming.

Abstract: Good combination of high strength and high toughness has been considered as a critical factor of ultra-high strength steel plates. In this paper, a novel high strength steel plate of HSLA type containing Cu with 910MPa yield strength and 1163MPa tensile strength has been developed using an advanced TMCP (thermo-mechanical control processing) technology. The steel plates provide excellent combination of high strength, toughness and deformability. Microstructural evolution and mechanical properties of this steel during hot-working have been investigated. It is demonstrated that, at the relatively higher finish rolling temperature and cooling rate, the microstructure consists of acicular and granular bainite structures and a small amount of low bainite /martensite whose lath width is approximately 200~300nm. For the as-rolled conditions, despite the high strength and so low yield ratio, impact energy about 154J and fully ductility fracture at -90°C can still be obtained as documented for as-hot rolled plates.