MPa Grade Research Articles

Experimental and numerical investigations of UHSS wire main cables for suspension bridges

As the demand for suspension bridges with large spans and high bearing capacities increases, main cables made of conventional materials must be designed with larger cross-sections, which leads to a significant reduction in constructability and economy. To this end, a 1960 MPa grade steel wire cable strand was recently developed to facilitate the miniaturization of components and increase the load-carrying efficiency of structures. Through a series of material and mechanical experiments, the tensile strength and torsion toughness of the developed ultra-high strength steel (UHSS) wires were investigated; then, the static and fatigue performances of the developed UHSS cable strands were evaluated. As a result, the mechanical performance of the 1960 MPa grade cable strand satisfied all the specified criteria. Based on analytical derivation and numerical simulation, the effects of the main cable of the UHSS wire on the load-carrying performance of suspension bridges were investigated. The feasibility and efficiency of the developed 1960 MPa grade main cables were demonstrated via successful application in the Nansha Bridge.

Effect of tempering on the microstructure and properties of a new multi-functional 460 MPa Grade construction structural steel

A new generation of multi-functional construction structural steel with high yield strength of ∼545 MPa, excellent toughness of ∼170 J/cm2 at −20 °C, lower yield ratio smaller than 0.83, good fire resistance, and good corrosion resistance was successfully developed by thermo-mechanical controlled processing plus tempering. The effects of tempering on the microstructure and mechanical properties were investigated. The results show that although the bainite lath slightly coarsens and the dislocation density slightly decreases as the tempering temperature increases, the yield strength of the steel increases mainly due to the precipitation strengthening. The samples tempered at 300 °C show the best combination of strength, toughness, and yield ratio. In addition, the high-temperature strength of the newly developed Q460 steel is obviously higher than the conventional one, which is mainly attributed to the bainitic strengthening and precipitation strengthening. Moreover, a denser rust layer forms on the surface of new Q460 steel during corrosion because of the addition of Cr and Cu, which increases the corrosion resistance of the steel.

Analisis Perhitungan Struktur Laboratorium Teknik Sipil Type II Fakultas Teknik Universitas Muhammadiyah (UMSU) Medan

The lack of supporting infrastructure facilities such as the Laboratory at Samudra University, especially in the Civil Engineering Study Program, Faculty of Engineering, has resulted in Samudra University having to work hard in building infrastructure to keep pace with advances in technology and science. This study aims to plan the dimensions and reinforcement of beams, columns, plates and stairs in the Civil Engineering Laboratory building. The laboratory building to be analyzed has a total of 3 floors with floor dimensions of 43 m x 27.49 m. Modeling and analysis of the structure of this building is assisted by the SAP2000 program using the Special Moment Bearing Frame System (SPRMK) and is designed according to SNI 03-1726-2012, SNI 03-2847-2013, and PPPURG 1987. The structure is planned to use concrete quality fc' 30 MPa and steel grade fy 400 MPa. The results of the analysis obtained that the floor slab thickness was 13 cm using D10-200 mm reinforcement for main reinforcement and D10-300 mm for split reinforcement. The thickness of the roof slab is 12 cm using D10-200 mm reinforcement for main reinforcement and D10-300 mm for split reinforcement. The dimensions of the B1 beam are 50 cm x 70 cm using 12D25 for the support area with D10-80 mm braces and 8D25 reinforcement for the field area with D10-120 mm braces. Begel B2 30 cm x 50 cm using 4D25 reinforcement for the support area and field with braces for D10-200 mm field and braces for D10-100 mm support. The dimensions of the K1 column are 60 cm x 80 cm using 10D25 reinforcement with D10-300 mm begel. The dimensions of the K2 column are 60 cm x 60 cm using 8D25 reinforcement with D10 -200 mm begel. The thickness of the ladder plate and landing was obtained 13 cm using D10-200 mm reinforcement.

Effect of shearing prestrain on the hydrogen embrittlement of 1180 MPa grade martensitic advanced high-strength steel

This work investigated the effect of shearing prestrain on hydrogen embrittlement. The strength and ductility values were similar to those in air for hydrogen precharging before tensile testing, but the ductility decreased significantly for tensile testing with in-situ hydrogen charging due to intergranular fracture initiation at the specimen surface. In contrast, there was a significant decrease in ductility for the hydrogen precharged steel after prestrain. The hydrogen-facilitated fracture was transgranular. The hydrogen fracture grew by fracture tip blunting, new fracture initiation, and coalescence, consistent with a hydrogen enhanced localized plasticity (HELP) mechanism.

Relationship between Microstructure and Properties of 1380 MPa Grade Bainitic Rail Steel Treated by Online Bainite-Based Quenching and Partitioning Concept

According to the concept of the bainite-based quenching and partitioning (BQ&P) process, we designed the online heat treatment routes of bainitic rail steel for heavy haul railway. The new heat treatment process reduced the fraction and size of the blocky martensite/austenite (M/A) islands formed during the conventional air-cooling process. The M/A islands are coarse and undesirable for mechanical properties. A new kind of 1380 MPa grade bainitic rail steel with more uniform microstructure and better mechanical properties was produced by the online BQ&P process. We characterized the multiphase microstructures containing bainite, martensite, and retained austenite of 1380 MPa grade bainitic rail steels via optical microscope, scanning electron microscopy, transmission electron microscopy, and X-ray diffractometer. We investigated in-depth the relationship between the microstructure, retained austenite stability, and mechanical properties, particularly the resistance to wear and rolling contact fatigue, of the new 1380 MPa grade bainitic rail steels. Meanwhile, the conventional air-cooling bainitic rail steel was studied as a comparison.

Effect of paint baking thermal cycle on joint strength of spot welds

Advanced high strength steel sheet (AHSS) is widely used in the automotive body for weight reduction and the improvement of crash performance. Such use requires higher joint strength of the resistance spot weld in AHSS. In laboratory tests, the joint strength of specimens is evaluated in as-welded condition. The effect of paint baking cycles is usually not considered, so the actual joint strength in the automotive body is not clear. In this study, we focus on the effect of the thermal cycle corresponding to paint baking treatment on the joint strength of spot welds. Two types of tensile test, shear tensile test, and L-shaped peel tensile test were carried out. The material strength grades used in this test were from 270 to 980 MPa. The weld nugget diameter was varied from three to five square root t in each material. A paint baking thermal cycle (170 °C for 20 min) was applied to the welded joints before the tensile tests were carried out. The paint baking treatment does not cause a change in the shear strength of joints in any of the conditions (materials and nugget diameter). On the other hand, in the case of materials of 590 MPa grade or higher is used, the paint baking treatment can cause an increase in peel strength of the joint. Especially, the increase of joint strength by the paint baking treatment is most obvious in smaller nugget conditions. The results of this study suggest that the improvement in peel strength by paint baking treatment is caused by a tempering effect in the weld nugget. From these results, we concluded that the joint strength of paint-baked specimens would be more practical data, representing the actual joint performance in automotive bodies.

Colour-stability analysis for estimation of deterioration in concrete due to chemical attack

Inaccessibility and subjectivity in damage evaluation during visual inspection may often lead to faulty assessment of concrete. Digital imaging tools can be used to identify and quantify the extent of distress due to deteriorating agents on concrete. Structures subjected to environmental degradation manifest deterioration in terms of changes in surface characteristics. It is strongly believed that there lies a co-dependency between the extent of deterioration and the reduction in the mechanical and durability performance. In the present study, digital image analysis technique, namely Colour-Stability Analysis (CSA), has been performed on cube samples of 30 MPa grade concrete, immersed in acid solutions (HCl, H2SO4), chloride (NaCl) and sulphate (MgSO4) at 5% concentration, exposed for various periods of 3, 7, 14 and 28 days, after the end of the requisite 28-day curing period. The CSA is conducted in CIE-LAB colour space as it is device-independent and represents the human perception of colour. The colour profiles of the deteriorated surfaces before and after immersion in the above reagents for 3, 7, 14 and 28 days have been quantified. The successive and relative differences in the surface colour profiles for respective reagent-immersion and exposure conditions have been computed and analysed. The current study revealed the influence and mechanism of various reagent’s impact on the deterioration of concrete surface with time and the same is quantified. The correlation between the extent of damage in concrete in terms of change in colour profiles, residual strength and durability is established.

Microstructures and Mechanical Properties of a New Multi-functional 460 MPa Grade Construction Structural Steel

Microstructures and Mechanical Properties of a New Multi-functional 460 MPa Grade Construction Structural Steel

The mechanical properties and microstructure of 1,000 MPa grade Cu-Ni TRIP steel at different bainitic isothermal temperatures

For developing TRIP steel with good coordination on strength and plasticity, a TRIP steels containing copper and nickel at different bainite isothermal temperatures (350-470°C) were investigated to explore the best process. The microstructure of the tested steel was investigated by X-ray diffraction, transmission electron microscope, scanning electron microscope, and electron backscatter diffraction, as well as its mechanical properties were tested and analysed by uniaxial tensile test. It can conclude that when holding bainitic isothermal temperature at 410°C, the steel obtained the excellent mechanical properties, e.g., the elongation is 16.88%, the strength of extension is 1,088 MPa and the strength and ductility product is 18,365 MPa%. The crystallite dimension and carbon level of retained austenite play an important role in its stability. Moreover, in terms of morphology, the film-like austenite makes an important impact in the gentle transition during deformation and the stability of retained austenite is affected by its film thickness.

Study on microstructure evolution and toughening of coarse grain heat affected zone of 690 MPa grade bridge steel

Study on microstructure evolution and toughening of coarse grain heat affected zone of 690 MPa grade bridge steel

Interaction between Dislocations, Precipitates and Hydrogen Atoms in a 2000 Mpa Grade Hot-Stamped Steel

Interaction between Dislocations, Precipitates and Hydrogen Atoms in a 2000 Mpa Grade Hot-Stamped Steel

Study on microstructure evolution and toughening of coarse grain heat affected zone of 690 MPa grade bridge steel

Study on microstructure evolution and toughening of coarse grain heat affected zone of 690 MPa grade bridge steel

The mechanical properties and microstructure of 1000 MPa Grade Cu-Ni TRIP Steel at different bainitic isothermal temperatures

The mechanical properties and microstructure of 1000 MPa Grade Cu-Ni TRIP Steel at different bainitic isothermal temperatures

Characterization of the Stretch Flangeabitity of High-Strength Bainitic Steel: The Significance of Variant Pairs.

Variant pairs have an indispensable function on mechanical properties such as low impact toughness. Therefore, it was assumed that they would also affect the HER (Hole Expansion Ratio, an indicator to evaluate stretch flanging performance). To clarify this, a comprehensive analysis of the common influential factors in an 800 MPa grade low carbon micro-alloyed steel, i.e., the retained austenite, the M/A (Martensite/Austenite) island, the titanium precipitations, the grain diameter, the density of high angle grain boundaries and the textures, was first conducted. It was found that they did not match well with the HER, suggesting that they were not the governing factor for HER in this steel. However, the dominating crystallography groups and the variant pairing results indicated that they fitted well with the HER. In the samples with high HERs, the CP (Close Packed) groups dominated the transformation, wherein one individual CP group consisted of two or more Bain groups, whereas it evolved into the domination of joint CP groups and Bain groups for the low HER sample. Further analysis on the variant pairing features indicated that a correlation occurred between the HER and the high angle variant pairs. In the steels with high HERs, high-angle variant pairs of V1/V2, V1/V3 that transformed from the same CP group, particularly of V1/V2 pair, were mostly generated. They turned to V1/V9, V1/V10, V1/V12, V1/V15, V1/V17, and V1/V18 pairs from differential CP groups, especially the V1/V12 and V1/V15 pair for low-HER steel. This result showed that V1/V2, V1/V12, and V1/V15 might have accounted most for the HER in this steel. The underlying reason was that the V1/V2 pair was specialized in supplying a slip passage for dislocation transmission across a grain boundary with little resistance, whereas the dislocation transmission ability for V1/V12 and V1/V15 pair was particularly poor. Thus, to efficiently enhance the HER, one should regulate the variant pairs by augmenting the V1/V2 fraction and suppressing the formation of the V1/V12 and V1/V15 pair.

Analytical and experimental investigation of the bond behavior of confined high-strength recycled aggregate concrete

This study investigates the bond behavior between 600 MPa grade reinforcement and high-strength recycled aggregate concrete (RAC) by carrying out 22 beam tests. Test parameters include the recycled coarse aggregate (RCA) replacement ratio, reinforcement diameter, concrete cover thickness, stirrup ratio, concrete strength and the addition of steel fibers. The influences of different parameters on the failure modes, bond-slip curves and bond strength are discussed. The results indicate that the RCA replacement ratio has little effect on the failure mode and the bond-slip curve, while the bond strength decreases with its increase. Similar to normal aggregate concrete, the bond strength is positively correlated with f′c1/2. Increasing the concrete cover thickness or the stirrup ratio can significantly improve the bond strength and decrease the crack width. The addition of steel fibers can avoid specimen splitting, but this addition will disturb the reinforcement-concrete interface, which has little effect on the bond strength of 50 MPa grade RAC, however, the addition slightly increases the bond strength of 70 MPa grade RAC. The design bond strength of steel fiber concrete should not be lower than the design bond strength of plain concrete with the same compressive strength. The splitting failure of specimens is further classified, and the effective confinement Factor K for predicting the failure mode is presented. In view of different confinement conditions, bond-slip models between the 600 MPa grade reinforcement and high-strength recycled concrete are established.

Investigation on Residual Compressive Distribution of High-Strength Steel for Bridges by Base Metal Hammer Impact Peening

Various peening techniques have been used to improve the fatigue strength of steel structures. Among them, base metal impact hammer peening shows significant improvement in fatigue strength in ordinary steel, but the effect on high-strength steel has not been sufficiently studied. Accordingly, this study applied base material hammer impact peening to test specimens of 780 MPa grade high-strength steel (HT780) and 490 MPa grade ordinary steel (SM490), and the residual stress was measured and simulated. The experimental results clarified that a large compressive residual stress was introduced into the inner part of the plate thickness near the indentation in the high-strength steel, although the range of introduction of residual stress was equivalent in both the ordinary steel and high-strength steel.

Effect of cooling rates after annealing on the microstructure and properties of 1000 MPa grade automobile steel for cold forming

The effects of different cooling rates (0.05 °C s−1, 0.1 °C s−1, and 0.2 °C s−1) on the microstructure and mechanical properties of 1000 MPa grade automobile steel for cold forming after two-phase annealing were studied. The microstructure of the experimental steel was observed by SEM and TEM, and its mechanical properties were tested by a universal tensile testing machine. The results showed that by increasing the cooling rate of two-phase annealing, more massive retained austenite, more uniform and fine ferrite, better elongation and higher ultimate tensile strength of steel can be obtained, so as to obtain better production of tensile strength and total elongation (product of tensile strength and elongation, PSE). The final result shows that after the test steel is quenched at 800 °C + 10 min and annealed in the two-phase region at 690 °C + 10 min, the faster the cooling rate, the better the mechanical properties. The mechanical properties of the steel plate are the best when the cooling rate reaches 0.2 °C s−1, and PSE can reach 27.44 GPa·%.

Concentrically and eccentrically loaded high-strength concrete columns with high-strength reinforcement: An experimental study

The demand for high-strength steel (HSS) in concrete structures has been steadily increasing as it has potential to reduce congestion in heavily reinforced section, decrease steel quantity and lower the labour cost. Although typical design standards such as ACI 318 limit the design strength to 550 MPa, research focuses on developing design guidelines for using HSS. ACI ITG-6R-2010 has developed design procedures for the use of ASTM A1035 Grade 100 (690 MPa) steel bars as longitudinal reinforcement. ACI 318-2019 permits the use of 690 MPa bars as spiral transverse reinforcement in column. Australian Standards AS 3600-2018 allows HSS up to 600 MPa for longitudinal reinforcement and 800 MPa for transverse reinforcement (tie) in columns. While several design codes permit higher yield strength for steel bars, comprehensive test data are required to enhance the confidence in the application of the high-strength concrete (HSC) in conjunction with HSS in concrete columns. In this study, 39 HSC columns reinforced with HSS were tested under static loading. The compressive strength of concrete and yield strength of the longitudinal reinforcement varied between 100 and 115 MPa and 520–670 MPa, respectively, and tie was provided with 810 MPa steel. The ties were placed at a maximum spacing calculated based on AS 3600-2018 design model, resulting in 29% larger spacing than that for 500 MPa steel ties. The other test variables were section geometry, tie arrangement, tie bar areas and loading eccentricities. The columns section capacities were compared with AS 3600-2018 and ACI 318-2019 design models and ductility of the columns was studied too. It is shown that columns reinforced with HSS generally have a larger strength than that of the columns reinforced with 500 MPa Grade bars. The study also concluded that detailing HSS (810 MPa) tie reinforcement with HSS longitudinal bars meet the minimum confinement and the static ductility requirements of AS 3600-2018.

Comprehensive Analysis of Cold-Cracking Ratio for Flux-Cored Arc Steel Welds Using Y- and y-Grooves.

This study investigates various factors that influence the cold-cracking ratio (CCR) of flux-cored arc welds through Y- and y-groove tests. Factors affecting the CCR include the alloy component, diffusible hydrogen content, microstructure, hardness, and groove shape. In weld metals (WMs; WM375-R and WM375-B) of a low-strength grade, the diffusible hydrogen content has a more significant effect on the CCR than the carbon equivalent (Ceq) and microstructure. However, the combined effects of the microstructure and diffusible hydrogen content on the CCR are important in high-strength-grade WM. The CCR of the WM increased upon increasing Ceq and the strength grade because hard martensite and bainite microstructures were formed. Moreover, y-groove testing of the 500 MPa grade WM revealed a more significant CCR than that of the 375 MPa grade WM. Therefore, in high-strength-grade WMs, it is necessary to select the groove shape based on the morphology in the real welds.

Role of minor addition of B in submerged arc weld metal for 500 MPa grade seismic steel plates

In this study, we investigated the effects of boron content on the toughness of a 500 MPa-class structural steel weld. Submerged arc welding was performed using welding consumables with boron contents of 0, 0.001, and 0.003 wt% for heat input conditions of 34, 42, and 56 kJ/cm, respectively. The addition of boron reduced the grain boundary ferrite (GBF) and ductile–brittle transition temperature, resulting in improved impact toughness. Moreover, the addition of 0.001 wt% boron further increased the toughness of the weld metal. This was because the presence of boron at the austenite grain boundaries reduced its surface energy, thus delaying ferrite nucleation. In addition, the minor boron element prevented the formation of grain boundary ferrite (GBF) structures during solidification, and an acicular ferrite structure was created in the alloy during sufficiently slow cooling rates (higher heat input condition).