Advanced high strength steels (AHSSs) are regarded as the most promising materials for vehicles in the 21st century. AHSSs are complex and sophisticated materials, with microstructures being ...controlled by precise thermomechanical processing (TMP) technologies. TMP is an established and strategic method for improving the mechanical properties of AHSSs through control of microstructures and is among the most important industrial technologies for producing high quality AHSSs with the necessary mechanical properties. This article aims to provide a comprehensive review of recent progress in TMP of AHSSs, with focus on the processing-microstructure-property relationships of the processed AHSSs. We first present an introduction to the background of the TMP of AHSSs. Then, the recent progress and the latest achievements in TMP of the first, second and third generations of AHSSs and Nano Hiten steels are reviewed in detail, and the mechanisms of the TMP-induced microstructural evolution and mechanical properties variation are addressed and discussed. The present review concludes with a summary on the TMP of AHSSs currently under development, and also offers an outlook of the future opportunities which will inspire more in-depth research and eventually advance practical applications of this innovative field.
•Studied the effect of heat input on the mechanical properties welded high strength steel.•S700, S960 and S1100 steel plates were butt welded using GMAW and laser welding.•Micro-hardness measurements ...were performed at the through-thickness of weldments.•Microstructure of the weldments were examined especially at the heat affected zone.
In this study, the mechanical properties of butt-welded thin plates made of S700, S960 and S1100 steels under various heat inputs (HI) are investigated. The gas metal arc welding (GMAW) process with two different levels of HI, and laser welding (LW) are implemented for this purpose. Fully automated welding process is employed to attain high quality and homogeneous weldments. Standard tensile tests of the butt-welded joints, together with micro-hardness measurements are conducted in this study. The microstructure of the heat affected zones (HAZ) of the weldments are closely examined using scanning electron microscopy (SEM). It was observed that while the fracture was occurred at the base materials of all S700 and S1100 weldments, the S960 suffered from failure at the HAZ which resulted in reduction of the joint’s strength and ductility. For all the studied steels, it was found that the joint’s ductility is highly dependent on HI values over the range of 0.3–1.4 kJ/mm for each welding pass. Though, the S1100 steel showed the best performance under welding HI with a moderate change in its mechanical properties and a stable microstructure after welding compared to S700 and S960.
The microstructure, precipitates and mechanical properties of Nb-V-Ti microalloyed ultra-high strength steel under different tempering temperatures are investigated. With the increasing tempering ...temperature, the width of martensitic laths gradually increased with reduced dislocations within them, and the volume fraction of retained austenite first increased and then decreased. Furthermore, the Charpy impact toughness, reduction of area and elongation are enhanced at the sacrifice of the strength. Four kinds of precipitates are identified at different tempering temperatures, namely M3C, M2C, M23C6 and M7C3. M3C precipitated when tempering at 200–400°C, and it was replaced partially by M2C when the temperature is elevated to 500°C, at which M23C6 also precipitated. For a higher temperature, above 600°C, M3C disappeared, and some M2C transformed into M7C3. The other two types of MC precipitates are found to be the stable phases existing over different tempering temperatures. The correlation between the mechanical properties and microstructure was established, and the precipitation mechanisms of carbides at the different tempering temperatures are explained.
•A refined and distorted lath martensite structure was generated on the surface of 300M steels through UNSM.•UNSM significantly induced high surface hardness and compressive residual stresses.•UNSM ...treated 300M steels exhibited higher wear resistance by forming a surface plastic deformation layer.
In this study, the effects of ultrasonic nanocrystal surface modification (UNSM) treatment on the surface integrity, microstructures and wear resistance of 300M ultra-high strength steel (300M steel) were investigated. The results showed that surface roughness of 300M steels after UNSM processing was significantly decreased with a lower scanning speed even though the surface roughness values were higher than that of mechanically polished control samples. In addition, the surface hardness of 300M steel was significantly enhanced as the static load increased. It was found that using a static load of 50 N and a scanning speed of 250 mm/min in the UNSM process can significantly improve surface hardness (797 HV) while slightly increasing the surface roughness. With these parameters, the resulting microstructure of UNSM-processed samples have three layers: the layer of severe plastic deformation, the layer with gradual plastic deformation, and the unaffected layer. Due to the plastic deformation, greater and deeper compressive residual stresses were induced in the UNSM-processed samples. In addition, the wear resistance of UNSM-processed samples was significantly improved, which was attributed to the refined martensite laths, work hardening and compressive residual stress.
•Stub column tests were conducted on press-braked S960 ultra-high strength steel angle and channel sections.•Numerical models were developed and validated against test results, and then used to ...perform parametric studies.•The existing codified design rules were assessed against the test and numerical results, indicting inaccuracy.•Revised design rules were proposed and shown to yield improved design accuracy.
A comprehensive experimental and numerical study of the cross-sectional compressive behaviour and resistances of press-braked S960 ultra-high strength steel (UHSS) angle and channel section stub columns is reported in this paper. The experimental study was carried out on four equal-leg angle sections and eight plain channel sections, and comprised material testing, initial local geometric imperfection measurements and 18 stub column tests. The experimental setups, procedures and key observations were fully presented. The experimental study was then supplemented by a finite element (FE) simulation programme, in which FE models were firstly developed to replicate the test structural responses and subsequently used to generate further numerical data over a wide variety of cross-section sizes. It is worth noting that the current international standards established in Europe, America and Australia/New Zealand only cover the design of structural members with material grades up to S700, and thus the examined S960 UHSS angle and channel section stub columns are out of the scope of the existing design standards. In this study, the experimentally and numerically acquired data was adopted to assess the applicability of the codified provisions and formulations to the design of S960 UHSS angle and channel section stub columns. The assessment results generally indicated that the current European code leads to overall consistent and accurate predictions of cross-section compression resistances, but with many overestimated predicted resistances for S960 UHSS channel section stub columns, while the American and Australian/New Zealand standards yield unduly scattered design cross-section compression resistances, with unsafe and overly conservative predicted resistances respectively for S960 UHSS channel section stub columns and slender angle section stub columns. Revised codified design rules were also proposed, and shown to yield safe, accurate and consistent design cross-section compression resistances for S960 UHSS angle and channel section stub columns.
The transformation-induced plasticity (TRIP) in advanced high-strength steels (AHSS) is reviewed, where the main concepts and the recent progress in the processing and properties of AHSS are ...introduced. The metastable austenitic stainless and multiphase TRIP-assisted steels, as well as the more recent third generation AHSS grades, namely the medium-Mn and quenching and partitioning (Q&P) steels, are critically discussed. These steels utilize the TRIP effect and the enhanced work-hardening rate through the transformation of (retained) austenite in their microstructures to martensite during plastic deformation for the improvement of strength-ductility balance, which make them especially suitable for the automotive industry to be used in the lightweight car body for addressing the safety, fuel consumption, and air pollution issues. The kinetics of strain-induced martensitic transformation (SIMT) as well as the effects of chemical composition, grain size, deformation temperature, strain rate, and deformation mode on the austenite stability are reviewed. The effects of holding temperature and time during the isothermal bainitic transformation (IBT) in TRIP-aided steels, during the austenite-reverted-transformation (ART) annealing in medium-Mn steels, and during the quenching and partitioning steps in the Q&P steels are critically discussed towards enhancement of the amount of retained austenite and optimization of strength-ductility trade off. The alternative thermomechanical processing routes as well as the modified grades such as δ-TRIP and quenching-partitioning-tempering steels are also introduced.
This work focused on ultra-high strength steel strengthened by Cu-rich multistructured precipitates and toughened by bainite. A Cr–Mo bearing bainitic steel was designed and contrasted with a ...ferritic steel to examine the effects of Cr and Mo on microstructural transformation and precipitation evolution as well as the corresponding mechanical properties. By adding Cr and Mo elements, bainitic steel was obtained by an air cooling process after hot rolling, thus omitting controlled cooling and off-line quenching. Cr and Mo decreased the γ/α transformation temperature, such that the ferritic matrix was modified to fine bainite. Cu-rich multistructured particles and (Nb,Ti)C particles were found to be the two main precipitation phases in this bainitic steel. Cu-rich multistructured particles contained B2-ordered structure and transition-state structure between B2-ordered and 9R structure. Notably, this Cr–Mo bearing bainitic steel had better strength and toughness compared with ferritic steel. Its yield strength reached 1155 MPa, owing to precipitation and grain boundary strengthening, which were estimated to be 596 and 311 MPa, respectively. The impact absorbed energy of this steel at −40 °C was ~55.3 J and its fracture mode a brittle-ductile mixed mode, compared with the cleavage fracture mode of ferritic steel. The small grain size of this steel compensated for toughness deterioration caused by precipitation and contributed to high impact toughness.
Aerospace is a key market driver for the advancement of additive manufacturing (AM) due to the huge demands in high-mix low-volume production of high-value parts, integrated complex part geometries ...and simplified fabrication workflow. Rapid and significant progress has been made in the laser additive manufacturing (LAM) of aeroengine materials, including the advanced high-strength steels, nickel-based superalloys and titanium-based alloys. Despite the extensive investigation of these three families of materials by the research community, there is a lack of comprehensive review on LAM of high strength steels, and existing gaps in published reviews on Ti-based alloys and Ni-based superalloys. Furthermore, although emerging materials such as high/medium entropy alloys and heterostructured materials exhibit promising mechanical performance, rigorous characterization, testing, qualification, and certification are still required before actual application in engine parts. Thus, it is still important and relevant to have a deep understanding on the relationship between process parameters – microstructures – mechanical properties in these widely used aeroengine materials, to drive the development of superior high-value alloys. This review aims to provide a critical and in-depth evaluation of laser powder bed fusion (LPBF) and laser directed energy deposition (LDED) technologies of the mentioned aeroengine materials. The review will summarize the material properties, performance envelops and outlines the research gaps of these aeroengine materials. Furthermore, perspectives on research opportunities, materials development, and new R&D approaches of LAM for the aeroengine materials are also highlighted.
This work comprehensively reviews the recent development status of the laser additive manufacturing (LAM) process and key aeroengine materials in terms of process window, microstructure characteristics, mechanical properties, and their relationship (inner circle). On this basis, the perspectives on research opportunities, materials development and new R&D approaches for the aerospace components are also highlighted (outer circle). Display omitted
•Summarized correlations among process, microstructure and mechanical properties.•Outlined strength and weakness of laser additive manufacturing key aeroengine materials.•Elucidated Advancement of new laser additive manufacturing technologies.•Highlighted future directions of laser additive manufacturing aeroengine materials.
The antagonism between strength and resistance to hydrogen embrittlement in metallic materials is an intrinsic obstacle to the design of lightweight yet reliable structural components operated in ...hydrogen-containing environments. Economical and scalable microstructural solutions to this challenge must be found. Here, we introduce a counterintuitive strategy to exploit the typically undesired chemical heterogeneity within the material's microstructure that enables local enhancement of crack resistance and local hydrogen trapping. We use this approach in a manganese-containing high-strength steel and produce a high dispersion of manganese-rich zones within the microstructure. These solute-rich buffer regions allow for local micro-tuning of the phase stability, arresting hydrogen-induced microcracks and thus interrupting the percolation of hydrogen-assisted damage. This results in a superior hydrogen embrittlement resistance (better by a factor of two) without sacrificing the material's strength and ductility. The strategy of exploiting chemical heterogeneities, rather than avoiding them, broadens the horizon for microstructure engineering via advanced thermomechanical processing.
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