Microbiologically influenced corrosion (MIC) has been an important reason leading to the damage and failure of pipeline steels, bringing a great economic loss. Development of MIC resistant pipeline steel is a new strategy to mitigate MIC from the aspect of material itself, having important scientific significance and application value. By proper Cu alloying design to the traditional pipeline steels, aiming at continuous release of Cu ions to kill the bacteria and inhibit the formation of bacterial biofilm, a creative strategy for improving the MIC resistance of pipeline steels has been proposed. This article briefly introduces the MIC of pipeline steel and its research status, and then the research progress on alloy design, microstructure, mechanical properties, hydrogen induced cracking resistance and MIC resistance of novel Cu-bearing pipeline steels are reviewed, and the research results on MIC resistance of the novel Cu-bearing pipeline steels under the laboratory conditions are stressed, and finally the future tendency on research and development of this type of novel steels is suggested.
An important topic is the achievement of high strength and high plasticity for the development of automotive steels. Present article reviews the M3 (multiphase, metastable and multiscale) microstructure and property control theory and technology of high-strength and high-ductility third-generation automotive steels, as well as new challenges. M3 microstructure and property-microstructure control theory provide theoretical support for the development of steels with high strength and high plasticity. Transformation induced plasticity (TRIP) effect of metastable austenite has a significant influence on properties and microstructure of steels. On the one hand, it can enhance the work-hardening rate and thereby improve strength and plasticity of steels. On the other hand, it causes some new problems, such as the increase of the shear edge crack sensitivity, the decrease of hydrogen induced delayed fracture properties, and more complex transformation behavior of metastable austenite under cyclic loading. At present, the quality consistency and basic research on application are insufficient for the high-strength and high-plasticity steels with metastable austenite. As a widely-applied product, the automotive steels need be evaluated in microstructure evolution and properties from the whole chain including composition design, microstructure control, cutting process, forming process, joining process and service performance. The evaluation results will provide the basis for the improvement of microstructure control theory and technology. Full consideration will be given in the technical applicability and cost of products.
Ultrahigh strength steels are highly competitive materials for vehicles to concurrently meet the increasing demand of the weight reduction and passenger safety. Hot stamping is the key forming technology to manufacture automobile components with high strength. Hot stamping steel and its manufacturing technology experienced a fast development in the past decade. This paper reviewed the state of the art of the manufacturing and applications of hot stamping steels/components in the following aspects: (1) hot stamping steels (from traditional MnB steels to recently newly developed hot stamping steels); (2) forming technologies (from traditional hot stamping process to industry 4.0 intelligent production); (3) novel hot stamping + quenching & partitioning (Q&P) process and fundamentals of deformation assisted heat treatments; (4) simulation techniques for hot stamping process (modeling of the temperature-stress field, microstructure field and simulation of the manufacturing process); (5) the assessments of in-service performance of hot stamped components. Finally, the trends of the development of hot stamping steels and related forming technologies in the future will be discussed.
Press-hardening steels (PHS) are increasingly used for vehicle body structure components because of their lightening potential owning to superiorly high strength, adequate ductility and fracture resistance. New PHS grades with higher strength and enhanced fracture resistance are being widely studied now for achieving further vehicle weight reduction, and the recent development in this field is reviewed in this article. Combining quenching and partitioning (Q&P) with the hot stamping process has been explored by some researchers, as well as tempering after the hot stamping using the medium-Mn steels. A certain amount of austenite could remain by the above processes and the resulted tensile strength can exceed 1500 MPa while tensile ductility of 10%~16% can be achieved utilizing the transformation-induced plasticity (TRIP) effect. A V micro-alloyed steel (34MnB5V) for hot stamping has been designed, utilizing both grain refinement and precipitation strengthening of VC. The tensile strength of the newly developed 34MnB5V exceeds 2000 MPa which is much higher than that of the most commonly used PHS 22MnB5 (1500 MPa). Meanwhile, the ductility and bending properties of the above two steels are comparable. Al-Si coated PHS is usually adopted to avoid oxidation during heating and improve its corrosion resistance after stamping. However, its bendability after forming is lower than that of the bare grade when surface decarburization is absent. The thickness of the brittle Fe2Al5 phase was reduced and the carbon enrichment at the interface of α-Fe and martensite matrix was weakened after hot stamping by thinning of the Al-Si coating. Thus, the bending property was improved. The applicability of the new designed processes for the existing production lines should be considered in future studies. The bending test should be adopted for the deformability evaluation rather than the uniaxial tensile test simply. The welding property and the mechanism of hydrogen embrittlement should also be studied for industrial application of the new developed steels.
This paper overviewed the current research status and important results of the hydrogen embrittlement (HE) of the representative steel types from 1st to 3rd generation advanced high-strength steel (AHSS): transformation induced plasticity (TRIP) steel, twinning-induced plasticity (TWIP) steel, quenching & partitioning (QP) steel and medium manganese steel. The main conclusions are as follows: the HE sensitivity of TRIP steel is mainly reflected in the reduction of plasticity and the small loss of strength. The HE sensitivity of TWIP steel depends heavily on the strain rate, i.e., the HE susceptibility is significantly increased as the strain rate decreases. Deformation twin boundaries and ε/γ phase interfaces are generally prone to hydrogen-induced cracking, while Σ3 annealing twin boundaries are not. However, the ε/γ phase interfaces with Nishiyama-Wassermann orientation relationship, which is similar to the Σ3 twin boundaries, could hinder the propagation of hydrogen-induced cracks. HE sensitivity of QP steel is similar to that of TRIP steel. For medium manganese steel containing a large volume fraction of austenite phase, which result in a strong TRIP effect during deformation, the HE susceptibility represented by plasticity loss and strength loss is very high. For TRIP steel, QP steel and medium manganese steel with austenite structure, the main strategy to improve their hydrogen embrittlement is to control the morphology and distribution of austenite structure; for TWIP Steel, the measures to improve hydrogen embrittlement can be taken by controlling the prestrain rate and Al Alloying.
With the deepening and improvement of the research on the conventional mechanical properties of metallic materials, the long-term service properties, such as fatigue and creep, showed more and more critical influence on the development of metallic materials. As one of the most important engineering structural materials, in order to clarify the fatigue failure mechanism, the research of steels on the relationship between microstructure and fatigue properties has been a hot and difficult problem for a long time. With the rapid development of smelting technology for steels, the research on the influencing factors of fatigue gradually changes from inclusions to microstructures as metastable austenite, precipitates, etc. Therefore, in order to further analyze the feasible direction of the research on the influence of microstructure on fatigue, this paper summarizes the influence and mechanism of metastable austenite on the fatigue property of advanced steel materials. The influence mechanism of metastable austenite on fatigue property by relevant scholars under different service conditions such as low cycle fatigue and high cycle fatigue was reviewed. Based on the experimental results, the relationship between metastable austenite and fatigue properties was quantitatively evaluated by machine learning. The quantitative relationship between the content/stability of metastable austenite and fatigue life was established, which could provide the basis direction for the further study of the mechanism of fatigue for steels.
With the development of automotive industry, it is necessary to develop advanced high-strength steels for the purpose of lightweight of car. Based on the systematic studies on the strengthening and toughening as well as fatigue design of the twinning-induced plasticity (TWIP) steels, the recent progress in this aspect is summarized and discussed. Among them, the strengthening and toughening mechanisms have been analyzed and further developed in terms of several influencing factors, including compositions, microstructure, strain rate and so on. Furthermore, the low-cycle and high-cycle fatigue behaviors and damage mechanisms were explored. For better understanding the intrinsic fatigue damage mechanism, a new low-cycle fatigue prediction model regarding the hysteresis loop energy during cyclic deformation was introduced. It is found that the energy damage model can well explain and evaluate the fatigue damage mechanism and predict the low-cycle fatigue life of the TWIP steels and other materials. Based on the new fatigue damage model, new TWIP steels with high service performance can be developed by adjusting their deformation and damage mechanisms rationally.
The modified Williamson-Hall method, which has been widely used to calculate dislocation densities of high-strength steels and other structural alloys, is re-examined in this work, and is further applied to calculate the dislocation density of a deformed twinning-induced plasticity (TWIP) steel by using its neutron diffraction patterns and synchrotron X-ray diffraction patterns. This paper aims not only to promote the proper use of the method but also to shed light on its underlying pre-requisites and assumptions, and is thus expected to help avoid any errors during its usage.
Ultra-high strength steels have been widely used in the critical engineering structures in both military and civilian applications due to the combination of ultra-high strength and excellent toughness. In this paper, firstly, the typical ultra-high strength steel grades that have been employed were introduced, and their compositions, mechanical properties, application and histories of development were summarized with the emphasis on their microstructures and strengthening/toughening mechanism; secondly, the latest progress on the emerging ultra-high strength steel grades was reviewed, including their compositions, microstructures, strengthening mechanism and mechanical properties; thirdly, the newly emerging demands on replacing the currently employed ultra-high strength steels in China were defined, including steels for low-density but ultra-strong armors, the large ball grinding mill, cutters of tunnel boring machine and high pressure fracturing pump; finally, recent research results on ultra-high strength and high-toughness medium Mn steel were presented, which overcame the trade-off of strength and toughness to a greater extent; on this basis, some suggestions were put forward for the future development of these steel grades to meet the urgent national demands.
This paper reviewed the development history of the first generation bearing steel GCr15, the second generation bearing steels M50 and M50NiL, and the third generation bearing steels Cronidur30 and CSS-42L. The fourth generation bearing alloy characterized by light weight is put forward. Based on the analysis of metallurgical quality and fatigue properties of traditional bearing steel, the direction of metallurgical quality control of bearing steel with fine quality and homogenization of large particle inclusions and carbide was proposed, and the contact fatigue control mechanism of bearing steel and two different anti-fatigue mechanisms of carbide control were revealed. According to the latest development of quality control technology and quantitative characterization technology for traditional bearing steel GCr15, the development direction of quality control for high-end bearing steel is proposed. Through the research on the overall heat treatment technology and surface carburizing technology of superfine matrix and carbide of bearing steel GCr15 and CSS-42L steel, the double heat treatment and surface superhardening heat treatment are innovatively developed, which can increase the contact fatigue life of bearing steel GCr15 at room temperature to 5 times and more than 10 times, respectively. Finally, it is pointed out that the application of quantitative inspection and testing technology is an important guarantee for high-performance bearing steel with good metallurgical quality and high performance.
In this paper, the development history of iron and steel wear-resistant materials is introduced, and the composition, microstructure, wear property, antiwear mechanism and modification technology of three typical wear resistant materials, namely high manganese steel, high chromium cast iron and high vanadium high-speed steel, are mainly reviewed. The wear-resistant steel represented by high manganese steel relies on the matrix with high strength and toughness to resist wear, while the wear-resistant alloy represented by high chromium cast iron and high vanadium high-speed steel mainly relies on the wear-resistant phase with high hardness to resist wear. High vanadium high speed steel has better wear resistance than high chromium cast iron, which is related to VC characteristics with high hardness and good shape. It is proposed that high performance wear-resistant materials should have three elements: high strength and toughness matrix, multi-scale synergistic action of high quality wear-resistant phase with high hardness and good morphology, as well as good bonding interface between wear-resistant phase and matrix.
To date, the 600 ℃ ultra-supercritical (USC) fossil fired power plant is the most advanced in the world. The research and development of 630~700 ℃ advanced ultra-supercritical (A-USC) fossil fired power plant will lay the thermal power technology in China in the international leading position, which is of important strategic significance to realize the national energy conservation and emissions reduction targets. Heat resistant material is the technical necking to further increase the steam parameter of thermal power plants. This paper briefed the-state-of-the-art of heat resistant materials used for 630~700 ℃ A-USC fossil fired power plant worldwide and clarified the critical candidate materials which are on the top priority to develop in China. The selective metallurgical processing design and selective strengthening mechanism, concluded by the author to design and improve heat resistant materials, was introduced. Under the guidance of the selective strengthening mechanism, G115? martensitic steel used for 630~650 ℃, C-HRA-2? and C-HRA-3? alloy used for 650~700 ℃, and C-HRA-1? alloy used for 700~750 ℃ have been successfully developed, which built a complete heat resistant material system to cover 630~700 ℃ A-USC fossil fired power plant. The boiler tubing and piping of these novel heat resistant materials have been industrially manufactured.
In the present work, the development and research on ultra-high strength stainless steels (UHSSS) have been systematically reviewed. Specifically, the focus was primarily placed on the precipitation hardening and austenite phase toughening mechanisms. And, the hydrogen-induced stress corrosion cracking (SCC) and hydrogen embrittlement (HE) behaviors of high-strength stainless steels were also retrospected. It is suggested that the future development of UHSSS is on the basis of computer-aided alloy designing system, strengthening via multiple high-coherency precipitates and toughening by filmy high-stability austenite phase. Besides, verification of the SCC and HE underlying mechanisms is vital to further optimizing the performance of UHSSS.
Strengthening and toughening are the main topics of steels, and accompanied fatigue failure and delayed fracture requiring to be solved simultaneously. Not just more than that, better performances in fabrication and service are quite important for an intentional steel to be used eventually. It is worth to pay close attention to match up three main courses: steel processing, component fabrication and service evaluation. Over past two decades, ferrite grains can be refined to micron scale in both plain low carbon steel products and microalloyed steel products and lead to remarkable increase of strength. The reason to define the limitation of ferrite grain refinement to microns is ductility decrease, low processing efficiency and heat affected zone (HAZ) coarsening. Ten years ago, a novel microstructure M3 (multiphase, metastable and multiscale) was proposed to overcome the problems stated above, and led to ductility and/or toughness improvement. It based on the idea of crack initiation and propagation retardment. It led to prevalence of the 3rd generation advanced high strength steel (AHSS) and the 3rd generation high strength low alloy (HSLA) steel, presenting higher ductility and/or toughness at high strength level. In the near future, it is imaginable that polymorphic alloying will be taken into consideration instead of recent hot issue on microstructure control during whole processing. From the view point of classic alloying theory, solution and precipitation of alloying elements play an important role on processing and then final microstructure. The distribution and occurrence of small atom radius elements (e.g. C and N) and comparable atom radius elements (e.g. Cr, Mn, Ni, Co) in iron seem quite clear. The ambiguous situation still remains for B and P, and even larger atom radius elements such as rare earth (RE) elements. Segregation of small amount of them to defects and boundaries maybe lead to decrease of energy and result in remarkable change of microstructure characterization. Thanks to the advancement in processing and instrumentation technologies, the distribution and occurrence of alloying elements in steel and the advantages of different alloying elements in steel matrix and surface can be taken, so called the polymorphic alloying. The practices of polymorphic alloying in steel development are engaged to improve corrosion resistance, strengthening and toughening. The performance enhancements are discussed in cases of weathering steel microalloyed with RE, ultrahigh strength steel strengthening by carbide and intermetallic precipitates, bolt steel with C and microalloying elements, austenitic stainless steel alloyed with N, and martensitic stainless steel alloyed with C and Ag.
Electromagnetic metallurgy technology is an essential method of high quality steel production. This article reviews the development of electromagnetic metallurgy technology in recent years, focusing on the whole process of continuous casting, including electromagnetic purification of steel in tundish, nozzle flow control, mould electromagnetic stirring and electromagnetic brake, flow field control via magnetic field, electromagnetic soft contact electromagnetic continuous casting, electromagnetic field regulation of solidification structure, solid phase transformation and microstructure control under electromagnetic field, the mechanism of electromagnetic field action is explained, the principle and characteristics of electromagnetic field technology are analyzed, and the concept of multi-mode magnetic field is proposed in the field of flow field control by using electromagnetic field to meet the requirements of complex states in high quality steel continuous casting. In the field of static magnetic field control solidification structure, a new principle of applying high thermal electromagnetic force is proposed, and it is presented that the development of electromagnetic metallurgy technology needs to combine the artificial intelligence of big data to play a better role.
New generation advanced steel has been studied with the increased requirement for high property steel by various engineering fields since the 21st century. Correspondingly, their welding materials and welding techniques are crucial for the application of the steels. In this paper, the research status and the development of the welding processes, microstructure and properties of welded joint of the advanced steel, including ultra-fine grained steel, low carbon bainitic steel, high nitrogen austenite stainless steel and high strength automotive steel are introduced. The microstructure evolution of welded joints, the microstructure and properties of welded joints, the formation of inclusions and martenite-austenite (M-A) components and its influence on properties, and the influence of alloying elements and heat input on weld properties are reviewed. Study results show that heat affected zone (HAZ) is the main area which affects the performance of welded joints, and proper welding materials and processes are required to achieve a matching welded joint. The strengthening and toughening mechanism of weld joint, mechanism of fatigue crack growth, effect of welding thermal process on microstructure and properties of steel, are also reviewed. At last, the research prospect on welding materials and welding techiques is presented.
The metallurgical process involves complex phenomena comprising high temperature, the multiphase flow, and the physical and chemical reactions in the process reactors. Because of the complexity of the metallurgical process and the limitation conditions for the direct measuring and observation, numerical and physical simulations have become indispensable and effective tools to analyze and reproduce the transport phenomena and mechanisms occurring in the process. Transport phenomena of the gas-liquid two-phase flow plays a dominant role in process metallurgy since their respective movement laws govern the kinetics of the various physical phenomena in the metallurgical reactors. The gas-liquid two-phase flow has complex interface structures, and the accuracy of the interfacial momentum transfer models, including the interfacial forces, which is one of the keys to predicting the distribution of gas phase in the two-phase flow system successfully. This paper is aiming at reviewing the two-phase flow models based on the Euler-Euler system, the interfacial force model, and the turbulence model for gas-liquid two-phase flow. The use and extent of numerical and physical simulation for transport phenomena of two-phase flow in the steelmaking and casting processes are summarized and explored, including the basic oxygen furnace, electric arc furnace, refining, tundish, and molds. The methods and typical application in the numerical and physical simulation of gas-liquid two-phase flow will provide useful guides for the research.
It is shown by the studies that silver nano particles and silver-bearing materials have noticeable antiviral effects. The research progresses of silver nano particles and silver-bearing materials as antiviral agents are summarized and reviewed based on the aspects of possible antiviral mechanisms as well as bio-safety. The antibacterial effects of Ag-bearing iron and steels, and the effects of Ag on mechanical properties and corrosion resistance, are also summarized. It is shown by the results that silver alloying and silver nano particles could promote the inhabitation of ferrous materials to bacteria and virus.
Nickel is a very important material, yet the resources are deficient. 08Cr19Ni10 (S30408) steel is expensive with containing 8% (mass fraction) nickel and has a low strength, while low nickel austenitic stainless steel has poor corrosion resistance property.In order to save nickel resources, the strength of austenitic stainless steel was improved by partly replacing Ni with Mn and N on the basis of ensuring that the corrosion is as well as S30408, 08Cr19Mn6Ni3Cu2N (QN1803) high strength nitrogen alloyed low nickel austenitic stainless steel was designed by Thermo-Calc software in place of S30408 steel. Microstructures, mechanical and corrosion resistant properties of QN1803 steel were investigated by means of OM, SEM, electrochemistry workstation and other methods. The results reveal the grain size of QN1803 steel is smaller than that of S30408, and difference of average grain size is increased from 1.8 μm to 16.27 μm with temperature rising from 1040 ℃ to 1120 ℃. Yield strength of QN1803 steel is increased to more than 400 MPa, and is 1.3 times than that of S30408 steel for nitrogen playing a role of grains refining and solution reinforcing. The impact energy of QN1803 steel is significantly lower than that of S30408 steel for nitrogen atoms reducing low temperature toughness of nitrogen alloyed austenitic stainless steel below -60 ℃. After 600~900 ℃ temperature ageing, chromium-rich carbideparticles first occur in grain boundaries, nose temperature of precipitation phase is 800 ℃; the inter-granular corrosion of QN1803 steel need more ageing time than S30408 steel, because nitrogen atoms can impede nucleation and growth of carbides, inter-granular corrosion of QN1803 steel is occured with double ageing time of S30408 steel at ageing temperature 700 ℃. Compared with S30408 steel, the passivation film depth of QN1803 steel has higher content of nitrogen and chromium; QN1803 steel has similar pitting corrosion rate (4.72 g/(m2·h)) and more stable austenitic microstructure and higher corrosion potential (327 mV); the pitting resistance of QN1803 steel is 1.15 times than that of S30408 steel with 60% cold reduction, and products have lower risk of stress cracking than S30408 steel. Due to addition of 1.65%Cu element improving corrosion resistance capability in dilute sulfuric acid solution, the surface of QN1803 steel can be enriched with a layer of copper-rich film protecting substrate, as a result, its corrosion resistance reaches 6.6 times than that of S30408 steel in 5% dilute sulfuric acid solution.
In this study, two dual-phase steels with different ferrite-bainite/martensite ratios were obtained by rolling in two-phase region and setting the relaxation time after rolling. The tested steel with smaller ferrite content obtained higher yield strength and tensile strength, greater total elongation and lower ductile-brittle transition temperature; while the steel with higher ferrite content obtained higher uniform elongation and lower yield strength ratio. The EBSD characterization of the two steels shows that for the ferrite-ferrite boundaries and ferrite-bainite/martensite boundaries, if the interface has a large overall misorientation angle, it usually has a large cleavage plane misorientation angle and large slip plane misorientation angle; but for the variant-variant boundaries within bainite or martensite, if the interface has a large overall misorientation angle, it usually has a large cleavage plane misorientation angle, but not necessarily has a large slip plane misorientation angle, and this phenomenon is more significant in martensite microstructure. The ductility of dual-phase steel is not only affected by the proportion of the two phases, but also influenced by the grain refinement of the two phases. Therefore, in order to improve the comprehensive mechanical properties of the dual phase steel, it is necessary to refine the dual phase microstructure from the view of effective slip unit and the effective cleavage unit.
In general, the wear resistance of traditional low alloy wear-resistant steels can be improved by increasing the hardness of steel matrix, but this significantly deteriorates the processing properties of steel, such as weldability, formability and machinability. Therefore, how to improve the wear resistance of steels without increasing the hardness has become an important issue for the study of wear-resistant steels in recent years. In this work, it is prosposed to introduce ultra-hard TiC particles into the matrix of steel by means of high-Ti microalloying and in situ reaction of TiC in billets (ingots), so as to achieve a significant increase in the wear resistance without increasing the hardness. Seven tested steels with different Ti and C contents were firstly fabricated by smelting, hot rolling and heat treatment, then the morphology, size distribution and fraction of precipitates were characterized by means of OM, SEM, EPMA, TEM, physical-chemical phase analysis, etc. Finally, the wear resistance and its mechanisms of the tested steels were investigated. The results show that TiC particles in the tested steels exhibit an unique trimodal distribution characteristic of "micron-submicron-nanometer". The micron-sized TiC particles were originated from the eutectic reaction of L→γ+TiC occuring at the end of solidification; the eutectic TiC was broken up into small fragments and homogenized gradually during the subsequent hot rolling. The submicron-sized particles were mainly precipitated from austenite at relatively high temperature after solidification, and the nano-sized particles were mainly precipitated from deformed austenite at relatively low temperature during hot rolling. The size of precipitates becomes finer at lower precipitation temperature. The relative precipitation-temperature-time (PTT) diagrams of both submicron-sized and nano-sized TiC were calculated, and it is shown that the most rapid precipitation temperature of the submicron-sized TiC is about 208 ℃ higher than that of the nano-sized TiC. The relative wear resistance of the tested steels is found to increase linearly with increasing TiC fraction, and the improvement of wear resistance is mainly due to the obstruction of micron-sized particles on wear furrow.