Properties Of High-strength Low-alloy Steel Research Articles

Effects of Partially Replacing Mo with Nb on the Microstructure and Properties of High-Strength Low-Alloy Steel during Reverse Austenization

This study investigated the effects of partially replacing expensive Mo with cheaper Nb on the microstructure and properties of high-strength low-alloy (HSLA) steel during reverse austenisation. The mechanical properties of the steel in the hot-rolled state were lower with a partial replacement of Mo by Nb. However, after pre-tempering and reheating and quenching, the strength increased greatly while the ductility and toughness did not decrease much. Thus, the negative effects of replacing Mo with Nb were mostly alleviated, and a good balance between strength, ductility and toughness was achieved. After heat treatment, the mass percentage of precipitates increased substantially, which helped to pin grain boundaries during austenisation. The percent of high-angle grain boundaries greatly increased while the average effective grain size decreased, which improved grain refinement. The results showed that combining a partial replacement of Mo by Nb with heat treatment allows the microstructure and mechanical properties of HSLA steel to be effectively controlled while improving the balance between cost and performance. These findings provide valuable insights into the preparation and design of steels with similar microstructures.

A Comparative Study of Microstructural Characteristics and Mechanical Properties of High-Strength Low-Alloy Steel Fabricated by Wire-Fed Laser Versus Wire Arc Additive Manufacturing

A Comparative Study of Microstructural Characteristics and Mechanical Properties of High-Strength Low-Alloy Steel Fabricated by Wire-Fed Laser Versus Wire Arc Additive Manufacturing

Microstructure, Texture, and Anisotropic Properties of High-Strength Low-Alloy Steel

The effects of cold rolling reduction rates and recrystallization annealing temperature on the microstructure, texture, and anisotropic properties of high-strength low-alloy (HSLA) steel were investigated using scanning electron microscopy and electron backscatter diffraction. The results revealed that the constituents of recrystallized, substructured, and deformed structures were strongly affected by cold rolling reduction rates ranging from 33.3% to 66.7% and recrystallization temperatures ranging from 780 to 840 °C. At an annealing temperature of 820 °C, when the cold rolling reduction rate was 33.3%, HSLA steel exhibited a low percentage of recrystallization, with cubic, γ-linear, rolled, and Z-texture (the texture at Euler angles φ1 = 30° and Φ = 20°–30°) structures. The rolled texture and Z-texture increased the strength anisotropy and disappeared at high cold rolling reduction rates. When the annealing temperature was increased from 780 °C to 820 °C, the proportion of recrystallized grains increased, the rolling texture disappeared, and grain orientation gradually gathered in the cubic texture and γ line texture, resulting in low anisotropy of strength. At an annealing temperature of 840 °C, the deformation of the grain disappeared; however, the anisotropy increased compared to annealing at 820 °C because of the formation of a new texture of {001}<−1–20>.

Microstructures and Fatigue Properties of High-Strength Low-Alloy Steel Prepared through Submerged-Arc Additive Manufacturing

Submerged arc additive manufacturing (SAAM) is a viable technique for manufacturing large and complex specialized parts used in structural applications. At present, manufacturing high-strength low-alloy steel T-branch pipe through SAAM has not been reported. This paper uses this technology to manufacture low-alloy structural steel parts. The microstructures of the samples were characterized, which revealed that they were mainly composed of polygonal ferrites. The tensile properties in the horizontal and vertical directions of deposits were studied. Results show that the horizontal tensile strength of deposits was quite close to the vertical one, while the elongation rate in the vertical direction was obviously lower than that in the horizontal direction. Fatigue results indicate that the strain fatigue limit of high-strength low-alloy steel samples in vertical direction was 0.24%. The fatigue fractures of fatigue samples of deposits showed multi-source crack initiation characteristics and the crack propagation regions exhibited typical fatigue striations, so the final instantaneous fracture region showed a ductile fracture. Fatigue performance is very important for the safe service of structural parts, but there is a lack of relevant research on this additive manufacturing part. The results of this paper may support the popularization of the SAAM for high-strength low-alloy steel T-branch pipe.

Effects of titanium content on the impact wear properties of high-strength low-alloy steels

In this study, the mechanical properties, wear behavior, and microstructures of high-strength low-alloy steels with titanium contents of 0, 0.04, 0.1, and 2 wt% were systematically investigated. Steel microstructures were examined via scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The wear properties of the steel samples were evaluated by measuring their weight losses, while the wear mechanism was elucidated via scanning electron microscopy. The worn steel surfaces exhibited very rough topographies with well-defined craters and grooves, which were produced by high-angle and low-angle impacts, respectively. The wear resistance of the steels strongly depended on their microhardness and impact toughness. Compared with the other steel specimens, the steel with 0.04 wt% titanium, which contained martensite and lower bainite particles, possessed superior mechanical properties, i.e., a hardness of 745 HV and an impact toughness of 97 J/cm3. Meanwhile, the steel with 2.0 wt% titanium exhibited the lowest abrasive resistance, impact toughness, hardness, tensile strength, and yield strength among all the specimens. These results indicate that excessive titanium content promotes the precipitation of large particles in the steel matrix, which degrades its mechanical properties.

Effect of Alloying Elements on Mechanical Properties of High-Strength Low-Alloy Steel

In this study, the two types of high-strength low-alloy steels were melted and cast in a vacuum induction furnace. Phase transition temperature of HSLA steel was calculated by JMatPro software. The calculation results show that the two different types of HSLA steels which have equal phase proportions of ferrite and austenite at a temperature of approximately 820 and 800 °C in HSLA-I and HSLA-II, respectively. In addition, the effect of chemical composition on the microstructure and mechanical properties of steels were studied. The results indicate that the ultimate tensile stress value of HSLA-II samples was greater than the HSLA-I samples by about 35%, and the yield stress and breaking strength value of HSLA-II were higher than HSLA-I as well.

Effects of different deoxidization methods on high-temperature physical properties of high-strength low-alloy steels

AbstractThis study was aimed at examining the effects of different deoxidization methods on the physical properties of metallic melts by measuring the changes in the kinematic viscosity, electrical resistivity, surface tension, and density of the metallurgical melts during the heating and cooling processes. Our results indicate that high-temperature physical properties are consistently affected by specific elements and compounds.

Structure and Properties of High-Strength Low-Alloy Steel Melted by the Laser Beam

Abstract In this article, examinations were presented of laser beam remelting of microalloyed high-strength low-alloy steel—28MnTiNbVB (UTS = 1,600 MPa), 12 mm thick. The remelting process was carried out with variable linear energy in the range from 0.6 to 2.6 kJ/cm. The examinations have shown that remelted zones have a correct geometry but also include gas pores that could be caused by very high cooling rates, resulting in the hindering of gas evacuation from remelted zones. These gas pores are caused by trapping gases dissolved in metal or vaporizing alloying elements. Remelted zone is martensitic with a lath structure and a hardness up to 600 HV10. Laths are smaller, and smaller precipitations are more tightly packed relative to parent material. The examination results show that steel 28MnTiNbVB exhibits limited weldability.

Influence of Deformation and Heat Treatment on the Microstructure and Properties of High-Strength Low-Alloy Steel with Boron

The microstructure, fine structure, and mechanical properties of high-strength low-alloy steel with boron are studied after two different rolling technologies: (1) high-temperature hot rolling; (2) two-stage controlled rolling with accelerated cooling and subsequent quenching with tempering. The tempering temperature corresponding to irreversible tempering brittleness of the first kind is established. The reasons for embrittlement at that temperature are analyzed.

Effect of Deformation Temperature on the Microstructure and Mechanical Properties of High-Strength Low-Alloy Steel During Hot Compression

The microstructure and mechanical properties of high-strength low-alloy steel were investigated at deformation temperatures of 800-1100 °C and strain rates of 0.1-10 s−1 using an MMS-200 thermal mechanical simulator. The results indicated that the increased deformation processes observed between the starting and finishing temperatures during hot compression testing caused a polygonal ferrite transformation in the material. The polygonal ferrite grain sizes increased with increasing transformation temperatures and gradually grew larger at higher deformation temperatures. Widmanstatten ferrite and acicular ferrite were also formed at high temperatures from 1000-1100 °C, which accordingly led to an increase in Vickers microhardness. In addition, the flow stress in the material increased with an increase in the strain and a decrease in the deformation temperature.

Study of load history effects on the high cycle fatigue properties of high-strength low-alloy steel from self-heating measurements

In the context of high cycle fatigue (HCF), the experimental characterization of the fatigue properties is often performed by using specimens in a virgin state (i.e., without preliminary loading), and with a constant stress amplitude for each specimen. However, the load history applied to a real structure is more complex and the fatigue life prediction remains a difficult task because of the time dedicated to the classical fatigue tests (i.e., the specimen is loaded until failure) and the dispersion of fatigue lives. The load history effects on the HCF properties is characterized using an alternative method: self-heating measurements under cyclic loadings. This method is based on the observation of the mean steady state temperature evolution of a specimen under a successive series of cyclic loadings with increasing stress amplitude for each loading series. A probabilistic two-scale model was developed from the self-heating method able to predict HCF properties. Some self-heating tests are performed to study the influence of a load history effects. It seems that the plasticity is the most influential factor. So, the evolution of the plasticity is observed at the surface of the material under cyclic loading. There is a significant evolution in function of the plastic pre-strain.

Effect of Microadditives on Center Segregation and Mechanical Properties of High-Strength Low-Alloy Steels

One of the main tasks of steelmaking is to obtain the necessary thermodynamic conditions that ensure fine and homogeneous solidified microstructure. The relatively economical solution is to feed microadditives into liquid steel. The metallurgical considerations and techniques on the feeding of microadditives are described in the present work. The effect of small addition of reactive fine particles and ultra-high melting point powders on the control of non-metallic inclusions, slab center segregation, and mechanical properties, especially the Z-direction properties, was investigated. The results showed that the microadditives had composite effects on microalloying and modification of inclusions. The segregation of elements in the slab center of high strength steels was remarkably reduced. The mechanical property along the Z-direction of steel plates was greatly improved.

Effect of Multistage Heat Treatment on Microstructure and Mechanical Properties of High-Strength Low-Alloy Steel

The influence of Cu-rich precipitates (CRPs) and reverted austenite (RA) on the strength and impact toughness of a Cu-containing 3.5 wt pct Ni high-strength low-alloy (HSLA) steel after various heat treatments involving quenching (Q), lamellarization (L), and tempering (T) is studied using electron back-scatter diffraction, transmission electron microscopy, and atom probe tomography. The QT sample exhibits high strength but low impact toughness, whereas the QL samples mostly possess improved impact toughness but moderate strength, but the QLT samples again have degraded impact toughness due to additional tempering. The dispersion of nanoscale CRPs, which are formed during tempering, is responsible for the enhanced strength but simultaneously leads to the degraded impact toughness. The RA formed during lamellarization contributes to the improved impact toughness. Based on the present study, new heat treatment schedules are proposed to balance strength and impact toughness by optimizing the precipitation of CRPs and RA.

Effect of Zr-Ti combined deoxidation on the microstructure and mechanical properties of high-strength low-alloy steels

Effect of Zr-Ti combined deoxidation on the microstructures and mechanical properties of high-strength low-alloy steels were investigated by means of microstructure analysis, tensile- and Charpy impact-tests. Experimental results showed the addition of Zr-Ti based deoxidizing agent resulted in the formation of fine Zr-Ti complex oxides. Owing to abundant finely oxides dispersed in the matrix uniformly, the microstructures deoxidized using Zr-Ti was uniform and the strength was enhanced comparing against the steels deoxidized using Al based deoxidizer. The ductility and toughness of the thick steel plates deoxidized using Zr-Ti were also considerably improved, apparently due to the spheroidization and uniform dispersion of MnS.

Effect of Microalloying Elements on Mechanical Properties in the High Strength Low Alloy Steel

The effect of microalloying elements in Ti-Nb-V containing high strength low alloy (HSLA) steel has been investigated in the present study. The addition of low alloying elements (such as Ti, Nb and V) and distinct heating treatment processes has been used to improve the mechanical properties of HSLA steel. The effect on the microstructure and mechanical properties of normalizing treatment (at 950°C) of as forged steel has been investigated. The microstructural characterization of microalloyed HSLA steel is carried out by using different techniques such as optical microscopy, scanning electron microscopy (SEM) etc. The hardness, tensile testing and Charpy V notch impact tests are performed to study the mechanical behaviour of the alloy. It has been concluded that the precipitation strengthening mechanism for the improvement of impact toughness due to secondary precipitates such as TiN, Ti(C, N), VN etc.

Continuous Cooling Transformation, Microstructure and Mechanical Properties of High-Strength Low-Alloy Steels Containing B and Cu

This study investigated the continuous cooling transformation, microstructure, and mechanical properties of highstrength low-alloy steels containing B and Cu. Continuous cooling transformation diagrams under non-deformed and deformed conditions were constructed by means of dilatometry, metallographic methods, and hardness data. Based on the continuous cooling transformation behaviors, six kinds of steel specimens with different B and Cu contents were fabricated by a thermomechanical control process comprising controlled rolling and accelerated cooling. Then, tensile and Charpy impact tests were conducted to examine the correlation of the microstructure with mechanical properties. Deformation in the austenite region promoted the formation of quasi-polygonal ferrite and granular bainite with a significant increase in transformation start temperatures. The mechanical test results indicate that the B-added steel specimens had higher strength and lower upper-shelf energy than the B-free steel specimens without deterioration in low-temperature toughness because their microstructures were mostly composed of lower bainite and lath martensite with a small amount of degenerate upper bainite. On the other hand, the increase of Cu content from 0.5 wt.% to 1.5 wt.% noticeably increased yield and tensile strengths by 100 MPa without loss of ductility, which may be attributed to the enhanced solid solution hardening and precipitation hardening resulting from veryfine Cu precipitates formed during accelerated cooling.

Effect of chemical composition and production parameters of hot rolling and recrystallization annealing in continuous hot dip galvanizing units on the structure and properties of high-strength low-alloy steels

Changes in mechanical properties and microstructure parameters are studied during heat treatment in a continuous hot dip galvanizing unit for high-strength rolled sheet of different alloying systems and strength classes. Optimum heat treatment temperatures are established for obtaining a specified and stable set of properties, and also the possibility of preparing low-alloy steels of different strength classes by varying the heat treatment temperature.

Comparison of Both Creep Resistance and Material Properties of High-Strength Low-Alloy Steel and Stainless Steel

Abstract In this paper, a creep resistance comparison of high-strength low-alloy ASTM A618 steel with stainless steel AISI 316L has been considered. Stress versus strain diagrams, the curves related to temperature effects on mechanical properties, as well as creep behavior curves for both of mentioned steels are presented. Material elongation curves and the rheological simulation of creep response are also provided. Experimental investigations have been made using modern computer-directed material testing system.

MODELLING TMCP OF HSLA STEELS BY PETRI NEURAL NETWORK TECHNIQUE

The optimization of the architecture of the Petri neural network (PNN) model for thermomechanically controlled processed (TMCP) high strength low alloy (HSLA) steel is done through the comparison of test errors with training errors at different model complexities. The development of the PNN models on the basis of phenomenological relationships between the input and the output variables of TMCP steels has been done. Physical metallurgy principles which govern the property response to the combined actions of chemical composition and process parameters and describe the operative strengthening mechanisms are embedded in the Petri neural network in such a way that the metallurgical reasoning are duly regarded in TMCP steels in predictive activities. It has been found that the Petri neural network is a good tool for modelling the effect of alloy composition and process parameters on the mechanical properties of HSLA steels with certain limitations.L’optimisation de l’architecture du modèle de réseau neuronal de Pétri (PNN) de l’acier haute résistance faiblement allié (HSLA), traité par contrôle thermomécanique (TMCP), est faite par comparaison des erreurs d’évaluation par rapport aux erreurs d’entraînement à différents niveaux de complexité du modèle. On a effectué le développement des modèles PNN en se basant sur les relations phénoménologiques entre les variables d’entrée et de sortie des aciers TMCP. Les principes de métallurgie physique qui gouvernent la réponse de la propriété aux actions combinées de la composition chimique et des paramètres de traitement et qui décrivent les mécanismes fonctionnels de renforcement sont inclus dans le réseau neuronal de Pétri de manière telle que le raisonnement métallurgique est proprement considéré dans les aciers TMCP dans les activités prédictives. On a trouvé que le réseau neuronal de Pétri était un bon outil pour la modélisation de l’effet de la composition de l’alliage et des paramètres de traitement sur les propriétés mécaniques des aciers HSLA, avec certaines limitations.

Morphology control of ductile second phase and improved mechanical properties in high-strength low-alloy steels with mixed structure

Mixed structures of martensite and non-martensitic decomposition product (ductile second phase) can often be produced in commercial heat treatments of low-alloy steels. Such mixed structures can sometimes produce a detrimental effect on the mechanical properties of steels, but they can significantly improve strength, ductility and notch toughness if the ductile second phase appears in a suitable morphology (size, shape and distribution) in association with tempered martensite. Therefore, microstructures have recently been produced in a deliberate attempt to improve the mechanical properties of ultrahigh-strength low-alloy steels. In this review, an attempt has been made to present the effect of the morphology (shape, size and distribution) of the ductile second phase on improved mechanical properties of ultrahighstrength low-alloy steels having mixed structures, This review first discusses the effect of the morphology of the second-phase bainite on mechanical properties of high-strength low-alloy steels with mixed structures of martensite and bainite, in which great improvement in the mechanical properties of the steel has been associated with the morphology of the bainite. Then, knowledge of the recent development of a steel having the mixed structures for low-temperature ultrahigh-strength applications is also reported.