Mechanical Properties Of High-strength Low-alloy Steel Research Articles

Achieving 1.7 GPa Considerable Ductility High-Strength Low-Alloy Steel Using Hot-Rolling and Tempering Processes

To achieve a balanced combination of high strength and high plasticity in high-strength low-alloy (HSLA) steel through a hot-rolling process, post-heat treatment is essential. The effects of post-roll air cooling and oil quenching and subsequent tempering treatment on the microstructure and mechanical properties of HSLA steels were investigated, and the relevant strengthening and toughening mechanisms were analyzed. The microstructure after hot rolling consists of fine martensite and/or bainite with a high density of internal dislocations and lattice defects. Grain boundary strengthening and dislocation strengthening are the main strengthening mechanisms. After tempering, the specimens’ microstructures are dominated by tempered martensite, with fine carbides precipitated inside. The oil-quenched and tempered specimens exhibit tempering performance, with a yield strength (YS) of 1410.5 MPa, an ultimate tensile strength (UTS) of 1758.6 MPa, and an elongation of 15.02%, which realizes the optimization of the comprehensive performance of HSLA steel.

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.

Effect of hot rolling process parameters on the microstructure and mechanical properties of continuously cooled low-carbon high-strength low-alloy (HSLA) steel

Abstract In this work, high-strength low-alloy (HSLA) steel with 0.22 wt% carbon was produced in laboratory scale and hot rolled with a total deformation of 42% via 4, 5, or 6 passes. After multipass hot rolling process, samples were examined either in as-rolled (AR) or as-rolled and heat-treated (ARH) conditions. The results indicated that microstructural and mechanical properties of HSLA steels are influenced by hot rolling conditions for both cases. It was observed that strength values in AR samples have a tendency to increase with increment in rolling pass number. In contrast to AR samples, it was seen that the mechanical properties were slightly decreased in ARH samples that were austenitized at 1150 °C for 45 min and then cooled in still air. Microstructural investigations showed that finer precipitates in AR samples are obviously more than that of ARH samples, as an evidence for higher strength results by precipitation hardening. In addition to precipitation strengthening, refinement of lath bainite and amount of blocky martensite/austenite in AR samples favor the increase in strength.

Examination of fatigue life of HSLA Domex 700 MC welded joints

Manufacturing of steel which meets the conditions of a high-strength low alloy (HSLA) steel, requires three key criteria: low carbon content, microalloying and thermomechanical treatment. Mechanical properties of HSLA steels have shown higher yield strength and toughness as well as good weldability and formability without long-standing loss of these superior mechanical characteristics. Few researchers have already addressed the main problem of HSLA steels which is decreasing their mechanical properties during welding. Most studies have only focused on mechanical properties during welding processes, but it is also very important to test the fatigue behaviour of those steels in the heat-affected zone (HAZ) on welded joints. The present paper discusses the fatigue life of gas metal arc welded (GMAW) joints of HSLA steel Domex 700 MC comparing to the fatigue properties of as-received material. Rotating bending fatigue tests were used for analysis of fatigue life and showed a reduction of the fatigue limit on welded specimens.

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.

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.

Effect of Coiling Temperature and Alloying Elements on the Mechanical Properties and Precipitation Behavior in High Strength Hot Rolled Steel Sheets

The high strength low alloy(HSLA) steels microalloyed with Nb, Ti and V have been widely used as the automobile parts to decrease weight of vehicles. The effects of process conditions are investigated in the aspects of the precipitation behavior and the mechanical properties of HSLA steel microalloyed with Nb and Ti using TEM, SANS and mechanical testing. When Ti was added to a 0.07C-1.7Mn steel which was coiled at , the specimen revealed the property of higher tensile strength of 853.1 MPa and the stretch-flangeability of 60%. The stretch-flangeability was increased up to 97.8% for coiling temperature above . The precipitation hardening cannot be achieved in the 0.045C-1.65Mn steel which was the lower density of fine precipitates. However, the 0.07C-1.7Mn steels containing Nb and/or Ti which was coiled at X have a high precipitates density of $210^{ 5}$/㎥. The high strength of these steels was attributed to the precipitation hardening caused by a large volume froction of (Ti, Nb)C precipitates with a size below 5 nm in ferrite matrix.

Thermodynamic model for precipitation of carbonitrides in high strength low alloy steels containing up to three microalloying elements with or without additions of aluminium

AbstractTo control austenite grain growth in high strength low alloy (HSLA) steels, additions of micro alloying elements showing chemical affinity for interstitial elements (C and N) are used. These elements have a significant effect on the mechanical properties of the steels. The mechanical properties of HSLA steels depend both on the amounts of the microalloying elements dissolved in the austenite and on undissolved carbonitrides. In the present work, a thermodynamic model enabling calculation of the composition of the austenite as well as the composition and quantity of the carbonitrides in HSLA steels containing up to four microalloying elements is presented. This model can be a useful tool in determining the optimum chemical compositions for steels as well as the heat treatment parameters required to maximise hardenability and to control austenite grain growth.MST/1471

Thermodynamic model for precipitation of carbonitrides in high strength low alloy steels containing up to three microalloying elements with or without additions of aluminium

To control austenite grain growth in high strength low alloy (HSLA) steels, additions of micro alloying elements showing chemical affinity for interstitial elements (C and N) are used. These elements have a significant effect on the mechanical properties of the steels. The mechanical properties of HSLA steels depend both on the amounts of the microalloying elements dissolved in the austenite and on undissolved carbonitrides. In the present work, a thermodynamic model enabling calculation of the composition of the austenite as well as the composition and quantity of the carbonitrides in HSLA steels containing up to four microalloying elements is presented. This model can be a useful tool in determining the optimum chemical compositions for steels as well as the heat treatment parameters required to maximise hardenability and to control austenite grain growth.MST/1471