Microalloyed Steel Research Articles

Corrosion characteristics of vanadium micro-alloyed steel reinforcement bars exposed in concrete environments and industrially polluted atmosphere

Corrosion resistance performance of rebars rolled from vanadium micro-alloyed (VMA) steel was evaluated vis-à-vis rebars rolled from steel having similar chemistry to the (VMA) steel without vanadium and subjected to thermomechanical treatment after hot rolling (TMT). Three test environments namely simulated concrete pore solution, mortars, and industrially polluted atmosphere were used to assess the performance of these rebars. Mass loss, electrochemical impedance spectroscopy, DC polarization and potential-time studies were employed to acquire quantitative data and explain the observed results. Raman spectroscopy was used to identify the corrosion products formed on the surface of the exposed rebars in different environments. The corrosion resistance of VMA rebars was better than TMT especially with increased duration of exposure in chloride contaminated concrete environments. However, under the industrially polluted atmosphere, both rebars exhibited comparative corrosion rates. Lesser detrimental effect of chloride present in concrete environment on the VMA steel rebars is attributed to the higher grain boundary per unit area in these rebars than in the TMT rebars. It is suggested that owing to the stronger tendency of the higher-grain-boundary- material to interact with oxygen and moisture, a thicker film of Fe(OH)3 was formed on its surface than on the surface of the TMT rebar, prior to their exposure to the test environments. This hydroxide film dissolved in alkaline environment of concrete, nucleated and grew as a protective FeOOH film on the surface of the rebars.

Effect of Heat Treatment in Pipe Processing Stage on Corrosion Resistance of Micro-Alloyed Steel Hot-Rolled Products

The effect of heat treatment on corrosion resistance of low-alloy pipe steels is investigated in relation to oilfield pipeline operating conditions. It is established that after pipe bulk heat treatment at 720 °C metal corrosion resistance increases, but at a lower temperature of 680 °C no significant change is detected. Analysis of the corresponding structural changes is performed and the main factors facilitating an increase in corrosion resistance are determined: cementite component spheroidization in the areas of pearlite or degenerated pearlite, and a reduction in dislocation density. The role of nanoscale precipitate type on pipe corrosion resistance is noted. It is established that at a higher processing temperature there is a larger fraction of ferritic precipitates. In contrast to interphase precipitates these particles do not adversely affect steel corrosion resistance.

Ethanolic Media Effect on the Susceptibility to Stress Corrosion Cracking in an X-70 Microalloyed Steel with Different Aging Treatments

The objective of this research was to evaluate the stress corrosion cracking (SCC) of X-70 micro-alloyed steel in contact with bio-ethanol and E-50 gasohol. Environmental factors, including water (1%, 3% and 5%) and NaCl (10 mg/L and 32 mg/L), as well as two aging treatments were studied. Experimental values were obtained by the Slow Strain Rate Test (SSRT) technique, X-ray fluorescence (XRF), and tensile test according to the information reported in the literature. The results of the SSRT for the SCC determination showed that this steel in these conditions did not show evidence of SCC, which was attributed to the formation of an oxide (Fe2O3) not soluble in ethanol. The oxide layer acts as a protector preventing the formation of pitting, one of the main causes of cracks initiation in SCC.

Modeling and mining dual-rate sampled data in corrosion potential online detection of low alloy steels in marine environment

With the rapid development of the Internet of Things technology, the use of front-end sensors makes the corrosion potential online detection of low alloy steels in marine environment a reality, thereby obtaining oceans of corrosion data. However, the monitoring frequency of seawater environmental data is usually much lower than corrosion potential data, which produces the dual-rate sampled corrosion datasets. In this paper, firstly, a method based on comprehensive index value (CIV) is proposed to process the dual-rate sampled corrosion data, which retains more information of original data compared with the mean value method. Secondly, the relevance vector regression model named CIV–RVR is established to predict the corrosion potential, which outperforms other modeling methods like artificial neural networks and support vector regression. Moreover, key corrosion resistance elements including Cr, Ni, Mo, P, Cu, Si and V of experimental steels are determined by Spearman correlation analysis, which have been pointed out as positive elements by previous studies. Finally, the effects of key corrosion resistance elements on seawater corrosion potential are quantitatively mined and visualized by applying the CIV–RVR model. The results mined by the proposed model show that elements Cu and P have a positive synergistic effect and can help to promote the corrosion potential of the micro-alloy steel, which is consistent with accepted conclusions. It can be concluded that the CIV–RVR model proposed in this paper can be well applied to model and mine dual-rate sampled data in corrosion potential online detection of low alloy steels under the marine environment.

A Microstructurally Based Model for Recrystallization in Dual-Phase Steels

Adjusting and predicting the ferrite recrystallization kinetics of cold-rolled Advanced High-Strength Steels during annealing is necessary to control their final microstructure and thus their mechanical properties. This study proposes a microstructurally based model for predicting the recrystallization kinetics of Dual-Phase steels that takes into account the effect of several physical parameters (chemical composition, temperature, cold rolling reduction ratio, and precipitation state). First, ternary Fe-C-Mn grades were used to validate the parameters of the model relative to the Mn content and to the reduction ratio. Second, the effect of other alloying elements (Si, Cr, Mo) was analyzed using recrystallization kinetics from the literature, before testing the model on two industrial Dual-Phase grades: a DP600 steel and a micro-alloyed DP1000 steel. The effect of the micro-alloyed elements (Nb,Ti) either in solid solution or as precipitates was detailed. Lastly, the model was used to build interaction maps between recrystallization and austenite formation during continuous heating with different heating rates.

Control of TiN precipitation behavior in titanium-containing micro-alloyed steel

As a kind of high-strength steel, low-carbon titanium-containing micro-alloyed steel has been widely used in the industry recently. Fine TiN precipitates can refine the austenite grains, improve the toughness of the steel, strengthen the good formability and weldability of the steel, and reduce the production costs of the process. However, due to the improper technical operations or steps, a large amount of TiN will precipitate in the billet, which will affect the crack sensitivity of the steel. According to the thermodynamic calculation results, when the nitrogen content is reduced from 50 ppm to 20 ppm, the precipitation temperature of TiN can be reduced to 1400 °C, whilst the amount of TiN precipitate quantity will be significantly reduced. This article conducted the Oxygen and Nitrogen Analysis towards the samples throughout the entire steelmaking process. The results indicated an abnormal increase in nitrogen content during the Ladle Furnace (LF) process. In addition to the reaction between air and molten steel, the raw and auxiliary materials for steelmaking may also be the reasons which caused the increase of nitrogen content in the molten steel, as they contain nitrogen as well. However, there are only a small number of studies that had explored the impact of raw and auxiliary materials on steel quality. This article investigated the cleanliness of ferrotitanium alloys. The results showed that the cleanliness (inclusions and nitrogen content) of TiFe-30 is much higher than that of TiFe-70. When TiFe-70 was replaced by TiFe-30 for steelmaking, the content of nitrogen in the molten steel as well as the content of TiN were reduced, whilst the size of TiN was correspondingly decreased. In this experiment, not only was the performance of steel improved, the cost of steelmaking was also reduced. At last, this work could also awaken the judgment standards for steelmaking alloys.

Concerning the Production and Application of Ferroalloys with REM and AEM for Steel Modification and Microalloying

The state-of-the-art technology in the production and application of ferroalloys containing rare earth and alkaline earth metals is considered. The possibility of developing wasteless production of such ferroalloys using ore-coal briquettes is demonstrated. It is shown that for out-of-furnace processing of steel, multicomponent alloys with a microcrystalline structure are most efficient.

Thermodynamic analysis of liquid steel refining by complex alloy containing La - Ce -Al

Alloys containing rare-earth metals (REM) are increasingly used in production of steels and alloys. After modification and microalloying of steel with REM, structure of primary metal is refined, its mechanical characteristics are upgraded, concentration of oxygen dissolved in liquid iron is decreased significantly, and originated nonmetallic inclusions do not exceed several microns in size and are of predominantly globular shape. Due to relatively high cost of REM, it is proposed to calculate their consumption at each stage of technological process to determine optimal amount required for deoxidation or modification. In this work, thermodynamic modeling of phase equilibria in liquid metal of Fe - La - Ce -Al - O system has been performed. The authors provide a base of thermodynamic data of the system under study: temperature dependences of the equilibrium constants of reactions between the components, values of the first-order interaction parameters (according to Wagner) for elements in liquid iron, values of energy parameters of the theory of subregular (for oxide melt) and regular (for solid solution) ionic solutions. Based on coordinates of calculated isothermal (1600 °С) isostructural (0.01 wt. % aluminum) cross section of solubility surface of components in metal (SSCM) of the Fe - La - Ce -Al - O system, lanthanum and cerium flow diagrams were constructed for various initial oxygen concentrations (metal is pre-deoxidized with aluminum). It has been shown that costs of expensive REM used in microalloying and metal modification strongly depend on composition of the initial metal.

Effect of inclusions on microstructure and mechanical behavior of multi-pass welded naval grade steel

This paper assesses the metallurgical characteristics and mechanical properties of multi-pass gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) of micro-alloyed steel DMR 249-A. The prime objective was to carry out a comparative study of the microstructure and mechanical properties of the joints produced by the two types of welding. A high volume of larger sized inclusions in GMAW contributed to inferior mechanical properties. The coarse-grained part of the heat-affected zone (CGHAZ) showed a lower microhardness. Fracture always occurred in the heat-affected zone, and it is believed that it is associated with CGHAZ. GTAW joints showed low tensile residual stress, higher hardness, and tensile strength. GTA weldment also showed superior impact toughness at sub-zero temperature (–60 °C). Mn-containing inclusions were seen in GTA weldments; it is believed that they promote the formation of acicular ferrite. This is believed to be responsible for the superior mechanical properties of GTA weldments. The microstructural analysis of the two weldments revealed the presence of a higher volume fraction of acicular ferrite in the GTAW. All in all, GTAW joint was found to perform better than GMAW joint.

The possibility of enhanced hydrogen embrittlement resistance of medium-Mn steels by addition of micro-alloying elements

In the present study, we elucidated the possibility of improvement in H embrittlement (HE) resistance of micro-alloyed medium-Mn steels by MC carbides formation. The Fe-6Mn-0.08C (wt%) steel was used as a base material, and the different amount of Nb, Ti, and V was added to form MC carbides. All steels exhibited the nano-sized globular morphology with dual-phase of α ferrite plus γR retained austenite, and the phase fraction was almost identical regardless of steel compositions. The steels showed an almost similar grain size of γR phase, regardless of composition. However, the micro-alloyed steel revealed the smaller size of α phase relative to base steel owing to MC carbides precipitation in the α phase. The micro-alloyed steel exhibited higher strength and lower ductility compared to the base material due to precipitation hardening and fine grain size of α. Considering HE resistance, we realized that the addition of the micro-alloying element resulted in a trivial effect on the medium-Mn steels, because MC carbides in the α phase could not act as influential trap sites of diffusible H. Most of the H atoms were preferentially trapped in the γR phase, and the H-enriched γR phase caused H-assisted nano crack when it transformed to strain-induced martensite. After that, the nano crack developed to the intergranular crack, leading to premature fracture.

A New Cooling Strategy in Curved Continuous Casting Process of Vanadium Micro-alloyed YQ450NQR1 Steel Bloom Combining Experimental and Modeling Approach

In the continuous casting process of steel, the bloom surfaces would experience intensive cooling from the water-cooled copper mold to secondary cooling water spray. If the cooling process is not controlled properly, hot ductility of the bloom surface microstructures would deteriorate, and bloom surface cracks would form easily under straightening deformation in a curved caster. Considering the above facts, the cooling scheme for the continuous casting of YQ450NQR1 steel bloom, a kind of vanadium-containing micro-alloyed steel, is studied with both experimental investigation and mathematical modeling in this work. The authors first investigate the hot ductility of bloom surface microstructures at various cooling rates using a Gleeble thermal simulator. Then, the precipitation of V(C, N) particles and its influence on ferrite formation during continuous cooling are studied and characterized using High-Temperature Laser Scanning Confocal Microscopy. Based on these, the preferred cooling rate for surface microstructures at the straightening position in the caster is obtained. To further reduce the solute macro-segregation through enlargement of the equiaxed crystal zone, a cellular automaton-finite element model is used to calculate heat transfer and solidification structure evolution during the continuous casting process. After calibration with industrial trials, the model is utilized to determine the critical position for columnar to equiaxed transition and to adjust the pouring temperature for the melt. Combining the above research, a new cooling strategy for YQ450NQR1 steel bloom is obtained, which can improve crack resistance of bloom surface microstructures and reduce solute macro-segregation at the same time.

Revealing the Two-Step Nucleation and Growth Mechanism of Vanadium Carbonitrides in Microalloyed Steels

Combining high-resolution transmission electron microscopy (HR-TEM) and 3-dimensional atom probe tomography (3D-APT), the early stages of nucleation and growth of vanadium carbonitrides (VCN) were revealed. VCN nucleation starts with locally distorted body-centered cubic (bcc) lattices due to a substitution of Fe atoms by V atoms, which results in the formation of an intermediate coherent crystal structure within the ferrite matrix. Misfit strain self-accommodation leads to twining within the VCN particles. As the particles grow, the precipitates gradually lose coherency and grow into discs or plates. Simultaneously, the intermediate crystal structure of the nucleus transforms into the equilibrium VCN-structure.

Hot deformation behavior and constitutive modelling of low carbon micro-alloyed steel YQ450NQR1 during isothermal compression

In this paper, the flow stress curves of YQ450NQR1 low carbon (wt. 0.12%) vanadium micro-alloyed YQ450NQR1 steel are obtained by conducting isothermal compression tests using Gleeble-1500 thermal simulation machine covering the temperature range of 1143K-1433K. To better describe the complex and abrupt deformation during the hot rolling process of the “Z-shaped” YQ450NQR1 products used for train beams, three deformation strain rates (1s−1, 10 s−1 and 30s−1) are selected to study the hot deformation behavior. On this basis, a constitutive model considering deformation activation energy is established from the experimental stress-strain data. The model is further validated against multiple sets of hot compression test data and shows a good accuracy between predicted and tested flow stress with a correlation coefficient of 0.988 and an average error of 8.4%, which indicates the accuracy and reliability of the constitutive model for YQ450NQR1 steel.

Static Softening Behavior of Low Carbon High Niobium Microalloyed Steel

The MMS-200 thermal simulation testing machine was used to study the static softening behavior of low carbon high niobium microalloyed steel. The effect of niobium to the static recrystallization softening behavior of the microalloy steel had been analyzed by establishing the kinetics model of static recrystallization and the micro-morphology of precipitates. The results indicated that: the static softening behavior of the tested steel significantly influenced by the deformation temperature and the interval pass time of the rolling processing. At relatively high deformation temperature and long interval pass time, the ratio of static softening was increased. Then the deformation temperature was lower to 950°C, and the static softening behavior of the test steel was ceased. But when the deformation temperature was higher than 1000°C, the static softening behavior of the test steel completely occurred. The activation energy of the test steel was 325·mol-1 by the established model calculated.

Mechanical properties and microstructure characterization of GTAW of micro-alloyed hot rolled ferritic XPF800 steel

The gas tungsten arc weldability of micro-alloyed hot-rolled ferritic XPF800 steel, which is newly produced by Tata Steel, has been studied. The weld geometry profile, mechanical properties and microstructure affected by heat input have been investigated. The micro examination of the welded joint has been characterized utilizing optical microscope and scanning electron microscope. Atomic concentrations of metallic elements in carbides have been determined by energy dispersive X-ray spectrometry. The optimum parameters for current, welding speed and heat input have been found to be 140 A, 100 mm/min and 0.62 kJ/mm in the GTAW of XPF800 plates, respectively.

Welding of Cold-Resistant Micro-Alloed Steels 10HSNDA and 15HSNDA in the Atmosphere of Carbon Monoxide (II)

Micro-alloyed steels are widely used in the manufacture of critical welded structures operating under extreme conditions of the North. Microalloying of V, Nb and B is a simple and effective method of transferring known grades of structural steel and alloys to the category of increased and high strength, cold resistance, etc. The possibility of arc welding of steels grade 10CrSiNiAl and 15CrSiNiAl (10, 15ХСНДА in Russian), initially alloyed with trace amounts of niobium and vanadium to increase their cold resistance in carbon monoxide is considered. It is established that the use of the specified reducing atmosphere prevents the oxidation of the weld metal. The thermodynamic substantiation of the chemical reactions of microalloying elements proceeding in the weld pool, leading to the preservation of the steel composition, is presented. The chemical and metallographic analysis of welds was performed. The efficiency of using low-cost CO, or its mixtures with CO2, as substitutes for expensive argon and helium, when welding micro alloyed steels is shown.

The Selection of Materials for the Auto-Body Deformation Zones

Nowadays, it is important to select the proper material for parts of the car-body’s deformation zones in terms of passenger safety. Due to wide range of high-strength steels on the market, the article presents the way of selecting the material by determining the deformation work and the stiffness constant, both measured by the stretch-bending test. The procedure was verified on a high-strength micro-alloyed steel HSLA, high-strength multi-phase steels DP 600 and TRIP, and an austenitic stainless steel AISI 304. The results indicate the austenitic steel is better to use in the deformation zones for the frontal impact, while multi-phase steels are more suitable for deformation zones at the lateral impact. The regression model describing the dependence of the deformation work measured at the stretch-bending test and the deformation work measured at uniaxial tensile test was defined as well. The model allows predicting the deformation work at stretch-bending test based on the mechanical properties measured by the tensile test.

Influence of Zirconium Content on Corrosion Resistance of Micro-Alloyed Steel Reinforced Concrete in Chloride Solutions

Influence of Zirconium Content on Corrosion Resistance of Micro-Alloyed Steel Reinforced Concrete in Chloride Solutions

Mechanical properties of micro-alloyed steels studied using a evolutionary deep neural network

ABSTRACT The existing Evolutionary Neural Net Algorithm (EvoNN) for data-driven modeling has been augmented during this study using an evolutionary deep neural net strategy to give rise to a novel algorithm named EvoDN, which has been further upgraded to an improved version named EvoDN2. This study reports an application of EvoDN2 to study vanadium and niobium based micro-alloyed steels. For this purpose, a dataset for ultimate tensile strength, elongation and Charpy impact energy at −40°C is collected and trained using aforementioned EvoNN, EvoDN2, and another in house algorithm named Bi-objective genetic programming (BioGP). This trained models are then optimized to get optimized properties using a constrained version Reference Vector Evolutionary Algorithm (cRVEA). The results are thoroughly compared with the existing correlations and prior work and found to be well within the acceptable range.

Data on Chloride-related electrochemical deterioration of micro-alloyed steel in E20 simulated fuel ethanol blend

Abstract The data existing in this work relate to the study (Chloride effects on the electrochemical degradation of micro-alloyed steel (MAS) in E20 simulated fuel ethanol blend (SFGE) (Joseph, 2017) [1] . Corrosion rates of MAS versus chloride concentration in E20 are presented. Potentiodynamic polarization tests data were also covered. Composition analysis of the corrosion products as well as images of the samples' surfaces before and after testing were also presented. The calculations are based on ASTM Standard G1-03 for determining mass loss and corrosion rates. Data are valuable to assess that there is increase in corrosion rate with increase in chloride. Hence, it is noted that chloride could be reduced to the barest minimum in fuel ethanol. Pitting form of corrosion are presented in the scanning electron microscopic images.