Microalloyed Steel Research Articles

The effect of RRA treatment on mechanical properties and wear behavior in vanadium micro-alloyed Hadfield's steel

To solve the ongoing problems of micro-alloyed Hadfield's steel, insufficient hardness and excessive deformation in the early working period, expensive alloying elements like Ti, Nb, and V have been utilized. However, traditional long-time, single-stage aging exacer-bates vanadium to assemble at the edge of initial precipitates, which diminishes estimated effects. For this, here we report the tremendous impact of retrogression and re-aging process (RRA) in this steel by booming the V (C, N) mean sized in 11 nm. The procedure enhances the micro-hardness, yielding strength, tensile strength, and impact-wear resistance for more than 27.4%, 29.5%, 22.2%, and 51.5%, respectively. Moreover, the wear mechanism of RRA samples has been investigated in that micro-sized precipitates surrounded by numerous nano V (C, N) stick in the matrix and hinder the abrasive embedding consistently, thus decreasing the micro-cutting and micro-plowing. This new process maximizes the utilization of costly and nonrenewable vanadium and magnifies the impact-wear resistance under either mild or medium-intensity working conditions.

Influence of vanadium, niobium and boron on kinetics of austenite recrystallization of steels with different strength levels under hot deformation conditions

Summarized results of research of the dynamic and static austenite recrystallization kinetics of low-carbon low-alloy and alloyed steels of strength classes 420, 620, 690, 750 and 890 and medium-carbon steels of strength class 1700 containing different amounts of vanadium, niobium and boron are presented. Studies were carried out by the plasmetric method under deformation conditions close to hot rolling. It was found that vanadium has a weak effect on recrystallization, and niobium in all the studied steels significantly slows it down in the hot rolling temperature range, regardless of the total doping level; microalloying of steels with boron leads to acceleration of austenite recrystallization.

Strategy of complex carbides in microalloyed 4Mn steels processed by quenching and austenite reversion

This work describes a strategy to employ complex carbides for high-yield microalloyed 4Mn steels processed by quenching and reversion (Q&R). The nano/microstructural details are investigated by using electron microscopy and atom probe. It is found that complex carbides are classified into two types and contribute to yield strength in different ways. First, coarse carbides (MC1), which are retained after austenization and quenching, provide the Zener pinning effect and contribute to strengthening by microstructure refinement and precipitation hardening. Second, nanoscale carbides (MC2), which precipitate in martensite during austenite reversion, provide precipitation hardening. Furthermore, the precipitation of MC1 accelerates austenite reversion due to the finer martensite microstructure. Hence, the strengthening effects and TRIP effect can be tuned by controlling the proportion of the two types of carbide. This concept is validated in Ti-Mo 4Mn steel, which exhibits a high yield strength of about 850 MPa, a high ultimate tensile strength of about 950 MPa, and excellent elongation of over 20%. The complex carbide strategy is able to increase yield strength without sacrificing much ductility for Q&R medium-Mn steels.

The Prediction of the Mechanical Properties for Hot-Rolled Nb Micro-Alloyed Dual-Phase Steel Based on Microstructure Characteristics

The Prediction of the Mechanical Properties for Hot-Rolled Nb Micro-Alloyed Dual-Phase Steel Based on Microstructure Characteristics

Effect of Mg on Inclusion and High Cycle Fatigue Behavior in Titanium Microalloyed Beam Steel

In this paper, the fatigue behavior of titanium microalloyed beam steels were studied by high cycle fatigue test and fatigue crack growth rate test. The effect of Mg addition on the fatigue behavior in titanium microalloyed beam steel was systematically analyzed. According to the experimental results, the addition of magnesium can effectively modify the inclusions by reducing the size of Al2O3 and TiN and promoting the formation of finer complex inclusions with a MgO·Al2O3 core in titanium microalloyed high-strength beam steel. The number of inclusions in the experimental steels had far less of an impact on the fatigue characteristic than inclusion size. With the heterogeneous nucleation effect of MgO·Al2O3, the inclusions are refined after the Mg addition. The tensile strength of Beam-2 steel decreased by approximately 54 MPa, while its fatigue strength increased by about 33 MPa, showing favorable fatigue resistance. These findings are essential for optimize the fatigue properties of titanium microalloy steel and promoting the development of automobile beam steel with excellent fatigue properties.

Adjustment of the Hot Rolling Technology of Micro-Alloyed Pipe Steel Using a Digital Twin to Provide the Targeted Structure and Properties of the Metal

The results of computer and physical modeling of pipe steel hot rolling on a continuous rolling mill 2000 are presented. The moment of growth of austenite grains and the reasons for their growth are determined. The possibility of grinding the microstructure of the metal before controlled cooling, and the thermal deformation conditions conducive to grinding are investigated. It is shown that Nb (C,N) are not a factor in stopping the growth of austenite grains, but only inhibit the growth processes.

The consequences of hot deformation and control cooling on the microstructure of medium carbon microalloyed steel − 38MnSiVS5 grade

Medium carbon micro-alloyed steels are mostly being utilized in the application where quenched and tempered steels are needed for cost-productive processing. However, the impact toughness of micro-alloyed steels is inferior to that of quenching & tempered steels, which resist their use in critical applications. Conventional techniques are used for hardness enhancement of micro-alloyed steels due to reduction in carbon percentage, the addition of relevant chemical constituent such as titanium to achieve the reduction in the amount of pearlite and controlling the microstructure during thermomechanical processing, subsequently after cooling and forging. In this research work, the effect of hot deformation and control cooling temperature on the microstructure of medium carbon micro-alloyed steel 38MnSiVS5 was studied. Different approaches were performed to improve the impact toughness and hardness and found out that forced air cooling of the micro-alloyed steel 38MnSiVS5 forgings resulted in the finest microstructure and exhibiting a higher hardness of 45.93 RC.

The carbon content effect on hot-rolled C–Mn micro-alloyed E410 structural steel

Engineering usage of hot-rolled C–Mn micro-alloyed IS 2062 structural steels are inevitable as they majorly contribute to sustainable development of public infrastructure such as steel bridges, storage tanks, riveted and welded structures, etc. Herein, effect of carbon concentration (0.04 wt%C and 0.17 wt%C) upon mechanical strength and microstructural modifications was explored on hot-rolled E410 steel. A decline with ⁓22% and ⁓8% in yield stress (YS) and ultimate tensile strength (UTS) was observed in 0.17 wt%C than 0.04 wt%C steel. However, elongation of 0.17 wt%C improved by ⁓4% than 0.04 wt%C steel. Likewise, micro-hardness of 0.17 wt%C was increased by ⁓47% than 0.04 wt%C steel. Principal reasons for such behaviour were variation in secondary phases, grain boundary distribution, texture and deformation gradient, local microstructural strain, recrystallized and un-recrystallized grain fraction, and resulting mode of tensile failure amongst two hot-rolled heats.

Specimen geometry design for plasticity and fracture characterization of sheet metal under high testing speed and various stress states

To model a vehicle crash event using the finite element (FE) method, accurate material properties of automotive sheet metals at high strain rates and various stress states need to be known. In this paper, a series of specimen geometries were designed for dynamic tensile tests in a servo-hydraulic tensile machine to get rid of the system ringing effect. These specimen geometries, which consist of different Stress triaxialities and Lode angle parameters, were optimized according to a similar physical principle as that used for the Gen. III specimen of Fang and Grams using FE simulations. Oscillation-free forces were obtained during the high-speed tests in the strain rate range of up to 103 s−1 using specimens that have a novel design. The deformation and local strain fields of the specimens were measured using digital image correlation (DIC) techniques. Furthermore, the deformation and fracture behavior of a micro-alloyed steel (H340) were characterized and analyzed. The determination of the model parameters for plasticity, damage/fracture modeling, and the material’s strain-rate dependency could be conducted more accurately based on the improved oscillation-free force measurements, which resulted in an improved prediction of the plasticity and fracture behavior of the investigated steel.

Effect of Nitrogen Content on the High Cycle Fatigue Properties of Titanium Microalloyed Steel

The high cycle fatigue properties of three industrial 0.12% Ti microalloyed steels with different nitrogen contents (56, 40, and 30 ppm in molten steel of tundish) are investigated. The results show that <20% of the fatigue crack initiation sites are oxide inclusions of size in 16.8 μm ≈ 55.9 μm, while the rest 80% are surface defects. No TiN inclusions cause fatigue failure and the fatigue limit strength slightly decreases with increasing N contents as the yield strength decreases with a coarser ferrite grain. Inclusions characterization in the section near the fracture shows that the average sizes of TiN inclusions in H56, M40, and L30 steels are 3.50, 3.22, and 2.89 μm, and the maximum sizes are 6.92, 6.67, and 6.23 μm, respectively. Calculating for a cooling rate of 0.2 K s−1 using ChemAppPy precipitation model, the size of TiN inclusions will increase from 6.1 to 7.1 μm, when increasing N content from 30 to 60 ppm. The relationships between nitrogen content, TiN inclusions, and fatigue failure quantified by experimental test and modeling show that the nitrogen content in steel can be relaxed up to 60 ppm when considering economical denitrogenization and fatigue safety.

Study on Hot Flow Behaviors and Deformation/Diffusion Mechanisms of V and V–Ti Microalloyed Steels by Physical Constitutive Modeling

The hot compression tests of medium carbon V and V–Ti microalloyed steels are carried out at the temperature of 900–1100 °C and strain rate of 0.01–10 s−1. Three physical constitutive models based on creep theory are studied, the prediction accuracy is compared and analyzed by employing the correlation coefficient (R) and average absolute relative error (AARE), and the deformation/diffusion mechanisms are discussed. The results show that Ti has obvious hardening effect in V microalloyed steel and retards the onset of dynamic recrystallization. The physical constitutive model containing the theoretical value of creep exponent 5 can accurately describe the hot flow behavior of both steels, the prediction accuracy of which is comparable to that of the model containing exponent n, reflecting that the dominant deformation mechanism of both steels is dislocation climbing. Furthermore, a modified physical constitutive model combining diffusion mechanisms of lattice diffusion and grain boundary diffusion shows higher accuracy (R = 0.996, AARE = 3.81% of V steel and R = 0.994, AARE = 4.52% of V–Ti steel), indicating that the diffusion mechanism is controlled not only by lattice diffusion but also by grain boundary diffusion.

Effect of annealing temperature on the properties of phosphorus micro-alloyed non-oriented electrical steels

Microstructure, texture, mechanical properties, and magnetic properties of low carbon and silicon non-oriented electrical steels annealed at 800 °C, 820 °C, and 860 °C were studied. Fine precipitates (Al, Si, Mn)xNy-P, a small quantity of (Al, Si, Mn)xNy, and the aforementioned composite precipitates containing MnS were detected in the samples annealed at 820 °C and 860 °C. Compared with the samples annealed at 820 °C, the number density of precipitates decreased by 20% and the average size increased by 25 nm in the samples annealed at 860 °C. The average grain size was 22 μm, 26 μm and 46 μm in the samples annealed at 800 °C, 820 °C, and 860 °C, respectively. The magnetic induction increased by 0.027 T after the annealing temperature of the samples increased from 800 °C to 820 °C. The iron loss reduced 0.94 W/kg when the annealing temperature increased from 800 °C to 860 °C. The tensile strength and yield strength of the samples decreased by 21 MPa and 40 MPa when the annealing temperature increased. The loss iron was 4.27 W/kg(P1.5/50) and magnetic induction was 1.764 T(B50) for the samples annealed at 860 °C. Magnetic properties of the experimental samples were superior to the same grade of commercially available steels.

Continuous-cooling-transformation Diagrams for Boron-low Carbon Micro Alloy Hot Rolled Enamel Steel

The addition of Element B to micro-alloyed low-carbon steels helps to improve the scale burst resistance of the enameled steel while being able to improve the strength properties of the base steel. It is known that the differences in alloy content change the phase transition temperature and CCT diagram. To test the phase transformation temperature and CCT diagram of B-micro-alloys low carbon steel, this paper uses the thermal expansion method to determine the transformation temperatures Ac1, Ac3, Ar1, and Ar3 with a Gleeble-1500 thermal simulator, and conducts hot compression experiments at 950 °C with a true strain of 0.3 and strain rate of 10 s−1, followed by cooling to room temperature at 0.1, 0.5, 1, 5, 10, and 25 °C/s rates of cooling to room temperature. Based on the expansion diagrams, metallography and hardness are combined to determine the microstructure composition at the corresponding cooling rates. Therefore, the CCT diagrams are plotted. The results show that when the cooling rate is less than 5 °C/s, the phase transformation consists of ferrite and a very small amount of pearlite; when the cooling rate is greater than 5 °C/s, it consists of ferrite, a small amount of pearlite, and bainite, and when the cooling rate is from 5 °C/s to 25 °C/s, it consists of ferrite and bainite.

Effect of Laser Shock Peening without Coating on Grain Size and Residual Stress Distribution in a Microalloyed Steel Grade

This study aimed to identify the optimal combination of wavelength and laser pulse density to achieve the optimal pulse pressure that can induce the maximum compressive residual stress at the subsurface of microalloyed steel. For this, laser shock peening without coating (LSPwC) was performed on microalloyed steel samples at the fundamental wavelength (1064 nm) with pulse densities of 3, 6, 9, and 12 GW/cm2 and at the second harmonic wavelength (532 nm) with pulse densities of 3, 6, and 9 GW/cm2. The residual stress distributions were studied to a depth of 500 µm in the laser-treated samples. Tensile residual stress was observed at the surface of laser-peened specimens in both wavelength conditions (1064 and 532 nm). The significant impartment of compressive residual stress across the depth was achieved at the fundamental wavelength (1064 nm). The maximum compressive residual stress was attained with a laser pulse density of 9 GW/cm2 in the 1064nm wavelength condition. The optical micrographic analysis in the subsurface regions of the LSPwC specimen at 1064 nm and 9 GW/cm2 shows evidence of a high degree of plastic deformation. Electron backscatter diffraction (EBSD) analysis shows that there is grain refinement due to plastic deformations in samples subjected to the fundamental wavelength. Microhardness distribution analysis across the subsurface region shows work-hardening effects in the laser-processed samples in the 1064 nm condition. This study also shows that there is an indication of a thermal softening effect in the samples treated with the 532 nm wavelength, and it is correlated with lower compressive residual stress across the depth.

Effect of ausforming on the bainitic transformation and microstructure in medium carbon V–N micro-alloyed steel

Ausforming at 900 °C with 30% reduction in V and N micro-alloyed steel could induce VN precipitation, which has low lattice misfit (1.8%) with bainitic ferrite in a particular crystal orientation. The incubation period of bainitic transformation was shortened by introducing VN. A further ausforming at 300 °C with different strains prior to isothermal transformation was carried out, which provided more nucleation points and more distortion-energy storage for bainitic transformation. The incubation period was dramatically shortened and bainitic transformation was notably accelerated. There existed a competition between accelerating nucleation and suppressing growth after low temperature ausforming with different strains, and a small strain resulted in a more significant acceleration and a higher degree of bainitic transformation. In addition, thinner bainitic ferrite and finer blocky retained austenite were obtained after low temperature ausforming. The orientation relationship between bainitic ferrite and austenite in the ausformed steel were K–S and N–W relationships.

The mechanism of increasing the wear resistance of steel 110G13L by modification, dispersion and dispersion nitride hardening

The current state of industrial production of wear-resistant cast parts from high-manganese steels using various alloying, micro-alloying and modification technologies is analyzed in order to increase wear resistance not only in conditions of shock-abrasive, but also in conditions of purely abrasive wear. It is shown that despite the large number of technologies for the production of wear-resistant parts from these steels, there are no simple and highly effective methods. Prospective directions are dispersion hardening of metal by modification and microalloying of steels, in particular with nitrogen and vanadium, dispersion hardening by alloying of steels with titanium, niobium, etc. and the use of optimal modes of heat treatment. For the conditions of intensive shock-abrasive wear, it is important to establish the regularities of the influence of the degree of shock deformation on the formation of the surface martensitic layer in products after microalloying and modification of steels with nitrogen, dispersion and dispersion nitride hardening of the metal. It has been shown that dispersion nitride strengthening of metal by modifying steel with nitrogen or joint addition of nitrogen and vanadium to it and dispersion strengthening of metal after simultaneous addition of nitrogen, titanium and niobium significantly disperse the austenite grain of steel both in the cast state and after quenching. The change in the structure of steels due to the strengthening of the metal significantly affects their mechanical properties after various modes of heat treatment. Dispersive vanadium nitride strengthening increases strength by 15...17 % and plasticity by 45...50 %, and dispersed nitride strengthening increases plasticity by 45...60 % while maintaining the level of strength and slightly reducing impact toughness. The influence of the degree of impact deformation on the formation of e and a-martensite is shown, and a clear relationship between the increase in the degree of impact deformation and the increase in the amount of a-phase in the deformed layer is established. Impact deformation of about 16.6 % increases the amount of a-martensite in the deformed layer from 40 % to 98 %, which ensures an increase in the hardness of the deformed layer from 24 HRC to 36 HRC. It was noted that nitrogen modification, dispersion nitride and impact hardening of high-manganese steels increase their wear resistance by 1.5...2.0 times under conditions of dry sliding friction and 1.7...2.0 times under conditions of abrasive wear using unfixed and fixed abrasive.

Effect of electropulsing treatment on the precipitation behavior of MnS in sulfur-containing microalloyed 49MnVS3 steel

An experimental investigation has been conducted with respect to the influence of electropulsing treatment (EPT) on the 2D and 3D morphologies, distribution, number and size of MnS precipitates in the high-sulfur micro-alloyed 49MnVS3 steel. After the application of electric current pulse with a peak pulsed voltage of 30 V, the microstructure was refined due to the increasing nucleation rate of particles in liquid steel. Moreover, compared with the untreated steel with spherical MnS randomly distributed in the matrix, the MnS precipitates moved directionally to aggregate on the bottom and top surfaces of the ingot in order to minimize the free energy of the system in case of EPT. For untreated steel samples, the number of MnS was 409 (bottom), 579 (middle) and 437 (top), while that of the treated samples were 226 (bottom), 38 (middle) and 224 (top) in the scanning area of 2.65 × 107 µm2 with ASPEX. The number of MnS with small size decreased while the large-size MnS increased with the application of EPT.

Porovnanie deformačných charakteristík vysokopevných ocelí používaných v automotive

The goal of the research was to compare the deformation properties such as absorption capacity, resistance to deformation, stiffness of high-strength steels with the properties of microalloyed steel based on the results of the tensile test and the three-point bending test. HTC 590X dual-phase steel and RAK 40/70 steel have the potential to reduce intrusion into the passenger compartment, as the maximum deformation resistance, stiffness and energy absorbed in the three-point bending test were greater compared to H220PD microalloy steel reinforcement.

Вплив мікролегування титаном, алюмінієм та азотом вуглецевої сталі на особливості структури та механічні властивості

The purpose of this paper is to investigate the effect of microalloying with titanium, nitrogen, and aluminum on the set of mechanical properties of carbon steels with increased manganese and silicon content. This is due to the fact that steels with improved mechanical and operational properties are of great significance in the current situation of technology development. The studies are based on a comparison of the mechanical properties of known steel grades 2 and T, experimental industrial steel grade K and steels microalloyed with complexes – aluminum, titanium and nitrogen; aluminum and nitrogen of steel grade K. Metallographic analysis, determination of mechanical properties, chemical analysis and X-ray microanalysis are used. It is shown that complex microalloying with aluminum, titanium and nitrogen; aluminum and nitrogen of K grade steel contributes to the formation of a more fine-grained structure of pearlite and inclusions, compared to steel grades 2, T and K. In the structure of K steel, which is microalloyed with aluminum, titanium, and nitrogen, after casting, the formation of oxides, nitrides, carbonitrides, and multilayer inclusions located at the grain boundaries and in the grain volume is observed. After a full cycle of deformation and heat treatment, carbides, nitrides, and titanium carbonitrides remain in the steel structure. Whereas in steel, which is additionally microalloyed with aluminum and nitrogen on the basis of K steel, after solidification, a fine-grained structure with an increased volume fraction of pearlite is formed, the formation of inclusions of oxides, monosilicides of manganese and iron; sulfides and complex carbides in comparison with known steel grades K, 2 and T occurs. According to the research results, K2 steel is proposed, which provides a high complex of mechanical properties after accelerated cooling with an average cooling rate of 11.0°C/s from a temperature of 850±10°C and further tempering at a temperature of 550±10 °C for 2 hours due to an increase in dispersivity of the ferrite-pearlite structure, strengthened by dispersed inclusions, in comparison with K1 steel. In steel K2, factors of strength, hardness and impact toughness are 10–15% higher than the same factors for steel K1.

A strategy combining machine learning and physical metallurgical principles to predict mechanical properties for hot rolled Ti micro-alloyed steels

Determining the exact relationships between rolling parameters and mechanical properties is important to predict and even control the mechanical properties of hot rolled Ti micro-alloyed steel products. In this paper, two data dimension reduction strategies, respectively guided by physical metallurgical (PM) principles and data-driven (DD) strategy were proposed to preprocess the high dimensional steel composition and rolling parameters, and a comprehensive set of machine learning (ML) models was developed to predict yield strength (YS) and elongation (EL) combined with the reconstructed inputs. The artificial neural network (ANN) with the inputs including dislocation density, fractions, and sizes of ferrite and TiC precipitate transferred by PM principle outperformed that with the inputs extracted low variance feature elimination (LVFE) and autoencoder (AE) algorithms. Based on the proposed model, the effects of alloying elements, rolling temperatures, and microstructures on mechanical properties were comprehensively analyzed. Also, the variations of microstructures and mechanical properties over the strip length were discussed, which were consistent with the measured results. • PM-guided dimension reduction was proposed to transfer rolling parameters to microstructures. • The dimension reduction guided by PM performed better than that guided by DD methods with LVFE and AE. • The predicted effects of process and microstructures on YS and EL were consistent with experiments. • The predicted variations of YS and EL over strip length were consistent with measured results.