Ferrite Grains Research Articles

Sulfide stress cracking (SSC) of a commercial Q345 pressure vessel steel in a wet H2S environment

The steel Q345 is extensively used in pressure vessels with low and medium pressure because of good mechanical properties and low cost. Good resistance to sulfide stress cracking (SSC) is required for the pressure vessel steel, but the SSC behavior of the Q345 has received little attention. This work investigated the SSC behavior of the Q345 in a wet H2S environment. The microstructure contained the irregular various-sized polygonal-like ferrite grains plus a carbon-rich degenerate pearlite banded structure. The Q345 had high ductility but failed to pass the SSC tests. The SSC cracking involved hydrogen embrittlement. The SSC preferentially occurred at the carbon-rich degenerate pearlite banded structure. The elimination of the carbon-rich degenerate pearlite banded structure is necessary to improve the SSC resistance of the Q345 pressure vessel steel.

Microstructure Formation and Its Effect on Mechanical Properties for Duplex Stainless Steel 2205 Plasma Arc Welded Joint

The control of phase balance has always been a tough challenge for the welding of duplex stainless steel, which heavily restricts its optimal serving performance in engineering. The microstructure development and mechanical characteristics of SAF2205 plasma arc welded joints were thoroughly examined in this paper. It was proven that the phase balance can be well controlled by plasma arc welding, and the austenite content of the welded joints was about 60%. Despite successful phase control, there was still grain coarsening and distortion; i.e., at the center of the welded zone, the gain size was about eight times that of the base metal, and the austenite was mainly in the form of grain boundary austenite and intragranular austenite, while more Widmanstatten austenites were found in the heat-affected zone. In addition, a transition region between the heat affected zone and the center exhibited columnar ferritic grains. Furthermore, the plasticity and toughness of the welded joints were significantly decreased, especially the elongation in the longitudinal direction, which is about 10% lower than that of the base metal, and transversal tensile strength remained comparable to the base metal, with only a slight reduction in longitudinal tensile strength. Lastly, the formation mechanism of microstructure and its correlation with mechanical properties were revealed. This investigation offers valuable insights into the structural integrity of duplex stainless steel welded joints in engineering applications.

Effect of prestrain on tensile behavior of HS800 steel sheet

With the development of advanced high strength steels like HS800 and HS1000, it is imperative to develop an understanding of their tensile properties. The effect of 0%, 5%, 7.5%, and 10% prestrain on the tensile behaviour of HS800 steel sheet was investigated in the current research. The optical micrograph of as received HS800 steels reveals the presence of ferrite grains with polygonal morphology without the presence of pearlite or cementite. Moreover, in higher pre-straining conditions, both polygonal and acicular ferrite phases are observed to coexist with the second phase (martensite/austenite). Tensile tests were performed on base HS800 steel sheets in three different directions (rolling, transverse, and diagonal), and it was found that the strength and ductility in the transverse direction were greater than the rolling and diagonal direction. Tensile strength had a linear relationship with the prestrain condition, whereas ductility had an inverse relationship. XRD analysis was used for phase identification and determination of dislocation density. A scanning electron microscope (SEM) was used to observe the ductile fracture behaviour in tensile specimens. The strain hardening exponent of HS800 steel was determined by comparing tensile data to Hollomon and Ludwik's mathematical equations. To understand the dislocation structure evolution of as received and various prestraining conditions samples, a transmission electron microscope (TEM) study was performed. The prestraining study of the HS800 steel gives a new horizon to high strength materials that can be utilized to design the current and future automobile industries requirements.

Thermomechanical Control of Microstructure and Precipitation in Vanadium Microalloyed Steel: Influence of Finish Rolling and Coiling Temperatures

Six hot compression tests are conducted using the Gleeble3500 thermomechanical simulator to investigate the microstructural evolution and precipitation behavior in low‐C–Mn V‐microalloyed steel. The specimens are subjected to hot isothermal compression deformation of 87%. The optical microscopy and transmission electron microscopy using carbon extraction replica method are used to characterize the microstructures and precipitation after the simulated thermomechanical controlled process and coiling. The results indicate that increasing the finish rolling temperature benefits the refinement of ferrite grains but has little influence on the refinement of the precipitates. It is also observed that lower coiling temperatures (CTs) promote the formation of fine precipitates. When the CT is 500 °C, the average precipitate size is found to be 86 nm. Furthermore, it is found that the CT significantly influences the nucleation sites of the precipitates inter alia, the matrix, interphase, grain boundaries, and dislocations. As expected, at higher CTs, nucleation is predominantly on the defects rather than the matrix.

Investigations on dry sliding wear and friction behaviour of alloy steel obtained by powder metallurgy

The present work investigates the dry sliding wear and friction behaviour of an alloy steel developed through powder metallurgy. Prealloyed Atomet 4601 powder was thoroughly mixed with elemental powders of 0.35 C, 0.25 Mn, 0.1 Si and 0.9 Cr (in wt. %) to create this alloy steel, whose composition closely matches EN24 (AISI 4340) wrought steel. The dry sliding friction and wear test experiments were performed in a pin-on-disc tribometer. For the various cases considered in friction and wear tests, the wear rate is lowest (0.32 × 10–3 mm3/m) at 15 N and 1.77 m/s and highest (1.02 × 10–3 mm3/m) under severe conditions of 32.5 N and 2.83 m/s. The coefficient of friction is highest (0.673) at 15 N and 0.71 m/s and lowest (0.1311) at 32.5 N and 2.83 m/s. Subsequently, regression models are developed based on experimental results and the interaction effect of load and speed on the response parameters are plotted using MATLAB. An R2 value of 0.98 indicates a strong correlation between the response and the input variables. X-ray diffraction (XRD) and optical and scanning electron microscope (SEM) analyses of the most worn specimens revealed carbides and oxides in the ferrite grain matrix, with adhesive, abrasive and oxidative wear being the primary mechanisms observed.

Structure and mechanical properties anisotropy of a steel product manufactured by layer-by-layer electric arc wire 3D printing

The work presents the study of structure and mechanical properties anisotropy of a metal wall obtained using electric arc wire 3D printing (WAAM) with ER70S-6 wire. The layers were deposited in the protective gases of carbon dioxide and argon. As a result of structural studies, it was found that the internal structure of the model product in form of a wall can be divided into three zones. Repeated heating, cooling cycles and degree of accumulated heat influence the formation of different wall zones. As a result of rapid heat removal to the substrate during deposition of the first layers, the wall base (zone 1) contains large elongated grains with acicular ferrite structure. The wall middle part (zone 2) consists of ferrite-pearlite structure, which was formed as a result of recrystallization under conditions of repeated heating and cooling during 3D printing. The size of ferrite grains in zone 2 varies from 11 to 16.3 µm with increasing the number of layers. The gradual accumulation of heat during 3D printing led to the formation of structures in zone 3 under conditions of overheating and a reduced cooling rate. As a result, the wall upper part (zone 3) consists of large ferrite grains (up to 29.8 μm), sorbite, and a small proportion of Widemanstatten ferrite and acicular ferrite. It is shown that the most uniform level of mechanical characteristics (σ0.2 = 340 MPa, σu = 470 MPa, ε = 28 %) correspond to the samples cut from zone 2 in a direction parallel to 3D prin­ting direction. The samples cut in the vertical direction relative to 3D printing and from zone 3 show the lowest level of microhardness and mechanical characteristics (σ0.2 = 260 MPa, σu = 425 MPa, ε = 20 %).

Structure and properties of low-alloy steel 10G2FBYu after rolling in embossed rolls under conditions of electroplasticity

The article describes the features of grain structure formation and mechanical properties of low-alloy steel 10G2FBYu after rolling in flat and embossed rolls under the conditions of ordinary and electroplastic deformation. When rolling in embossed rolls, a significant non-uniformity of deformation is achieved over the rolling cross-section, expressed in localized macroshifts directed at an angle of 45° to the rolling plane. It is shown that local shear deformation during rolling in embossed rolls leads to an increase in the ultimate strength of the steel under study with a decrease in plasticity of the rolled material. Rolling 10G2FBYu steel in embossed rolls under conditions of electroplasticity provides maximum strength characteristics with a high hardening coefficient at the stage of macrodeformation. At the same time, the plasticity is maintained at a level sufficient for technological purposes. Structural metallographic and electron microscopic studies showed that increase in strength of steel when rolling in embossed rolls under conditions of electroplastic effect is caused by the refinement of ferrite grains to sizes less than 0.5 µm. Fractographic studies revealed changes in the nature of fracture in steel during rolling in embossed rolls, which is expressed in appearance of areas of brittle fracture in the rolled samples. Rolling under conditions of electroplasticity increases the proportion of ductile fracture and ductility of 10G2FBYu steel.

Deformation law and bonding mechanism of 45 carbon steel/316L stainless steel cladding tubes fabricated by three-roll skew rolling bonding process

Realizing the continuous forming and metallurgical bonding in bimetallic cladding tubes with high-strength and corrosion-resistance is the key bottleneck to be solved urgently. In this study, 45 carbon steel/316L stainless steel (CS/SS) cladding tubes were fabricated by the three-roll skew rolling bonding process under different radial reduction rates. The deformation law, interfacial microstructure characteristics, and deformation mechanism were analyzed. With the increase of the radial reduction rates from 11.7 % to 19.3 %, the 45 CS/316L SS cladding tubes were elongated along with the diameter and wall thickness decrease. Besides, the wall thickness ratio between 45 CS and 316L SS was unchanged due to the coordinated deformation. Tensile shear fracture locations of CS/SS cladding tubes were on the 45 CS matrix, and the average diffusion distances in the longitudinal section and the cross section were consistent, proving that uniform metallurgical bonding was achieved. Besides, average decarburized layer thickness decreased and average diffusion distances increased with the increase of radial reduction rates. Furthermore, spherical and fibrous Mn-Si-Cr-O oxides, generated in the insulation heating process, were dispersed near the bonding interface. The refined grains were formed close to the interface, and deformation twins were formed away from the interface on the 316L SS side, whereas only elongated ferrite grains evolved due to the decarburization adjacent to the interface on the 45 CS side. Therefore, the interfacial bonding mechanism was illustrated as three stages, namely the insulation heating stage, the skew rolling bonding stage, and the air cooling stage. The three-roll skew rolling bonding process provides a high-efficiency method to prepare CS/SS cladding tubes with uniform metallurgical bonding, which adopts axial forming and contributes to breaking through the product length size limit.

Refinement mechanism of large heat-input welding CGHAZ microstructure by N addition and its effect on toughness of a V-Ti-N microalloying weathering steel

The large heat input welding performance of uncoated weathering steel remains a great challenge since their coarse grain heat-affected zones (CGHAZs) are usually occupied by coarse and brittle microstructure consisting of granular bainitic ferrite (GBF) and martensite/austenite (M/A) constituents. In this article, a V-Ti-N microalloying weathering steel suitable for large heat input welding was achieved through the N addition, and the mechanism dominating the modified microstructure and the enhanced impact toughness of CGHAZ was deeply elucidated mainly by HRTEM. The results indicated that in the simulated CGHAZ with large heat input of 80 kJ/cm, the increase of N content from 0.0030 wt% to 0.0075 wt%, and 0.0115 wt% elevated the density of nano- and submicron-sized particles of (Ti, V)(C, N) containing VN, which in turn resulted in the refinement of prior austenite grains (PAGs) by the improved grain boundary pinning effect and the enhancement in heterogeneous nucleation of intragranular ferrite (IGF) by the decreased lattice disregistry (δ) between (Ti, V)(C, N) and IGF. The fraction of high-angle grain boundaries (HAGBs) with misorientation tolerance angles (MTAs) higher than 15° was thereby increased while the mean equivalent diameter (MED) of ferritic grains with HAGBs was decreased. Simultaneously, the N addition scattered the M/A constituents, promoted the internal substructure of dislocation-type M/A at the expense of twin-type M/A, and accordingly reduced the hardness difference between the M/A constituents and the matrix. All these factors retarded brittle crack initiation and propagation, and low-temperature impact toughness of simulated CGHAZ increased from 62.8 J to 141.2 J.

UPAYA PERBAIKAN SIFAT MEKANIK BAJA PLAT JOIN G 3131 SPHC MELALUI SIMULASI PROSES INTERCRITICAL ANNEALING DI INDUSTRI KONSTRUKSI BAJA

Improvement of the mechanical properties of G3131 SPHC equivalent to JIS G 3101 SS330 plate joint steel through intercritical annealing simulations has been carried out. The JIS G 3131 grade SPHC steel was gradually heated by intercritical annealing at temperatures of 750–850 oC for holding times of 1–15 minutes. After intercritical annealing treatment, the tensile strength and yield strength of steel increased compared to non-treatment samples. The average tensile strength obtained was 573 MPa with an increase of 76.85% compared to the tensile strength before the intercritical annealing process. Meanwhile, the yield strength of steel increased by 60% to 421 MPa. Increasing the annealing temperature and holding time will promote the formation of the martensite phase, as well as enlarge the austenite and ferrite grains. Optimal heating variable obtained at a temperature of 750 ℃ with a holding time of 15 minutes. Using these variables produced a tensile strength of 625 MPa and a yield strength of 434 MPa with an elongation of 23% which is standardly included in JIS G 3101 SS400.At the optimal value, the grain growth kinetic of K and n values were 0.280466778 and 0.6905, respectively, with an activation energy (Q) of 12.4268517 J/mol.

Quasi‐hexagonal nanopatterned porous cobalt ferrite thin films prepared via block copolymer self‐assembly

AbstractWe present a novel method for fabricating dense and nanopatterned porous cobalt ferrite (CoFe2O4) thin films with a remarkable thickness of 65 nm, achieved through direct block copolymer self‐assembly. By decomposing the block copolymer and inducing crystallization of the spinel phase, we successfully produce films exhibiting quasi‐hexagonal arrays of pores with an average diameter ranging from 60 to 80 nm. The resulting nanopatterned porous thin films demonstrate exceptional orderliness, as the pores are intricately designed by the cobalt ferrite grains, and the platinum substrate offers complete accessibility in the pore area. Our findings reveal high magnetization values, comparable to those of bulk CoFe2O4, in the dense film. Additionally, in the case of the nanopatterned porous film, we observed a distinctive contribution of perpendicular magnetization. This innovative approach holds great promise for advanced magnetization and thin‐film engineering applications.

Semi in-situ investigations on deformation-induced micro-damage in high-strength dual-phase steels

This work investigates deformation-induced micro-damage modes in ferrite-martensite dual-phase (DP) steels utilizing a state-of-the-art semi in-situ deformation apparatus integrated with scanning electron microscope. By integrating secondary electron imaging, electron backscatter diffraction, and electron channeling contrast, we provide comprehensive statistical results on micro-damages and strain localization events of their formation in DP780 and DP980 steels. The current observations indicate that interface decohesion plays a critical role in DP780, particularly under plastic instability. Based on maps of Kernel averaged misorientation, interface decohesion arises from the accumulation of geometrically necessary dislocations, which serve to compensate for the deformation incompatibility between ferrite and martensite. In contrast, the dominant damage mode in DP980 under plastic instability involves ferrite cracking within martensite-surrounded ferritic grains. This type of micro-damage is a result of strain localization by shear bands that accommodate the global deformation while the grain is constrained by martensite islands. Martensite cracking does not show as predominate sites under the condition of plastic instability in both steels. In summary, our findings highlight the importance of deformation incompatibility and constraint on occurrence of micro-damages through distinct strain localization events, which are determined by both microstructure of damage site and its environmental microstructure. In this work, we shed light on the role of microstructural engineering as a critical strategy for enhancing the resistance of DP steels or hetero-phase steels against deformation-induced damage.

Influence of Hot Rolling Practice and Furnace Residence Time on the Strength and Toughness of Normalised Nb-Ti-V Structural Steel Plate

The influence of moderate thermomechanical rolling and heat treatment time on the microstructure and mechanical properties of normalised Ni-containing Nb-Ti-V microalloyed plate steels was investigated. Conventional rolling (CR) and low austenitic temperature rolling (TM) schedules were applied to 25 and 55mm thick plates. Predicted plate thermal profiles were used to simulate normalising of 25 and 55mm thick plates at the mid-thickness. As expected, the microstructure after TM rolling was finer due to austenite sub-structure development below the no-recrystallisation temperature which increases the amount of ferrite nucleation sites. The tensile strength of the CR plates was generally higher due to a larger pearlite volume fraction resulting from slow cooling from a relatively coarse austenite. In 25mm plate, the presence of acicular ferrite after CR resulted in a higher yield strength than that obtained after TM rolling. Furnace residence times of 0.75min/mm and longer allowed for plates to be completely normalised – characterised by continuous, well-defined polygonal ferrite grain boundaries. Short furnace residence times restricted the plate temperature to below the end of the ferrite-to-austenite transformation (Ac3), where untransformed ferrite is retained from the as-rolled microstructure and is characterized by poorly defined grain boundaries. Rolling practice and normalising residence time had little to no effect on impact toughness, but significantly influenced the normalised yield strength of thicker plate.

Influence of the Holding Thickness and Process in the Microstructure and Mechanical Properties of a Microalloyed 380 MPa Structural Steel

Flat low carbon microalloyed structural steels processed by controlled rolling have excellent mechanical properties, particularly regarding toughness, since austenite is rolled with full recrystallization between rolling passes (roughing stage at high temperatures), and, subsequently, with no recrystallization at all between passes (finishing stage at low temperatures), maximizing nucleation of ferrite grains during austenite transformation after hot rolling. However, rolling must be prompted in an intermediate temperature range where recrystallization of austenite between rolling passes occurs partially, as this can lead to great heterogeneity in the grain size distribution of the product, a potential condition to impairs its low temperature toughness. On the other hand, this holding period that is necessary to avoid rolling within this temperature range can last several minutes, reducing the productivity of the rolling line and, in this way, potentially harming the financial performance of the plant. This work was developed to analyze several proposed rolling conditions for the finishing stage during controlled rolling of 16 mm thick strips of a low C Nb-Ti microalloyed steel strip, 380 MPa structural grade, processed in a Steckel mill, to identify the best condition that provides maximum productivity without affecting the required microstructural, toughness and mechanical characteristics of the final product.

Low Temperature Hot Press Forming of a Zinc Coated Third Generation Advanced High Strength Steel

A 7 wt.% Mn steel was designed and was cast and processed to 1.5 mm sheets. The sheets were continuous annealed and coated with a Zn alloy by hot dip galvanizing before subjecting them to hot press forming cycles. The final microstructure was characterized by ultrafine ferrite grains and a high fraction of retained austenite. Excellent combinations of in-service strength-ductility-bendability were achieved for hot forming in the temperature range of 530-675 °C. The use of the low temperature hot forming minimized the liquid metal embrittlement induced cracking with Zn coating during hot forming and spot welding. Various application properties such as oxidation resistance, corrosion resistance, and springback were found at optimum levels for hot forming at 675 °C.

Thermomechanical Processing of V-N Structural Plate Steels in Low Temperature Austenite

Austenite restoration during thermomechanical (TM) rolling of typical vanadium-microalloyed structural steels was studied to optimize strength in the as-rolled and air-cooled condition. Multi-pass plate rolling simulations were performed on V-N microalloyed and CMn steels to compare recrystallisation behaviour in various temperature regions. Included were a conventional schedule ending at high temperature and two TM schedules with mill exit temperatures in the intermediate and low austenite regions. Increasing delay periods after roughing enhance the suppression of recrystallisation after the start of finishing thereby increasing both nucleation site density and nucleation rate for ferrite formation and refinement in grain size. Good agreement was found between microstructures after industrial TM rolling and those obtained from laboratory simulations. Although precipitation of vanadium carbonitrides is an effective strengthening mechanism, appreciable gains in yield strength due to grain refinement can be achieved by rolling in the lower austenite region. Low nitrogen contents in V steels produce coarser final ferrite grain sizes and lower strengths probably due to a larger precipitate size. V-N steels display similar flow behaviour to CMn grades down to approximately 825°C at low to intermediate strain rates but may experience alternate regions of work hardening and dynamic softening at lower temperatures in austenite.

Effect of Alternating Magnetic Field on the Organization and Corrosion Resistance of 2205 Duplex Stainless Steel Narrow-Gap Laser-MIG Hybrid Weld Head

In this study, an alternating magnetic field is applied in the narrow-gap laser-MIG hybrid welding of 2205 duplex stainless steel with a thickness of 25 mm to achieve the purpose of balancing the ration of the two phases, refining the grains and improving the corrosion resistance. With the help of OM, EBSD, TEM, and other microstructural analysis methods, the organization evolution of a 2205 duplex stainless steel narrow-gap laser arc hybrid weld under the effect of alternating magnetic field is revealed. The corrosion resistance of the welded joints is investigated by electrochemical tests. The results show that the use of a 40 mT applied alternating magnetic field can not only effectively inhibit the generation of porosity and unfused defects in the weld, but also that the addition of an alternating magnetic field improves the ratio of austenite to ferrite in the weld, and the ratio of the two phases is increased from 0.657 without a magnetic field to 0.850. The weld grain preferential orientation is affected by the magnetic field, and the weld austenite grains are shifted from the Goss texture to the Copper texture. Under the electromagnetic stirring effect of the applied magnetic field, the average austenite grain size decreased from 4.15 μm to 3.82 μm, and the average ferrite grain size decreased from 4.99 μm to 4.08 μm. In addition, the effect of the alternating magnetic field increases the density of twins in the organization. Electrochemical test results show that the addition of an alternating magnetic field increases the corrosion potential by 75.2 mV and the pitting potential by 134.5 mV, which indicates that the corrosion resistance of the cover-welded specimens is improved by the effect of an alternating magnetic field. The improvement in corrosion resistance mainly depends on the austenite grain refinement and the increase in the austenite content.

Pulsed gas metal arc additive manufacturing of low-carbon steel: Microstructure observations and mechanical properties

Gas metal arc additive manufacturing (GMA-AM), also known as wire arc additive manufacturing (WAAM), uses an electric arc to melt a wire electrode and deposit objects layer by layer. This study focuses on creating single-pass wall structures using a low-carbon steel wire (ER70S-6) and examining the relationship between pulse frequency and weld geometry, microstructure, and mechanical properties. Microscopic observations showed a typical columnar microstructure with three distinct regions: acicular ferrite, bainite, and allotriomorphic ferrite in the first and last layers, while the mid-region exhibited homogenous polygonal ferrite grains with some pearlite at the grain boundaries. The tensile test results demonstrated a dependency of strength on the applied pulse frequency, with the highest strength (i.e., the ultimate tensile strength of 522 MPa and yield strength of 375 MPa with ductility of ∼52%) achieved in parts processed at a frequency of 100 Hz. Vickers microhardness values revealed uniform hardness in the middle region, consistent with the microstructure observation. Analyzing thermal cycles, coupled with microstructure analysis and continuous cooling transition diagrams, provided insight into how phase and microstructure evolution occurred in low-carbon low-alloy steels processed through PGMA-AM.

Micromechanical properties and deformation behavior of the constituent phases in 3rd generation complex phase AHSS: In-situ neutron experiment and crystal plasticity simulation

This paper investigated the micromechanical properties and deformation behavior of the constituent phases in 3rd generation (GEN) complex phase advanced high-strength steel (AHSS). The hybrid method was a comprehensive combination of uniaxial tensile test with digital image correlation (DIC), electron backscatter diffraction (EBSD), in-situ neutron diffraction (NED) and crystal plasticity finite element method (CPFEM). Results reveal that the microstructure of 3rd GEN AHSS exhibits a complex phase of ferrite (46.2 %), bainite (36.1 %), martensite (9.4 %) and austenite (8.3 %), which would be promising microstructure in the development of new-generation complex phase AHSS. The significant findings are: (1) excellent ductility is obtained while high strength is preserved despite small martensite volume fraction, which can reduce the tendency of martensite cracking; (2) macroscopic stress-strain relationships and microscopic hardening properties of constituent phases are successfully determined, which are very important for predicting the overall performance of complex phase AHSS; (3) presence of bainite with high volume fraction plays a critical role in inducing plastic strain localization in ferrite, resulting in the heterogeneous stress/strain distribution. It is disclosed that pronounced strain localization is mostly initiated in ferrite grains while the deformation bands are mainly located in ferrite/bainite grain boundaries. Furthermore, strain partitioning between ferrite and bainite results in the high-stress concentration in bainite grains. As a result, these “hot zones”, i.e., ferrite grains, ferrite/bainite grain boundaries and bainite grains, experience high strain, strain gradient and stress, respectively, which can be a primary origin of ductile fracture initiation in the 3rd GEN complex phase AHSS. The findings reported in the present investigation would be of great interest in the development of new-generation complex phase automotive steels.

Grain refinement, strain hardening and fracture in thermomechanically processed ultra-strong microalloyed steel

The current research in microalloyed steel has witnessed a continuous improvement in strength-ductility combination. The intention is to reduce the gauge thickness of automotive body sheets without compromising formability, thereby enhancing fuel efficiency. In this light, the present work has devised a novel thermomechanical controlled processing (TMCP) for a low-carbon automotive-grade (Nb+V)-stabilized microalloyed steel. The microstructural modification by TMCP has resulted in an excellent combination of yield strength (782 MPa), ultimate tensile strength (1059 MPa) and ductility (21%). The critical factor translating the investigated alloy towards advanced high strength steel is the ferrite grain refinement by dynamic recrystallization (DRX) and deformation-induced ferrite transformation (DIFT). The DRX predominated during TMCP at the intercritical temperature domain of 800–700 °C, imparting the average recrystallized grain size of 2 ± 0.8 µm. In contrast, the DIFT starts well above the upper intercritical temperature regime (i.e., around 810 °C), but it contributes less to the ferrite grain refinement. The thermodynamic reason has been analyzed keeping in view the changes in grain boundary energy and dislocation energy. The plastic deformation additionally leads to precipitation of cubic (Nb, V)-rich carbides in ferrite. The incoherency, coarse precipitate size (70–80 nm), and a poor phase fraction (⁓0.5%) are the key factors that the strengthening mechanism is governed by ferrite grain refinement majorly, followed by dislocation and solid solution strengthening. The segregation of Mn, Nb and S leads to MnS-type inclusion formation, which acts as potential sites for crack initiation due to plasticity mismatch with ferrite matrix during the tensile deformation.