Search Results (332)

We investigated the effects of two-way cold rolling and subsequent annealing on the microstructure and tensile properties of low-carbon steel with different initial microstructures. Two types of hot-rolled sheet specimens were prepared: specimen P, consisting of ferrite and pearlite, and specimen M, consisting of martensite. The hot-rolled sheets were cold-rolled in two directions and subsequently annealed. Two-way cold rolling promoted shear-band formation compared with one-way cold rolling. Furthermore, the two-way cold-rolled specimens showed higher strain homogeneity than the one-way cold-rolled specimens. When annealed below the Ac₁ temperature, two-way cold rolling accelerated recrystallization in specimen P, but not in specimen M. In the intercritically annealed specimen P, two-way cold rolling increased the average size of recrystallized ferrite grains while reducing their aspect ratio. In addition, the strength–ductility balance of the two-way cold-rolled specimen P was similar to that of the one-way cold-rolled specimen P. In contrast, in the intercritically annealed specimen M, two-way cold rolling reduced the average size and the aspect ratio of recrystallized ferrite grains. As a result, the strength–ductility balance of the two-way cold-rolled specimen M was improved by approximately 15% compared with that of the one-way cold-rolled specimen. This improvement was attributed to the formation of fine and equiaxed recrystallized ferrite grains. The present findings provide a basis for applying two-way cold rolling as a microstructure-control strategy in high-strength steels. Full article

This study presents a systematic investigation of laser surface hardening of 9CrSi tool steel with the aim of establishing the relationships between processing parameters, microstructural evolution, and resulting mechanical and tribological properties under the applied laser conditions. The influence of laser power, modulation frequency, and scanning speed on the hardened layer depth, microstructure, and surface properties was analyzed. Laser treatment produced a martensitic surface layer with varying fractions of retained austenite, while the transition zone consisted of martensite, granular pearlite, and carbide particles. X-ray diffraction identified the presence of α′-Fe, γ-Fe, and Fe₃C phases, with peak broadening associated with increased lattice microstrain induced by rapid self-quenching. The surface microhardness increased from approximately 220 HV_0.1 in the untreated state to 950–1000 HV_0.1 after laser hardening, with hardened layer thicknesses ranging from about 500 to 750 µm depending on the processing regime. Instrumented indentation showed higher elastic modulus values for all hardened conditions. Tribological tests under dry sliding conditions revealed reduced coefficients of friction and more than an order-of-magnitude decrease in wear rate compared with untreated steel. The results provide a parameter–microstructure–performance map for laser-hardened 9CrSi steel, demonstrating how variations in laser processing conditions affect hardened layer characteristics and functional performance. Full article

To investigate the effects of multiple-element rare earth addition on U75V steel, this study produced three types of steel: sample 1 steel without rare earths, sample 2 steel containing 0.0035% La and 0.018% Ce, and sample 3 steel containing 0.02% La and 0.0023% Ce. Microstructural analysis showed that the addition of rare earth elements modified the MnS and silicoaluminate inclusions into RE₂O₂S and RE₂O₂S–oxide complexes, which reduced the number and size of inclusions while simultaneously refining the microstructure, including the grain size and the spacing of pearlite layers. Concurrently, RE addition enhanced the steel’s mechanical properties, with the degree of enhancement dependent on RE content; sample 2 exhibited the most balanced improvement. Compared to sample 1, the hardness of samples 2 and 3 increased by 15.3% and 3.6%, respectively, and their tensile strength increased by 7.9% and 6.8%, respectively. Meanwhile, their coefficients of friction decreased significantly, by 69.5% and 22.1%. The impact toughness was also enhanced by RE addition, with both samples 2 and 3 showing higher values than sample 1 at room temperature and moderate low temperatures. Nevertheless, a distinct reversal was observed at −60 °C, where the impact energy of sample 3 was 23.5% lower than that of sample 2. This result implies that while moderate RE addition is beneficial, an excessive amount can adversely affect the toughness under cryogenic conditions. Full article

SA 178 grade C carbon steel is a material commonly used in boiler tubes. Boilers are crucial in the energy industry; however, their service life degrades over time. If a boiler malfunctions, processing operations must be halted, resulting in financial losses for the company. The aim of this study is to examine the effect of microstructural evolution, especially the transformation of lamellar pearlite into spheroidized pearlite, on the service life degradation of boiler tubes. Understanding these changes is essential for preventing catastrophic system failures. The methodology involves the use of Small-Angle X-ray Scattering (SAXS) supported by metallographic analysis, Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray (EDX) Spectroscopy, and mechanical testing. The SAXS results indicate that the microstructure of SA 178, which initially consisted of ferrite and lamellar pearlite, gradually transforms into spheroidized pearlite. These microstructural changes lead to reductions in tensile strength from 523 MPa for 0% spheroidization to 335 MPa for 100% spheroidization, as well as a reduction in hardness from 175 HV to 89 HV, ultimately decreasing the service life of the boiler tube. Full article

The ZnO piezoelectric coatings were deposited on the surface of 15CrMo steels by magnetron sputtering to directly excite the ultrasonic signal, effectively solving the coupling problem between the traditional probe and the pipe surface. The microstructure, mechanical properties, and ultrasonic longitudinal wave velocity of the aged samples were carried out systematically. The spheroidization grade of pearlite, evolution of carbide morphology, hardness, strength, and ultrasonic wave velocity were systematically analyzed. As the degree of aging intensifies, the material undergoes significant pearlite spheroidization and carbide coarsening. The Vickers hardness drops from 158 HV in the original state to 134.2 HV, and the yield strength and tensile strength decrease by 22.7% and 17.9%, respectively. The ultrasonic longitudinal wave velocity shows a monotonically upward trend with the increase in spheroidization grade, increasing from 5925.6 m/s in the original state to 5976 m/s at the highest spheroidization grade. Full article

Comprehensive investigations of the serviceability of pearlite (R260) steel have been performed and, especially, of the serviceability of their welded joints (WJ) during long-term operation in hydrogen-containing environments for application in additive manufacturing technology. It is important to estimate the durability of these steels and their WJ in hydrogen and develop the procedures of analysis of the influence of hydrogen during long-term operation. It has been experimentally observed that hydrogen absorbed (0.4 … 0.8 ppm) by the pearlite (R260) steel while welding, and subsequent operation thereof, exercises considerable influence on fatigue and brittle fractures of the constructions from which they are manufactured. Accordingly, in hydrogen-saturated (up to 4.7 ppm) specimens, the desired fatigue crack can be obtained at a considerably lower number of cycles of the same dynamic load than in non-hydrogenated ones. Increased hydrogen content can also affect crack propagation. Tests have shown that critical fracture occurs faster in hydrogenated specimens (46.6 MPa m^0.5) than in non-hydrogenated ones. Also, hydrogenated specimens exhibit lower fracture toughness than their non-hydrogenated counterparts. Finally, it has been demonstrated that the fracture toughness of specimens taken from rail negligibly (49.7 … 50.7 MPa m^0.5) depend on their orientation (L–S or S–L). Full article

The increased test frequency inherent in Ultrasonic Fatigue Testing (UFT) is commonly observed to result in an increased fatigue resistance for ferritic, low-carbon steels. In this investigation, the fatigue response of S275J2 ferritic structural steel is evaluated at both 20 kHz and 50 Hz. At the ultrasonic frequency, an increase in the fatigue limit of 136 MPa and an increase in the finite life region of 150 MPa was observed, alongside a reduction in the slope of the S-N curve. By combining the S275J2 results with additional data from the literature, generalised versions of previously proposed frequency sensitivity models are produced by evaluating the model coefficients as a function of different combinations of the material properties. Additionally, a new frequency sensitivity model was proposed by evaluating the empirical change in the S-N curve coefficients as a function of these material properties. For all of the models, it was found that the best correlation was against the ferrite content divided by the tensile strength. The generalised forms of these models were rearranged to produce correction factors, which allow the conventional frequency fatigue response to be estimated based on the UFT test. The most reliable correction method was found to be using the empirical change in the S-N curve exponent. Full article

The study presents a comprehensive analysis of the effects of high temperatures (500 °C and 700 °C) on the microstructure, mechanical properties, and acoustic emission (AE) parameters of cold-drawn prestressing steel. The investigations included mechanical testing, AE signal acquisition, and numerical verification using the finite element method (FEM). It was demonstrated that increasing temperature leads to significant microstructural changes (pearlite spheroidisation, carbide coarsening), resulting in strength degradation and a shift in the failure mechanism from quasi-brittle (initial state) to transitional (500 °C), and finally to ductile (700 °C). For the first time, AE parameters (Counts to Peak and RA-value) were correlated with local axial strains ε₂₂ and von Mises equivalent stress, enabling the identification of the moment of onset load-bearing capacity loss and the determination of critical material damage thresholds. A multi-criteria diagnostic indicator was proposed to assess the condition of prestressing steel after fire exposure. The results confirm the high potential of AE as a non-invasive tool for evaluating the safety of prestressing tendons and cables in reinforced concrete structures subjected to overheating or fire. Full article

A microalloyed (MA) steel, combined with titanium diboride (TiB₂), was utilised to create a unique steel matrix composite (SMC), enhancing the modulus of the MA steel while also improving its strength. Through thermomechanical processing stages, including hot rolling and plane-strain compression (PSC) testing, followed by various final cooling methods, a cooling rate of 0.1 °C/s was identified as the most effective for achieving a ferrite–pearlite microstructure, which is suitable for toughness and ductility. With TiB₂ reinforcement successfully incorporated via Fe-Ti and Fe-B additions during vacuum induction melting (VIM), it was observed that the TiB₂ particles were homogeneously dispersed in both 5% and 7.5% nominal volume fraction additions, exhibiting faceted and hexagonal morphology. TiB₂ was found to exert a grain-pinning effect on recrystallised austenite at 1050 °C, as evidenced by the retention of grain orientation from hot rolling, in contrast to the MA steel deformed without the composite reinforcement. Increasing the volume fraction of TiB₂ improved the stiffness and strength of both composite alloys, verified through mechanical testing. Full article

This study investigated the electrolytic-plasma hardening (EPH) of cast 20GL steel, used for railway spring beams. The main objective was to analyze the spectral characteristics of the cathodic discharge and establish correlations between the plasma parameters, processing regimes, and resulting surface properties. Optical emission spectroscopy revealed that the plasma at 260 V exhibited a high-energy state with an electron density of ~5.3 × 10¹⁶ cm⁻³ and an electron temperature of 10,031 K. Using these parameters, the heat flux from the plasma to the steel surface was estimated at ~1.5 × 10⁷ W/m², confirming that the discharge provides sufficient energy for surface austenitization. Microstructural analysis demonstrated that the electrolyte flow rate, which determines the cooling rate, is the key parameter controlling phase transformations. At low flow rates, ferrite–pearlite and bainitic structures formed, while a fully martensitic structure and maximum hardness (1046 HV) were achieved at 10 L/min. Tribological tests confirmed the superior wear resistance of the martensitic layers, showing a friction coefficient of 0.454 and a wear volume 3.4 times lower than in the as-cast state. These findings verify that EPH offers an energy-efficient, low-cost method for improving the surface performance and service life of 20GL steel components in heavy-duty railway applications. Full article

This study investigated the influence of the cooling process on the microstructure and mechanical properties of high-strength, high-ductility ship plate steel. The transformation temperature ranges for ferrite (F) and bainite (B) for the experimental steel were determined through thermal simulation experiments. Based on these findings, hot-rolling experiments in laboratory were designed to elucidate the influence of three different cooling paths on the resultant microstructure and mechanical properties. The results demonstrate that the two-stage (air cooling + water cooling) and three-stage (water cooling + air cooling + water cooling) processes after rolling enhance the strength through phase transformation and precipitation strengthening mechanisms. The three-stage process provides an additional fine-grain strengthening effect. Compared to the F+Pearlite (P) or B microstructures produced by single-stage cooling, the F+B dual-phase steel obtained through these multi-stage cooling routes exhibits superior ductility at a comparable yield strength grade. Notably, the two-stage cooling mode proves particularly effective in enhancing ductility. These findings provide a theoretical foundation for designing cooling processes for high-strength, high-ductility ship plate steel. Full article

The paper presents designing thermomechanical processing routes for medium-carbon boron-bearing microalloyed steel and investigates their effect on microstructure–property characteristics obtained through controlled cooling directly from hot forging temperature. Direct cooling was carried out in situ within the industrial process of hot forging, replacing conventional heat treatment with slow and accelerated air cooling, realized with a fully automated fan-cooling laboratory conveyor which accommodates the desired cooling strategy. Comparative analysis of conventionally normalized and direct-cooled microstructure and mechanical properties obtained under varied thermo-mechanical conditions is presented to investigate the potential of medium-carbon microalloyed steel with boron addition for producing tailored properties comparable to those of the normalized condition. The obtained microstructure composed of grain-boundary ferrite and pearlite which resulted in tensile properties as good as Re ≈ 610 MPa, Rm ≈ 910 MPa, and elongation A5 ≥ 12%. Although the achieved microstructure–property parameters differ from those achieved through conventional normalizing (Rm ≤ 780 MPa, Re ≤ 460 MPa, and A ≥ 14%), they are considerable in terms of selected machinability aspects. The observed effect of the imposed treatment strategies on interlamellar spacing and morphology of ferrite showed possibilities regarding the control of mechanical properties and application of direct cooling as a beneficial alternative to conventional normalizing, where energy consumption is the main concern in manufacturing high-duty parts made of boron-bearing microalloyed steel 35MnTiB4. Full article

Reliable modeling and prediction of the long-term strength of materials are relevant, as they allow for accurate determination of the service life of structures and components made from these materials. The aim of this work is to develop models of the long-term strength of rheonomic materials under constant stress and step loading using the principle of damage accumulation, as well as a model for predicting their long-term strength under constant stress based on short-term test data. Using the developed models, the long-term strength of optical fiber with a moisture of 30% and 85% under constant stress from 1600 to 2100 MPa and aluminum alloy under a step change of stress at a temperature of 180 °C were predicted with high accuracy; the long-term strength of pearlitic steel was predicted based on short-term tests under constant stress at temperatures from 98 °C to 293 °C. The developed models have important practical significance, as they can be used for modeling and predicting the long-term strength of rheonomic materials in practice, particularly in cases where the conditions of their operation and loading history are known. Full article

High-strength low-alloy (HSLA) steel is widely used in automotive industry for reduction of consumption and emissions. The microstructure and mechanical properties of two automotive HSLA steels with different strength grades were systematically investigated in present study. Microstructural characterization was conducted using optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD), while mechanical properties were evaluated with Vickers hardness tester and tensile tests. Both steels exhibited a ferrite matrix with spheroidized carbides/pearlites. However, Sample A displayed equiaxed ferrite grains with localized pearlite colonies, while Sample B featured pronounced elongated ferrite grains with a band structure. Tensile testing revealed that Sample B had higher ultimate tensile stress and yield stress compared to Sample A. Texture analysis indicated that both steels were dominated by α-fiber and γ-fiber textures, with minor θ-fiber texture, resulting in minimal mechanical anisotropy between the rolling direction (RD) and transverse direction (TD). The quantitative assessment of strengthening mechanisms, based on microstructural parameters and experimental data, revealed that grain boundary strengthening dominates, with dislocation strengthening also contributing significantly. This work provides the first comprehensive quantification of individual strengthening contributions in automotive HSLA steels, offering critical guidance for developing further higher-strength automotive steels. Full article

The present study examines the effect of a modified oval–round rolling scheme incorporating inclined oval calibers on the mechanical behavior and microstructural evolution of Mn–Si low-alloy steel (25G2S). Cylindrical billets were hot rolled through both classical and modified sequences under identical thermal and kinematic conditions. Tensile testing demonstrated that, relative to the unrolled condition (σ_0.2 ≈ 269 MPa; σᵤ ≈ 494 MPa), the classical route increased yield and ultimate strengths to ~444 MPa and ~584 MPa, respectively, whereas the modified scheme yielded comparable values (~433 MPa and ~572 MPa) while providing superior ductility (δ ≈ 26.8%, ψ ≈ 68.6%). Vickers microhardness decreased systematically from 244 HV (unrolled) to 213 HV (classical) and 184 HV (modified), with the modified scheme exhibiting the lowest scatter (±4.8 HV), confirming enhanced structural uniformity. Scanning electron microscopy revealed ferrite–pearlite refinement under both rolling sequences, with the modified scheme producing finer equiaxed ferrite grains (~3–5 µm) and attenuated longitudinal banding. These features are indicative of shear-assisted dynamic recrystallization, activated by the inclined oval calibers. The findings highlight that the modified rolling strategy achieves a favorable strength–ductility balance and improved homogeneity, suggesting its applicability for advanced thermomechanical processing of low-alloy steels. Full article