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Pearlitic (stainless) steel is used in automotive, aerospace, and other industries where high strength, hardness, and wear resistance are required. Its quality control can be performed using mechanical tests or by examining the lamellar microstructure, namely, determining interlamellar distance. One of the related approaches is the circular line method (CLM). This paper reviews the challenges to automate employment of the CLM using custom Python code in order to reduce human time costs during image-based quality assessment of pearlite. The goal is to perform intersection counting automatically once the human operator has configured the application and selected the locations of measuring circles. Performance assessment using manually processed data from some 465 images is performed. We divide the imaged pearlite microstructures into different “types” when the code performs well or, respectively, not so well. We conclude with possible extensions of the work presented here.

The use of a rapid heating method to achieve heterogeneity of Mn in medium-manganese steel and improve its comprehensive performance has been widely studied and these techniques have been widely applied. However, the heating rate (from α to γ) has not received sufficient attention with respect to its microstructure-evolution mechanism. In this study, the effect of heating rate on the microstructure evolution and hardness of heterogeneous medium-manganese steel was investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and DICTRA simulation. The results showed that the Mn distribution was heterogeneous in the initial microstructure of pearlite due to strong partitioning of Mn between ferrite and cementite. At low heating rates (<10 °C/s), the heterogeneity of Mn distribution was diminished to some extent due to the long-distance diffusion of Mn in high-temperature austenite. Contrastingly, at high heating rates, the initial heterogeneity of the Mn element could be largely preserved due to insufficient diffusion of Mn, which resulted in more ghost pearlite (GP: pearlite-like microstructure with film martensite/RA). Moreover, the high heating rate not only refines the prior austenite grain but also increases the total RA content, which is mainly composed of additional film RA. As the heating rate increases, the hardness gradually increases from 628.1 HV to 663.3 HV, due to grain refinement and increased dislocation density. Dynamic simulations have also demonstrated a strong correlation between this interesting microstructure and the non-equilibrium diffusion of Mn.

As railway transportation advances towards higher speeds and increased axle loads, the fatigue damage between wheels and rails has become more severe, significantly limiting the service life and safety of trains. Therefore, developing upgrade wheel-rail materials with enhanced contact fatigue properties has been considered an effective approach to avoid damage. This study reports a newly developed heavy-haul wheel steel with a superior rolling contact fatigue performance and the fatigue damage of wheel was studied by a novel RCF tester with a vision system. The results indicate that the newly developed heavy-haul wheel steel (NW) consists of smaller pearlite layer spacing and reduced proeutectoid ferrite. The NW steel demonstrates outstanding fatigue resistance in both oil and dry conditions, with a fatigue life 2.7 times longer than CL65 wheel steel and superior performance compared to most typical wheel steels. With increasing in pearlite content and decreasing in pearlitic interlamellar spacing, the fatigue damage degree of wheels under oil or dry contact conditions decreases obviously, leading to a significant enhancement in fatigue life. Properly controlling the pearlite content and the interlamellar spacing can optimize the fatigue properties of wheel materials. The vision system observed that the average area and perimeter of the defects gradually increased on the sample surface. The shape of the defect became more rounded under oil contact conditions but showed the opposite result in dry contact. When subjected to cyclic loading, surface cracks propagated along various paths after initiation, eventually forming different morphologies of peeling. The results will not only help optimize wheel materials for heavy-haul railways, but also offer an effective means for analyzing damage evolution in wheel-rail contact. Graphical abstract

In this study, we quantitatively investigate the impact of 1.4 wt.% chromium and 1.4 wt.% molybdenum additions on pearlitic microstructure characteristics in 1 wt.% carbon steels. The study was carried out using a combination of experimental methods and phase field simulations. We utilized MatCalc v5.51 and JMatPro v12 to predict transformation behaviors, and electron microscopy for microstructural examination, focusing on pearlite morphology under varying thermal conditions. Phase field simulations were carried out using MICRESS v7.2 software and, informed by thermodynamic data from MatCalc v5.51 and the literature, were conducted to replicate pearlite formation, demonstrating a good agreement with the experimental observations. In this work, we introduced a semi-automatic reliable microstructural analysis method, quantifying features like lamella dimensions and spacing through image processing by Fiji ImageJ v1.54f. The introduction of Cr resulted in longer, thinner, and more homogeneously distributed cementite lamellae, while Mo led to shorter, thicker lamellae. Phase field simulations accurately predicted these trends and showed that alloying with Cr or Mo increases the density and circularity of the lamellae. Our results demonstrate that Cr stabilizes pearlite formation, promoting a uniform microstructure, whereas Mo affects the morphology without enhancing homogeneity. The phase field model, validated by experimental data, provides insights into the morphological changes induced by these alloying elements, supporting the optimization of steel processing conditions.

Lüders deformation is one type of discontinuous yielding in ferrite–pearlite steel. The yield-point phenomenon and localized plastic bands are two features of the Lüders phenomenon. It is believed that the yield-point phenomenon is related to the formation of plastic bands, but the correlation between them is unclear. In this study, this correlation was investigated by examining the global and local deformation behaviors in the tension processes of four ferrite–pearlite steels (carbon content, 0.05–0.3%; pearlite fraction, 1.2–32%) via an extensometer and digital image correlation (DIC) technique. The main obtained results are as follows: (1) the degree of yield drop decreased with an increase in the pearlite fraction (the magnitude of the yield stress drop was 8.6–0 MPa), and (2) a plastic band was formed at a certain stress level smaller than the upper yield stress; when the stress level was larger than 92% of the upper yield stress, the upper yield point disappeared.

The emerging technology of wire arc additive manufacturing (WAAM) has been enthusiastically embraced in recent years mainly by the welding community to fabricate various grades of structural materials. In this study, ER70S-6 low-carbon low-alloy steel wall was manufactured by WAAM method, utilizing a gas metal arc welding (GMAW) torch translated by a six-axis robotic arm, and employing advanced surface tension transfer (STT) mode. The dominant microstructure of the fabricated part contained randomly oriented fine polygonal ferrite and a low-volume fraction of lamellar pearlite as the primary micro-constituents. Additionally, a small content of bainite and acicular ferrite were also detected along the melt-pool boundaries, where the material undergoes a faster cooling rate during solidification in comparison with the center of the melt pool. Mechanical properties of the part, studied at different orientations relative to the building direction, revealed a comparable tensile strength along the deposition (horizontal) direction and the building (vertical) direction of the fabricated part (~ 400 MPa and ~ 500 MPa for the yield and ultimate tensile strengths, respectively). However, the obtained plastic tensile strain at failure along the horizontal direction was nearly three times higher than that of the vertical direction, implying some extent of anisotropy in ductility. The reduced ductility of the part along the building direction was associated with the higher density of the interpass regions and the melt-pool boundaries in the vertical direction, containing heat-affected zones with coarser grain structure, brittle martensite–austenite constituent, and possibly a higher density of discontinuities.

This paper studies the drawing-induced intercolonial microdamage (ICMD) in pearlitic microstructures. The analysis was performed from the direct observation of the microstructure of the progressively cold-drawn pearlitic steel wires associated with the distinct steps (cold-drawing passes) of a real cold-drawing manufacturing scheme, constituted by seven cold-drawing passes. Three types of ICMD were found in the pearlitic steel microstructures, all affecting two or more pearlite colonies, namely: (i) intercolonial tearing; (ii) multi-colonial tearing; and (iii) micro-decolonization. The ICMD evolution is quite relevant to the subsequent fracture process of cold-drawn pearlitic steel wires, since the drawing-induced intercolonial micro-defects act as weakest links or fracture promoters/initiators, thereby affecting the microstructural integrity of the wires.

In this study, the cause of failure of a low-carbon steel pipe meeting standard KS D 3562 (ASTM A135), in a district heating system was investigated. After 6 years of operation, the pipe failed prematurely due to pitting corrosion, which occurred both inside and outside of the pipe. Pitting corrosion occurred more prominently outside the pipe than inside, where water quality is controlled. The analysis indicated that the pipe failure occurred due to aluminum inclusions and the presence of a pearlite inhomogeneous phase fraction. Crevice corrosion occurred in the vicinity around the aluminum inclusions, causing localized corrosion. In the large pearlite fraction region, cementite in the pearlite acted as a cathode to promote dissolution of surrounding ferrite. Therefore, in the groundwater environment outside of the pipe, localized corrosion occurred due to crevice corrosion by aluminum inclusions, and localized corrosion was accelerated by the large fraction of pearlite around the aluminum inclusions, leading to pipe failure.

In response to issues such as low efficiency and unstable quality in manual welding of marine bulb flat steel in the shipbuilding industry, a flash welding process for 160×9 mm DH32 marine bulb flat steel was developed, and the influence of feed rate during the accelerated flashing stage on welded joint performance was investigated. The results demonstrate that flash butt welding is a feasible and efficient method for welding marine bulb flat steel. The welded joints exhibit aesthetically sound formation without defects such as cracks or porosity. The heat-affected zone primarily consists of equiaxed blocky ferrite and pearlite, while the weld center comprises coarse blocky ferrite with minor pearlite. The average tensile strength of the joints reaches 469.7 MPa, meeting standard requirements. Optimal flash butt welding parameters for DH32 marine bulb flat steel were achieved at accelerated flashing stage feed rates V (V1=0.5 mm/s, V2=0.8 mm/s, V3=1.1 mm/s, V4=1.4 mm/s, V5=1.7 mm/s, V6=2.1 mm/s).

Considering the U75V 60 kg/m heavy rail as the research object, compressed air was selected as the cooling medium, and the temperature fields of the rail surface before and after heat treatment were recorded by using a thermal imager. Pearlite in the hardened layer was examined for its morphology by using a scanning electron microscope, and Rockwell hardness was tested. Important basic data for the formulation and optimization of the heat treatment process of the U75V 60 kg/m heavy rail is determined by analyzing the correlation between the cooling rates of the rail head surface, the microstructure, and the properties of the hardened layer.