The effect of the initial microstructure and soft annealing temperature on cementite spheroidization and microstructure softening is studied on an AISI 5140 hot-rolled wire. In coarse pearlite microstructure (λ: 0.27 μm), the cementite spheroidization progresses slowly under subcritical treatment, and the microstructure does not achieve the minimum G2/L2 IFI rating defined in the ASTM F2282 to be used in cold forming operations under any of the annealing treatment studies. Fine pearlite (λ: 0.10 μm) and upper bainite microstructures are more prone to spheroidization, and the minimum G2/L2 IFI rating is achieved under subcritical annealing at 720 °C for 6 h. Independent of the initial microstructure, even in the case of martensite, low hardness values within 165–195 HV are attained after imposing a 10 h long treatment at 720 °C. Annealing treatments conducted at 660 °C and 600 °C on pearlitic microstructures give rise to very poor softening. The G2/L2 rating is not achieved in any of the treatments applied at these two temperatures in this study. In pearlitic microstructures, the spheroidization progresses according to a fault migration mechanism, enhanced by the presence of defects such as lamella terminations, holes, and kinks. In the upper bainite, the row-like disposition of the cementite along the ferrite lath interface provides necks where dissolution and consequent lamellae break-up take place quickly under annealing.

In the design of L-DED (laser-directed energy deposition) cladding processes, the chemical composition of the metallic powders is typically assumed to match that of the intended coating. However, during the deposition of the first layer, dilution with the substrate alters the weld metal composition, deviating from the nominal powder chemistry. Although the application of multiple layers can gradually reduce this dilution effect, it introduces additional complexity and processing time. This study proposes an alternative strategy to counteract substrate dilution from the very first deposited layer, eliminating the need for multilayer coatings. Specifically, to achieve a corrosion-resistant monolayer of AISI 316L stainless steel on a high-strength, quenched-and-tempered AISI 4140 steel substrate, a dilution-compensating alloy powder is added to the standard AISI 316L feedstock. Single-layer coatings, both with and without compensation, were evaluated in terms of chemical composition, microstructure, and corrosion resistance. The results show that unmodified coatings suffered a chromium depletion of approximately 2 wt.%, leading to a reduced pitting potential of Ep = 725 ± 6 mV in synthetic seawater. In contrast, the use of the compensation alloy preserved chromium content and significantly improved corrosion resistance, achieving a pitting potential of Ep = 890 ± 9 mV.

The effect of different pre-strain application paths on the microstructure evolution of a medium carbon steel after soft annealing is studied. The strain applied on an undercooled austenite induces fine ferrite and pearlite transformation at austenite grain boundaries leading to an average grain size much finer than that in the case where no pre-strain is applied (around 4 and 7 µm, respectively) and a drastic reduction of the fraction of large grains (>20 µm) that become the 17% rather than the 40%. Cementite direct precipitation at the induced ferrite α/α interface and the induced pearlite quick decomposition, give rise to an improved degree of spheroidisation after annealing and a L2 IFI rating regarding the ASTM F2282 standard. When the strain is applied on pearlite, diffusion through the matrix is enhanced which accelerates the lamellae break-up and leads to fully spheroidised microstructures after annealing (degree of spheroidisation above 90% and G1 on IFI rating). When both strain sequences are applied consecutively, the resulting annealed microstructure combines the features corresponding to each individual strain paths, i.e., homogeneous and refined ferrite grain size and enhanced spheroidisation degree, which confers optimal cold workability properties to the steel. In addition, such characteristics are attained without an excessive increase in hardness (in the range 155–180 HV), which is interesting when considering cold forming tool wear.