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A microalloyed high-carbon low-alloy steel was designed to clarify the combined effects of austenitizing temperature and deep cryogenic treatment (DCT) on microstructural evolution and mechanical performance. Specimens were austenitized at 770–900 °C, water-quenched, subjected to DCT at −196 °C, and subsequently tempered at 180 °C. Microstructural characterization by XRD, EBSD, and TEM indicates that the quenched microstructure is dominated by martensite and cementite, with retained austenite below 1% at moderate austenitizing temperatures. DCT does not fundamentally alter the martensitic morphology but promotes the transformation of retained austenite and induces substructure fragmentation, dislocation reorganization, and a more homogeneous lattice strain distribution. Concurrently, carbon redistribution during cryogenic exposure facilitates the formation of finely dispersed carbides. After tempering, partial recovery and stabilization of the martensitic substructure lead to reduced lattice distortion while maintaining a high density of effective strengthening features. Mechanical testing shows that DCT combined with appropriate austenitizing (770–790 °C) improves hardness and ultimate tensile strength with acceptable ductility, whereas excessive austenitizing at 900 °C results in severe grain coarsening and intergranular brittle fracture. The results demonstrate that optimized integration of microalloying and DCT enables a favorable strength–toughness balance in high-carbon tool steels.

The quenching and partitioning (Q&P) process has been shown to be quite promising in the development of a third generation of Advanced High-Strength Steels. As in other metallurgical processes, the austenitic grain size (AGS) is crucial to obtain a microstructure that provides a great mechanical behavior. Hence, this work evaluated the effect of the austenitizing temperature on the AGS and, consequently, on the constituents formed under continuous cooling at different rates. Then, a Q&P modeling for a commercial CMnSi steel, predicting the microstructural evolution and the final phase fractions as a function of the AGS and other parameters, was performed. The AGS increased exponentially with the austenitizing temperature, in the way that the smaller the AGS the finer the martensitic structure formed after cooling. The decrease in the continuous cooling rate leaded to the formation of diffusional constituents prior to the martensitic transformation, which promoted the increase in M s temperature for larger AGS. In conclusion it is possible to state that an austenitizing condition that provides the smallest possible AGS, followed by an optimized Q&P cycle, has the potential to generate an advanced steel with a final microstructure assisted by the TRIP effect due to the retained austenite content.

The relationship between microstructure and corrosion behavior of martensitic high nitrogen stainless steel 30Cr15Mo1N at different austenitizing temperatures was investigated by microscopy observation, electrochemical measurement, X-ray photoelectron spectroscopy analysis and immersion testing. The results indicated that finer Cr-rich M2N dispersed more homogeneously than coarse M23C6, and the fractions of M23C6 and M2N both decreased with increasing austenitizing temperature. The Cr-depleted zone around M23C6 was wider and its minimum Cr concentration was lower than M2N. The metastable pits initiated preferentially around coarse M23C6 which induced severer Cr-depletion, and the pit growth followed the power law. The increasing of austenitizing temperature induced fewer metastable pit initiation sites, more uniform element distribution and higher contents of Cr, Mo and N in the matrix. In addition, the passive film thickened and Cr2O3, Cr3+ and CrN enriched with increasing austenitizing temperature, which enhanced the stability of the passive film and repassivation ability of pits. Therefore, as austenitizing temperature increased, the metastable and stable pitting potentials increased and pit growth rate decreased, revealing less susceptible metastable pit initiation, larger repassivation tendency and higher corrosion resistance. The determining factor of pitting potentials could be divided into three stages: dissolution of M23C6 (below 1000 °C), dissolution of M2N (from 1000 to 1050 °C) and existence of a few undissolved precipitates and non-metallic inclusions (above 1050 °C).

The microstructure evolution and mechanical properties of air-hardening steel subjected to different austenitizing annealing treatments were investigated in this study and, especially, the precipitation behavior of the steel was analyzed, as well as the strengthening mechanism of the steel was elucidated on the basis of systematic microstructural characterization. Results reveal that a ferrite + martensite dual-phase structure with about 700 MPa tensile strength and 20% elongation can be obtained by austenitizing the experimental steel in the range of 750∼800 °C; while austenitizing between 850 °C and 950 °C results in granular bainite + lath bainite with about 950 MPa tensile strength and 12% elongation. The experimental steel has the highest strength after austenitizing at 900 °C with lots of nano-scale (Ti, Mo, V)C particles distributed in its matrix. Quantitative calculation results illustrate that the main strengthening factors are grain refinement strengthening, dislocation strengthening and precipitation strengthening. In addition, due to the potential interaction effect between different strengthening factors, a modified strengthening model is proposed to describe the strengthening behavior of the air-hardening steel when it is heat-treated in the two-phase region.

The effect of austenitizing on the microstructure and hardness of two martensitic stainless steels was examined with the aim of supplying heat-treatment guidelines to the user that will ensure a martensitic structure with minimal retained austenite, evenly dispersed carbides and a hardness of between 610 and 740 HV (Vickers hardness) after quenching and tempering. The steels examined during the course of this examination conform in composition to medium-carbon AISI 420 martensitic stainless steel, except for the addition of 0.13% vanadium and 0.62% molybdenum to one of the alloys. Steel samples were austenitized at temperatures between 1000 and 1200 °C, followed by oil quenching. The as-quenched microstructures were found to range from almost fully martensitic structures to martensite with up to 35% retained austenite after quenching, with varying amounts of carbides. Optical and scanning electron microscopy was used to characterize the microstructures, and X-ray diffraction was employed to identify the carbide present in the as-quenched structures and to quantify the retained austenite contents. Hardness tests were performed to determine the effect of heat treatment on mechanical properties. As-quenched hardness values ranged from 700 to 270 HV, depending on the amount of retained austenite. Thermodynamic predictions (using the CALPHAD™ model) were employed to explain these microstructures based on the solubility of the carbide particles at various austenitizing temperatures.

The effects of austenitizing temperature and holding time on the austenite grain growth behavior of GCr15 bearing steel are reflected in this paper. SEM and EBSD deeply reveal the effect of austenite grain size on the misorientation angle of grain boundary. The results show that both the holding time and the austenitizing temperature will make the austenite grain size grow to a certain extent. However, the change of temperature will cause a greater change in grain size. The grain size will also have different growth trends in different austenitizing temperature ranges. The grain size of Gcr15 test steel is combined with the Sellars model to derive its growth kinetics model.

The existence of angular and hard AlN inclusions would seriously deteriorate the service life of high-nitrogen stainless bearing steels (HNSBSs). In this work, the formation mechanism of AlN inclusion in HNSBSs under as-cast, annealing and austenitizing states was systematically investigated by microstructure observation and thermodynamic, kinetic analyses. The results showed that the concentration product of Al and N could exceed the critical solubility of AlN inclusion at liquidus temperature with the Al content higher than 0.050 wt pct, which led to the formation of AlN inclusions about 1 to 5 μm (equivalent diameter) in liquid steel. Based on the ‘Clyne-Kurz’ model, AlN inclusion could form at the solidifying front due to the enrichment of N in the residual liquid steel with the Al content higher than 0.030 wt pct. Besides, the precipitation of Cr2N and the extremely low diffusion coefficient of Al in α phase restrained the precipitation of AlN during annealing at 1023 K. However, AlN and AlN-MnS composite inclusions less than 0.6 μm could precipitate during austenitizing at 1323 K with the Al content higher than 0.006 wt pct, which was the critical Al content to avoid AlN formation in HNSBSs after melting, solidification, and heat treatment processes.

The objective of this research is to examine the impact of welding parameters on the surface roughness, hardness, and tensile strength of welds produced by a single-pass TIG welding process in austenitic stainless-steel plates (AISI 316L). Furthermore, the optimal processing variable settings will be identified in order to provide the highest levels of hardness, lowest levels of surface roughness, and highest levels of tensile strength. This study focuses on three parameters: arc current, voltage, and shielding gas flow rate, which were altered across three levels. A large number of tests were carried out on 3-mm thick AISI 316L stainless steel plates in order to determine the efficient and realistic operating limits of TIG welding settings. The welding process parameters’ operational limitations were determined by visual examination and bead shape. The values of current are taken as 100, 125, and 150 (A); voltage as 16, 18, and 20 (V); and gas flow rate as 6, 9, and 12 (L/min). Their impact on tensile strength, microhardness, and surface roughness was inspected. The experiments were conducted using Taguchi L9 orthogonal array (OA). Each input parameter was found to have an impact on the response. The optimized welding parameters for improved mechanical properties and surface roughness were identified. The results indicated an optimum tensile strength, 624.92 MPa, achieved at the parametric combination of 100 A current, voltage of 16 V, and gas flow of rate 6 L/min. The microhardness results indicated an optimum value, of 319.2 HV, achieved at the parametric combination of a current of 125 A, 16 V of voltage, and a gas flow rate of 9 L/min. A minimum surface roughness, 7.33 µm, was attained at 125 A current, voltage of 16 V, and gas flow rate of 9 L/min. These results highlight the significant impact of welding parameters on the mechanical properties and surface roughness of AISI 316L stainless steel welds.

To address the inhomogeneous microstructure and improve the mechanical properties of DT300 ultra-high strength steel specimens fabricated by laser powder bed fusion, different post-heat treatment schedules are performed. With the increase in austenitizing temperature and time, the migration rate of austenite grain boundaries continuously increases with the dissolution of nano-carbides, and the formation of nano-oxides and twin martensite is also inhibited accordingly. The rapid growth in the size of prior austenite grains and martensite laths, as well as the decrease in the content of nano-oxides and twin martensite, led to a rapid decrease in the strength (yield strength and ultimate tensile strength) from HT2 to HTF specimens. The HT1 specimens (austenitizing at 830 °C for 30 min, then oil quenching and tempering at 300 °C for 120 min and finally air cooling) display excellent mechanical properties of yield strength of 1572 MPa, ultimate tensile strength of 1847 MPa, elongation of 9.84%, and fracture toughness of 106 MPa m 1/2 , which are counterparts to those of conventional DT300 steel forgings after heat treatment.