Stability Of Austenite Research Articles

A Novel Design to Eliminate Lüders Band in Medium-Mn Steel and Its Microstructure-Property Relationship

In the current work, we design a novel medium Mn steel with a superior mechanical property and no Lüders band. For industrial applications, a “low Mn addition” chemical composition and two kinds of different annealing processes with various initial microstructures were introduced. Consequently, the sample subjected to full austenitized quenching plus intercritical annealing process exhibited an outstanding mechanical property without the Lüders band. The microstructural evolution and austenite reverted transformation behavior were discussed in detail. In addition, austenite stability was estimated by chemistry stability and mechanical stabilization. It seemed that the austenite stability was significantly influenced by the morphological component. Thus, the sample with single lath-like ferrite and austenite exhibited the most excellent mechanical property. Furthermore, the “Lüders band” phenomenon was considered to rely on the restriction of martensitic recovery and recrystallization by lath-like morphology. The occurrence of the Lüders band was attributed to the low work-hardening ability caused by dynamic recovery. The formation of lath-like morphology could prevent the occurrence and propagation of the Lüders band by increasing the dislocation density and active TRIP effect.

Influence of Austenite Stability on the Machinability of Different Grades of Austempered Ductile Iron (ADI) During Dry Turning Machining

This work evaluated the machinability characteristics of three different austempered ductile irons using three machinability indicators: cutting force, tool wear, and surface roughness. Additionally, this paper addresses the interplay among the production conditions of ADIs, microstructural development, the TRIP effect arising from transformations of the retained austenite into martensite, and the machinability behavior of ADIs. Various characterization studies including hardness measurement, X-ray diffraction analysis, light and electron microscope were used. Machinability results indicated that the increase in cutting force is always associated with a corresponding increase in the martensite content when the cutting depth was increased from 0.5 to 2.0 mm. Such correlation is more evident with ADI grade austempered at high austempering temperature, 375 °C (ADI-375). It was noticed that although ADI-375 has only 0.46% martensite in the structure before machining, this ratio increases with the highest depth of cut of 2.0 mm to reach about ~ 23% martensite with a corresponding increase in the cutting force. Ferrite content and morphology have a great impact on the overall surface finish of each grade as it leads to deteriorating the surface characteristics of the investigated alloys. This could explain the highest roughness values across all processing experiments obtained in the ADI grade austenitized in the intercritical region (IADI), which mainly contains the highest ferrite content. Tool wear and chip characteristics were also studied in this work.

Test and application of 60 kg·m−1 bainite rails for heavy-haul railway

PurposeIn order to develop high-strength, high-toughness and high-wear-resistance rails suitable for the development and application of heavy-haul railways.Design/methodology/approachBased on the trial production of 60 kg·m−1 bainite rails, the Zeiss inverted optical microscope, transmission electron microscope and static hydraulic universal tester were used to test the microstructure and property of rail base metal and welded joints. Meanwhile, a trial laying of rails, wing rails of frogs and switch rails for turnouts was performed to systematically analyze their strength, toughness and wear resistance.FindingsThe results show that the base metal of 60 kg·m−1 bainite rail is of a uniform microstructure, with a carbide-free bainite matrix, a few of stable residual austenite and M/A islands, and it features high hardness, good wear resistance and good strength-toughness balance. The welded joint is of a uniform microstructure and has good properties.Originality/valueA bainite rail, laid in a curve section of heavy-haul railway is able to serve for 48 months with a gross traffic tonnage of nearly 600 million tons, whose service life is more than one time longer than that of pearlite rail; the service life of the wing rail of frog and the switch rail for turnout with 60 kg·m−1 bainite rails is 3–4 times longer than that with U75V rails, and no serious damage occurs. The bainite rails also have strong peeling and spalling resistance.

Effect of retained austenite on the fatigue behavior of modified bainitic 100Cr6 steels considering local phase transformation

Since highly loaded components, such as roller bearings, tend to have relatively high lifetime scatter caused by microstructural defects, an increased defect tolerance of the material can improve the performance as well as the reliability of these highly stressed components. To increase the defect tolerance of the roller bearing steel 100Cr6, two different laboratory melts with either 1.5 wt.-% Al or 1.5 wt.-% Si in addition to the standard composition were developed. After an adapted heat treatment, both steels exhibited a bainitic microstructure with a relatively high content of retained austenite with more than 20 vol.-%. Considering the effects of the retained austenite, a defined mechanical stability is essential to avoid excessive deformation-induced transformation from the retained austenite into α′-martensite, which can lead to shape deviations in components. However, besides the increased deformability of the austenitic phase, local phase transformations in the vicinity of defects can increase the defect tolerance. The fatigue tests performed at ambient temperature (AT) and at T = 100 °C, show a higher fatigue strength of the Si-alloyed steel due to a refined microstructure and revealed for both steels a relatively high austenite stability, since no macroscopic phase transformation was observed. The high austenite stability can be explained by a relatively high carbon content of the austenitic phase. However, in contrast to the Al-alloyed steel, a decrease in the fatigue strength and in the defect tolerance due to the increased temperature were observed for the Si-alloyed steel, which indicates a more pronounced phase transformation at AT. The lower carbon content and the finer distribution of the retained austenite, when compared to the Al-alloyed steel, are supposed to be the reason. While a smaller carbon content decreases the phase stability, the refined austenite distribution results in a higher probability of retained austenite presence in the vicinity of a defect.

Roles of Al in enhancing the thermal stability of reverted austenite and mechanical properties of a medium-Mn TRIP steel containing 2.7 Mn

Often, the addition of more than 4 wt.% Mn to medium-Mn steels is necessary to enhance the thermal stability of intercritical austenite for achieving sufficient amounts of retained austenite (RA) at room temperature. In this paper, a medium-Mn steel with Mn content as low as 2.7 wt.% was designed via alloying with a small amount of Al, and the microstructure and mechanical properties of the steel, subjected to intercritical annealing (IA) at 745 °C for different times followed by oil quenching, were investigated. Results show that the volume fraction of RA increases first and then decreases with IA time, with the maximum of 0.36 obtained at IA time of 50 min. It is demonstrated that Al addition slows down the interface migration and growth kinetics of reverted austenite via retarding C diffusion in ferrite during IA, which, hence, decreases the amount and size of the reverted austenite and partitions more C and Mn into it. This suggests that Al plays a favorable role in enhancing the thermal stability of reverted austenite and increasing the amount of austenite retained at room temperature. Due to the presence of large amounts of RA and the strong transformation-induced plasticity effect generated during plastic deformation, the steel exhibits persistent high strain hardening and superior mechanical properties, comparable to those of reported medium-Mn steels containing higher Mn content. The present result offers a new insight into the role of Al in adjusting microstructure-property relationships and opens a promising way for designing low-cost, high performance medium-Mn steels with low Mn content for industrial applications.

Effect of austenite fraction and stability on strength-hardening-ductility in additively manufactured 17-4 PH stainless steel containing nitrogen

Additively-manufactured (AM) 17-4 precipitation-hardening (PH) martensitic stainless steel (SS) built from nitrogen-atomized powder often retains a large volume fraction of austenite. The retained austenite lowers the yield strength compared to both wrought and AM 17-4 SS built from argon-atomized powder, hindering its use in many applications. However, retained austenite allows for high work hardening and high ductility through deformation-induced martensitic transformation (DIMT). This work systematically investigates the influence of various heat treatments on the volume fraction and stability of the retained austenite from tensile loading in AM 17-4 SS containing a mass fraction of 0.13% nitrogen (AM 17-4N SS). Synchrotron-based high-energy x-ray diffraction (HEXRD) is used to quantify the austenite volume fraction resulting from the heat treatments and the extent of DIMT in tensile specimens loaded to various plastic strains and specimens loaded to fracture. We show that by altering the volume fraction and stability of the retained austenite in AM 17-4N SS using different heat treatments, the DIMT process can be utilized to vary the strength, work hardening, and ductility, thus enabling its use in a wide range of applications. The AM 17-4N SS is also shown to meet or exceed the peak aged requirements for wrought 17-4 SS with yield strength (YS) of >1200 MPa, an ultimate tensile strength (UTS) of >1500 MPa, and a uniform elongation of ≥13% while retaining ≈ 20% volume fraction of austenite.

Microstructure–Mechanical Property Relationship and Austenite Stability in Transformation-Induced Plasticity Steels: Effects of Quenching and Partitioning Processing and Quenching and Tempering Treatments

Microstructure–Mechanical Property Relationship and Austenite Stability in Transformation-Induced Plasticity Steels: Effects of Quenching and Partitioning Processing and Quenching and Tempering Treatments

Influence of intercritical annealing temperature on microstructure, microtexture, and tensile behavior of TRIP-assisted medium manganese steel

The present work investigates, the effect of intercritical annealing temperature on the microstructure, microtexture, tensile behavior, and mechanical stability of austenite in thermomechanically processed Fe-0.18C-4Al-7Mn (wt.%) medium manganese steel. The steel is subjected to thermomechanical processing (hot forging and hot rolling) followed by intercritical annealing at various temperatures (700, 750 and 800 °C) for 1 hour. The development of a complex microstructure with blocky and lath-type reverted austenite (RA), fine polygonal and blocky type intercritical ferrite (IF), coarse elongated ferrite (EF), and lath martensite (M) is revealed by the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses. The steel annealed at 750 °C exhibits an excellent ultimate tensile strength (UTS) of 802 MPa and total elongation (TE) of 61% owing to its high RA content, high transformation-induced plasticity (TRIP) effect and low mechanical stability of RA. Further, to understand the dislocation phenomena during tensile deformation, the tensile samples are analyzed using TEM, which reveals dislocation interactions, dislocation tangles, and dislocation accumulations at the IF grain boundaries and martensite lath boundaries. The manifestation of the TRIP effect is elucidated by XRD and EBSD studies. In addition, to study the texture evolution and the role of texture components on the TRIP effect, the orientation distribution function is employed. The major texture component, i.e., Ms Brass {011} 〈211〉 indicates the TRIP effect resulting in the deformation-induced martensitic transformation under tensile deformation. Additionally, Ms Brass component shifts towards G/B (Goss/Brass) twin {011} 〈111〉 component by grain rotation to accommodate the deformation.

Microstructure and Wear Resistance in Medium and High C Steels Treated by Quenching and Partitioning

The quenching and partitioning (Q&P) steels have shown to be promising candidates to be applied in fields where wear resistance is required. In this study, a medium and a high C steel are heat treated by Q&P and the resulting microstructure, hardness, and wear resistance are characterized. The mechanical stability of the austenite phase under wear test conditions is investigated. It is found that the stability of austenite is very high in the high C steel and decreases in the medium C steel. Additionally, the hardness and wear behavior of the Q&P‐treated steels are compared with the results obtained for quenching and tempering (Q&T) treated samples, showing that, although the hardness of Q&P steels is quite lower, the obtained wear rates are similar. It means that in the studied Q&P steels, although the austenite transformation into martensite does not occur considerably, the presence of austenite might play a key role in the wear resistance.

Role of surrounding phases on deformation-induced martensitic transformation of retained austenite in multi-phase TRIP steel

Deformation-induced martensitic transformation is a key phenomenon to manage both high strength and large ductility in low alloy multi-phase steels. Significant enhancement of strain hardening ability could be achieved by the phase transformation from soft austenite to hard martensite during deformation, which is known as transformation induced plasticity (TRIP) effect. The occurrence of TRIP effect can be controlled by austenite characteristics like carbon content, grain size and morphology. Additionally, the mechanical interaction with other phases surrounding each austenite grain during deformation would affect the stability of austenite, which has not been clarified. The current study has clarified how surrounding phases affect the mechanical stability of austenite against deformation-induced martensitic transformation. Two types of multi-phase microstructures composed of three different phases, i.e., ferrite (α) + austenite (γ) + martensite (M) and two phases of ferrite (α) + austenite (γ) were fabricated in Fe-1.6Mn-1.4Si-1.0Ni-0.5Al-0.2C, maintaining the characteristics of retained austenite nearly the same. It was found that the α+γ+M specimen exhibited slower rate of deformation-induced martensitic transformation during tensile deformation than the α+γ specimen, indicating higher austenite stability in the α+γ+M specimen. The in-situ synchrotron XRD measurements during tensile deformation revealed that there was significant stress partitioning between austenite and adjacent phases (ferrite, martensite and deformation-induced martensite), which influenced the phase transformation rate of austenite into deformation-induced martensite. Furthermore, it was also clarified by the in-situ synchrotron XRD that the austenite in the α+γ+M specimen always had higher stress than that in the α+γ specimen due to higher dislocation density in austenite introduced by martensitic transformation to form pre-existing martensite, so that higher stress was required for deformation-induced martensitic transformation in the α+γ+M specimen during tensile deformation than the α+γ specimen.

High throughput structure–property relationship for additively manufactured 316L/IN625 alloy mixtures leveraging 2-step Bayesian estimation

While the fabrication of graded materials by directed energy deposition (DED) has led to accelerated materials discovery, the ability to rapidly explore sufficiently large material composition spaces is limited due to the time-intensive nature of conventional materials characterization techniques. The present study investigates the viability of small punch test (SPT) protocols for rapidly evaluating DED-fabricated alloy mixtures of stainless steel 316L (316L) and Inconel 625 (IN625). The SPT protocols evaluated in this study include both the recently established two-step Bayesian estimation framework as well as the empirical relationships established in prior literature. It is shown that these protocols are capable of reliably and quantitatively tracking the changes in the mechanical properties of the alloy mixtures studied. Enhancement of mechanical properties was observed with the addition of IN625 to 316L, which is attributed to the austenite stabilization in the matrix and the formation of fine δ - Ni3Nb precipitates. It is shown that CALPHAD-based Scheil model simulations predicted the formation of different precipitate phases for each composition. The novel protocols presented in this paper open new avenues for high throughput material explorations for additive manufacturing.

Effects of Mn content on austenite stability and mechanical properties of low Ni alumina-forming austenitic heat-resistant steel: a first-principles study

Low Ni alumina-forming austenitic (AFA) heat-resistant steel is an advanced high-temperature stainless steel with reduced cost, good machinability, high-temperature creep strength, and high-temperature corrosion resistance. Using the First-principles approach, this study examined the effect of Mn content on austenite stability and mechanical properties at the atomic level. Adding Mn to low Ni-AFA steel increases the unit cell volume with an accompanying increase in the absolute value of formation energy; the austenite formed more easily. The austenitic matrix binding energy decreases and remains negative, indicating austenite stability. As the Mn content increases from 3.2 to 12.8 wt%, the system's bulk modulus (B) rises significantly, and the shear modulus (G) falls. In addition, the system's strength and hardness decrease, and the Poisson ratio of the austenite matrix increases with improved elasticity; the system has excellent plasticity with an increase in the B/G. For the Fe22–Cr5–Ni3–Al2 system, with the increase of Mn content, the electron density distribution between the atoms is relatively uniform, and the electrons around the Mn atoms are slightly sparse, which will slightly reduce the structural stability of the matrix. The experiment demonstrated the matrix maintains the austenitic structure when adding 3.2–12.8 wt% Mn elements to low Ni-AFA steel. At an Mn content of 8 wt%, the overall mechanical properties of the high-Mn AFA steel are optimal, with a tensile strength of 581.64 MPa, a hardness of 186.17 HV, and an elongation of 39%.

Yield Strength Enhancement Without Ductility Loss Through Controlling the Intercritical Annealing Time in Medium‐Mn Steels

Herein, the effect of shortening the intercritical annealing (IA) time in a two‐step process “intercritical annealing and tempering (IAT)” on the microstructure and the mechanical properties of medium‐manganese steel (MMnS) made of Fe–0.05C–7Mn–1.5Cu–1.5Ni–1.5Al–1.5Si–0.5Mo (wt%) and containing copper‐rich (CRP) and Ni(Al/Mn) precipitates is investigated. The atom probe tomography (APT), electron backscattering diffraction (EBSD), and the synchrotron X‐ray diffraction (SYXRD) are used to study precipitation, phase microstructure evolution, the austenite stability, and deformation mechanisms. Shortening the IA step, which is carried out at 700 °C, from 2 min (IAT‐2) to 1 min (IAT‐1), results in a yield strength (YS) increment of around 218 MPa with less than 1% loss of ductility. While the enhanced yield strength in IAT‐1 is attributed to the four times higher precipitates’ number density (n), the insignificant loss of ductility is attributed to the enhanced austenite stability factor from 4.5 to 9.2 in IAT‐2 and IAT‐1, respectively. The simultaneous increase in YS without ductility loss reflects that controlling the IA time is a promising strategy to overcome the yield strength and ductility trade‐off without the need for higher additions of costly alloying elements such as Ni, Al, Mn, and Cu.

Microstructure and mechanical properties of medium manganese steel in intercritical annealing

A new type of cold-rolled medium manganese steel was investigated. The test steel was treated by Q&P process. With the increase in annealing temperature, the grain size gradually increases, the carbides dissolve progressively and the fine lath grains transform into massive or equiaxed grains. Both the volume fraction and the stability of the retained austenite are continuously decreasing, which together affect the change of mechanical properties. At the intercritical annealing temperature of 680°C, the specimens have higher retained austenite content and transformation rate. At the same time, due to the discontinuous TRIP effect caused by the retained austenite stability gradient inside the specimen, it exhibits excellent comprehensive mechanical properties, and the product of strength and elongation is 43.5GPa·%.

Effect of tempering and partitioning (T&P) treatment on microstructure and mechanical properties of a low-carbon low-alloy quenched and dynamically partitioned (Q-DP) steel

We performed a direct quenching and dynamical partitioning (Q-DP) process, following intercritical annealing, to a low-carbon low-alloy steel. Performing an additional tempering treatment on the Q-DP steel, we investigated the carbon partitioning behavior upon tempering. We emphatically analyzed the effect of tempering and partitioning (T&P) treatment on the microstructure evolution and mechanical properties of the Q-DP steel, especially on carbon partition, retained austenite stabilization, TRIP effect and work hardening. Results show that the synergetic partition of carbon and Mn from ferrite to austenite during intercritical annealing and the dynamical partition of carbon upon quenching jointly achieve the stabilization of retained austenite in the Q-DP sample. The actual volume fraction of retained austenite is larger than the theoretical calculating value, which is attributed to the dynamical partition of carbon. The T&P treatment at 300 °C for 15 min does not result in obvious decomposition of retained austenite, but leads to apparent carbon partition from martensite to retained austenite. The carbon partition upon tempering enhances the mechanical stability of retained austenite, thus weakening the TRIP effect during tensile deformation and promoting the TRIP effect to occur at higher true strain level. The much higher work hardening rate at the late deformation stage near necking, for the quenched tempered and partitioned (Q-T&P) sample, leads to a higher uniform elongation, compared with the Q-DP sample. The existence of carbon-enriched stable retained austenite after necking happens finally enhances the post necking elongation of the steel.

A New Approach to the Optimization of the Austenite Stability of Metastable Austenitic Stainless Steels

Austenitic steels used for components in high-pressure hydrogen storage systems in the automotive sector have to meet high requirements in terms of material properties and cost efficiency. The commonly used 1.4435/AISI 316L type steels fulfil the technological requirements but are comparatively expensive and resource-intensive. Lower alloyed steel grades are less costly, though prone to α-martensite formation and therefore sensitive to hydrogen embrittlement. Segregation-related fluctuations of the local element concentrations exert a strong impact on the austenite stability, thus controlling the segregation behavior can improve the austenite stability of lean alloyed steel grades, making them suitable for hydrogen applications. In this work, a novel approach for the optimization of alloy compositions with the aim of improving the homogeneity of the austenite stability is developed. The approach is based on combining automated Scheil–Gulliver solidification simulations with a multi-objective optimization algorithm. The solidification simulations provide information about the influence of the segregation profiles on the local austenite stability, which are then used to optimize the alloy composition automatically. The approach is exemplarily used for an optimization within the compositional range of 1.4307/AISI 304L. It is shown that a significant increase in the homogeneity of the austenite stability can be achieved solely by adjusting the global element concentrations, which has been validated experimentally.Graphical

Mechanistic role of Mn heterogeneity in austenite decomposition and stabilization in a commercial quenching and partitioning steel

Manipulating chemical heterogeneity, which could substantially alter austenite decomposition behavior upon cooling, has recently proven to be very effective in tailoring retained austenite and architecting novel microstructures in steels. However, the mechanistic role of chemical heterogeneity in austenite decomposition and stabilization has not been fully understood, and its potential in microstructural architecting in commercial advanced high strength steels (AHSSs) has not been explored. In this study, we investigate the potential effects of Mn heterogeneity, which originates from the starting microstructure of Mn-lean ferrite and Mn-rich cementite, on austenite decomposition and stabilization in a commercial Quenching and Partitioning (Q&P980) steel. It is interestingly found that there is a strong kinetic interaction between the Mn enriched region in austenite and the migrating austenite/ferrite interface upon cooling, and phase field model predicts that the austenite/ferrite interface could migrate through the Mn-rich region via either a cutting through or by-passing manner, depending on the absolute Mn content of the Mn-rich region and the degree of Mn heterogeneity. The by-passing interaction could substantially promote C partitioning into the Mn-rich region, which further enhances the region's stability. The current study demonstrates austenite decomposition and C partitioning behavior can even be altered by a weak Mn heterogeneity, which needs to be carefully considered in the future design of AHSSs.

Microstructure evolution and tensile behaviors of dissimilar TLP joint of austenitic steel and high-Cr ferritic steel

In this study, austenitic steel and high-Cr ferritic steel were joined by transient liquid phase (TLP) bonding technique with a Fe–Si–B amorphous interlayer. The effects of bonding time (10–60 min) on joints microstructure evolution and tensile behaviors were investigated. On the high-Cr ferritic steel side of the prepared dissimilar TLP joint, Cr2B particles are precipitated at diffusion affected zone (DAZ-α, the α denotes ferrite) and dissolve subsequently when the bonding time is extended to 30 min. In contrast, Cr2B particles are precipitated at the grain boundaries of DAZ-γ (the γ denotes austenite) on the TP347H steel side, which has an apparent orientation relationship with the base metal (BM). Furthermore, when Ni and Cr atoms diffuse from DAZ-γ to isothermal solidification zone (ISZ), a martensitic layer develops at the ISZ/DAZ-γ interface and widens as bonding time increases. Because DAZ-γ is a Ni/Cr-depleted zone with lower austenite stability, deformation-induced martensite forms in DAZ-γ during tensile testing. The in-situ tensile test results and digital image correlation analysis show that strain localization gradually transfers from the interface to the BM-γ during the deformation process, causing the specimen to fracture within TP347H matrix after tensile tests, indicating that TLP bonding achieves sufficient metallurgical bonding. Furthermore, with the extension of bonding time, the grain size of BM-γ decreases first and then increases, which leads to the similar change of the total elongation and the opposite change of the ultimate strength of the joint.

Effect of Mn Content on the Toughness and Plasticity of Hot-Rolled High-Carbon Medium Manganese Steel

The tensile and impact deformation behavior of three different Mn content test steels, xMn-1.0C-0.25V-1.5Cr-0.3Mo (5, 8 and 13 wt%), were investigated using mechanical properties testing, SEM-EBSD and TEM. The elongation and -20 °C impact energy of the three types of Mn content test steels increased as the Mn content increased. The room temperature tensile elongation was 9%, 23% and 81%, and the -20 °C impact energy was 9 J, 99 J and 241 J, respectively. The fracture morphologies of 5 Mn and 8 Mn were found to be cleavage fractures with secondary cracks and micro-voids. The 13 Mn fracture morphology was a plastic fracture with many coarse dimples. Transverse cracks perpendicular to the tensile direction occurred on the surface of the gauge area of 5 Mn and 8 Mn tensile specimens, reducing plasticity dramatically. This was mainly related to the martensitic transformation produced by stress. We characterized the martensite near the tensile fracture and speculated the main mode of crack propagation. Furthermore, a little amount of sharp-shaped BCC phase was found in the 5 Mn, which was determined to be a hard phase relative to the austenite matrix by nanoindentation test. These steels have stacking fault energies ranging from ~15 to ~29 mJ/m2 with increasing Mn content 13 Mn has high stacking fault energy (SFE) and austenite stability. Twin-induced plasticity (TWIP) was the deformation mechanism.

Microstructure and properties of X100 large-deformability pipeline steel based on heating on-line partitioning

It is often assumed that high strength and good plasticity cannot be obtained at the same time. However, a kind of X100 pipeline steel with a multiphase structure of bainite and fine M/A constituent has not only high strength and toughness but also excellent plasticity. In this paper, Heating on-line partitioning (HOP) was performed on a type of X100 pipeline steel to achieve the multiphase structure. Carbon atoms diffuse from bainite to austenite during the HOP process, improving the stability of austenite and increasing the volume fraction of retained austenite. Meanwhile, bainite laths widen and dislocation density drops, increasing the plasticity. On the other hand, carbides precipitation and the formation of martensite provide the steel with high strength.