Dislocation Strengthening Effect Research Articles

Analysis of abrasive impact wear of the Mn8/SS400 bimetal composite using a newly designed wear testing rig

In this study, the abrasive impact wear behaviour of a bimetal composite made of medium manganese steels (MMSs) and low carbon steels (LCSs), i.e., the Mn8/SS400 bimetal composite, was investigated using a newly designed wear-testing rig. The need for a new rig arose from the difficulty in replicating real-world wear conditions. Our rig allows for precise control and measurement of wear, simulating harsh environments more accurately than other wear-testing rigs. The bimetal composite Mn8/SS400 demonstrated superior wear resistance, showing an improvement of up to 2.8 times compared to benchmark steels, attributed to its enhanced work hardening sensitivity. Scanning electron microscopy (SEM), X-ray diffractometer (XRD), and electron backscatter diffraction (EBSD) analyses were employed to elucidate the wear mechanisms. After 300 h of abrasive impact wear, the subsurface microhardness of Mn8 reached 601.31 HV, significantly higher than that of the matrix hardness of 292.24 HV, indicating a substantial work hardening effect. The wear mechanism of the Mn8/SS400 bimetal composite was found to be a synergistic effect of grain refinement strengthening, dislocation strengthening, and twin strengthening. Initially, twin strengthening was the dominant mechanism up to 200 h of wear testing. However, after 300 h, contributions from all three mechanisms became increasingly significant, enhancing the overall wear resistance of the composite.

Microstructure, aging behavior, and friction and wear properties of ultrafine-grained 7050 aluminum alloy produced by cryogenic temperature extrusion machining

Cryogenic temperature extrusion machining (CT-EM), as a novel cryogenic temperature severe plastic deformation (CT-SPD) process, is an effective method to produce ultrafine-grained (UFG) materials. In this paper, the microstructure, microhardness, friction and wear properties of the UFG chips prepared by CT-EM and room temperature extrusion machining (RT-EM) were analyzed. The results show that CT-EM has a better grain refinement effect. The grain size of the CT-EM samples is smaller, the dislocation density is larger, and the microhardness is higher. After aging treatment, a large number of small secondary precipitates (η '/η) appear in the microstructure of the samples, which further improves the microhardness. This is the result of a synergistic effect of fine grain, dislocation, and precipitation strengthening. Cryogenic treatment can increase the precipitation kinetics of the secondary phase and shorten the time for the samples to reach peak hardness. The CT-EM samples have a lower friction coefficient and wear mass. With the increase of the machining velocity, the wear mechanism of the samples changes from abrasion wear to oxidation, adhesion, and fatigue wear.

Microstructure evolution, mechanical response, and corrosion resistance for a 2195 Al-Li alloy under different rolling reductions during cryorolling

This study used cryorolling (CR) and room temperature rolling (RTR) with different rolling reductions to process the 2195 aluminum-lithium alloy (Al-Li alloy, AA2195) sheets. Subsequently, the AA2195 sheets were artificially aged to the peak aging stage. Their mechanical properties, corrosion resistance, and microstructural evolution sheets were investigated using methods such as hardness testing, tensile testing, intergranular corrosion (IGC) experiments, electrochemical experiments, transmission electron microscopy (TEM), and electron probe microanalysis (EPMA). Compared to the RTR samples, the CR samples exhibited higher hardness, ultimate tensile strength, and elongation under the same rolling reduction conditions due to the combined effect of dislocation strengthening, grain boundary strengthening, and precipitation strengthening. The corrosion resistance of the RTR samples showed a declining trend with the increased rolling reduction. However, the corrosion potential of the CR samples exhibited a non-monotonic trend, first increasing and then decreasing, with the increased rolling reduction. The CR and RTR samples had similar microstructural evolution trends, leading to predominantly IGC morphologies in the IGC tests. The RTR and CR samples exhibited partial pitting morphologies at 70% rolling reduction, and the CR samples had more pronounced pitting characteristics than the RTR samples.

Enhancing wear resistance of laser-clad AlCoCrFeNi high-entropy alloy via ultrasonic surface rolling extrusion

The AlCoCrFeNi high-entropy alloy (HEA) coating was synthesized by laser cladding and subsequently processed by ultrasonic surface rolling extrusion (USRE) with varying static loads of 100 N, 200 N, and 300 N. This study aimed to explore the effects of static load on the microstructure, mechanical properties, and tribological characteristics of the coatings. The findings indicate that increased static load results in the precipitation of martensitic phases, grain refinement, enhanced microhardness, and an elevated dislocation density. Specifically, after USRE with 300 N static load, the coating's microhardness reaches 753 HV, 1.4 times greater than the un-USRE coating. This enhancement is attributed to the synergistic effect of martensite phase transformation, grain refinement, and dislocation strengthening. The volume wear rate of the coating decreases to 1.31 × 10−4 mm3·N−1·m−1 following USRE at 300 N, demonstrating superior resistance to abrasive wear due to the high microhardness. Besides, the high-density dislocations facilitate rapid migration and diffusion of oxygen elements, thereby enhancing the oxide layer's protective properties and improving the coating's resistance to oxidation wear.

In-situ monitoring of additive friction stir deposition of AA6061: Effect of rotation speed on the microstructure and mechanical properties

The AA6061 alloy depositions fabricated under three rotation speeds (Ω, 450, 500 and 550 rpm) are obtained by the additive friction stir deposition (AFSD) technique in this study. The real-time temperature, force and torque during the AFSD process were monitored by a self-developed process-aware kit, helping to thoroughly investigate the influence of Ω on the microstructure and mechanical properties of the depositions. Combined with the results of the electron back scattered diffraction (EBSD) analysis on a large area (4 × 4 mm2), it is found that the grain size increases with the increase of Ω due to high heat generation. The proportion of deformation texture components reduces because of the lower strain distribution as well as the slight deformation behavior. A higher average micro-hardness is found on the 550 rpm-deposition because of the dislocation strengthening effect. Furthermore, the values of yield strength (87.8 MPa) and ultimate tensile strength (147.2 MPa) of the depositions are the highest when the Ω is the lowest (450 rpm), owing to the lowest thermal cycle. All the results are intended to provide useful guidance and a theoretical basis for producing high-performance Al-based alloys through AFSD.

Nanocrystallization and strengthening of Mg-Dy-Zr alloys by room temperature rotary swaging

In this study, bulk Mg-Dy-Zr alloys with an average grain size of 78.8 nm and a diameter of 12.1 mm were prepared by room temperature rotary swaging (RTRS). The evolution of the microstructure and texture during the grain refinement process was investigated using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results show that the original texture consisting of arbitrarily oriented recrystallized grains and ED∥[10 1‾ 0] deformed grains is transformed into an ED∥[10 1‾ 0] texture after the alloy processed by RTRS. The formation of nanograins is induced by a large number of tensile twins, deformation bands, and dislocation arrays synergistically adapting to the strain. The yield strength and ultimate tensile strength of the nanograin alloys obtained are substantially increased to 281% and 190% of those of the as-extruded alloys. The strength improvement of the alloys is a result of the combined effect of grain refinement and dislocation strengthening, in which nanograin strengthening dominates.

Hybrid interlayer hot rolling and wire arc additive manufacturing of Al-Mg alloy: Microstructure, mechanical properties and strengthening mechanism

Considering the deformation-strengthening benefits of Al-Mg alloy and the high forming efficiency offered by wire and arc additive manufacturing (WAAM), the microstructure evolution and strengthening mechanism of hybrid interlayer hot rolling and wire arc additive manufacturing (HR-WAAM) samples have been systematically investigated in this study. The results indicate that interlayer hot rolling can effectively reduce the size and number of pores, which diminishes the stress concentration areas. Additionally, rolling deformation significantly enhances the effect of dislocation strengthening. Furthermore, a high density of dislocations can promote recrystallization to refine grain size, while also improving grain orientation, all of which contribute to better stress distribution. Due to these reasons, the strength and toughness of the alloy are notably improved. The average ultimate tensile strength (UTS), yield strength (YS), and elongation (EL) values achieved by HR-WAAM samples were 338 MPa, 276 MPa, and 20.9%, respectively. These values represent increases of 28.5%, 41.5%, and 38.4% compared to conventional WAAM samples. These findings are expected to provide an efficient and cost-effective method for additive manufacturing (AM) of deformation-strengthened aluminum alloys.

Investigation on microstructural evolution and strengthening mechanism in Zr-2.5Nb alloy with multi-scale lamellar structure

Zr-2.5Nb alloy was subjected to a solid solution treatment at 900 °C for 30 min, followed by aging between 500 and 700 °C for 60 min. It was found that there were two distinct martensitic microstructures after the solid solution treatment: nano-twins and dislocation lamellar structures. As the aging temperature increased, the α’ martensite lath gradually decomposed, which was mainly manifested in the precipitation of the β-Zr phase, annihilation of nano-twins, and reduction of dislocation density. EBSD experiments revealed that the precipitated phase formed during aging treatment shared its (101) plane with the (011¯1) plane of nano-twins. The precipitation of the β-Zr phase along the twinning plane resulted in twin shrinkage and gradual decomposition. The yield strength of the Zr-2.5Nb alloy initially increased and then decreased with an increase in aging temperature. It is worth noting that the sample aged at 600 °C exhibited excellent strong plasticity matching, which can be attributed to the combined effect of dislocation strengthening, grain boundary/twin boundary strengthening, solid solution strengthening, and precipitation strengthening.

Insights into microstructure evolution and fracture mechanisms of welded joints of high strength steel patchwork components

The hot roll bending patchwork components of B1500HS uncoated ultra-high strength steel processed at industrial scale were welded with filler wire. The microstructure, grain orientation, mechanical properties and fracture behavior of the joint were investigated. The results showed that the weld metal (WM) was mainly composed of lath martensite and lower bainite (LB). Various microstructure appeared in different positions of the HAZ, among which martensite-austenite (M-A) constituents in the incompletely quenched zone and tempered martensite (TM) in the tempered zone were the key factors determining the performance of the joint. The welded joint exhibited complex structure and anisotropic mechanical response due to the decarburization and rolling texture of the original base material (BM). In the tempered zone, lath merge and boundaries disappear lead to the annihilation of dislocations, carbide precipitation leads to reduction of mobile dislocations, and recrystallization and recovery eliminate work hardening. The reduction of the effect of dislocation strengthening results in the formation of a softening belt at 6 mm from the center of the weld, with a minimum hardness of 266 HV. The tensile strength of the joint in the rolling direction (RD) was 983 MPa, and the fracture occurred in the softening belt. Both brittle and ductile fracture features were observed. The reason why the fracture occurs in the high temperature tempered zone instead of the incompletely quenched zone was the difference in the effect of “constraint strengthening”. Fracture occurred through delamination cracking along the “weak interface” owing to precipitated high-hardness cementite particles and the unfavorably oriented ferrite cleavage planes.

Effect of continuous dynamic-recrystallisation on high-property multilayer Cu foils joint by friction-stir-welding

In this experiment, friction-stir-welding was proposed to research the flexible connection of multilayer Cu foils. It studies the correlation between hardness, conductivity, and continuous dynamic-recrystallisation. New grains of continuous dynamic-recrystallisation have a correlation between the dislocation density and the grain size, such that a lower dislocation density corresponds to a higher grain size and vice versa. It is shown that after friction-stir-welding of multilayer Cu foils, the hardness increases and the conductivity decreases due to the combined effect of fine grain strengthening and dislocation strengthening for new grains of continuous dynamic-recrystallisation of the weld zone. However, the hardness gradually decreases and conductivity gradually increases within the weld zone with continuous dynamic-recrystallisation degree.

Pre-precipitating promoted by microshear bands effectively circumvents strength-ductility trade-off of RT-rolled Al–6Zn–1Mg alloy

The aging precipitated phases are of great significance for the strengthening and toughening of Al–Zn–Mg alloys. In this work, pre-precipitating was realized through equal channel angular pressing (ECAP) immediately followed by solid solution treatment at 475 °C for 6 h. Its corresponding strengthening and toughening effect on the room temperature (RT)-rolled Al–6Zn–1Mg alloy was systematically studied. The results indicate that pre-precipitating by ECAP can effectively improve the strength of the RT-rolled Al–6Zn–1Mg alloy and circumvent the strength-ductility trade-off. Microstructure characterization reveals that ECAP induces a large number of microshear bands, which can not only encourage recrystallization but also effectively promote the precipitation of the η′ phase. The synergistic effect of precipitation strengthening and dislocation strengthening contributes to the high strength of Al–6Zn–1Mg alloy, with UTS and YS increasing to ∼522 MPa and ∼400 MPa, respectively. Meanwhile, the ductility remains almost unchanged mainly due to the coordinated grain boundary sliding and the uniform and finely dispersed second phase particles. As a result, the strength-ductility trade-off is effectively avoided. The findings shed some light on optimizing the traditional aging treatment.

Stimulating adequate strengthening effect through alloying regulation for powder metallurgy CNTs reinforced aluminum matrix composites

Carbon nanotubes (CNTs) reinforced aluminum matrix composites (AMCs) have light weight and high specific strength, showing great potentials for making key structural components in aerospace and transportation industries. Aiming to address the bottleneck problem of unsatisfactory strengthening effect caused by the weak intrinsic interface and adverse interface reaction between CNTs and Al matrix, Si alloying element was added into Al-CNTs system via powder metallurgy method in this study. It was found that the introduction of Si element led to an inhibitory effect on Al-CNTs interface reaction. The discontinuous Al/Si/CNTs composite interface formed by the precipitation of Si significantly improved the wettability of Al/CNTs interface and enhanced its interface bonding through the pinning effect of Si particles, effectively promoting the full play of the load-bearing effect of CNTs. Furthermore, Si particles were effectively refined and passivated through appropriate heat treatment, which facilitated its dispersion strengthening and dislocation strengthening effect, and significantly reduced cracks of coarse Si particles. As a result, the synergistic strengthening effect of CNTs and micro-nano Si particles was significantly exerted in AMCs, remarkably improving the performance of Al–Si-CNTs composites.

High-density dislocation and ductile precipitate synergistically reinforced TiAl/Ni-based superalloy joint using novel multi-principal element interlayer

An extremely high-strength TiAl/Ni-based superalloy dissimilar joint was obtained using a designed Ni25Zr25Sn20Cu10Hf10Cr5Fe5 multi-principal element interlayer via contact reaction brazing. It was found that a joint mainly composed of eutectic structure of (Ni)ss, (Ni, Cr, Fe)ss, and (Cr, Ni, Fe, Mo)ss, as well as micro-nano precipitates of (Ti)ss and (Hf, Zr)ss, could be achieved through the interaction between the interlayer and the base metals. The joint exhibited a shear strength of 498 MPa when brazed at 1190 °C for 10 min, while the fracture occurred within the TiAl base metal, and the retention rate of high-temperature (HT) strength (650 °C) was ∼100%. The strengthening mechanism of the brazed joint was systematically discussed by transmission electron microscopy (TEM). It was shown that high-density dislocations existed in each phase of the seam as well as twinning and stacking faults existed in the micro-nano precipitates, caused by a mass of solute atoms, greatly strengthened the joint. At HTs, the dislocation strengthening effect weakened due to grain recovery and recrystallization, but the joint could be additionally toughened by multi-cracking. Meanwhile, granular (Ti)ss dispersed through the seam and ductile reticular structure (Ni)ss toughened the joint via the mechanism of crack termination and bridging. The proposed method provides a new approach for high strength and heat resistance joining of TiAl/Ni-based superalloy in aeroengine components.

Microstructure and mechanical properties of Inconel 718 thin walls prepared by laser direct energy deposition and selective laser melting

This paper systematically investigates the microstructure, crystal structure and related mechanical properties of Inconel 718 thin walls prepared by two different methods, laser direct energy deposition (LDED) and selective laser melting (SLM), which are representative technologies for laser additive manufacturing of high-performance metal parts, and compares with conventional forged parts. The microstructure of SLM-part consists of columnar and equiaxed crystals with disordered growth directions, while LDED-part is mainly composed of coarse columnar crystals that grow perpendicular to the plane of the molten pool free surface. Unlike a strong 〈001〉 texture in the LDED-part, the SLM-part has a {110} texture in the XY plane, achieving stronger tensile strength due to different grain boundary strengthening and dislocation strengthening effects, which is found by comparing with LDED and forged Inconel 718 alloy. In addition, the difference in crystallographic texture between SLM and LDED-parts results in the different mechanical property anisotropy. The comparative study of two laser additive manufacturing technologies provides guidance for an in-depth understanding about the mechanism of laser additive manufacturing high-performance metal parts.

Chemistry and microstructure of duplex stainless steel powders from recycled Z100 mixed with 316L steels

Recovered metallic waste can be used in additive manufacturing as a feedstock if the subsequent steps of the waste-to-product process are sufficiently mastered. In this study, impact of recycling of Z100 duplex steel mixed with 316L steel on the resulting powders microstructure and chemical composition was investigated. The utility of the original method of recycling stainless steels into a high-grade powder suitable for additive techniques has been demonstrated. By examining three gradations of powders, namely 20–50 μm, 50–100 μm and 125–250 μm, differences in selected properties in relation to the average particle size are shown. The results suggest that with increasing the particle diameter, fine-crystalline γ-austenite is favoured to precipitate at the boundaries and within the volume of the originally formed large δ-ferrite grains. It is reflected by a decrease of δ/γ fraction ratio from 0.64 in the 20–50 μm powders to 0.20 in the 125–250 μm, respectively. Obtained results indicate non-diffusional, shear or semi-shear character of δ → γ + δ phase transformation. The resulting fine-crystalline austenite is characterised by a significant dislocation density, which induces dislocation strengthening effect, responsible for an increase in Vickers hardness from 145 HV and Young's modulus from 29 GPa in the 20–50 μm group to 310 HV and 146 GPa in the 125–250 μm fraction, respectively.

Microstructure and mechanical properties of superficial surface and subsurface layers in the cutting of hardened steel under cryogenic cooling

Hardened steel parts extensively utilized in manufacturing fields, including automobiles and molds, are difficult to cut and process. Cryogenic cooling is an effective method for reducing tool wear and improving surface quality. However, knowledge about the microstructure and mechanical properties of the hardened steel cutting under a cryogenic cooling condition is severely limited. Herein, low-speed and high-speed cutting experiments with different wear tools were designed to investigate the characteristics and mechanisms of the microstructure, residual stress distribution, and hardness distribution of the superficial surface layer (SSL, including the white and transition layers) and subsurface layer (SL) of hardened steel cutting via cryogenic cooling. Results showed that microstructure changes caused by plastic deformation occurred in both the white and transition layers, whereas no changes occurred in the area below the transition layer. No phase transformation and recrystallization occurred in the white layer, the transition layer, and the area below the transition layer. The intense dislocation slip and strong plastic deformation are the keys to the formation of the white and transition layers. The hardness distribution curve included the surface hardening peak, SL softening valley, and SL hardening peak. The combined effect of fine grain strengthening and dislocation strengthening is the primary mechanism for forming the surface hardening peak. The peak residual tensile stress induces a SL softening valley in the hardness curve, whereas the peak residual compressive stress induces a SL hardening peak in the hardness curve.

Simultaneous regulation of strength and ductility of laser powder bed fusion manufactured Haynes 230 alloy

Haynes 230 alloy is widely used in aero-engines with high strength, fatigue resistance, oxidation resistance and other properties. However, the powder metallurgy process limits its application due to hot cracks and low strength. In this work, crack inhibition and mechanical properties improvement of the laser powder bed fusion (L-PBF) manufactured Haynes 230 alloy using 25 groups of different laser energy densities and scanning strategies were investigated. Results show that the high density, nearly crack-free, fine microstructure, and excellent strength and ductility were achieved by a laser energy density of 59.4 J/mm3 and rotation angle of 90° for the L-PBF manufactured Haynes 230 alloy. The microstructure was composed of γ matrix, carbides (M6C, M23C6), and La2O3 nanoparticles. Interestingly, many carbides were found to be mainly uniformly distributed at the grain or sub-grain boundaries with the following orientation relation: [011]γ//[011]M23C6. Simultaneously, by adjusting laser energy density and scanning strategy, the liquid film, low-melting eutectic phase, hot stress concentration, and high-angle grain boundaries (HAGBs) were suppressed, and the hot cracks were reduced. In addition, yield strength and ultimate tensile strength enhancement of the L-PBF manufactured Haynes 230 alloy was attributed to the synergistic effect of solid solution strengthening, dislocation strengthening, Orowan strengthening, and grain refinement. Whereas ductility enhancement was the main effect of defect inhibition, grain refinement, and nanoprecipitate. This work has verified the feasibility of crack inhibition and mechanical properties improvement of the L-PBF manufactured Haynes 230 alloy by various laser energy densities and scanning strategies.

Effect of vanadium microalloying on phase transformation and strengthening mechanism of 1000 MPa low carbon bainitic steel

To develop an ultrahigh-strength hot-rolled strip, the yield strength of low-carbon bainitic steel was increased from 804 to 1074 MPa via V microalloying. The effects of V microalloying on the microstructure and mechanical properties of the alloys are discussed in detail. The microstructures of the test steel containing 0.2 wt % V element is finer, and the Degenerate Upper Lath Bainite (DUB) is replaced by Lower Lath Bainite (LLB). This was clearly due to the addition of V, which promoted the formation of LLB. In this study, the effect of V dissolved in the matrix on the phase transformation kinetics was investigated. This is because it is difficult for V to precipitate during quenching and non-isothermal partitioning (QNP) processes, and it mainly exists in the matrix in the form of a solid solution. The main effect of V is to reduce the activation energy Q* of bainite by 1.76 kJ/mol, increase the nucleation rate of lath bainite, and further refine the bainitic lath. However, a high dislocation density exists in the bainite laths, and the comprehensive strengthening effect of lath strengthening and dislocation strengthening can explain the change in the mechanical properties of the 0.2V steel.

Revealing hot deformation behavior of Ti2C-Ti composite and associated dynamic recrystallization mechanism of ceramic matrix

Titanium carbide based composites have attracted much attention owing to their light weight, high elastic modulus, and excellent wear resistance. However, the hot working of these composites has been facing great challenges, especially for the coordinated deformation of brittle phase. Here, soft Ti phase was introduced to improve the thermal deformation ability. In particular, the dynamic recrystallization (DRX) mechanism, crack propagation, and dislocation motion behavior of brittle Ti2C matrix were unveiled in this study. Firstly, a Ti2C-Ti composite was hot compressed at 770–1000 °C with strain rates of 0.012–0.0013 s−1. The results showed that the optimal processing temperature was 950 °C, at which the microstructure can be refined by DRX behavior without the occurrence of macro instability. In the later softening stage of hot compression, the recrystallized Ti2C grains were formed through both discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX). The intergranular Ti phase, which acts as a binder, coordinated the deformation of the Ti2C-Ti composite, and the phase boundaries attracted dislocations on the side of the brittle Ti2C phase. This dislocation motion behavior mitigated stress concentration but inhibited the DRX behavior of the Ti2C phase near the binary phase interfaces. The lamellar Ti precipitates within Ti2C grains facilitated the occurrence of CDRX by promoting the formation of subgrains. The subgrain boundaries were formed when the average distance between dislocation on the dislocation wall was lower than 8.68 nm. Compared with the as-sintered composite, the nanohardness of the Ti2C matrix in the composite deformed at 950 °C increased by 17%. The enhanced hardness was mainly attributed to grain boundary and dislocation strengthening effect, as well as the reduction of Ti precipitates.

Microstructural evolution and mechanical properties of 60Si2CrVNb spring steel under quenching-tempering heat treatment process

This study investigated the evolution of microstructure and mechanical properties of 60Si2CrVNb spring steel under different quenching and tempering processes. The morphology of martensite, precipitate phases, and carbides, as well as the analysis of mechanical properties, were examined. The results revealed that the highest ultimate tensile strength (2260 MPa) and yield strength (2091 MPa) of 60Si2CrVNb spring steel were achieved through austenitization at 900 °C and subsequent tempering at 350 °C, which is related to the maximum dislocation strengthening effect. The optimal combination of mechanical properties for 60Si2CrVNb spring steel was obtained by quenching at 900 °C for 30 min and tempering at 400 °C for 90 min. Under these conditions, the steel exhibited an ultimate tensile strength of 2084 MPa, yield strength of 1846 MPa, elongation of 10.8%, and area reduction of 41.5%. Increasing the quenching temperature resulted in the gradual dissolution of undissolved carbides, an increase in the average grain size of austenite, coarsening of martensite, and an initial increase and subsequent decrease in tensile strength and plasticity. Furthermore, the fracture type transformed from ductile fracture to mixed fracture of ductile and brittle. On the other hand, the increasing tempering temperature led to a decrease in dislocation density and gradual decomposition of martensite lath boundaries. Additionally, the type of carbides changed from small-sized M2C and MC carbides to large-sized M3C, M7C3, and M23C6 carbides. As a result, the tensile strength of the steel decreased significantly, while its plasticity steadily increased. Moreover, the fracture behavior transformed from brittle fracture to ductile fracture.