Showing papers on "Tempering published in 2021"

Additive manufacturing of steels: a review of achievements and challenges

Abstract: Metal additive manufacturing (AM), also known as 3D printing, is a disruptive manufacturing technology in which complex engineering parts are produced in a layer-by-layer manner, using a high-energy heating source and powder, wire or sheet as feeding material. The current paper aims to review the achievements in AM of steels in its ability to obtain superior properties that cannot be achieved through conventional manufacturing routes, thanks to the unique microstructural evolution in AM. The challenges that AM encounters are also reviewed, and suggestions for overcoming these challenges are provided if applicable. We focus on laser powder bed fusion and directed energy deposition as these two methods are currently the most common AM methods to process steels. The main foci are on austenitic stainless steels and maraging/precipitation-hardened (PH) steels, the two so far most widely used classes of steels in AM, before summarising the state-of-the-art of AM of other classes of steels. Our comprehensive review highlights that a wide range of steels can be processed by AM. The unique microstructural features including hierarchical (sub)grains and fine precipitates induced by AM result in enhancements of strength, wear resistance and corrosion resistance of AM steels when compared to their conventional counterparts. Achieving an acceptable ductility and fatigue performance remains a challenge in AM steels. AM also acts as an intrinsic heat treatment, triggering ‘in situ’ phase transformations including tempering and other precipitation phenomena in different grades of steels such as PH steels and tool steels. A thorough discussion of the performance of AM steels as a function of these unique microstructural features is presented in this review.

Effect of solution annealing and precipitation hardening at 250 °C–550 °C on microstructure and mechanical properties of additively manufactured 1.2709 maraging steel

Abstract: Post-processing heat treatment of additively manufactured (AM) maraging steel is an important issue in the tailoring of the final mechanical properties of a product. Up to now, mainly precipitation hardening at temperatures of 450 °C–500 °C has been studied either in as-built or solution-annealed samples. This work, however, presents an overview of the effect of much broader tempering temperatures of 250 °C–550 °C on the microstructure and mechanical properties of as-built maraging steel. Furthermore, the effect of previous solution annealing of AM steel at a lower temperature of 820 °C and at a higher temperature of 940 °C on subsequent precipitation hardening is also described. The results obtained for the precipitation behaviour of AM maraging steel are compared with those of conventionally produced maraging steel. The microstructure and mechanical properties of AM samples pre-annealed at 940 °C and precipitation hardened were found to be comparable to the conventionally processed reference sample at all hardening temperatures. On the other hand, the microstructures and properties of AM samples pre-annealed at 820 °C and precipitation hardened strongly resembled the results of as-built samples. However, even after a 6-h hold at the highest tempering temperature of 550 °C, distinct differences could still be found in the samples prepared with various initial conditions.

Impact of steel type, composition and heat treatment parameters on effectiveness of deep cryogenic treatment

Abstract: In recent years, promising technique of deep cryogenic treatment (DCT) is taking a new step in improving properties of various materials, especially steels. This study is focusing on influence of selected heat treatment process involving deep cryogenic treatment on the microstructure and microstructural evolution of four different steel grades (bearing steel 100Cr6, cold work tool steel X210Cr12, hot work tool steel X38CrMoV5-3 and stainless steel X17CrNi16-2). The study was performed for different heat treatment conditions, focused on effectiveness of DCT when using different austenitizing and tempering temperatures. The evolution of the microstructure was investigated in a sequential manner with various analytical techniques. The study indicates that the microstructure and microstructural evolution and changes are strongly related to the chemical composition of steel and the predefined matrix microstructure. DCT increases precipitation of carbides and induce their more homogenous distribution. The magnitude of increased carbide precipitation after DCT is correlated with the higher carbon content, whereas the content of other alloying elements does not scale with the precipitation behavior. The obtained results indicate that incorporation of DCT with heat treatment with higher austenitizing and lower tempering temperature is the most suitable for improving steels’ properties with DCT, due to the stronger impact of DCT on the carbide precipitation and matrix modification.

The Role of HAZ Softening on Cross-Tension Mechanical Performance of Martensitic Advanced High Strength Steel Resistance Spot Welds

Abstract: Giga-grade martensitic advanced high-strength steels are prone to sub-critical heat-affected zone (SCHAZ) softening during resistance spot welding. The article aims at understanding the role of HAZ softening on the fracture mode, load-bearing capacity, and energy absorption capability of MS1400 resistance spot welds during the cross-tension test. The highest load-bearing capacity was obtained when pullout failure was initiated from the martensitic coarse-grained HAZ. However, more severe HAZ softening and formation of a wider softened zone, promoted at high heat input conditions, encourages strain localization in SCHAZ, promoting transition in failure location to sub-critical HAZ. This change in pullout failure location is responsible for the observed reduction in the weld peak load at high welding currents. Therefore, control of martensite tempering in the HAZ is critical to obtain strong and reliable resistance spot welds in martensitic advanced high-strength steel sheets. To preclude the detrimental effect of the martensite tempering on the weld strength, the minimum welding current, which enables pullout failure mode, should be used for resistance spot welding of MS1400 advanced martensitic steel.

Improving strength and ductility of low activation martensitic (LAM) steel by alloying with titanium and tempering

Abstract: In sequel to our previous study (Mater. Sci. Eng. A, 769 (2020) 138,471), we elucidate here the determining role of alloying with Ti and tempering effect on tensile and creep properties in low activation martensitic steel (LAM) and compare with the coarse-grained (CG) LAM steel. When the tempering temperature was decreased from 760 °C to 730 °C, while maintaining time constant at 30 min, grain size and MX carbide density was constant at ~7.0 ± 0.5 μm and (8.20 ± 0.05) × 1024 m−3 in 0.1 Ti LAM steels, compared to ~20.0 ± 0.5 μm and (3.20 ± 0.05) × 1024 m−3 in Ti-free CG LAM steel. However, the thickness of martensitic lath decreased from 450 ± 10 nm to 370 ± 10 nm and the density of M23C6 carbides increased from (4.30 ± 0.05) × 1019 m−3 to (1.10 ± 0.05) × 1020 m−3, which were 320 ± 10 nm and (6.05 ± 0.05) × 1019 m−3 in CG LAM steel. Yield strength (σy) increased with the decrease of tempering temperature. At room temperature, σy of 0.1 Ti LAM steels increased from 660 ± 10 MPa to 700 ± 10 MPa, accompanied by no apparent decrease in elongation (25 ± 1% to 24 ± 1%). In CG LAM steel, σy was 570 MPa and elongation was 23%. Creep life at 600 °C/170 MPa increased from 145 ± 5 h to 190 ± 5 h with the decrease of tempering temperature from 760 °C to 730 °C, while it was 120 h for CG LAM steel. Furthermore, σy increased with the decrease of subgrain size and the increase of M23C6 density. At 600 °C/170 MPa, the coarsening of martensitic lath and the decrease of M23C6 carbide density reduced the strength, leading to crack initiation in the vicinity of large M23C6 carbides and fracture. The mechanisms involving differences in the mechanical behavior are discussed.

Optimization of postweld tempering pulse parameters for maximum load bearing and failure energy absorption in dual phase (DP590) steel resistance spot welds

Abstract: Resistance spot welds of dual phase (DP) steels are prone to low fracture toughness due to the formation of brittle martensitic structure in the fusion zone (FZ). In-process tempering of martensite via applying second pulse current is considered a new pathway to improve mechanical performance of the welds. The success of in-process tempering depends upon precise controlling the amount of heat input and uniform temperature distribution which in turn influenced by postweld tempering pulse parameters. This paper aims to investigate the effect of three postweld tempering pulse parameters such as welding current, welding time and cooling time applied after main pulse current on microstructure and mechanical properties of DP590 steel resistance spot weld. Mechanical properties in terms of peak load and failure energy were determined after performing cross tension (CT) test. Taguchi quality design based on L16 orthogonal array has been used to determine the optimum conditions for maximum peak load and failure energy. Moreover, microstructure-property relationship is also studied. The results show that at optimum conditions maximum improvement of 62% in peak load and 62.3% in failure energy is achieved in double pulse welds compared with conventional single pulse weld. It was found that improvement in peak load and failure energy resulted from (i) enhanced weld nugget size (WNS) and (ii) tempering of martensite in FZ and heat affected zone (HAZ). These factors are influenced by heat input (Q) during postweld heating cycle (PWHC) which in turn increased with increasing second pulse current and time.

Austenite reversion through subzero transformation and tempering of a boron-doped strong and ductile medium-Mn lightweight steel

Abstract: Effects of subzero treatment and B doping on austenite reversion are investigated in quenched and tempered Fe–9Mn–5Al-0.3C and Fe–9Mn–5Al-0.3C-0.005B (wt.%) lightweight steels. In the as-quenched condition, the steel microstructure consist of a triplex structure of austenite, ferrite, and martensite. B doping leads to a reduction in the prior austenite grain size by grain boundary segregation and precipitation of boro-carbides, which increases the stability of austenite against the athermal martensitic transformation. After tempering at 200 °C for 2 h, nano-lath reverted austenite is formed by the C-enrichment instead of the carbide precipitation owing to the high Al content. This reversion effect is promoted further by the subzero treatment at −196 °C for 0.5 h prior to tempering, which enables the remaining austenite in the as-quenched state to transform and, thus, provides additional sites for austenite reversion. In addition, the subzero treatment and B doping result in the synergistic effect of the delay of crack initiation through the transformation of retained austenite in contact with ferrite and the improvement of bonding strength. Thus, the B-doped steel subjected to quenching, subzero treatment, and tempering exhibits a very high yield strength of approximately 1 GPa, the tensile strength of over 1.3 GPa, and an excellent elongation of 29.4%, which outperform the tensile properties of conventional austenitic or (austenite + ferrite) duplex lightweight steels.

Effects of friction stir processing on the microstructure, mechanical and corrosion behaviors of an aluminum-magnesium alloy

Abstract: This article deals with the corrosion behavior of friction stir processed aluminum-magnesium alloys undergoing electrochemical measurements, including potentiodynamic polarization and electrochemical impedance spectroscopy. The effects of friction stir processing (FSP) critical parameters such as the rotational tool speed (w in the range of 800–1400 rpm) and traverse velocity (v in the field of 50–200 mm/min) along with varying cooling rates imposed using submerged cooling medium (air, water/dry-ice mixture, and liquid nitrogen) on the microstructural features and mechanical properties of Al-Mg alloys in two tempering states of annealed and wrought were characterized. Then, by assessing the electrochemical behavior of the friction stir-modified stirred regions produced using varying cooling rate and initial temper, a correlation between the microstructural details with the mechanical and chemical properties was established. The experimental results revealed the significant grain refinement down to ~1 μm following FSP treatment by controlling the processing conditions, which had a detrimental impact on the electrochemical behavior due to the activation of grain boundary corrosion phenomenon. The primary tempering state of alloy in the form of stored strain energy played a critical role by controlling the fraction of sub-boundaries and recrystallized grains upon FSP modification. The inferior electrochemical property reported for the FSP treated annealed Al-Mg alloy under processing conditions of w = 800 rpm and v = 200 mm/min, as the less noble structure with the highest corrosion rate (CR) of 0.01814 mm/year.

Effect of NbC and VC carbides on microstructure and strength of high-strength low-alloyed steels for oil country tubular goods

Abstract: High-strength low-alloyed (HSLA) steels for oil country tubular goods (OCTGs) are usually microalloyed with niobium (Nb) and vanadium (V). In this work, the microstructure and strength of HSLA steels with different Nb and V contents were studied with the purpose of investigating the role of NbC and VC carbides. The results showed that NbC carbides were responsible for restraining the growth of prior austenite grains, and when the austenitizing temperature was below 910 °C, it has been found that the prior austenite grain size was similar in steels with 0.02 and 0.006 wt% Nb addition. VC carbides could impede dislocation annihilation and refine Cr-rich carbides and martensitic blocks during tempering. Moreover, VC carbides mainly contributed to the tempering softening resistance so that the V-bearing steels exhibited a higher strength than the V-free steel after tempering at 690 °C–730 °C. To illustrate the high tempering softening resistance of V-bearing steels, the changes in various strengthening contributions induced by V addition were quantitatively evaluated. The calculation results indicated that the main reason for the high tempering softening resistance of V-bearing steels was precipitation strengthening by nanosized VC carbides, in contrast to dislocation strengthening, substructure strengthening, and precipitation strengthening due to the refinement of Cr-rich carbides.

Nanoscale precipitation and ultrafine retained austenite induced high strength-ductility combination in a newly designed low carbon Cu-bearing medium-Mn steel

Abstract: A novel low carbon Cu-bearing medium-Mn steel was designed and subjected to intercritical annealing (IA) and tempering (IAT). The yield strength and uniform elongation significantly increased from 659 MPa and 10% to 911 MPa and 20% by tempering. The microstructure of sample IAT was comprised of ferrite, ultrafine retained austenite, tempered martensite, and hierarchical Cu particles. Large size precipitates (9.7 ± 3.1 nm) were formed during intercritical annealing, while fine particles (1.85 ± 0.36 nm) were formed during tempering. Hierarchical Cu particles increased yield strength of ferrite by ~267 MPa, which compensated the strength loss induced by intercritical annealing and tempering. The carbon and alloying elements were further partitioned to austenite from martensite during tempering, which increased austenite stability. As a consequence, TRIP effect occurred over a wide strain regime, which contributed to a superior ductility. Before tempering, yielding of retained austenite was caused by martensite transformation at a low stress because of poor stability, which was avoided by the enhanced stability of retained austenite after tempering. As a result, the yield strength of austenite, and thereby the yield strength of the steel was increased.

Radio frequency tempering multiple layers of frozen tilapia fillets: the temperature distribution, energy consumption, and quality

Abstract: Tempering is an important step for the seafood processing industry. Selecting an appropriate tempering method can optimize the quality of tilapia. Volumetric radio frequency heating is able to compete tempering within minutes regardless product sizes. Twelve pieces of frozen tilapia fillets in four layers were used as target samples for a radio frequency tempering study. To improve the tempering uniformity, a thin layer of polyurethane foam was applied in-between layers. The present study explored the optimum radio frequency (RF) tempering processing parameters including three input powers (600, 800, 1000 W) and three electrode gaps (10, 12, 14 cm), batch and continuous mode, and compared it to water-tempering effects on the temperature distribution, drip loss, color, TBARS and texture of tilapia. Results demonstrated that the temperature distribution of tilapia with the optimum RF tempering condition (800 W, 12 cm) was more uniform than water tempering, and the TBARS value of samples tempered by RF is lower than that of water tempering. RF-tempering processes retained the L* value (58.76) and a* value (6.54) of tilapia samples, and also resulted in the highest hardness at 298.59 g. Most of the texture indexes of the tempered tilapia fish show no significant difference (p > 0.05) among all tempering conditions. Thus, RF shows a great potential in fish-tempering industry with its fast, uniform and controllable characteristics and a better retention of fish quality

Effect of deep tempering on microstructure and hardness of carburized M50NiL steel

Abstract: Through the deep medium-temperature tempering treatment, microstructure observation and hardness test of the carburized M50NiL bearing steel, the influence of the temperature and times of deep tempering on the microstructure and hardness of the steel were studied. The results show that the deep medium-temperature tempering is beneficial to the dissolution of large-size carbides in the carburized layer of the steel at the initial state, uniform distribution of carbides, and the precipitation of granular carbides from lath martensite. During deep tempering treatment, some granular carbides are connected to form rod-like carbides. With the increase of the number of deep tempering, the lath martensite in the steel is decomposed and the size is obviously refined, and more carbides in the core area are precipitated, whose distribution is more dispersed uniform. The deep tempering at 460 °C and 480 °C can slightly increase the surface hardness of bearing steel, but five times of medium temperature tempering at 500 °C makes the hardness of the steel slightly decreased. There exists the lowest point of hardness in the subsurface layer of the initial-stated M50NiL steel, which is however eliminated after 5-time deep tempering at 460 °C and 500 °C, and this is related to the elimination of stripe-like carbides after the two deep tempering processes.

Microstructure evolution and mechanical property enhancement of high-Cr hot work die steel manipulated by trace amounts of nano-sized TiC

Abstract: Simultaneously increasing the strength and ductility of hot work die steels is of significant interest for broad applications. The in-situ development of a nano-phase in steels is a promising method for achieving this objective. However, little success has been reported so far. In this study, trace amounts of TiC nanoparticles were successfully introduced into a high-Cr hot work die steel (HHD) through an innovative method using a nano-TiC/Al master alloy. Upon adding 0.02 wt% nano-TiC, an incompletely recrystallized ferrite phase was observed in the HHD containing nano-TiC. Moreover, more globular pearlite was distributed at the ferrite grain boundaries in the HHD with nano-TiC than in the unmodified HHD. The added nano-TiC provided nucleation sites for γ-Fe dendrites and prevented γ-Fe growth during solidification and an austenitizing heat treatment. Furthermore, it noticeably increased the precipitation of more uniform nanoscale chromium carbides and significantly refined the carbides in the HHD during quenching and tempering. Finally, adding nano-TiC simultaneously enhanced the strength and toughness of the HHD. After quenching at 1353 K and tempering at 833 K, the yield strength, tensile strength, tensile strain, and impact toughness of the HHD with nano-TiC were 1330 MPa, 1620 MPa, 14.4 % and 460 J/cm2, respectively, which are all higher than those of the HHD without nano-TiC.

Precipitation behavior of Ti–Nb–V–Mo quaternary microalloyed high strength fire-resistant steel and its influence on mechanical properties

Abstract: The microstructures and mechanical properties of Ti–Nb–V–Mo quaternary microalloyed high strength fire-resistant steel are investigated under different experimental conditions The results show that the fire-resistant steel with high strength (ultimate tensile strength (UTS), 746 MPa; yield strength (YS), 597 MPa) and a low yield ratio (YS/UTS, 080) is successfully developed by rapid cooling combined with a low final cooling temperature The microalloyed high strength fire-resistant steel tempered at 600 °C × 15 min and 600 °C × 180 min exhibit yield strength of 440 and 419 MPa, which values significantly exceed two-thirds of the specified yield strength at room temperature (ie, 307 MPa) for the Q460 (YS ≥ 460 MPa) fire-resistant steel The mechanical properties at room temperature and 600 °C even meet the requirements for the Q550 fire-resistant steel The ferritic grain boundaries in the experimental steel tempered for 180 min at 600 °C show excellent stability The analysis indicates that solid-solution strengthening and precipitation strengthening are important in improving the strength of the studied fire-resistant steel at room temperature and 600 °C, respectively M(C, N) (M = Nb, V, Ti, and Mo) and M3C (M = Fe, Cr, Mn, and Mo) particles in small quantities are found in the matrix of the as-rolled sample However, after reheating and tempering at 600 °C, large amounts of M(C, N) (mainly MC) and M3C particles precipitate With an increasing in tempering time, the amount of nanoscale MC precipitate increases; especially, the amount of the MC particles size smaller than 10 nm, and the mass fraction of Nb, V, and Mo in the MC precipitate also increases, which is consistent with the equilibrium thermodynamic calculation results This enhancement of the precipitation strengthening of secondary phase particles compensates for strength loss attributing to a decrease in shear elastic modulus and solid solution strengthening at 600 °C

Microstructure and mechanical properties of a novel Nb–Mo bearing medium-Mn alloy affected by intercritical annealing and tempering

Abstract: The influence of intercritical annealing plus tempering treatments on the microstructure and mechanical properties of a novel Nb–Mo bearing medium Mn steel was investigated in this work. Based on the experimental results, the microstructure of experimental steel affected by intercritical annealing plus tempering treatments could be included as follows: (1) the retained austenite (RA) fraction fluctuated slightly (~41%) when the samples tempered between 150 °C and 350 °C, then decreased up to 32% at 450 °C for the austenite decomposition; (2) RA mechanical stability increased with the increase in tempering temperatures; (3) (Nb,Mo) (C,N) precipitates density increased from 150 °C to 450 °C by decreasing mismatch degree between precipitates and ferrite; (4) the coarsening rate of (Nb,Mo) (C,N) precipitates decreased from 150 °C to 450 °C, which led to a decrease in mean size of precipitates. The increase in tempering temperatures from 150 °C to 450 °C led to the yield strength increasing from 581 MPa to 765 MPa. The total elongation increased from 29% to 37% with the tempering temperatures increased from 150 °C to 350 °C, then decreased up to 25% at 450 °C.

Tempering response and improved mechanical properties in secondary hardened steel by introducing an optimized austempering process

Abstract: The tempering response and mechanical properties of the austempered Cr4Mo4V steel with bainite/martensite multiphase structure were investigated During the tempering, the retained austenite (RA) decomposed almost entirely in the specimens without or with a short austempering, while massive blocky RA still remained in the specimens with a long austempering process (4 h) Meanwhile, the significant coalescence and coarsening of bainite occurred during the tempering of the specimens with longer austempering After the tempering, the diameter of packets in the specimens austempered for 1 h decreased from 195 to 106 μm, which could be attributed to the second division of austenite grain during austempering and the minimum degree of bainite coarsening during tempering Additionally, the phase transformation texture was weakened while the dislocation density was increased, as compared with the martensitic quenched specimens Due to the synergistic effect of the finer packet, higher dislocation density and weaker texture, the ultrahigh strength (2604 MPa) combined with an improved impact toughness (93 J) was achieved in the Cr4Mo4V steel austempered for 1 h without compromising hardness (630 HRC) However, with the increase of austempering time, the mechanical properties would deteriorate due to the coarsened packets and undecomposed blocky RA These results indicate that by introducing an optimized austempering process, the mechanical properties of Cr4Mo4V steel can be dramatically improved, while the content of bainite should be strictly regulated to prevent blocky RA and bainite coarsening

Effects of post-printing heat treatment on the microstructure and mechanical properties of a wire arc additive manufactured 420 martensitic stainless steel part

Abstract: In this study, microstructural features and mechanical properties of a wire arc additively manufactured 420 martensitic stainless steel were investigated in as-printed and heat-treated conditions. Initial microstructural investigations on the as-printed part revealed the formation of residual δ-ferrite during the solidification process, which is known as a deleterious phase to both mechanical and corrosion performance of stainless steels. To remove the residual δ-ferrite and obtain a fully martensitic microstructure, the as-printed samples were subjected to different austenitizing temperatures of 950, 1050, 1150, and 1300 °C. Austenitizing at 1150 °C was selected as the optimum cycle due to removal of undesirable phases, such as δ-ferrite and carbides, resulting in a fully martensitic microstructure. Following the austenitizing heat treatment, the samples were tempered at different temperatures including 200, 300, 400, 500, and 600 °C. Increasing the tempering temperature was found to vary the size, morphology, and distribution of chromium carbides precipitated during the tempering process. Although, tempering at lower temperatures (200 and 300 °C) decreased the hardness due to the formation of tempered martensite and stress relieving of the structure, the intermediate temperature of 400 °C increased the hardness value by virtue of the formation of carbides at optimum size and distribution. However, tempering at 500 and 600 °C decreased the hardness as compared to 400 °C due to intergranular segregation and coarsening of carbides. The results of uniaxial tensile testing were consistent with the hardness measurements and confirmed that the tempering temperature of 400 °C led to the optimal combination of strength and ductility ascribed to the formation of fine and homogenously distributed chromium carbides embedded in a moderately tempered martensitic matrix.

The effects of a ferritic or martensitic matrix on the tensile behavior of a nano-precipitation strengthened ultra-low carbon Ti–Mo–Nb steel

Abstract: This work investigates the correlation between microstructure and mechanical properties of a nano-precipitation strengthened ultra-low carbon (NPS- ULC) Ti–Mo–Nb steel. Two types of matrix microstructures (ferrite and martensite) with nano-precipitates were obtained through hot rolling and isothermal transformation in the case of ferrite, or by quenching and tempering, for martensite. The martensitic microstructure showed increases in both YS and UTS by ~110 and ~100 MPa, respectively, over the ferritic microstructure without sacrificing tensile ductility. All ferritic and martensitic specimens exhibited a two-stage work hardening behavior with different work hardening rates at high strain levels. Quantitative analysis of the strengthening contributions confirms that the increase in yield stress of the NPS-ULC specimens with a martensitic matrix was a result of the fine martensitic laths as well as the higher dislocation density and nano-precipitates.

A 2000 MPa grade Nb bearing hot stamping steel with ultra-high yield strength

Abstract: This study reports a novel 2000 MPa grade ultra-strong hot stamping steel, which contains lath martensite, nanometer-sized film-shaped retained austenite and precipitates. The yield strength significantly increases with increasing tempering temperature as the precipitation strengthening, grain refinement strengthening and reducing microstructure residual stress. Multi-strengthening mechanisms (i.e. grain refinement strengthening, precipitation strengthening and transformation-induced plasticity effect) work together to improve the strength and plasticity at the same time. The yield strength reached 1600 MPa, together with an ultimate tensile strength of 1939 MPa and total elongation of 9.14% when tempered at 573 K. Compared with commercial 22mnB5 steel, the tested steels have remarkable improvement in mechanical properties.

Superior strength-ductility in laser aided additive manufactured high-strength steel by combination of intrinsic tempering and heat treatment

Abstract: This work investigated laser aided additive manufacturing (LAAM) high-strength steel by leveraging the intrinsic tempering effect to facilitate the formation of high-fraction of metal carbides (e.g...

Effect of heat treatment on microstructure and impact toughness of a Tungsten-Molybdenum powder metallurgical high-speed steel

Abstract: Effect of quenching, tempering and deep cryogenic treatment (DCT) on microstructure and impact toughness of a new tungsten-molybdenum high-speed steel produced by powder metallurgy was investigated. The obtained results infer that the microstructure is mainly composed of martensite, M6C and VC. The impact toughness decreases with the increasing of austenitizing temperature, but when the austenitizing temperature increases to 1180 °C, the impact toughness changes little. DCT after quenching improves impact toughness slightly, but DCT followed tempering has little effect on impact toughness. The fracture micromechanism can be identified as that crack initiates at the interface between M6C and martensite caused by the inconsistency deformation, M6C carbides exhibit broken or cleavage fracture and VC carbides decohere at the interface. In addition, the variation of impact toughness value has been explained by the characteristics of martensite, the fracture ductility, compressive strain of martensite lattice and grain refinement are beneficial to impact toughness.