Precipitation Of Fine Particles Research Articles

On the nature of nano twin-induced shear band formation in a dispersion strengthened copper alloy under micro-mechanical loading

A key challenge in metallic alloys with high ductility is understanding how microstructural inhomogeneities influence shear localization, leading to localized plastic deformation and material failure. In this study, we explore the phenomenon of shear localization in coarse-grained copper, a material traditionally regarded as having low susceptibility to such behavior. Contrary to conventional understanding, our findings reveal that microstructural inhomogeneities play a pivotal role in inducing extensive strain localization during low strain rate micro-mechanical loading. The presence of fine precipitate particles leads to strain localization at small strains and low strain rates by activating shear localization driven by void formation mechanisms. Furthermore, nanoscale precipitates act as sites for dislocation pile-up within deformed structures of shear bands, leading to the formation of nano twins within these bands. Consequently, precipitate particles serve a dual role: contributing to strain localization and potential cracking, while also enhancing the alloy’s strength and ductility through nano-twinning mechanisms. This investigation offers a novel perspective on the interplay between material microstructure and deformation behavior, challenging existing paradigms in materials science.

Study on dynamic recrystallization and precipitation behavior of hot compressed Al-20Zn-0.5Mg-0.5Sc alloy

The dynamic recrystallization (DRX) behavior of the Al-20Zn-0.5Mg-0.5Sc alloy was investigated under specific conditions using a Gleeble-3500 thermal simulator. The resultant grain size, recrystallization degree and precipitated phases were studied. The results indicate that the sensitivity of DRX grain size is highly affected by temperature, feebly influenced by strain and intermediately affected by strain rate. The DRX grains are grown by an average of 3.49 μm with increasing temperature. The DRX behavior is sensitive to temperature, strain and strain rate, resulting in changes in average grain size, percentage of HAGBs and degree of recrystallization under different parameters. At 400 ℃ / 40 % / 0.1 s−1, the average grain size is refined to 12.90 μm, and the corresponding HAGBs and recrystallization degree are approximately 46.2 % and 34.3 %, respectively. The Al3Sc, Zn and η (MgZn2) phases are precipitated in the hot-compressed alloy. The Al3Sc phase promotes the precipitation of the Zn and η phases. The size, amount and morphology of Al3Sc, Zn and η phases at different parameters have an important influence on the movement of dislocations and nucleation of grains, which leads to changes in DRX grain size and the degree of recrystallization. The fine precipitated phase particles Al3Sc and η inhibit the growth of recrystallized grain by pinning grain boundaries and exerting a blocking force on dislocations. Dynamic precipitation is the dominant mechanism for the changes in DRX grain size and degree of recrystallization. To achieve the refined grains and homogeneous microstructures, the optimum parameters are recommended as 400 ℃, 0.1 s−1 and 50 %.

Effect of operating condition on the properties of ectoine particles for improving the purification process

Ectoine, which is produced from methane by methane-oxidizing bacteria, has attracted attention because of its many useful functions in living organisms. It is known that the purification process using alcohol-based solvents is a limiting step in the ectoine production process because of the precipitation of fine particles. This study investigated quantitatively the effects of operating conditions (cooling rate and solvent) on the properties of ectoine particles for improving the efficiency of the ectoine purification process. The experimental results showed that the properties of ectoine particles were significantly influenced by operating condition such as the cooling rate and solvent of feed solution. Furthermore, it was revealed that the critical supersaturation ratio at the nucleation using methanol was approximately ten times higher than using water. Consequently, it was found that the high critical supersaturation ratio at the nucleation induces the precipitation the fine particles that have high filtration resistance. In conclusion, we succeeded in finding the relationship between the operating conditions and properties of ectoine particles.

Discovery of Guinier-Preston zone hardening in refractory nitride ceramics

Traditional age hardening mechanisms in refractory ceramics consist of precipitation of fine particles. These processes are vital for widespread wear-resistant coating applications. Here, we report novel Guinier-Preston zone hardening, previously only known to operate in soft light-metal alloys, taking place in refractory ceramics like multicomponent nitrides. The added superhardening, discovered in thin films of Ti-Al-W-N upon high temperature annealing, comes from the formation of atomic-plane-thick W disks populating {111} planes of the cubic matrix, as observed by atomically resolved high resolution scanning transmission electron microscopy and corroborated by ab initio calculations and molecular dynamics simulations. Guinier-Preston zone hardening concurrent with spinodal decomposition is projected to exist in a range of other ceramic solid solutions and thus provides a new approach for the development of advanced materials with outstanding mechanical properties and higher operational temperature range for the future demanding applications.

Effects of Normalizing Temperature on the Precipitation of Fine Particles and Austenite Grain Growth during Carburization of Al- and Nb-Microalloyed Case-Hardening Steel

This paper deals with the precipitation behaviors of AlN and Nb(C, N) particles during normalizing of hot-forged Al- and Nb-microalloyed case-hardening steel, and investigates the effects of the number density and volume fraction of these particles on the grain growth behavior of austenite (γ) during the subsequent high-temperature carburization. When the sample was cooled from the hot forging temperature at 16°C/min, AlN did not precipitate at all and was completely supersaturated in the matrix, although fine Nb(C, N) particles precipitated during cooling. When reheated to the normalizing temperature, AlN particles started precipitation at approximately 620–640°C on the grain boundaries of the bainitic ferrite matrix and the interfaces between the cementite particles and the matrix, and the AlN particles contained Cr and Mn, and had an NaCl structure and Bain orientation relationship with the matrix. The AlN structure changed from NaCl type into wurtzite type at approximately 800°C. AlN particles grew during reheating to the normalizing temperature and holding at the temperature. Both the number density and volume fraction of the AlN particles were dramatically increased by reducing the normalizing temperature from 1070 to 900°C. The distribution of these particles strongly affected the γ grain structure formed during carburization. As the normalizing temperature was reduced from 1070 to 950 and 900°C, the γ grain structure became finer. Some abnormally large grains were formed near the carburized surface, when normalized at 1070°C. However, no abnormal grain was found when normalized below 950°C.

Deep separation of critical metals of Mo and Re from waste solution by stepwise precipitation flotation: Selective chelation underlying separation mechanism

Conventional selective precipitation method has disadvantage in the low-efficiency filtration of fine precipitated particles during the treatment of waste solutions. To overcome this shortcoming, a stepwise precipitation flotation process was proposed to deeply separate Mo and Re from Mo-Re mixing waste solution with low concentrations in this work. Chelating agents are critical for the selective separation of Mo and Re. Experimental results show that the rhenate can be firstly separated from mixing solution by the synergistic effect of cetyl trimethyl ammonium bromide (CTAB) and dodecyl trimethyl ammonium bromide (DTAB). In the weak alkaline solutions with pH range of 6–10, CTAB shows a stronger competitive adsorption capacity with rhenate than molybdate through electrostatic interactions and coordination reactions. Meanwhile, DTAB has a great inhibition effect on the chelation of molybdate by CTAB in this pH range, which can further enhance the selective chelation of rhenate by CTAB. After Re separation, molybdate can be further recovered by CTAB from the residual solution with pH range of 3–5. In this pH range, Mo mainly exists in the form of isopolymolybdates acid, and molybdate shows a stronger competitive adsorption ability with CTAB than DTAB. Molybdate reacts with CTAB to form precipitate, and the fine precipitated particles are readily separated via flotation. The turbidity of the residual liquid after flotation is less than 5 NTU, meeting the wastewater discharge standard. In the Re precipitation flotation procedure, the comprehensive efficiencies of Re and Mo are 96.6% and 0.14% under the main conditions of temperature of 25°C, n(CTAB)/n(Re) molar ratio of 2:1, n(DTAB)/n(CTAB) molar ratio of 2:1, and pH of 6. In the further Mo flotation separation, Mo comprehensive recovery of 97.9% is achieved by using CTAB and KH2PO4 as chelation agent and flocculant, respectively. The technological parameters of the conventional selective precipitation method and precipitation flotation method as well as the Mo and Re distributions in these two processes were compared in this study. Moreover, compared with the conventional selective precipitation method using inorganic precipitators, the precipitation flotation process shows a unique advantage in the easy purification of obtained products due to the utilization of organic agents.

Preparation of high-performance Mg-Gd-Y-Mn-Sc alloy by heat treatment and extrusion

A high-performance Mg-8Gd-4Y-0.5Mn-0.2Sc (wt%) alloy was fabricated by the combination of homogenization, hot extrusion and ageing. The microstructure evolution during the homogenization at 550 °C was investigated, and the optimum time of 18 h was obtained to minimize the volume fraction of second phase particles and to keep fine grain structure. The alloy was extruded after the optimized homogenization, and the mechanical properties were investigated with the detailed characterization of the strengthening mechanisms. A typical bimodal microstructure with coarse deformed un-DRXed grains and fine DRXed grains was fabricated. The as-extruded alloy contains amounts of fine precipitated particles as well as dense nano-scale γ’ precipitates. After peak-aged treatment, the alloy exhibited excellent age-hardenability and strength with a tensile yield stress of 441 MPa and an ultimate tensile strength of 506 MPa. The high yield strength was attributed to the co-existing of the bimodal microstructure, fine DRXed grains, dense dynamically precipitated particles, and nano-scale precipitated phases. The co-existing β’ precipitates and γ’ precipitates are the largest contributor to the strength of the peak-aged alloy, the dominant strengthening mechanism is revealed as precipitation strengthening.

Design of a new 11Cr martensitic steel and evaluation of its long-term creep rupture strengths

A new grade of 11 wt% Cr steel was designed in which no nitrogen was added to minimise the driving force of the Z-phase formation and hence to maximise the stability of the fine MX precipitate particles. But, 6 wt% Co was added to completely suppress the δ-ferrite formation in the matrix. The creep data were measured in the range of 650–725 °C at different stresses and rationalised on the basis of a new creep model, which revealed that the effect of stress on creep was equivalent to that of temperature. The model parameters so determined was used to predict the 100,000 h creep rupture strengths. The results showed that these long-term creep rupture strengths were higher than those for the P92 Steel, which is a 9 wt% Cr and the strongest steel grade among commercial 9–12 wt% Cr steels at present. The reliability of the long-term creep rupture strength predictions for the new steel is also analysed.

Combination of enhanced strength and sufficient tensile ductility in a sintered ultrafine-grained CoFeMnNi medium-entropy alloy

A CoFeMnNi medium-entropy alloy (MEA) was prepared by mechanical alloying (MA) and spark plasma sintering (SPS). The mechanically alloyed powders were sintered to near-full density and the as-sintered material consists of FCC matrix comprising a minor distribution of oxide particles. A high twin density is observed in MEA bulk samples. The twins are not generated during high-energy ball-milling but formed in the recrystallized grains during the sintering process. Compressive and tensile tests were performed on the sintered specimen at room temperature. The tension-compression yield asymmetry is weakened with increasing sintering temperature. An ultrafine-grained microstructure with an average grain size of 535 nm is obtained at a sintering temperature of 1000 °C. The sintered MEA exhibits an enhanced yield strength of 740 MPa, which is by 244% higher than that of its coarse-grained counterpart, meanwhile maintaining a sufficient tensile ductility of 14.4%. These excellent mechanical properties mainly stem from the high relative density, fully recrystallized ultrafine grains, and precipitation of fine particles that significantly strengthen the material while simultaneously providing high strain-hardening capability.

Effects of Trace Amounts of Mn, Zr and Sc on the Recrystallization and Corrosion Resistance of Al-5Mg Alloys

This study aimed to explore the effects of trace amounts of Mn, Zr, and Sc on the recrystallization behavior and corrosion resistance of Al-5Mg alloys after process annealing by means of alloy design and microstructure analysis of electron backscatter diffraction (EBSD), electron microprobe (EPMA), and electron microscopes (TEM and SEM). The main objective was to obtain alloys with better corrosion resistance. The results show that the fine Al3Zr and Al3Sc precipitated particles were both superior to the MnAl6 particles in inhibiting grain and sub-grain boundary migrations. Therefore, the Zr-containing and Sc-containing alloys were better than the Mn-containing alloy in inhibiting recrystallization. For further comparison, the thermal stability of the Al3Sc particles was better than that of the Al3Zr particles, so the Sc-containing alloy at the high temperature above 350 °C inhibited grain growth better than the Zr-containing alloy. During the recovery stage of the alloy in the recrystallization process, the β-Mg2Al3 phase precipitated on the sub-grain boundary, thus reducing the occurrence of intergranular corrosion. However, in the initial stage of recrystallization, the β-Mg2Al3 phase continuously precipitated on the grain boundary, causing obvious intergranular corrosion. For the Sc-containing alloy, because there was no obvious grain growth stage, the β-Mg2Al3 phase continuously precipitated on the grain boundary, and thereby intergranular corrosion occurred. Therefore, its corrosion resistance was greatly reduced. By contrast, for the alloy containing Mn or Zr, because of obvious grain growth, magnesium atoms aggregated. As a result, the β-Mg2Al3 phase discontinuously precipitated on the grain boundary. The corrosion morphology was local pitting corrosion rather than intergranular corrosion, and thus the corrosion resistance of the alloy was enhanced. As a novelty, this study clearly observed the sensitized precipitation and corrosion morphology of the β-Mg2Al3 phase of Al-5Mg alloy under different recrystallization methods. This will be of benefit to the design of anti-corrosion measures for the future manufacturing and application of Al-5Mg alloy.

Effects of Cooling Rate after Hot Forging on Precipitation of Fine Particles during Subsequent Normalizing and Austenite Grain Growth during Carburization of Al- and Nb-microalloyed Case-hardening Steel

Effects of Cooling Rate after Hot Forging on Precipitation of Fine Particles during Subsequent Normalizing and Austenite Grain Growth during Carburization of Al- and Nb-microalloyed Case-hardening Steel

Effect of Hot Extrusion on Microstructure and Mechanical Properties of Mg–5Sn–xZr Alloys

The effects of Zr addition (0, 0.5 and 1 wt%) and extrusion ratio (6:1 and 12:1) on microstructure and mechanical properties of the Mg–5Sn alloy were studied. Results showed that the dendritic structure of the as-cast M–5Sn alloy gradually transformed into a nearly globular structure with Zr addition. The effect of Zr addition was evident through refining the microstructure, promoting the tendency to form partially divorced eutectic and increasing the Mg2Sn volume fraction, which improved the thermal stability of the alloy during homogenizing treatment at high temperatures. Hot extrusion was found to be very effective for enhancing both strength and ductility of the Mg–5Sn–xZr alloys. Grain refinement induced by twin dynamic recrystallization and dynamic precipitation of fine particles were realized as the main strengthening mechanisms of the extruded alloys. It was found that an increase of the extrusion ratio led to relatively coarser grains, lower yield strength, and higher hardening capacities. However, the Mg–5Sn–1Zr alloy extruded with the area-reduction ratio of 12 exhibited the best combination of tensile strength and elongation of 243 MPa and 10.6%, respectively. Moreover, tensile fracture studies revealed the intergranular cracking and quasi-cleavage fracture as the dominant fracture modes of the as-cast and extruded alloys, respectively.

Microstructural analysis of forged Al-11Si-2.5Cu-0.6Fe alloy at different processing conditions

Present investigations demonstrate the microstructural analysis of complex eutectic Al-Si alloy namely Al-11Si-2.5Cu-0.6Fe during forging at different processing conditions. The alloy forged through converging die with reduction ratios (R) 1.5 and 2.0 at 300, 400 and 500 °C elevated processing temperatures. X-Ray diffractometer was used to evaluate the various phases present in the alloy. Optical microscopy was executed to characterize the microstructural features induced during process (forging). The obtained results are critically observed to investigate the interaction of different processing parameter. The diffraction patterns confirmed that various complex intermetallic phases (β-Al4.5FeSi and Al2Cu) were formed due to the higher temperature during casting. Significant microstructural refinement observed during forging due to precipitation of fine particles while the coarse particulates fractured and fragmented during the process. The present study delivers valuable insight into microstructural development during forging of Al-11Si-2.5Cu-0.6Fe alloy.

Vehicle Washing (Doorsmeer) Wastewater Treatment using Flotation Electroagulation Combination

Vehicle washing business services in the current era are growing in numbers, both simple and those that have used technology. As a consequence, the production of wastewater more and more, which if not controlled will have an impact on environmental pollution. Conventional wastewater treatment technology is sometimes less effective because it requires chemicals in the process and requires relatively longer, so the need for land to build a treatment unit is relatively wider. To provide an alternative treatment process that is simpler and has good results and does not require large tracts of land, it is necessary to develop electro-coagulation technology combined with flotation. Electrocoagulation is the process of clumping and precipitation of fine particles contained in water by using electrical energy. This study was to determine the ability of electrocoagulation-flotation technology in decreasing the parameters of COD, detergents, and oil in motor vehicle washing wastewater based on the type of electrodes used at 12 and 24-volt electric voltages with contact times of 30 and 60 minutes. This study is an experimental study with a "pre and post-test group design" design. The results showed that the combination of electrocoagulation-flotation at 24-volt voltage and 60 minutes contact time with aluminum electrodes could reduce COD 82.7%, oil 46.5%, and detergent 68.9%. Whereas with iron electrodes the COD decreased by 81.1%, oil by 43.7% and detergents by 65.1%. With an average reduction, aluminum electrodes are better than iron electrodes. Although aluminum and iron electrodes are better, statistically the two are not different (p <0.05), this shows that there is no difference in the ability to decrease test parameters. Other than that, the longer the contact time, the greater the decrease in test parameters. The conclusion is that the electrocoagulation-flotation combination method can be used to reduce the COD, oil/fat and detergent parameters in motor vehicle washing wastewater. The results of this study are expected to be applied to motor vehicle washing activities by utilizing iron waste as an electrode.

The Effect of Equal-Channel Angular Pressing on Microstructure, Mechanical Properties, and Biodegradation Behavior of Magnesium Alloyed with Silver and Gadolinium

The effect of equal channel angular pressing (ECAP) on the microstructure, texture, mechanical properties, and corrosion resistance of the alloys Mg-6.0%Ag and Mg-10.0%Gd was studied. It was shown that ECAP leads to grain refinement of the alloys down to the average grain size of 2–3 μm and 1–2 μm, respectively. In addition, in both alloys the precipitation of fine particles of phases Mg54Ag17 and Mg5Gd with sizes of ~500–600 and ~400–500 nm and a volume fraction of ~9% and ~8.6%, respectively, was observed. In the case of the alloy Mg-6.0%Ag, despite a significant grain refinement, a drop in the strength characteristics and a nearly twofold increase in ductility (up to ~30%) was found. This behavior is associated with the formation of a sharp inclined basal texture. For alloy Mg-10.0%Gd, both ductility and strength were enhanced, which can be associated with the combined effect of significant grain refinement and an increased probability of prismatic and basal glide. ECAP was also shown to cause a substantial rise of the biodegradation rate of both alloys and an increase in pitting corrosion. The latter effect is attributed to an increase in the dislocation density induced by ECAP and the occurrence of micro-galvanic corrosion at the matrix/particle interfaces.

Effect of extrusion ratio and temperature on microstructures and tensile properties of extruded Mg-Gd-Y-Mn-Sc alloy

This study analyzed the effect of extrusion parameters on the microstructural evolution and tensile properties of a Mg-8.0Gd-4.0Y-1.0Mn-0.4Sc (wt.%) alloy. The variation in the dynamic recrystallization (DRX) and dynamic precipitation behavior of the alloy under different extrusion parameters were investigated in detail, and the DRX behavior during hot extrusion and strengthening mechanism were revealed. The primary DRX mechanisms are discontinuous dynamic recrystallization (DDRX), continuous dynamic recrystallization (CDRX). The as-extruded alloy with larger extrusion ratio exhibits smaller dynamic recrystallized (DRXed) grains and a high number of fine precipitated particles. With increasing the extrusion temperature, both the average size and volume fraction of DRXed grain increase, but the fine particle fraction decreases. The alloy extruded at 400 °C and ratio of 20:1 shows the superior strength with tensile yield strength of 352 MPa and ultimate tensile strength of 425 MPa, and the alloy extruded at 450 °C and ratio of 10:1 shows higher elongation to failure of 12%. The enhanced strength is mainly attributed to the combined action of strong basal texture, refined DRXed grains and dense distribution of fine particles, on the other hand, the higher fraction of DRXed grains and lower amount of precipitate particles are beneficial to increase the ductility of the alloy.

Effects of Cu addition on resistance to hydrogen embrittlement in 1 GPa-grade duplex lightweight steels

Hydrogen embrittlement (HE) has arisen as one of main issues for developing high-strength lightweight steels. The precipitation of fine particles providing as stable H-trapping sites is preferred to overcome the intrinsic HE of high-strength steels. However, studies on HE in high-strength lightweight steels along with roles of B2 particles have not been reported yet. In this study, three Fe–0.8C–15Mn–7Al–(0,1,3)Cu duplex lightweight steels were fabricated, and their resistance to HE was evaluated. Roles of Cu addition were investigated by the loss of elongation measured from slow-strain-rate tensile tests and by the concentration and diffusivity of H measured from electrochemical H permeation tests. The Cu addition results in the decreased elongation loss and the lower concentration and effective diffusivity of reversible H, indicating the higher resistance to HE. The unraveled mechanism is that the Cu addition increases the fraction of austenite, where the diffusivity of H is much lower than ferrite, and decreases the strain localization along ferrite grains to reduce the internal diffusion of H during deformation. In addition, it promotes the formation of complex semi-coherent Cu-rich B2 particles, which provides misfit dislocations at interfaces as stable and irreversible H-trapping sites. The B2 particles preferentially nucleated at reversible sites such as grain boundaries and phase interfaces promote a transition from reversible to irreversible sites, which further reduces the diffusivity of H. The present work, thus, would suggest the Cu addition to enhance both tensile properties and resistance to HE for designing high-strength lightweight steels.

Experimental and simulation studies of metal sulfide precipitates separation in copper smelting waste acid using a gravitation field-flow fractionation method

Sulfide precipitation method has been widely used in the removal of arsenic and heavy metals from copper smelting waste acid. Nevertheless, tiny metal sulfide particles are generated during the process, making it difficult to achieve solid-liquid separation as well as solid-solid separation. This study designed an innovative gravitational field-flow fractionation (GFFF) tank to effectively separate fine sulfide precipitate particles of different heavy metals, relying on the difference in particle sizes. To achieve better tank performance, the effects of process conditions on the size variation of precipitate particles produced in metal sulfide precipitation process (Cu(Ⅱ), Zn(Ⅱ), or As(Ⅲ)) were firstly investigated. The results show that supersaturation level, sulfide to metal molar ratio, and pH have significant effects on the precipitate particle size, while reaction time affects slightly. The optimum conditions were identified to achieve the greatest possible differences in particle sizes of the three metal sulfide precipitates. To further analyze its performance, a 3D model of the GFFF tank was built, with the fluid flow field and precipitate particle movement simulated under the optimum conditions. The simulation results demonstrate that the designed GFFF tank can realize efficient separation of fine metal sulfide precipitates for the recovery of valuable metals.

Experimental ballistic performance determination of friction stir welded magnesium (AZ31B) targets

Nowadays there is an increasing demand to develop light weight defense vehicles, fighter aircrafts and warships in order to enhance their mobility and fuel economy. It can be achieved by using the light weight structures made up of Aluminum and Magnesium plates which will reduce the weight, increase the payload carrying capacity and efficiency of the vehicles. In the present work, experimental ballistic performance of Magnesium (AZ31B) Base Metal (BM), friction-stir-welded (FSW) and post-weld-heat treated (PWHT) target plates have been determined by using the 7.62 mm Armor Piercing Projectiles (APP). Prior to ballistic testing, Magnesium joints were prepared by the FSW process for various tool rotational and welding speeds. Defect-free welds with better tensile and impact properties, were obtained with tool rotational speed of 1200 rpm and the welding speed of 50 mm/min. PWHT was carried out with the annealing temperature at 250 °C for about 1 hour. Microhardness and microstructure of the FSW and PWHT joints were investigated. Highest hardness (67 HV) was obtained for fine grain structure and precipitated particles were observed for PWHT targets. Depth of Penetration of PWHT target plates was approximately 17.55% and 16.31% lower than the BM and FSW target plates respectively. Scanning Electron Microscopic observation of projectile penetrated channel showed the formation of Adiabatic Shear Bands (ASBs). Due to a larger number of ASB lines, ballistic impacted FSW surface showed more number of macro cracks compared to PWHT surface. The PWHT joints showed the absence of fragmentation failure, lesser cracks and ASB lines which increased the ballistic performance.

Effects of Deep Cryogenic Treatment on the Microstructures and Tribological Properties of Iron Matrix Self-Lubricating Composites

The effects of deep cryogenic treatment on the microstructures and tribological properties of the self-lubricating iron matrix composites are investigated. The self-lubricating composites are deeply cryogenically treated at about −196 °C. The results show that with deep cryogenic treatment, the martensite phase transformation occurred from phase γ to α′, and the fine particle carbides precipitated between martensites with the extension of cryogenic treatment time, measured by X-ray diffractometry (XRD) and scanning electron microscope (SEM). Compared with the as-sintered specimen, the maximum hardness of the specimens processed by cryogenic treatment increases by 172.8% from 253.2 HV to 690.7 HV. The materials with deep cryogenic treatment for 8 h show the best tribological properties, i.e., the average friction coefficient decreases by 75% from 0.36 to 0.09, and the wear coefficient decreases by 63% from 341 to 126 × 10−6 mm3/Nm at 150 N and 8 mm/s. The improvement of the tribological property can be primarily attributed to the martensite phase transformation from γ to α′ and the precipitation of fine particles carbides between the martensites, which increase the hardness and the wear resistance after the cryogenic treatment.