Search

To study and understand the solidification behavior of super austenitic stainless steel under different cooling rates and segregation laws of alloying elements is of great significance to optimize the subsequent diffusion annealing homogenization treatment process and improve product quality. According to Thermo-Calc thermodynamic simulation results and combined with high temperature laser confocal scanning electron microscope (HT-CSLM), the tissue morphology of 904L super austenitic stainless steel was observed in-situ during solidification. The solidification path of the test steel was determined via calculation with the Scheil-Gulliver model. Microscopy techniques, including true color microscopy, scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and electron probe microanalyzer (EPMA) were used to analyze the influence of different cooling rates (6 ℃/min, 50 ℃/min, and 100 ℃/min) on the solidification structure and determine the main distribution law of alloying elements. This analysis determined that the solute distribution coefficient (K) of Cr, Mn, Mo, Cu, and Si elements is less than 1 during the solidification process, which means that they will accumulate in the liquid phase. Among them, elemental Mo segregation is the most severe, while elemental Ni hardly segregates. As the cooling rate increases, the crystallization temperature of the test steel decreases, and the secondary dendrite arm spacing λ2 decreases, the concentration of Mo in the residual liquid phase increases.

The effect of Al content on the microstructure and ductile-brittle transition temperature (DBTT) of 18Cr–Al–Si ferritic heat-resistant stainless steel have been studied by Charpy impact testing over temperatures ranging from 20 to 90 ℃. Charpy impact test results show that DBTT increased with increasing Al content. Meanwhile, fracture morphology changed with increasing Al content, where the amount of dimples decreased and cleavage facets increased, indicating increases in the tendency for brittle fracture. Furthermore, ferrite grain size, volume fraction and size of (Cr, Fe)23C6 carbides increased with increasing Al content, which led to decreasing toughness and increasing DBTT.

The effect of Al content on the high-temperature oxidation (800 and 900 °C) of 18Cr–Al–Si FHSS (ferritic heat-resistant stainless steel) for up to 180 h in air was investigated via the isothermal oxidation method. The oxidation kinetic curves followed a parabolic law. A higher Al content reduced the oxidation rate and improved the oxidation resistance and also promoted the formation of a denser and more continuous Al2O3 film during the early oxidation stages, which provided an effective barrier that hindered the diffusion of oxygen into the matrix. The oxide films that formed on the 0.63Al FHSS and 1.06Al FHSS were composed of spinel MnCr2O4 in the outer layer, MnO and Cr2O3 in the middle layer, and Al2O3 and SiO2 in the inner layer. The middle layer of 0.63Al FHSS also contained a small amount of Fe2O3. The oxidation mechanism was also discussed based on oxidation kinetics, morphological observations, and phase analysis of oxide films.

The poor corrosion/wear resistance of Mg alloy seriously limits its industrial application. Graphene-based anti-corrosion coatings show the excellent imperviousness, but they can provide the additional cathodic sites for Mg alloys, which accelerates the galvanic corrosion behaviors near the interfaces. A novel design of cerium-based intermediate layer (Ce(Ⅳ)) is reported in this study, which exhibits a synergistic effect of hydrogen/ionic bond on the graphene oxide (GO)/polyvinyl alcohol (PVA) biomimetic coating. It overcomes the problems of galvanic corrosion and low interfacial adhesion between Mg substrate and hybrid coating through a prominent barrier effect. Furthermore, the GO/PVA coating with “bricks and mortar” structure effectively blocks the permeation of electrolyte due to the reduced porosity and enhanced densification. The corrosion rate of Ce(Ⅳ)/GO/PVA coating is 11 and 19 times lower than bare Mg alloy and single GO/PVA film, respectively. The wear rate of GO/PVA and Ce(Ⅳ)/GO/PVA samples is decreased by 98.8% and 97.6%, which is ascribed to the high hardness and lubrication of GO sheets. Moreover, the relatively interlayer slipping between GO sheets can lubricate the sliding process. Compared with GO/PVA, the slightly decreased wear resistance of Ce(Ⅳ)/GO/PVA coating is resulted from the enhanced shear force.

To evaluate the influence of cobalt on the microstructure and pitting behavior of martensitic age-hardened stainless steel (MASS), the microstructures and electrochemical behaviors were characterized by optical microscopy, scanning electron microscopy, transmission electron microscopy, x-ray photoelectron spectroscopy, potentiodynamic curve, electrochemical impedance spectroscopy, and Mott–Schottky analysis. Results indicated that adding cobalt reduced the grain size of the original austenite, refined the lath martensite, inhibited the precipitation of Cu-rich phases, and increased the content of reversed austenite. Compared with the cobalt-free steel, the cobalt-containing steel has a higher pitting potential, lower corrosion current density, and higher pitting resistance. The primary components of the passive film grown on the cobalt-free steel included (Cr, Fe) oxides, such as Cr2O3, Cr(OH)3, FeOOH, and Fe2O3. The cobalt-containing steel included the aforementioned components as well as Co, which was attributed to the formation of the passive film in the forms of CoFe2O4, Co(OH)2, and CoO. In addition, the synergy of the refined lath martensite and the precipitation of the Cu-rich phase induced an increase in corrosion resistance in MASS containing cobalt.

A comparative study of the high-temperature oxidation behavior and mechanism of 0Cr25Ni20 austenitic heat-resistant stainless steel (AHSS) and 0Cr18AlSi ferritic heat-resistant stainless steel (FHSS) at 800°C, 900°C, and 1000°C in air up to 140 h was performed using isothermal oxidation tests. The oxidation kinetics of 0Cr25Ni20 AHSS and 0Cr18AlSi FHSS followed the parabolic law. The oxide films on 0Cr25Ni20 AHSS were composed of continuous and dense Cr2O3, MnCr2O4, and a small amount of NiMn2O4, whereas silicon exhibited internal oxidation and deteriorated the adhesion between the oxide film and substrate. Nickel-free 0Cr18AlSi FHSS exhibited good oxidation resistance at 800°C and 900°C due to dense, continuous, and well-adhered multicomponent oxide films containing Al2O3, Cr2O3, MnCr2O4, and a small amount of MnFe2O4. The oxidation resistance of 0Cr18AlSi FHSS declined at 1000°C, mainly due to the formation of nonprotective Fe2O3 and severe internal oxidation of aluminum.

The high temperature oxidation behavior of a high Al-containing ferritic heat-resistant stainless steel at temperatures of 800, 900, and 1000 °C in air were studied in isothermal oxidation tests. The results showed that the isothermal oxidation kinetic curves obtained at different temperatures followed the parabolic law, and the weight gain per unit at 1000 °C was significantly higher than that at 800 and 900 °C. The oxidation rate at 1000 °C was about three times faster than that at 800 and 900 °C. Continuous and compact multicomponent oxide films mainly composed of Cr2O3, Al2O3, spinel MnFe2O4, and MnCr2O4 were obtained at 800 and 900 °C. The oxide film started delaminating at 1000 °C; the outer layer was composed of Cr2O3, spinel MnCr2O4, and MnFe2O4, the middle layer was composed of Fe2O3 and Fe-Cr matrix, and the inner layer was composed of Al2O3 and SiO2. Oxidation resistance at 1000 °C was reduced mainly because of porous Fe2O3 and inner oxidation of Al and Si. In addition, the oxidation mechanism was discussed based on kinetic and morphological observations.

X10CrAlSi18 FHSS (ferritic heat-resistant stainless steel) has received a lot of attention due to its advantageous combination of creep resistance and oxidation resistance. The influence of Si content on the high-temperature oxidation resistance of X10CrAlSi18 FHSS after oxidation at 700 and 800 °C for up to 180 h in air was investigated in this study. According to the results, a higher Si content could coarsen the grain of ferrite and simultaneously increased the amount of (Cr, Fe)23C6 carbides, which caused cracks and reduced the adhesion between the oxide film and the matrix. After oxidation at 700 °C, the oxide film of 0.77Si FHSS and 1.35Si FHSS were found to be primarily composed of Al2O3, SiO2, Cr2O3, Fe2O3, Mn2O3 and MnCr2O4, with thickness of 5.10 μm and 5.56 μm, respectively. The oxide films formed at 800 °C were primarily composed of Al2O3, SiO2, Cr2O3, FeCr2O4, Mn2O3 and MnCr2O4 with thickness of 5.55 μm and 7.37 μm, respectively. A higher Si content was discovered to increase the amount of MnCr2O4 in the outer layer of the oxide film, which resulted in a looser spinel structure and reduced the oxidation resistance of X10CrAlSi18 FHSS.

The industrial applications of Mg and its alloys are restricted by their poor corrosion resistances, owing to the rapid dissolution and hydrogen evolution behaviors. In this study, a sequentially bridged reduced graphene oxide (RGO)/bistriethoxysilylethane (BTSE) coating is successfully grafted on the surface of Mg alloy substrate, to simultaneously inhibit the corrosion and wear behaviors. It exhibits well-aligned biomimetic nacre-like “bricks and mortar” structure connected by covalent bonding networks, consisting of the Si-O-C bonds between the RGO sheets and the Si-O-Si bonds derived from BTSE self-crosslinking reactions. The reduced porosity and defects lead to a high continuity and integrity of the RGO/BTSE coating, which decreases the corrosion rate by an order of magnitude compared with bare Mg substrate and RGO coated sample, owing to the enhanced barrier effect and weakened galvanic corrosion. In addition, the hybrid coating also performs well anti-wear property due to the intrinsic lubrication of RGO sheets, which can protect the substrate from friction and wear. The wear rate decreases from 3.5 × 10−3 mm3N-1 m-1 of bare Mg alloy to 5.13 × 10-5 mm3N-1 m-1 of RGO/BTSE coated sample. The interlayer slipping between the RGO sheets effectively decreases friction resistance, although the incorporation of BTSE slightly increases their shear resistance.

In order to expand the applied range of Mg alloy, a variety of coatings have been designed to improve their corrosion and wear resistance. Here, we report a 3-aminopropyl triethoxysilane (APTES) modified Mg(OH)2/reduced graphene oxide (RGO) hybrid coating with integrated anti-corrosion/wear property on Mg alloy, which is prepared by in-situ crystallization using a facile hydrothermal method. The ultra-thin Mg(OH)2/RGO layer with 250 nm exhibits a dual-structure, in which the inner layer is composed of Mg(OH)2, and then RGO sheets hybrid with Mg(OH)2 via the hydrogen bond to form the outer layer. The lubrication of RGO sheets and the high hardness of dense Mg(OH)2 give rise to the significant decrease of wear rate, which is two orders of magnitude less than that in Mg substrate. Next, the APTES layer effectively fills the pores and defects on the surface of Mg(OH)2/RGO via the Si-O-Mg and amide bond, and it forms a barrier film enriched with Si-O-Si bond via the self-crosslinking reaction. The effective combination of inorganic and organic layer contributes to the improved anti-corrosion property.

In this study, an ultra-high yield strength (~417 MPa) and moderate ductility (~12.9%) was obtained in Mg–8.2Gd–3.8Y–1.0Zn–0.4Zr (wt%) alloy through a method of decreased-temperature multi-directional forging (MDF) processing followed by aging treatment. The ultra-fine grained structure with average grain size of ~0.9 μm was prepared after 6 passes of forging progress, which was ascribed to the occurrence of dynamic recrystallization (DRX). Both the decreased MDF temperature and precipitation of fine Mg5(Gd, Y) phase particles effectively hinder the DRX grain growth, so that the grain refinement can realize their full potential in strengthening effect. The formation of some DRX grains is also accompanied with the consumption of LPSO structures. Additionally, a weak fiber texture with c-axis perpendicular to normal direction was gradually formed during the reduplicative MDF process. As compared to the hot-extruded counterpart, the significant improvement in the yield strength of MDF-processed Mg-Gd-Y-Zn-Zr alloy can be attributed to the combined strengthening effects of the grain refinement, dynamic precipitation and broken secondary phase particles. Meanwhile, the homogenous microstructure induced by decreased-temperature MDF is also responsible for a resulting moderate ductility.

The metadynamic recrystallization (MDRX) behavior of as-cast 904 L superaustenitic stainless steel was investigated by double pass isothermal compression tests at temperatures of 950 — 1150 °C, strain rates of 0.05 — 5 s −1 and interval of 1 — 100 s. The effects of working parameters (deformation temperature, strain rate, pre-strain and interval time) on the flow curves and microstructural evolution were discussed. The MDRX fraction increased obviously with the increase of deformation temperature, strain rate and interval time. The MDRX softening was controlled by the migration of grain boundary, annihilation of dislocation and dynamic recrystallization. Moreover, the kinetic model was established for the prediction of MDRX behavior of as-cast 904 L superaustenitic stainless steel based on the experimental data. A good agreement between the predicted and the experimental values was achieved (correlation coefficient R 2 =0.98), indicating a satisfactory accuracy.

The 0.1C-18Cr-1Al-1Si ferritic heat-resistant stainless steel has attracted considerable attention to high-temperature applications due to its favorable combination of creep and oxidation resistance. In this paper, the microstructural evolution and precipitation behavior of the 0.1C-18Cr-1Al-1Si ferritic heat-resistant stainless steel is studied from the compression deformation data in the temperature range of 850 °C–1050 °C and the strain rate range of 0.01–1 s−1. Experimental results demonstrate that higher temperatures and lower strain rates enhance the dynamic recrystallization (DRX) process with remarkable effectiveness. The main precipitates are proved as the AlN phases and the (Cr,Fe)23C6 carbides during hot deformation. With an increase in the deformation temperature, the size of (Cr,Fe)23C6 and AlN gradually increases, and volume fraction gradually decreases. When the strain rate decreases, the average size and volume fraction of (Cr,Fe)23C6 and AlN gradually increase. At the lower temperatures, the occurrence of dynamic recrystallization (DRX) is strongly influenced by (Cr,Fe)23C6 formed on the grain boundaries, mainly because it causes a pinning effect, which hinders the movement of dislocations and delays the occurrence of the DRX.

To promote the application of resource-saving heat-resistant stainless steels, the study on high temperature oxidation behavior and oxide-scales formation mechanism of X10CrAlSi18 ferritic heat-resistant stainless steels (FHSSs) and 310S austenitic heat-resistant stainless steels (AHSSs) was carried out in air up to 140 h, and the microstructure of oxide scales, oxidation kinetics and thermodynamics theories, and the classical hypothesis of the third-element effect analyzed. The results showed that the cost-effective X10CrAlSi18 FHSSs presented good oxidation resistance at 800 and 900 °C due to the compact multicomponent oxide scales composed of Al2O3, Cr2O3, MnCr2O4 and MnFe2O4 and good adhesion to the matrix. However, the oxidation resistance of the alloy at 1000 °C was deteriorated, which is mainly due to the non-protective Fe2O3. The oxide scales of 310S AHSSs containing Cr2O3, MnCr2O4 and inner SiO2 exhibited good oxidation resistance, while the internal oxidation of silicon weakened the adhesion to the substrate.

The deformation behavior and microstructural evolution of as-cast 254SMO super-austenitic stainless steel (SASS) were studied by hot compressive tests in the temperature range 900–1200 °C, and in the strain rate range 0.01–10 s −1 . The results show that the single peak characteristic appears on almost all the obtained flow curves, indicating that DRX is the primary softening mechanism. Either increasing deformation temperature or decreasing strain rate makes the flow stress level reduce remarkably. The hot deformation activation energy and the stress exponent are calculated to be 577.845 kJ/mol and 4.62 by the regression analysis of sine hyperbolic function, respectively. From the deformed microstructures, it is found that the DRX nucleates mainly through grain boundary bulging but occasional through subgrain evolution only occurred at high strain rates and high temperatures. The critical stress and corresponding strain for DRX can be expressed through the dimensionless parameter, Z / A . The critical ratios of σ c / σ p and e c / e p are also identified, which are 0.98 and 0.72, respectively. Moreover, the DRX kinetics for as-cast 254SMO SASS can be represented in the form of Avrami equation, and the predicted volume fraction of new grains based on the developed model agrees well with the experimental results.

The semiconducting properties of passive films grown on 00Cr13Ni5Mo2 supermartensitic stainless steel were investigated in comparison with conventional 2Cr13 martensitic stainless steel. Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were used for the studies. 00Cr13Ni5Mo2 steel exhibited a good corrosion resistance performance, attributing to its passive capability. The results of Mott-Schottky analysis demonstrated n-type semiconductors for the passive films with doping densities of about 1O 20 − 10 21 cm −3 , and the thickness of spacecharge layers was also calculated. The experimental results confirmed that Mo plays an important role in improving the corrosion resistance of 00Cr13Ni5Mo2 steel due to its impact on the doping density.

The microstructural evolution and mechanical property of 00Crl3Ni5Mo2 supermartcnsitic stainless steel (SMSS) subjected to different heat treatments were investigated. Room tensile tests, hardness tests, scanning electron microscopy, transmission electron microscopy and X-ray diffraction were conducted on the heat-treated steels. It is found that the microstructure of the heat-treated steel is composed of tempered lath martensite, retained austenite and δ-ferrite. The austenitizing temperature and tempering temperature have a significant effect on the microstructural changes, which leads to the complex variations of mechanical properties. The fine tempered lath martensite and more dispersed reversed austenite in the microstructure facilitate improving the comprehensive mechanical properties of the studied steel. The optimal heat treatment process of 00Crl3Ni5Mo2 SMSS is obtained by austenitizing at 1000 °C for 0.5 h + hair cooling followed by tempering at 630 °C for 2 h + hair cooling, where the excellent combination of tensile strength, elongation and hardness can be achieved.

The deformation characteristics of as-cast S31254 superaustenitic stainless steel (SASS) have been investigated by the isothermal compression testing at temperature of 1173–1473 K and strain rate of 0.01–10 s−1 on a Gleeble-1500D thermo-mechanical simulator. The approach of processing map (PM) was used to reveal the hot workability affected by the process parameters (such as e , T and e) and microstructural evolution during the hot deformation. It is found that the process parameters have obvious effects on the power dissipation efficiency, instability factor and softening characteristic. The safe deformation domain can be identified from the PM, and the variation of peak efficiency with strain is obtained in the safe domain. The optimal hot working condition at large strains (⩾0.7) corresponds to the temperature range of 1376–1473 K and the intermediate strain rate range of 0.07–1.38 s−1, with a peak efficiency of 35% at ∼1473 K and 0.4 s−1. In this field, the original coarse grains can be substituted by the fine recrystallized grains, indicating that the high power is dissipated by the dynamic recrystallization. Meanwhile, three instable regions, which should be avoided in hot processing, are detected from the PM and the related instability mechanisms are also discussed.

Dynamic recrystallisation (DRX) behaviour in 904L superaustenitic stainless steel was studied by isothermal hot compression tests conducted in the temperature range of 900–1200°C and strain rate range of 0·001–10 s−1. The critical conditions for initiation of DRX are identified from the stress dependence of the derivative of strain hardening rate versus stress curves (dθ/dσ versus σ curves). The Z parameters combined with the temperature and strain rate effects during hot deformation are obtained by the regression analysis. Moreover, the kinetics model of DRX is established and the complete DRX grain size of 904L superaustenitic stainless steel is a power-law function of Z parameter with an exponent of –0·27.

Hot compression tests in the temperature range from 1273 to 1423 K and strain rate range from 0.01 to 10 s–1 were carried out on a Gleeble 1500D thermo-mechanical simulator for as-cast 21Cr economical duplex stainless steel (EDSS). The deformation behavior and microstructural evolution were investigated. It is found that the flow behavior strongly depends on the strain rate and deformation temperature, and the flow stress increases with the increase of strain rate and the decrease of temperature. The softening degree of ferrite becomes larger with decreasing strain rate and increasing deformation temperature, and the austenite is gradually spheroidizing. The flow localization band easily happens at high strain rate and low temperature because of the uneven deformation in the microstructure. Moreover, the constitutive model with the compensation of strain was developed on the basis of hyperbolic sine equation to predict the flow stress of as-cast 21Cr EDSS. The material constant in the model such as α, n, Q and ln A was functioned with the strain by sixth order polynomial. The results show that the developed constitutive model has excellent predictability of flow stress under the experimental deformation conditions for as-cast 21Cr EDSS.

Hot compression tests of as-cast 904L austenitic stainless steel were carried out at deformation temperatures of 1000–1150 °C and strain rates of 0.01–10 s−1 with different strains. The hot working behavior was investigated by the analyses of flow curves, deformed microstructures and kinetics. The results show that the flow stress depends strongly on the deformation temperature and the strain rate, and it increases with the deformation temperature decreasing and the strain rate increasing. Also, the flow curves combined with microstructural evidence indicate that the dynamic recrystallization process of this material is very sluggish with the increase of strain. High temperature and low strain rate together with large deformation can provide the right changes for obtaining more equiaxed dynamically recrystallized grains. The deformation energy (Q) in the whole range of conditions is calculated to be 459.12 kJ/mol by regression analysis and the constitutive equation embraced the Zener–Hollomon parameter is developed. Furthermore, the processing maps (PMs) are generated to reveal the correlation between microstructural evolution and process parameters based on the flow stress data. It is observed from the PM that two regions of deformation stability and instability are characterized. An optimal processing window available for the hot deformation can be obtained to achieve the desired microstructure with dynamic recrystallization. In addition, the predicted instability regions are verified and the reasons of these instabilities are revealed.

Combining the intermetallic compound with the ductile metal at the eutectic composition is one promising method to improve the ductility of the intermetallic compound. This paper reports the microstructure and the micro-hardness of the Ni–Ni 3 Si eutectic in situ composites prepared by electron beam floating zone melting technique. Ni–Ni 3 Si eutectic in situ composites display regular lamellar eutectic structure at the solidification rate R =0.3–4.0 mm/min. The lamellar spacing is decreased with the increase of the solidification rate. The phase composition of the Ni–Ni 3 Si eutectic in situ composites is also determined by X-ray diffraction. Ni–Ni 3 Si eutectic in situ composites present lower micro-hardness than pure Ni 3 Si, although a small quantity of metastable Ni 31 Si 12 phase is formed during the directional solidification process.

The hot workability of 00Cr13Ni5Mo2 supermartensitic stainless steel was investigated by hot compression and hot tension tests conducted over the temperature range of 950–1200 °C and strain rates varying between 0.1 and 50 s −1 . The processing map technique was applied on the basis of dynamic materials model and Prasad instability criterion. Microstructure evolutions, Zener–Hollomon parameter as well as hot tensile ductility were examined. The results show that, as for the hot working of 00Cr13Ni5Mo2 supermartensitic stainless steel in the industrial production, the large strain deformation should be carried out in the temperature range 1140–1200 °C and strain rate range 0.1–50 s −1 , where the corresponding Zener–Hollomon parameters exhibit low values. Moreover, when deformed under high strain rate range (above 15 s −1 ), the deformation temperature can be reduced reasonably.

The nose temperature for σ-phase precipitation in super-duplex stainless steel (SDSS) UNS S32750 was evaluated by hardness method. Color-optical microscopy, scanning electron microscopy, energy spectrum analysis, impact and corrosion testing were carried out to investigate characteristics of microstructure and properties of the SDSS aged at the nose temperature. The experimental results indicate that the nose temperature of precipitation is 920 °C and aging at this temperature tiny σ phases can precipitate at phase interfaces or ferrite grain boundaries within 2 min. Prolonging aging duration the amount of σ-phase increases and a dual structure with σ and γ is obtained when aging for 120 min. The precipitation of σ-phase leads to severe deterioration in impact toughness (longitudinal/transverse direction) and corrosion resistance of SDSS.

The hot deformation behavior of 00Cr23Ni4N duplex stainless steel under medium–high strain rates (5–50 s − 1 ) has been analyzed using the Zener–Hollomon parameter and processing maps, which is based on compression tests made at temperatures ranging from 900 to 1150 °C. The results display the significant influence of high strain rate and high temperature on hot deformation behavior of 00Cr23Ni4N duplex stainless steel. A classical hyperbolic sine equation is applied to reveal the relations between the peak stress, strain rate and deformation temperature, in which the activation energy, Q and stress exponent, n are 263.4 kJ/mol and 2.6, respectively. The Zener–Hollomon parameters at low and high temperatures are calculated respectively to reflect the microstructural evolutions. Based on the processing map obtained, an ideal hot working condition for commercial processing is in the temperature range between 1075 and 1150 °C with a strain rate of 10 to 30 s − 1 . Under such condition, both ferrite and austenite dynamic re-crystallizations can be obtained and the corresponding Zener–Hollomon parameter is relatively low. Furthermore, the unstable domains are indicated by the processing map.

The effects of phase transformation on mechanical properties and pitting corrosion of 2205 duplex stainless steel were investigated. The amount of σ phase in the test specimen varied up to a maximum of 6% by thermal treatment at 850 °C for up to 60 min. The results showed that σ phase markedly increased the hardness and decreased the impact toughness of the test steel. But the increasing tendency of the ultimate tensile strength and the yield strength was not obvious, while the total elongation abruptly decreased with the aging time from 5 to 60 min. SEM impact microfractograph analysis revealed that the types of impact fracture changed from ductile mode to transcrystalline mode when the specimens were aged for 5—60 min. Furthermore, the extent of pitting potential reducing was found to be strongly temperature dependent, more pronounced at the higher temperature. During the incubation period of σ phase nucleation, the pitting corrosion test temperature and the aging time had collaborative effects on evidently displacing the pitting potential towards less noble values. After 15 min, the higher temperature contributed more to decreasing the pitting potential than the aging time.

To investigate the influence of tempering process on microstructural evolutions and mechanical properties of 00Cr13Ni4Mo supermartensitic stainless steel (SMSS), specimens were tempered in the temperature range of 520–720 °C for 3 h followed by air cooling and an optimized tempering temperature was chosen to prolong holding time from 3 to 12 h. After heat treatments, microstructure examination was conducted by scanning electron microscope, X-ray diffraction examinations, hardness measurements and tensile tests. The results revealed that the superior mechanical properties were achieved by quenching at 1040 °C for 1 h+water cooling and tempering at 600 °C for 3 h + air cooling. Increasing isothermal tempering time could improve the toughness notably. It was believed that the property was correlated with the microstructure of tempered lath martensite and retained austenite. More retained austenite content is beneficial to the higher toughness of the SMSS.

This article reports the results of an experimental program aimed at improving ball mill availability by increasing the wear resistance of ball mill liners. The ball mill liners made from the wear-resistant alloy steel containing 0.8–2.0 wt%B (viz. boron alloy steel) have been developed. The effects of quenching temperature on the microstructural modification, mechanical properties, and wear resistance of boron alloy steel have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, impact tester, hardness tester, and impact wear tester. The results show that the hardness of boron alloy steel increases, and impact toughness has no obvious change, when the quenching temperature increases. When the quenching temperature reaches 1000°C, the matrix of boron alloy steel transforms into the lath martensite, and there is excellent wear resistance. After quenching at 1000°C and tempering at 220°C, boron alloy steel liners have excellent wear resistance a...

The effects of rare earth (RE) on the microstructures and properties of high carbon high speed steel (HCHSS) were investigated. The results show that when suitable RE is added to the HCHSS, the effect of RE on the austenite and eutectic carbides is obvious. The austenite grain and coarse eutectic structure are refined, and flake carbides in the eutectic structures become short and fine. After heat treatment, most of the eutectic carbides are spheroidized and distributed in a uniform manner. The hardness and red hardness of modified HCHSS are slightly increased; impact toughness is greatly increased by 37. 81% and reaches 10. 17 J/cm2. The mechanism by which RE improves the structures and properties of HCHSS is also analyzed.