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Effect of Forging and Heat Treatment Processes on Properties of 40CrNi2Mo Subsea Valve Stem Forgings
摘要：The requirements for mechanical properties and reliability of subsea oil and gas equipment are extremely stringent. This research focuses on 40CrNi2Mo subsea valve stem forgings， systematically analyzes the roles of major alloying elements， and investigates the effects of chemical composition， forging ratio， and heat treatment processes on mechanical properties. Through the preparation and testing of qualification test coupons （QTCs）， it was ultimately determined that under a drawing forging ratio of 4.5∶1， the subsea valve stem forgings exhibit excellent performance after 910 ℃ full annealing + （890-900） ℃ dual-medium quenching +（620-630 ） ℃ high temperature tempering. For batch-produced valve stem forgings， the mechanical properties obtained from specimens taken from the body itself are as follows： yield strength of 950 MPa， tensile strength of 1 080 MPa， elongation of 19.5%， reduction of area of 62.0%， average impact absorbed energy of 71.8 J at -29 ℃， and a product surface hardness of 331 HBW， fully meeting the technical requirements.关键词：40CrNi2Mo;Subsea Valve Stem;Forging;Heat Treatment Process;Mechanical Properties13|4|0更新时间：2026-06-30 - 摘要：To investigate the effect of cold rolling process parameters on the thickness deviation of SUS301L stainless steel plate， a quarter-symmetry model of a 20-high cold rolling mill was established using ABAQUS finite element software. The control variable method was employed to analyze the effects of front tension， back tension， and rolling speed on the thickness uniformity of the steel plate. The standard deviation of the thickness deviation was used to quantify the thickness fluctuation. The results show that as the front tension increases from 130 MPa to 160 MPa， the standard deviation decreases from 6.46×10⁻3 to 6.19×10⁻3； when the front tension is further raised to 190 MPa， the standard deviation increases to 7.22×10⁻3. A minimum standard deviation of 5.75×10⁻3 is obtained at a back tension of 85 MPa， and the flatness deteriorates when the back tension exceeds 115 MPa. The thickness distribution is most uniform when the rolling speed is in the range of 6-7 m/s， with a standard deviation of 5.75×10⁻3 at 6 m/s. When the speed increases to 8 m/s， the standard deviation rises to 8.06×10⁻3. Comprehensive analysis indicates that the optimal combination of process parameters for achieving the most uniform thickness distribution of the SUS301L stainless steel plate is a front tension of 160 MPa， a back tension of 85 MPa， and a rolling speed of 6-7 m/s. This study provides a theoretical basis for improving thickness uniformity and reducing waviness and other shape defects in actual production.关键词：SUS301L Stainless Steel;Cold Rolling;Thickness Deviation;Finite Element Modeling;Process Parameter Optimization9|4|0更新时间：2026-06-30
- 摘要：N06625 nickel-based alloy plates were produced by two different process routes， namely VIM+ESR and EAF+AOD+continuous casting. The segregation characteristics， microstructure and mechanical properties were systematically investigated by means of mechanical testing machine， optical microscope， SEM， EDS and electron probe microanalyzer. The results show that the segregation degrees of Mo and Nb in the continuous casting slab are lower than those in the conventional electroslag ingot， providing favorable conditions for subsequent homogenization treatment and hot working. Owing to the finer original dendrites and milder segregation， the continuous casting slab requires a shorter homogenization holding time to eliminate elemental segregation and exhibits better process applicability. Under the actual production conditions in this work， the optimal homogenization parameters for the
- 摘要：Fe-13Cr-0.7C-0.3V martensitic stainless steel is widely used in various fields due to its high strength and hardness. However， its high carbon and high alloy content lead to the precipitation of networked carbides during solidification， which severely deteriorates the mechanical properties of the steel. In this paper， （Differential Scanning Calorimetry）DSC was used to determine the phase transformation temperatures of the hot-rolled Fe-13Cr-0.7C-0.3V martensitic stainless steel. The effect of austenitizing temperature on the microstructure and properties of the test steel was investigated， and the appropriate quenching temperature was determined； on this basis， the influence of tempering temperature in the range of 100-700 ℃ on its microstructure and properties was studied in depth. Experimental evidence validates that the austenite start and finish for the transformation of ferrite to austenite of Fe-13Cr-0.7C-0.3V steel are 834.3 ℃and 879.6 ℃， respectively. In the course of austenitizing temperature elevation， the introduction of V inhibits the dissolution and coarsening of carbides and refines their particle size； meanwhile， the volume fraction of retained austenite increases， resulting in reduced hardness of the material. During tempering， the increase in temperature promotes the decomposition of martensite， and supersaturated carbon precipitates from the solid solution to form dispersed carbides. A tensile strength of 1 930 MPa and fracture elongation of 3.8% are achieved through tempering at 200 ℃.关键词：Martensitic Stainless Steel;Heat Treatment;Carbides;Mechanical Properties;Microstructure12|2|0更新时间：2026-06-30
- 摘要：The Q490DRL2 steel used for large-thickness pressure vessels often exhibits fluctuations in transverse impact energy specifically manifested as significant variations in individual impact values. In this study， for Q490DRL2 steel with a thickness of 48 mm， specimens taken from the half-thickness position with superior and inferior impact energy were comparatively analyzed in terms of microstructural characteristics and inclusion distribution patterns. The results indicate that the matrix microstructures of the two types of specimens are essentially consistent. However， the fracture surface of the specimen with inferior impact energy exhibits a distinct serrated morphology， with numerous fine cracks present near the fracture surface. Some of these cracks pre-existed in the material， while others initiated and propagated during impact loading. Additionally， pronounced microstructural segregation and propagated large-sized cracks were observed in the matrix of this specimen， with fragmented square silicate inclusions visible inside the cracks. In contrast， the fracture surface of the specimen with superior impact energy is relatively flat and smooth， with few observable microcracks and a reduced presence of large inclusion particles in the matrix. In summary， large-particle silicate inclusions and microstructural segregation are the primary factors contributing to the fluctuation in low-temperature impact energy of Q490DRL2 steel used for large-thickness pressure vessels.关键词：Pressure Vessel Steel;Impact Energy;Metallographic Microstructure;Inclusion10|2|0更新时间：2026-06-30
- 摘要：To improve the cleanliness of high-quality 51CrV4 spring steel strip， this study systematically investigates the evolution characteristics of inclusions throughout the entire non-steady casting process by industrial sampling experiments， inclusion analysis， and oxygen-nitrogen analysis. The limiting factors and improvement measures for cleanliness are proposed. The results indicate that inclusions in the slab are primarily complex inclusions composed of CaO-MgO-Al2O3， CaO-Al2O3， MgO-Al2O3， and Al2O3 respectively combined with precipitates （MnS， TiN， and CaS）. During RH calcium wire feeding and soft argon blowing， the molten steel experiences both reoxidation and a significant nitrogen pickup. Furthermore， severe reoxidation occurs in the tundish during the first heat， with significant fluctuations in the molten steel level in the early casting stage， leading to noticeable gas absorption and an increase in the number of oxide and nitride inclusions. Consequently， the number of inclusions at the head of the slab formed after casting is relatively high. Adjustments should be made to the RH calcium wire feeding and soft argon blowing processes to reduce molten steel exposure. Ensuring the quality of the tundish refractory material during the first heat， extending the argon blowing time before casting， controlling molten steel level fluctuations in the early casting stage， and cutting off the slab head at 3 m from its beginning are recommended.关键词：51CrV4 Spring Steel;Non-Steady Casting;Inclusions;Cleanliness;Continuous Casting;Oxygen and Nitrogen Content14|3|0更新时间：2026-06-30
- 摘要：This study systematically investigated the effect of isothermal spheroidizing annealing on the microstructure and properties of a novel hot-work die steel 5CrNiMoVNb. The as-forged microstructure primarily consists of lath bainite， martensite， and a small amount of carbides， exhibiting a hardness of 528 HV. The results demonstrated that the austenitizing temperature and isothermal temperature play a decisive role in determining the spheroidized microstructure and hardness. An ideal spheroidized pearlite structure with a high spheroidization rate and uniformly distributed carbides was achieved at an austenitizing temperature of 790 ℃ and an isothermal temperature of 690 ℃. Excessively high austenitizing temperature （810 ℃） led to carbide coarsening and a decreased spheroidization rate， while an excessively low isothermal temperature （630 ℃） inhibited the spheroidization process， resulting in the formation of lamellar pearlite. Surface hardness analysis confirmed that the increase in the spheroidization rate of the pearlite structure directly resulted in a significant reduction in material hardness. The optimal process window for isothermal spheroidizing annealing under the conditions of this study has been determined. The low-hardness， high-spheroidization-rate microstructure obtained under this process is expected to be beneficial for subsequent machining and final heat treatment.关键词：Hot-work Die Steel;5CrNiMoVNb;Isothermal Spheroidizing Annealing;Spheroidized Pearlite;Microstructure;Hardness14|2|0更新时间：2026-06-30
- 摘要：The coarse and non-uniform grain structures arising from microstructural heredity in large rotors fabricated from 9Cr-3 W-3Co martensitic heat-resistant steel present a significant challenge to mechanical property uniformity. This study investigates the influence of isothermal annealing pretreatment （single-step and stepwise） in conjunction with tempering temperature （700 ℃， 710 ℃， and 720 ℃） on microstructural homogeneity and mechanical properties. Both annealing routes， followed by normalizing， refined the prior austenite grains to ASTM No. 7.0 or finer. Notably， stepwise isothermal annealing substantially enhanced the spatial uniformity of the grain size and effectively mitigated the post-forging microstructural heredity. Following quenching and tempering， differences in strength and ductility between specimens subjected to the different isothermal annealing cycles were negligible （<5%）. However， stepwise annealing significantly improved impact toughness and reduced data scatter. Tempering temperature was identified as the dominant factor controlling the strength-toughness balance： increasing the tempering temperature from 700 ℃ to 720 ℃， decreased the tensile strength from 852 MPa to 817 MPa， while concurrently increasing the impact absorbed energy from 22.3 J to 33.3 J. The optimal combination of properties （Rm >830 MPa， Rp0.2 >680 MPa， impact energy >24 J） was achieved through stepwise isothermal annealing followed by tempering at 710 ℃. This improvement is primarily attributed to the refinement and homogeneous distribution of carbides， as well as improved prior austenite grain uniformity. These findings provide a critical theoretical and experimental foundation for the engineering application of this material in 630 ℃ ultra-supercritical high-pressure turbine rotors.关键词：Martensitic Heat-resistant Steel;Stepwise Isothermal Annealing;Tempering Temperature;Grain Refinement;Strength-toughness Balance10|3|0更新时间：2026-06-30
- 摘要：The microstructure， mechanical properties， wear resistance， and wear mechanism of NM550RE steel alloyed with 0.001 2% rare-earth w［Ce］ were systematically studied， and compared them with those of conventional NM550 steel. The results show that the conventional NM550 steel has an average original austenite grain size of 9.48 μm and a hardness of 553HBW. The addition of Ce refines the grain size， reducing the average austenite grain size to 7.55 μm and increasing the hardness to 579HBW. Meanwhile， the impact energy at -40 °C increases from 29.43 J to 34.63 J. The G65 abrasive wear test results show that the wear resistance of NM550RE steel is 1.11 times that of conventional NM550 steel. After rare-earth modification， the inclusions exhibit better compatibility with the matrix， while the steel possesses a fine grain size， higher hardness， and toughness. During wear， this helps hinder abrasive particles from penetrating into the matrix and prevents further development of ploughing grooves， thereby reducing their width and depth and resulting in superior wear resistance.关键词：Rare Earth Element Ce;Abrasive Wear;Wear Resistance;Wear Mechanism14|4|0更新时间：2026-05-14
- 摘要：To study the continuous cooling transformation behavior of 4330V low alloy high strength steel， experiments were conducted at different cooling rates 0.05-30 ℃/s using a quenching dilatometer. Optical microscopy， field emission scanning electron microscopy， and microhardness tester were used to detect and analyze the microstructure and Vickers hardness of the material after phase transformation at different cooling rates， and the continuous cooling transformation （CCT） curve of its supercooled austenite was plotted. The results showed that when the cooling rate was 0.05-0.15 ℃/s， the microstructure was mainly bainite + ferrite， belonging to the high-temperature and medium-temperature two-phase composite transformation zone， and the hardness values were all below 450 HV； when the cooling rate was 0.2-1 ℃/s， the microstructure was mainly bainite + martensite， belonging to the medium-temperature and low-temperature two-phase composite transformation zone， and the hardness was between 472-577HV； when the cooling rate was greater than or equal to 3 ℃/s， the microstructure was fully martensitic， belonging to the low-temperature martensitic transformation zone， and the hardness values were all above 593 HV.关键词：4330V Low Alloy High Strength Steel;Continuous Cooling Transformation;CCT curve;Microstructure;Hardness17|4|0更新时间：2026-05-14
- 摘要：The evolution of primary carbides and the mechanism of microstructural stability in powder metallurgy AISI M3：2 steel during holding at different temperatures were systematically investigated. Scanning Electron Microscopy （SEM） was employed to characterize the microstructure and carbide precipitation characteristics of the material， and room temperature impact toughness tests were conducted to analyze the influence of microstructural evolution on mechanical properties. The research results indicate that during holding at temperatures of 1 100 ℃ and below， the M₆C-type （tungsten-rich） and MC-type （vanadium-rich） primary carbides in the steel exhibit good thermal stability. Their average size and volume fraction do not significantly change with increasing holding temperature and prolonging holding time. This phenomenon is primarily attributed to the initial microstructural homogeneity imparted to the material by the powder metallurgy preparation process， as well as the extremely high thermodynamic stability of the two carbides themselves. When the holding temperature is raised to 1 150 ℃ and the holding time is prolonged， the M₆C-type carbides with relatively low thermodynamic stability undergo substantial dissolution， leading to a sharp decrease in the overall volume fraction of carbides. Simultaneously， the undissolved residual M₆C-type carbides undergo significant coarsening and form discontinuous ring-like distribution characteristics at grain boundaries. The aforementioned microstructural evolution ultimately results in a significant reduction in the impact toughness of the material. Therefore， under prolonged holding conditions， 1 150 ℃ serves as the critical temperature for the microstructural stability of primary carbides in this type of high-alloy tool steel， providing crucial experimental data support for optimizing heat treatment process parameters and precisely controlling the hot working window.关键词：Powder Metallurgy Tool Steel;Carbide;Alloying Element;Austenitizing;Heat Treatment16|3|0更新时间：2026-05-14
- 摘要：The service performance of GCr15SiMn bearing steel， a core material for critical components in high-end manufacturing， is highly sensitive to the mechanical properties of non-metallic inclusions. This study investigates CaO-SiO2-Al2O3 composite inclusions in GCr15SiMn steel and systematically examines the effect of the w（CaO）/w（SiO2） on their phase composition， silicate network structure， and micromechanical properties using X-ray diffraction， Raman spectroscopy， and nanoindentation. The results show that the inclusions initially form as amorphous glassy phases， and their crystallinity increases significantly with increasing w（CaO）/w（SiO2）. The phase composition evolves from an amorphous-dominated structure at low w（CaO）/w（SiO2） to stable crystalline phases such as CaSiO3， CaAl2Si2O8， and CaAl2O4 at high w（CaO）/w（SiO2）. With increasing w（CaO）/w（SiO2）， the silicate network undergoes pronounced depolymerization： the fraction of medium and high-polymerization units decreases， while that of low-polymerization units increases， accompanied by a continuous rise in non-bridging oxygen content. In terms of mechanical properties， the hardness of the inclusions generally decreases， whereas the elastic modulus increases steadily to 104.04 GPa. The fracture resistance parameter H3/E2 decreases from 0.071 GPa to 0.052 GPa， and the energy dissipation ratio Wp/Weincreases from 0.99 to 1.2. Inclusions with low w（CaO）/w（SiO2） possess a highly polymerized and dense network structure， endowing them with superior hardness and damage resistance， which contributes to enhanced overall hardness and damage tolerance of the GCr15SiMn bearing steel.关键词：GCr15SiMn Bearing Steel;Inclusions;Amorphous Phase;Silicate Network;Mechanical Property15|9|0更新时间：2026-05-12
- 摘要：The thermal compression deformation behavior and microstructure evolution of 2 200 MPa ultra-high-strength steel were experimentally investigated using a Thermomastor-Z thermal simulation machine. Stress-strain curves under different strain rates （0.01 s⁻¹， 1 s⁻¹， and 5 s⁻¹） and deformation temperatures （850–1 150 ℃） with an engineering strain of 60% were tested. By analyzing the stress-strain curves and conducting EBSD analysis on deformed samples， the effects of strain rates and temperatures on the deformation resistance and dynamic recrystallization process of 2 200 MPa ultra-high-strength steel were studied. The recrystallization activation energy of the experimental steel was determined through regression calculations. The results indicate， 1） Higher deformation temperatures and lower strain rates result in lower deformation resistance of 2 200 MPa ultra-high-strength steel； 2） Dynamic recrystallization is activated at the strain rate of 0.01 s⁻¹ when the temperature ≥900 ℃； at strain rates of 1 s⁻¹ and 5 s⁻¹， dynamic recrystallization is activated when the temperature ≥1 000 ℃. During hot working processing， higher strain rates should be applied at temperatures ≥1 000 ℃， while lower strain rates are recommended below 1 000 ℃； 3） The calculated recrystallization activation energy of 2200 MPa ultra-high-strength steel is 421.20 kJ/mol； 4） A constitutive model for the flow stress of 2 200 MPa ultra-high-strength steel was established.关键词：2 200 MPa-grade Ultra-High Strength Steel;Thermal Simulation;Hot Deformation Behavior;Dynamic Recrystallization;Recrystallization Activation Energy13|8|0更新时间：2026-05-12
- 摘要：To study the effects of different deoxidation methods on the evolution of inclusions and carbides in Cr12MoV steel， experimental steels smelted by three deoxidation processes （Al deoxidation， Al deoxidation combined with rare earth Ce composite deoxidation， and vacuum carbon deoxidation） were analyzed using scanning electron microscopy-energy dispersive spectroscopy （SEM-EDS） and the OTSInca automatic inclusion analysis system （Oxford Instruments）. The effect of the three deoxidation methods on the mass fractions of total oxygen （T.O） and total nitrogen （T.N）， the number， size， composition and morphology of inclusions， as well as the precipitation characteristics and distribution of carbides in Cr12MoV steel were explored. The results show that at 480 Pa， carbon exhibits stronger deoxidation and denitrification effects than Al and Ce. The mass fractions of T.O and T.N in the as-cast samples can be reduced to 0.000 7% and 0.002 7%， respectively. In the experimental steels produced by single Al deoxidation and vacuum carbon deoxidation， inclusions are dominated by fine Al₂O₃， with number densities of 165/mm² and 95/mm²， and average areas of 0.70 μm² and 0.66 μm²， respectively. After Al deoxidation combined with rare earth treatment， inclusions are mainly Ce₂O₂S， with an inclusion number density of 120/mm² and an average area of 2.0 μm². The participation of Ce in deoxidation reduces the total number of inclusions but increases their size. Carbides in both single Al deoxidation and vacuum carbon deoxidation samples exhibit a fish-bone morphology and distribute continuously along grain boundaries to form a network structure， with area fractions of 12.15% and 12.29%， respectively. In contrast， carbides in the Al deoxidation + Ce treatment sample are fine lamellar or granular， distributing discontinuously along grain boundaries in a chain-like or particulate form without forming a continuous network structure， and the carbide area fraction is 11.70%. Ce treatment can significantly refine carbides， break the continuous network structure and reduce the precipitation amount. Compared with Al deoxidation， vacuum carbon deoxidation has no obvious effect on the morphology and precipitation of carbides. This study suggests that， without considering time， replacing partial Al deoxidation with vacuum carbon deoxidation in the smelting of Cr12MoV steel is feasible. It can purify molten steel and optimize the properties of inclusions without affecting carbide precipitation. Al deoxidation combined with rare earth composite deoxidation has a significant effect on carbide control.关键词：Cr12MoV Die Steel;Inclusions;Carbides;Rare Earth Treatment;Vacuum Carbon Deoxidation19|12|0更新时间：2026-05-12
- 摘要：The high-temperature plastic deformation behavior of 2 200 MPa grade ultra-high strength steel was investigated using a Gleeble 3 800 thermal simulation test machine. The stress-strain curves of high-temperature tensile deformation at strain rates of 0.1 s-1 and 0.001 s-1 within the temperature range of 750 ℃-1 100 ℃ were obtained. Metallographic observation and EBSD analysis were conducted on the microstructure of the longitudinal section near the fracture surface， and scanning electron microscopy （SEM） was used to observe the fracture morphology. The high-temperature plasticity and dynamic recrystallization behaviors of 2 200 MPa grade ultra-high strength steel were investigated. The research results showed： 1） At both strain rates， the tensile strength of the test steel continuously decreased with increasing deformation temperature； 2） at the strain rate of 0.1 s-1， the reduction of area increased with increasing temperature during tensile deformation at 750 ℃-1 000 ℃， and decreased with increasing temperature when T> 1 000 ℃； at the strain rate of 0.001 s-1， the reduction of area showed two troughs， near 800 ℃ and 925 ℃， respectively； the reduction of area peaked at T=1 050 ℃， after which it decreased with increasing temperature； 3） based on the strength and reduction of area， the forgeability of the test steel can be calculated. At the strain rate of 0.1 s-1， the forging temperature range of the test steel was 880 ℃-1 100 ℃， and at the strain rate of 0.001 s-1， the forging temperature range was 850 ℃-1 100 ℃； 4） when the deformation temperature was ≥1 050 ℃， high-temperature molten dendrites appeared on the tensile fracture， and the initial forging temperature should be below 1 050 ℃； 5） when the strain rate was 0.001 s-1， the onset temperature of dynamic recrystallization was 750 ℃. When the strain rate was 0.1 s-1， the onset temperature of dynamic recrystallization was 880 ℃. When the deformation temperature was ≥ 900 ℃， the grain size at the strain rate of 0.1 s-1 was finer than that at a strain rate of 0.001 s-1， so the rapid forging process should be adopted in the early stage of forging； when the deformation temperature is less than 900 ℃， the dynamic recrystallization fraction is higher at a strain rate of 0.001 s-1. Therefore， a slow forging process should be adopted in the later stages of forging to obtain a uniform and fine forged microstructure. The optimal forging temperature range for 2 200 MPa grade ultra-high strength steel is between 880 ℃ and 1 050 ℃.关键词：2 200 MPa Grade Ultra-High Strength Steel;Thermal Simulation Tensile Test;High-Temperature Plasticity;Forgeability;Dynamic Recrystallization10|7|0更新时间：2026-05-09
- 摘要：In order to systematically study the effect of quenching and tempering temperature on the mechanical properties of 21Cr12MoV martensitic heat-resistant stainless steel， specimens of the steel were prepared using various heat treatment processes. Subsequently， tensile tests， hardness tests， impact tests， as well as metallographic and fracture surface analyses were conducted. The results show that the tensile and impact properties of the material are optimal when the quenching temperature is 1 050 ℃. The tensile strength is 973 MPa， and the impact energy is 37.6 J. As the tempering temperature increases， the strength and hardness of the material gradually decrease， while the impact toughness gradually increases. To achieve the optimal strength - toughness balance and the best overall performance of the product， the recommended heat treatment process consists of a quenching temperature of 1 050 ℃ and a tempering temperature of 680 ℃.关键词：21Cr12MoV Steel;Martensitic Heat-resistant Steel;Heat Treatment Process;Mechanical Properties17|9|0更新时间：2026-05-09
- 摘要：To improve the efficiency and reduce the energy consumption of an electromagnetic induction heater for steel ingot riser， an optimization method for the yoke is proposed. Using ANSYS multi-physics coupling simulation， the effects of the yoke on the magnetic field distribution， heating efficiency， and solidification of the steel ingot riser were analyzed. The results show that when the yoke is expanded to 130% of the coil area and its thickness is increased to 120 mm， magnetic flux leakage at the edges is suppressed under the same working conditions. This increases the magnetic flux density on the molten steel surface by approximately 80% and increases the Joule heating power by about 2.5 times. Meanwhile， the temperature distribution in the riser region becomes more uniform， solidification of the ingot is delayed， and the feeding channel duration at the riser line is extended by 18 min. Under the same excitation current of 692 A， this optimized design increases the heating power from 10.67 kW before optimization to 26.58 kW， achieving an efficient heating mode of "low current， high power" while reducing coil losses.关键词：Yoke;Induction Heating;Steel Ingot Riser;Heating Efficiency;Numerical Simulation21|100|0更新时间：2026-04-08
- 摘要：GCr15 is a typical representative of high-carbon chromium bearing steel， and surface decarburization can severely degrade its surface quality and service performance. This paper presents an experimental investigation and mechanism analysis on the isothermal decarburization behavior of GCr15 bearing steel in air， N₂+H₂+H₂O and N₂+H₂O atmospheres. The results show that in air atmosphere， no decarburization layer was observed at 700 ℃， a fully decarburized layer and a partially decarburized layer were observed at 800 ℃， and only a partially decarburized layer was present above 900 ℃. Compared with hypoeutectoid steel， GCr15 exhibits a decarburization layer covering a wide range of carbon content. Coupled with the strong sensitivity of room-temperature microstructure to the cooling rate after isothermal decarburization， the evolution of room-temperature microstructure in the decarburization layer with decarburization time is complex. The hardness method， rather than the metallographic method， is the preferred method for measuring decarburization depth. The total decarburization layer thickness increases with rising temperature and holding time， reaching 511， 690， 960， and 1 270 μm after isothermal treatment at 700， 800， 900， and 1 000 ℃ for 120 min respectively. In comparison with the N₂+H₂+H₂O atmosphere， the strong oxidizability of the N₂+H₂O atmosphere results in the oxidative ablation of the decarburized ferrite layer and even a certain proportion of the partially decarburized layer. The results of this study provide guidance for decarburization layer control during the thermal processing design of GCr15 steel.关键词：GCr15 Bearing Steel;Surface Decarburization;Heating Atmosphere;Hardness Method27|114|0更新时间：2026-04-08
- 摘要：Laser polishing can effectively improve the surface quality of cold work die steel Cr12MoV. To explore the influencing factors of surface quality during laser polishing， an orthogonal experimental design was employed to formulate the experimental protocol. Cr12MoV die steel surfaces were treated using varying laser polishing parameters. Through characterization of the polished layer microstructure and geometric features such as cracks， the mechanisms underlying crack initiation and propagation during laser polishing of Cr12MoV die steel were examined. SPSS software was utilized to assess the influence patterns of laser polishing parameters on surface quality metrics of the polished regions， including remelted zone depth， polished layer depth， surface roughness， and crack formation. The results show that the surface roughness of all polished die steel specimens across experimental groups was reduced compared to the original surface， with the minimum value reaching 0.944 μm， decreased by 88.8% relative to the original surface. Crack formation was observed on the polished surfaces of die steel specimens in certain groups subjected to higher polishing power. During laser polishing of Cr12MoV die steel， laser process parameters directly effect surface quality indicators such as remelted zone depth， polished layer depth， crack dimensions， and surface roughness. Among these parameters， laser power and scanning speed are significant factors affecting the aforementioned surface quality metrics， whereas the influence of overlap rate is non-significant. Optimal selection of laser polishing process parameters can effectively enhance the surface quality of Cr12MoV die steel.关键词：Cr12MoV;Laser polishing;Process Parameter;Cracking;Thermal effect18|86|0更新时间：2026-04-08
- 摘要：Hot-work die steel（DHA） steel was selected as the research object and adds Niobium （Nb） elements with mass fractions of 0， 0.009%， 0.019%， 0.028%， and 0.038% to the steel. The influence of Nb on the microstructure and mechanical properties of DHA steel was investigated. The results show that Nb addition promotes the formation of large-sized primary carbonitrides during solidification， and aggravates the secondary dendrites segregation in the as-cast microstructure. Nb addition refines the grain size of the experimental steel after tempering. With the increase of Nb mass fraction， toughness gradually decreases after tempering at 560 ℃ and 590 ℃， and first increases and then decreases after tempering at 620 ℃. Strength first increases and then decreases with increasing Nb content. Considering the comprehensive mechanical properties， when the mass fraction of Nb element is 0.019%， DHA steel has the best performance.关键词：Hot-work Die Steel;Niobium Content;Microstructure;Mechanical Properties17|53|0更新时间：2026-04-07
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