In the context of integrated die-casting forming technology for new energy vehicles， a new type of extra-large， highly uniform， high-toughness， and high- isotropy die-casting mold steel GY-DCK20 was developed and produced. The microstructural uniformity of samples taken from different locations and their room-temperature mechanical properties were investigated by characterization methods such as metallographic analysis， SEM analysis， and ASPEX inclusion analysis. The results indicate that the high-cleanliness smelting process （EAF +AOD） → RH → Continuous Casting → PESR effectively controls the content of harmful and gaseous elements. Fine inclusions measuring 2-5 μm account for over 73.4% of the total， with oxides being the primary type. No significant banding segregation was observed in samples taken from different locations； the spheroidized microstructure was well-developed， and carbides were fine and uniformly distributed. The heat-treated hardness after quenching at 1 030 ℃ was approximately 1HRC higher than that at 1 010 ℃， and the steel exhibited better impact performance. During the tempering stage， the secondary hardening peak occurred near 540 °C， primarily due to the precipitation of fine， granular alloy carbides； at 650 ℃， martensite began to undergo recovery and recrystallization， forming equiaxed ferrite grains； at 700 ℃， the lath structure of the martensite disappeared， carbides aggregated along the grain boundaries， and recrystallized grains coarsened significantly. At a service hardness of 44-46HRC， the test steel exhibits a transverse and longitudinal V-notch impact absorbed energy of over 35 J at various locations， with an isotropy ratio of up to 0.97 in the core， demonstrating excellent comprehensive mechanical properties.
To address the engineering issue of surface cracking in the production of large-sized P92 steel ingots， this study established a thermo-mechanical coupling model for 19 t P92 martensitic heat-resistant steel ingot casting with a height of 2 720 mm using ProCAST simulation software. The thermophysical property parameters of P92 steel were obtained by JMatPro calculations and on-site production measurements. On this basis， the effects of pouring temperature and pouring rate on the stress field of the 19 t P92 steel ingot were systematically investigated. Numerical simulation results indicate that the bottom of the ingot tail is a zone prone to severe stress concentration， and the pits at the edge of the ingot tail serve as the critical risk zones for hot cracking initiation. At pouring temperatures of 1 540， 1 550 and 1 560 ℃， the stress concentration intensifies with increasing pouring temperature， and maximum stress values all appear at the pits on the ingot tail edge. Compared with the high-temperature pouring condition at 1 560 ℃， low-temperature pouring at 1 540 ℃ reduces the maximum stress at this position by 4.7%. When the pouring rates are set as 2， 3 and 4 t/min respectively， increasing the pouring rate intensifies the cracking tendency. The maximum principal stress at the edge at a low pouring rate （2 t/min） is 9% lower than that at a high pouring rate （4 t/min）. To mitigate the hot cracking risk at the ingot tail， a low pouring rate process with a temperature of （1 550 ± 5） ℃ is recommended. This process can effectively relieve stress concentration and reduce the hot cracking risk.
This study systematically investigated the effect of different tempering temperatures （170 ℃， 230 ℃， and 290 ℃） on the microstructure and mechanical properties of NM400 wear-resistant steel. The results show that after tempering， the microstructures of the specimens with thicknesses of 30 mm and 50 mm are lath martensite + M/A constituents and lath martensite + M/A constituents + granular bainite， respectively. As the tempering temperature increases， the degree of dislocation entanglement within the martensite laths decreases， the dislocation density declines， and the precipitates gradually transforms from ε-carbides to θ-carbides. In terms of mechanical properties， the tensile strength of specimens with a thickness of 30 mm is 1 250 MPa–1 300 MPa， whereas that of 50 mm-thick specimens is 1 000 MPa–1 050 MPa. The elongation first increases and then decreases with rising temperature. The dominant strengthening mechanisms are identified as dislocation strengthening and solid solution strengthening. The contribution of carbon interstitial solid solution strengthening is about 622.3 MPa. In addition， as the temperature increases， the dislocation strengthening contribution decreases from 442.7 MPa to 343.4 MPa （for the 30 mm-thick specimens）.
To address the problem of austenite grain coarsening that is prone to occur in cold-extruded gears during high-temperature carburizing， a high-temperature carburizing gear steel resistant to grain coarsening has been developed. After high-temperature carburizing of the gear， the austenite grains did not undergo coarsening， and direct quenching was carried out by utilizing the residual heat， thereby eliminating the intermediate cooling treatment process. Through composition design and size control of second-phase precipitates， the effects of elements such as B， Ti， Nb， Al， and N on grain size， hardenability， and precipitation behavior were systematically investigated. The results showed that in B-containing steels， B preferentially combines with N to form BN， thereby reducing the precipitation amount of AlN and weakening its pinning effect on grain boundaries， which ultimately leading to grain coarsening； while in steels without B and with a higher N content， nanoscale precipitates such as AlN and Nb（C，N） can be fully formed， exerting a strong grain boundary pinning effect and significantly inhibiting grain growth. Further research indicated that by optimizing the heating process of the continuous casting billet （holding at 1 220 ℃ for 200 min）， large precipitates can be fully dissolved， and fine and dispersed second-phase precipitates can be formed during subsequent cooling， significantly enhancing the pinning force and achieving a carburized structure free of coarse grains. The developed steel adopts an optimized B-free composition （mass fraction）： 0.16-0.25 C， 0.10-0.30 Si， 0.90 Mn， 1.80 Cr， 0.05 Nb， 0.05 Al， 0.016 N， by which fine grains are formed through the combined precipitation of AlN and Nb（C，N）. Through the proper control of the heating process （heating temperature ≥ 1 220 ℃， holding time ≥ 200 min）， AlN and Nb（C，N） precipitates smaller than 0.2 μm are obtained. While the hardenability values of J9 （38 HRC） and J15 （33 HRC） meet the target requirements （J9， 34-40 HRC，and J15， 28-35 HRC）， it can achieve direct quenching after carburizing， thereby eliminating the intermediate cooling treatment process， providing a material foundation for efficient and energy-saving gear manufacturing.
To meet market demands for steel materials featuring high polishability， superior corrosion resistance and excellent strength-toughness balance， a high-quality corrosion-resistant plastic die steel with improved comprehensive properties is developed via optimizing chemical composition and heat treatment processes. The steel was smelted by the process route of "electric arc furnace + vacuum refining + electroslag remelting"， and large flat steel with a cross-sectional dimension of 230 mm×710 mm was manufactured using a 35MN rapid forging press. The effect of different post-forging heat treatment processes on the microstructure and properties of a novel corrosion-resistant plastic die steel 3Cr13NiMoVN was studied using JMatPro software， OM， SEM， hardness tester and impact testing machine. The results show that the post-forging process of 1 050 ℃ normalizing + isothermal annealing yields a more uniform spheroidal pearlite microstructure. The microstructure obtained by 1 000 ℃ normalizing + isothermal annealing is identical to that of the conventional annealing process， namely carbide-depleted zones exist in the microstructure， and chain-like carbides precipitate along twin boundaries， and these features are inherited by the tempered microstructure. The non-uniform annealed microstructure has a significant effect on the impact toughness of the steel. The impact toughness of the steel treated by 1 050 ℃ normalizing + isothermal annealing + quenching and tempering is 77%–80% higher than that of the steel treated by 1 000 ℃ normalizing + isothermal annealing + quenching and tempering process.
The demand for super-large plastic mould steel blocks is growing day by day， to reveal the microstructure at different positions of a super-large 1.2738 plastic mould steel block with dimensions of 1 200 mm × 1 300 mm × 2 700 mm during quenching， the cooling rate ranges at various locations of the large block were non-destructively determined using the DEFORM software. On this basis， continuous cooling transformation tests were carried out using a dilatometer. Combined with the test results of metallography， hardness and retained austenite， the phase transformation characteristics of 1.2738 steel at an ultra-low cooling rate of 0.008 °C/s were analyzed. The results indicate that during the “water-air-water” quenching process of the super-large block， the cooling rate at the core is only 0.026 °C/s， which is far lower than that of conventional rolled medium-thick plates and small-to-medium blocks. Considering comprehensive material properties， the quenching cooling rate range of 0.02 °C/s to 0.03 °C/s is the lower limit for controlling the final microstructures of large blocks. When the cooling rate is above this range， the obtained microstructures are dominated by martensite and upper and lower bainite； when the cooling rate falls below this range， granular bainite is the primary phase.
In this study， the continuous cooling transformation （CCT） behavior and microstructural evolution of NM400 low-alloy high-strength wear-resistant steel under both static and dynamic conditions were systematically investigated using a Gleeble-3800 thermal simulation machine， combined with metallographic observation， scanning microstructural characterization， and microhardness testing. The results indicate that for the static CCT curve， when the cooling rate ≤ 5 °C/s， the microstructure consists primarily of ferrite and pearlite； within the range of 5 °C/s–20 °C/s， the microstructure transforms to bainite； when the cooling rate exceeds 20 °C/s， a fully martensitic microstructure forms. The dynamic CCT curves show that hot deformation significantly promotes phase transformation， shifting the transformation ranges for bainite and martensite toward higher cooling rates. The critical martensite cooling rate decreases to 15 °C/s， while the material exhibits the highest peak hardness （444 HV） at a deformation temperature of 900 °C， significantly higher than the values at 950 °C （408 HV） and 850 °C （442 HV）.
Cr12MoV die steel is a typical high-carbon， high-chromium cold-work die steel. Due to its high carbon and chromium content， segregation during the late stages of solidification and the aggregation of eutectic chromium carbides are prone to occur during continuous casting， leading to defects such as surface cracks and localized fractures. Against the backdrop of Cr12MoV Die Stee continuous casting production， and based on the macroscopic defect characteristics observed on-site， the microstructure of the crack zones， and the distribution of eutectic carbides， the relationship between cracks in continuous casting billets and carbide enrichment was analyzed. Optimal process parameters were determined as follows： mold flux basicity of 0.85， viscosity of 0.05 Pa·s at 1 300 ℃， and melting point of 990 ℃； water flow rate of the mold wide face at 115 m³/h， water flow rate of the narrow face at 20 m³/h， and a cooling water temperature difference of 2.2-2.4 ℃. Based on these findings， the mold flux and mold cooling regimes were optimized. Existing industrial validation results indicate that， following optimization， the non-destructive testing pass rate for continuous casting products reached 95%-97%， with the center porosity grade controlled at 1.0-2.0 and the eutectic carbide grade at 2.0-3.5. Overall quality has approached the level of mold-cast products of the same specification. These research findings provide a reference for crack control and carbide regulation in the continuous casting of high-carbon， high-chromium die steels.
To address the issues of coarse prior austenite grains， wide martensite laths， and carbide coarsening in conventionally quenched and tempered H13 hot-work die steel， the effects of a carbide pre-precipitation–assisted critical quenching process on microstructure evolution and thermal fatigue behavior were investigated. The results show that， after a treatment comprising quenching at 1050 ℃， carbide pre-precipitation at 730 ℃， and critical quenching at 930 ℃， the prior austenite grain size was significantly refined from 126.9 μm （obtained after 1 050 ℃ quenching） to 36.3 μm， while the average martensite lath width decreased from 1.23 μm to 0.54 μm. The fine dispersed carbides formed in the pre-precipitation stage were not completely re-dissolved during subsequent critical austenitization， thereby exerting a strong pinning effect on grain boundary migration and facilitate nucleation， which resulted in a synergistic refinement of the microstructure. During long-term tempering at 610 ℃ and 700 ℃， both processes exhibited carbide dissolution and coarsening； however， the carbide pre-precipitation–assisted critical quenching sample showed smaller carbide size， more uniform distribution， and a significantly reduced coarsening rate. Both samples exhibited a two-stage softening behavior characterized by an initial rapid decrease followed by a gradual decline. Compared with conventional treatment， the carbide pre-precipitation–critical quenching sample demonstrated a lower softening rate under high-temperature long-term tempering， indicating markedly improved resistance to tempering softening. Thermal fatigue tests further revealed that after 1 000 thermal cycles， the treated samples exhibited fewer cracks and shorter average crack length， more tortuous crack propagation paths， and a significantly suppressed crack growth rate， demonstrating superior thermal fatigue resistance.
To address the billet selection requirements for industrial mass production of 110-grade SUP13Cr super martensitic stainless steel， this paper takes seamless steel pipes fabricated from continuously cast billets and forged billets via the piercing and continuous rolling process as research objects， and analyzes the microstructure evolution and property differences throughout the whole process from the as-rolled state to the heat-treated state. The results show that there is no essential difference in the phase transformation behavior between the two types of billets， with only martensitic transformation occuring under conventional industrial cooling rates and no precipitation of abnormal phases； under identical process parameters， pipes made from forged billets exhibit superior microstructure homogeneity and property stability， with stable high-temperature ductility over the 1 100 ℃ -1 300 ℃ temperature range， while pipes produced from continuously cast billets exhibit obvious as-rolled microstructural heredity， where the banded structure and δ-ferrite segregation cannot be completely eliminated by heat treatment， their hardness uniformity and both longitudinal and transverse toughness from 0 ℃ to -40 ℃ are inferior to those of forged-billet pipes， and a distinct ductility trough appears in the 1 160 ℃ -1 200 ℃ interval. Nevertheless， all performance indicators of pipes manufactured from both billet types meet the relevant industrial procurement specifications， and the findings can provide data support for billet selection and hot working process parameter setting of oil casing and tubing made of this steel grade.
The effect of the forging process on the isotropy and impact properties of hot work die steel FS450 （4Cr5Mo2V）， smelted by EAF + LF + VD + protective atmosphere electroslag remelting， was investigated using optical microscopy， scanning electron microscopy， and impact testing. A comparative analysis was conducted on the microstructure and properties of the steel processed by two methods： the axial repeated upsetting and drawing method and the multi-directional forging （MDF） method. The spheroidized microstructures of the tested steels produced by both processes reached AS4 level according to NADCA#207 standard. However， MDF significantly alleviated the banded segregation. In terms of impact properties， the average transverse and longitudinal impact absorbed energies of the MDF specimens were 25.1 J and 26.2 J， respectively， with a transverse-to-longitudinal ratio of 0.96. For the axial repeated upsetting and drawing specimens， the corresponding values were 20.6 J and 24.8 J， with a ratio of 0.83. The impact fracture surfaces of the MDF specimens exhibited larger and deeper dimples， fewer quasi-cleavage planes， and more numerous tearing ridges， indicating better toughness. After quenching and tempering， the microstructures of both tested steels consisted of tempered martensite with dispersed carbides， and the grain sizes were both finer than Grade 7. Nevertheless， the MDF process resulted in a more uniform and finer grain structure. In summary， the MDF method improves microstructural uniformity and alleviates banded segregation， thereby significantly enhancing the impact toughness and isotropy of FS450 steel， outperforming the conventional axial repeated upsetting and drawing process.
In order to study the effect of high-temperature diffusion annealing on the microstructure of 6Cr5Mo2V1 alloy tool steel， thermodynamic phase diagram calculations were conducted， and high-temperature diffusion annealing experiments at different temperatures were performed to analyze the effects of high-temperature diffusion annealing on the microstructure and alloying elements of 6Cr5Mo2V1 alloy tool steel， while friction and wear performance tests were also carried out. The results show that after holding 6Cr5Mo2V alloy tool steel at 1 230 ℃ for 3 hours， Cr-rich carbides diffuse and dissolve into the matrix， significantly alleviating compositional segregation. However， primary carbides rich in V and Mo with sizes ranging from 10 to 50 μm are highly stable and difficult to dissolve during the homogenization process. When the diffusion annealing temperature reaches 1 250 ℃， the low-melting-point eutectic structure remelts， forming micropores after cooling. Friction and wear tests indicate that samples subjected to 1 230 ℃ diffusion annealing exhibit the highest tribological stability.
Taking as-cast H13 hot-work die steel as the research material， specimens were austenitized at 1 100 ℃ for 20 min followed by oil quenching， and subsequently subjected to tempering treatments at 560 ℃， 620 ℃ and 650 ℃ with varying tempering durations and cycles. Optical microscopy （OM）， scanning electron microscopy （SEM）， electron probe microanalysis （EPMA）， X-ray diffraction （XRD）， electron backscatter diffraction （EBSD）， hardness measurements and Charpy impact tests were employed to investigate the effects of tempering parameters on microstructure evolution and mechanical properties of the steel. The results reveal that tempering temperature dominates the microstructure evolution of H13 steel. With increasing tempering temperature， time and number of cycles， the lath feature of martensite gradually weakens； precipitated fine dispersed carbides undergo aggregation， spheroidization and coarsening， while the retained austenite content and dissolved carbon content in martensite show an overall decrease， and the microstructure evolves from tempered martensite to high-temperature tempered microstructure. Tempering at 560 ℃ retains relatively high hardness， among which the group tempered at 560 ℃ for 65 min with three cycles achieves the maximum hardness of 54.6 HRC， yet a low impact absorbed energy. Tempering at 650 ℃ accelerates matrix recovery and carbide spheroidization， and the group tempered at 650 ℃ for 65 min with two cycles achieves the highest impact absorbed energy of 15.39 J with superior impact toughness. The fracture morphology gradually transforms from cleavage/quasi-cleavage fracture at low tempering temperature to dimple ductile fracture at high tempering temperature. Optimized regulation of tempering temperature， time and number of cycles enables synergistic improvement in hardness and toughness of H13 steel.
Through the analysis of the chemical composition and non-metallic inclusions data of sampling experiments using two groups of different remelting slag systems to investigate the effect of electroslag remelting slag systems on non-metallic inclusion in corrosion-resistant die steel FS136， under identical experimental conditions， experiments with the binary（CaF2-Al2O3） and the quaternary（CaF2-Al2O3-CaO-MgO） slag systems showed no significant difference in alloying element loss. Metallographic observation and SEM analysis show that the non-metallic inclusions in FS136 steel are mainly Type D inclusions consist of Al2O3-based granular inclusions. In FS136 steel processed with the quaternary experimental slag system， the Type D non-metallic inclusions were controlled to a rating level of 0.5–1.0. Compared with the binary slag system， the quaternary slag system exhibited better performance in wetting， absorption， and removal. The quaternary slag system can further improve the cleanliness of corrosion-resisant die steel FS136.
To address the issue of excessive DS-type inclusions in 1.2343 hot-work die steel produced by electroslag remelting （ESR）， a process approach involving slag system optimization was proposed. Two new slag systems （E40F and E50F） were evaluated in industrial trials. Using FactSage software and empirical formulas， key physical properties of the slag systems—such as basicity， viscosity， conductivity， and activity of certain components—were calculated， forming the basis for the ESR process. Industrial trials revealed that the E50F slag system exhibited the best overall performance， with moderate SiO₂ content enabling the modification of hard Al₂O₃ inclusions into low-risk spherical inclusions. It also combined moderate fluidity with Al₂O₃ inclusion suppression capability， making it the preferred choice for inclusion control in the finished product in production. The E40F slag system exhibited strong modification capability but suffered from high viscosity， leading to difficulties in inclusion flotation and higher residual inclusion levels， resulting in inferior performance compared to E50F. The 37 slag system exhibited the highest Al₂O₃ activity， causing significant secondary hard inclusion precipitation without modification capability， yielding the poorest inclusion control performance. Using the optimized E50F pre-melted slag significantly decreased the DS inclusions in 1.2343 hot-work die steel， achieving a rating level of 0.5 with all inclusions smaller than 15 μm. The total inclusion count decreased by 27% compared to the original slag system. The E50F slag system is more effective in removing inclusions from 1.2343 hot-work die steel.
Taking a 100 t ladle from a steel plant as the research object， a combination of physical simulation and numerical simulation was employed to systematically study the effects of bottom argon blowing parameters on fluid flow， mixing time， slag eye formation， and wall shear stress inside the ladle. By comparing different types of permeable plugs， bottom blowing flow rates， and positions， the evolution law of the flow field and the utilization mechanism of stirring energy were revealed. The results show that the stirring effect of diffusive plugs is superior to that of slotted plugs， and increasing the bottom blowing flow rate significantly reduces the mixing time. The optimal eccentricity for single-plug bottom blowing is 0.75R， and either excessively low or high eccentricity is detrimental to the effective utilization of stirring energy. The mixing effect of dual-plug bottom blowing is significantly influenced by the angle between the plugs. At an eccentricity of 0.6R and an angle of 135°， the minimum mixing time is obtained， and this configuration effectively reduces the slag eye area and wall shear stress， thereby mitigating refractory erosion.
To investigate the solidification structure and inclusion behavior during the vacuum arc remelting process of ultra-large die-casting die steel， and to explore and study the process parameters of vacuum arc remelting， computer numerical simulation technology was employed to investigate the evolution of the molten pool shape during the smelting process of ultra-large die-casting die steel ingots （diameter 1 250 mm） under three different melting rates. The segregation patterns of elements were analyzed， and the relationship between melting rate and inclusion removal trajectory， as well as the effect of different helium pressures on the solidification quality of the ingots， were studied. The results showed that， during steady-state melting， the growth rate of molten pool depth was directly proportional to the melting rate. When remelting at melting rates of 12.50 kg/min， 13.65 kg/min， and 15.0 kg/min， the simulated increasing rates of molten pool depth were 0.257 mm/min， 0.307 mm/min， and 0.397 mm/min， respectively. The inclusion removal trajectories were reasonable at all three melting rates. When the melting rate was set at 12.50 kg/min and 13.65 kg/min， the solidification front of the molten pool could not reach or fully reach the edge of the crystallizer， posing a higher risk of subsurface inclusions on the lower surface of the ingot. The water cooling effect at the bottom of the crystallizer was extremely strong during the initial stage of remelting， resulting in a high cooling rate. Simulation calculations showed that C， V， Cr， and Mo all exhibited negative segregation to varying degrees at the three melting rates， with C and V being the most pronounced， followed by Mo， and Cr showing relatively less segregation. When the ingot height reached 500 mm， the negative segregation of Cr and Mo was essentially eliminated， and the negative segregation trend of C and V significantly weakened. Computational simulations studied the effect of helium cooling on the depth of the two-phase region at two melting rates. The introduction of helium significantly reduced the depth of the two-phase region， reducing the depth by over 40%. Within a certain range， the pressure of the introduced helium was inversely proportional to the depth of the molten pool's two-phase region. The introduction of helium significantly reduced the segregation effects of various alloying elements in the top region of the ingot， with the shape of the severely segregated elements zone changing from conical to flatter. The concentration distribution of elements became more uniform. Elements in the core of the ingot tended to show positive segregation， while elements on the surface of the ingot tended to show negative segregation.
Hot-forging die steel is a critical material used in the hot-forging of metal components. It is subjected to harsh service conditions involving high temperatures， high stresses， and repeated thermal cycling， making it prone to failure mechanisms resulting from the coupling of various complex processes， such as thermal wear， thermal fatigue， plastic deformation， and creep. Therefore， the in-service performance of hot-forging die steel directly affects the quality of forgings and production costs， making it imperative to fully understand the evolution of its failure behavior and propose effective strategies for performance enhancement. Addressing this need， this paper reviews research progress on the in-service behavior and failure mechanisms of hot-forging die steels and systematically summarizes four typical performance enhancement strategies—alloy composition optimization， precise control of heat-treated microstructure and properties， surface modification and strengthening， and nanoparticle-reinforced matrix—along with their respective effects. Based on this， the paper summarizes the significant potential of the synergistic application of multiple strategies in extending die life and improving in-service performance； highlights the limitation that a single strengthening strategy cannot fully account for the dynamic evolution of failure behavior under the coupled effects of multiple factors； and notes the current inadequacy of collaborative strengthening design and in-service performance prediction models tailored to actual operating conditions. Finally， the outlook indicates that future research should focus on the organic synergy of various strengthening technologies and the application of artificial intelligence in material design and performance prediction. These two areas mutually reinforce each other and are expected to provide the theoretical foundation and technical pathways for the continuous development of hot-forging die steels toward the goals of longer service life， higher reliability， and greater economic efficiency.
To study the continuous cooling transformation behavior of QGF17 non-quenched and tempered steel， a dilatometer was used to measure the expansion curves of the tested steel at different cooling rates. The effects of cooling rate on microstructure， phase transformation characteristics， and hardness were systematically analyzed by optical microscopy， scanning electron microscopy， and microhardness testing. The results show that the critical transformation temperatures of QGF17 steel are Ac₁ ≈ 751 ℃ and Ac₃ ≈ 863 ℃. As the cooling rate increases from 0.1 ℃/s to 10 ℃/s， the microstructure of the tested steel gradually transforms from relatively coarse ferrite/bainite mixed structure to a mixed structure mainly composed of acicular ferrite and lath bainite. Under low cooling rate conditions， the phase transformation occurs at higher temperatures， resulting in a higher ferrite fraction in the microstructure and lower hardness； with the increase of cooling rate， the stability of undercooled austenite is enhanced， diffusion-controlled transformation is suppressed， and the fraction of bainitic and martensitic structures increases， leading to an increase in microhardness from 718HV1 at 0.1 ℃/s to 943HV1 at 10 ℃/s. The microhardness at 0.2 ℃/s and 0.5 ℃/s is comparable to that of as-forged condition， about 920HV1. Based on the expansion curves， microstructure observation， and hardness results， the continuous cooling transformation （CCT） curve of QGF17 steel was established， which provides an experimental basis for the design of controlled cooling process and strength–toughness regulation of this steel.
GH3625 is a typical high-temperature alloy， and its smelting process is usually carried out using a duplex process. However， some processes are invisible， making parameter measurement and result prediction challenging. In such cases， numerical simulation methods are required to investigate the relevant processes. For the VIM and ESR process control of GH3625 alloy， by combining Procast and Meltflow software and constructing a computational model， the solidification process can be simulated and analyzed， and the influence of tooling dimensions and process parameters on the VIM and ESR processes can be revealed. The results show that for ϕ400 mm ingots of GH3625 alloy， without using risers in vacuum induction melting and casting， a shrinkage cavity as deep as 580 mm forms at the head of the ingot. Increasing the riser height can significantly reduce defects； reducing the pouring speed can shorten the length of the internal shrinkage cavity， amd the length at a pouring speed of 7 kg/s is 300 mm shorter than that at 13 kg/s. Increasing the mold preheating temperature increases the volume of the internal shrinkage porosity and cavity. During the electroslag remelting process， as the slag height increases， the peak value of secondary dendrite spacing increases by 20 μm， and the probability of spot segregation decreases； as the remelting rate increases， the width of the mushy zone increases from 160 mm to 200 mm. This method and related research results provide theoretical references for process optimization in the VIM and ESR smelting processes of GH3625 alloy.
