High-toughness high-chromium casting process

Abstract

The invention relates to the technical field of metal casting processes, and discloses a high-toughness high-chromium casting process. According to the method, precise regulation and control of a melt microstructure are achieved through composite modification treatment, carbide is distributed in a three-dimensional dispersion mode in combination with a multi-gradient centrifugal casting technology of a five-layer composite module, and the adverse effect of a net-shaped structure on toughness is thoroughly eliminated; the matrix structure and the residual stress field are synergistically optimized through the multi-mode heat treatment and the gradient cryogenic-tempering coupling process, and the interface bonding strength and the impact resistance are remarkably improved; the cross-process parameter transmission system dynamically associates the melt state, the solidification structure and the heat treatment parameters to ensure the process stability and the product homogeneity; the high hardness is maintained, the toughness bottleneck is broken through, the service life of a casting section is prolonged, the high performance and low-cost preparation requirements are considered through technological parameter optimization path design, and the method is suitable for batch production under the heavy load working conditions of mines, cement and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of metal casting segment processes, and specifically to a high-toughness high-chromium casting segment process. Background Art

[0002] High-chromium cast iron casting segments are wear-resistant casting components with an iron-carbon-chromium matrix. The chromium content usually exceeds 12% (commonly 15 - 30%). They are formed into segment shapes (cylindrical or spherical) through the casting process and are mainly used as the core consumables for grinding media in industries such as mining and cement. Currently, the production processes of high-chromium cast iron casting segments generally adopt an alloy system dominated by chromium and carbon. By adjusting the Cr / C ratio (usually 6 - 8) and adding alloying elements such as molybdenum and nickel, the matrix properties are improved. Existing technologies mostly use conventional sand casting or single-speed centrifugal casting, combined with a heat treatment process of oil quenching + single tempering to obtain casting segment products with high hardness (≥58HRC). Some improved solutions enhance wear resistance by adding elements such as copper and tungsten, or use cryogenic treatment to reduce the content of retained austenite.

[0003] The traditional high-chromium cast iron casting segment process has the following technical bottlenecks:

[0004] 1) Carbides are prone to forming a coarse continuous network structure, becoming a crack propagation channel, resulting in insufficient impact toughness (usually <10J / cm 2 );

[0005] 2) Conventional heat treatment is difficult to eliminate quenching stress and carbide interface stress concentration, resulting in early spalling failure during service;

[0006] 3) Insufficient control of the solidification structure, dendritic segregation leads to composition inhomogeneity, deteriorating the isotropy of the material;

[0007] 4) Dependence on high-cost alloying elements (such as copper and tungsten) to improve performance, resulting in a decline in economy.

[0008] Therefore, a high-toughness high-chromium casting segment process is proposed. Summary of the Invention

[0009] Aiming at the deficiencies of the prior art, the present invention provides a high-toughness high-chromium casting segment process to solve the problems in the background art.

[0010] To achieve the above object, the present invention provides the following technical solution: A high-toughness high-chromium casting segment process, including the following steps:

[0011] Step 1, compound modification treatment: Before melting, add a rare earth-nitride compound modifier to the raw materials. The modifier contains a LaCe mixed rare earth (0.08 - 0.15wt%), TiN (0.05 - 0.12wt%), AlN (0.03 - 0.08wt%), and the particle size is 20 - 50nm;

[0012] Step 2, multi-gradient centrifugal casting: Adopt a five-layer composite structure centrifugal module. Based on the high melt fluidity characteristics formed in Step 1, implement three-stage variable-speed centrifugation. In the first stage, maintain at 800 - 1000 rpm for 3 - 5 min to eliminate the agglomeration of the modifier. In the second stage, maintain at 1200 - 1500 rpm for 8 - 12 min to achieve the directional arrangement of carbides. In the third stage, maintain at 600 - 800 rpm for 2 - 3 min to promote the formation of equiaxed crystals;

[0013] Step 3, in-situ synthesis of nano-carbides: Based on the catalytic effect of TiN in Step 1, under the condition of V / Nb composite microalloying (V / Nb atomic ratio 1:1.2 - 1.5), through the forced convection generated by the centrifugation in the second stage of Step 2, precipitate (V,Nb)C@TiN core-shell structure nano-particles (size 50 - 150 nm) in the melt;

[0014] Step 4, multi-modal heat treatment: Aiming at the nano-carbide distribution characteristics formed in Step 3, implement pulsed magnetic field-assisted austenitization (0.5 - 1.2 T, 5 - 10 Hz) and double-medium quenching, where the termination temperature of the water-cooling stage forms a mapping relationship with the axial temperature gradient of the centrifugal module in Step 2;

[0015] Step 5, gradient cryogenic-tempering coupling treatment: Based on Step 4, the dislocation network formed by quenching, apply an axial compressive stress (0.2 - 0.5σs) synchronously during the liquid nitrogen treatment at -196 °C, and achieve the topological optimization of the stress field and carbide distribution through three-stage variable-temperature tempering.

[0016] Preferably, the preparation method of the composite modifier in Step 1 includes:

[0017] Mix LaCe mixed rare earth and TiN / AlN in a mass ratio of 1:0.6 - 0.8 under argon protection by ball milling. The ball-to-material ratio is 8:1, the rotation speed is 300 rpm, and the time is 4 - 6 h to obtain nitride composite particles with a rare earth layer-coated surface.

[0018] Preferably, the centrifugal module in Step 2 adopts a five-layer composite structure:

[0019] Inner contact layer: Nano-zirconia coating (thickness 50 - 80 μm);

[0020] Second layer: Copper alloy water-cooling jacket (cooling water flow rate 2 - 5 m / s);

[0021] Third layer: Silicon carbide foam ceramic layer (porosity 60 - 70%);

[0022] Fourth layer: Graphite / boron nitride composite lubricating layer (thickness 0.1 - 0.3 mm);

[0023] Outer layer: High-strength steel support frame.

[0024] Preferably, in step three, the melt superheat degree is controlled by dynamic electromagnetic stirring, the stirring frequency is 15 - 25 Hz, and the stirring intensity and the melt temperature satisfy the relational expression: I = 0.05×ΔT + 3, where I is the current intensity, in kA; ΔT is the time.

[0025] Preferably, the specific parameters of the double - medium quenching in step four are as follows:

[0026] Water - cooling stage: The cooling rate is 80 - 100 °C / s, and the termination temperature is detected by an infrared - thermocouple dual - signal feedback system;

[0027] Polymer quenching stage: Use a polyalkylene glycol solution (concentration 18 - 22%), and the cooling rate is 15 - 20 °C / s.

[0028] Preferably, an axial compressive stress is applied during the gradient cryogenic treatment in step five, the pressure value is controlled at 0.2 - 0.5 times the material yield strength, and the pressure direction is the same as the centrifugal force direction during centrifugal casting.

[0029] Preferably, a B micro - alloying element (0.005 - 0.015%) is introduced in the raw material ratio of step one, and it satisfies the relational expression: (B%) = 0.2×(Cr%) / (C%) 2 - 0.03×(Mo%).

[0030] Preferably, establish a carbide distribution regulation mechanism across processes:

[0031] Based on the modifier addition amount in step one, dynamically adjust the centrifugal speed N (rpm) in the second stage of step two, and it satisfies the relational expression: N = 250×(TiN wt％ +AlN wt％ ) + 800;

[0032] Based on the size d (nm) of the nano - carbide in - situ synthesized in step three, control the axial compressive stress P (MPa) in the cryogenic treatment in step five, and it satisfies: (where σs is the material yield strength);

[0033] Use the equiaxed crystal ratio η (%) of the solidification structure in the third stage of step two to set the pulse magnetic field frequency f (Hz) in step four, and it satisfies: f = 0.1×η + 5.

[0034] Preferably, establish a parameter transfer system across processes:

[0035] Take the solidification structure characteristics (equiaxed crystal ratio, secondary dendrite arm spacing) at the end of the third stage of step two as the regulation basis for the pulse magnetic field frequency in step four, and it satisfies f (Hz) = 0.8×(equiaxed crystal ratio)+0.05×(dendrite arm spacing μm);

[0036] Feed back the average size of the nano-carbide synthesized in-situ in Step 3 to the pressure parameter of the cryogenic treatment in Step 5, satisfying P(MPa) = 120 / (d(nm)) 0.5 ;

[0037] Based on the residual stress distribution data after quenching in Step 4, dynamically optimize the temperature gradient of the three-stage tempering in Step 5 to control the tempering temperature fluctuation ≤ ±3°C.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] Through composite modification treatment, the present invention realizes precise regulation of the melt microstructure. Combining with the multi-gradient centrifugal casting technology of the five-layer composite module, the carbides are distributed in a three-dimensional dispersion manner, completely eliminating the adverse effect of the network structure on toughness; the multi-modal heat treatment and the gradient cryogenic-tempering coupling process synergistically optimize the matrix microstructure and the residual stress field, significantly improving the interface bonding strength and impact resistance; the cross-process parameter transfer system dynamically correlates the melt state, solidification structure and heat treatment parameters to ensure process stability and product homogeneity; while maintaining high hardness, it breaks through the toughness bottleneck, extends the service life of the casting section, and through the process parameter optimization path design, takes into account the preparation requirements of high performance and low cost, and is suitable for batch production under heavy load working conditions such as mines and cement.

[0040] Other features and advantages of the present invention will be described in the following specification, and, in part, will be obvious from the specification, or will be understood by implementing the present invention. The objectives and other advantages of the present invention can be realized and obtained by the structures pointed out in the specification, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a process flow chart of the high-toughness high-chromium casting section of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art in the technical field of the present invention without creative efforts based on the embodiments of the present invention belong to the protection scope of the present invention.

[0043] Please refer to Figure 1 , a high-toughness high-chromium casting section process in the present invention. Taking the high-chromium alloy casting section as an example, the present invention includes the following contents:

[0044] Example 1

[0045] Step 1: Composite modification treatment

[0046] Operation process:

[0047] 1. Pretreatment and weighing of raw materials

[0048] 11. Accurately proportion the ingredients by mass percentage (weighing error ≤ ±0.02%), and select high-purity raw materials (purity ≥ 99.5%):

[0049] Electrolytic chromium block (Cr ≥ 99.8%, particle size 10 - 20mm);

[0050] Graphite powder (fixed carbon ≥ 99.9%, D50 = 20μm);

[0051] Ferromolybdenum alloy (Mo 60%, crushed to 1 - 3mm particles);

[0052] Ferrovanadium alloy (V 50%, passing through 80 - mesh sieve).

[0053] 12. Accurate addition of element B:

[0054] According to the formula:

[0055] Example calculation: Cr = 28%, C = 2.8%, Mo = 2.0% → B% = 0.2×28 / (2.8) 2 - 0.03×2.0 = 0.008; Weigh 20% of ferroboron alloy (B).

[0056] 2. Preparation of rare earth-nitride composite modifier:

[0057] Raw material ratio:

[0058] Mixed rare earth of LaCe: 0.08 - 0.15wt% (take 0.12% in the example);

[0059] TiN: 0.05 - 0.12wt% (take 0.08% in the example);

[0060] AlN: 0.03 - 0.08wt% (take 0.05% in the example);

[0061] Accounting for the total mass percentage of the smelting alloy raw materials: 0.12% + 0.08% + 0.05% = 0.25%; Process the raw materials by ball milling:

[0062] Use QM-WX4 type planetary ball mill (vacuum argon protection type), ball-to-material ratio 8:1 (zirconia grinding balls with a diameter of 5mm), rotation speed 300rpm (accurately controlled by frequency converter), time 5h (pause for 10min every 30min to prevent overheating), and generate rare earth-nitride composite modifier with a particle size of 20 - 50nm.

[0063] Step two: Multi-gradient centrifugal casting

[0064] Adopt a five - layer composite structure centrifugal module. Based on the high melt fluidity characteristics formed in Step 1, implement three - stage variable - speed centrifugation to achieve the directional distribution of carbides and the refinement of equiaxed grains;

[0065] Operation process:

[0066] 1. Module pretreatment

[0067] Five - layer structure assembly:

[0068] Inner contact layer: Prepare a nano - zirconia coating using the atmospheric plasma spraying process, with a power of 45 kW, a powder feeding rate of 30 g / min, and a spraying distance of 100 mm; the thickness control target is 65 ± 5 μm;

[0069] Second layer: Process a spiral water channel on the inner wall of the copper alloy sleeve and connect it to the circulating water system (flowmeter set at 3.5 m 3 / h, pressure 0.4 MPa);

[0070] Third layer: Use silicon carbide foam ceramics with the porosity controlled at 63%;

[0071] Fourth layer: Use a graphite / boron nitride composite lubricating layer (mass ratio 7:3);

[0072] Outer layer: Use a high - strength steel support frame.

[0073] 2. Three - stage centrifugation control

[0074] For the five - layer composite structure centrifugal module, based on the high melt fluidity characteristics formed in Step 1, implement three - stage variable - speed centrifugation;

[0075] 21. First stage (800 - 1000 rpm for dispersing modifiers):

[0076] Inject the melt into the five - layer composite module, start the centrifuge to 900 rpm, and use a high - speed camera system to monitor the melt flow state in real - time; and use image analysis software (Matlab algorithm) to identify agglomerates (threshold diameter 50 μm);

[0077] When the number of detected agglomerates > 5 pieces / cm 2 , instantaneously increase the speed to 1000 rpm (duration 10 s);

[0078] Secondary sampling metallographic inspection shows that the number of agglomerates decreases from 15 pieces / cm 2 to 2 pieces / cm 2 .

[0079] 22. Second stage (1200 - 1500 rpm for directional arrangement):

[0080] Rotational speed calculation formula: N = 250×(TiN 0.08％ +AlN 0.08％ ) + 800 = 250×(0.08 + 0.05) + 800 = 1130 rpm. Taking a safety factor of 1.2 → actual rotational speed 1350 rpm.

[0081] 23. Third stage (600 - 800 rpm promotes the formation of equiaxed grains):

[0082] Solidification structure feedback regulation:

[0083] Use an infrared thermal imager (FLIR A700) to monitor the surface temperature gradient of the module; when the temperature difference between the center and the edge > 80°C, trigger the speed reduction program;

[0084] Rotational speed curve equation:

[0085] n(t) = 800×e -0.1t

[0086] where t is time;

[0087] When the initial value t = 0, n = 800 rpm, and it drops to 700 rpm after 2.5 min; calculated value: 800×e ∧ {-0.25} = 622 rpm. Taking a safety value of 700 rpm.

[0088] Step three: In-situ synthesis of nanocarbides

[0089] Based on the TiN substrate in step one and the forced convection generated by centrifugation in the second stage of step two, (V,Nb)C@TiN core-shell nanoparticles are formed in the melt;

[0090] Operation process:

[0091] 1. Activation of the TiN catalytic substrate:

[0092] It is carried out synchronously when the centrifugation enters the second stage;

[0093] Melt pretreatment:

[0094] When the centrifugation enters the second stage (rotational speed stabilized at 1350 rpm), the melt temperature is maintained at 1550°C, the liquidus temperature is 1455°C, and the superheat ΔT = 95°C;

[0095] Purify the melt by argon gas blowing to remove surface oxides (oxygen content ≤ 20 ppm).

[0096] Surface activation of TiN:

[0097] The TiN particles added in step one (surface coated with La-Ce rare earth layer) release rare earth elements in the high-temperature melt to form active sites;

[0098] SEM observation shows that the thickness of the rare earth coating layer is 5 - 8 nm, which can effectively reduce the nucleation energy barrier of (V,Nb)C.

[0099] 2. V / Nb microalloying and diffusion control:

[0100] It is carried out in the second stage of centrifugation from the 2nd to the 8th minute.

[0101] Addition of alloying elements:

[0102] Weigh ferroniobium and ferrovanadium according to the V / Nb atomic ratio of 1:1.2 (V 0.6%, Nb 0.72%).

[0103] Add them to the melt in three times (with an interval of 2 minutes). Start electromagnetic stirring after each feeding: The stirring frequency is 20 Hz, and the current intensity I = 0.05×95 + 3 = 7.75 kA; and the stirring reverses every 3 minutes to eliminate the segregation of the melt composition.

[0104] Forced convection promotes diffusion:

[0105] The Coriolis acceleration a = ω 2 r = (1350×2π / 60) 2 ×0.3 m = 12.5 g, driving the melt to form a radial - circumferential composite flow (flow velocity 0.8 m / s); The high - shear flow field (shear rate ≥500 s -1 ) accelerates the migration of V and Nb atoms to the surface of TiN particles.

[0106] 3. Control of the formation and growth of the core - shell structure:

[0107] The operation is carried out from the 8th to the 12th minute of centrifugation.

[0108] V and Nb combine with C in the melt and preferentially nucleate at the active sites of TiN to generate the primary (V,Nb)C phase, and the nucleation density reaches 1×10 5 grains / mm 2 (SEM statistics);

[0109] Ti atoms diffuse to the surface of (V,Nb)C under the action of melt convection to form a continuous TiN shell; By controlling the melt superheat (ΔT = 95 ± 5 °C) and stirring intensity, the growth rate of the shell is restricted to ensure a thickness of 5 - 8 nm;

[0110] The turbulent effect generated by centrifugal convection (Reynolds number Re = 1.2×10 5 ) inhibits particle aggregation, making the particle size stable at 50 - 150 nm; At the end of centrifugation, the volume fraction of nanoparticles in the melt is 0.8%, and the main peak of the size distribution is 85 nm.

[0111] 4. Real-time monitoring and adjustment:

[0112] The laser Doppler velocimeter monitors the flow rate (≥0.5 m / s) to ensure effective forced convection; when the superheat degree is out of tolerance (ΔT > 100 °C), the induction heating power is automatically reduced.

[0113] Samples are taken at the 10th minute of centrifugation. After being rapidly cooled by high-pressure argon gas, TEM-EDS analysis shows that: the core component is (V 0.5 Nb 0.5 )C, and the outer shell is TiN; La and Ce elements are enriched at the interface (atomic concentration ≥ 5%), confirming the rare earth catalytic effect.

[0114] Step Four: Multimodal heat treatment

[0115] Orient the austenitization process through pulsed magnetic field control, combine double-medium quenching to achieve grain refinement, and correlate the centrifugal temperature gradient to control the thermal stress distribution;

[0116] Operation process:

[0117] 1. Pulsed magnetic field-assisted austenitization:

[0118] Magnetic field parameter setting:

[0119] The magnetic field intensity is 0.8 T, which is achieved by adjusting the pole spacing of the permanent magnet.

[0120] Frequency calculation: According to the solidification structure characteristics (equiaxed crystal ratio 78%, secondary dendrite arm spacing 45 μm) at the end of the third stage of Step Two, according to the formula:

[0121] f = 0.8×78 + 0.05×45 = 67.8 Hz (rounded to 68 Hz)

[0122] Magnetic field loading operation:

[0123] Place the casting on the magnetic field treatment table and turn on the circulating water cooling system (to prevent the coil from overheating);

[0124] Use a gaussmeter to detect the magnetic field uniformity at 5 points on the surface of the casting (deviation ≤ 3%).

[0125] 2. Double-medium quenching control:

[0126] Water cooling stage:

[0127] Start the high-pressure water spraying system (pressure 0.7 MPa), and the nozzle array covers the surface of the casting.

[0128] Synchronously monitor through an infrared thermal imager (surface temperature) and an embedded thermocouple (core temperature): when the surface temperature reaches 420 °C and the core temperature reaches 480 °C, trigger the medium switching signal.

[0129] The real-time water cooling rate is displayed as 93 °C / s.

[0130] Polymer quenching stage:

[0131] Quickly transfer the casting to a polyalkylene glycol solution tank (concentration 20%, temperature 40 °C).

[0132] Adjust the flow rate of the solution circulation pump to stabilize the cooling rate at 18 °C / s.

[0133] Use a refractometer to detect the solution concentration every 5 minutes. When the deviation exceeds ±1%, automatic liquid replenishment is carried out.

[0134] Step Five: Gradient cryogenic-tempering coupling

[0135] Through stress co-regulation, enhance the interfacial bonding strength between carbides and the matrix;

[0136] Operation process:

[0137] 1. Cryogenic treatment and compressive stress loading:

[0138] Liquid nitrogen perfusion:

[0139] Open the liquid nitrogen storage tank valve and inject liquid nitrogen into the cryogenic box at a rate of 20 kg / min until the temperature stabilizes at -196 °C.

[0140] The temperature sensor monitors in real time. When the fluctuation exceeds ±3 °C, an alarm is triggered.

[0141] Axial compressive stress calculation and loading:

[0142] According to the average size of the nanoparticles generated in Step Three, d = 85 nm, calculate the pressure according to the formula:

[0143]

[0144] Set the hydraulic press loading rate to 2 MPa / s, and the final pressure is 13.0 MPa (material yield strength 450 MPa, 0.29σs);

[0145] The pressure direction is strictly aligned with the centrifugal force direction during centrifugal casting (laser alignment system calibration deviation ≤ 1°).

[0146] 2. Three-stage variable-temperature tempering control:

[0147] Initial parameter setting:

[0148] Primary tempering: 200 °C × 1 h (9-point temperature measurement in the furnace, maximum temperature difference 4 °C);

[0149] Secondary tempering: 350 °C × 2 h (insert a sample detection rod, the surface residual stress measured by an X-ray stress meter is -320 MPa);

[0150] Level 3 tempering: dynamically adjusted to 440℃×1.5h (originally set at 450℃, lowered by 10℃ due to excessive residual stress).

[0151] Dynamic optimization basis:

[0152] According to the residual stress distribution data after quenching in step 4 (surface -320MPa, core -280MPa), calculate the tempering temperature gradient:

[0153] ΔT 回火 =0.1×(σ 表面 -σ 目标 )=0.1×(320-300)

[0154] =2℃(actual adjustment 10℃)

[0155] Temperature control accuracy:

[0156] The PID temperature control system ensures that the tempering temperature fluctuation in each section is ≤±3℃ (thermocouple redundancy verification).

[0157] Example 2

[0158] This embodiment and Example 1 adopt the same five-layer composite module structure, three-stage centrifugal control strategy and cross-process parameter transmission system, and only adjust the raw material ratio and some process parameters to verify the adaptability of the process.

[0159] 1. Adjustment of raw material ratio

[0160] C 3.0%, Cr 30%, Mo 2.5%, Ni 1.8%, V 0.8%, B 0.015%

[0161] Composite modifier: LaCe 0.15%, TiN 0.12%, AlN 0.08% (total 0.35%).

[0162] 2. Modification of process parameter adaptability

[0163] Eccentric phase:

[0164] The first stage: 1000 rpm × 3 min (due to the increase in Cr content, the dispersion force needs to be enhanced);

[0165] Second stage: 1500 rpm × 12 min (formula N = 250 × (0.12 + 0.08) + 800 = 1100 rpm, taking 1.36 times the safety factor);

[0166] The third stage: 600 rpm × 3 min (extending the low-speed stage to compensate for the rapid solidification of the high-Cr melt).

[0167] Heat treatment adjustment:

[0168] The austenitizing temperature is increased to 1080°C (matching the high Cr content);

[0169] Cryogenic pressure press (Nanoparticle d = 105 nm).

[0170] Example 3

[0171] This embodiment simplifies the process within the framework of embodiment 1, retains the five-layer module and three-stage centrifugal core features, and adjusts some parameters to reduce production costs.

[0172] 1. Optimization of raw material ratio

[0173] C 2.5%, Cr 25%, Mo 1.5%, Ni 0.8%, V 0.3%, B 0.005%

[0174] Composite modifier: LaCe 0.08%, TiN 0.05%, AlN 0.03% (total 0.16%).

[0175] 2. Measures to improve process efficiency

[0176] Eccentric phase compression: total duration reduced from 21.5 minutes to 15 minutes;

[0177] The first stage: 800 rpm × 2 min (end early after high-speed video confirmation that the dispersion effect meets the standards);

[0178] The second stage: 1200 rpm × 10 min (maintaining carbide gradient distribution);

[0179] The third stage: 700 rpm × 3 min (the effect of time shortening is compensated by increasing water cooling).

[0180] Simplified heat treatment:

[0181] Single tempering 400℃×3h (replacing three-stage tempering, reducing costs by 40%);

[0182] Deep cooling time is shortened to 1h (pressure is still implement).

[0183] Comparative Example 1

[0184] Using conventional casting and heat treatment process

[0185] Raw material ratio:

[0186] C 2.8%, Cr 18%, Mo 1.0%, Si 1.2%, Mn 1.0%.

[0187] Melting process:

[0188] Smelted in a common medium-frequency furnace at a temperature of 1500°C without vacuum protection;

[0189] The measured melt viscosity is 5.8 mPa·s (without modification treatment, poor fluidity)

[0190] Pouring method:

[0191] Sand casting (without centrifugal control), pouring temperature 1380°C;

[0192] Naturally cooled after solidification, without microstructure control.

[0193] Heat treatment:

[0194] Conventional oil quenching: Heat preservation at 980°C for 2 h, oil cooling to room temperature;

[0195] Single tempering: 400°C × 3 h, air cooling.

[0196] Comparative Example 2

[0197] Only a constant centrifugal speed is adopted.

[0198] Raw material ratio:

[0199] Same as Example 1 (including composite modifier and B element)

[0200] Centrifugal pouring:

[0201] Centrifugal module: Ordinary steel mold (without five-layer composite structure);

[0202] The rotation speed is constantly 1000 rpm, and the time is 15 min.

[0203] Pouring temperature 1420°C.

[0204] Heat treatment:

[0205] Conventional oil quenching (without pulsed magnetic field assistance);

[0206] Cryogenic treatment: -80°C × 2 h (axial pressure not applied).

[0207] Comparative Example 3

[0208] Each process is independently controlled.

[0209] Raw materials and modification treatment: The same as Example 1.

[0210] Centrifugal pouring:

[0211] The three-stage rotational speed is fixed as: 900 rpm × 5 min → 1200 rpm × 10 min → 800 rpm × 3 min; the rotational speed is not dynamically adjusted according to the melt viscosity.

[0212] Synthesis of nano-carbides:

[0213] The electromagnetic stirring current is not adjusted according to the ΔT value (fixed I = 5 kA);

[0214] The size of nano-particles fluctuates greatly (60 - 180 nm).

[0215] Heat treatment and cryogenic treatment:

[0216] The pulse magnetic field frequency is fixed at 10 Hz (not related to the proportion of equiaxed grains);

[0217] The cryogenic pressure is fixed at 0.3σs (not adjusted according to the nano-particle size).

[0218] The hardness, impact toughness, carbide size and process cost of the alloys produced in Examples 1 - 3 and Comparative Examples 1 - 3 are tested, and the test results are shown in Table 1;

[0219] Table 1

[0220]

[0221] Compared with the traditional process (Comparative Example 1, the impact toughness is only 6.3 J / cm 2 and the carbide size is 28 μm), in Examples 1 - 3 of the present invention, through the synergistic effect of optimizing the melt fluidity (the viscosity is reduced by 44%) with a composite modifier + five-layer module gradient centrifugation (the carbide size ≤ 2.5 μm), a breakthrough improvement in the impact toughness of 18.9 - 25.3 J / cm 2 is achieved, while maintaining a hardness ≥ 61 HRC; in Comparative Example 2 (single centrifugal rotational speed), due to the network distribution of carbides, the toughness is less than 40% of that in Example 1, and in Comparative Example 3 (no parameter transfer), although the hardness is similar, the retained austenite content exceeds 8%, verifying the key regulatory role of the cross-process parameter transfer system (the proportion of equiaxed grains → magnetic field frequency, nano-particle size → cryogenic pressure) on the tissue uniformity. In Example 2, a hardness of 68 HRC is achieved by increasing the Cr content (30%), and in Example 3, the cost is reduced by 30% through process simplification, demonstrating the scalability of the present technical solution between performance and cost.

[0222] The present invention optimizes the melt composition through composite modification treatment (introducing LaCe-TiN-AlN modifier), controls the carbide distribution (size ≤ 2.5 μm) by five-layer module gradient centrifugal casting, and a cross-process parameter transfer system (dynamically correlating the centrifugal rotational speed, magnetic field frequency and cryogenic pressure), successfully breaks through the "high hardness - low toughness" technical bottleneck of high-chromium casting segments, and realizes an impact toughness of 18.9 - 25.3 J / cm2 (200-300% improvement over traditional processes) while maintaining a hardness of ≥61 HRC. Example 2 increases the Cr content (30%) to push the hardness to 68 HRC. Example 3 verifies the cost-effectiveness of the simplified process. The comparative examples demonstrate that the absence of any core technology (such as modifiers, centrifugal control, or parameter transfer) leads to a drastic drop in performance, highlighting the innovative synergistic effects and industrial application value of this invention.

Claims

1. A high-toughness high-chromium casting process, characterized in that, It includes the following steps: Step 1, composite modification treatment: Before melting, add a rare earth-nitride composite modifier to the raw materials. The modifier contains LaCe mixed rare earth (0.08 - 0.15wt%), TiN (0.05 - 0.12wt%), and AlN (0.03 - 0.08wt%), with a particle size of 20 - 50nm; Step 2, multi-gradient centrifugal casting: Use a five-layer composite structure centrifugal module. Based on the high fluidity characteristics of the melt formed in Step 1, implement three-stage variable-speed centrifugation. In the first stage, keep at 800 - 1000rpm for 3 - 5min to eliminate the agglomeration of the modifier. In the second stage, keep at 1200 - 1500rpm for 8 - 12min to achieve the directional arrangement of carbides. In the third stage, keep at 600 - 800rpm for 2 - 3min to promote the formation of equiaxed crystals; Step 3, in-situ synthesis of nano-carbides: Based on the catalytic effect of TiN in Step 1, under the condition of V / Nb composite microalloying (V / Nb atomic ratio 1:1.2 - 1.5), through the forced convection generated by the centrifugation in the second stage of Step 2, precipitate (V,Nb)C@TiN core-shell structure nano-particles (size 50 - 150nm) in the melt; Step 4, multi-modal heat treatment: For the nano-carbide distribution characteristics formed in Step 3, implement pulsed magnetic field-assisted austenitization (0.5 - 1.2T, 5 - 10Hz) and double-medium quenching, where the termination temperature of the water-cooling stage forms a mapping relationship with the axial temperature gradient of the centrifugal module in Step 2; Step 5, gradient cryogenic-tempering coupling treatment: Based on Step 4, for the dislocation network formed by quenching, apply an axial compressive stress (0.2 - 0.5σs) synchronously during the liquid nitrogen treatment at -196°C, and achieve the topological optimization of the stress field and carbide distribution through three-stage variable-temperature tempering.

2. The process for high-toughness high-chromium casting segments according to claim 1, wherein The preparation method of the composite modifier in Step 1 includes: Mix LaCe mixed rare earth with TiN / AlN at a mass ratio of 1:0.6 - 0.8 under argon protection by ball milling. The ball-to-material ratio is 8:1, the rotation speed is 300rpm, and the time is 4 - 6h to obtain nitride composite particles with a rare earth layer coated on the surface.

3. The process for a high-toughness high-chromium casting segment according to claim 1, characterized in that, The centrifugal module in Step 2 adopts a five-layer composite structure: Inner contact layer: Nano-zirconia coating (thickness 50 - 80μm); Second layer: Copper alloy water-cooling jacket (cooling water flow rate 2 - 5m / s); Third layer: Silicon carbide foam ceramic layer (porosity 60 - 70%); Fourth layer: Graphite / boron nitride composite lubricating layer (thickness 0.1 - 0.3mm); Outer layer: High-strength steel support frame.

4. A high-toughness high-chromium casting process according to claim 1, characterized in that, In Step 3, the melt superheat control is achieved through dynamic electromagnetic stirring. The stirring frequency is 15 - 25Hz, and the stirring intensity and melt temperature satisfy the relationship: I = 0.05×ΔT + 3, where I is the current intensity in kA; ΔT is the time.

5. A high-toughness high-chromium casting process according to claim 1, characterized in that The specific parameters of the double-medium quenching in Step 4 are: Water-cooling stage: Cooling rate 80 - 100°C / s, and the termination temperature detection uses an infrared-thermocouple dual-signal feedback system; Polymer quenching stage: Use a polyalkylene glycol solution (concentration 18 - 22%), and the cooling rate is 15 - 20°C / s.

6. A process for producing high-toughness high-chromium casting segments according to claim 1, characterized in that, During the gradient cryogenic treatment in Step 5, an axial compressive stress is applied, and the pressure value is controlled within 0.2 - 0.5 times the yield strength of the material, and the direction of the pressure is the same as the direction of the centrifugal force during centrifugal casting.

7. A process for high-toughness high-chromium casting segments according to claim 1, characterized in that, In the raw material ratio of Step 1, introduce B micro-alloying element (0.005 - 0.015%), and satisfy the relationship: (B%) = 0.2 × (Cr%) / (C%) 2 - 0.03 × (Mo%).

8. A high-toughness high-chromium casting segment process according to claim 1, characterized in that, Establish a carbide distribution regulation mechanism across processes: Based on the addition amount of the modifier in Step 1, dynamically adjust the centrifugal speed N (rpm) in the second stage of Step 2 to satisfy the relational expression: N = 250×(TiN wt％ +AlN wt％ ) + 800; The size d (nm) of the nanocarbide synthesized in-situ through Step 3 and the axial compressive stress P (MPa) of the cryogenic treatment in Step 5 are controlled to satisfy: (where σs is the yield strength of the material); Using the equiaxed crystal ratio η(%) of the solidification structure in the third stage of Step 2, set the pulse magnetic field frequency f(Hz) in Step 4 to satisfy: f = 0.1×η + 5.

9. A high-toughness high-chromium casting process according to claim 1, characterized in that Establish a parameter transfer system across processes: Take the solidification structure characteristics (equiaxed crystal ratio, secondary dendrite arm spacing) at the end of the third stage of Step 2 as the regulation basis for the pulse magnetic field frequency in Step 4, satisfying f(Hz) = 0.8×(equiaxed crystal ratio) + 0.05×(dendrite arm spacing μm); Feed back the average size of the nano-carbide synthesized in-situ in Step 3 to the pressure parameter of the cryogenic treatment in Step 5, satisfying P(MPa) = 120 / (d(nm)) 0.5 ; Based on the residual stress distribution data after quenching in Step 4, dynamically optimize the temperature gradient of the three-stage tempering in Step 5 to control the tempering temperature fluctuation ≤ ±3°C.

Images