An in-situ foaming shrinkage compensator for die-cast steel ingots and its preparation method

Abstract

This invention belongs to the field of iron and steel metallurgy and is mainly applied to in-situ foaming and shrinkage compensating agent for in-situ cast steel ingots and its preparation method. The agent comprises the following components by mass percentage: nano-titanium nitride particles: 0.5%–3.0%; aluminosilicate-based foaming carrier: 40%–60%; exothermic reaction composition: 15%–30%; grain refiner: 5%–12%; binder: 3%–8%; and the balance is calcium oxide-stabilized zirconium dioxide micropowder. This invention integrates foaming, exothermic, and grain refinement functions, breaking through the technical bottleneck of traditional single-function insulation riser materials; it also solves the problems of easy agglomeration of nanoparticles and uncontrollable reaction rates.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy and is mainly applied to die casting of steel. In particular, it relates to an in-situ foaming shrinkage compensating agent for die casting steel ingots and its preparation method. Background Technology

[0002] In the production of die-cast steel ingots, riser feeding is a key process for controlling shrinkage defects and improving yield. Traditional methods mainly rely on the combined use of heat-insulating riser covering agents (such as carbonized rice husks) and exothermic agents (aluminothermic agents) to achieve sequential feeding by delaying riser solidification. However, with the continuous development of steel ingots towards larger and more specialized sizes, the requirements for internal density of steel ingots have increased, and existing feeding technologies face the following problems: (1) Single function: Traditional feeding agents only have the single function of heat preservation or heat release, resulting in limited feeding efficiency; (2) Uncontrollable reactivity: Conventional aluminothermic agents react violently and for a short period of time, with low matching degree with the solidification shrinkage curve of molten steel, which easily causes feeding delay or excessive burning; (3) Obstacles to the application of nanomaterials: Although attempts have been made to introduce nanoparticles into feeding agents to refine grains, nanophases are prone to agglomeration and oxidation in high-temperature molten steel, and the actual utilization rate is less than 30%. Therefore, there is an urgent need to develop a feeding agent that can achieve synergistic effects of heat insulation, heat release and grain refinement, which is beneficial to improving the internal quality of steel ingots, reducing riser removal rate and increasing yield.

[0003] For example, Chinese patent document CN103949593A discloses a novel riser composite heating agent and its preparation method. The heating agent has a complex composition and a lengthy and complicated preparation process, and its function is relatively simple, only used for heating and heat preservation.

[0004] For example, Chinese patent document CN113732273A discloses an environmentally friendly riser insulation agent and its preparation method. The insulation agent is composed of diatomaceous earth, expanded perlite, and mullite powder. Its advantages are simple composition and simple preparation method. Its disadvantages are that the main components of the mixture of diatomaceous earth, expanded perlite, and mullite powder are alumina and silicon dioxide, which have poor heat dissipation capacity and are prone to reacting with molten steel. Summary of the Invention

[0005] To address the problems existing in the background technology, the purpose of this invention is to provide an in-situ foaming and shrinkage compensating agent for ingot casting and its preparation method, which integrates foaming, heat release, and grain refinement functions into one, breaking through the technical bottleneck of the single function of traditional heat insulation riser materials; at the same time, it solves the problems of easy agglomeration of nanoparticles and uncontrollable reaction rate.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] An in-situ foaming shrinkage compensator for die-cast steel ingots comprises the following components by mass percentage: nano-titanium nitride particles: 0.5%–3.0%; aluminosilicate-based foaming carrier: 40%–60%; exothermic reaction composition: 15%–30%; grain refiner: 5%–12%; binder: 3%–8%; and the balance is calcium oxide-stabilized zirconium dioxide micropowder.

[0008] Furthermore, the exothermic reaction composition is a mixture of aluminum powder and iron oxide powder, with a mass ratio of Al:Fe3O4=1:(2-4).

[0009] Furthermore, the grain refiner comprises a composite of La-Ce-Al ternary alloy powder and boron carbide, wherein the La:Ce molar ratio is 1:(1-3).

[0010] Furthermore, the particle size of the La-Ce-Al ternary alloy powder in the grain refiner is 10-50 μm, the particle size of the boron carbide is 0.5-5 μm, and the mass mixing ratio of the La-Ce-Al ternary alloy powder to the boron carbide is (2-5):1.

[0011] Furthermore, the adhesive is a composite solution of water glass and polyvinyl butyral.

[0012] Furthermore, the nano-titanium nitride particles have a particle size of 20–80 nm and are coated with a silicon carbide interface layer with a thickness of 1–3 nm, which is formed by chemical vapor deposition.

[0013] Furthermore, the aluminosilicate-based foaming carrier has a porous mullite framework structure with a porosity of 60% to 85% and a pore size distribution of 50 to 300 μm, and the pores are preloaded with 5% to 10% by mass of nano-magnesium oxide particles.

[0014] A method for preparing an in-situ foaming shrinkage compensating agent for die-cast steel ingots includes the following steps:

[0015] a) A porous mullite framework is placed in a vacuum impregnation furnace and injected with an ethanol suspension containing nano-magnesium oxide under a negative pressure of 0.01-0.1 MPa. After impregnation for 30-60 minutes, it is dried to obtain an aluminosilicate-based foamed carrier.

[0016] b) The aluminosilicate-based foamed carrier obtained in step a) is mixed with nano-titanium nitride particles, exothermic reaction composition, grain refiner, and calcium oxide-stabilized zirconium dioxide micro powder in a three-dimensional vortex under inert gas protection. The mixing speed is 200-400 rpm and the time is 20-40 minutes.

[0017] c) Add the binder to the mixed powder in step b) by atomization spraying, and simultaneously centrifuge granulation. The centrifuge speed is 800-1200 rpm, and the granulation particle size is controlled at 2-8 mm.

[0018] d) The granulated product is dried in stages at 120–180°C with a final moisture content of ≤0.5%.

[0019] Furthermore, the drying process used in step a) is microwave-hot air coupled drying, with microwave power of 3-5kW, hot air temperature of 80-120℃, and drying time of 20-30 minutes.

[0020] Furthermore, in step c), the droplet size of the atomized spray is 50–150 μm, and the binder addition rate is dynamically coupled and controlled with the centrifuge speed, satisfying the following relationship: V = k·N 1.5 Where: V is the binder addition rate, in mL / min; N is the centrifuge speed, in rpm; k is the adjustment coefficient and k = 0.002~0.005, in (min·rpm) / mL.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] 1. This invention (1) utilizes the porous structure of the aluminosilicate carrier to form a uniform microbubble layer in situ at high temperature, which can reduce the heat loss at the top of the riser and achieve the foaming and heat preservation effect; (2) utilizes the long reaction time of the Al / Fe3O4 exothermic reaction to improve the matching degree with the solidification shrinkage curve of the molten steel, and achieve the matching of continuous heat release and slow release of foaming gas; (3) utilizes the heterogeneous nucleation effect of La-Ce-Al alloy with nano-titanium nitride (TiN) and boron carbide (B4C) to improve the equiaxed crystal ratio and grain size of the steel ingot head; (4) utilizes the gradient thermal conductivity of calcium oxide stabilized ZrO2 micro powder, combined with the heat insulation effect of the foaming layer, to form a temperature field of "slow cooling at the top and fast cooling at the bottom" in the riser area, and finally forms a highly efficient shrinkage compensator that integrates foaming, heat release and refinement.

[0023] 2. The present invention uses silicon carbide interface coating technology to ensure the dispersion stability of nano-titanium nitride in molten steel. By preloading nano-MgO, the aluminosilicate-based foaming carrier can maintain high compressive strength at high temperature, ensuring that the foamed structure does not collapse under the impact of molten steel.

[0024] 3. The preparation method of the shrinkage compensator of the present invention is simple and suitable for use in large heavy steel ingots, high alloy steel and rapid casting processes. It can improve the yield, save costs and has environmental advantages. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the specific implementation methods of this invention will be further described below in conjunction with the embodiments. The following embodiments are used to specifically illustrate the content of this invention. These embodiments are only general descriptions of the content of this invention and do not limit the content of this invention.

[0026] Example 1:

[0027] 1. Composition of shrinkage compensation agent (mass percentage);

[0028] Nano-sized titanium nitride particles (50nm, SiC coating layer 2nm): 1.5%; Aluminosilicate-based foaming carrier (porosity 70%, pore size distribution 50-100μm, pre-loaded with 8wt% nano-MgO): 55%; Exothermic reaction composition (Al:Fe3O4=1:3): 22%; Grain refiner (La-Ce-Al alloy:boron carbide=3:1, La:Ce=1:2, La-Ce-Al alloy powder particle size is 10-20μm, boron carbide particle size is 0.5-2μm): 9%; Binder (water glass:PVB=4:1): 5%; Calcium oxide stabilized zirconium dioxide micropowder: balance.

[0029] 2. Preparation method;

[0030] Carrier pretreatment: The porous mullite carrier was placed in a vacuum impregnation furnace (vacuum degree 0.05MPa), and an ethanol suspension containing 8wt% nano MgO was injected. After impregnation for 45 minutes, it was dried by microwave-hot air coupling (microwave 4kW, hot air 100℃, 25 minutes).

[0031] Mixing: The pretreated carrier and the remaining components (excluding binder) are mixed in a three-dimensional vortex under argon protection (300 rpm, 30 minutes).

[0032] Granulation: Atomized spraying of binder (droplet size 100μm), simultaneous centrifugal granulation (speed 1000rpm, binder addition rate at V=0.003×1000). 1.5 =94.9mL / min), to obtain spherical particles with a particle size of 4-6mm.

[0033] Drying: Gradient drying (120℃×1h→150℃×1h→180℃×0.5h), with a final moisture content of 0.4%, which is the final product.

[0034] Example 2:

[0035] 1. Composition of shrinkage compensation agent (mass percentage);

[0036] Nano-sized titanium nitride particles (30nm, SiC coating layer 1nm): 3.0%; Aluminosilicate-based foaming carrier (porosity 85%, pore size distribution 200-300μm, pre-loaded with 5wt% nano-MgO): 40%; Exothermic reaction composition (Al:Fe3O4=1:4): 30%; Grain refiner (La-Ce-Al alloy:boron carbide=5:1, La:Ce=1:1, La-Ce-Al ternary alloy powder particle size 20-35μm, boron carbide particle size 2-4μm): 7%; Binder (water glass:PVB=3:1): 6%; Calcium oxide stabilized zirconium dioxide micropowder: balance.

[0037] 2. Preparation method;

[0038] Carrier pretreatment: The porous mullite carrier was placed in a vacuum impregnation furnace (vacuum degree 0.1MPa), and an ethanol suspension containing 5wt% nano MgO was injected. After impregnation for 30 minutes, it was dried by microwave-hot air coupling (microwave 5kW, hot air 80℃, 30 minutes).

[0039] Mixing: The pretreated carrier and the remaining components (excluding binder) are mixed in a three-dimensional vortex under argon protection (400 rpm, 20 minutes).

[0040] Granulation: Binder is atomized and sprayed (droplet size 50μm), with simultaneous centrifugation at 1200rpm (V=0.005×1200). 1.5 =207.8mL / min), granulation particle size 2-4mm.

[0041] Drying: Segmented drying (150℃×1.5h→180℃×1h), with a moisture content of 0.3%, which is the final product.

[0042] Example 3:

[0043] 1. Composition of shrinkage compensation agent (mass percentage);

[0044] Nano-sized titanium nitride particles (80nm, SiC coating layer 3nm): 0.5%; Aluminosilicate-based foaming carrier (porosity 60%, pore size distribution 100-200μm, pre-loaded with 10wt% nano-MgO): 60%; Exothermic reaction composition (Al:Fe3O4=1:2): 15%; Grain refiner (La-Ce-Al alloy:boron carbide=2:1, La:Ce=1:3, La-Ce-Al ternary alloy powder particle size 40-50μm, boron carbide particle size 4-5μm): 12%; Binder (water glass:PVB=5:1): 3%; Calcium oxide stabilized zirconium dioxide micropowder: balance.

[0045] 2. Preparation method;

[0046] Carrier pretreatment: The porous mullite carrier was placed in a vacuum impregnation furnace (vacuum degree 0.01MPa), and an ethanol suspension containing 10wt% nano MgO was injected. After impregnation for 40 minutes, it was dried by microwave-hot air coupling (microwave 3kW, hot air 120℃, 20 minutes).

[0047] Mixing: The pretreated carrier and the remaining components (excluding binder) are mixed in a three-dimensional vortex under argon protection (200 rpm, 40 minutes).

[0048] Granulation: Atomized spraying of binder (droplet size 150μm), simultaneous centrifugation at 800rpm (V=0.002×800). 1.5 =45.3mL / min), granulation particle size 6-8mm.

[0049] Drying: Gradient drying (100℃×2h→160℃×1h), with a moisture content of 0.45%, which is the final product.

[0050] The feeding agents from Examples 1, 2, and 3 were used to cast 10 tons of 4340 alloy steel ingots (riser diameter 800mm), 15 tons of H13 hot work die steel ingots (riser diameter 1200mm), and 8 tons of 20CrMnTi gear steel ingots (riser diameter 600mm). The experimental results were compared with those obtained by using conventional carbonized rice husks and thermite as heat-insulating and heating agents in die casting of steel, as shown in Table 1. It can be seen that the feeding agent of the present invention significantly reduces the riser removal rate and increases the equiaxed crystal ratio in the die casting production of medium-to-high-end, large-section high alloy steel and ordinary steel, thereby improving the yield. In addition, no particle agglomeration was observed during the die casting process, and the overall foaming and heating phenomenon was stable and controllable.

[0051] Table 1

[0052]

Claims

1. An in-situ foaming shrinkage compensator for die-cast steel ingots, characterized in that, The composition by weight percentage includes: nano-titanium nitride particles: 0.5%–3.0%; aluminosilicate-based foaming carrier: 40%–60%; exothermic reaction composition: 15%–30%; grain refiner: 5%–12%; binder: 3%–8%; the balance is calcium oxide-stabilized zirconium dioxide micropowder. The grain refiner comprises a composite of La-Ce-Al ternary alloy powder and boron carbide, wherein the La:Ce molar ratio is 1:(1-3). The nano-titanium nitride particles have a particle size of 20–80 nm and are coated with a silicon carbide interface layer with a thickness of 1–3 nm. The silicon carbide interface layer is formed by chemical vapor deposition.

2. The in-situ foaming shrinkage compensator for die-cast steel ingots according to claim 1, characterized in that, The exothermic reaction composition is a mixture of aluminum powder and iron oxide powder, with a mass ratio of Al:Fe3O4=1:(2-4).

3. The in-situ foaming shrinkage compensator for die-cast steel ingots according to claim 1, characterized in that, The grain refiner contains La-Ce-Al ternary alloy powder with a particle size of 10–50 μm and boron carbide with a particle size of 0.5–5 μm, and the mass mixing ratio of La-Ce-Al ternary alloy powder to boron carbide is (2–5):

1.

4. The in-situ foaming shrinkage compensator for die-cast steel ingots according to claim 1, characterized in that, The adhesive is a composite solution of water glass and polyvinyl butyral.

5. The in-situ foaming shrinkage compensator for die-cast steel ingots according to claim 1, characterized in that, The aluminosilicate-based foaming carrier has a porous mullite framework structure with a porosity of 60% to 85% and a pore size distribution of 50 to 300 μm. The pores are preloaded with 5% to 10% by mass of nano-magnesium oxide particles.

6. A method for preparing an in-situ foaming shrinkage compensating agent for die-cast steel ingots as described in any one of claims 1-5, characterized in that, Includes the following steps: a) A porous mullite framework is placed in a vacuum impregnation furnace and injected with an ethanol suspension containing nano-magnesium oxide under a negative pressure of 0.01-0.1 MPa. After impregnation for 30-60 minutes, it is dried to obtain an aluminosilicate-based foamed carrier. b) The aluminosilicate-based foamed carrier obtained in step a) is mixed with nano-titanium nitride particles, exothermic reaction composition, grain refiner, and calcium oxide-stabilized zirconium dioxide micro powder in a three-dimensional vortex under inert gas protection. The mixing speed is 200-400 rpm and the time is 20-40 minutes. c) Add the binder to the mixed powder in step b) by atomization spraying, and simultaneously centrifuge granulation. The centrifuge speed is 800-1200 rpm, and the granulation particle size is controlled at 2-8 mm. d) The granulated product is dried in stages at 120–180°C, with a final moisture content of ≤0.5%.

7. The method for preparing the in-situ foaming shrinkage compensating agent for die-cast steel ingots according to claim 6, characterized in that, The drying process used in step a) is microwave-hot air coupled drying, with microwave power of 3-5kW, hot air temperature of 80-120℃, and drying time of 20-30 minutes.

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