A method for in situ synthesis of al2o3-tic reinforced iron matrix composites

Abstract

The application discloses a method for in-situ synthesis of Al2O3-TiC reinforced iron-based composite material. The method first uses CH4-H2 gas as a reducing agent to preliminarily reduce iron oxides and titanium oxides in titanium concentrate into metallic iron and Ti(C, O) at low temperature, and then uses metallic aluminum to perform deep deoxidation reduction on the reduced titanium concentrate while in-situ synthesizing Al2O3-TiC reinforced iron-based composite material. The method can realize the reduction of iron in the titanium concentrate and the preliminary carbonization of titanium at low temperature through a two-step reduction method, and can control the content of Al2O3 in the Al2O3-TiC reinforced iron-based composite material by precisely controlling the oxygen content in the reduction product Ti(C, O), so as to realize the preparation of high-quality iron-based composite material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metallurgy, in particular to a method for synthesizing Al2O3-TiC reinforced iron-based composite material in-situ from titanium concentrate by two-step reduction. BACKGROUND

[0002] Steel material is a general term for iron-carbon alloy system materials. The abundant iron ore reserves and relatively low smelting cost make steel material the most widely used structural material at present, known as the "industrial skeleton", which is widely used in petroleum and chemical industry, metallurgical machinery, mining, aerospace and transportation fields. Steel material itself has excellent mechanical properties, and can improve its special properties in wear resistance, corrosion resistance, high temperature stability, etc. by adding various alloying elements (such as nickel, chromium, manganese, etc.). However, with the increasing production demand and rapid development of industrial technology, the aerospace, high-speed railway, high-performance automobile and other advanced industrial fields have put forward higher requirements on the performance of materials. The traditional single steel material has been unable to meet the needs of advanced industries.

[0003] Metal matrix composite is a composite material in which one or more metal or non-metal fibers, whiskers, particles, etc. with specific properties (such as wear resistance, corrosion resistance, high temperature stability, etc.) are used as reinforcing phase, and the two are metallurgically combined through external or in-situ generation. Metal matrix composite has become the preferred structural material to replace traditional single metal material due to its unique high specific strength and specific stiffness, excellent properties such as wear resistance and high temperature resistance, and has attracted widespread attention from domestic and foreign material researchers. It has become an important branch of modern composite material system.

[0004] The raw material resources of steel materials are abundant, the cost is low, and the steel materials have excellent properties, so the steel matrix composites prepared by using the steel materials as the matrix have great application prospects. However, the research on the metal matrix composites is mainly focused on Al, Mg, Ti and other metals or alloys as the matrix, and the research on the steel matrix composites is still in its infancy. The particle reinforced steel matrix composites have attracted extensive attention of researchers due to the advantages of low cost and easy forming. The preparation methods of the particle reinforced steel matrix composites are mainly divided into the external reinforcement composite method and the in-situ generation composite method, and the reinforcing phase particles are mainly oxide ceramic particles, carbide ceramic particles and nitride ceramic particles. The external reinforcement composite method such as casting composite and powder metallurgy composite often uses high-purity steel materials and reinforcing phase particles as the raw materials, and has the problems of complex process, high cost, easy agglomeration of the reinforcing phase particles and the like. In comparison, the in-situ generation composite method has attracted increasing attention of researchers due to the advantages of relatively simplified preparation process, low material manufacturing cost, excellent and controllable material performance and the like. The oxide ceramic particles such as Al2O3 have high hardness, good wear resistance and high temperature stability, and can effectively improve the high temperature creep resistance of the iron matrix composite as the reinforcing phase. However, the wettability of the Al2O3 particles with the steel is poor, and when the external reinforcement composite method is used, the interface bonding between the Al2O3 particles and the matrix is not tight enough and casting defects are easily generated. The in-situ generation composite method can fundamentally solve the problem of poor wettability of the oxide ceramic particles such as Al2O3 with the steel matrix. The carbonides such as TiC have good wettability with the steel materials, and have the characteristics of high hardness, wear resistance, corrosion resistance and high elastic modulus. However, the high temperature creep resistance of the carbonide reinforced iron matrix composite is poor, which will greatly affect the application value of the composite material.

[0005] Although China has abundant steel resources, most of the iron ore has low grade, and the proportion of polymetallic intergrowth ore is high. The rich vanadium-titanium magnetite resources in the Panxi region of Sichuan Province are typical polymetallic intergrowth ores, and the reserves of vanadium, titanium and iron resources are among the top in China. After several beneficiation processes, the vanadium-titanium magnetite concentrate and titanium concentrate can be obtained from the vanadium-titanium magnetite in the Panxi region. The main component of the titanium concentrate is FeTiO3. Since it is impossible to recover and utilize Fe and Ti at the same time, the iron oxide in the titanium concentrate is usually reduced and separated by electric furnace smelting, and then the titanium resources are recovered and utilized, so the utilization process of the titanium concentrate is relatively complex, time-consuming, energy-consuming and high-carbon-emission.

[0006] In view of the difficulty in simultaneously recycling Fe and Ti elements in titanium concentrate, relevant scholars propose to directly synthesize Al2O3-TiC double reinforced phase iron-based composite material in situ by using the rich Ti and Fe resources in ilmenite through aluminum and carbon reduction. This method is to add a certain proportion of aluminum powder and carbon powder to the titanium concentrate, and use the metal aluminum to reduce and remove the oxygen in FeTiO3 at high temperature, and generate Al2O3 in situ, and the reduced titanium combines with C to generate TiC in situ, and then Al2O3-TiC reinforced iron-based composite material is obtained. However, the aluminum reduction of FeTiO3 is a strong exothermic process, and the self-generating TiC reaction is too violent, and the interface between the in-situ generated reinforced phase and the matrix is easy to produce casting defects due to the too high temperature, which affects the overall performance of the composite material. At the same time, the oxygen in FeTiO3 in the titanium concentrate will react with Al to generate Al2O3, which will cause the content of Al2O3 generated in situ in the composite material to be too much, and relevant research shows that the proportion of Al2O3 in Al2O3 reinforced iron-based composite material should be less than 10%, and too much Al2O3 will affect the overall performance of the iron-based composite material. Therefore, the method of synthesizing Al2O3-TiC double reinforced phase iron-based composite material in situ by aluminum and carbon reduction of titanium concentrate in one step has poor controllability, and the product quality is difficult to control, and is not suitable for large-scale industrial production. SUMMARY

[0007] In view of the above-mentioned deficiencies in the prior art, the purpose of the present application is to provide a two-step reduction method for synthesizing Al2O3-TiC reinforced iron-based composite material in situ from titanium concentrate, which has strong controllability and low energy consumption.

[0008] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: a method for synthesizing Al2O3-TiC reinforced iron-based composite material in situ, comprising the following steps:

[0009] S1: grinding and selecting the titanium concentrate to obtain powder particle raw materials with a particle size of 0.1-0.2mm, and then reducing and carbonizing the powder particle raw materials under a reducing atmosphere to obtain a reduction-carbonitrided product, the reduction temperature is 1100-1200℃, the reduction time is 2-3h, and the reduction atmosphere is CH4-H2-Ar, the volume ratio of each gas in the reduction atmosphere is: CH4 is 4-8%, H2 is 72-96%, and Ar is 10-20%.

[0010] S2: mixing aluminum powder with the reduction-carbonitrided product obtained in S1 and ball milling to below 0.074mm, and pressing into blocks by using a sample press.

[0011] Among them, the addition amount of aluminum powder is 5-15wt% of the total weight of the reduction-carbonitrided product. Among them, and are the molar amounts of TiO2 and Ti(C, O) in the reduction-carbonitrided product of S1, and x+y=1.

[0012] S3: vacuum hot-press sintering the block obtained in S2, the sintering temperature is 1100-1200 DEG C, the sintering time is 0.5-2h, and the hot-press pressure is 20-25Mpa.

[0013] S4: polishing the sintered product obtained in S3, thus obtaining the Al2O3-TiC reinforced iron-based composite material.

[0014] Further, the titanium concentrate in S1 is subjected to pre-oxidation treatment to improve the reduction kinetics of the titanium concentrate, the pre-oxidation treatment temperature is 900-1000 DEG C, the time is 3-4h, and the air atmosphere is used.

[0015] Further, the pressure of the sample pressing machine in S2 is set to 20-25Mpa, and the pressing time is 2-4min.

[0016] Further, the polishing process in S4 needs to ensure that the surface of the sintered block is bright and has no visible scratches.

[0017] Further, the reduction rate of iron oxide in the reduction-carbonitriding product in S1 is greater than or equal to 99%, and the reduction rate of titanium oxide is greater than or equal to 96%.

[0018] An Al2O3-TiC reinforced iron-based composite material is prepared by the above-mentioned method for in-situ synthesis of Al2O3-TiC reinforced iron-based composite material.

[0019] Compared with the prior art, the present application mainly has the following advantages:

[0020] 1. The traditional external reinforcement composite method cannot solve the problem of poor wetting of the oxide ceramic particle reinforcement phase and the matrix. The present application generates Al2O3 reinforcement phase in-situ by deep deoxidizing Ti(C, O) with Al powder, solving the problem of poor wetting of the Al2O3 ceramic particle reinforcement phase and the matrix. At the same time, compared with the single TiC reinforced iron-based composite material, the Al2O3-TiC reinforced iron-based composite material prepared by the present application has good high-temperature creep resistance due to the addition of Al2O3 particles.

[0021] 2. The one-step reduction in-situ synthesis method needs to use aluminum metal to reduce all iron oxides and titanium oxides in the titanium concentrate, so the number of Al2O3 reinforcement phase particles generated in-situ is fixed and cannot be controlled, and too high Al2O3 content will adversely affect the performance of the iron-based composite. The present application generates Al2O3 reinforcement phase particles in-situ by reducing Ti(C, O) reduction products of titanium concentrate with Al powder deep deoxidization, not only reduces the amount of Al2O3 generated, but also controls the oxygen content in Ti(C, O) by adjusting the reduction temperature, reduction time and gas composition ratio during gas-based reduction, thereby precisely controlling the content of Al2O3 generated in-situ, and obtaining an iron-based composite with superior performance.

[0022] 3. The present application uses gas-based reduction method to reduce FeTiO3 in titanium concentrate to Fe and Ti(C, O), Fe and Ti(C, O) have good wettability and good interface bonding, and are uniformly distributed, and Al2O3 generated by deep deoxidization of Ti(C, O) with Al powder is uniformly distributed around TiC particles after deoxidization. Therefore, the in-situ generated Al2O3 and TiC particles can be uniformly distributed in the iron matrix, which can greatly improve the overall performance of the iron-based composite. At the same time, the entire deoxidization process is relatively slow in heat release compared with the aluminum thermal reduction of FeTiO3 and the self-generating TiC reaction, which can greatly avoid the influence of local overheating reaction on the microstructure of the composite.

[0023] 4. The present application uses titanium concentrate as the main raw material to synthesize Al2O3-TiC reinforced iron-based composite in-situ, which not only greatly reduces the raw material cost, but also realizes the simultaneous recycling of iron and titanium resources in the titanium concentrate. The trace amounts of V, Cr and Mn elements present in the titanium concentrate are also beneficial alloy elements that can improve the performance of steel materials, and the impurity MgO reacts with Al2O3 to form MgAl2O4 during hot-pressing sintering, which is also a potential reinforcement phase material. At the same time, the present application uses CH4, H2 and other clean energy as reducing agent, which is environmentally friendly and clean, has no CO2 emission, and the tail gas can be recycled, also reducing the amount of aluminum powder used in the subsequent hot-pressing sintering process, to a certain extent, reducing the preparation cost. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The process flow diagram of the method of the present application. DETAILED DESCRIPTION

[0025] A method for in-situ synthesis of Al2O3-TiC reinforced iron-based composite material, comprising the following steps:

[0026] S1: the titanium concentrate is ground and separated to obtain a powder raw material with a particle size of 0.1-0.15 mm, and then the powder raw material is selectively reduced at a low temperature under a reducing atmosphere to obtain a reduced-carbonitrided product, the reduction temperature is 1100-1200℃, the reduction time is 2-3h, and the reduction atmosphere is CH4-H2-Ar, the volume ratio of each gas in the reduction atmosphere is: CH4 is 4-8%, H2 is 72-96%, and Ar is 10-20%. Specifically, the reduction temperature can be 1100℃, 1110℃, 1120℃, 1130℃, 1140℃, 1150℃, 1160℃, 1170℃, 1180℃, 1190℃ or 1200℃; the reduction time can be 2h, 2.2h, 2.5h, 2.6h, 2.8h or 3h; the volume fraction ratio of CH4 to H2 and Ar can be 8:82:10, 8:77:15, 8:72:20, 6:84:10, 6:79:15, 6:74:20, 4:86:10, 4:81:15 or 4:76:20.

[0027] S2: a certain proportion of aluminum powder is mixed with the reduced titanium concentrate obtained in S1 to be ball milled to below 0.074 mm, and a briquetting machine is used to press into a block; wherein the addition amount of aluminum powder wherein and are the molar amounts of TiO2 and Ti(C, O) in the reduced-carbonitrided product of S1, and x+y=1.

[0028] S3: the block obtained in S2 is subjected to hot-pressing sintering, the sintering temperature is 1100-1200℃, the sintering time is 0.5-2h, and the hot-pressing pressure is 20-25Mpa. Specifically, the sintering temperature can be 1100℃, 1110℃, 1120℃, 1130℃, 1140℃, 1150℃, 1160℃, 1170℃, 1180℃, 1190℃ or 1200℃, the sintering time can be 0.5h, 0.8h, 1.0h, 1.2h, 1.5h, 1.8h or 2h, and the hot-pressing pressure can be 20Mpa, 22Mpa or 25Mpa.

[0029] S4: the sintered product obtained in S3 is polished, and then subjected to Vickers hardness detection, the hardness detection method is Vickers hardness detection, and the unit is Gpa.

[0030] Specifically, the titanium concentrate in S1 is subjected to pre-oxidation treatment to improve the reduction kinetics of the titanium concentrate. The pre-oxidation treatment is performed at a temperature of 900-1000℃ for 3-4h in an air atmosphere. CH4 in the reduction gas mainly acts as a reducing agent and a carbonizing agent, H2 mainly acts as an auxiliary reducing agent and inhibits the rapid cracking of CH4 at high temperatures, and Ar acts as a protective gas while reducing the amount of H2. Specifically, the pre-oxidation treatment can be performed at a temperature of 900℃, 920℃, 950℃, 980℃ or 1000℃ for 3h, 3.2h, 3.5h, 3.8h or 4h.

[0031] Specifically, the reduction-carbonization process in S1 is the reduction of iron oxides in the titanium concentrate, and the reduction rate of iron oxides in the reduction-carbon-nitride product is ≥99%, and the reduction rate of titanium oxides is ≥96%. The reduction-carbon product of titanium oxides is Ti(C, O), which is a solid solution of TiC and TiO, and TiC / TiO≥1.

[0032] Specifically, the pressure of the sample pressing machine in S2 is set to 20-25Mpa, and the pressing time is 2-4min. The addition amount of aluminum powder is determined according to the oxygen content of the titanium-containing phase in the product of S1, and the normal addition amount is 0.5-1.5wt.%. However, considering the high-temperature evaporation loss of metallic aluminum during the hot-pressing sintering process and the trace amount of residual iron oxides in the reduction product of S1, the improved addition amount of aluminum powder is 1.1 times the normal addition amount.

[0033] Specifically, the polishing process in S4 is to polish with 400, 600, 800, 1000, 1500 and 2000 grit sandpaper in turn, and then polish with a polishing agent. The final sample needs to be free of visible scratches.

[0034] The application will be further described in detail below with reference to the accompanying drawings and specific examples.

[0035] The main chemical components of the Panzhihua vanadium-titanium magnetite are shown in Table 1.

[0036] Table 1 Chemical composition analysis of Panzhihua titanium concentrate (calculated as pure oxide, wt. %)

[0037]

[0038] Example 1: A method for in-situ synthesis of Al2O3-TiC reinforced iron-based composite material by two-step reduction of titanium concentrate, the specific steps are as follows:

[0039] S1: The powder particles with a particle size of 0.1-0.2 mm were obtained by grinding, screening and classifying the Panzhihua titanium concentrate pre-oxidized at 900℃ for 3h, 10.0g of the sample was placed in a high-temperature tube furnace for heating, Ar was introduced to remove air in the furnace tube during the heating process, and CH4-H2 gas was introduced to reduce iron oxides and reduce and carbonize titanium oxides after the temperature was raised to the reduction temperature. The reduction temperature was 1100℃, the reduction time was 2 hours, and the volume fraction ratio of CH4, H2 and Ar was 8:82:10.

[0040] S2: After the high-temperature tube furnace was cooled to room temperature, the reduced titanium concentrate powder particles were taken out, crushed and ball milled to below 0.074 mm, and a certain proportion of aluminum powder was added to obtain the sintering raw material of the iron-based composite material, and the sintering raw material after mixing was pressed into a 2cm diameter cylinder by a sample pressing machine. The reduction rate of iron oxides in the titanium concentrate was 99.3%, the reduction rate of titanium oxides was 96.3%, and the chemical composition of the reduction product Ti(C, O) was TiC 0.61 O 0.39 ; the normal addition amount of aluminum powder was 0.474g, and the improved addition amount was 0.521g.

[0041] S3: The sintering raw material block was placed in a vacuum hot pressing furnace for hot pressing sintering, the sintering temperature was 1200℃, and the sintering time was 2 hours.

[0042] S4: After the vacuum hot pressing furnace was cooled to room temperature, the sintered sample was taken out, and the surface of the sample was polished with sandpaper and polishing paste, and the Vickers hardness of the sintered product was detected to be 22.3Gpa.

[0043] Examples 2-9 used the same preparation method as Example 1, except that the process parameters were selected, as shown in Table 2:

[0044] Table 2

[0045]

[0046] The detection results of the reduction and carbonization products and the hot-pressed sintered products obtained in Examples 1-9 are shown in Table 3:

[0047] Table 3

[0048]

[0049] It can be found from Table 3 that the experimental results of the nine groups of examples are slightly different, but all reach the condition standard of the method of the application based on different process parameter settings. The results of the nine groups of examples show that within the range of the related process parameters, the method of the application can precisely control the oxygen content in the reduced carbonized product TiCO of the titanium concentrate, thereby precisely control the in-situ generated Al2O3 content, and obtain the best performance of the iron-based composite material by adjusting the reducing gas composition, the reduction temperature and time, etc.

[0050] Finally, it should be pointed out that the above examples are only used to illustrate the technical solutions of the application and are not limiting. Although the application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the application can be modified or replaced equivalently without departing from the purpose and scope of the technical solutions of the application, and they should all be covered in the technical requirement range of the application.

Claims

1. A method for in-situ synthesis of Al2O3-TiC reinforced ferrous matrix composite material, characterized by: It comprises the following steps: S1: grinding and separating the titanium concentrate to obtain powder particle raw material with particle size of 0.1-0.2mm, then reducing and carbonizing the powder particle raw material under a reducing atmosphere to obtain a reduction-carbonitrided product, the reduction temperature is 1100-1200℃, the reduction time is 2-3h, and the reducing atmosphere is CH4-H2-Ar, the volume ratio of each gas in the reducing atmosphere is: CH4 is 4-8%, H2 is 72-86%, and Ar is 10-20%; The titanium concentrate in S1 is first subjected to pre-oxidation treatment to improve the reduction kinetics conditions of the titanium concentrate, the pre-oxidation treatment temperature is 900-1000℃, the time is 3-4h, and the air atmosphere is used; The reduction rate of iron oxide in the reduction-carbonitrided product in S1 is ≥99%, and the reduction rate of titanium oxide is ≥96%; S2: mixing aluminum powder with the reduction-carbonitrided product obtained in S1 and ball milling to below 0.074mm, and using a sample pressing machine to press into a block; wherein the amount of the aluminum powder added is wherein and are the molar amounts of TiO2and Ti(C,O) in the S1 reduction-carbonitriding product, respectively, x+y = 1. S3: vacuum hot-pressing sintering the block obtained in S2, the sintering temperature is 1100-1200℃, the sintering time is 0.5-2h, and the hot-pressing pressure is 20-25MPa; S4: polishing the sintered product obtained in S3 to obtain an Al2O3-TiC reinforced iron-based composite material.

2. A method for in-situ synthesis of Al2O3-TiC reinforced ferrous matrix composite as claimed in claim 1 wherein: The sample pressing machine pressure in S2 is set to 20-25MPa, and the pressing time is 2-4min.

3. A method for in-situ synthesis of Al2O3-TiC reinforced ferrous matrix composite as claimed in claim 1 wherein: The polishing process in S4 needs to ensure that the surface of the sintered block is bright and has no visible scratches.

4. An Al203-TiC reinforced iron-based composite material, characterized by: The obtained product is prepared by the method of any one of claims 1-3. The obtained product is prepared by the method of any one of claims 1-3.

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