CN106676463B

CN106676463B - Surface deep layer strengthening method using graphitized micro-nano carbon material as diffusion source

Info

Publication number: CN106676463B
Application number: CN201710123878.8A
Authority: CN
Inventors: 陶庆; 王健; 付立铭; 沈承金; 赖伟
Original assignee: China University of Mining and Technology CUMT; Shanghai Jiaotong University
Current assignee: China University of Mining and Technology CUMT; Shanghai Jiaotong University
Priority date: 2017-03-03
Filing date: 2017-03-03
Publication date: 2020-03-31
Anticipated expiration: 2037-03-03
Also published as: CN106676463A

Abstract

The invention relates to a material surface deep layer strengthening method using graphitized micro-nano carbon material as a diffusion source, which comprises the steps of firstly mixing graphitized product micro powder with a catalyst by utilizing the graphitization effect of the micro-nano carbon material, carrying out solid thermal diffusion treatment on the surface of a base material, carrying out phase change treatment on the base material after the solid thermal diffusion, tempering, and stabilizing the structure, wherein the obtained material surface layer microstructure is a nano mixed phase structure. The surface layer of the material has high hardness which is 1-800HV higher than that of the interior of the matrix, the thickness of a hardened layer with the magnitude of 0.1 mu m-50mm can be obtained from the surface layer to the core part of the material, and the depth of the hardened layer can be controlled by adjusting the process parameters of each treatment stage.

Description

Surface deep layer strengthening method using graphitized micro-nano carbon material as diffusion source

Technical Field

The invention relates to a method for strengthening the surface of a material, in particular to a method for strengthening the deep surface by taking a graphitized micro-nano carbon material as a diffusion source.

Background

The case hardening method is a treatment in which the surface layer of a part is hardened by an appropriate method and the core of the part is still tough. By this treatment, the wear resistance and fatigue resistance of the part can be improved, while the core of the part still has good toughness and strength, thus having good resistance to impact loads. The common surface hardening treatment methods mainly comprise carburizing, nitriding, hard anodizing, chromium plating, surface quenching, metal infiltration and the like.

The introduction of external elements on the surface of a material through chemical heat treatment is the most common method for modifying the surface of the material, so that the hardness, the wear resistance and the corrosion resistance of the surface of the material are improved, and meanwhile, certain toughness in the matrix can be ensured, and the method is widely applied to industrial production. After long-term development, people invest a great deal of effort and material resources to research the chemical heat treatment methods, including optimization of surface modification processes of various materials, influence of various process parameters in the chemical heat treatment process, analysis and test of properties such as hardness, frictional wear and corrosion of the modified surface, and the like. Wherein surface modification methods such as nitriding, carburizing and the like are most widely applied. However, the traditional treatment method generally has the technical problems of high energy consumption, long period, weak strengthening layer and the like which are difficult to solve, and the application of the traditional treatment method under complicated and severe working conditions is limited for a long time.

The prior art only improves the component formula and the content proportion of the solid carburizing agent to obtain good surface performance, for example, the carburizing agent which can lead the hard alloy to be in a gradient structure is formed by mixing 30 to 50 weight percent of alumina, 10 to 30 weight percent of graphite particles and 30 to 50 weight percent of carbonate/bicarbonate, the grain diameter of the adopted graphite is 0.2 to 2mm, the carburizing treatment time can be shortened by 50 to 65 percent, and the thickness of the surface layer is improved by 10 to 30 percent; and improving Cr₁₂The optimized carburizing process for the comprehensive performance of MoV steel comprises the steps of mainly using carburizing agent to perform carburizing on the MoV steel, wherein the carburizing agent mainly comprises carbon carbide, potassium fluorocarbon, silicon carbide, activated carbon, charcoal powder, urea, rare earth chloride and the like. However, the prior art does not relate to surface modification treatment by adopting a carbon source with ultra-high activity and a micro-nano scale, and still has the technical problems of high energy consumption, long period, weak strengthening layer, uncontrollable thickness of the strengthening layer and the like.

In recent years, the emergence of novel carbon materials having ultrahigh performance has attracted considerable attention in various industries. However, the industrial application of the novel carbon material in structural materials, wear-resistant materials and functional materials is rarely seen. Particularly, for micro-nano carbon materials, attention is rarely paid to the aspect of practical engineering application at present, and particularly, the micro-nano carbon materials are not used for reinforcing the surfaces of materials at present.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention provides a surface deep layer strengthening method using a graphitized micro-nano carbon material as a diffusion source, which can effectively improve the strengthening efficiency and shorten the strengthening period, greatly improves the thickness, strength and hardness of a strengthening layer formed on the surface of the material, and has controllable depth of a hardening layer and low energy consumption.

The technical scheme adopted by the invention for solving the technical problems is as follows:

a surface deep layer strengthening method using a graphitized micro-nano carbon material as a diffusion source comprises the following steps: firstly), carrying out graphitization treatment on micro-nano carbon material micro-powder to obtain graphitized product micro-powder; secondly), carrying out diffusion treatment on the matrix material by using the graphitized product micro powder to generate a solid-state thermal diffusion effect on the matrix material; thirdly), carrying out phase change treatment on the base material after the diffusion treatment.

Compared with the existing material surface hardening method, particularly carburization treatment, the deep surface strengthening method using the graphitized micro-nano carbon material as the diffusion source innovatively applies the micro-nano carbon material to the strengthening method for the material surface, the method introduces the nano-scale carbon material and the graphitized product thereof as the diffusion source in the diffusion treatment process, effectively improves the diffusion rate, can shorten the strengthening period, improves the material strength, causes a large amount of microstructure such as lattice distortion, dislocation group and the like due to the fact that carbon elements in the matrix can be dissolved in a special mode in a solid state, and enables the surface of the matrix material to have ultrahigh strength and hardness after solid state phase transition. The method can make the surface layer of the material have high hardness 1-800HV higher than that of the interior of the matrix, the thickness of the hardened layer from the surface layer to the core of the material can be 0.1 μm-50mm, and the depth of the hardened layer can be controlled by adjusting the treatment process at each stage.

Drawings

The invention is further illustrated with reference to the following figures and examples.

FIG. 1 shows a transmission electron microscope microstructure of the surface layer of the obtained mild steel matrix.

FIG. 2 is a graph showing the hardness distribution of the matrix obtained in example 3 from the surface layer to the core.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, belong to the scope of the present invention.

The invention relates to a surface deep layer strengthening method using a graphitized micro-nano carbon material as a diffusion source, which comprises the following steps: firstly, utilizing the graphitization effect of the micro-nano carbon material, mixing graphitized product micro powder with a catalyst, carrying out solid thermal diffusion treatment on the surface of a base material, carrying out phase change treatment on the base material subjected to solid thermal diffusion, tempering, stabilizing the structure, wherein the obtained material surface layer microstructure is a nano-scale mixed phase structure, and finally enabling the material surface layer to have high hardness which is 1-800HV higher than that of the interior of the base body. The thickness of the hardened layer with the magnitude of 0.1 mu m-50mm can be obtained from the surface layer to the core of the material, and the depth of the hardened layer can be controlled by adjusting the carbon source diffusion process.

In this embodiment, the first step and the second step may be performed in steps, that is, the graphitization treatment is performed first, and then the diffusion treatment is performed, with an intermediate time interval, or the graphitization treatment and the diffusion treatment may be performed continuously without an intermediate time interval, and the graphitization product generated by the graphitization treatment is directly used as a carbon source for the diffusion treatment, so as to ensure that the reaction change of the internal carbon is performed continuously and simultaneously without a time interval. The phase transformation treatment of the matrix material can be carried out immediately without cooling after the solid-state thermal diffusion treatment process of the matrix material by the graphitized product, and can also be carried out with austenitizing treatment after the matrix material is cooled along with the furnace. And when the thermal diffusion effect in the second step is completed for furnace cooling, the microstructure of the obtained matrix material contains a high-density dislocation structure, so that the substructure of the matrix metal is refined, and the mechanical property of the matrix material is improved.

The graphitization treatment in the first step can be carried out in a vacuum or inert gas protection environment at the temperature of 300-1500 ℃, and finally a high-activity graphitization product is obtained. Wherein, the micro-nano carbon material is one or a mixture of any more than one of allotrope isomers of micro-nano carbon.

The diffusion treatment in the second step can be carried out by mixing the graphitized product micro powder with a catalyst under the condition that the temperature is 1-500 ℃ higher than the austenitizing temperature of the matrix material in a vacuum or inert gas protection closed environment, uniformly spreading the catalyst on the surface of the matrix material, keeping the spread thickness within the range of 0.1-50mm, and carrying out heat preservation for 0.1-200 hours. Wherein, the catalyst is one or more of active catalysts, for example, the adopted active catalyst is Na2CO3, NaCl or BaCO3, and the catalyst is one or more of Na2CO3, NaCl, BaCO3 or other active catalysts. The matrix material used in this step is an iron-based material, and a multi-component alloy material with an iron content of more than 30%, such as aluminum, magnesium, titanium alloy, multi-component superalloy, amorphous alloy material or composite material containing metal elements, can be used.

The phase change process in step three may be: and cooling the obtained austenite-state matrix material to room temperature by water cooling or oil cooling, and performing low-temperature tempering treatment to obtain a nano-scale mixed phase structure on the surface microstructure of the material. Specifically, the obtained matrix material is rapidly cooled in an austenite state by using oil, water, saline water or a special coolant, and then is subjected to isothermal treatment for 0.1-10 hours in an environment with the temperature of 80-500 ℃ and then is cooled to room temperature by water.

The specific process parameters and performances in the examples refer to table 1, and in examples 1-8, the spreading thickness of the mixture of the micro-nano carbon material and the catalyst on the surface layer of the base material is set to be 20mm, and the diffusion treatment temperature is 300 ℃ higher than the austenitizing temperature of the base. Different surface hardness and depth of hardened layer can be obtained corresponding to different holding time. In the following examples, the cooling medium used in the phase change treatment after completion of diffusion is oil or water. The graphitization of the micro-nano carbon material micro powder and the solid-state thermal diffusion treatment of the graphitized product on the matrix material can be carried out simultaneously or step by step.

TABLE 1 Process parameters and Properties in the examples

As can be seen from the data in the examples in the table, the method of the present invention can make the surface layer of the material have a high hardness of 1-800HV higher than that of the interior of the matrix, and can obtain a hardened layer thickness of 0.1 μm-50mm from the surface layer to the core of the material, and can control the hardened layer depth by adjusting the carbon source diffusion process.

Referring to fig. 1, the surface transmission electron microscope structure image obtained after the low carbon steel matrix is strengthened by the method of the invention contains nanometer-scale superfine structures with the dimension less than 100nm in the inside, including a mixed structure of nanometer-scale α phase and gamma phase, martensite, bainite and retained austenite structures.

Referring to FIG. 2, corresponding to example 3, the low carbon steel is used as the matrix, the diffusion heat preservation is carried out for 5 hours, after the phase transformation treatment, the hardness of the material is gradually reduced from the surface of the material to the inside of the matrix, the hardness of the outermost surface reaches more than 1000MPa, and the hardness of the inside of the matrix is maintained at 200-300MPa, i.e. the surface layer is hardened while the core still has toughness, so that the purpose of surface hardening is achieved, and the depth of the hardened layer of the material is 2000 μm. The method proves that the surface layer with ultrahigh hardness and an ultra-thick hardened layer can be obtained.

Compared with the prior art, the invention has the following advantages:

firstly, the diffusion source adopted by the invention is a micro-nano carbon material and a graphitized product thereof, and the micro-nano carbon material has a pure and fresh microstructure and high surface activity, and does not introduce destructive impurities, thereby ensuring the structural integrity of the micro-nano carbon material. The graphitized product can be continuously provided by the micro-nano carbon material, so that the enough dosage of the matrix material in the solid-state thermal diffusion process is ensured. And the micro-nano carbon material has low consumption in the thermal diffusion treatment process, does not generate byproducts, and can be recycled.

Secondly, compared with the traditional solid chemical heat treatment method, the method can quickly and effectively introduce a special nano carbon structure into the base material, and can obtain an ultra-thick diffusion layer which is 2-50 times as thick as the traditional carburization layer under the same time condition. And the carbon element is solid-dissolved on the surface of the base material in a special way, and has ultrahigh strength and hardness after solid-state phase change.

Thirdly, the technical process of the invention is flexible and controllable, and the required depth of the diffusion layer can be obtained by regulating and controlling the processing time and the temperature range according to the requirements of actual engineering. The cooling speed of the solid phase transition process and the subsequent heat preservation temperature range and duration can be controlled, and the required strength range of the surface strengthening layer can be obtained.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and all simple modifications and equivalent variations of the above embodiment according to the technical spirit of the present invention are included in the protection scope of the present invention.

Claims

1. A surface deep layer strengthening method using a graphitized micro-nano carbon material as a diffusion source is characterized by comprising the following steps:

firstly), carrying out graphitization treatment on micro-nano carbon material micro-powder to obtain graphitized product micro-powder; the graphitization treatment process comprises the following steps: in a vacuum or inert gas protection environment and at the temperature of 300-1500 ℃, finally obtaining a high-activity graphitized product; the micro-nano carbon material is one or a mixture of any more of allotropic isomers of micro-nano carbon;

secondly), carrying out diffusion treatment on the matrix material by using the graphitized product micro powder to generate a solid-state thermal diffusion effect on the matrix material, and cooling the matrix material along with the furnace after the solid-state thermal diffusion effect is completed to enable the microstructure of the matrix material to contain a high-density dislocation structure; the diffusion treatment process comprises the following steps: in a vacuum or inert gas protected closed environment, mixing the graphitized product micro powder with a catalyst at the temperature of 1-500 ℃ higher than the austenitizing temperature of the matrix material, uniformly spreading the catalyst on the surface of the matrix material, keeping the spread thickness within the range of 0.1-50mm, preserving heat for 0.1-200 hours, and performing diffusion treatment; the matrix material is an iron-based material, a multi-element alloy material with the iron content of more than 30 percent, an amorphous alloy material or a composite material containing metal elements; the catalyst is active catalystAgent Na₂CO₃、NaCl、BaCO₃One or more of the above;

thirdly), performing phase change treatment on the base material subjected to diffusion treatment; the phase change treatment process comprises the following steps: and cooling the obtained austenite-state matrix material to room temperature by water cooling or oil cooling, and performing low-temperature tempering treatment to obtain a nano-scale mixed phase structure on the surface microstructure of the material.

2. The method for deep surface strengthening by using the graphitized micro-nano carbon material as the diffusion source as claimed in claim 1, wherein: the step one and the step two are carried out at intervals, graphitization treatment is carried out firstly, and then diffusion treatment is carried out, or graphitization treatment and diffusion treatment are carried out continuously.

3. The method for deep surface strengthening by using the graphitized micro-nano carbon material as the diffusion source as claimed in claim 1, wherein: the obtained matrix material is rapidly cooled in an austenite state, the cooling medium is oil, water, saline water or a special coolant, then the matrix material is placed in an environment with the temperature ranging from 80 ℃ to 500 ℃ for isothermal treatment for 0.1 hour to 10 hours, and then water is cooled to the room temperature.