Mechanical-assisted chemical heat treatment method for metal surfaces

Abstract

The invention relates to a mechanical-assisted chemical heat treatment method for metal surfaces. The method comprises the following steps that 1, a metal workpiece substrate to be subjected to chemical heat treatment is pretreated; 2, a chemical heat treatment electrode is prepared; 3, chemical heat treatment equipment is assembled; 4, chemical heat treatment preparation is conducted; and 5, the metal workpiece substrate to be subjected to chemical heat treatment is ground and polished. The mechanical-assisted chemical heat treatment method for metal surfaces has the advantages of being simple in equipment, low in investment, and low in maintenance and machining cost; a strengthened layer is mainly of a solid solution structure, and is compact, uniform and high in quality; the strengthened layer and the substrate are subjected to metallurgical bonding, and are free of obvious interfaces and high in bonding force; chemical heat treatment and grinding are conducted at the same time, the surface polishing effect of low surface roughness and high smoothness can be achieved, and secondary machining such as polishing and deburring is not needed; no special requirement for the shape and precision of workpieces exists, treatment of thin-walled parts made of composite materials can be achieved, and applicability is high; and operation is easy and feasible, efficiency is high, and the mechanical-assisted chemical heat treatment method can be used for large-scale treatment of the workpieces.

Description

technical field [0001] The invention relates to the technical field of surface treatment, in particular to a mechanically assisted chemical heat treatment method for metal surfaces. Background technique [0002] In modern heat treatment technology, the proportion of chemical heat treatment is increasing; taking automobile parts as an example, about 70% of the heat treatment adopts chemical heat treatment process; Divided into: gas infiltration, plasma infiltration, solid infiltration, liquid infiltration, paste infiltration and so on. [0003] Among them, solid infiltration, liquid infiltration, and paste infiltration have high cost, complicated process, poor performance, and limited permeable elements, which are only suitable for some parts with specific needs. [0004] Gas infiltration and plasma infiltration are the two most widely used chemical heat treatment processes, but there are also shortcomings; the disadvantages of gas infiltration are: (1) long treatment cycle ...

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Problems solved by technology

[0003] Among them, solid infiltration, liquid infiltration, and paste infiltration have high cost, complicated process, poor performance, and limited permeable elements, which are only suitable for some parts with specific needs.

[0004] Gas infiltration and plasma infiltration are the two most widely used chemical heat treatment processes, but there are also shortcomings; the disadvantages of gas infiltration are: (1) long treatment cycle and low efficiency; (2) deep brittleness and poor quality controllability; (3) The equipment is complex, energy and gas consumption are large; (4) Local strengthening treatment cannot be realized; (5) High temperature, especially difficult-to-treat materials such as titanium alloys require higher processing temperatures, which will affect the structure and mechanical properties of parts have a huge negative impact

[0005] The disadvantages of plasma infiltration include: (1) High technical requirements for equipment and processing; (2) There is atomic volume stress, which is not suitable for processing thin-walled parts, composite materials, etc.; (2) There is an edge effect, which leads to uneven processing (3) Similarly, for non-ferrous metals such as titanium alloys, there is a high processing temperature, which leads to a decrease in the structure and mechanical properties of the parts

[0006] In terms of new process development, the document "Study on Surface Carburization of Titanium Alloy EDM" discloses a method of using capacitor pulse discharge to deposit graphite electrode material on the surface of the metal substrate and react with the substrate to form a strengthening layer; however, micro-arc The spark deposition speed is slow and the efficiency is low. As a result, this technology is only suitable for micro-repair of surface weight loss defects of precision parts, and is not suitable for repairing large coating thickness (coating thickness > 0.25mm), let alone large-area treatment; Moreover, the processing process is complex and cumbersome, and requires machining, surfacing welding thickening and repairing, grinding and smoothing; therefore, the application field of micro-arc spark deposition technology is very limited

[0007] Documents "Synthesis of TiN Coatings by EDM on Flexible Titanium Electrodes" and "Research on EDM Strengthening Experiments on Surfaces of Flexible Electrodes on Titanium Alloys" published a flexible EDM deposition method; The speed and quality control have been improved, but the defects of this process are more obvious: (1) The process does not solve the shortcomings of slow EDM deposition speed and low efficiency; (2) The electrode size becomes larger, resulting in increased difficulty in on-site or manual operation (3) In order to obtain a more sufficient spark discharge effect and stability, it is necessary to ensure that the gap between the single electrode wire and the substrate in the circular wire disk is controlled within a reasonable range, and the strengthening layer is completely obtained by electrode deposition, As a result, it is difficult to carry out long-term and large-area processing; among them, the reaction with nitrogen gas as described in the document "Synthesis of TiN Coating by EDM on Flexible Titanium Electrodes" The choice of filament electrode material is limited, and the formed TiN is a ceramic material, which is brittle and has a smaller scope of application. Vigorous reaction occurs to form oxides and there are a large amount of granular electrode material impurities, the coating uniformity is poor, the density is low, the brittleness is large, and the surface roughness is difficult to control

[0008] Chinese patent announcement number CN 101817159A discloses "a method of EDM grinding and polishing the surface of flexible electrode parts, which is characterized in that: the speed-regulating motor drives the conductive flexible electrode to rotate, and pulses are passed between the flexible electrode and the surface of the part as the other pole. Power supply / DC, driven by the stepping motor on the insulating table, the flexible electrode approaches the surface of the part, and when it reaches the discharge gap, spark discharge is generated, and the polishing medium is sprayed into the discharge area or the discharge area is invaded by the polishing medium, and the spark discharge energy is used , etch away the surface material of the protruding part of the surface of the part, and at the same time, the rotating flexible electrode has a mechanical grinding effect on the surface of the part, and the rotating flexible electrode drives the polishing medium to polish the surface of the part”; this process is different from the traditional EDM The principle of polishing is the same, that is, the protrusions on the surface of the workpiece are removed by capacitive pulse discharge to achieve the purpose of polishing, and the requirements for the accuracy of the workpiece are reduced; similarly, in the process of this process, it is necessary to ensure that there is a suitable discharge between the brush and the workpiece. gap, so the mechanical grinding effect of the brush can be ignored; on the contrary, due to the strong stirring of the liquid by the flexible electrode and the huge resistance caused, higher requirements are put forward for the protection and processing of the equipment; on the other hand, the Although the process avoids the violent reaction between the melt and the medium in the above literature through the protection of the polishing medium, it also loses the strengthening effect of the electric spark; therefore, this process is only suitable for the deburring of some small and fine parts, and it is difficult to obtain Widespread application, especially when dealing with large parts, large areas or when a good strengthening effect is required, the defects of the process become very obvious

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