File is a multi-edged cutting tool, mainly used for filing hardness in the range of 18 ~ 58HRC metal materials, work is often subject to bending deformation and impact, so the requirements of the file in order to ensure high wear resistance at the same time should have a certain degree of toughness. A considerable number of Chinese filings have entered the international market. Because of their poor quality, their prices are only one-eighth to one-fifth of those of the international famous brand, the American double-blade file. Although the chemical composition of the two materials is similar, their failure modes are completely different. The double-blade file is mainly normal wear failure, while the domestic file is mainly abnormal failure, such as broken teeth and broken edges, and the life gap is very big. In order to improve the quality of domestic file, firstly, the imported high-life file is analyzed and dissected, and then the rectification measures are put forward.
1) quality analysis of double tool file.
(1) chemical constituents. As can be seen from Table 3-8, the chemical composition of the double-blade file is similar to that of the domestic file, and the material used is equivalent to that of the domestic T12A, but there are some differences in trace elements.
表3-8 锉刀用钢化学成分（质量分数） (%)
Table 3-8 chemical composition (mass fraction) of file steel (%)
Chemical composition (mass fraction) of steel for file
Filing test. The experiment with 8-minute thin flat file shows that the curve of the double-blade file is smooth after cutting for a certain number of times. It shows that the file has good durability and long service life, and the surface of the file teeth remains in a sharp state when it reaches 500,000 times. On the contrary, after 300,000 times of domestic filing, a large number of broken teeth and broken edges appear and can not be continued to use.
(3) histomorphology and fracture morphology. In the microstructure of the double-blade file, it was found that the size of carbide particles was uneven, a considerable number of large particles of carbide were uniformly distributed in the microstructure, and the edges and corners of carbide particles were passivated. Under transmission electron microscope, the matrix structure is cryptocrystalline martensite, and there are many lath martensite. The microstructure of domestic files is lamellar martensite and dispersed carbide particles.
(4) quality analysis. The chemical composition of the double-blade file is similar to that of the domestic file, but the difference of the structure is only the difference of the carbide shape and the matrix structure. The special structure of the double knives file is the main reason for its good quality. T12A steel is hypereutectoid high carbon steel with high brittleness. Conventional heat treatment aims to obtain fine dispersed carbides and improve their toughness in order to obtain strength and toughness. However, the abrasion resistance of the workpiece under this special working condition is the first. To obtain good filing performance, it is an effective method to keep a certain amount of large particles of carbide in the structure. Only in this way will the toughness of the material which is already fragile become lower. Therefore, the lath martensite with excellent toughness must be obtained by heat treatment and the edges and corners of carbide particles must be passivated.
It can be seen from the above analysis that if a special heat treatment method is adopted to obtain the microstructure similar to that of the double-blade file, the service life of the domestic file will be greatly improved.
2) file heat treatment process.
(1) pretreatment process. In order to achieve the above strengthening and toughening effect, the two-stage isothermal spheroidizing annealing process as shown in Fig. 3-5 was adopted to change the original microstructure of the file. Firstly, the steel was heated to 840 ~ 850 C higher than that of Accm (820 C), so that only a few carbide particles were retained in the microstructure and the austenite structure was inhomogeneous. Then the first stage, spheroidizing annealing stage, is shorter than the isothermal stage above Ac1 (730 C). Undissolved carbide and high concentration carbon segregation zone in inhomogeneous austenite will become the core of large carbide sprouting and growth. At the same time, the carbon concentration in the surrounding tissues is reduced, so as to prepare the lath martensite after quenching. When entering the second stage of spheroidizing annealing, i.e. below Ac1, the carbide further diffuses, precipitates, aggregates and spheroidizes, resulting in further spheroidizing and growth of large particles of carbide, and the formation of many small particles of dispersed carbide. This resulted in the formation of a large number of large granular carbides and a large number of low carbon matrix structures. This pre organization creates a good organizational condition for final heat treatment.
Two stage spheroidizing annealing process of T12A steel
Fig. 3-5 two stage spheroidizing annealing process for T12A steel
(2) the final heat treatment process. Heat treatment process with quick heating and short time insulation is adopted. Because the heating temperature is low, holding time is short, carbide particle size is uneven, dissolution rate is different, so a very uneven composition of austenite and a certain number of carbides. The microstructure after quenching is similar to that of American double-blade file. It is lath martensite and more cryptocrystalline martensite. The size of carbide is uneven and the edges and corners are passivated.
The fracture morphology of T12A steel file made in China is similar to that of double-blade file. A large number of shallow dimples and tearing edges appear. However, the fracture morphology of T12A steel file treated by traditional process is quasi-cleavage and intergranular. Filing test can reach more than 500,000 times, reaching the level of double-blade file, the failure form is normal wear failure, basically eliminating abnormal failure such as tooth breakage, edge breakage and so on.
标签:   环氧地坪 地坪 环氧地坪漆 环氧地坪施工 钢锉 锉刀