Aircraft composite roller cracking in the rack

Aircraft integrated within the rack roller cracking - 2019 01 - 06 Li Shile, bao-lin Yang, xiu-li zhang ( Shijiazhuang seamounts industrial development corporation) 3 cr13 martensitic stainless steel with high strength, the advantages of high hardness and good wear resistance, thus has been widely used. At the same time, because the carbon content is higher, its relatively poor corrosion resistance, and has a certain quenching cracking resistance. Recently our factory in aircraft maintenance checks of something, found on the left side of the integrated within the rack roller cracking. The roller is 3 cr13 material, use time accumulated about 1300 h. To this, the author through to the roller for macro microscopic observation, metallographic examination, and so on, the research analyzes the cracking reason of roller, and improvement Suggestions are put forward. 1. Test procedures ( 1) Appearance inspection wheel appearance is shown in figure 1. Roller surface fracture level, fracture around without obvious mechanical damage. Roller outer surface can be seen in two radial crack ( Marked a, b) respectively , crack extended the supreme end face and squeeze the traces on the surface. Figure 1 roller, macro ( 2) Micro fracture observation wheel microscopic morphology of fracture is shown in figure 2. Fracture can be divided into two areas: the intergranular fracture zone and quasi cleavage fracture zone. Among them, the intergranular fracture zone of the fracture surface area of 60% ~ 70%, and the rest of the cleavage fracture zone. No obvious source region and the entire section is relatively flat, mechanical damage, there is no signs of corrosion. Is visible on the fracture along crystal and quasi cleavage line, quasi cleavage fracture zone is started in the intergranular/quasi cleavage border extension ridge. Figure 2 roller fracture microstructure ( 3) Postures and metallographic examination on the roller end face, after polishing etching in asana microscope to look at the roller crack, as shown in figure 3. Roller on the face besides known a and b crack, there is also the internal cracks and extended to smaller crack on the surface of the c. Article 4 the crack characteristics: crack morphology twists and turns, crack fracture exists between small particles. In 200 times metallographic microscope observation of crack enlarged b, can find crack is serrated, no decarburization phenomenon, cross section along the crystal characteristics, as shown in figure 3 d. Roller of tempered martensite matrix organization. Figure 3 rollers postures, cracking morphology ( 4) Hardness test on the roller end test the rockwell hardness value is 45. 6HRC。 According to the GB/T11721999 'black metal hardness and intensity scale values' converted to strength value is about 1440 mpa; Meet process & delta; b = 1375± 100 mpa's request, but is close to upper limit. 2. Analyze and discuss the role of the roller in the rack for: the installation on the roller shaft, through their own rotation between the transfer release the rocker arm and rocker arm by sliding friction into rolling friction. Overall, roller bear rolling extrusion, without tension stress, there is no high temperature, corrosion, such as environment, so can rule out the possibility of stress corrosion. Release on the rocker arm has a sharp corners, which can lead to surface of roller indentation; Release the radial rotation is a shock action, so the extrusion roller bear for impact stress. Fracture analysis shows that the fracture is composed of the intergranular area and quasi cleavage area. Quasi cleavage zone extension ridge originated in the intergranular/quasi cleavage area of the junction, it shows that the crystal area ahead of quasi cleavage area, and then the intergranular crack tip gradually expanded form quasi cleavage fracture, fracture finally. Combining with the existing multiple surface and inside the intergranular crack, can be concluded that the intergranular crack should be produced in the process of manufacturing, namely the quenching crack; Quasi cleavage cracks continue to expand in the process of crack for use. 3 cr13 martensitic stainless steel, heat treatment process usually for quenching + tempering; Due to carbon and chromium content is higher, thus has a larger quenching cracking resistance, the solid solution heat treatment process has strict requirements, such as temperature, quenching liquid; If the improper control of the operation, easy to produce quenching crack. 3. Conclusions and recommendations, 1) The roller cracking was due to the production process of the intergranular quenching crack, crack in use process gradually formed extension. （ 2) Suggest to check the actual production process of roller, screening factors leading to quenching crack. Source: the metal processing ( Hot working) Magazine,