End of the spindle in the finishing mill roller shaft sleeve fracture analysis

End of the spindle in the finishing mill roller shaft sleeve 2019 - fracture analysis 10 - 30 yan xiaohong, zhang jian ( Taier Heavy Industry Co. , Ltd. ) The spindle is strip strip finishing mill group of key transmission parts, the performance and quality and the yield and quality of strip products have a direct relationship, its technology demand is higher and higher, and the roller end shaft sleeve as the key part of the spindle and finishing mill roll connection stress, its importance is self-evident. 1. Technical requirements from the spindle assembly drawing can be seen in figure 1. A complete set of finishing mill, roller end shaft sleeve right inside the outer teeth tooth and tooth shaft sleeve, the other end of the flat hole with roll, transfer unidirectional torque and rolling process, the impact of the roller end bushing bear. I company for a certain steel mill production 1700 mm finishing of the spindle online using eight months later, F1 roll end bushing internal tooth broken into four parts. The roller end sleeves made of low carbon alloy steel 17 cr2ni2mo whole carburizing treatment, the depth of carburizing layer 2 ~ 2. Module 12, 5 mm, teeth carries on single tooth after induction hardening gear grinding, grinding amount of 0. 5 mm, tooth surface hardness for 58 to 62 HRC. The main manufacturing process for the roller end shaft sleeve: hot forging & rarr; Normalizing + tempering & rarr; Rough machining & rarr; Tempering stability & rarr; Machining ( Gear shaper) → Carburizing & rarr; Single tooth tooth department induction hardening & rarr; Gear grinding ( The remaining parts of the car, plug-in processing) 。 The spindle roller at left end finishing mill sleeve tooth department cooperate with external gear shaft sleeve transmission torque, flat hole position with roll ( See figure 1) 。 2. Fracture and sampling locations for the entire 2 roll collar fracture after the tooth of form, the macro to the naked eye observation, crack produced expands gradually, from bottom of inner hole tooth under constant torque tear has been broken into 4 parts including two pieces directly. The fractures are arbitrary cut take a block of tooth profile, and macrostructure of substrate, hardness and depth of carburizing layer, the microstructure features and the hardening parts of the mechanical properties testing, material chemical composition analysis. 3. The analysis process, 1) Not detect the macrostructure of the hardening layer of cutting tooth section according to the GB/T105612005 under 100 times the amount of non-metallic inclusions in steel standards for testing, in the field of non-metallic inclusions size has reached the largest category five or so ( See figure 3) 。 （ 2) Tooth of hardness test using alcohol 4% nitric acid corrosion fracture tooth section, macroscopic observation and hardness test, the whole tooth addendum and tooth flank as shown in figure 4, the distribution of the hardening layer on upper tooth top and tooth side have hardened layer, tooth side lower part and no hardening layer close to the location of the root. According to the hardness gradient method is examined to detect hardness gradient of hardening layer, from the surface interval 0. 5 mm, hardness tests on desktop microhardness meter, the results are shown in table 1. Table 1 can be seen from table 1, tooth surface after carburizing and hardening the surface of the hardened parts hardness and depth of hardening layer in 2. 0 mm left and right sides, accord with the requirement of design, but the lower part of tooth flank and root no hardening layer. （ 3) Organizational characteristics of carburized layer and the core detection by microstructure observation, parts of the hardening layer for quenching martensite, and uniform organization, level of martensite in level 2, did not see obvious retained austenite, conform to the carburizing and quenching organization. The core organization of pearlite and ferrite more ( See figure 5) 。 （ 4) Chemical composition detection using spectro mobile spark direct reading spectrometer measured material chemical composition as shown in table 2. Table 217 cr2ni2mo collar chemical composition ( The mass fraction) （ %） Visible, the chemical composition of material conform to the standard of GB/T170171997 17 cr2ni2mo steel requirements. （ 5) Matrix mechanics performance test and mechanical performance test results as shown in table 3. In table 34. Conclusion through the macro fracture observation, macro analysis, hardness test, microstructure observation and chemical composition analysis and other means to roll collar fracture reasons for analysis. The analysis results show that the roller end shaft sleeve of single gear quenching after carburizing, uneven tooth surface quench hardened layer, from the tip to the tooth surface gradually thinning, central central tooth surface and tooth root ministry no hardening layer. And can see from the part of broken tooth root root have obvious traces of extrusion, mainly from the root of hardening layer. Materials in line with the requirements of design drawings. See from low power testing material itself exists inclusions, and the level is higher, the material purity is not in conformity with the requirements. Dedendum within department no hardening layer, cooperate with the outside of the tooth in meshing transmission over a long period of time to its roots in the process of continuous extrusion, and forging internal large inclusion and the matrix strength is low. Inner gear tooth root of low hardness and high hardness tooth addendum continuous extrusion friction in the process of meshing transmission is the main damage factors produce crack and expanding. Based on the analysis of the above, low matrix strength, non-metallic inclusions, no hardness measurement of tooth bottom and root layer, is a major cause of early fracture of workpiece. Source: the metal processing ( Hot working) Magazine,