A method for predicting austenite grain size of cold extruded gear steel after carburizing

Abstract

A method for predicting the austenite grain size of cold-extruded gear steel after carburizing belongs to the field of metal material testing technology. The method mainly includes the following steps: taking samples from hot-rolled round steel and processing them into specimens of specified dimensions; normalizing the specimens; then performing spheroidizing annealing; cold-heading the spheroidized annealed specimens; then performing pseudo-carburizing treatment; finally, preparing the specimens into metallographic samples, etching them with picric acid aqueous solution, and observing the grain size under a metallographic microscope. This invention, through a coupled process of heat treatment and cold heading deformation, can effectively detect the austenite grain size of cold-extruded gear steel after carburizing, directly characterizing the material's resistance to grain coarsening during the carburizing process after cold extrusion.

Description

Technical Field

[0001] This invention belongs to the field of metal material testing technology, and relates to a method for detecting the austenitic grain size of cold-extruded gear steel. Background Technology

[0002] Carburized gear steel is a key material for manufacturing high-load gears in automobiles, wind power equipment, and construction machinery. Currently, there are two main types of gear processing procedures: one is hot forging followed by machining (such as hobbing, gear shaping, and milling); the other is spheroidizing annealing followed by cold extrusion forming. However, cold-extruded gears are prone to abnormal austenite grain growth during the carburizing process. To prevent abnormal grain growth during carburizing, the material composition is typically designed to improve its resistance to grain coarsening. However, material testing generally only allows for intrinsic grain size testing according to GB / T6394, which has no significant reference value for whether abnormal grain growth will occur during carburizing after cold extrusion. Evaluation can only be conducted after actual gear production, which takes a long time. If the material fails to meet standards, it will cause greater losses, which is detrimental to both raw material manufacturers and gear processing companies.

[0003] Therefore, developing a method to predict the austenite grain size after carburizing cold-extruded gear steel is of great practical significance for solving the above problems. Summary of the Invention

[0004] The purpose of this invention is to provide a method for predicting the austenite grain size of cold-extruded gear steel after carburizing. This method can effectively detect the grain size of cold-extruded gear steel after carburizing and assess whether the material possesses resistance to grain coarsening during carburizing after cold extrusion.

[0005] The technical solution of the invention: A method for predicting the austenite grain size after carburizing cold-extruded gear steel includes the following steps: 1) Take a sample from the hot-rolled round steel at 1 / 4D, where D is the diameter of the round steel (20-200mm); process the sample to 10mm×10mm×15mm or Φ10mm×15mm. 2) Normalize the processed sample. The normalizing process is to hold at 900-950℃ for 20 minutes and then air cool it after removing it from the furnace. 3) The normalized sample is subjected to spheroidizing annealing. The spheroidizing annealing process is to hold at 20-40℃ above Ac temperature for 300-400 min, furnace cool to below 500℃ and then air cool. 4) The spheroidized annealed sample is cold-forged to 2 / 3 of its height, i.e., from 15mm to 10mm; 5) The cold-headed sample was subjected to pseudo-carburizing treatment. The pseudo-carburizing process was to hold at 930℃ for 8.5 hours, water-cool after taking it out of the furnace, and then hold at 200℃ for 20-50 minutes. 6) Prepare the sample as a metallographic specimen, etch it with picric acid aqueous solution, and observe the grain size with a metallographic microscope.

[0006] The beneficial effects of this invention are: by using a process that combines heat treatment and cold heading deformation, the austenite grain size after cold extrusion deformation and carburizing can be effectively detected, providing a direct characterization of the material's resistance to grain coarsening during carburizing after cold extrusion. Attached Figure Description

[0007] Figure 1 The sample is fabricated as a sample diagram.

[0008] Figure 2 The austenitic grains are those of the sample in Example 1.

[0009] Figure 3 The austenitic grains of the gear in Example 1.

[0010] Figure 4 The austenitic grains are those of the sample in Example 2.

[0011] Figure 5 The austenitic grains of the gear in Example 2. Detailed Implementation Example 1

[0012] The steel's chemical composition (by mass percentage) is: C=0.17%, Si=0.19%, Mn=0.76%, P=0.008%, S=0.021%, Cr=1.75%, Nb=0.046%, Al=0.048%, Cu=0.14%, N=0.0144%, O=0.0008%. Testing steps: 1) Take a sample from the hot-rolled round steel at 1 / 4D and process the sample to 10mm×10mm×15mm; 2) Normalize the processed sample by holding it at 900℃ for 20 minutes, and then air-cool it after removing it from the furnace; 3) The normalized sample was subjected to spheroidizing annealing. The spheroidizing annealing process was to hold at 760℃ for 300 min, furnace cool to 400℃ and then air cool. 4) The spheroidized annealed sample is cold-headed to 2 / 3 of its height, i.e., from 15mm to 10mm; 5) The cold-headed sample was subjected to pseudo-carburizing treatment. The pseudo-carburizing process was to hold at 930℃ for 8.5 hours, water-cool after taking it out of the furnace, and then hold at 200℃ for 25 minutes. 6) Prepare the sample as a metallographic specimen, etch it with picric acid aqueous solution, and observe the grain size under a metallographic microscope. The grain size is grade 9, and there are no abnormally large grains.

[0013] After the round steel was cut into blanks, it underwent spheroidizing annealing, cold extrusion, carburizing, quenching, and low-temperature tempering. The grain size was tested and found to be grade 9, with no abnormally large grains. Example 2

[0014] The steel's chemical composition (by mass percentage) is: C=0.19%, Si=0.17%, Mn=1.25%, P=0.009%, S=0.022%, Cr=1.21%, Nb=0.005%, Al=0.032%, Cu=0.002%, N=0.0114%, O=0.0012%. Testing steps: 1) Take a sample from the hot-rolled round steel at 1 / 4D and process the sample to 10mm×10mm×15mm; 2) Normalize the processed sample by holding it at 920℃ for 20 minutes, and then air-cool it after removing it from the furnace; 3) The normalized sample was subjected to spheroidizing annealing. The spheroidizing annealing process was to hold at 780℃ for 350 min, furnace cool to 400℃ and then air cool. 4) The spheroidized annealed sample is cold-headed to 2 / 3 of its height, i.e., from 15mm to 10mm; 5) The cold-headed sample was subjected to pseudo-carburizing treatment. The pseudo-carburizing process was to hold at 930℃ for 8.5 hours, water-cool after taking it out of the furnace, and then hold at 200℃ for 30 minutes. 6) The sample was prepared as a metallographic sample and etched with picric acid aqueous solution. The grain size was observed to be 8.5 grade under a metallographic microscope, and there were abnormally large grains of grade 0.

[0015] After the round steel was cut into blanks, it underwent spheroidizing annealing, cold extrusion, carburizing, quenching, and low-temperature tempering. The grain size was tested and found to be grade 8.5, indicating the presence of grade 0 abnormally large grains. Example 3

[0016] The steel's chemical composition (by mass percentage) is: C=0.17%, Si=0.17%, Mn=0.9%, P=0.009%, S=0.022%, Cr=1.71%, Nb=0.035%, Al=0.032%, Cu=0.002%, N=0.0114%, O=0.0012%. Testing steps: 1) Take a sample from the hot-rolled round steel at 1 / 4D and process the sample to 10mm×10mm×15mm; 2) Normalize the processed sample by holding it at 920℃ for 20 minutes, and then air-cool it after removing it from the furnace; 3) The normalized sample was subjected to spheroidizing annealing. The spheroidizing annealing process was to hold at 780℃ for 350 min, furnace cool to 400℃ and then air cool. 4) The spheroidized annealed sample is cold-headed to 2 / 3 of its height, i.e., from 15mm to 10mm; 5) The cold-headed sample was subjected to pseudo-carburizing treatment. The pseudo-carburizing process was to hold at 930℃ for 8.5 hours, then water-cool after taking it out of the furnace and then hold at 200℃ for 30 minutes. 6) Prepare a metallographic sample, etch it with picric acid aqueous solution, and observe it with a metallographic microscope. The austenite grain size is grade 8.5, and there are grade 0 abnormally large grains.

[0017] After the round steel was cut into blanks, it underwent spheroidizing annealing, cold extrusion, carburizing, quenching, and low-temperature tempering. The austenitic grain size of the gear was tested and found to be grade 8.5, with grade 0 abnormally large grains present.

Claims

1. A method for predicting the austenite grain size after carburizing cold-extruded gear steel, characterized in that... Includes the following steps: 1) Take a sample from the hot-rolled round steel at 1 / 4D, where D is the diameter of the round steel (20-200mm); process the sample to 10mm×10mm×15mm or Φ10mm×15mm. 2) Normalize the processed sample. The normalizing process is to hold at 900-950℃ for 20 minutes and then air cool it after removing it from the furnace. 3) The normalized sample is subjected to spheroidizing annealing. The spheroidizing annealing process is to hold at 20-40℃ above Ac temperature for 300-400 min, furnace cool to below 500℃ and then air cool. 4) The spheroidized annealed sample is cold-forged to 2 / 3 of its height, i.e., from 15mm to 10mm; 5) Perform pseudo-carburizing treatment on the cold-headed sample. The pseudo-carburizing process is to hold at 930℃ for 8.5 hours, water-cool after taking it out of the furnace, and then hold at 200℃ for 20-50 minutes. 6) Prepare the sample as a metallographic specimen, etch it with picric acid aqueous solution, and observe the grain size with a metallographic microscope.

Images