Journal of Jilin University(Engineering and Technology Edition) ›› 2020, Vol. 50 ›› Issue (2): 520-525.doi: 10.13229/j.cnki.jdxbgxb20190012

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Effect of isothermal heat treatment temperature on microstructure and mechanical properties of super bainite

Wen-cui XIU1,2(),Hua WU1(),Ying HAN1,Yun-xu LIU1   

  1. 1.Key Laboratory of Advanced Structural Materials of Ministry of Education，Changchun University of Technology，Changchun 130012, China
    2.School of Mechanical and Civil Engineering，Jilin Agricultural Science and Technology University, Jilin 132101, China
  • Received:2019-01-04 Online:2020-03-01 Published:2020-03-08
  • Contact: Hua WU E-mail:xiuwencui@jlnku.edu.cn;wuhua@ccut.edu.cn

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Abstract:

In order to study the super-bainite structure transformation of 70Si2Mn2CrMo steel after isothermal heat treatment at different temperatures, the precipitation of carbide and its mechanical properties were studied. The temperature and type of carbide precipitation were determined by the analysis of the microstructure and mechanical properties of the sample. It is shown that the precipitation of carbide reduces the carbon content in the overcooling austenite, resulting in low stability of the steel and the volume fraction of retained austenite in super-bainite is reduced. Compared with the sample of no carbide precipitation at 220 °C isothermal heat treatment, the tensile strength of the sample steel decreased by 11%, the strong plastic product decreased by 16%, and the fatigue cycle fracture times decreased by 55%, at 245 ° C isothermal heat treatment.

Key words: metal material, super-bainite, carbide precipitation, isothermal heat treatment temperature, mechanical property

CLC Number: 

  • TG142.1

Fig.1

Diagram of heat treatment process of experimental steel"

Table 1

Technical parameters of heat treatment of steel for test"

实验号温度TA/℃，时间/h温度T/℃，时间/h
1910，1195，48
2910，1220，48
3910，1245，48
4910，1350，48

Fig.2

Microstructures of experimental steel isothermal treated at different temperatures"

Table 2

Hardness value of experimental steel isothermal treated at different temperatures"

等温温度/℃硬度值/HRC
35043
24551
22054
19556

Fig.3

TEM characterization of microstructures in experimental steel isothermal treated at different temperatures"

Fig.4

XRD diffraction patterns of experimental steel isothermal treated at different temperatures"

Table 3

AR content and carbon concentration in microstructures of specimens isothermal heat treated at different temperatures"

等温热处理温度/℃残余奥氏体质量分数/%残余奥氏体中C质量分数/%
2457.730 00.878 7
2208.416 91.020 4
1955.079 31.090 9

Fig.5

Tensile stress-strain curves of specimens after isothermal heat treatment at 220 ℃ and 245 ℃"

Table 4

Tensile and fatigue test data of specimens after isothermal heat treatment at 220 ℃ and 245 ℃ respectively"

等温处理温度/℃抗拉强度/MPa伸长率/%强塑积/(MPa·%)疲劳断裂/103次
2202 3477.6417 931184
2452 0827.2415 07483

Fig.6

Fatigue fracture morphology of the experimental steel isothermal treated at different temperatures"

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