The development and application of ultra-high strength spring flat steel is of great significance in achi
eving automotive lightweight. Understanding the continuous cooling transformation behavior of this type of steel aids in developing its post-hot rolling cooling and quenching-tempering processes. On the basis of mechanical property testing, this study focuses on a newly designed ultra-high strength flat spring steel, 50SiMnCr, to investigate the effect of cooling rate on the microstructure and hardness of experimental steel by a combination of metallographic-hardness and thermal expansion method, thereby constructing continuous cooling transformation (CCT) curves. The results show that the strength and ductility of 50SiMnCr steel meet the requirements of the 2 000 MPa level, with phase transition point
A
c1
=721 ℃,
A
c3
=758 ℃,
M
s
=220 ℃ and
M
f
=103 ℃. Ferrite and pearlite transformation occurs when the cooling rate is 0.05 ℃/s-0.5 ℃/s. Bainite transformation takes place when the cooling rate is increased to 1 ℃/s. Martensite transformation happens when the cooling rate is above 2 ℃/s. The hardness of the this steel increases with increasing the cooling rate.
Bhatt C D , Nadarajan M , Balaji R , et al . Leaf spring model for heavy load vehicle using solid works and ANSYS analysis [J]. Materials Today: Proceedings , 2020 , 33 : 4764 - 4770 .
Noronha B , Yesudasan S , Chacko S . Static and dynamic analysis of automotive leaf spring: A comparative study of various materials using ANSYS [J]. Journal of Failure Analysis and Prevention , 2020 , 20 ( 3 ): 804 - 818 .
Venkatesan M , Devaraj D H . Design and analysis of composite leaf spring in light vehicle [J]. International Journal of Modern Engineering Research , 2012 , 2 ( 1 ): 2249 - 6645 .
Matjeke V J , van der Merwe J W , Vithi N L . Determination of critical transformation temperatures for the optimisation of spring steel heat treatment processes [J]. Metals , 2021 , 11 ( 7 ): 1014 .
Wang X W , Hu Q F , Zhang C L , et al . Optimization of heat treatment for 38Si7 spring steel with excellent mechanical properties and controlled decarburization [J]. Materials , 2022 , 15 ( 11 ): 3763 .
Liu F B , Chen K , Kang C P , et al . Effects of V-Nb microalloying on the microstructure and properties of spring steel under different quenching-tempering times [J]. Journal of Materials Research and Technology , 2022 , 19 : 779 - 793 .