Mechanical properties of carbide-free lower bainite in complex-alloyed constructional steel: Effect of bainitizing treatment parameters
Year: 2020
Type: article
Abstract: Tensile/impact behaviour of lower bainite obtained in high-Si steel 55Si3Mn2CrMoVNb was studied using SEM, TEM, and XRD.Specimens were austenitized at 900 • C and isothermally treated at 250, 270, and 300 • C with holding up to 600 min.The heat treatment results in the formation of cementite-free lower bainite/retained austenite structure, where retained austenite was found as blocky "islands" and interlaths "films".The width of bainitic ferrite laths decreases from 170-240 µm to 45-80 µm with holding temperature decreasing.This results in increasing UTS (to 1700 MPa) and hardness (to 52 HRC).The optimal combination of mechanical properties (UTS 1397-1522 MPa, hardness 45-47 HRC, total elongation 18-21 %, U-notched impact toughness 105-139 J cm -2 ) refers to holding at 300 • C to be associated with higher amount of retained austenite (30-33 %).With prolonging the bainitizing duration the hardness and ductility decreases while impact toughness increases.Prolonged holding at 300 • C leads to a continuation of bainite transformation and precipitation of transitional carbides within ferrite laths.K e y w o r d s : carbide-free lower bainite, retained austenite, phase transformations, microstructure, mechanical properties
Language: English
Subfield: Mechanical Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: diamond
OpenAlex ID: W3015259589