Effect of La on inclusions and fracture toughness of low-alloy ultra-high-strength 40CrNi2Si2MoVA steel

Journal:Journal of Iron and Steel Research International

Volume:28

DOI Number:10.1007/s42243-021-00579-1

Place of Publication:China

Summary:The effect of La on inclusions and fracture toughness of 40CrNi2Si2MoVA steel was investigated via the optical
microscope, scanning electron microscope, image software and electronic universal testing machine. The results reveal that
the inclusions in steel without La are mainly MnS and Al2O3–MnS, while the inclusions in steels with La primarily contain
La–O–S, La–S and other rare earth complex inclusions contain P and As. La–O–S and La–S are formed under the
steelmaking temperature and act as the nucleation core of rare earth complex inclusions containing P and As. According to
the segregation model, La–O–S–P–As and La–S–P–As are formed through chemical reactions during the solidification
stage. As La content in steels increases from 0 to 0.032 mass%, the average spacing of inclusions is gradually increased
from 5.28 to 15.91 lm. The volume fraction of inclusions in steels containing less than 0.018 mass% La approaches
0.006%; however, it is significantly improved to 0.058% when La content is increased to 0.032 mass%. With the increase
in La content, the fracture toughness is firstly improved from 63.1 to 80.0 MPa m1/2 due to the increase in average spacing
of inclusions and then decreases to 69.6 MPa m1/2 owing to the excessive increase in volume fraction of inclusions. The
optimal fracture toughness is found in 40CrNi2Si2MoVA steel with 0.018 mass% La.

Project Source:General project of National Natural Science Foundation of China

Key Words:40CrNi2Si2MoVA steel; La; Inclusion; Thermodynamic calculation; Fracture toughness

Indexed by:SCI

Discipline:Engineering

First-Level Discipline:Metallurgical Engineering

Page Number:1408–1416

Translation or Not:No