The effect of M (M = Ce, Zr, Ce–Zr) on rolling microstructure and mechanical properties of FH40

Meng Xianghai,Wang Meng,Wang Zhe,Li Yungang,Li Mengxing

doi:10.1515/htmp-2020-0082

Abstract

AbstractCe, Zr and Ce–Zr composite experimentl steel were prepared by vacuum induction furnace and 550 twin-roll reversible rolling mill. Optical microscope (OM), scanning electronic microscopy (SEM) and energy dispersive spectrometer (EDS) were used to observe the rolling microstructure of the experimental steel. The mechanical properties of the experimental steel were tested and analyzed. The effect of cerium zirconium oxide inclusions on nucleation, tensile and impact fracture mechanism of intragranular acicular ferrite (IAF) was investigated. The results show that the rolling microstructure of steel containing 0.0052% Ce and the steel under composite treatment containing 0.0053% Ce and 0.0055% Zr is refined. IAF generation can be induced by Al–Ce–O inclusion of the size of 4 µm or induced by Al–Ce–Zr–O + MnS inclusion of the size of 3 µm. The yield strength and tensile strength of the steel treated by Ce–Zr are 428 and 590 MPa, respectively, the elongation is 23.55%, the longitudinal impact energy at −60°C is 189 J, which are 31, 45, 46 J and 6.25%, respectively, higher than those of the matrix steel. The dimple of the experimental steel at the fracture surface is larger and deeper than that of the matrix steel. The small inclusions in uniform distribution contribute to the high tensile strength of the experimental steel.

Highlights

To improve the welding efficiency of the shipbuilding industry, high heat input welding is wildly used
Yamashita et al [12], and Yang et al [13,14] reported that adding a small amount of rare earth Ce can convert the largesize, long strip and irregular rare-earth sulfide inclusions into spherical inclusions and weaken the segregation phenomenon and obviously refine the grains
Milyuts et al [15] reported that the original coarse and irregular inclusions in the shipbuilding steel plate treated by rare earth La and Ce changed into small and spherical rare earth oxides

Summary

Introduction

To improve the welding efficiency of the shipbuilding industry, high heat input welding is wildly used. Studies have shown that the treatment of Ce or Zr alone can produce a large number of fine second-phase inclusions in steel [6,7,8,9,10,11] This kind of particles can effectively induce ferrite nucleation, pin austenite grain boundary, refine microstructure of HAZ and improve low-temperature-impact toughness. Thewlis [16] reported that fine and dispersed secondary phase particles such as rare earth oxides and rare earth sulfides can form a low degree of mismatch with α-Fe. The secondary phase particles can promote heterogeneous nucleation of acicular ferrite and refine microstructure even under high heat input welding conditions. The results established the foundation for the development of Ce–Zr composite treatment to improve the tensile strength and impact toughness of HAZ of shipbuilding steel plate for high heat input welding

Experiment

Results and discussion

Tensile test

Low temperature impact