Effect of Cerium Content on the Evolution of Inclusions and Formation of Acicular Ferrite in Ti-Mg-Killed EH36 Steel

Zhen Liu,Xiaokang Cui,Zirui Song,Bo Song,Longfei Li,Zhanbing Yang,Lei Wang

doi:10.3390/met10070863

Zhen Liu, Xiaokang Cui + Show 5 more

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https://doi.org/10.3390/met10070863

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Abstract

Ce has been widely used in oxide metallurgy for modifying inclusions and refining microstructure. Effect of Ce contents on the evolution and characteristics of non-metallic inclusions and the formation of acicular ferrite (AF) in Ce-treated Ti-Mg-killed EH36 steel was investigated. The results showed that the main type of inclusions in Ti-Mg deoxidized steel was MgO·Al2O3-MnS. After 0.014%, 0.024% and 0.037% Ce were added into the steels, dominant inclusions became CeAlO3-MgO-MnS, Ce2O2S-MgO-MnS and Ce2O2S-MnS, respectively. The precipitation of pure MnS was suppressed in the steel with 0.024% Ce, while the number density of total inclusions increased significantly in the steel with 0.037% Ce, causing the inclusions distributing densely. Ce addition refined the microstructure of tested steels by promoting AF formation and polygonal ferrite distributing evenly. Dispersive distribution, low lattice mismatch against α-Fe, as well as lower number density of pure MnS caused the highest number density of effective inclusions (nucleus of AF formation) in 0.024% Ce-treated steel.

Highlights

The development of the shipbuilding industry and the application of high heat input welding (HHIW) have put forward higher requirements for the performances of ship plate steel featuring low carbon, high manganese and micro-alloying [1,2]
Mg addition has been reported to promote the formation of acicular ferrite (AF) in EH36 steel [8,9,10]
It is expected that the current study provides a basis for the control of potential inclusions working as the nucleus of AF nucleation in shipbuilding steels

Summary

Introduction

The development of the shipbuilding industry and the application of high heat input welding (HHIW) have put forward higher requirements for the performances of ship plate steel featuring low carbon, high manganese and micro-alloying [1,2]. EH36, the most widely used ship plate steel, has to meet the requirements of strength, toughness and weldability. The typical grain-refining particles in EH36 steel, AlN and TiN, will dissolve and lose their pinning effect during HHIW process, causing the microstructure in heat affected zone (HAZ) coarsening rapidly and HAZ toughness decreasing significantly [3,4]. Mg treatment refines the inclusions in the steel, increases the number density of inclusions and promotes MnS precipitation on oxide inclusions, which is conducive to induce the nucleation of AF. The typical inclusions in Ti-killed ship plate steel, such as Ti2 O3 , are favorable for the formation of AF due to the existence of a manganese-depleted zone (MDZ) around the inclusions [11].

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