In-situ observation on the influences of Ti on phase transformation of weld metal processed by high-heat input welding

Song Fengyu,Li Yanmei,Yao Lingzhen

doi:10.1177/1687814020962289

Song Fengyu, Li Yanmei + Show 1 more

Open Access

https://doi.org/10.1177/1687814020962289

Copy DOI

Abstract

The in-situ observation of the phase transformation processes of weld metal during high-heat input welding were carried out by a high temperature laser confocal microscope. The influences of Ti content on the phase transformation process were investigated. It was found that the Ti inclusions could act as the nucleation sites for α→γ transformation during the heating stage of welding thermo cycle and inhibit the growth of austenite grains. The number of inclusions was increased with increasing Ti content. During the cooling stage of welding thermo cycle, the inclusions could induce the nucleation of acicular ferrites when the Ti content was below 0.078%. With increasing Ti content, more acicular ferrites collided with each other and restricted their further growth. When the Ti content was increased up to 0.115%, a proportion of Ti atoms were dissolved in the matrix, which increased the hardenability and thus generated the lath bainite microstructure instead of acicular ferrite.

Highlights

The in-situ observation of the phase transformation processes of weld metal during high-heat input welding were carried out by a high temperature laser confocal microscope
When the inclusion is formed with Ti and other elements, and the content of Ti is controlled within a reasonable range, the formation of acicular ferrite (AF) structure can be effectively promoted in the inclusion, which would dramatically improve the mechanical properties of high-heat input weld metal
The mechanical properties of weld metal are determined by the microstructure, and the specific characterisation results of the microstructure were shown in Figure 2(a), (c) and (e) were the optical micrographs of the weld metals, while Figure 2(b), (d) and (f) were the scanning electron microscope (SEM) micrographs

Summary

Introduction

The in-situ observation of the phase transformation processes of weld metal during high-heat input welding were carried out by a high temperature laser confocal microscope. The AFs are normally considered as the ideal microstructure in the weld metal processed by high-heat input. In this way, the composition and distribution of inclusions show critical influences on the formation and development of AFs.[6,7,8] As one of the common element in high-heat input weld metal,Ti has a strong binding force with oxygen. When the inclusion is formed with Ti and other elements, and the content of Ti is controlled within a reasonable range, the formation of AF structure can be effectively promoted in the inclusion, which would dramatically improve the mechanical properties of high-heat input weld metal. The investigations on the microstructure during the phase transformation have not yet been reported

Objectives

Methods

Results

Discussion

Conclusion