Inclusions and Microstructure of Steel Weld Deposits with Nanosize Titanium Oxide Addition

Cuixin Chen,Haitao Xue,Liang Yan,Sixu Wang,Lei Zhi,Huifen Peng

doi:10.1155/2014/138750

Abstract

Nanosize TiO2particles were added directly into welding molten pool through electrode for the difficulty of accurate control of oxygen potential and production processing parameters. The characteristics of phase transformation and thermal behavior of inclusions for Fe-C-Mn-Si-Ti-O system and Fe-C-Mn-Si-TiO2system were analyzed. Results show that the added TiO2particles are more helpful for the formation of Mn-Ti-O complex inclusion and can induce the decrease of phase transformation temperature of austenite to ferrite. Intragranular ferrite can be obtained under the condition of continuous cooling transformation with cooling rate of 293 K/s–373 K/s. The inclusions in steel welds are spherical in shape and mainly composed of TiO2, Ti3O5, Ti2O3, MnO, and SiO2. The mean size of inclusions is 0.67 μm. These complex inclusions can supply a large number of nucleating cores for their precipitation at higher temperature, which will disturb the growth of columnar crystal during solidification. Moreover, Mn-containing titanium oxides will promote the transformation of austenite to intragranular ferrite for the formation of manganese depleted zones in steel welds around oxides. So it can be concluded that nanosize titanium oxide added directly in welding molten pool can be effectively used to control phase transformation and achieve fine and favorable microstructure.

Highlights

Titanium is one of the most effective alloying elements to improve the mechanical properties of materials in steelmaking and welding metallurgy
This is because Ti-containing phases, such as TiC, TiN, Ti(CN), TiOx, and MnTiOx, can inhibit grain growth by Zener pinning effect resulting in grain refinement and can act as the nucleation sites of acicular ferrite [1,2,3,4].Among these phases, the complex inclusions containing titanium oxide have been recognized as one of the most effective ones [5, 6]
Under the cooling rate of 373 K/s, phase transformation temperature is in the range of 989 K to 584 K for Ti-O system and 951 K to 718 K for 0.2% TiO2 added case

Summary

Introduction

Titanium is one of the most effective alloying elements to improve the mechanical properties of materials in steelmaking and welding metallurgy This is because Ti-containing phases, such as TiC, TiN, Ti(CN), TiOx, and MnTiOx, can inhibit grain growth by Zener pinning effect resulting in grain refinement and can act as the nucleation sites of acicular ferrite [1,2,3,4].Among these phases, the complex inclusions containing titanium oxide have been recognized as one of the most effective ones [5, 6]. In case of Ti2O3, the development of local manganese depleted zones (MDZs) around particles has been the most influential hypothesis [5, 10]

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Results

Conclusion