Ferrite Formation Dynamics and Microstructure Due to Inclusion Engineering in Low-Alloy Steels by Ti2O3 and TiN Addition

Significance Statement

Microstructure control in steel according to inclusion engineering

Previous researches have been conducted on study of final microstructural characteristics of the formed intragranular ferrite and grain boundary ferrite. However, a better understanding on microstructural changes and phase deformation process at critical temperatures is needed in view of having a desirable balance between the formed intragranular ferrite and grain boundary ferrite with use of either oxide metallurgy or inclusion engineering.

In line with this, Dr. Wangzhong Mu and colleagues investigated the dynamic formation of intragranular ferrite and grain boundary ferrite in inclusion engineering steels with either titanium (III) oxide Ti2O3 and  titanium nitride TiN additions. The work which was published in the journal, Metallurgical and Materials Transactions B provided information on effects of the inclusions, cooling rate and prior austenite grain size on ferrites formation.

In their experiment, the steel specimens with the addition of titanium (III) oxide and titanium nitride were named alloy A and B respectively. The specimens were then placed in high temperature confocal laser scanning microscopy CLSM and heated to a temperature of 14000C. Constant cooling rates of 3.6, 70 and 6780C/min were also observed. Specimens were at some specific temperatures in order to control the prior austenite grain size.

The experimental calculations of thermodynamic driving forces on misfit strain energy between inclusions and austenite/ferrite showed good agreement with previous studies as a method for calculating the grain boundary nucleation from grain boundaries was also defined.

Electron probe microanalysis on alloy A showed that the atomic ratio of oxygen to titanium was in the range of 1.55 and 1.69. Manganese sulfide inclusions and small amounts of Mn-Al-Si-O oxide were also randomly distributed on the corners of the titanium oxide core. Aluminum, manganese and sulfur were also present in the oxide phase.

For alloy B, elements such as silicon, aluminum, manganese, titanium and oxygen with presence of manganese sulfide were found in the core part of titanium nitride. The atomic ratio of nitrogen to titanium found between 0.8 and 1.3.

An increase in prior austenite grain size was observed for both alloys but alloy A had a greater grain size compared to alloy B. Area fraction of the intragranular ferrite was larger in alloy A compared to alloy B at a constant cooling rate and grain size. However, the intragranular ferrite fraction for both alloys increased with an increase in prior austenite grain size with the highest fraction found at a cooling rate of 700C/min.

When specimens were visualized by confocal laser scanning microscopy showed that the starting temperature of grain boundary ferrite formation in steel was higher for smaller grain size while that of intragranular ferrite was not affected by the grain size. Starting temperature of grain boundary ferrite formation for alloy A was lower compared with alloy B but the starting temperature of intragranular ferrite formation remained the same for both alloys. Both starting temperatures of grain boundary ferrite and intragranular ferrite formation decreased with an increase in cooling rate.

This study provided profound additional information on the preferential formation of intragranular ferrite and grain boundary ferrite.  

Ferrite Formation Dynamics and Microstructure Due to Inclusion Engineering in Low-Alloy Steels by Ti2O3 and TiN Addition. Advances in Engineering

 

About the author

Dr. Wangzhong Mu is currently a postdoctoral researcher in Steel Research Center, McMaster Uniersity, Canada. He received his PhD degree from KTH Royal Institute of Technology in 2015, and has been a visiting research scholar in Tohoku University.

His research field mainly focuses on the oxide metallurgy, clean steel manufacturing, and recycling of metallurgical waste. He has published over 20 papers in peer-reviewed journals and over 10 publications in the international conferences till November 2016.

 

About the author

Prof. Shibata is a full professor in the institute of multidisciplinary research for advanced materials, Tohoku University in Japan. His reasearch mainly focuses on physicochemical approach to interfacial phenomena and thermophysical properties at high temperatures for high efficiency materials processing.

He is also the main contributor to develop the first high temperature confocal laser scanning microscope (HT-CLSM), which is used in the process metallurgy in the world.

 

About the author

Dr. Peter Hedström is an associate professor in the department of materials science and engineering, Royal Institute of Technology (KTH). Also, he is the head of advanced instrumentation laboratory in KTH.

His research interest includes advanced materials characterization, structure-property relations in engineering materials, deformation of metals, phase transformations in inorganic materials, powder metallurgy, materials design.

 

About the author

Prof. Pär Jönsson is a full professor in Applied Process Metallurgy at the department of Materials Science and Engineering, Royal Insititute of Technology (KTH) since 1998. His research group mainly focuses on the computational fluid dynamic simulation of different aspects of process metallurgy, and also experimetnal studies related to oxide metallurgy and inclusion engineering.

His has published 232 publications in peer-reviewed journals and 165 publications in international conferences. He has supervised 52 students receiving a doctor degree at KTH.

 

About the author

Prof. Keiji Nakajima is now a visiting professor at KTH Royal Institute of Technology, Sweden, after he has retired Tohoku University, Japan in 2003. He was also a concurrent professor at Northeastern University, China from 2005 to 2011.

He has been researching mainly the process metallurgy, especially, 1) casting process designs for material production, and 2)  control of microstructure formation and new materials production, and published over 170 research papers. Parts of them were done using the combination techniques of the high temperature confocal scanning laser microscope and the high temperature differential scanning calorimetry, as well as the modelling and the simulation.

On the other hand, he has organized three times “International Symposium on Cutting Edge of Computer Simulation of Solidification, Casting and Refining” (CSSC2010, CSSCR2013 and CSSCR2016), as a symposium chairman.

 

Journal Reference

Wangzhong Mu1,2, Hiroyuki Shibata3, Peter Hedström1, Pär Göran Jönsson1, Keiji Nakajima1. Ferrite Formation Dynamics and Microstructure Due to Inclusion Engineering in Low-Alloy Steels by Ti2O3 and TiN Addition, Metallurgical and Materials Transactions B 47 (2016) 2133-2147.

Show Affiliations
  1. Department of Materials Science and EngineeringKTH Royal Institute of Technology, Stockholm, Sweden.
  2. Department of Materials Science and Engineering, McMaster Steel Research Center, McMaster  University, Hamilton, Canada.
  3. Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Japan.

 

Go To Metallurgical and Materials Transactions B

 

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