Assistants @ Metallurgical & Materials Eng. Dept. / METU

	Kemal DAVUT
	Room: D-111 Lab: B-203
	(+90)312 210 5832 (room) (+90)312 210 5845 (lab)
	E-mail: kdavut@metu.edu.tr
	Personal Web Page Research Group Web Page

Courses/Labs:

Metallography, SEM, Residual Stresses in Material Processing, Basic Concepts in Materials Science

Interests:

SEM, Metallography, Materials Characterization, Non-Destructive Testing

Former Degree: B.S., M.S.; Metallurgical and Materials Engineering Dept, METU

Current Degree: Ph.D.; Metallurgical and Materials Engineering Dept, METU

Characterization of Steel Microstructures by Magnetic Barkhausen Noise (MBN)

Supervisor: Dr. C. Hakan GÜR

The aim of this study is to examine the possibility of using Magnetic Barkhausen noise (MBN) technique in characterizing the microstructures of quenched and tempered low alloy steels. Specimens were prepared from AISI/SAE 1040, 4140 and 5140 steel bars. After austenitizing and quenching identically, the specimens were tempered between 200^oC and 600^oC. Formation of the desired microstructures was ensured by metallographic examinations and hardness measurements. The results show that as tempering temperature increases the Barkhausen activity increases due to the enhancement of domain wall displacement with softening of the martensite. It has been shown that MBN is a powerful tool for evaluating the microstructures of martensitic steels.

Using color etching in order to reveal ferrite grains with enchanced contrast. After polishing, the specimens were etched first by 5% Nital (nitric acid + ethanol) followed by Beaujard`s reagent. Nital which is used as a wetting agent reveals the grain boundaries of ferrite. The reagent deposits a complex oxide-sulfide-sulfate film on the surface which is responsible for coloring of ferrite grains.

Figure shows the correlation of hardness with MBN for the AISI/SAE 1040 specimen. As the tempering temperature increases, in contrast to the reduction in hardness, the MP peak value increases due to the enhancement of domain wall displacement with softening of the martensite. Considering the excellent correlation of hardness with RMS (root-mean-square value of the MBN signal), MBN can be used to predict hardness of heat treated steel components.