ISSN: 1546-962X
CODEN: JAIOAD
Published Online: 23 June 2009
Page Count: 12

A New Method to Study the Effect of Cooling Rate on the Decomposition of Austenite in Advanced High Strength Sheet Steels

Cho, K.
Researcher, Basic Metals Processing Research Institute, Dept. of Mechanical Engineering and Materials Science, Univ. of Pittsburgh, Pittsburgh, PA

Garcia, C. I.
Research Professor, Basic Metals Processing Research Institute, Dept. of Mechanical Engineering and Materials Science, Univ. of Pittsburgh, Pittsburgh, PA

Hua, M.
Research Assistant Professor, Basic Metals Processing Research Institute, Dept. of Mechanical Engineering and Materials Science, Univ. of Pittsburgh, Pittsburgh, PA

Lee, J.
Assistant Manager, Quality Control Dept. Hot & Cold Rolled Steel QC Group, POSCO, Pohang,

Ahn, Y. S.
Senior Researcher, Automotive Steel Products Research Group Technical Research Labs., POSCO, Gwangyang-si,

DeArdo, A. J.
Finland Distinguished Professor, Oulu Univ.Basic Metals Processing Research Institute, Dept. of Mechanical Engineering and Materials Science, Univ. of Pittsburgh, OuluPittsburgh, PA

(Received 21 April 2008; accepted 21 May 2009)

Abstract

A new modified Jominy holder and specimen were developed to study the effect of chemical composition, intercritical annealing temperature, and cooling rates on the transformation behavior of a series of dual-phase sheet steels. Correlations between temperature, time, and the distance from the water quenched end were developed using a laboratory view data acquisition program. In addition, the hardness and microstructure along the length of the sheet steel sample were determined as a function of cooling rate from the intercritical annealing temperature. Special chemical regents were used to reveal new ferrite, bainite, and other microstructural components, which were also evaluated by optical, scanning, and transmission electron microscopy. Critical cooling rate equations, based on steel composition, volume fraction of austenite and intercritical annealing temperatures, were developed to avoid or minimize the formation of new ferrite and bainite. The results of this work show that the modified Jominy test is an effective and efficient way to evaluate the hardenability of sheet steels.

Keywords:
austenite, bainite, critical cooling rate and equation, dual-phase steel, hardenability, martensite, modified Jominy holder and specimen, new ferrite

Paper ID: JAI101822
DOI: 10.1520/JAI101822
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