1. Effects of Elevated Temperatures on Structural Steel
Jeffrey A. Roberts
Department of Civil & Environmental Engineering
Michigan State University
East Lansing, MI, USA

2. Iron-Iron Carbide Phase Diagrams
Steel has Carbon concentrations between 0.1 and 2.0 wt % Carbon
Structural Steel – Plain-Low Carbon steel less than 0.4 wt % C

3. Crystal Lattice Structures
Body-Center Cubic Face-Center Cubic
Examples of two different lattice structures that Iron can exist in

4. Lattice Structure at different temperatures
γ-iron is Pearlite – BCC
α-iron is Austenite – FCC
Face-Centered Cubic are softer metals when made of atomic similar materials because of the increased number of slip planes

5. Dislocations
A crystalline defect around which there is atomic misalignment
Types of dislocations are substitutional or interstitial atoms and vacancies
More dislocations will usually mean a stronger material
Movement of dislocations through a metal matrix is one of the mechanism that translates into material plastic deformation
The more movement available the more deformation that will occur, equaling a weaker material

6. Plastic Deformation
Plastic Deformation at elevated temperatures shows the increased grain size and reduction in number of dislocations
As this continues the material becomes softer and more malleable

7. Steel Microstructure
Hypoeutectoid Composition
Large Austenite Grains – allow for easier movement of dislocations
Pearlitic Composite of Ferrite and Iron Carbide (Fe3C). More complex microstructure means a stronger material

8. Creep
Creep is a time dependent permanent deformation when subjected to constant load or stress
Up to 0.4*Tm Creep does not have much affect on plastic deformations
As temperatures increase above 0.4*Tm, Creep increases dramatically

9. Creep Deformation
As temperature increases the creep rate also increases
The amount of stress required to produce those creep rates decreases

10. References
(1) Ju Chen, Ben Young. Experimental investigation of cold-formed steel material at elevated temperatures. Thin-Walled Structures 2007; 45:
(2) Ju Chen, Ben Young. Stress-strain curves for stainless steel at elevated temperatures. Engineering Structures 2006; 28:
(3) D. Hull, D.J. Bacon. Introduction to Dislocations, Third Edition. Pergamon Press 1984
(4) Ju Chen, Ben Young, Brian Uy. Behavior of high strength steel at elevated temperatures. Journal of Structural Engineering 2006; :
(5) William F. Smith. Structure and Properties of Engineering Alloys, second edition. McGraw-Hill, Inc. 1993; 72-73
(6) Jyri Outinen, Pentti Makelainen. Mechanical properties of an austenitic stainless steel at elevated temperatures. Advances in Steel Structures 1999:
(7) K.T. Ng, L. Gardner. Buckling of stainless steel columns and beams in fire. Engineering Structures 2007; 29:
(8) Leroy Gardner. Stainless steel structures in fire. Structures & Buildings 2007; 160:
(9) Albert Hanson, J. Gordon Parr. The Engineer’s Guide to Steel. Addison-Wesley Publishing Company, Inc. 1965; &
(10) George E. Dieter. Mechanical Metallurgy, Third Edition. McGraw-Hill Publishing Company 1986
(11) William D. Callister, Jr. Materials Science and Engineering An Introduction, Second Edition. John Wiley & Sons, Inc. 1991

11. Any Questions?