Texture induced cleavage delamination of warm-rolled low carbon steel
- PDF / 1,763,552 Bytes
- 4 Pages / 603.28 x 788 pts Page_size
- 13 Downloads / 216 Views
Texture Induced Cleavage Delamination of Warm-Rolled Low Carbon Steel
~ _ 1
~
~
/~/"
ROLLING
Fig. 1--Impact specimen orientations chosen for this investigation.
the procedure given in ASTM Standard E23-72, at test temperatures varying between - 9 3 ~ and 23 ~ Selected fracture surfaces of impact tested specimens were studied using scanning electron microscopy. Results of the impact testing are given in the Table. The Charpy energy data are plotted in Figure 2 v s test temperature. It is seen that the longitudinal specimens fractured at higher energy levels than the diagonal specimens for all test temperatures. Also, the longitudinal data reflect cleavage delamination behavior as indicated by the constant low temperature plateau at a nonzero energy level. 3 The fracture behavior of longitudinal and diagonal specimens is different. Figure 3 shows fracture surfaces of a
D. L. BOURELL and O. D. SHERBY Table I.
Cleavage delaminations appear on fracture surfaces of failed tension and impact specimens of ferrous metals which have been deformed excessively prior to testing. Cleavage delaminations are observed as cracks which lie normal to the main crack plane. Proposed mechanisms of cleavage delamination have been discussed elsewhere L2'3 and include intergranular fracture, fracture of elongated inclusions, and texture induced transgranular failure. It is the present intent to show from a fractography study that the mechanism of cleavage delamination is texture related in steels which are subcritically warm rolled to large strains without recrystallizing. AISI-SAE 1018 steel 76 mm thick was chosen. Its composition was 0.19 C, 0.81 Mn, 0.01 P, 0.028 S, 0.10 Si. The steel was preheated at 650 ~ for 30 minutes and rolled at approximately 8 pct reduction per pass to a total true thickness strain of - 3 . 0 (95 pct total reduction). Between passes the billet was returned to the furnace for approximately six minutes. The billet was water cooled after the last pass. Subsize Charpy impact specimens (2.5 mm • 10 mm) were machined according to dimensions given in ASTM Standard E23-72. Two orientations were chosen, as illustrated in Figure 1. In both cases, the root of the Charpy notch was parallel to the short transverse direction. Longitudinal specimens were made with the impact specimen axis parallel to the rolling direction. Diagonal specimens were made with the impact specimen axis at 45 deg to both the rolling direction and the long transverse direction. Specimens of both orientations were impact tested according to D.L. BOURELL is Assistant Professor, Materials Science Program, University of Texas at Austin, Austin TX 78712. O.D. SHERBY is Professor, Department of Materials Science and Engineering, Stanford University, Stanford CA 94305. Manuscript submitted January 13, 1983. METALLURGICALTRANSACTIONS A
Results of Charpy Impact Tests
e,~
T,~, ~
-3.0
650 ~
Longitudinal
-3.0 Diagonal
650 ~
T (Test), ~
Cv,J
-93
5.8
- 75 -60 -50 -40 -15 2 23 -93 - 60 -50 -38 -13 8 23
8.1 7.1 10.5 10.2 10.5 14.9 15.8 2.7 5.8
Data Loading...
