Effect of carbon content and ferrite grain size on the tensile flow stress of ferritic spheroidal graphite cast iron
- PDF / 1,059,761 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 2 Downloads / 280 Views
I.
INTRODUCTION
THE graphite
volume fraction, ferrite grain size, and graphite nodule diameter affect the flow stress on ferritic spheroidal graphite cast irons (S.G.I.'s). ~With regard to the graphite nodules as spherical voids, it is important to examine the stress state in the inter-nodule ferrite matrix under the tensile deformation, for investigation of the elevated temperature brittleness in this material. The ferrite grains will become finer as the graphite volume fraction increases or the graphite nodule diameter decreases.~ The carbon content and casting section area was varied to obtain the different microstructures. The ferritizing heat treatment was performed under an identical condition. Sixteen kinds of microstructures were investigated to understand the individual influence of graphite volume fraction, graphite nodule diameter, and ferrite grain size on S.G.I.'s tensile flow stress. The tensile test was carried out at room temperature under the air atmosphere and at 623 K under the vacuum, where the serrated flow still occurs. II.
perature in air atmosphere, and at 623 K The strain rate was k = 2.8 x 10 4s type extensometer and a chromel-alumel used to measure the displacement and III.
in 10 -2 P,, vacuum. ~. The clip gauge thermocouple were test temperatures.
RESULTS
A. Microstructure of Specimens A quantitative analysis of microstructures was carried out as follows: (1 ~ Graphite volume fraction (V~,): point-count analysis was applied. (The number of measured graphite nodules was above 300. )
L S
EXPERIMENTAL PROCEDURE
Melting the raw pig iron in a basic high frequency induction furnace, spheroidizing with Fe-45 wt pet Si-4 wt pct Mg alloy, and inoculating with Fe-75 wt pet Si alloy, four kinds of Y-block shape castings were then produced as shown in Figure 1 and Table I. Here. the letter M means permanent mold and S means sand mold. All castings were given an annealing treatment, which involved soaking at 1203 K for three hours prior to furnace cooling to 973 K and holding at this temperature for five hours before finally furnace cooling to room temperature. The chemical compositions and microstructure photos of the irons are shown in Table II and Figure 2, respectively. Parallel parts of specimens were machined into dimensions of 6 6 mm x 30 ram. The tensile tests were carried out in a high temperature-vacuum vessel installed in an lnstron-type tensile testing machine. The tests were conducted at room ternO. YANAGISAWA, Associate Professor. is with the Faculty of Engineering, Hiroshima University, Saijo-Shitami Higashi-Hiroshima 724, Japan. T.S. LUI. formerly Graduate Student, Faculty of Engineering. Hiroshima University, is now with Taiwan Institute of Technology, Taipei, R.O.C. Manuscript submitted January 16. 1984. METALLURGICAl. TRANSACTIONS A
T
C
Fig. I ---Shape of castings.
Table I.
M SA SB SC Table II.
No. No. No. No.
I 2 3 4
Dimensions of Castings (mm) a
b
c
28 14 3O 65
9O 90 9O 9O
200 80 8O 120
Chemical Compositions of Specimens in Wt Pet
C
Si
Mn
P
S
2.15 3.
Data Loading...
