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VOLUME 14A, AUGUST 1983-- 1681

Table I.

Compositions (Wt Pct) of 304 Stainless Steel Used by Other Investigators and Present Authors

Research By: Suzuki, et al. ~ Hintze2'3 Powell, et al. 4 Hecker, e t a l . 7 Cook 9

Ryan, et al. jz Present authors

C 0.07 > 1) which can be imposed in torsion and the ability to simulate actual hotworking practices. Sellars and Tegart m and Barraclough and Sellars" have reported limited flow-stress data on 304 and have interpreted those data in terms of a dynamic-recrystallization mechanism. When such a process occurs, torquetwist curves usually exhibit a maximum in torque followed by a drop to a steady-state value that persists until fracture. Perhaps the most complete phenomenological study of the hot deformation of 304 stainless steel is that performed by Ryan, et al.,~2 who studied stainless steel grades 316 and 317 as well. That work used hot torsion testing at temperatures of 900 to 1100 ~ and at strain rates between 0.1 and 5 s -]. It was demonstrated that the steady-state flow stress for 304 at those temperatures and strain rates could be correlated through the logarithm of the temperaturecompensated strain rate (often known as the Zener-Hollomon parameter, Z = b e x p ( + Q / R T ) , where Q denotes the activation energy for the softening process controlling the deformation, T is the test temperature, and R the ideal gas constant). Ahlblom and Sandstr6m have summarized similar flow stress correlations in an excellent review article on the hot workability of stainless steels. =3 The present investigation was undertaken to answer many of the questions raised by previous research and to obtain a complete and self-consistent body of flow-stress data which, with proper interpretation, could be used in deformation process models. This objective was met through compression and torsion tests on 304L stainless steel accompanied by appropriate metallographic investigation. These results were analyzed to establish the basic flow behavior and sources of flow softening (deformation heating, dynamic recrystallization, e t c . ) , and to determine the applicability of continuum plasticity concepts such as effective stress and effective strain to the modeling of plastic flow behavior of 304 stainless steel.

II.

MATERIALS AND PROCEDURES

A. Materials

The material used was 304L austenitic stainless steel. The composition of the material used in this study is compared to that of other workers in Table I. In the as-received condition, the 304L was in the form of hot-rolled bar stock

1682--VOLUME

14A, A U G U S T

1983

.

1.86 1.19 0.48 1.76 1.8

.

.

.

-0.14 -0.08 0.03

.

.

0,52 -0.43 0.68 0.64

*

- -

- -

-0.07

.,~.

- -

0.002 0.004

"Z z~

' ,S~

0.020 0.012

!

~V r

/,

/. ~

L ~84 .

.

~,,..L~':~

~r /

9 J" '\\

\!-

I B a r

.

I

A x i s

Fig, 1--As-received microstructure of annealed 304L austenitic stainless steel,

which had been solution annealed (950 ~ minutes) and quenched following fabrication. This treatment resulted in a microstructure (Figure 1) of equiaxe