A surface segregation study in phosphorus-and sulfur-doped type 304 stainless steels
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I.
INTRODUCTION
TYPE304 stainless steel is a ductile, high strength alloy that is noted for corrosion resistance. However, under certain conditions such as heat treatments in the range of 500 to 900 ~ type 304 stainless steel is susceptible to intergranular corrosion and intergranular stress corrosion cracking (IGSCC). 1'2 This heat treatment is sometimes unavoidable, as for example in welding, so that the regions adjacent to welds become susceptible to IGSCC and the steel is said to be sensitized. 3 Sensitization usually refers to chromium carbide formation at the grain boundaries and the subsequent chromium depletion that occurs adjacent to the carbide. However, carbide formation may not be the sole contributing cause to IGSCC. There has been evidence that solute segregation may be an important contributing factor to sensitization. 4 There has also been evidence that cosegregation of the solute and the major constituents of the steel is also occurring. In a recent study, Briant and Mulford5 used Auger electron spectroscopy (AES) to study the surface chemistry of two commercial stainless steels (Type 304 and 316 L) and four specially prepared stainless steels with compositions similar to Type 304. They found that besides phosphorus, sulfur, and nitrogen, nickel and chromium also segregate to the surfaces of these steels. The present work presents results similar to those of Briant and Mulford. Our work was carried out on a systematically doped commercial Type 304 stainless steel. Previous work on heats of these steels 6 has shown that the impact properties of phosphorus-doped steels are severely degraded when Table I.
He~s 304 P1 304 P2 304 P3 304 P4 304 S1 304 $2
P 0.033 0.064 0.070 0.350 0.028 0.016
S 0.038 0.028 0.028 0.026 0.002 0.082
C 0.040 0.060 0.067 0.066 0.055 0.050
II.
E X P E R I M E N T A L DETAILS
A. Specimen Preparation Six experimental heats based on a commercial heat and an ultra-low sulfur heat of type 304 stainless steel have been produced in a vacuum induction furnace. Table I shows the compositions of these six heats. The ingots of each heat to be investigated were solutionized at 1100 ~ for
Compositions of Type 304 Stainless Steels (Wt Pct)
Mn 1.40 1.05 1.20 0.88 1.75 0.96
Cr 18.8 18.8 18.8 18.6 18.3 18.8
Ni 8.70 8.80 8,60 8.50 8.45 8.90
YONGBIN IM, Research Assistant, and STEVEN DANYLUK, Associate Professor, are with the Department of Civil Engineering, Mechanics, and Metallurgy, University of Illinois at Chicago, Box 4348, Chicago, IL 60680. Manuscript submitted February 14, 1986. METALLURGICALTRANSACTIONS A
these are heat treated in the temperature range of 550 to 850 ~ for times as short as 3600 seconds. This degradation of impact properties was indirectly linked to the phosphorus segregation to the grain boundaries. A surface segregation study using similar heat treatment conditions can provide insight on the grain boundary segregation. Direct evidence of the influence of solute segregation on IGSCC is difficult to obtain, but a number of researchers have used Auger electr
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