Precipitation in CF-8M duplex stainless steel welds
- PDF / 2,847,122 Bytes
- 8 Pages / 603.28 x 788 pts Page_size
- 75 Downloads / 240 Views
I.
INTRODUCTION
SINCE the hot-cracking propensity of austenitic stainless steel weldments is directly related to the microstructure, such welds have been extensively characterized by numerous researchers using optical microscopy, as well as microprobe, 1'2'3 TEM, 4 and STEM/EDS 5'6 methods. In recent years, special attention has been focussed on the position of the ferrite within the bulk microstructure, 7 since alloys which solidify as primary austenite have been found to be much more susceptible to hot cracking than alloys which solidify as primary delta-ferrite. This is due to the segregation of elements with low solubility in austenite to interdendritic volumes, thereby lowering the effective solidus temperature of these regions. In an earlier investigation, 8 it was established that the eutectic ferrite which forms in such solute-enriched regions could be distinguished from primary delta-ferrite both by morphology and by compositional gradients as measured by microprobe. These data were corroborated by a continuation of that effort, involving a 316-type and a 304 stainless steel which were forced, by the addition of nitrogen to the shielding gas during GTA welding, to shift solidification modes from primary deltaferrite to primary austenite. 9 In the present work the CF8M, or 316-type, stainless steel welds are further characterized by observation of the chemistry of the intragranular precipitates and of the phases present at the ferrite/austenite interfaces. II.
EXPERIMENTAL P R O C E D U R E
A heat of CF-8M cast stainless steel, the composition of which is given in Table I, was tested for hot-cracking susANN M. RITTER is Staff Metallurgist, General Electric Corporate Research and Development, Schenectady, NY 12301. MICHAEL J. CIESLAK, Steel Founders' Society of America Graduate Fellow, and WARREN E SAVAGE, Professor and Director of Welding Research, are both with the Materials Engineering Department, Rensselaer Polytechnic Institute, Troy, NY 12180. Manuscript submitted December 7, 1981.
METALLURGICAL TRANSACTIONS A
ceptibility using the Varestraint Test. l~ Shielding gases were composed of 100 pct Ar and mixtures of 99 pct Ar/1 pct N2, 97 pct Ar/3 pct N2, and 94 pct Ar/6 pct N2. Magne-Gage readings were taken on the resulting specimens to determine ferrite contents, which were then related to the amount of hot cracking observed, as described in the previous paper. 9 Optical microscopy was performed on the specimens, which had been mounted, metallographically polished, and etched using a 10 pct oxalic acid electroetch. Thin foils for TEM/STEM microanalysis were prepared with an electropolishing solution of 20 pct perchloric acid/80 pct methanol. The polishing was done using a Fishione twin-jet apparatus, at 30 V and approximately - 4 0 ~ Extraction replicas of metallographically polished surfaces were prepared in order to obtain spectra from phases alone, without contribution from the surrounding matrix. The replicas were made using a two-stage technique ~2 instead of the standard etch-plus-carbon depo
Data Loading...
