An investigation of the high-temperature and solidification microstructures of PH 13-8 Mo stainless steel
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I.
INTRODUCTION
P H 13-8 Mo is a precipitation hardenable martensitic stainless steel (Fe-13Cr-8Ni-2Mo-IAI wt pet) which can, in the wrought condition, achieve a tensile yield strength in excess of 200 ksi. ill Chemically balanced to effectively eliminate ferrite (8) in the wrought condition and produced by double vacuum melting techniques, this alloy also has superior ductility and fracture toughness when compared to 17-4 PH and 15-5 PH stainless steels. Recent interest in this material as a casting alloy has driven the need to understand the development of microstructure in as-solidified product. The literature is virtually bereft of information concerning as-cast PH 13-8 Mo. t21What litfie information exists relative to the solidification of this alloy concerns its weldability.E3,a.5] The propose of the present investigation, therefore, was to establish the phase relationships which occur during the melting and solidification of this alloy in order to allow for improved metallurgical interpretation of microstructures observed in cast and welded products. In doing so, this paper describes, through the analysis of microstructures quenched from high homologous temperatures and from interrupted solidification experiments, the evolution of microstructure as a result of solidification processing of PH 13-8 Mo.
M.J. CIESLAK, Supervisor, Physical Metallurgy Division, C.R. HILLS, Member of Technical Staff, and P.F. HLAVA, Senior Member of Technical Staff, Electron Optics and X-ray Analysis Division, are with Sandia National Laboratories, Albuquerque, NM 87185. S.A. DAVID, Group Leader, Materials Joining, is with the Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831. Manuscript submitted December 13, 1989. METALLURGICALTRANSACTIONSA
II.
EXPERIMENTAL PROCEDURE
The composition of the PH 13-8 Mo stainless steel used in this study is given in Table I. The product form was rectangular bar stock (Condition A--solution annealed) approximately 25 by 6 mm in cross section. The martensitic microstructure of the as-received bar stock is shown in Figure 1. From this material, samples were prepared for both differential thermal analysis (DTA) and high-temperature water-quench (WQ) experiments. Rectangular samples 5 g or less in weight were used for both the DTA and WQ experiments. Differential thermal analysis experiments were performed using a Netsch STA 429 Thermal A n a l y z e r . Tungsten was the reference material. Both the reference material and the PH 13-8 Mo samples were held in highpurity alumina crucibles during the DTA tests. All tests were run in a flowing He environment at heating and cooling rates of 0.33 ~ The peak temperature during testing was 1550 ~ All tests were terminated at 1000 ~ and then furnace cooled to room temperature. The WQ tests were performed in a vertical Astro Model 1000 alumina tube furnace with graphite heating elements equipped with a waterdrop-quenching chamber. Samples were held in the hot zone in high-purity alumina crucibles which were, in turn, suspended b
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