A Fim/Atom-Probe Study of Phase Transformations in Molybdenum Steels

Abstract

AlSXRMPFIM/AP,T!%,~ X-ray analysis ard dilatonetry irdicate that both 3 C precipitation and a solutedreglike effect are associated with reacticn retaz&tim i n F d H b allay. %ere is no e v i h for molybdennn or carbcn/wlybdenm clustering in awtenite. INIIICDUCPIZHThe inhibiting effects of mlybdmm rn the t r a m f o m i c n of Fe++b alloys are d i a m m [1-6], but their origin d m mlear. What is clear is that l d of mlyb&mu of only a.few tenths of an atomic per cent significantly retard the rate of deccmposition of atstedte t o ferrite 4% carbids at a l l temperatures. This effect is particularly marked a t i n t e n d l a t e teapetahlres ( 50 C -703 C ) resulting in the deep lsys in the lllkwws of mny mlyWenrm steels. Similar effects are observed with other solute additions tut n b t o the sare degree a s with molylxbum. The molybdenum effect has been mriously attributed t o (1) Mo/ C clustering in the azsrenite pinning the interface [4], (2)solutedrag at the transPonnaticn ineerfaoe [3,6,7] a d (3)Merphsse interface precipitation [8,9]. There is no strong preferential evidence for any one of these hypotheses, * = Less than 2 s t a n d a r d d e v i a t i o n s .