The stability of retained austenil. Is the most ImportwIrrt ~ram.ter controlling tne tre".fOlmaliOfI pI~tlelty offoeu In mulb'~II" low alloy TRIP 1t.,I,. In this wone !he merTnOdynamtc stability 01 me retllr.ad austenite hIlS been determined e_penm!ntally try mElcu.uring the Mf t.mperatv,e ~ I lurtCtlon of bainite i$OlhtlM'nal transformation (elT) t.mpal1lture and 1ime In two low alloy TRIP steels. A single,,~ imtn l,mperalure-vlJri.!l.ble tensIon lest tschniqlJe [SS-TV-TT) nas bHn ImploY$d. whict'l .lIowtcl to link tha appearance 01 yield poh"ltlln tha straM-strain curve with the mechanically-Induced martlll1Slllc transformation of the retOlined austaoi1e. The results Indicattd Ih',lne M.7 Ilimpenrture varies with BIT tempenrture .nd tiN. Highe, austllnlte !I~blilty i!l M!I(leiMeCI with 8 BIT tempe~tur8 of 4OQ'C rather than 37S"C. In addition. the chemical st8blliutlon 01 the retalnQlj austllnlte I'IslSociated with carbon er'lrlchment from the growing btllnlte 15 lowered al snol1 81T tirT'lftS. This $f8billty drop Is dua to cerblde precipijtstion and (lomes earHer In the NkQn\~nlng stlieL At longer elT tlrntS the retained aust8flite dispersion becomes finer am! it:!I !liability rl"!1 due to size swblilution. Tha expe~m.nta\ relulls are In good agreement with model ptet:lieUons within the range of 8f1~clpeted ~rbon enrichment ollhe retained austenite:end maasurttd austenite particle size.