Effect of alloy content on microstructure and microchemistry of phases during short term thermal exposure of 9Cr-W-Ta-0⋅1C reduced activation ferritic/martensitic (RAFM) steels

Abstract

This paper presents the results of an experimental study on the microstructural evolution in 9Cr reduced activation ferritic/martensitic steels during short term thermal exposures. Since the microstructure is strongly influenced by the alloying additions, mainly W, Ta and C contents, the effect of varying W and Ta contents on the martensite structure that forms during normalizing treatment and the subsequent changes during tempering of the martensite in the temperature regime of 923-1033 K have been studied. Microstructural changes like subgrain formation and nature of precipitates have been evaluated and correlated to hardness variations. The systematic change in size distribution and microchemistry of M 23 C 6 carbide is studied with variation in W content at different temperatures.

Effects of yttrium on microstructure and properties of reduced activation ferritic-martensitic steel

“…Although yttrium addition improves the property of the RAFM steel [9,10], all of the previous studies have added Y 2 O 3 with an yttrium mass fraction exceeding 0.15wt-% to the ODS-RAFM steel. When present in excessive amounts, the yttrium segregates and many yttrium-rich blocks appear in the alloy.…”

Decomposition modes of austenite in 9Cr–W–V–Ta reduced activation ferritic–martensitic steels

“…(i) presence of the small exothermic peak at a temperature higher than M s in the DSC thermogram of 1?4W steel corresponding to M 3 C precipitation, which is supported by TEM results, as reported in the section on 'Thermal analysis study of 1?4W steel' (ii) temperature interval between M s and M f is ,100 and 50 K for 1W and higher W steel respectively (Table 2); an autotempering process, if it happens, should be more pronounced in 1W rather than in 1?4 or 2W steels, whereas experimental results prove the contrary (iii) the presence of the carbides has been observed in relatively wide laths of low dislocation density; formation of such wide laths implies the self-diffusion of Fe and substitutional solutes, which is favoured at higher temperatures 51 and is sluggish below the M s temperature; in our earlier study, 55 no significant coarsening of laths was observed during tempering of martensite even until 2 h at 1023 K, a temperature far higher than M s ; hence, the observed coarse laths correspond to ferrite formed at temperature higher than M s (iv) analysis of the SAED pattern of 1?4W steel normalised at 1253 K given in Fig. 4b showed the presence of M 3 C and a-Fe along [0 2 21] and [0 21 2] zone axis respectively; a stereographic analysis of the above diffraction pattern did not satisfy the following Bagaryatsky orientation relationship 56,57 between ferrite and cementite, which results from the decomposition of martensite during initial stages of tempering…”

“…the presence of the carbides has been observed in relatively wide laths of low dislocation density; formation of such wide laths implies the self-diffusion of Fe and substitutional solutes, which is favoured at higher temperatures 51 and is sluggish below the M s temperature; in our earlier study, 55 no significant coarsening of laths was observed during tempering of martensite even until 2 h at 1023 K, a temperature far higher than M s ; hence, the observed coarse laths correspond to ferrite formed at temperature higher than M s…”

Aplicação Do Método Calphad No Desenvolvimento De Novos Aços Ferrítico Martensítico De Atividade Reduzida

“…A taxa de coalescimento na matriz ferrítica aumenta com a adição de Mn e diminui com a adição de V e W, uma vez que estes elementos de liga alteram o coeficiente de difusão do Cr na matriz. No entanto, V é mais eficaz que W. Em maiores intervalos de envelhecimento, o teor de V no carboneto aumenta e substitui os átomos de Fe e W, desta maneira desempenha um papel fundamental no controle do coalescimento desta fase [10][11][12][13]. A composição química LFN1 teoricamente apresentará menores taxas de coalescimento, já que possui o menor teor de Mn e o maior teor de V entre as composições simuladas.…”