Details

Autor(en) / Beteiligte

• Talonen, Juho Aleksi

Titel

Effect of strain-induced α′-martensite transformation on mechanical properties of metastable austenitic stainless steels

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

2007

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• Metastable austenitic stainless steels undergo a strain-induced martensitic transformation, where the metastable austenite phase is transformed to the thermodynamically more stable α'-martensite phase due to the plastic deformation. The strain-induced martensitic transformation enhances the work hardening of metastable austenitic stainless steels. This thesis concentrated on the effects of the strain-induced martensitic transformation on the mechanical properties of metastable austenitic stainless steels, focussing on the interaction between the strain-induced martensitic transformation and the work hardening. The effects of chemical composition, temperature and strain rate on the strain-induced martensitic transformation were also studied. The experiments were carried out on steel grades EN 1.4318 (AISI 301LN) and EN 1.4301 (AISI 304). Mechanical testing was performed by means of uniaxial tensile tests. The α'-martensite volume fractions were measured with a Ferritescope. X-ray diffraction was used for the phase identification, dislocation density measurements and to measure the stacking fault energies of the test materials. Microstructure investigations were carried out by means of the scanning electron microscopy, transmission electron microscopy and optical metallography. Load distribution between the austenite and α'-martensite phases was studied by in-situ X-ray diffraction stress measurements. Increasing strain rate and temperature were found to suppress the formation of strain-induced α'-martensite. This was attributed to the temperature-dependence of the stacking fault energy. A direct relationship between the work-hardening rate and the rate of the strain-induced α'-martensite transformation was found. Based on the strengthening mechanisms, the work hardening was divided in four stages. Influence of the strain-induced martensitic transformation on the work-hardening rate during each stage was discussed.