Title

CREEP BEHAVIOR ON TYPE 310 STAINLESS STEEL. PART 3: CORRELATIONS OF THE STRESS EXPONENT AND ACTIVATION ENERGY VALUES WITH THE DORN CONSTANT

CREEP BEHAVIOR ON TYPE 310 STAINLESS STEEL. PART 3: CORRELATIONS OF THE STRESS EXPONENT AND ACTIVATION ENERGY VALUES WITH THE DORN CONSTANT

Authorship

Campanelli, José Luiz; Bueno, Levi de Oliveira

DOI

10.5151/2594-5327-23666

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Abstract

Creep strain rate behavior was studied by small stress increments/decrements performed at six strain levels from 2 to 25% involving primary, secondary and tertiary creep stages, during constant stress creep tests at six stress levels from 90 to 250 MPa, at 700oC, on Type 310 stainless steel, as continuation of the works reported in Part 1 and Part 2. Relationship between the stress exponents n and the Dorn constant A for power law creep at the different strain levels was verified in the form: Log A ≈ 2.5(n – 2.9 ), as suggested by Stoker and Ashby and other authors in the past, from the analysis of secondary creep data with different materials. In the same way, with a set of small temperature change experiments, above and below the test temperature, in the same strain levels, for three values of applied stress:120,180 and 240 MPa, a linear correlation could be established between the constant A and values of the apparent creep activation energy Qc in the form LnA=0,136(Qc - 269). The set of values: n=3, A=1 and Qc=270 kJ /mol (the activation energy for lattice selfdiffusion of Iron in austenite) seems to represent a natural creep condition for the material, when the effect of internal stresses is taken into account during this deformation process, regardless the creep stage (primary, secondary or tertiary).The results presented in Parts 1 and 2 of this work are considered and a general discussion implemented involving internal stress and the parameters n, A, and Qc.

 

Creep strain rate behavior was studied by small stress increments/decrements performed at six strain levels from 2 to 25% involving primary, secondary and tertiary creep stages, during constant stress creep tests at six stress levels from 90 to 250 MPa, at 700oC, on Type 310 stainless steel, as continuation of the works reported in Part 1 and Part 2. Relationship between the stress exponents n and the Dorn constant A for power law creep at the different strain levels was verified in the form: Log A ≈ 2.5(n – 2.9 ), as suggested by Stoker and Ashby and other authors in the past, from the analysis of secondary creep data with different materials. In the same way, with a set of small temperature change experiments, above and below the test temperature, in the same strain levels, for three values of applied stress:120,180 and 240 MPa, a linear correlation could be established between the constant A and values of the apparent creep activation energy Qc in the form LnA=0,136(Qc - 269). The set of values: n=3, A=1 and Qc=270 kJ /mol (the activation energy for lattice selfdiffusion of Iron in austenite) seems to represent a natural creep condition for the material, when the effect of internal stresses is taken into account during this deformation process, regardless the creep stage (primary, secondary or tertiary).The results presented in Parts 1 and 2 of this work are considered and a general discussion implemented involving internal stress and the parameters n, A, and Qc.

Keywords

Type 310 stainless steel, creep behavior, stress/temperature changes, stress exponent, Dorn constant, creep activation energy.

Type 310 stainless steel, creep behavior, stress/temperature changes, stress exponent, Dorn constant, creep activation energy.