Effect of load cyclicity on the fracture toughness characteristics of steels. Report 1

Brittle-to-ductile transition in steels and the critical transition temperature

“…In Fig. 6 the data is presented on the temperature dependence for 15H2MFA steel, the chemical composition of which is close to that of the steel studied in the present work but which is not alloyed with nickel, The results were obtained on 10 × l0 × 55 mm specimens (three-point bending) and on 150 mm thick specimens (compact tension) [18], as well as on 25 mm thick specimens of the same steel [19]. Dashed lines in Fig.…”

“…l -')/2o(I<1 +'*)/21 (16) As a result of Pc, o,, independence of and n weak dependence on the temperature and loading rate, the yield strength o v is the main characteristic depending on those two parameters. Its temperature and strain rate dependence can be described [22,23] Considering the fact that at low temperature the first term in square brackets exceeds markedly the % value, after the transformation it is possible to write as a first approximation: n B 1 -n kTps e0 n~ 1 lg flK~ l~n°C = A~-71gT -lg %°" (19) This relationship constitutes a linear dependence between Tps and lg B, as well as between 1/Tps and lg ~. In this case k represents the strain rate at the crack tip, which according to [21] for a small scale yielding can be written as where v is Poisson's ratio and G is the shear modulus.…”

“…In accordance with (19), the loading rate effect on the transition temperature should be expressed by a linear relationship between l/Tp, and lg ~ and, consequently, between l/Tp.,, and lg k~. The experimental data presented in Fig.…”