K.G. Samuel

Evaluation of ageing-induced embrittlement in an austenitic stainless steel by instrumented impact testing

Fracture properties of a thermally aged Type 316 stainless steel have been investigated at room temperature by an instrumented impact test. The impact energy is found to depend on the heat treatment conditions. Several alternative estimates for toughness are evaluated and compared with the conventional Charpy impact energy, Cv, to assess the degree of embrittlement. Sensitivity of these parameters to monitor the ageing-induced embrittlement in comparison with Cv is discussed.

Characterization of irradiation-induced embrittlement in an ASTM A 203D steel using instrumented impact testing

Abstract This paper reports the results of analysis of the load-temperature data obtained from instrumented impact tests carried out at various temperatures using half-thick Charpy V-notch specimens of a 3·5% Ni (ASTM A 203D) steel. The material was tested after irradiation and after an annealing treatment following irradiation; all-weld specimens were also tested in the irradiated condition. Conservative values of the dynamic fracture toughness, K 1 d , of the material in the virgin and the severest irradiated condition are estimated to be 44 MPa m and 32 MPa m respectively. This degree of embrittlement could not be simulated by testing unirradiated and precracked half-thick Charpy specimens at 77 K.

An empirical relation between yield stress and general yield load for a charpy U-notch specimen

Abstract An empirical expression for obtaining the dynamic yield stress, σ yd , from the general yield load, p gy , of a Charpy U-notch specimen has been experimentally derived assuming: (i) σ yd is the same for both Charpy U- and V-notch specimens; and (ii) the functional relations between P GY and σ yd for both the geometries are the same except for a dimensionless proportionality constant.

An empirical relation between strain energy and time in creep deformation

Abstract The stored energy of creep defined as W= ∫ 0 e σ d e and estimated as the area under the isochronous stress–strain curve is found to vary with time t and temperature T (in particular Wt m = C , where m and C are constants). The work of creep defined as W c = σe also varies similarly ( W c t p = B where p and B are constants). From the relationships, a new method for generating isochronous stress–strain curves from three or more short-term creep tests is proposed. The method is useful particularly for newly developed materials.

A substructure characterizing parameter in creep

A substructure characterizing parameter which is the ratio of applied stress, σ, in creep test to yield stress, σYS, of the material at the test temperature is introduced. A correlation is found to exist between this parameter and the creep rate for the data obtained in the temperature range 820–975 K when the initial yield strength is modified by (i) introducing different amounts of prior cold work by two modes of deformation at room temperature in a type 316 LN stainless steel and (ii) grain size, chemistry and grain size variation in a type 316 stainless steel. The correlation was found to exist also for a Cr-Mo-V steel at 823 K, in which different yield strengths were due to different heat treatments. Minimum creep rate when plotted against the substructure characterizing parameter yields an exponent similar to Nortons creep exponent and it is postulated that the value of the exponent reflects on the type of substructure developed in creep. Another parameter σ/Fys where Fys is a function of the ratio of the yield strength of a given microstructure to that of a reference microstructure (zero cold work for cold worked material, largest grain size when the microstructure variation is through grain size and solution annealed microstructure among heat treatments) also gives a unique correlation with the minimum creep rate at a test temperature with the exponent identical to Nortons creep exponent.