P.R. Sreenivasan

A toughness study of the weld heat-affected zone of a 9Cr-1Mo steel

Abstract The toughness of the weld heat-affected zone microstructures of a 9Cr–1Mo steel has been studied with simulated samples. From the Charpy impact test results, the highest toughness in terms of the highest upper-shelf energy and the lowest ductile-to-brittle transition temperature have been observed in the intercritical region. The lowest toughness was observed in the coarse prior-austenitic grained martensite region adjacent to the fusion line. The microstructural effect on the toughness has also been discussed.

Plastic n-factor for three-point bend specimens: Analysis of instrumented Charpy impact test results for AISI 308 weld and AISI 316 stainless steels

In this paper, instrumented impact test results obtained using V-notch and precracked Charpy specimens of AISI 308 weld and AISI 316 stainless steels are analysed for determining the plastic η-factor for three-point bend specimens used in J-integral evaluation. Tested 316 stainless steel specimens were in various thermal aging/cold-work conditions whereas 308 weld specimens were in the as-welded condition. The results are analysed using the various procedures proposed in the literature and compared with experimental and finite element results reported in the literature. Based on our analysis, two polynomial expressions of a/W for ηpl are presented: one gives a sort of upper-bound in the a/W range 0.05–1.0 while the other gives conservative values (i.e., use of this results in J-R curves and J sufficiently conservative for engineering purposes). Both provide a smooth variation of ηpl over the entire a/W range unlike some of the expressions given in the literature which show a discontinuous change at an intermediate a/W.

Dynamic fracture toughness and Charpy impact properties of an AISI 403 martensitic stainless steel

Abstract Dynamic fracture toughness and Charpy impact properties of a normalised and tempered AISI 403 martensitic stainless steel obtained from instrumented impact tests are presented. Procedures for estimating dynamic fracture toughness ( K Id ) from the load-time traces obtained in instrumented tests of unprecracked Charpy V-notch (CVN) specimens are considered. The estimated K Id values show reasonable agreement with those obtained from instrumented drop-weight and precracked Charpy tests. Also, except in the upper transition and uppershelf regions, the ASME K IR curve is generally conservative (i.e. gives lower K Id values) when compared to the above K Id estimates. The conservatism of the ASME K IR at the upper transition and uppershelf temperatures needs verification/validation. The lowest K Id values estimated at the lower shelf temperatures for the above steel, namely, 33–42 MPa√m are in good agreement with the reported values of 35–50 MPa√m for the same steel in the literature.

Dynamic fracture toughness properties of a 9Cr1Mo weld from instrumented impact and drop-weight tests

This paper reports the RTNDT and KId results obtained from instrumented impact and drop-weight tests of 9Cr1Mo welds. RTNDT results for welds prepared using electrodes of diameter 2–5, 3–15 and 4 mm agree within 5K, the respective values being 264, 269 and 268K. For all the three welds, 269K can be taken as the conservative RTNDT. The procedures presented in this paper enable estimation of reasonably conservative values of KId from instrumented impact test of unprecracked Charpy V-notch specimens. For the range of temperatures 193–303K, the lower bound KId estimates obtained for the 9Cr1Mo welds are higher than the ASME KIR curve; hence, the ASME KIR curve will give conservative KId values for the welds of this 9Cr1Mo steel in the above temperature range; at higher temperatures, the applicability of the ASME KIR curve to the welds of the present 9Cr1Mo steel needs verification/validation. Microcleavage fracture stress or cleavage fracture strength, σf, estimated for the 9Cr1Mo welds is about 2160 MPa and is much lower than the 2550–2850 MPa reported for a normalised and tempered 9Cr1Mo plate material.

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.

Instrumented drop-weight test results for normalised and tempered 9Cr1Mo steel

From instrumented drop-weight tests, the nil ductility transition temperature (TNDT), and a conservative estimate of dynamic fracture toughness (KId), at TNDT for normalised and tempered 9Cr1Mo steel, are determined to be −25°C and 70 MPa√m, respectively. The latter value agrees well with that determined from pre-cracked Charpy tests. The KIdσYd (σYd is the dynamic yield stress) ratio at TNDT is estimated to be 0·076 √m, in agreement with previous estimates. The uncertainties in crack profile measurement and effect of microstructural variation in the heat affected zone on fracture loads are also discussed.