Abstract
The principal difference between the small punch (SP) testing technique and standardized impact testing lies in the fact that the SP tests carried out in accordance with CWA 15627 Small Punch Test Method for Metallic Materials use disc-shaped test specimens without a notch. Especially in tough materials, the temperature dependence of SP fracture energy ESP in the transition area is very steep and lies close to the temperature of liquid nitrogen. In this case, the determination of SP transition temperature TSP can lead to significant errors in its determination. Efforts to move the transition area of penetration testing closer to the transition area of standardized impact tests led to the proposal of the notched disc specimen 8 mm in diameter and 0.5 mm in thickness with a “U” shaped notch 0.2 mm deep in the axis plane of the disc. The paper summarizes the results obtained to date when determining the transition temperature of SP tests TSP, determined according to CWA 15627 for material of pipes made of P92, P22, and a heat treated 14MoV6-3 steel in the as delivered state. Although the results obtained confirmed the results of other works in that the presence of a notch in a SP disc is insufficient to increase the transition temperature significantly and certainly not to the values obtained by Charpy testing, comparison of the different behaviors of the alloys tested reveals some evidence that the notch reduces the energy for initiation. This implies that the test on a notched disc is more a test of crack growth and would be a useful instrument if included in the forthcoming EU standard for SP testing.
Highlights
IntroductionCWA 15627 Part B: A Code of Practice for Small Punch Testing for Tensile and Fracture Behavior (“the Code”) describes the procedures recommended for determination of yield stress YS, ultimate tensile strength UTS, ductile brittle transition temperature (DBTT) (measured by fracture appearance transition temperature (FATT) and/or absorbed energy transition temperature (TT) (for example 41J) and fracture toughness JIC of the metallic materials from the results of small punch (SP) tests [1,2]
(“the Code”) describes the procedures recommended for determination of yield stress YS, ultimate tensile strength UTS, ductile brittle transition temperature (DBTT) (measured by fracture appearance transition temperature (FATT) and/or absorbed energy transition temperature (TT) and fracture toughness JIC of the metallic materials from the results of small punch (SP) tests [1,2]
The SP transition temperature TSP is determined according to the Code as the temperature where ESP has its mean value of the highest and the lowest values in the transition region, by intersecting the smooth curve fitted from the energy versus temperature dependence of fracture energy ESP [1]
Summary
CWA 15627 Part B: A Code of Practice for Small Punch Testing for Tensile and Fracture Behavior (“the Code”) describes the procedures recommended for determination of yield stress YS, ultimate tensile strength UTS, DBTT (measured by fracture appearance transition temperature (FATT) and/or absorbed energy transition temperature (TT) (for example 41J) and fracture toughness JIC of the metallic materials from the results of SP tests [1,2]. On a disc removed from reactor pressure vessel steel Both types of notch contributed significantly to the initiation of the fracture process they were found to have little effect on the ductile brittle transition temperature, even with high strain rate testing closer to Charpy conditions. The first results of SP tests at lower temperatures carried out on 14 MoV6-3 steel indicated that the use of the notched specimens could shift the transition temperature TSP to higher temperatures to a limited extent but not to the much higher transition temperatures obtained using Charpy testing (Table 2 below). The first results of SP tests at lower temperatures carried out on 14 MoV6-3 steel indicated that the use of the notched specimens (a)could shift the transition temperature (b) TSP to higher temperatures to a limited extent but not to the much higher transition temperatures obtained using Charpy testing. In as received state made of P92 steel and tube ø 508 × 25 mm in as received state made of P22 steel
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