The dominating role of austenite stability and martensite transformation mechanism on the toughness and ductile-to-brittle-transition temperature of a quenched and partitioned steel

Abstract In this paper dynamic properties of low-alloy boron steels – Hardox 500, B27 and HTK 900H in delivered state (after hardening and tempering) are considered. Charpy V-notch (CVN) test results in connection with fractography in the ductile-to-brittle transition temperature region were analyzed. Obtained from CVN test the impact transition curve, not always predicts properly a behavior of materials in conditions of dynamic loading. So an analyze of character of fracture helps to evaluate the real behavior of materials. Tested samples were cut out longitudinally in relation to cold work direction. The results of CVN test for selected steels, in temperatures: −40°C, −20°C, 0°C and +20°C are presented. Regarding ductile-to-brittle transition temperature, there is a significant difference taking into account values of Charpy V energy absorbed and a character of fracture.

Download Full-text

Retraction Note to: Modeling ductile to brittle transition temperature of functionally graded steels by fuzzy logic

Journal of Materials Science ◽

10.1007/s10853-020-05008-4 ◽

2020 ◽

Vol 55 (29) ◽

pp. 14702-14703

Author(s):

Ali Nazari ◽

Amir Ali Milani

Keyword(s):

Fuzzy Logic ◽

Transition Temperature ◽

Functionally Graded ◽

Brittle Transition ◽

Brittle Transition Temperature ◽

Ductile To Brittle Transition

Download Full-text

Variables Affecting Fracture Toughness of Welds in T-K-Y Connections

Volume 5: Materials Technology; Petroleum Technology ◽

10.1115/omae2014-24205 ◽

2014 ◽

Author(s):

Radhika Panday ◽

Shenjia Zhang ◽

Jon Ogborn ◽

Badri K. Narayanan

Keyword(s):

Heat Treatment ◽

Fracture Toughness ◽

Transition Temperature ◽

Weld Metal ◽

Welding Process ◽

Post Weld Heat Treatment ◽

Factors Affecting ◽

Brittle Transition ◽

Brittle Transition Temperature ◽

Ductile To Brittle Transition

Fracture toughness of tubular welded joints is one of the critical factors affecting the structural integrity and reliability of offshore structures, such as platforms and subsea pipelines. The factors affecting the design fracture toughness of these structures are related to, both, the welding process as well as the chemical composition of the weld metal. The welding process in this application typically comprises of depositing weld metal in the tubular joints of varying thicknesses through series of weld passes. The number of weld passes required for welding these joints subjects the weld metal to repetitive cycles of heating and cooling. The effect of the thermal cycling introduces significant heterogeneity in the microstructure. This is further exacerbated by the presence of micro-alloying elements such as Niobium (Nb) and Vanadium (V) that form complex carbides, nitrides and carbo-nitrides during post weld heat treatment (PWHT). The focus of this work is to evaluate the effect of micro-alloying elements on the ductile to brittle transition temperature and the mode of fracture at temperatures relevant to offshore applications. A threshold Nb and V level has been determined for achieving acceptable weld metal toughness. The improvement in the fracture toughness using this approach has been quantified by Charpy V-Notch (CVN) and Crack Tip Opening Displacement (CTOD) measurements. The Ductile to Brittle Transition Temperature (DBTT) has been shown to be shifted to lower temperatures by 25 °C after post weld heat treatment in the welds where the total amount of Nb and V are controlled to less than 40 ppm. A wet precipitate extraction technique was used to extract precipitates from the welds to establish the presence of fine Nb rich precipitates in the welds with the higher DBTT. The weld deposited with controlled levels of Nb and V was further tested in different joint configurations and base plate thickness. The fracture toughness was evaluated by CTOD testing of the weld in two different thicknesses (50 mm and 70 mm). Increased specimen thickness resulted in lower CTOD values.

Download Full-text