Session: MF-06-02 Materials and Technologies for Nuclear Power Plants-2

Paper Number: 154662

154662 - Weldability of a Microalloyed Carbon-Manganese Steel for Nuclear Power Plants : The Hardness Criterion and Fracture Toughness on the Haz 

Abstract: 

Microalloyed carbon-manganese steels are used in the Main Steam Supply System (MSSS) piping of modern nuclear power plants. Such steels shall comply with more stringent mechanical properties required to withstand the service conditions such as pressure and temperature. However, it has been observed that under certain welding parameter conditions, the hardness in the Heat Affected Zone (HAZ) near the fusion line can hardly comply with the criterion imposed after Post-Weld Heat Treatment (PWHT) by the applicable specifications. This is particularly true in the parent metal HAZ induced by the last weld beads of the weld joint if the microalloying elements such as V and Nb approach the upper-bound wt.% contents.

This paper deals with the weldability of a microalloyed carbon-manganese steel from the hardness and fracture toughness stand points. This work also proposes a method to predict the maximum hardness level in the HAZ after PWHT by using Artificial Neural Networks (ANN).

It is demonstrated that despite the presence of local hardness values in the HAZ higher than the hardness requirement imposed by the applicable specification (ISO 15614-1), the component design requirements in terms of fracture toughness level and ductile initiation behavior at the operating temperatures are not questioned. The hardness predictive model seems to capture well enough the link between chemical composition, PWHT temperature and hardness, since the predictions are in well agreement with observations.   

Finally, this work highlights some inconsistencies between the applicable specification and the use of modern micro-alloyed carbon-manganese steels.

Presenting Author: Miguel Yescas Framatome

Presenting Author Biography: Miguel YESCAS obtained his Ph.D. degree in 2002 from the University of Cambridge, UK. Then he joined CORUS RD&T in Sheffield, UK, where he worked 4 years in the Steel Metallurgy group developing new steels and new steel applications mainly for the Energy sector.
In early 2006 he joined Aubert & Duval in France which allowed him to broaden his materials processing horizon since he worked in the forging facilities to manufacture high performance forged steel, superalloys, and titanium alloy parts for the aerospace, energy and transport industries. At the end of 2008, he joined the materials department of Framatome where he has been dealing with various subjects such as Steel metallurgy, Characterisation of residual stresses, Thermal aging of dissimilar metal welds, and metallurgy of welding. Mr Yescas is now a senior Materials expert of Framatome SAS France.

Authors:

Miguel Yescas Framatome
Ghassen Ben Salem Framatome
Stéphane Marie Framatome