Characterization of CA6NM steel submitted to different thermal cycles on the simulator Gleeble

• Grant number: 16/01114-8
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: April 01, 2016
• End date: March 31, 2017
• Field of knowledge: Engineering - Mechanical Engineering - Manufacturing Processes
• Principal Investigator: Maria Ismênia Sodero Toledo Faria
• Grantee: Bruna Giacchero Lima
• Host Institution: Escola de Engenharia de Lorena (EEL). Universidade de São Paulo (USP). Lorena , SP, Brazil

Abstract

The CA6NM (ASTM 743, 13% Cr, 4% Ni e 0,4% Mo) martensitic stainless steel grade is used in manufacturing hydraulic turbines. In welding of the material for repair of cavitation damage, it is necessary to pre-heat and subsequently heat-treat the component in order to control the residual stresses after welding, due to the formation of hard and brittle martensite, which can lead to the development of cracks. The local heating of the HAZ region causes very complex microstructural changes, considered the most critical section of the weld. As these regions are usually quite small, it is difficult to characterize them, because of the insufficient volume of each sub-region of the HAZ. Work around this limitation, the base metal will be submitted to physical simulation in order to obtain the different regions of the HAZ. The welding simulation will be carried out on a Gleeble ® 3800, considering different thermal cycles and heat inputs, aiming at reproducing the same microstructure found in HAZ, but in higher volumes, allowing a better microstructural and mechanical characterization of the different regions of the HAZ. The physically simulated welding samples will be characterized via OM and SEM for microstructural analysis. The knowledge of process parameters and the way the weldability can affect the microstructure and mechanical properties of steel are essential to technological development and to help the national industry in the understanding of the post-weld heat treatment (PWHT), ensuring quality improvement and cost reduction of welded turbine components.