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Influence of peak temperature during simulation and real thermal cycles on microstructure and fracture properties of the reheated zones

Moeinifar, S ; Sharif University of Technology | 2010

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  1. Type of Document: Article
  2. DOI: 10.1016/j.matdes.2009.12.023
  3. Publisher: 2010
  4. Abstract:
  5. The objective of this paper is to study the influence of the second peak temperature during real and simulated welding on properties of the subcritically (S), intercritically (IC) and supercritically (SC) reheated coarse grained heat affected (CGHAZ) zones. The X80 high strength pipeline microalloyed steel was subject to processing in a double-pass tandem submerged arc welding process with total heat input of 6.98 kJ/mm and thermal cycles to simulate microstructure of reheated CGHAZ zones. This involved heating to a first peak temperature (TP1) of 1400 °C, then reheating to different second peak temperatures (TP2) of 700, 800 and 900 °C with a constant cooling rate of 3.75 °C/s. Toughness of the simulated reheated CGHAZ regions were assessed using Charpy impact testing at 0 °C, -25 °C and -50 °C. The microstructure of the real and simulated reheated CGHAZ regions was investigated using an optical microscope and field emission scanning electron microscope. Morphology of the martensite/austenite (MA) constituent was obtained by the use of a field emission scanning electron microscope. The blocky and connected MA particles, along prior-austenite grain boundaries, act as a brittle phase for the initiation site of the brittle fracture. Charpy impact results indicated that IC CGHAZ had less absorbed energy with higher transition temperature and hardness. The SC CGHAZ region showed higher absorbed impact energy with lower hardness. Design of multipass weld joints with less IC CGHAZ regions can result in a higher toughness property
  6. Keywords:
  7. D. Welding ; F. Microstructure ; Absorbed energy ; Austenite grain boundaries ; Brittle phase ; Charpy impact ; Coarse-grained ; Constant cooling rate ; Double pass ; E. Fracture ; F. Microstructure ; Field emission scanning electron microscopes ; Fracture property ; Heat input ; High strength ; Impact energy ; Initiation sites ; Lower hardness ; Microalloyed Steel ; Multi-pass ; Optical microscopes ; Peak temperatures ; Submerged arc ; Thermal cycle ; Toughness properties ; Transition temperature ; Weld joints ; Brittleness ; Charpy impact testing ; Electric welding ; Electron microscopes ; Field emission ; Grain boundaries ; Hardness ; High strength steel ; Microstructure ; Scanning electron microscopy ; Submerged arc welding ; Submerged melt welding ; Thermal cycling ; Welds ; Brittle fracture
  8. Source: Materials and Design ; Volume 31, Issue 6 , June , 2010 , Pages 2948-2955 ; 02641275 (ISSN)
  9. URL: http://www.sciencedirect.com/science/article/pii/S0261306909007250?np=y&npKey=7a9ef2c7e7dfc18e778e63a5d99889d82012c6c28944cb1f0791d86105aaba2f