A coupled Thermal-mechanical FE Model of Flow Localization during the Hot Torsion Test

作者：Mirzakhani Bahman^*; Khoddam Shahin; Arabi Hossein; Salehi Mohammad Taghi; Sietsma Jilt

来源：Steel Research International, 2009, 80(11): 846-854.

DOI：10.2374/SRI08SP156

• flow localization
• hot torsion test
• specimen geometry
• non-isothermal modelling
• finite element
• microalloyed steel

The hot torsion test (HTT) has been extensively used to analyse and physically model the flow behaviour and microstructure evolution of materials and alloys during hot deformation processes. The geometry of the specimen is a key factor for obtaining reliable results. In the present work, a thermo-rigid viscoplastic FE code, THORAX.FOR, was developed to describe the interaction of thermal-mechanical conditions and geometries of the HTT specimens. This was used to recommend the conditions for avoiding flow localization during HTT of API-X70 microalloyed steel. The simulation results show how an inappropriate choice of both test specimen geometry and twist rate of deformation could lead to a significant temperature raise in the middle of the gauge section and temperature gradient in the radial and longitudinal direction of the specimen. This consequently causes flow localization during the test. Therefore, assumptions of isothermal forming conditions or uniform strain softening may not be valid in many test scenarios. These assumptions could introduce significant errors in the post results of the test such as flow curve and interpretation of microstructure evolution. Recommendations on proper specimen geometry for a specified strain rate will be given to avoid flow localization during the hot torsion test.

• 出版日期2009-11