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Hot Deformation Behaviour of Low Alloy Steel
Author(s) -
Poletti C.,
Six J.,
Hochegger M.,
Degischer H. P.,
Ilie S.
Publication year - 2011
Publication title -
steel research international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.603
H-Index - 49
eISSN - 1869-344X
pISSN - 1611-3683
DOI - 10.1002/srin.201000276
Subject(s) - materials science , strain rate , ferrite (magnet) , flow stress , metallurgy , deformation (meteorology) , austenite , dissipation , metallography , ultimate tensile strength , instability , composite material , ductility (earth science) , tensile testing , microstructure , thermodynamics , creep , mechanics , physics
Hot deformation of a continuously cast low alloyed steel is studied by means of hot compression and tensile tests by using a Gleeble® 1500 machine after austenitization in a wide range of strain rates and between 720–800 °C. The flow data are evaluated to obtain the strain rate sensitivity and the processing maps. A new calculation method is used, yielding on the instability parameter defined as κ J which correlates well with the microstructural changes. The strain rate sensitivity does not predict any instability but all the others instability parameters do, including the new κ J . Flow instability appears at high temperatures and low strain rates where pores are formed at the austenitic grain boundaries, causing a decay of ductility in the tensile test. During hot deformation more ferrite is formed than corresponding heat treatments without deformation. In these conditions, the deformation is concentrated in the softer ferrite phase. The deformation induced ferrite deforms by dynamic recovery forming new grains as revealed by metallography and is correlated with low coefficients of power dissipation. The sinh type constitutive equation represents the flow data well with a stress exponent n = 4.1 and an apparent activation energy Q = 218 kJ/mol.