Characterization of hot deformation behaviour of Nb-Ti microalloyed high-strength steel

Abstract

The hot deformation behaviour of Nb-Ti microalloyed high-strength steel was investigated. Hot compression tests were conducted in the temperature range 900 to 1100°C under strain rates of 0.1, 1, and 5 s-1. Dynamic recrystallization (DRX) occurs as the main flow softening mechanism at high temperature and low strain rate. The hot deformation activation energy was calculated to be about 404 699 J/mol. The constitutive equation was developed to describe the relationship between peak stress, strain rate, and deformation temperature. The characteristics of DRX at different deformation conditions were extracted from the stressstrain curves using the work hardening parameter. The Cingara-McQueen equation was developed to predict the flow curves up to the peak strain. The processing maps were obtained on the basis of a dynamic materials model. The results predict an instability region in the temperature range 1010 to 1100°C when the strain rate exceeds 0.78 s-1 .

Identification of Cracking Issues and Process Improvements through Plant Monitoring and Numerical Modelling of Secondary Cooling during Continuous Casting of HSLA Steels

“…31,32) It has been demonstrated that Nb has a strong detrimental effect when its content ranges between 0,03-0,04 wt.%Nb, which could promote cracking due to carbo-nitrides precipitation associated with low ductility. 22,28,[33][34][35][36] Yet, Nb is still used due to its beneficial effects on final mechanical properties. A possible way to circumvent this issue is to combine Nb with V and Ti which have a lesser effect on ductility loss.…”

Flow-Stress Model of 300M Steel for Multi-Pass Compression

“…Plenty of work has been carried out to study the influences of process parameter and microstructure evolution on flow-stress evolution of various steels. The effects of strain rate, strain, and temperature on flow-stress were considered, and the flow-stress models of Nb-Ti steel [1] and 5CrNiMoV steel [2] for single-pass compression were constructed based on the Arrhenius model. To reflect the influence of dislocation, segmented flow-stress models of AZ61 magnesium alloy [3] and 34CrNiMo6 steel [4] were established based on the Kocks-Mecking model during hot compression.…”

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In this work, multi-pass compressions were performed at various strain rates (0.01 s −1 , 0.1 s −1 , 1 s −1 , 10 s −1 ), temperatures (950 • C, 1050 • C, 1150 • C), inter-pass holding time (1 s, 10 s, 30 s, 120 s, 600 s), interrupt strains (0.3, 0.4, 0.5, 0.6), and total pass numbers (1,2,3,4). The intriguing finding was that the recrystallized fraction, average dislocation density, and plastic cumulative strain were partly eliminated during inter-pass holding, resulting in the early occurrence of recrystallization in subsequent compression.

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