Microstructures developed during thermomechanical treatment of HSLA steels

Cuddy, L. J.

doi:10.1007/bf02642345

“…In Cuddy's other papers [3,113,114], he has reported that the TGC is about 70-100°C lower than TDISS. However, Palmiere et al [72] has reported that the solubility product Cuddy used has a tendency to underestimate the dissolution temperature by about 40-100°C.…”

Section: Grain Growth Inhibition By Particle Pinningmentioning

confidence: 94%

“…In practice, many researchers [3,57,114,125] have discovered that the influence of the initial austenite grain size to the final recrystallised austenite grain size at the end of rough rolling is minor. This is because the recrystallised austenite grain size tends to converge after several passes regardless of the initial grain sizes, as can be seen in Figure 2-19.…”

Section: Conventional Rough Rolling Processmentioning

confidence: 99%

“…This is because the recrystallised austenite grain size tends to converge after several passes regardless of the initial grain sizes, as can be seen in Figure 2-19. Hence there is a limit degree of refinement which can be achieved through rough rolling [3,57,114,125]. Within the capabilities of conventional rolling mills, the finest austenite grain size has been reported to be about 15μm [46].…”

Section: Conventional Rough Rolling Processmentioning

confidence: 99%

“…Therefore, there is tendency for the austenite to have a duplex microstructure consisting of fine recrystallised grains and coarse deformed original grains [3,35,89,113,114,147].…”

Section: Deformation In Partially Recrystallised Region (T5% < Tdefmentioning

confidence: 99%

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Thermomechanical Processing of Structural Steels with Dilute Niobium Additions

Cui¹,

Patel²,

Palmiere³

2015

HSLA Steels 2015, Microalloying 2015 &Amp; Offshore Engineering Steels 2015

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-i - AbstractIn this thesis, the influence of various dilute Nb additions (0.005-0.02 wt%) on austenite microstructure evolution along thermomechanical processing, in terms of austenite recrystallisation and grain growth, were investigated using steels with three carbon content levels.At the homogenisation temperature of 1250°C, all dilute Nb additions were dissolved in low carbon steels whereas the Nb dissolution limits for 0.4 wt% and 0.6 wt% C steels were 0.012 wt% and 0.08 wt%, respectively. Dilute Nb additions did not show significant influence on homogenised austenite grain size. The dramatic increase in C contents was more influential, which decreased the homogenised austenite grain size.The influence of dilute Nb additions and C contents on dynamic recrystallisation behaviour was studied by rough rolling at high deformation temperature with low strain rate. The dilute Nb additions were found to increase the critical strain of dynamic recrystallisation whereas C contents showed no influence on the dynamic recrystallisation behaviour.The austenite recrystallisation behaviour after finish rolling and after the holding period between finishing passes were studied by means of interrupted plane strain compression (PSC) tests and double hit PSC tests. It was found that with low Nb supersaturation, recrystallisation happened prior to Nb precipitation. Solute Nb in austenite delayed the onset of austenite recrystallisation through solute drag effect.With high Nb supersaturation, Nb precipitation occurred before the onset of recrystallisation which completely retarded austenite recrystallisation.The austenite grain growth during the holding period between finish rolling passes was studied by the evolution of prior-austenite grain size before and after the 20s holding period at the highest finish rolling temperature (1050°C). There was no Nb precipitation found and the difference in austenite grain growth behaviour was Abstract -iiattributed to the solute drag effect from both Nb and C in solution. It was found that Nb in solution suppressed austenite grain growth. However, the effectiveness of solute Nb in suppressing austenite grain growth was affected by the C content. Acknowledgement

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“…This is because once the duplex microstructure is created, it cannot be removed by any further deformation [114]. They will eventually be transformed into duplex ferrite microstructure which is detrimental for the mechanical properties of the steel, especially for those applications where both strength and toughness are very important [147].…”

Section: Deformation In Partially Recrystallised Region (T5% < Tdef <mentioning

confidence: 99%

Thermomechanical Processing of Structural Steels with Dilute Niobium Additions

Cui

¹

,

Patel²,

Palmiere

³

2016

HSLA Steels 2015, Microalloying 2015 &Amp; Offshore Engineering Steels 2015

View full text Add to dashboard Cite

-i - AbstractIn this thesis, the influence of various dilute Nb additions (0.005-0.02 wt%) on austenite microstructure evolution along thermomechanical processing, in terms of austenite recrystallisation and grain growth, were investigated using steels with three carbon content levels.At the homogenisation temperature of 1250°C, all dilute Nb additions were dissolved in low carbon steels whereas the Nb dissolution limits for 0.4 wt% and 0.6 wt% C steels were 0.012 wt% and 0.08 wt%, respectively. Dilute Nb additions did not show significant influence on homogenised austenite grain size. The dramatic increase in C contents was more influential, which decreased the homogenised austenite grain size.The influence of dilute Nb additions and C contents on dynamic recrystallisation behaviour was studied by rough rolling at high deformation temperature with low strain rate. The dilute Nb additions were found to increase the critical strain of dynamic recrystallisation whereas C contents showed no influence on the dynamic recrystallisation behaviour.The austenite recrystallisation behaviour after finish rolling and after the holding period between finishing passes were studied by means of interrupted plane strain compression (PSC) tests and double hit PSC tests. It was found that with low Nb supersaturation, recrystallisation happened prior to Nb precipitation. Solute Nb in austenite delayed the onset of austenite recrystallisation through solute drag effect.With high Nb supersaturation, Nb precipitation occurred before the onset of recrystallisation which completely retarded austenite recrystallisation.The austenite grain growth during the holding period between finish rolling passes was studied by the evolution of prior-austenite grain size before and after the 20s holding period at the highest finish rolling temperature (1050°C). There was no Nb precipitation found and the difference in austenite grain growth behaviour was Abstract -iiattributed to the solute drag effect from both Nb and C in solution. It was found that Nb in solution suppressed austenite grain growth. However, the effectiveness of solute Nb in suppressing austenite grain growth was affected by the C content. Acknowledgement

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