Determination of Non-Recrystallization Temperature for Niobium Microalloyed Steel

Area of Science:

• Metallurgical Engineering
• Materials Science

Background:

• The non-recrystallization temperature (TNR) is crucial for controlling steel properties during hot rolling.
• Existing TNR equations have limitations, necessitating experimental validation for specific steel compositions.

Purpose of the Study:

• To experimentally determine the non-recrystallization temperature (TNR) of niobium-microalloyed steel.
• To establish optimal rolling schedules for API X-70 grade steel.
• To validate the determined TNR through controlled rolling processes.

Main Methods:

• Laboratory-grade low-carbon Nb-microalloyed steels were used.
• Multiple-hit deformation tests were conducted using a Gleeble® 3500 system.
• Microstructural analysis was performed using optical microscopy (OM) and scanning electron microscopy (SEM).

Main Results:

• The determined TNR for 0.1 wt.% niobium-microalloyed steel is approximately 951°C.
• Rolling at TNR resulted in partially recrystallized grains with ferrite nucleation.
• Subsequent rolling tests near the determined TNR confirmed its validity through microstructural observations.

Conclusions:

• The experimentally determined TNR of 951°C provides a reliable parameter for rolling niobium-microalloyed steels.
• This finding supports the development of precise rolling schedules for API X-70 steel.
• The study validates the TNR's influence on microstructure and properties, confirming its practical applicability.