The burgeoning steel production industry is continuously seeking ways to optimize the properties of low-carbon steel to meet modern demands for durability and performance. A recent study has zeroed in on the effects of niobium (Nb) and boron (B) additives on the mechanical properties and high-temperature flow behavior of low-carbon steel produced via compact strip production (CSP).
The research, conducted at Al Ezz Dekheila Steel Company (EZDK) in Alexandria, Egypt, reveals significant findings about how these additives influence steel processing parameters. Notably, the study highlights the industrial benefits of incorporating boron alongside niobium for enhancing the strength and workability of low-carbon steel.
Using the CSP process, the study examined two alloy variants: 0.015% Nb-bearing low-carbon steel (15Nb alloy) and 0.015% Nb with 30 ppm B-bearing low-carbon steel (15Nb30B alloy). The investigation utilized data from CSP operations to determine the no-recrystallization temperature (Tnr), which is pivotal in controlling the hot rolling process.
Flow stress tests conducted with various deformation techniques indicated remarkable differences between alloys, especially under high temperatures. The mean flow stress log data showed how the addition of boron can alter microstructure-related attributes, contributing to reduced rolling load and lower finishing temperatures during production.
According to the authors, “the addition of B to the 15Nb alloy reduces Tnr from 975 to 955 °C, which requires forming at much lower temperatures during finishing passes.” This lowered processing temperature reflects the potential for reduced energy consumption and increased efficiency.
The study also asserts, “the addition of B to Nb-bearing steel slightly refines the grain size of the as-rolled alloy, which, in turn, has little beneficial effect on the strength.” This indicates the microstructural gains from boron do not come at the cost of strength, marking it as particularly advantageous for industries requiring lightweight and strong materials.
Understanding the interaction between Nb and B is key. Niobium is known to significantly raise Tnr, hindering recrystallization during processing, which is beneficial for maintaining steel properties under stress. Conversely, boron interacts with nitrogen present, promoting desirable precipitate formations and preventing detrimental ones such as Nb(C, N) which can lead to issues like transverse cracking during casting.
Through advanced techniques such as thermomechanical controlled processing (TMCP) and the Gleeble simulation, researchers investigated how different treatments affect steel microstructure at specific temperatures. The findings revealed how the addition of B influences the phase evolution of the 15Nb30B alloy, resulting in lower flow stress under certain processing conditions.
Overall, the results provide compelling evidence for integrating boron addition during the production of niobium-bearing low-carbon steels. By leveraging the favorable properties imparted by both elements, manufacturers can achieve not only enhanced performance characteristics but also improved processing efficiency. The study concludes with broad industry implications, particularly for achieving optimal mechanical properties of hot-rolled strips produced from CSP technology.