EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Introduction/Purpose

The need for steels with high strength, increased toughness and good weldability led to the development of high - strength low - alloy (HSLA) steels. In this steels a combination of microalloying elements and thermomechanical processing leads to the required properties. An understanding of the precipitation behavior of the nanometer - sized precipitates is essential for controlling the recrystallization behavior and can only be achieved using high - resolution characterization techniques such as scanning transmission electron microscopy (STEM) and atom probe tomography (APT).

Methods

In this study HSLA steels with different contents of microalloying elements, such as Nb and Ti, were investigated. Double - hit experiments were carried out under various process parameters to investigate the recrystallization and precipitation behavior. Different annealing temperatures were chosen with regard to the precipitation behavior of Nb(C,N) and the interaction with TiN precipitates. Therefore, STEM and APT measurements were carried out to analyze the precipitates in the as - rolled condition and after deformation in the dilatometer.

Results

In the as - rolled condition, TiN precipitates were found which were enriched with different Nb contents, depending on their size. A variation of the microalloying content and the annealing temperature in the double - hit experiments has shown that this leads to differences in the strain - induced precipitation behavior of Nb(C,N) and the recrystallization behavior.

Conclusions

The results of this study clearly show that an understanding of the relationship between the microalloy content and the process parameters is crucial for optimizing the properties of HSLA steels.