Influence of V and Nb Micro‐Alloying on Direct Quenched and Tempered Ultra‐High Strength Steels

Abstract

The construction of mobile crane booms requires the usage of ultra‐high strength steels. Micro‐alloying elements promote grain refinement during hot rolling and result in increased toughness. The relevant strength is given through a martensitic microstructure, which is accomplished by elements retarding the γ to α transformation. Direct quenching (DQ) from the rolling heat and quenching after a preceding re‐austenitization (RQ) are two different production routes. They differ regarding their productivity, their achievable strength levels, and their resulting microstructures. In order to explore the influence of the production route in combination with prominent micro‐alloying elements, which come to application during hot‐rolling, six steels with varying content of V and Nb are investigated concerning their different properties after DQ and RQ as well as their behavior after tempering. It is found, that Nb strongly improves the strength after thermomechanical processing in the as‐rolled condition. Furthermore, Nb compensates the loss of strength during tempering. This effect is not thoroughly discussed in literature so far. Although Nb leads to grain refining during re‐austenitization, the effects on the strength of RQ steels are minimal. The effect after tempering is also weaker than after direct quenching. It is also shown, that V offers a high strength potential after tempering, however weakens the impact toughness significantly.

Laserstrahl‐ und Laserhybridschweißverbindungen aus ultrahochfesten Feinkornbaustählen – Teil 1: Verfahren und Schweißnahtcharakterisierung

“…Die konventionellen Q‐Stähle erreichen die hohen Festigkeitswerte üblicherweise durch einen dem Walzen nachgeschalteten Vergütungsprozess, der sich in die Prozessschritte Austenitisieren, Abschrecken und Anlassen gliedert [12, 13]. Dagegen werden die hohen Festigkeitskennwerte bei thermomechanisch gewalzten Stählen durch eine Kombination aus Legierungskonzept und einer darauf abgestimmten, definierten Wärmeführung beim Walzen der Blechhalbzeuge erreicht.…”

Effect of Microalloying on Microstructure and Mechanical Properties of Laser Weld of PHS Steel

“…Jo et al 12 in South Korea also found that the grain size of the microstructure became smaller and grain refinement occurred when niobium alloying was performed in the 1.9 GPa hot stamping steel. Esterl et al 13 carried out rolling and quenching experiments on steels with different niobium contents, and found that niobium played an important role in delaying recrystallization and could effectively realize grain refinement.…”

Effect of V–Nb Composite Microalloying on Microstructure and Properties of Non‐Quenched and Tempered Forged Steel

“…Therefore, the combined addition of V and Nb elements may be an effective method to improve the strength and toughness of steel. Raphael Esterl et al [14] studied the effect of V and Nb microalloying on quenched and tempered ultrahighstrength steel, and found that Nb-containing steel compensated for the strength loss during tempering. V-containing steel has a DOI: 10.1002/srin.202300029 Herein, non-quenched and tempered forging steels containing V and V-Nb are designed, and the mechanical properties and microstructure of two steels are compared and analyzed.…”

“…Therefore, the combined addition of V and Nb elements may be an effective method to improve the strength and toughness of steel. Raphael Esterl et al [ 14 ] studied the effect of V and Nb microalloying on quenched and tempered ultrahigh‐strength steel, and found that Nb‐containing steel compensated for the strength loss during tempering. V‐containing steel has a high‐strength potential after tempering, but it will significantly weaken the impact toughness; Chen et al [ 15 ] studied the effect of V and Nb composite microalloying on the strengthening mechanism of high‐strength hot‐stamping steel, and found that the strength and hardness decreased with the increase of V content.…”