Effect of Molybdenum on the Impact Toughness of Heat-Affected Zone in High-Strength Low-Alloy Steel

Area of Science:

• Materials Science
• Metallurgy
• Physical Chemistry

Background:

• High-strength low-alloy (HSLA) steels are crucial in various industries.
• Understanding microstructural evolution is key to enhancing steel properties.
• The role of alloying elements like Molybdenum (Mo) in steel toughness requires detailed investigation.

Purpose of the Study:

• To investigate the effect of Molybdenum (Mo) addition on the microstructure and toughness of HSLA steel.
• To analyze the changes in precipitates and austenite grain structure.
• To elucidate the mechanism by which Mo improves steel toughness.

Main Methods:

• Characterization of microstructure, precipitates, and austenite grain using optical microscopy, transmission electron microscopy (TEM), and laser scanning confocal microscopy.
• Analysis of precipitate chemical composition, size, and number density.
• Calculation of lattice misfit between precipitates and ferrite.

Main Results:

• Addition of 0.07% Mo refined the microstructure and enhanced steel toughness.
• Mo suppressed Widmanstätten ferrite (WF) formation and promoted acicular ferrite (AF) transformation in the heat-affected zone (HAZ).
• Precipitate composition changed from Nb(C, N) to (Nb, Mo)(C, N), reducing lattice misfit with ferrite and affecting precipitate characteristics.

Conclusions:

• Molybdenum addition significantly improves the toughness of HSLA steel.
• The refinement of microstructure and promotion of acicular ferrite by Mo are key factors in toughness enhancement.
• Modified precipitates with reduced lattice misfit contribute to improved steel performance.