# Ultrastrong and ductile steel welds achieved by fine interlocking microstructures with film-like retained austenite

## TL;DR

Researchers developed a new steel welding method using niobium and chromium to create stronger, more durable welds at lower costs and with less environmental impact.

## Contribution

The novel use of Nb and Cr instead of Ni to form fine interlocking microstructures with retained austenite in steel welds.

## Key findings

- Nb and Cr additions create finer interlocking weld microstructures with higher retained austenite.
- The new alloy design improves tensile properties, impact toughness, and fatigue strength.
- The method reduces material costs by 45% and environmental impact by eliminating Ni.

## Abstract

The degradation of mechanical properties caused by grain coarsening or the formation of brittle phases during welding reduces the longevity of products. Here, we report advances in the weld quality of ultra-high strength steels by utilizing Nb and Cr instead of Ni. Sole addition of Cr, as an alternative to Ni, has limitations in developing fine weld microstructure, while it is revealed that the coupling effects of Nb and Cr additions make a finer interlocking weld microstructures with a higher fraction of retained austenite due to the decrease in austenite to acicular ferrite and bainite transformation temperature and carbon activity. As a result, an alloying design with Nb and Cr creates ultrastrong and ductile steel welds with enhanced tensile properties, impact toughness, and fatigue strength, at 45% lower material costs and lower environmental impact by removing Ni.

Weld integrity and performance determine lifetime and safety of structures. Here, the authors report advances in weld quality of ultrahigh strength steels resulting from fine interlocking weld microstructures with film-like retained austenite by utilizing Nb and Cr instead of Ni.