Strength-toughness synergistic enhancement mechanism in double-wire multilayer GMA-deposited HSLA steel via interlayer dwell time strategy

High-strength low-alloy (HSLA) steel has been widely applied in engineering machinery, marine engineering, automotive fields, and other sectors. This study developed an interlayer dwell time (IDT) strategy to enhance both strength and toughness in double-wire multilayer GMA-deposited HSLA steel (ER70-G). This method achieves high-efficiency deposition without alloy redesign. Thermal simulation confirmed that IDT regulation effectively alleviated heat accumulation and accelerated cooling rates from 26 °C/s to 48.1 °C/s. This suppressed the formation of grain boundary ferrite (GBF), reducing its content from 15.7% to 5.3%. Additionally, it refined acicular ferrite (AF) grains, decreasing the average size from 9.96 μm to 5.13 μm. Furthermore, it increased the proportion of high-angle grain boundaries (HAGBs) from 52.8% to 68.7%. In 40-mm-thick deposited multilayers, this microstructural engineering simultaneously elevated tensile strength from 692.3 MPa to 805.4 MPa and impact toughness from 135.67 J to 172.67 J, thereby eliminating the conventional strength-toughness trade-off. This strategy provides a cost-effective solution for manufacturing high-performance HSLA steel, requiring neither alloy redesign nor post-deposition heat treatment, demonstrating significant potential for practical applications to not only multilayer welding but also additive manufacturing.