The effects of Ti addition on the microstructure, mechanical properties and corrosion resistance of the Cu-30Zn-6Ni-1.5Ti (wt.%) alloy were investigated in the present study. Microstructure analysis confirms that the Ni₃Ti and NiTi phases are formed in the Cu-Zn-Ni-Ti alloy. Most of the Ni₃Ti particles dissolve into the matrix, whereas NiTi particles remained after the solution treatment. Moreover, nano-sized Ni₃Ti and Cu₂NiZn phases are precipitated from the matrix during the aging process. The yield strength improvement of the studied alloy is attributed to the Orowan strengthening (accounting for 42.5% of the total yield strength), then the grain boundary strengthening (31.1%), the dislocation strengthening (16.9%), the twin boundary strengthening (5.0%) and the solid solution strengthening (0.5%). After cold rolling with 90% deformation and aging at 440 °C for 1 h, the designed alloy has a hardness of 327.1 HV, a yield strength of 1192 MPa, an ultimate tensile strength of 1297 MPa, an elongation of 1.8%, an electrical conductivity of 11.2% IACS and a corrosion rate of 2.8 μm/month in 3.5% NaCl solution.

Nano Cu precipitation plays a crucial role in significantly improving the performance of the Cu-bearing high-strength low-alloy steel. The final cooling temperature effects the transformation products of austenite during the continuous cooling process, as well as the nano precipitations of steel. This study investigated the microstructure and hardness at different final cooling temperatures (750, 700, 650, 600, 550, and 500 °C) using the MMS-300 thermal simulation experimental machine (Northeastern University, Shenyang, China) and Vickers hardness tester. The changes in microstructure and the phase transformation law of austenite were determined during continuous cooling and then analyzed. The precipitation reaction of nano Cu precipitation during continuous cooling was studied using transmission electron microscopy (TEM), revealing the precipitation state under different final cooling temperature conditions. The results showed that the precipitations led to an increase and then a decrease in the microhardness, and the microhardness reaches its peak at 550 °C. The precipitations changed from spherical to elliptical, and the size gradually increased when the final cooling temperature increased.

A low-carbon Cu-bearing marine structural steel was fabricated based on the chemical composition of HSLA-100 steel. The microstructural evolution, variation in nanoscale Cu-rich precipitates, and their synergistic effects on the mechanical properties and hydrogen embrittlement (HE) behavior under different tempering durations were systematically investigated. The results showed that the original lath bainite gradually transformed into tempered bainite and equiaxed ferrite with a prolonged tempering time. The Vickers hardness exhibited a typical upward-then-downward trend and reached a peak value of 322 HV at the tempering time of 1 h. The average size of Cu-rich precipitates increased from 7.2 nm to 13.2 nm, while the number density rose rapidly and finally stabilized. The as-rolled sample exhibited the minimum plastic loss after hydrogen charging owing to the hydrogen-trapping effect of high-density tangled dislocations. Short-time tempering (0.5 h) generated fine Cu-rich precipitates with a weak hydrogen-trapping capacity and abundant mobile dislocations, resulting in severe HE deterioration. The optimal HE susceptibility was achieved after 1 h of tempering. Combined with our experimental microstructure-property results and previous published literature, this improvement is inferred to originate from the hydrogen-trapping effect of adequately grown Cu-rich precipitates, together with a substantial decrease in mobile dislocation density. Excessively long tempering (2 h) induced irreversible temper brittleness and grain boundary deterioration, which aggravated the hydrogen-induced plastic degradation. This work clarified the coupled regulation mechanism of the Cu precipitate morphology, dislocation configuration, and temper brittleness on the HE performance of low-carbon marine steel, providing a reliable theoretical basis for the process optimization and anti-hydrogen damage performance improvement of high-strength marine steels.