This paper presents a comprehensive study of the impact of quenching roll speed on enhancing the low-temperature toughness of a low-carbon copper-containing steel. The microstructure characteristics, such as the prior austenite grains, and the distribution and volume fraction of precipitates, are observed using optical microscopy, scanning electron microscopy, transmission electron microscopy, and small-angle scattering X-ray. The results show that a decrease in the quenching roller speed (2 m/min) contributes to the achievement of more excellent low-temperature toughness (the average value is 232 J), although the prior austenite grains exhibit a relatively larger size in this case. The tempering treatment results in the precipitation of a large amount of 9R-type Cu-rich particles, regardless of the quenching roller speed. Reducing the quenching roller speed contributes to the increase in the volume fraction of Cu-rich particles, which is considered to be the main factor contributing to the achievement of excellent low-temperature toughness.