Research on strength and toughness matching of 1.3GPa ultralow temperature resistant bulb flat steel

Abstract

In this study, an ultralow temperature resistant bulb flat steel with ultra-high strength and good toughness is prepared to meet the application requirements of hull structural steel for polar ships and large ships. The bulb flat steel with a yield strength of 1292 MPa, elongation of 18.5 % and an impact energy of 53 J at − 196 °C is obtained by quenching and tempering process. In order to reveal the tempering response and strengthening mechanism during the quenching and tempering process of bulb flat steel, multi-scale characterization is carried out to explore the microstructural evolution and nano-precipitation behavior of the ultralow temperature bulb flat steel under different tempering processes. The results indicate that the preferential precipitation of (V, Nb)(C, N) causes dislocation multiplication, and the higher dislocation density in the matrix provides more nucleation sites for M2C. The slower diffusion rate of Mo effectively suppresses the rapid coarsening of M2C, which keep a good coherent relationship between the M2C and the α-Fe matrix. Strain concentration is avoided by synergizing the (V, Nb)(C, N) precipitation and the M2C precipitation of the coherent lattice, thus enabling the ultralow temperature resistant bulb flat steel to maintain ultra-high strength with good plasticity and toughness.