The invention discloses special
hot work die steel for large-scale integrated
die casting and a preparation method of the special
hot work die steel, and belongs to the technical field of
hot work die steel. The steel comprises the following chemical components in percentage by
mass: 0.28%-0.35% of C, 0.01%-0.025% of La, 0.01%-0.02% of Ce, 0.4%-0.45% of Mn, 0.1%-0.2% of Si, 4.5%-5.5% of Cr, 1.50%-2.00% of W, 2.2%-2.8% of Mo, 0.8%-1.2% of V, 1.0%-1.5% of Co, 0.1%-0.3% of Nb and the balance of Fe and impurities (S and P are less than or equal to 0.015%). The preparation method comprises the composite processes of
vacuum induction melting and electroslag remelting purification,
hydrogen firing high-temperature homogenization and three-upsetting and three-drawing multi-directional
forging, spheroidizing annealing and subzero treatment, step
quenching and double
tempering, multi-element co-
permeation, supersonic particle bombardment surface nanocrystallization and
plasma boriding. The
rare earth element La / Ce refined
grain boundary is combined with multi-element
alloy strengthening and surface nanocrystallization-boronizing synergistic treatment, so that the
hardness,
impact toughness and
thermal fatigue life of the die steel are remarkably improved, and the die steel is suitable for high-temperature, high-pressure and high-wear working conditions of a large integrated die-
casting die.