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Abstract
The fracture properties of a new ultrahigh strength low alloy steel 0·3C–CrMoV(ESR), developed primarily as a cost effective material for space launch vehicle applications, have been evaluated through two different methods. The steel was processed through electroslag remelting (ESR) with inoculation using niobium to produce 4 tonne ingots, which were forged and rolled into plates. The fracture toughness of this steel has been evaluated by testing compact tension specimens and surface cracked tension specimens following the procedures in ASTM E–399 and ASTM E–740 respectively. The steel, after quenching and tempering, has a 0·2% proof strength of 1470 MPa, ultimate tensile strength of 1725 MPa and fracture toughness of 96 MPa √m. It has high residual strength also in the presence of surface cracks of 5 × 2 mm size. The microstructure consists of fine grains in the annealed condition and lath martensite in the hardened condition. After tempering, fine carbide precipitates distributed along the lath boundaries and within the laths were observed.