Abstract
The effect of notch-root radius, austenitizing temperature, and austenitizing time on the room-temperature impact strength and the ductile-brittle transition characteristics of tempered 300M steel have been investigated. For high-strength, medium-carbon, low-alloy steels high-temperature austenitizing treatments are known to give contradictory results with regard to the toughness characteristics. The plane-strain fracture toughness and the prefatigue-cracked impact strength are increased whereas the standard impact strength is decreased. The present investigation has shown that the impact strength is increased with increasing austenitizing temperature if the notch-root radius is less than 0·13 mm but for blunter notches it is decreased when the treatment temperature is above 1000°C. For high-temperature austenitizing treatments the impact strength, for all notch-root radii, is increased with austenitizing time but/or the low austenitizing treatments the impact strength is independent of time. The ductile-brittle transition temperature is increased with austenitizing temperature and decreasing notch-root radius. The notch-root radius effect, however, is more pronounced for low-temperature austenitizing treatments.
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