Influence of Martensite–Austenite constituents formed at different intercritical temperatures on toughness

•Impact toughness improves with increasing temperature within intercritical region.•Coarse necklace M–A formed at 760°C resulted in the lowest toughness (42J).•Samples reheated to 800°C/840°C had better toughness, respectively 80J and 105J.•Notable difference in toughness is due to size/distribution/carbon content of M–A.