Comparative Impact Behavior of High C Steel After Conventional Quenching and Tempering and Austempering

It is well known that austempering, producing a microstructure bainitic, is the preferred heat treatment when toughness is the main requirement of the component. Literature shows a several works where mechanical properties for tempered martensite are compared with bainite presenting both same hardness. Most part of the results demonstrate better properties for the bainite microstructure.

This work intends to verify impact properties in O1 alloy steels (high carbon tool steel) submitted to different heat treatment cycles.   Tempered martensite obtained from the conventional heat treatment followed or not cryogenic bath are compared with bainitic structure produced in austempering. Austempering bath was 350⁰C  and samples were kept  for different times: 20 minutes, 40 minutes and 60 minutes. Since hardness has influence on the impact behavior, comparative studies were made for the same surface hardness level. This means that hardness for bainite and tempered  similar each other.