Abstract
At low temperatures most metals show reduced ductility and impact toughness. Here, we report a compositionally lean, fine-grained Fe-30Mn-0.11C austenitic steel that breaks this rule, exhibiting an increase in strength, elongation and Charpy impact toughness with decreasing temperature. A Charpy impact energy of 453 J is achieved at liquid nitrogen temperatures, which is about four to five times that of conventional cryogenic austenitic steels. The high toughness is attributed to manganese and carbon austenite stabilizing elements, coupled with a reduction in grain size to the near-micrometer scale. Under these conditions dislocation slip and deformation twinning are the main deformation mechanisms, while embrittlement by α′- and ε-martensite transformations are inhibited. This reduces local stress and strain concentration, thereby retarding crack nucleation and prolonging work-hardening. The alloy is low-cost and can be processed by conventional production processes, making it suitable for low-temperature applications in industry.
Highlights
At low temperatures most metals show reduced ductility and impact toughness
These are: (i) that an ultrahigh impact energy can be achieved by enabling a transition with decreasing temperature from planar-slip dislocation activity at room temperature (RT) to deformation by mechanical nanotwinning at lower temperatures, and (ii) that to achieve an inverted toughness–temperature relationship, both strength and ductility should simultaneously increase with decreasing test temperature[8,12]
The decrease in grain size from 47.0 to 5.6 μm leads to increases in the yield strength (0.2% offset) and ultimate tensile strength (UTS) of about 25% and 7–10%, respectively, with a corresponding small reduction in total elongation
Summary
At low temperatures most metals show reduced ductility and impact toughness. Here, we report a compositionally lean, fine-grained Fe-30Mn-0.11C austenitic steel that breaks this rule, exhibiting an increase in strength, elongation and Charpy impact toughness with decreasing temperature. The high toughness is attributed to manganese and carbon austenite stabilizing elements, coupled with a reduction in grain size to the near-micrometer scale Under these conditions dislocation slip and deformation twinning are the main deformation mechanisms, while embrittlement by α′- and ε-martensite transformations are inhibited. An increase in impact toughness with decreasing temperature has been reported for some high- and mediumentropy alloys (HEAs/MEAs), e.g., CrMnFeCoNi, where an exceptionally high cryogenic impact toughness of ~400 J has been achieved[9,10] Despite this high cryogenic impact toughness, such alloys are likely to have only limited industrial application, as a result both of the high cost associated with the required amounts of expensive alloying elements (especially Co), and due to the complexity of large-scale production of components using HEAs and MEAs11. The simple alloy composition, low cost, and conventional processing route are expected to enable a broad range of cryogenic applications for this alloy
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
