Fracture and fatigue crack propagation properties of hardened 52100 steel |
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Authors: | J M Beswick |
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Affiliation: | (1) Department of Physical Metallurgy, SKF Engineering and Research Centre BV, 3430 DT Nicuwegein, The Netherlands |
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Abstract: | Good toughness in hardened 52100 ball bearing steel is important in order to prevent premature fracture during mounting or
service of bearing elements. Steel cleanliness, residual copper content, and carbon content effects have been investigated
in relation to fracture mechanics properties, and it was observed that only the carbon content has any relevance for the range
of compositions investigated. The effect of hardening and tempering temperatures for conventional furnace-hardening techniques
on toughness was investigated, theK
lcbeing generally much less sensitive to these parameters than blunt notch toughness testing. Cold deformation of the material
prior to martensitic hardening significantly increased the blunt notch toughness. Thermal grain refining treatments did not
give the same improved blunt notch toughness as observed for prior cold deformation. Short austenitization cycles (ten seconds)
for martensitic hardening resulted in microstructures with high retained austenite contents. This microstructure resulted
in higher fracture toughness and retardation of the crack growth rates, the mechanism being associated with transformation
toughening in the plastic zone. Inductive tempering of martensitic-hardened 52100 was observed to result in similar blunt
notch toughnesses as compared to furnace tempered material of the same hardness. A poor correlation between fracture toughness
and blunt notch toughness was observed, particularly for the unstable structures,i.e., microstructures with high levels of retained austenite. Fracture toughness does not represent the intrinsic toughness of
high carbon martensite with related high contents of retained austenite. |
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