F. Klocke et al., INFLUENCE EXERTED BY NONMETALLIC INCLUSIO NS IN STEEL ON THE CONTACT CONDITIONS DURING MACHINING, Stahl und Eisen, 117(10), 1997, pp. 61
Under certain circumstances, non-metallic inclusions in steel are capa
ble of forming intermediate layers between the tool and workpiece duri
ng machining which exert a positive influence on the contact condition
s. Suitable for forming such layers are modified oxide inclusions, as
in calcium-treated steels, and sulphide inclusions. The material compo
sition and the properties of these inclusions are governed by the stee
l's alloy composition. It is, as a result, not possible to assume, tha
t the intermediate layers have identical mechanisms of action for diff
erent Ca-treated steels, When Ca-treated quenched and tempered steels
42CrMo4 and 38MnSiVS5 are machined, the inter:mediate layers have a po
lyphase structure. This can lead to different contact conditions over
the effective area. The question whether the intermediate layers have
a friction-and wear-reducing effect depends essentially on their consi
stency. Tests performed on free-cutting steel revealed a loss of effec
tiveness during the transition from the viscous to the molten state. I
t was possible to demonstrate the reduced wear of Ca-treated steels by
the example of microalloyed quenched and tempered steel 38MnSiVS5. Wi
thin the scope of long-time machining tests, average tool life increas
es of over 400% were realised compared with conventional material of t
he same quality.