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US 5,961,747 AGranted
Tin-bearing free-machining steel
AssigneeUniversity of Pittsburgh
InventorsAnthony J. DeArdo, C. Issac Garcia
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AssigneeUniversity of Pittsburgh
InventorsAnthony J. DeArdo, C. Issac Garcia
Estimating the term…
The invention relates to free-machining steels which do not rely on lead as a means of enhancing machinability. Instead, the steels of the invention employ concentrations of tin at ferrite grain boundaries to replicate a role of lead, which the inventors have discovered, in enhancing machinability. This role is to cause an embrittlement at the localized cutting zone temperatures by changing the fracture mode from transgranular to intergranular at those temperatures. The invention's use of concentrations of tin at the ferrite grain boundaries of the steel permits the machinability-enhancing effect to be obtained while employing bulk tin contents below the levels at which hot tearing becomes problematic. The invention improves over lead-bearing, free-machining steels in that the machinability-enhancing embrittlement produced by concentrating tin at the ferrite grain boundaries is both controllable and reversible. The invention also relates to methods of producing the described tin-bearing, free-machining steels and the products of those processes.
A free-machining steel composition consisting essentially of, in weight percent, carbon up to about 0.25, copper up to about 0.5, manganese from about 0.01 to about 2, oxygen from about 0.003 to about 0.03, sulfur from about 0.002 to about 0.8, tin from about 0.04 to about 0.08, and a balance of iron and incidental impurities, wherein a ratio of the manganese to the sulfur is from about 2.9 to about 3.4 and a total of the sulfur plus the tin plus the copper is no more than about 0.9, the composition being characterized by a microstructure having a concentration of tin at ferrite grain boundaries in an amount of at least about ten times the bulk tin content of the steel.
A free-machining steel composition consisting essentially of, in weight percent, aluminum up to about 0.005, carbon from about 0.01 to about 0.25, copper up to about 0.5, manganese from about 0.5 to about 1.5, nitrogen up to about 0.015, oxygen from about 0.003 to about 0.03, phosphorus from about 0.01 to about 0.15, silicon up to about 0.05, sulfur from about 0.2 to about 0.45, tin from about 0.04 to about 0.08, and a balance of iron and incidental impurities, wherein a ratio of the manganese to the sulfur is from about 2.9 to about 3.4 and a total of the sulfur plus the tin plus the copper is no more than about 0.9, the composition being characterized by a microstructure having a concentration of tin at ferrite grain boundaries in an amount of at least about ten times the bulk tin content of the steel.
A process for preparing a free-machining steel, comprising the steps of:
A process for preparing a free-machining steel, comprising the steps of:
The process described in 23, wherein the step of redistributing the tin in the steel comprises the steps of:
Dependencies are inferred from the claim text.