| 摘要 |
The invention relates to medium carbon steels and low alloy steels having a concentration of a machinability enhancing agent ("MEA"), i.e. tin and/or antimony, at its ferrite grain boundaries which enhances the steel's machinability and to processes for producing such steels. The invention encompasses medium carbon steels and low alloy steels characterized by having MEA bulk contents of from about 0.02 to about 0.09 weight percent, by having the sum of the MEA bulk content and the copper bulk content being no greater than about 0.10 weight percent, and by having a microstructure at the time of machining having a concentration of MEA at ferrite grain boundaries in an amount at least about five times the MEA bulk content of the steel. The invention also encompasses processes for preparing medium carbon steels and low alloy steels with enhanced machinability comprising the steps of providing a steel containing a MEA, developing ferrite grain boundaries, and concentrating the MEA at the ferrite grain boundaries wherein the MEA bulk content of the steel is from about 0.02 to about 0.09 weight percent and the sum of the MEA bulk content and the copper bulk content being no greater than about 0.10 weight percent. The invention also encompasses processes further comprising the steps of machining the steel and of controllably redistributing the MEA more homogeneously throughout the steel so as to substantially remove any embrittlement resulting from the MEA concentration at the ferrite grain boundaries. |
