Inclusion engineering of steel to prevent chemical tool wear

Abstract

Trent introduced the concept of tribological conditions of seizure at the tool-chip interface, when the normal pressure exceeds the flow stress of asperities so that the asperities are squeezed to make atomic contact. In consequence, chemical dissolution of the tool into the chip occurs by a diffusion mechanism, causing chemical wear. Oxley incorporated the concept of seizure in his quantitative model for flow chip morphology. Oxley introduced the concept of equilibrium shear angle in his quantitative model for flow chip morphology, which incorporates the work of shear in the secondary shear zone instead of friction, once atomic contact is established, but Oxley's model ignored potential interaction from metallurgical softening events in the secondary shear zone, which led to prediction of unrealistically high temperature at high cutting speeds. In fact, metallurgical softening events do occur particularly at high cutting speeds, causing shear localisation, which leads to significant deviation from Oxley's model predictions. In this paper, Oxley's model will be extended to capture the interaction of shear localisation in the secondary shear zone on the mechanics of metal cutting. Dynamic recrystallisation, phase transformation of the matrix and geometric softening owing to second phase particles are identified as important microstructural softening events causing shear localisation, which could intervene before the equilibrium shear angle is reached. The occurrence of shear localisation is shown to alter the mechanics of metal cutting, chip morphology and the tool wear mechanism. A phenomenological database in model alloys will be presented to validate the model assumptions. The application of the model in the design of self-lubricating free cutting steel for moderate and high cutting speeds will be examined.

Effect of microstructure softening events on the chip morphology of AISI 1045 steel during high speed machining

“…The ϕ e should be dependent both on cutting parameters and properties of workpiece. Therefore, if the properties of workpiece were changed due to dynamic behaviors of the material, the ϕ e would be varied corresponding to properties of workpiece to reach "minimum energy" criterion [11].…”

Optimization of Sulfur-Free-Cutting Steelmaking Variables: Six Sigma-Based Approaches

“…Free cutting steels contain one or more of the elements: sulfur, phosphorous, lead, calcium, selenium, or tellurium. Because of their ability to prevent tools from wearing off in high speed manufacturing processes, the free cutting steels have become ideal materials for high-precision and full-automation machining [1,2]. Since the traditional free cutting steels consist of lead elements that evaporate toxic steams during production processes, the sulfur free-cutting steels are widely used due to its lower costs and friendlier effects on our environment [3,4].…”

“…In the steels, the sulfur forms MnS compounds which not only become the sources of stress concentration that sever continuity of ferrite making shavings breakable, but also provide the lubrication effect that keeps tools from wearing off. Therefore, as the sulfur content in the steel increases, the machining efficiency as well as the tool-life expectancy improve accordingly [1,5].…”