Metallurgy and tool life Tool life is generally improved when which microstructural characteristic is present in the work or tool material during machining?

Introduction / Context:
Tool life is influenced by cutting conditions and by the metallurgical structure of both the tool and the work. Finer microstructures typically machine more uniformly, reducing intermittent loads that accelerate wear or chipping.

Given Data / Assumptions:

• Conventional machining (turning/milling) with standard tool materials.
• Comparison of coarse versus fine grain structures in the work metal.
• Other factors like speed and feed held constant.

Concept / Approach:
A fine grain size in the work metal tends to reduce heterogeneity, banding, and large hard second-phase particles that can cause micro-chipping and abrasive wear of the tool edge. Uniform deformation lowers cutting force fluctuations and heat spikes, extending tool life. While hard carbides in tool microstructure are essential for tool hardness, simply “more hard constituents” without balance can reduce toughness and lead to brittle failure.

Step-by-Step Solution:

Verification / Alternative check:
Machining data often show improved machinability ratings after normalizing or refining grain size, which correlates with longer tool life at comparable parameters.

Why Other Options Are Wrong:
Large grain size: tends to promote uneven cutting and tear; can raise tool wear.Abundant hard constituents in the tool without proper balance can cause brittleness and chipping.Very coarse pearlite: increases hardness variations and abrasiveness.

Common Pitfalls:
Equating hardness alone with machinability; ignoring the balance between hardness and toughness in both tool and work.

Final Answer:

Small (fine) grain size in the work metal