Induction hardening — control of case depth State whether the statement is correct: In induction hardening, the depth of hardening (case depth) is controlled by controlling the voltage applied to the induction coil.

Introduction / Context:
Induction hardening produces a hardened surface layer by rapid, localized heating and quenching. Control of case depth is crucial for achieving desired wear resistance without compromising core toughness. Understanding the main control variables is a key practical skill in heat treatment engineering.

Given Data / Assumptions:

• Induction system characterized by frequency, power (kW), coil geometry, and process time.
• Steel composition allows martensite formation upon quench.
• Voltage is one of several electrical parameters related to power delivery.

Concept / Approach:
Case depth in induction hardening is governed primarily by electromagnetic penetration depth (skin depth) and thermal diffusion. Skin depth δ ≈ k / √f (where f is frequency, k depends on material properties) shows that higher frequency reduces penetration, yielding shallower cases. Heating time and power density influence how far heat diffuses before quench. Voltage alone is not the primary, independent knob; it is part of the circuit achieving required power but does not directly set case depth like frequency and time do.

Step-by-Step Solution:
Relate case depth to skin depth: δ ∝ 1 / √f.Adjust process: choose frequency for target δ, then set power and time to reach austenitising temperature at that depth.Recognize voltage is secondary and coupled to coil design and load; it does not uniquely determine depth.Hence, the statement attributing depth control to voltage is incorrect.

Verification / Alternative check:
Process documentation specifies frequency bands (e.g., medium vs. high frequency) for desired case depths (e.g., 1–6 mm), confirming frequency/time control.

Why Other Options Are Wrong:
Options asserting correctness overlook the dominant roles of frequency and heating time; carbon content affects hardness potential, not electromagnetic penetration. The explanatory option (e) correctly states the real dependencies.

Common Pitfalls:
Using excessive power causing overheating instead of greater depth; attempting deep cases with very high frequency, which inherently limits penetration.

Final Answer:
Incorrect