Martensite in steels — identify the microstructure and magnetic behavior State whether the following statement is correct: Martensite has a needle-like (acicular or lath/plate) microstructure and is magnetic at room temperature.

Introduction / Context:
Martensite is the hard transformation product formed when austenite in steel is rapidly cooled. Recognizing its typical morphology and magnetic character is essential for materials engineers because these traits influence heat treatment identification, hardness, and non-destructive testing approaches.

Given Data / Assumptions:

• Plain-carbon and low-alloy steels quenched from the austenite field.
• Room-temperature observations under optical or electron microscopy.
• No special alloying to suppress magnetism below the Curie temperature.

Concept / Approach:
Martensite in steels is a supersaturated solid solution of carbon in a body-centered tetragonal (BCT) lattice formed by a diffusionless shear transformation. The morphology appears as acicular (needle-like) plates or packets of parallel laths depending on carbon content and prior austenite grain size. Ferromagnetism in iron is associated with body-centered lattices (BCC/BCT) below the Curie temperature, so martensite is magnetic at ordinary temperatures. In contrast, austenite is face-centered cubic and, in most Fe-Cr-Ni compositions, is paramagnetic at room temperature.

Step-by-Step Solution:

Verification / Alternative check:
Hardness testing and magnetic response provide quick checks: a quenched martensitic steel shows high hardness and attracts a magnet strongly. Micrographs reveal acicular patterns; tempering modifies laths but does not immediately remove magnetism until temperatures approach the Curie point or austenitization occurs.

Why Other Options Are Wrong:

• Incorrect / equiaxed and non-magnetic: contradicts both microstructural evidence and ferromagnetic behavior of BCT iron.
• Correct only above Curie temperature: above Curie, ferromagnetism is lost; the option reverses reality.
• Correct only for stainless steels: martensitic behavior is not limited to stainless grades; many carbon and alloy steels form martensite.

Common Pitfalls:
Confusing martensite with tempered martensite or bainite; assuming all stainless steels are non-magnetic (only austenitic grades are typically non-magnetic).

Final Answer: