Hot working of metals — identify the combined effects: During hot working (deformation above the material’s recrystallisation temperature), which of the following outcomes are achieved in the workpiece?

Introduction / Context:
Hot working is a fundamental metal forming route where deformation is carried out above the recrystallisation temperature. This regime enables concurrent softening by dynamic recovery and recrystallisation, profoundly improving the internal quality and properties of the metal. Understanding the collective benefits of hot working is essential for selecting forming processes and setting parameters for forging, rolling, and extrusion.

Given Data / Assumptions:

• Deformation is performed above the recrystallisation temperature.
• Material exhibits dynamic recovery/recrystallisation during deformation.
• Sufficient strain and temperature are achieved to heal defects and refine grains.

Concept / Approach:
At elevated temperature, dislocations rearrange and new, strain-free grains form, breaking up prior coarse grains and eliminating work hardening. Pores and microvoids are reduced by plastic flow and diffusion-assisted healing. The net effect is a refined microstructure and improved mechanical properties, especially toughness and ductility. Directional flow may also align inclusions more favourably for service loading.

Step-by-Step Solution:
During hot deformation, recovery reduces dislocation density and lowers flow stress.Dynamic recrystallisation nucleates and grows new fine grains, refining the structure.Sustained pressure and temperature allow closure of porosity and weld internal voids.The refined, cleaner microstructure improves tensile ductility, impact toughness, and often fatigue resistance.

Verification / Alternative check:
Metallographic evidence after hot forging shows equiaxed fine grains and reduced porosity compared to as-cast material.

Why Other Options Are Wrong:
Each of options A, B, and C states a true partial effect; the most complete and therefore correct choice is the combination “all of the above”.

Common Pitfalls:
Assuming hot working always increases strength; strength at room temperature depends on final grain size and any post-process heat treatment. Confusing hot working with hot isostatic pressing (HIP); while both can reduce porosity, mechanisms and outcomes differ. Ignoring oxidation and scale formation, which must be managed by protective atmospheres or machining allowances.

Final Answer:
all of the above