Whitworth compressed steel (fluid-compressed): approximately what pressure is applied to the molten steel during the process? Select the closest standard value, expressed in kg/mm^2.

Introduction / Context:
Sir Joseph Whitworth pioneered fluid compression of molten steel to reduce blowholes and segregation, producing sounder ingots for critical components. Remembering the order of magnitude of pressure is useful for historical processes and comparison with modern casting techniques.

Given Data / Assumptions:

• Pressure is expressed in kg/mm^2 (1 kg/mm^2 ≈ 9.81 MPa).
• Historical descriptions cite several tons per square inch acting hydrostatically on the molten metal.

Concept / Approach:

References to Whitworth’s process typically mention about 6 tons/in^2 of pressure. Converting: 1 ton/in^2 ≈ 1.406 kg/mm^2, so 6 tons/in^2 ≈ 8.4–8.5 kg/mm^2. Rounding to practical, tabulated values used in exams, 10 kg/mm^2 is commonly adopted as the nearest standard figure representing the scale of pressure employed.

Step-by-Step Solution:

Verification / Alternative check:

Multiple engineering texts round the value; answers of 9–10 kg/mm^2 are often accepted, with 10 kg/mm^2 appearing as the conventional key where discrete options are given.

Why Other Options Are Wrong:

5 kg/mm^2: too low; would be ineffective for the intended densification. 9 kg/mm^2 is close but not the typical rounded figure used in many keys. 13 and 15 kg/mm^2: higher than commonly cited historical practice.

Common Pitfalls:

Confusing tons/in^2 with MPa directly; mixing up conversion factors and units (kg/mm^2 vs MPa).

Final Answer:

10 kg/mm^2