Soaking pits (lower courses): to withstand attack by molten slag and scale, the lower wall courses of soaking pits are constructed with which type of refractory bricks?

Introduction / Context:
Soaking pits reheat steel ingots before rolling. The lower wall courses face intense chemical and thermal attack from molten slag and iron scale. Selecting the correct refractory chemistry here has a major impact on pit life and maintenance intervals.

Given Data / Assumptions:

• Environment is rich in basic slags and iron oxide scale at high temperature.
• Compatibility between slag chemistry and lining chemistry reduces corrosion and dissolution.

Concept / Approach:
Under basic slag conditions, basic refractories such as magnesite (MgO) and chrome-magnesite (Cr2O3–MgO) exhibit superior chemical resistance, limiting reaction and washout. Acidic refractories like silica or standard fireclay tend to react with basic slags and iron oxide, leading to premature wear. Silicon carbide has excellent thermal-shock resistance but is not the standard choice for this specific chemical environment in lower courses of soaking pits.

Step-by-Step Solution:
Identify slag chemistry: predominantly basic.Match with basic refractories for chemical compatibility.Chrome or magnesite bricks meet this requirement; select them.

Verification / Alternative check:
Steel plant lining practices and handbooks specify chrome–magnesite or magnesia-based materials in hot zones exposed to basic slags, corroborating this selection.

Why Other Options Are Wrong:

• Silica/fireclay: acidic; prone to chemical attack by basic slags.
• Silicon carbide: valued for thermal shock, but not the conventional choice for this pit zone.
• High-alumina: more neutral, but chrome/magnesite show better resistance to highly basic slags and FeO-rich conditions.

Common Pitfalls:
Choosing by temperature rating alone while ignoring slag chemistry; overlooking that corrosion dominates failure in these zones.

Final Answer:
Chrome or magnesite bricks