Magnesite–chrome vs chrome–magnesite: which statement about magnesite chrome refractories is correct for typical steelmaking service and thermal-shock behaviour?

Introduction / Context:
Two closely related families of basic refractories are widely used in ferrous metallurgy: magnesite–chrome (magnesia-dominant with chromite) and chrome–magnesite (chromite-dominant with magnesia). Their naming reflects the major component. Distinguishing their thermal-shock (spalling) behaviour and corrosion response is important for furnace sidewalls, converter mouths, and burner blocks.

Given Data / Assumptions:

• “Magnesite chrome” = magnesia-rich composition with some chromite.
• Service includes temperature cycling and slag/oxidant exposure.
• Cold crushing strength (CCS) is normally in the hundreds to thousands of kg/cm^2 for quality bricks.

Concept / Approach:
Magnesia-rich bricks typically combine good basic slag resistance with acceptable thermal shock tolerance when properly bonded and graded. Chrome additions can improve corrosion resistance in certain oxidizing/slag conditions. The statement that magnesite–chrome bricks have better spalling resistance than the chrome–magnesite variants is a recognized generalisation in many textbook treatments, while the other statements are plainly incorrect or exaggerated.

Step-by-Step Solution:
Check (a): Magnesite–chrome often shows better spalling resistance → plausible/accepted.Check (b): “Very low thermal expansion” is false; MgO-based bricks have relatively high expansion.Check (c): Claiming “not at all resistant” to FeO corrosion is extreme and false; these bricks are used in oxidizing environments with appropriate slag control.Check (d): CCS values around 50 kg/cm^2 are unrealistically low for fired bricks; many applications use metal-cased shapes successfully.

Verification / Alternative check:
Supplier datasheets and handbooks list CCS far above 50 kg/cm^2 and document the use of magnesite–chrome in BOF/EAF sidewalls where thermal cycling occurs.

Why Other Options Are Wrong:
(b) Thermal expansion is not “very low.”(c) “Not at all resistant” is an overstatement; service life depends on slag chemistry.(d) CCS is typically much higher; metal-case forms are common.

Common Pitfalls:
Assuming naming implies identical performance; overlooking that spalling resistance depends on grain size distribution, bonding, and thermal gradients.

Final Answer:
Have better spalling resistance than chrome magnesite refractories.