Castings

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GGG -DUCTILE IRON
EN 1563 1997-08	Rm N/mm² min	Rp 02 N/mm² min	A5 %	HARDNESS HB	MICRO – STRUCTURE
EN-GJS-400-15	400	250	15	130 – 180	Ferrite
EN-GJS-400-18 LT	400	240	18	120 – 180	Ferrite
EN-GJS-400-18 RT	400	250	18	120 – 180	Ferrite
EN-GJS-500-7	500	320	7	170 – 220	Ferrite / Pearlite
EN-GJS-600-3	600	370	3	200 – 250	Pearlite / Ferrite

Overview of Steel Castings

Steel castings are metal components produced by pouring molten steel into a mold, where it solidifies into a desired shape. This process is used when cast iron lacks sufficient strength or shock resistance, making steel castings ideal for high-stress applications. Steel has a higher melting point (around 1450–1650°C) and greater shrinkage than iron, requiring careful mold design with larger risers to compensate for contraction during cooling. Castings often need post-processing like machining for precise tolerances and surface finish.

Advantages:

• Produces complex, intricate shapes in near-net form with fewer steps.
• High structural strength and durability.
• Recyclable (many foundries use scrap steel).
• Versatile for large parts weighing up to hundreds of tons.

Common Applications:

• Hydroelectric turbine wheels, gears, valve bodies, pump casings.
• Mining machinery, railroad truck frames, marine equipment, engine blocks.
• Heavy trucks, construction equipment, forging presses.

Here are examples of the steel casting process in a foundry, showing molten steel being poured:

Types of Steel Castings

Steel castings are primarily classified by chemical composition:

1. Carbon Steel Castings:

• Based on carbon content: Low (soft, ductile), Medium (balanced strength/toughness), High (hard but brittle).
• Most common and cost-effective.
• Used for general-purpose parts like train wheels, hammer frames, valves.

1. Low-Alloy Steel Castings (<8% alloying elements):

• Similar to carbon steel but with improved hardenability and strength.
• Elements like manganese, chromium, or nickel added.

1. High-Alloy Steel Castings (≥8% alloying elements):

• Designed for specific properties: corrosion resistance (e.g., stainless steel), heat resistance, wear resistance.
• Examples: Stainless steel (chromium-nickel), manganese steel (for impact resistance).

Here are visual examples of various steel casting parts:

Casting Technologies and Processes for Steel

Several technologies are used for steel castings, each suited to different scales, complexities, and costs:

• Sand Casting: Most common for steel. Uses disposable sand molds. Versatile for large/complex parts, cost-effective, but rougher surface finish.
• Investment Casting (Lost-Wax): High precision, excellent surface finish. Ideal for intricate parts like turbine blades. More expensive, used for smaller components.
• Die Casting: High-pressure injection into reusable steel dies. Typically for lower-melting metals, but cold-chamber variants can handle steel alloys. Fast for high-volume production.
• Centrifugal Casting: Rotates mold to force metal outward. Good for cylindrical parts with high density.
• Continuous Casting: For semi-finished products (slabs, billets). Efficient for mass production of raw steel shapes.
• Other: Permanent mold (reusable metal molds), shell molding.

Diagrams comparing sand casting (left) and investment casting (right) processes:

Modern advancements include simulation software for defect prediction, recycling of scrap, and hybrid processes for better quality. Steel casting remains essential in industries requiring robust, custom-shaped components.