Mould Steel Sheets and Plates: AISI 4340 High Strength Low Alloy Steel

1. Overview of AISI 4340 Steel

AISI 4340 is a premium high-strength low alloy steel renowned for its exceptional combination of toughness, fatigue resistance, and high tensile strength. It belongs to the chromium-nickel-molybdenum (Cr-Ni-Mo) alloy family, making it ideal for demanding applications such as molds, aerospace components, and heavy-duty machinery.

 

ASTM Standards:

AISI 4340 is covered under ASTM A29/A29M (general requirements for carbon and alloy steel bars) and ASTM A519 (mechanical tubing).

Key Properties:

High hardenability, excellent wear resistance, and superior performance under cyclic loading.

2. Chemical Composition (Weight %, AISI 4340)

Element	Content Range	Role
Carbon (C)	0.38–0.43	Provides hardness and strength when heat-treated.
Manganese (Mn)	0.60–0.80	Improves hardenability and acts as a deoxidizer.
Nickel (Ni)	1.65–2.00	Enhances toughness and corrosion resistance.
Chromium (Cr)	0.70–0.90	Improves hardness, wear resistance, and hardenability.
Molybdenum (Mo)	0.20–0.30	Prevents temper brittleness and boosts creep resistance.
Silicon (Si)	0.15–0.35	Improves resistance to oxidation and strengthens the matrix.
Sulfur (S)	≤0.040	Controlled to minimize hot cracking during machining.
Phosphorus (P)	≤0.035	Reduces brittleness and improves impact resistance.

 

 

Heat Treatment Notes:

Quenching: Typically in oil at 845–870°C, followed by tempering at 480–650°C to balance hardness and toughness.

Case Hardening: Optional for surface wear resistance (e.g., nitriding or carburizing).

 

 

 

 

 

 

 

 

 

 

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