What is the difference between the AISI 4145, 4330V, and 4340 Steels?

1. 4145 Steel
Chemical Composition (wt%):

Carbon (C): 0.43–0.48

Chromium (Cr): 0.80–1.10

Molybdenum (Mo): 0.15–0.25

Manganese (Mn): 0.75–1.00

Silicon (Si): 0.15–0.30

Key Feature: Lower nickel (Ni) content; no vanadium (V).

Mechanical Properties (Quenched & Tempered):

Tensile Strength: 930–1080 MPa

Yield Strength: 780–930 MPa

Elongation: ~12–15%

Impact Toughness: Moderate

Characteristics:

High fatigue strength and wear resistance (Cr-Mo synergy).

Ideal for high-stress, high-temperature applications (e.g., oil/gas drill collars).

Cost-effective (lower Ni content).

Moderate weldability (requires pre/post-heating).

2. 4330V Steel
Chemical Composition (wt%):

Carbon (C): 0.28–0.33

Nickel (Ni): 1.65–2.00

Chromium (Cr): 0.70–0.90

Molybdenum (Mo): 0.20–0.30

Vanadium (V): 0.05–0.10

Key Feature: Lower carbon; vanadium for grain refinement.

Mechanical Properties (Quenched & Tempered):

Tensile Strength: 930–1100 MPa

Yield Strength: 830–970 MPa

Elongation: ~15–18%

Impact Toughness: High

Characteristics:

Superior toughness and fatigue resistance (vanadium-enhanced).

Preferred for dynamic loads (e.g., aerospace landing gear).

Better weldability than 4340 (lower carbon).

Balanced strength-ductility for aerospace/defense.

3. 4340 Steel
Chemical Composition (wt%):

Carbon (C): 0.38–0.43

Nickel (Ni): 1.65–2.00

Chromium (Cr): 0.70–0.90

Molybdenum (Mo): 0.20–0.30

Key Feature: High Ni and C; no vanadium.

Mechanical Properties (Quenched & Tempered):

Tensile Strength: 1080–1300 MPa

Yield Strength: 930–1080 MPa

Elongation: ~12–15%

Impact Toughness: High (Ni-enhanced)

Characteristics:

Exceptional strength-to-weight ratio and fracture toughness.

Critical components (e.g., aircraft parts, crankshafts).

Prone to temper embrittlement if mishandled.

Poor weldability (strict heat treatment required).

Comparison Table AISI 4145 AISI 4330V AISI 4340

Property	4145 Steel	4330V Steel	4340 Steel
Carbon (C)	0.43–0.48 (Highest)	0.28–0.33 (Moderate)	0.38–0.43 (High)
Alloying	Cr-Mo focus; no Ni/V	Ni-Cr-Mo + V	Ni-Cr-Mo; no V
Tensile (MPa)	930–1080	930–1100	1080–1300 (Highest)
Toughness	Moderate	Best (V-enhanced)	High (Ni-enhanced)
Weldability	Moderate	Better (lower C)	Poor (high C)
Applications	Drilling tools, gears	Aerospace fasteners	Critical structural parts