4320 Alloy Steel-ASTM A29

4320 steel is an alloy carburizing steel containing at least 1.65% nickel,0.4% chromium，0.2% molybdenum as per American standard ASTM A29.

As a commonly used alloy carburizing steel, the surface of 4320 steel has a fairly high hardness, wear resistance and contact fatigue strength after carburizing treatment,while retaining good core toughness and impact load resistance.

4320 steel can be used as surface-strengthened carburizing steel for carburizing gears, carburizing bearings, etc. It can also be used for parts that require wear resistance and impact resistance.

4320 STEEL CHEMICAL COMPOSITION

Grade	C	Si	Mn	P	S	Cr	Ni	Mo
4320	0.17-0.22	0.15-0.35	0.45-0.65	≤0.035	≤0.04	0.4-0.6	1.65-2.00	0.2-0.3

4320 STEEL RELATED STANDARD & EQUIVALENT GRADE

China: 20CrNi2MoA

Japan:SNCM420

4320 STEEL FORGING

Initial Forging Temperature：1150-1200℃
Final Forging Temperature：>800℃
Forging Ratio：above 4:1
Cooling Method After Forged:In order to eliminate the internal stress generated during forging and taking into account the subsequent carburizing and quenching & tempering heat treatment, 4320 steel is usually annealed after forging.

4320 STEEL HEAT TREATMENT

Temperature Selection for Different Types of Heat treatment for 4320 steel

Normalizing: 890 – 910°C,Cooling in air.
Annealing:840 – 860°C,Cooling in furnace,hardness below 197HBW
Carburizing:920-940°C
Quenching:840 – 860°C,air/oil quench
Tempering:190-210°C

4320 Steel Normalizing Diagram

4320 Steel Annealing Diagram

4320 Mechanical Properties in Normalized and Annealed Condition

Condition	Tensile Strength	Yield Strength	Elongation	Reduction of Area	Impact Charpy-V,+21°C	Hardness
Normalized(+N)	795Mpa	465Mpa	20.8%	51%	73J	235HBW
Annealed(+A)	580Mpa	425Mpa	29%	58%	110J	163HBW