Alloy AISI 8620 20NiCrMo2-2 1.6523 SNCM220 Case Hardening Steel

Product Overview

ASTM 8620 is a low-carbon alloy steel optimized for carburizing processes. Its carbon content ranges from 0.18% to 0.23%, balancing excellent weldability with a robust carburizing response. The addition of nickel, chromium, and molybdenum enhances three critical properties:

• Hardenability: Enables deep, uniform hardness penetration even in thick-section components.

• Fatigue resistance: Withstands repeated load cycles without premature failure.

• Impact toughness: The tough core absorbs shocks and prevents cracking under high-stress conditions.

After carburizing, quenching, and tempering, AISI 8620 achieves a surface hardness of 58–62 HRC (ideal for wear resistance) and a core hardness of 28–32 HRC (for impact absorption). This dual performance makes it irreplaceable for high-contact, high-load parts like transmission gears, crankshafts, and heavy-duty fasteners.

Equivalent grades with chemical compositions and mechanical properties highly similar to AISI 8620 can be found in various national standards, such as 20NiCrMo2-2 / 1.6523 from European standard EN 10084 and ISO 683-11, SNCM220 from Japanese standard JIS G4105, 20CrNiMo from Chinese standard GB/T3077, 805M20 from British standard BS970.

Country	USA	Europe	China	British	Japan
Standard	ASTM A29	EN10084	GB/T3077	BS970	JIS G4105
Grade	8620	20NiCrMo2-2/1.6523	20CrNiMo	805M20	SNCM220

Key Product Features

Chemical Composition of 8620 Steel

The precise chemical makeup of AISI 8620 and its equivalents ensures consistent performance across batches. Minor variations align with regional standard requirements:

Grade	C	Si	Mn	P	S	Cr	Mo	Ni
8620	0.18-0.23	0.15-0.35	0.70-0.90	0.035Max	0.040Max	0.40-0.60	0.15-0.25	0.40-0.70
20NiCrMo2-2/ 1.6523	0.17-0.23	0.40Max	0.65-0.95	0.025Max	0.035Max	0.35-0.70	0.15-0.25	0.40-0.70
20CrNiMo	0.17-0.23	0.17-0.37	0.60-0.95	0.030Max	0.030Max	0.40-0.70	0.20-0.30	0.35-0.75
805M20	0.17-0.23	/	0.60-0.95	0.035Max	0.035Max	0.35-0.65	0.15-0.25	0.35-0.75
SNCM220	0.17-0.23	0.15-0.35	0.60-0.90	0.030Max	0.030Max	0.40-0.65	0.15-0.30	0.40-0.70

Mechanical Properties

Steel grades 20NiCrMo2-2 according to minimum tensile strength as a function of diameter after hardening and tempering at 200℃ according to EN10084.

Size range	Tensile strength
d≤16	1100Mpa Min
16＜d≤40	700Mpa Min
40＜d≤100	500Mpa Min

Mechanical properties for reference test bar in the simulated case-hardening condition according to ISO 683-11-1987.

Size range	Tensile strength	Yield strength	Alongation	Impact value At RT/J
d=16	810-1160Mpa	560Mpa Min	9% Min	25J Min
d=30	730-1080Mpa	510Mpa Min	10% Min	30J Min
d=63	660-1010Mpa	470Mpa Min	11% Min	30J Min

Sampling and preparation of test pieces for 20NiCrMo2-2 case-hardening steel.

1): According to EN10084, all samples shall be taken at a distance of 1/4 of the diameter or thickness below the heat-treated surface.

2): As stipulated in the contract between buyer and seller.

Surface Hardness & Hardenability

1. Surface Hardness by Heat Treatment Process

Heat Treatment	Hardness
Treated to improve shearability (+S)	HB255Max
Soft annealed (+A)	HB212Max
Treated to hardness range(+TH)	161-212HBW
Treated to ferrite-pearlite structure and hardness range(+FP)	149-194HBW

2. End-Quench Hardenability

Hardenability is classified by +H (normal), +HH (high), and +HL (low) requirements, with Rockwell C hardness values varying by distance from the quenched end:

• +H Grade: Hardness ranges from 41–49 HRC at 1.5mm, decreasing to 23 HRC at 40mm.

• +HH Grade: Ensures higher minimum hardness (44 HRC at 1.5mm) for strict performance applications.

• +HL Grade: Offers lower maximum hardness (46 HRC at 1.5mm) for components requiring controlled ductility.

Distance in mm from quenched end
Distance		1.5	3	5	7	9	11	13	15	20	25	30	35	40
Hardness In HRC + H	max	49	48	45	42	36	33	31	30	27	25	24	24	23
	min	41	37	31	25	22	20	/	/	/	/	/	/	/
Hardness In HRC + HH	max	49	48	45	42	36	33	31	30	27	25	24	24	23
	min	44	41	36	31	27	24	22	21	/	/	/	/	/
Hardness In HRC + HL	max	46	44	40	36	31	29	27	26	23	21	20	20	/
	min	41	37	31	25	22	20	/	/	/	/	/	/	/

Scatter bands for the Rockwell - C hardness in the end quench hardenability test.

Supply Size & Tolerance & Stock Size

Product Size Range

Product type	Size range	Length
Hot rolled bar	Φ8-Φ270mm	6000-9000mm
Hot forged bar	Φ100-Φ1200mm	3000-5800mm
Hot rolled plate/sheet	T:20-120mm; W:1500-2500mm	2000-5800mm
Hot Forged block	T: 80-800mm; W: 100-2500mm	2000-5800mm

Surface Finish & Tolerance

Surface Finish	Turned	Milled	Grinding(Best)	Polished(Best)	Peeled(Best)	Black Forged	Black Rolled
Tolerance	+0/+3mm	+0/+3mm	+0/+0.05mm	+0/+0.05mm	+0/+0.1mm	+0/+5mm	+0/+1mm
Straighness	1mm/1000mm max.					3mm/1000mm max.

Stock Size

Qilu steel stock hot rolled bar and forged bars more than ten thousands tons every month, below our our stock size.

Stock diameter for hot rolled bar

8	10	12	14	16	18	20	22	25	26	28	30	32	35	36
38	40	42	45	50	55	60	65	70	75	80	85	90	95	100
105	110	115	120	125	130	135	140	145	150	160	170	180	185	190
200	210	220	230	240	250	260	270

Since the stocks change everyday, if you want to know our stock available information, please contact our salesman.

Forging & Heat Treatment Guidelines

1. Forging Process

• Heat 20NiCrMo2-2 ingots to 1150–1200℃ in a furnace.

• Forge the ingot at a minimum temperature of 850℃ to avoid cracking.

• Cool the forged component in air to retain structural integrity.

2. Heat Treatment Process

Process Step	Temperature Range	Holding & Cooling Method
Soft Annealing	820–850℃	Furnace/air cooling
Normalizing	880–920℃	Air cooling
End quench test Austenitizing temperature	920℃	/
Carburizing	880–980℃	/
Core Hardening	860–900℃	/
Case Hardening	780–820℃	/
Quenching & Tempering	850–880℃ (quench) → 150–200℃ (temper)	Water/oil quench → air cooling after tempering

Note: Lower temperatures in the range are recommended for water quenching, while upper temperatures suit oil quenching.

Weldability of AISI 8620 Steel

AISI 8620 boasts excellent weldability, thanks to its low carbon content (0.18–0.23%, below the 0.25% threshold that impairs weldability). For most applications:

• No pre-heating is required for thin-section components.

• For thick plates (>50mm), pre-heating to 150–200℃ prevents weld cracking.

• Post-weld tempering at 200–300℃ restores ductility in critical joints.

The Ni-Cr-Mo alloy system ensures deep hardenability, so even large components (e.g., Φ1200mm forged bars) maintain consistent properties across their cross-sections.

Application Scenarios

AISI 8620 is the material of choice for components that demand a combination of wear resistance, strength, and toughness:

Gear Manufacturing

• Automotive: Transmission gears, differential gears, and clutch hubs.

• Industrial Machinery: Low-to-medium speed gears for crushers, conveyors, and presses.

• Wind Power: Gearbox gears that withstand cyclic loads and outdoor environmental conditions.

Shaft & Rotating Components

• Transmission shafts for heavy trucks and construction equipment.

• Crankshafts for diesel engines, balancing lightweight design with high durability.

High-Strength Fasteners

Bolts, nuts, and studs for automotive chassis and heavy machinery frames.

Tools & Molds

Cold work molds (stamping dies, blanking tools) with carburized wear-resistant surfaces.

FAQ

Q1: What is the surface hardness of AISI 8620 after carburizing?

A1: After proper carburizing, quenching, and tempering, the surface hardness ranges from 58–62 HRC, while the core remains tough at 28–32 HRC.

Q2: How does AISI 8620 differ from standard carbon steel (e.g., AISI 1020)?

A2: AISI 8620 is an alloy steel with Ni, Cr, and Mo additions, offering superior hardenability, fatigue resistance, and wear performance compared to low-carbon steels like AISI 1020.

Q3: What are the common machining practices for AISI 8620?

A3: AISI 8620 is machinable in its annealed state (HB ≤ 212). Use high-speed steel (HSS) or carbide tools; coolant is recommended to reduce tool wear during heavy cutting.

Q4: Can AISI 8620 replace 4140 steel in any applications?

A4: AISI 8620 is ideal for carburized wear-resistant parts, while 4140 is a medium-carbon alloy steel for direct hardening. AISI 8620 can replace 4140 in low-load wear applications but not in high-strength direct-hardened components.

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