8620 / 20NiCrMo2-2 / 21NiCrMo2 / 1.6523 Case-Hardening Steel
PRODUCT DESCRIPTION
8620 / 20NiCrMo2-2 / 21NiCrMo2 / 1.6523 is an alloy case-hardening steel used for gears, shafts, pins and transmission components requiring a hard wear-resistant case with a tough core.MATERIAL INFORMATION
8620 / 20NiCrMo2-2 / 21NiCrMo2 / 1.6523 Case-Hardening Steel
8620, also known as 20NiCrMo2-2 in European standards and 21NiCrMo2 in older German references, is an alloy case-hardening steel with material number 1.6523. Its low carbon content supports core toughness, while carburizing and hardening can provide a hard, wear-resistant surface.
The material is considered for gears, pinions, transmission shafts, axles, pins, bushes, connectors and other mechanical components exposed to high contact stress. Saf Çelik can evaluate hot-rolled and forged round-steel requirements between 22 mm and 820 mm according to stock and supply availability.
8620 / 1.6523: Overview
Unlike higher-carbon quenched-and-tempered steels, 8620 / 1.6523 is designed primarily for carburizing applications. The component surface is enriched with carbon during carburizing, then hardened and tempered. This process targets a hard, wear-resistant case with a tougher core that can withstand impact loading.
This behaviour is particularly valuable for gears and transmission components: the tooth surface requires wear and contact-fatigue resistance, while the core is expected to withstand shock loading without brittle failure. Final performance depends on case depth, carbon potential, component section, hardening medium, tempering and grinding quality.
Material Designations and Standards
| EN grade designation | 20NiCrMo2-2 |
| Older German designation | 21NiCrMo2 |
| Material number | 1.6523 |
| US grade designation | SAE/AISI 8620 |
| Steel group | Alloy case-hardening steel |
| Current standard references | EN ISO 683-3 and EN 10277 |
| Former standard references | EN 10084 and EN 10277-4 |
| Other international reference | JIS SNCM220 is a close international reference. |
Important: 8620, 20NiCrMo2-2, 21NiCrMo2 and 1.6523 may be discussed together in technical and commercial references. For critical components, they must not be treated as automatic certificate equivalents; the requested standard, chemical analysis, product form, carburizing procedure and EN 10204 3.1 certificate must be confirmed.
Chemical Composition
The following values show typical cast-analysis limits for 20NiCrMo2-2 / 1.6523. The supplied product certificate remains controlling.
| Element | Composition (%) |
|---|---|
| Carbon (C) | 0.17 – 0.23 |
| Silicon (Si) | 0.15 – 0.40 |
| Manganese (Mn) | 0.65 – 0.95 |
| Phosphorus (P) | 0.025 max. |
| Sulphur (S) | 0.035 max. |
| Chromium (Cr) | 0.35 – 0.70 |
| Nickel (Ni) | 0.40 – 0.70 |
| Molybdenum (Mo) | 0.15 – 0.25 |
| Copper (Cu) | 0.40 max. |
| Aluminium (Al) | 0.020 – 0.050 |
Delivery Conditions
| +A | Annealed to a maximum hardness requirement. Preferred before machining and subsequent carburizing. Reference maximum hardness is approximately 212 HBW. |
| +FP | Treated to a ferrite-pearlite structure and hardness range. A typical reference range may be approximately 149 – 194 HBW. |
| +TH | Treated to a specified hardness range. A typical reference range may be approximately 161 – 212 HBW. |
| After carburizing and hardening | A hard case and tough core are targeted. Final surface hardness, effective case depth and core properties must be defined by the project specification. |
Heat Treatment and Carburizing Information
- Hot forging: approximately 900 – 1150 °C
- Normalizing: approximately 850 – 880 °C
- Soft annealing: approximately 650 – 700 °C
- Carburizing: approximately 880 – 980 °C
- Core hardening: approximately 860 – 900 °C
- Post-carburizing hardening: approximately 780 – 820 °C
- Tempering: approximately 150 – 200 °C
These temperatures are general technical references. The final case depth, surface hardness, core strength and distortion tolerance must be established by a qualified heat-treatment provider according to component geometry, loading and project specification.
Machinability
8620 / 1.6523 offers good machinability in an annealed or suitable delivery condition before carburizing. Turning, milling, drilling and gear cutting are generally performed before carburizing. Final tolerances after hardening can be achieved through grinding, honing or other suitable finishing processes.
Potential distortion from carburizing and hardening should be considered during the design stage for precision gears and bearing surfaces. Tooling must be selected according to delivery condition, section size, hardness and required surface quality.
Weldability
Due to its low-carbon core composition, 8620 / 1.6523 may offer better weldability than high-carbon bearing or spring steels. However, welding can alter the local carburizing and hardening response. Critical components must not be welded without an approved welding procedure, assessment of any required preheating and post-weld treatment.
Welding of carburized or final heat-treated components is generally not preferred because it can impair both the hard case and the required core properties.
Typical Applications
- Gears, pinions, crown wheels and transmission components
- Shafts, axles, pins and connectors
- Automotive transmission and drivetrain components
- Machinery and heavy-equipment parts
- Bushes and bearing components requiring carburized wear resistance
- Aerospace and defence applications only under the applicable technical specification
Key Advantages of 8620 / 1.6523
- Ability to achieve a hard, wear-resistant case after carburizing
- Core-toughness advantage provided by the low-carbon base composition
- Balance of surface hardness and core strength for gears and transmission components
- Suitable machinability before carburizing
- Widely used technical reference for automotive, machinery and power-transmission applications
Quotation and Technical Information
Please state the requested grade clearly in your enquiry: 8620, 20NiCrMo2-2, 21NiCrMo2 or 1.6523. Product form, diameter or section dimensions, length, delivery condition, required case depth, target surface hardness, quantity and certificate requirements should also be provided.