AISI SAE 5120 Alloy Steel Bar 5120 Round Bars 5120 Rods

Product Description

AISI SAE 5120 is an American standard low-carbon, low-alloy chromium steel specifically engineered for case hardening (carburizing).

With a low base carbon content and targeted Chromium (~0.80%) additions, it offers an optimal balance of structural ductility and deep hardenability. AISI 5120 round bars, rods, and stock are highly favored in mass-production automotive and machinery manufacturing pipelines because they possess excellent cold-forming characteristics, crisp machinability in the annealed state, and develop a highly wear-resistant outer shell after heat treatment.

Technical Specifications & Chemical Composition

The primary alloying engine in 5120 is Chromium, which improves response to heat treatment, depth of hardness penetration, and resistance to surface abrasion.

Chemical Composition (Weight % per AISI/SAE)

Mechanical Properties (Core vs. Case Boundaries)

When heat-treated, AISI 5120 yields a dual-phase microstructure. The case gains a high-carbon, high-hardness martensitic structure to combat wear, while the low-carbon inner core remains highly structural and fracture-resistant.

Typical Core Mechanical Properties (Post-Quench & Temper)

Global Cross-Reference Equivalents

Because industrial components are sourced and designed worldwide, AISI 5120 aligns closely with these major international material standards:

• Europe (EN / DIN): 20Cr4 (1.7027) or 17Cr3 (1.7016)

• Japan (JIS): SCr420 / SCr420H

• China (GB/T): 20Cr

• United Kingdom (BS): 523M20

• Russia (GOST): 20X

Heat Treatment Parameters

• Forging / Hot Working: 1150°C – 850°C

• Normalizing: 870°C – 920°C (Air cool to normalize internal grain stresses)

• Pseudo-Annealing: 650°C – 700°C (Slow furnace cool to maximize drilling or milling speed)

• Carburizing Temperature: 900°C – 950°C (Introduced into gas or pack media to enrich the surface layer)

• Core Hardening Quench: 860°C – 900°C (Oil or modern polymer bath quench)

• Case Hardening Quench: 780°C – 820°C (Optimizes surface layer conversion to sharp martensite)

• Stress-Relieving Temper: 150°C – 200°C (Maintains maximum surface HRC while lowering brittle stress risks)

Primary Applications of AISI 5120 Round Bars

5120 round bars and rods are optimized for small-to-medium structural components that experience constant friction, moderate impact forces, or high localized contact pressure.

• Automotive Transmissions: Small gear wheels, pinion gears, manual gearbox selector forks, and splined drive shafts.

• Fastener Components: Case-hardened wrist pins, heavy-duty shackle pins, steering knuckles, and link studs.

• General Engineering: Camshaft components, indexing shafts, wear sleeves, and small-diameter industrial rollers.

• Power Tools: Internal drive gears and armature pinions for pneumatic or electric drills and impact wrenches.

Weldability Constraints: AISI 5120 is not recommended for standard structural welding. The carbon migration occurring during carburization, combined with chromium, creates highly brittle heat-affected zones (HAZ) that are very susceptible to immediate cracking. If welding is required, it must be performed on the raw base metal before the case-hardening steps take place.