SAE 4150 Steel
SAE 4150 Steel is the highest-carbon member of the 41xx chromium-molybdenum family (0.48–0.53% C), offering greater hardenability and higher achievable hardness than SAE 4140. When quenched and tempered, 4150 routinely achieves tensile strengths exceeding 220,000 psi, and through its full cross-section in sections up to approximately 2.5 inches. This capability makes it a preferred choice for heavily loaded aerospace gears, driving shafts, and precision tooling where deep, uniform hardness is essential.
The higher carbon content does reduce weldability relative to 4130/4140 — preheat of 300–400°F and post-weld heat treatment are required to prevent heat-affected zone cracking. SAE 4150 is typically supplied in the annealed or normalized condition for machining, then heat treated to final strength after roughing operations are complete.
Product Forms & Size Range of SAE 4150 Steel
SAE 4150 is primarily available as round bar and forging stock per AMS 6152, in diameters from 0.500 inch to 10.000 inches. Bar is furnished in the annealed condition for machining. Forging quality grades are available with chemistry restricted for critical aerospace applications requiring consistent through-hardness in large cross-sections.
HEAT TREATMENT OF SAE 4150 STEEL
Austenitize at 1500–1550°F (816–843°C), quench in oil, and temper at 350–1000°F (177–538°C) depending on the required strength-toughness balance. Lower tempering temperatures of 350–500°F produce the highest hardness (up to HRC 55–58) and are used for tooling and wear applications. Higher tempering temperatures of 800–1000°F produce strengths of 180,000–200,000 psi with improved fatigue resistance, suitable for aerospace structural shafts and gears under cyclic loading.
SAE 4140 Steel
Slightly lower carbon Cr-Mo alloy with better weldability and slightly lower hardness — the most common structural alloy steel for aerospace fittings.
SAE 4330 Steel
Ni-Cr-Mo-V alloy with superior toughness at equivalent strength levels — preferred for landing gear and critical structural aerospace forgings.
Certified Material for Critical Service
SAE 4150 steel for aerospace use is supplied to AMS 6152 (bars and forgings). Certified mill test reports document chemical composition and mechanical properties per heat and lot. Cleanliness requirements per AMS 2301 apply where specified for fatigue-critical applications.