AMS 6308 Bars, AMS 6308 Rods & AMS 6308 Rings

Product Description

AMS 6308 is an aerospace-grade, high-performance, low-alloy carburizing steel specification established by SAE International. It is commercially known as Pyrowear 53 (UNS K71040) and is produced via premium double-vacuum or triple-vacuum melting processestypically Vacuum Induction Melting followed by Vacuum Arc Remelted (VIM-VAR or VIM-VAR-VAR) or Electroslag Remelted (ESR)to achieve maximum micro-cleanliness, tight chemical control, and high fatigue resistance.

Below is an engineering breakdown of AMS 6308 in its standard supply forms: Bars, Rods, and Rings.

1. Material Properties & Characteristics

AMS 6308 is specifically engineered for components that operate under extreme cyclic loads and high temperatures.

• High Temper Resistance: Unlike standard carburizing steels (such as AISI 9310 or 8620) which soften dramatically above $300^\circ\text{F}$ ($149^\circ\text{C}$), AMS 6308 maintains its surface hot hardness and core fracture toughness at elevated service temperatures up to $450^\circ\text{F}$ ($232^\circ\text{C}$).

• Core Toughness: It features exceptionally high impact strength and fracture toughness in the core alongside high case fatigue life.

• Ultra-Clean Microstructure: Double or triple vacuum melting minimizes non-metallic inclusions, crucial for resisting subsurface-initiated rolling contact fatigue (RCF).

Nominal Chemical Composition (%)

2. Product Form Specifications

AMS 6308 Bars & Rods

Bars and rods represent the primary stock for subsequent machining, centerless grinding, or secondary forging.

• Supply Conditions: Typically supplied in the annealed, cold-finished, or hot-rolled condition, optimized for high machinability before the component undergoes the carburizing and heat-treatment cycle.

• Common Size Profiles: Standard rounds range from 1.500 to 7.000 in diameter, though smaller precision rod diameters and custom large-diameter bars are produced based on the mill run.

• Quality Controls: Subject to strict aerospace standards for decarb depth limits, surface finish, macroetch limits (per ASTM A604), and premium aircraft-quality magnetic particle inspection (AMS 2300).

AMS 6308 Rings

For seamless, high-integrity circular components, AMS 6308 is processed into forged and rolled rings.

• Manufacturing Process: Produced via seamless rolled ring forging to realign the grain flow circumferentially. This maximizes the tangential fatigue strength and structural integrity under high radial loads.

• Applications: Primarily utilized for bearing races, output shaft couplings, internal ring gears, and retaining rings.

3. Industrial Applications

AMS 6308 is selected almost exclusively for mission-critical drive systems where component failure is not an option:

• Aerospace & Rotorcraft: Main rotor transmission gearboxes, tail rotor drive gears, and planetary gear systems for helicopters and defense aircraft.

• Jet Engines: High-temperature accessory gearboxes, shafts, and bearing housings.

• High-Performance Motorsports: Heavily loaded drivetrain gears and pinions operating under thermal stress.

4. Heat Treatment & Carburizing Notes

To unlock its targeted properties, components machined from AMS 6308 stock are processed using a tailored thermochemical sequence:

1. Carburizing: Typically gas or vacuum carburized at temperatures between $1650^\circ\text{F}$ and $1750^\circ\text{F}$ ($899^\circ\text{C}$ to $954^\circ\text{C}$).

2. Core Hardening & Quenching: Often oil or gas quenched from a solution temperature to develop high core strength.

3. Sub-Zero Treatment: Deep freezing at $-100^\circ\text{F}$ to $-120^\circ\text{F}$ ($-73^\circ\text{C}$ to $-84^\circ\text{C}$) to eliminate retained austenite in the case.

4. High Tempering: Tempered at elevated temperatures (often around $400^\circ\text{F}$ to $500^\circ\text{F}$ / $204^\circ\text{C}$ to $260^\circ\text{C}$) to match its inherent high temper resistance, yielding a typical case hardness of 6064 HRC with superb core fatigue limits.