BMS-7-182 TYPE 2 Round Bar, BMS-7-182 TYPE 2 Alloy Steel Rods, Bars(Nickel Cobalt Aircraft Armour)

Product Description

BMS-7-182 Type 2 is a rigorous proprietary material specification established by The Boeing Company for an ultra-high-strength, premium aerospace alloy steel. It designates the highly specialized HP 9-4-30 chemistry (commercially known as Lescalloy HP 9-4-30 Vac-Arc; UNS K91283 / K91313).

This grade is heavily cross-referenced with general aerospace standards like AMS 6526 and AMS 6524, as well as legacy defense standards like McDonnell Douglas's MM-S-2102. Type 2 stock is engineered specifically for deep through-hardening, exceptional fatigue performance, and explosive shock absorption, making it a premier choice for aircraft structural components and military ballistic shielding (aircraft armor).

1. Core Metallurgy & Chemistry

The design philosophy behind BMS-7-182 Type 2 relies on a high-nickel, cobalt-stabilized formulation.

• 9% Nickel (Ni): Infuses the alloy with incredible structural matrix stability and high plane-strain fracture toughness ($K_{Ic}$), preventing structural breakdown under intense ballistic shock or sub-zero flight conditions.

• 4% Cobalt (Co): Accelerates the alloy's response to heat treatment, limits the formation of brittle retained austenite, and prevents softening when tempered at high temperatures.

• Vacuum Melting (VIM-VAR): Stock supplied to this specification must be produced via Vacuum Induction Melting followed by Vacuum Arc Remelting to eliminate microscopic trace impurities (like sulfur and phosphorus) that degrade fatigue life.

Nominal Chemical Composition (%)

2. Supply Profiles: Round Bars, Rods & Bars

When sourced to Boeing BMS-7-182 Type 2 standards, bar products are conditioned to withstand extensive machining and strict defense quality control gates:

• Delivery State: Most commonly stocked and delivered in the Normalized & Tempered (N&T) or sub-critically annealed state. This ensures a balanced hardness level (typically around 311352 HBW) optimized for clean band-saw cutting, turning, and multi-axis milling before final hardening.

• Dimensions: Round bars and rods are typically processed in size ranges from 10 mm precision rods up to 300 mm heavy-gauge structural forgings.

• Surface Finishes: Available as hot-rolled, centerless peeled, cold-drawn, or proof-machined bright bars.

• Non-Destructive Testing (NDT): Materials are subject to strict flight-safety sonic inspections, typically meeting MIL-STD-2154 Class A to guarantee absolute structural density and zero subsurface internal voids.

3. High-Performance Mechanics & Workability

The defining characteristic of BMS-7-182 Type 2 is its capability to achieve extreme tensile thresholds without displaying the characteristic brittleness of conventional high-strength steels (like AISI 4340).

Mechanical Properties (Post Heat Treatment)

• Ultimate Tensile Strength (UTS): 220,000 240,000 psi (1517 1655 MPa)

• Minimum Yield Strength: 200,000 psi (1379 MPa)

• Fracture Toughness ($K_{Ic}$): An exceptional 130 ksiin ($143\text{ MPa}\sqrt{\text{m}}$) at full tensile yield.

• Weldability: Highly weldable compared to other 220+ ksi steels. It can be clean TIG welded using a matching HP 9-4-30 composition filler wire under an inert gas shield, requiring post-weld tempering to homogenize structural integrity.

4. Key Strategic Applications

Thanks to its elite energy-absorption capabilities and deep through-hardening traits, BMS-7-182 Type 2 is deployed in hyper-critical areas:

• Aircraft Ballistic Defenses: Heavy-gauge machined bulkheads, cockpit armor assemblies, and shielding plates designed to suppress explosive fragmentation.

• Structural Flight Components: Main landing gear truck beams, wing-to-fuselage attachment joints, primary torque shafts, and engine mount adapters.

• Aerospace & Defense Pressure Cells: Deep-space missile fairing attachment rings, heavy-duty actuator housings, and rocket motor casings.