ASTM A638 660 Type 1 Round ASTM A638 660 Type 2 Bars

Product Description

ASTM A638 Grade 660 (commonly known as Alloy A286 or UNS S66286) is an iron-base, precipitation-hardening austenitic superalloy designed for high-temperature service (up to 1300°F / 704°C). It balances excellent high-temperature tensile strength, creep resistance, and oxidation resistance with comparable thermal expansion coefficients to standard austenitic stainless steels.

While the base chemical composition of Grade 660 remains identical for both types, the crucial distinction between Type 1 and Type 2 round bars lies in their heat treatment parameters, which adapt the material's microstructural stability and mechanical behavior for specific industrial environments.

Heat Treatment Specifications

The mechanical properties of ASTM A638 bars are developed via a two-stage process consisting of a solution treatment followed by a precipitation hardening (aging) treatment:

Core Distinctions & Applications

• Type 1 (Lower Solution Temperature): Processing at $1650^\circ\text{F}$ results in a finer grain structure. This variant optimizes short-time mechanical properties, prioritizing higher room-temperature tensile strength, yield strength, and superior fatigue life. It is highly favored for cryogenic structural applications up to moderate high-temperatures.

• Type 2 (Higher Solution Temperature): By dissolving more secondary phases during the $1800^\circ\text{F}$ solution soak, Type 2 promotes a slightly larger grain size. This provides superior creep-rupture strength and enhanced long-term microstructural stability when continuously subjected to extreme stress at elevated operating temperatures.

Typical Applications

• Fasteners & Hardware: Heavy-duty clamping hardware, high-temperature stud bolts, and engine flanging.

• Energy & Power Generation: Components for gas turbines, steam boilers, rotors, and pressure vessels.

• Oil & Gas / Aerospace: Downhole tooling, valve components, exhaust systems, and afterburner parts.