ASTM F256

This specification covers two chromium-iron alloys, one is UNS K91800 with nominally 18% chromium, balance iron, and the other is UNS K92801 with nominally 28% chromium, both in strip, bar, wire, and rod forms intended primarily for sealing to glass in electronic applications. The alloys are classified by nominal chemical composition, specifically by chromium content, in two types: Type I (UNS K91800) and Type II (UNS K92801). The materials shall show no evidence of transformation to martensite. For Type I alloy, the austenite formed during heat treating will transform to martensite at or above room temperature. The presence of austenite, as may be noted in Type II alloy, is acceptable if the thermal expansion requirement is met. Different tests shall be performed in order to determine the following properties of the alloys: thermal expansion, Rockwell hardness, and tensile strength.

This abstract is a brief summary of the referenced standard. It is informational only and not an official part of the standard; the full text of the standard itself must be referred to for its use and application. ASTM does not give any warranty express or implied or make any representation that the contents of this abstract are accurate, complete or up to date.

1. Scope

1.1 This specification covers two chromium-iron alloys, the former, (UNS K91800), nominally 18 % chromium, balance iron, the latter, (UNS K92801), nominally 28 % chromium, in strip, bar, wire, and rod forms intended primarily for sealing to glass in electronic applications.

Note 1—UNS K92801 should only be considered for use at service temperatures below 300°C. The alloy is prone to sigma phase formation at temperatures close to 620°C, and exhibits brittle mechanical behavior after prolonged exposures at temperatures close to 475°C.

1.2 The values stated in inch-pound units are to be regarded as the standard. The values given in parentheses are for information only.

1.3 The following hazard caveat pertains only to the test method portion, Sections 16 and 17, of this specification. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

2. Referenced Documents

ASTM Standards
A370 Test Methods and Definitions for Mechanical Testing of Steel Products
E18 Test Methods for Rockwell Hardness and Rockwell Superficial Hardness of Metallic Materials
E228 Test Method for Linear Thermal Expansion of Solid Materials with a Vitreous Silica Dilatometer
E29 Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
E3 Methods of Preparation of Metallographic Specimens
E38 Methods for Chemical Analysis of Nickel-Chromium and Nickel-Chromium-Iron Alloys
F14 Practice for Making and Testing Reference Glass-Metal Bead-Seal
F140 Practice for Making Reference Glass-Metal Butt Seals and Testing for Expansion Characteristics by Polarimetric Methods
F144 Practice for Making Reference Glass-Metal Sandwich Seal and Testing for Expansion Characteristics by Polarimetric Methods

Index Terms

glass-to-metal sealing; iron-chromium alloys; UNS K91800; UNS K; ICS Number Code 2801; 21.140 (Seals, glands)

Citing ASTM Standards

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