1. Scope
1.1 The purpose of this test method is to allow detection of the presence of detrimental chromium-containing phases in selected lean duplex stainless steels to the extent that toughness or corrosion resistance is affected significantly. This test method will not necessarily detect losses of toughness or corrosion resistance attributable to other causes. 1.2 Lean duplex (austenitic-ferritic) stainless steel is not a well-defined alloy category. For this test method to be considered applicable for a given alloy, the alloy has to be listed in Table 1. Typically, lean duplex stainless steels will have molybdenum contents below 1 %. Similar test methods for some higher alloyed duplex stainless steels are described in Test Methods A923, but the procedures described in this test method differs significantly for all three methods from the ones described in Test Methods A923. 1.3 Lean duplex stainless steels are susceptible to the formation of detrimental chromium-containing compounds such as nitrides and carbides and other undesirable phases during exposures in the temperature range from approximately 300 to 955C (570 to 1750F). The speed of these precipitation reactions is a function of composition and the thermal or thermo-mechanical history of each individual piece. The presence of an amount of these phases can be detrimental to toughness and corrosion resistance. 1.4 Correct heat treatment of lean duplex stainless steels can eliminate or reduce the amount and alter the characteristics of these detrimental phases as well as the composition of the matrix phase in the immediate vicinity of these phases. Adequately rapid cooling of the product from a suitable annealing temperature provides the maximum resistance to formation of detrimental phases by subsequent thermal exposures. 1.5 Compliance with the chemical and mechanical requirements for the applicable product specification does not necessarily indicate the absence of detrimental phases in the product. 1.6 This test method includes the following: 1.6.1 Test Method A-Etch Method for detecting the presence of potentially detrimental phases in Lean Duplex Stainless Steels; 1.6.2 Test Method B-Charpy Impact Test for determining the presence of detrimental phases in Lean Duplex Stainless Steels; 1.6.3 Test Method C-Inhibited Ferric Chloride Corrosion Test for determining the presence of detrimental phases in Lean Duplex Stainless Steels; and 1.6.4 Examples of the correlation of thermal exposures, the occurrence of detrimental phases, and the degradation of toughness and corrosion resistance are given in Appendix X1, Appendix X2, and the References. 1.7 Guidelines for the required data needed for Subcommittee A01.14 to consider listing a duplex stainless steel as a lean duplex stainless steel in this test method are given in Annex A1. 1.8 The values stated in SI units are to be regarded as the standard. The values given in parentheses are mathematical conversions to other units that are provided for information only and are not considered standard. 1.9 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.
There are no existing methods for this class of materials and the industry erroneously uses Test Methods A923, which creates confusion and wastes resources.
Keywords
lean duplex; duplex stainless steel; stainless steel; detrimental phases; secondary phases; acceptance testing; ferric chloride testing; inhibited ferric chloride; impact toughness testing; microstructure evaluation; etch methods
The title and scope are in draft form and are under development within this ASTM Committee.
Citing ASTM Standards
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