FAQ's

Are free-machining ferritic stainless steels allowed in NACE MR0175?

Can Free-Machining Grades Be Used in Ferritic Stainless Steels Under NACE MR0175/ISO 15156-3?

Introduction

This page addresses a common question regarding the use of free-machining grades in ferritic stainless steels under NACE MR0175/ISO 15156-3. The inquiry points out that sections A.2.1, A.3.1, and A.6.1 specifically forbid the use of free-machining grades in their respective steels, but there is no such requirement in section A.5.1 for ferritic stainless steels. The inquiry seeks clarification on whether free-machining ferritic stainless grades are allowed under the conditions of Table A.17.

The Answer

The answer to this question is no. Even though the current standard does not specifically mention it, no free machining ferrous alloys, including stainless steels or ferritic stainless steels, are acceptable. It is noted that past interpretations have also deemed free machining steels as unacceptable, and there have been no interpretations permitting their use. The standard may undergo wording changes to clarify this through ballot or editorial means.

Conclusion

This question pertains to NACE MR0175/ISO 15156-3 A.5.1, and the reference cited is ISO 15156 Maintenance Panel Inquiry #2013-10Q2. It is important to note that free-machining grades should not be used in ferritic stainless steels under any circumstances, as they do not meet the standards set forth by NACE MR0175/ISO 15156-3.

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