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


NACE MR0175/ISO 15156-3 sections A.2.1, A.3.1, and A.6.1 each forbid the use of their respective steels in “free-machining” grades. However, this requirement is notably lacking in section A.5.1 regarding ferritic stainless steels. Can I rightfully construe that there is no mistake here, and that free-machining ferritic stainless grades are therefore allowed under the conditions of Table A.17?


Even though not specifically stated in the current standard, no free machining ferrous alloys including stainless steels are acceptable. This applies also for ferritic stainless steels.

A search through historical answers to interpretations has revealed two instances where the interpretation has been that free machining covers all ferrous alloys including stainless steels and these are unacceptable; there have been no interpretations that have permitted the use of free machining steels including ferritic stainless steels. We will investigate wording changes through ballot or editorial means to clarify this.

This question is in relation to NACE MR0175/ISO 15156-3 A.5.1

Reference: ISO 15156 Maintenance Panel Inquiry #2013-10Q2

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