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Posted by suresh kanoje on January 22, 2003 at 12:13:08:

In Reply to: Re: Formation of the Compound Zone posted by M.A.K. Babi on August 02, 2001 at 12:40:58:

: : What are the mechanics of the formation of the compound zone? In other words, how does the white layer begin to form on the steel surface? David

: Dear Mr. Pye,
: The white layer, which is unavoidable in gas or ammonia nitriding [because the stoichiometry of NH3 is fixed at 25% nitrogen and 75%hydrogen], is nothing but a mix of two types of nitrides in a single layer -the epsilon type and the gamma prime type. The former is usually Fe2-3N type and the latter is F4N type [sorry about not being able to use subscripts here in this bald facility shorn of fancy features] and to complicate the matters, one is cubic and the other is hexagonal in the crystalline structure morphology. The presence of two disparate types of nitrides in one layer, causes the white layer to become brittle because the packing density is affected. That's why the WL is usually ground off after gas nitriding. Whew! the trouble we've taken here to educate the customers to forget the old practice and adopt the new.... I guess it must be the same all over the world... maxbabi

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Subject:	Re: Re: Re: Formation of the Compound Zone
Comments: : : : What are the mechanics of the formation of the compound zone? In other words, how does the white layer begin to form on the steel surface? David : : Dear Mr. Pye, : : The white layer, which is unavoidable in gas or ammonia nitriding [because the stoichiometry of NH3 is fixed at 25% nitrogen and 75%hydrogen], is nothing but a mix of two types of nitrides in a single layer -the epsilon type and the gamma prime type. The former is usually Fe2-3N type and the latter is F4N type [sorry about not being able to use subscripts here in this bald facility shorn of fancy features] and to complicate the matters, one is cubic and the other is hexagonal in the crystalline structure morphology. The presence of two disparate types of nitrides in one layer, causes the white layer to become brittle because the packing density is affected. That's why the WL is usually ground off after gas nitriding. Whew! the trouble we've taken here to educate the customers to forget the old practice and adopt the new.... I guess it must be the same all over the world... maxbabi
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