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How to bake a spring steel?

I have produced some parts by stamping spring steel (SK-5M) with thickness of 1mm. Then, I coat it with zinc plating. The rule is to have these part baked to avoid hydrogen embrittlement. The plating was done by a third party. At the end, these parts still break into two.

The breakdown of the occurrence is :

Close to 10% breaks through probably rough handling during packing.

Almost 40% breaks when under stress by bending them to normal expected level; either instantly or over time of not more than 3 months from installation.

Is this common even if proper procedures taken? If yes, how or what could have potentially gone wrong? What is the standard hours required for baking spring steel after zinc plating?

Thank you.

Jeremy Yap
- Selangor, Malaysia

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The standard is probably about 12 hours of baking, but that's probably not the problem. The problem is probably the delay before baking. You're going to have to have these parts baked where they are plated you can do it immediately after plating.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
 

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Ted's answer certainly is a possibility. My vote goes for the way they are racked, IE: under compression. They could very easily break coming off of the rack. They need to be plated in the same manner (shape) as they will be baked. This will very probably take new racks or a different design or tips.

James Watts
- Navarre, Florida

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Just an idea but are the parts cracked before plating? A small sample run through a flaw detection process may well show that the problem is with the stamping not the plating.

Martin Trigg-Hogarth
surface treatment shop - Stroud, Glos, England
 

A very common problem with tensile steel wire springs. I know because I plate these. My best solution is not to muck around with the baking or type of zinc plating there probably is not much problem with it. Also given low costs of plating these items most platers probably won't want to do complex plating procedure. Look at sourcing different types of wire from different supplier, there is such wires availiable in Malaysia as which has the springy effect and will not break after plating.

Tan Kay Leong
- Malaysia