banding

Hi,
i am working with a low alloy steel. When it has been quenched and hot coiled into a spring then tempered i am seeing straw coloured bands in
the microstructure. At higher magnification they appear white, possibily ferrite ? I'm guessing this is something to do with segregation. Can anybody help ? Does anybody know what effect this would have on the fatigue properties ?
thanks
toffeeman
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toffeeman wrote:

why are you trying to temper a low alloy steel?

first, what is your objective?
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I Quench the steel to give me a martensite structure, before quenching i hot coil into a spring. Springs are then tempered to give a tempered martensite structure. This structure has the best fatigue properties for these steels at the strength / hardness that i need. This is why i quench and temper them. Any idea about the bands i am seeing ?
thanks
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Unless you are using valve quality or tire cord quality steel, you can expect to see banding in the microstructure. Unless your product is going through 10,000,000 cycles or more, the banding will not effect the product.

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Try EDS using the SEM to determine the chemistry. They could be inclusions or elongated grains. Hard to say without seeing the microstructure. Is the sulfur and silicon content within spec requirements?
Are the bands directional? Longitudinal, transverse?
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wrote:

The bands are longitudinal. I think it may be caused by Mn segragation. Any thoughts about this. Does anybody else have any thoughts about the effect on fatigue life. I can't help but think that 'heavy' banding must effect the life or at least give anisotropy to the properties.
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