Yield Strength

[Tim Tim]

Any idea why steel bar Yield Strength difference is very high between the head and tail? The construction bars (ex: Y25mm) are rolled and cooled/quenched.  

[ThomasPowers]

probably differential heat treat on them.

[Frosty]

Welcome aboard Tim, glad to have you. If you'll put your name in the header you might be surprised how many Iforge members live within visiting distance.

That's a mighty vague question. We don't know the context for one. When are they tested, from the mill or after installation? Also, there's a mighty big difference between cooling and quenching steel. Rolling stock from the ingot produced by the continuous caster produces a LOT of heat so the steel is continuously sprayed with water to do two thing first is to blow the scale off before it gets to the next set of rolls the other is to prevent it from getting too hot. In neither case it it being "quenched."

I also have no idea what kind of steel you're referring to and that makes a huge difference.

I'm not being picky but these terms have specific meanings so it's hard to know what you're trying to say when you use them indiscriminately.

If this is stock you just purchased there may have been a quality control error at the plant. Another possibility is Chinese steel so poor quality control isn't an error.

On the other hand if the pieces you're (testing?) are sections that have been processed a differential heat treat is entirely possible as Thomas suggests either deliberate or poor quality control.

Does this give you an idea of the variables involved in your question and why we simply can't give you a meaningful answer with the scant information you provide?

Frosty The Lucky.