Boron Content of 10B21 1

[doakra]

What is the minimum boron content for 10B21 that will give consistent hardness of 28-32 Rc after heat treat?

Thanks

 

[swall]

What section size are you working with? Even with boron additions, these steels still have low hardenability relative to something like 4140 and will only fully harden in small sections. For consistency, you would need to specify an H grade, rather than boron content.

 

[doakra]

The material is .548" in diameter. It is being cold formed into 3/8" nuts and then heat treated. We generally don't have a problem with this, but we have a shipment of wire that the boron content is .0009%. It is generally in the area of 0.015%. This material doen't seem to want to harden. Any thoughts?

 

[swall]

Do you really mean .015 boron? Or .0015? .0005 min is typical for grade 5 fasteners per SAE J429. If you have the certs from several heats of steel, including some of those that worked OK, take a look at the residual elements such as Cr and Mo. Even though these steels are "boron steels" in name, some times the residuals are carrying much of the hardenabilty load.

 

[TVP]

doakra,

What is the concentration of Ti and N? B can be rendered ineffective if the N is not tied up by Ti. Was the steel Al-killed (Al > 0.015%)? As swall mentioned, B can be effective in hardening fasteners in concentrations as low as 0.0005% by mass, although it is more commonly limited to 0.0008-0.0030% along with a minimum Ti content of 0.01%.

 

[EdStainless]

Doakra has hit it. Without Ti and/or Al you will not get any benifit from the B.

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