Adjusting Hardness Values on Bolts 3

[Onursan]

Hello everyone,

Since i am a heat transfer guy, my question is maybe some kind of dumb

For example according to SA 193, maximum allowed hardness values are given on table 3.

Since it indicates "hardness, max" can i, or is it possible to produce a given bolt (for example grade 7) with lower hardness values indicated there?

Thanks for your answer.

 

[TVP]

Yes, it is possible to produce Grade B7 bolts with a hardness less than 35 HRC. The material must be liquid quenched (oil, water + polymer) and tempered at a minimum of 593 C.

 

[mrfailure]

Minimum hardness is not explicitly specified in A193, but you can estimate the required minimum value for ferritic steels (such as B7) based on specified minimum tensile strength. A table with these estimates is included in ASTM A370.

Aaron Tanzer

http://www.lehightesting.com

 

[Onursan]

Thanks TVP and mrfailure for valuable information.

I need around 225 Brinell and 860 Mpa tensile(B7), but according to tables on A370 it doesnt look possible.

In other way, table says these values are "approximate" and note indicates that values can be changed according to manufacturing process.

So according to you experience,is 225 Brinell and 860 Mpa tensile is possible to manufacture?

Thanks in advance.

 

[TVP]

225 HB (or ~ 20 HRC) is not possible for a minimum tensile strength of 125 ksi (860 MPa). The minimum hardness will be ~ 245 HB when the tensile strength is at the specification minimum.

 

[mrfailure]

To expand on TVP's point: Hardness is not independent of tensile strength. 860 MPa is the minimum tensile value specified for B7 bolts up to M64 size. You should tensile test if feasible. A370 values are estimates and I have seen enough variation that it is possible you are still meeting tensile requirements if you measure 225 HB but it is highly suspect and needs to be confirmed through tensile tests. (BTW: 860 MPa ~ 258 HB using the A370 conversions.)

Aaron Tanzer

http://www.lehightesting.com

 

[Onursan]

Thnaks all for your answers.