how to spec higher tensile steel

[jkls]

We had failures of a thin-wall Stressproof 1144 cutter. The parts that failed are designed to cut a 2" dia hole about 1" deep through HDPE and retain the cut plastic section. At cold temperatures the tensile stresses caused by trying to compress the HDPE for retention cracked the steel.

We successfully test a 4140 with a minimum tensile yield of 125Kpsi. Reading ASTM A400 I've guessed at the following spec. Does it make sense, and will it ensure a higher tensile yield?

4140-4150 oil quenched w/a minimum hardness of 293.

 

[NickE]

Thats pretty good. You will need to specify the method used to take the hardness reading. I'm guessing you used Brinell. If you are in the USA you might want to specify Rockwell. If the pipe is thick enough then you can specify using HRc (Hardness Rockwell C-Scale). 293Brinell converts to ~30HRc. The approximate conversion of the hardness to Ultimate Tensile Strength is 141-151ksi. Yield does not vary consistantly with hardness like UTS does.

I would use something like the following:

4140 Steel Quenched and Tempered to HRc30 min.

(That allows the heattreat house to use their skills to determine your heattreat parameters.)

I personally think that specifying by using hardness level is not the best way to go. I would get material test certifications from an accredited laboratory. (IE: A2LA or NLVAP)

good luck.



Nick
I love materials science!