.40 Carbon Steel Brinell Hardness vs. Tempering Temperature

Hardness of Quench and Tempered alloy steels is a function of the tempering temperature. The higher the tempering temperature, the lower the hardness.

This is called an inverse relationship.

And it’s why some people call tempering “drawing.”

The temper “draws the hardness out of the steel.”

Normalized at 1600F, Quenched in oil 1550 F, Tempered 2 hours

 These curves are a rough approximation of the as tempered brinell hardness for the grades shown. For example, I have other data for 4340 that shows 440 BHN at 800F; 410 at 900F; 380 at 1000F; 340 at 1100F, and 310 at 1200F temper temperature.

Fire! Can't do a blog on heat treat without a picture of fire.

Your mileage may vary, in other words, but this graph is close enough for ‘considered judgement.’

Additional 4140 data that I have from my notes suggests 397 BHN at 800F; 367 at 900F; 335 at 1000F; 305 at 1100F and 256 at 1200F.

If you have better data from your process – USE IT.

Better yet, if you have time, send a sample to your heat treater for a pilot study.

In the absence of data from your process, the above figure and data will give you “a place to stand” in understanding what is possible when heat treating .40 carbon alloy steels- the steels most commonly encountered in our precision machining shops for Automotive, Aerospace, Agricultural and general applications.

Here is a video from PMPA member company Nevada Heat Treating to give you an inside look at what goes on at a heat treat service provider.

Share

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s