Heat Treating 4140

[Crewdawg445]

Hi all, as the title reads I'm looking for some advice on heat treating 4140 tool steel. I've got a hawk head that will need treated and tempered once I'm finished with engravings and such. Never treated a piece as large as a hawk head. Question is, will it be necessary to pre-heat the piece before giving it a full forge treatment, or just heat her up till red and quench? Tempering will be delt with via the oven, thinking 450 for about an hour or until the eye says it's good. Thanks in advance. :hatsoff:

 

[Rifleman1776]

Hardening an entire hawk head is not a good idea. They take a lot of shock and a hard head might be prone to shattering.
DAMHIK :redface:
Only the edge needs to be hard for sharpening and other uses. That is why many hawks are made with folded softer steel over a hard piece for the cutting edge.

 

[LRB]

Here's a temper heat chart, but I think it is a tad optimistic on the hardness figures. Maybe not, but any how, heat the edge area to a bright red-orange and quench in thin oil heated to what you think is about 125°. Use enough oil for a fast cool, move it around in the oil, and expect some amount of flame up.





SAE 4140 Steel Tempering
Tempering
Temperature Hardness
Brinell Hardness
Rockwell Tensile
400°F 200°C 514 HB 55 HRc 297 KSI
500°F 260°C 477 HB 50 HRc 243 KSI
550°F 290°C 461 HB 48 HRc 235 KSI
600°F 320°C 444 HB 47 HRc 225 KSI
650°F 340°C 429 HB 46 HRc 217 KSI
700°F 370°C 415 HB 44 HRc 210 KSI
800°F 430°C 363 HB 39 HRc 182 KSI
900°F 480°C 331 HB 36 HRc 166 KSI
1000°F 540°C 293 HB 31 HRc 145 KSI
Data extrapolated from a hardness graph given in Brinell with nearest points taken from a conversion table for Rockwell hardness. Temperature conversion to Celcius rounded to nearest 10°. Tensile not specifically for 4140. All data +/- 10%

 

[Crewdawg445]

Sorry I didn't mentioned just the blade, I wouldn't do the whole head.