AISI 1144 Hardness Problem 5

[unp1]

Hi Friends,

I have a screw machine part drawing and it is a new part for us. The material is 1144 Steel and required hardness is RC 30 min. The drawing doesn't mention anything about heat treatment process. I checked few sources and couldn't find this material having RC 30 min hardness. The maximum hardness that I found was about RC 20 without secondary heat treatment operation.

Does this mean that there is a secondary operation of heat treatment on this part, but some how they missed to mention it on the drawing?

Thanks,
unp1

 

[TVP]

SAE 1144 requires a quench and temper operation in order to achieve a hardness of 30 HRC. It is my experience that most drawings for the automotive industry do not state a heat treatment process requirement on the drawing-- only the product requirements like hardness, strength, etc. You should discuss important items like this with the customer, as there may details like decarburization limits, surface cleanliness, etc. that have not been fully communicated on the drawing.

 

[Metalguy]

Also make sure the customer knows how "deep" he wants the Rc30 to be. 1144 steel doesn't harden deeply at all, so if the parts aren't small the cores will stay soft.

 

[BillPSU]

Your customer probably wants Stressproof or ASTM A311. They probably need 100ksi yield. The design engineer didn't know what was available in the market and put down a best guess.

This usually means getting the print changed. The answer will be this is the way its been for years. Why do YOU need a print change. Didn't you see this when you quoted it......

Find out what engineering really needs and make it out of that material. Try to avoid purchasing department.

Do I sound bitter. Been there.....done that.

 

[unclesyd]

As posted above ANSI 1144 is a water and oil hardening grade carbon steel with a poor core hardening characteristics. To achieve consistent hardness levels above Rc 30 you would have to water quench from 1550°F and temper in the 900°F-1000°F range and even then if there is any section above 1/2" you will get a softer core. If there are any abrupt changes in sections or threads, water quenching is always a problem.
I have this material marked for Oil quench only. I also have this material marked with the railroad symbol.

The advice posted above to use a material at the required hardness is a very good idea. I would talk with the design engineer and appraise him of the potential pitfalls depending on the complexity of the part.
If they insist on the ANSI 1144 material at the stated specifications it can be accomplished.

 

[limct]

Hi unp1,
Steel Tec of switzerland can provide a machine steel that is equivalent with 1144 but come with the hardness of RC 29~35 in as drawn condition.

Check this website.

http://www.steeltec.ch/index_produkte_e.html

Best regards,
ct