Recommended Hardnesses for Heat Treating Common Metals 1

[curiousmechanical]

Hello,

I have been searching for a general chart or table that would provide me with the maximum obtainable (or perhaps the recommended) hardness when heat treating various common metals. Is there such a thing? I can't seem to find one in the "Machinery's Handbook" or "Mark's Standard Handbook". I tried doing a fair amount of internet searching as well, but had no luck. Does this type of chart or table even exist? If so, where would I find it? If not, why is this not practical or feasible? It seems to me that people are using industry standards when specifying hardness on drawings. Although, no one seems to have a good answer when I ask them why they choose to specify a particular hardness on their drawings.

Thank very much you.

 

[metengr]

curiousmechanical;
There are no charts for general applications of recommended hardness because the design of objects or components for specific service conditions may require many inputs, with hardness as possibly one of them.

There are indeed charts that show the hardenability (depth of hardening) and range of hardness as a function of heat treatment for various metals. This information is compiled in ASM Handbooks available thru ASM International. They also have various reference books on the heat treatment of Steels. See below;

http://www.asminternational.org/

 

[Airmack]

CURIOUSMECHANICAL,

METENGR is right about ASM. I actually have the ASM Handbook, Vol. 1, "Properties and Selection: Irons, Steels, and High-Performance Alloys" sitting in front of me. It has about 150 pgs. of hardenability data for carbon and low-alloy steels. It contains material selection charts according to yield strength and hardness, classification of steels according to minimum hardness, and hardenability charts for many alloys. Among the hardenability curves data, there are "hardness limits for specification purposes" with every material listed.

I find this a valuable resource - at least for me.

 

[mechengdude]

Not sure if this is what you are looking for but ASTM A370 has a handy little chart I use on occasion. Page 22 of the specification gives a hardness chart for Nonaustenitic steels at various hardness with the cooresponding approximate tensile strength.

 

[israelkk]

Usually hardness is not important except when wear is an issue. Strength is what engineers are after. For steels there is a correlation between strength and hardness therefore, many times for non critical parts it is cheaper to test for hardness instead of tensile and yield strength. With experience you will get the feeling for hardness. For example, you will learn that for ball and roller bearing where compressive loads and wear are the main loads the common hardness is 58-65RC, for springs it is usually around 50RC, etc. However, the good practice is to specify strength when designing structural parts.

 

[curiousmechanical]

Thank you very much for the great feedback everyone! I looked into the ASM Handbooks and the mentioned ASTM spec. Although, I'm not sure if I am going to purchase them just yet. They seem to be a little too extensive for my needs. Instead, I am going to try to look for a general materials handbook. I think this is what my reference collection is lacking. Does anyone know a good one?

israelkk,

Thank you for identifying the relationship between strength and hardness. That really cleared things up for me. I was stuck on looking at hardness by itself. One more question if I may...When a material reaches its maximum hardness, does it necessarily reach its maximum strength? If so, wouldn't we want to heat treat materials to their maximum hardness?

Thank you very much!

 

[israelkk]

When the material reaches it maximum strength its toughness and ductility decreased to the point that it may become too brittle. The engineer needs to look for ductility and toughness i.e. the ability to sometimes yield and get into the plastic zone without a break or resist impacts. Therefore, always look for the elongation and reduction of area at the specified heat treatment. For structural parts in the aerospace business usually at least 10% elongation before break is common. Parts that designed for tensile, bending and shearing stresses should have enough ductility. Parts designed for wear or compressive stresses can go as low as 1% elongation.

 

[ijzer]

ASME B31.3 specifies hardness limits on materials /welds , this can be used as a guide.

 

[ajack1]

This is a fairly useful free website, obviously if you pay there is much more information, failing that most steel suppliers will offer a free handbook with all the technical data about there specific steels, this however may not include the more generic names for certain grades.

http://www.key-to-steel.com/default.aspx?ID=FreeDownload

 

[Philrock]

I find the following sources helpful in this area:

Ducommun Metals Stock List - this is an antique - Ducommun has been out of business for decades, but most of the information in this book is still valid - good luck finding a copy.

Jorgensen Steel & Aluminum Stock List and Reference Book. Don't know if this is still in print. Jorgensen is now known as EMJ Metals.

http://www.matweb.com