Mechanical properties of 4340 steel

A. Syed, if you'll take a look at the T-T-T curve you will see that you can you can get martensite, pearlite, or bainite with relative ease with 4340 -- that's one of the beauties of the alloy. I'm certain your presentation will cover the differences between these structures, and how they relate to the mechanical properties. Remember that 4340 is a 0.40% carbon steel, and carbon is the prime alloying ingredient with respect to properties. The nickel, chromium, and molybdenum merely effect the cooling rate necessary to get those aforementioned structures.

Most libraries in the States have a copy of The Making, Shaping and Treating of Steel [on Amazon affil links], and you can also look for Optical Microscopy of Carbon Steels ⇦[this on Amazon affil links] by Samuels, or just about any book or article by George Krauss. These should give fine insight into the wonderfully complex world of alloy steel heat treatment.

Good luck, and have fun!

A. Dear sir, If you look at CCt diagram of 4340 ASE and superimpose cooling curve on it you can see that if the rate of cooling increases the cooling cure passes through the martensite region and it means that the faster you cool your steel the harder you will have! For more info., see the AC3 software.

A. Hello Farhan!

Using 4340 in fatigue limited applications is a common practice. The key is having a properly designed, properly manufactured, and properly heat treated part, to maximize the benefit you get from this alloy.

A. Preethi,
The 4340 material as described does not match my data tables for annealed 4340 so you may be referring to a tempered batch. Nonetheless, here is some information on annealed 4340: Bulk modulus 140 GPa; Shear modulus 80 GPa; Elastic modulus 190-210 GPa; Poisson's ratio .27-.3; Elongation at break 22%; Reduction of area 50%; Vickers hardness 228.