EX.4

http://dl.iran-mavad.com/pdf95/Practical%20Heat%20Treating-ASM%20International%20(2006)_iran-mavad.com.pdf

http://www.utc.fr/~hagegebe/UV/MQ12/CORRECTIONS_TD/%5BASHBY99%5D%20-%20Materials%20Selection%20In%20Mechanical%20Design%202Ed.pdf