THE EFFECT OF SECOND AUSTENIZATION TIME IN DOUBLE QUENCHING TEMPERING AND DEEP CRYOGENIC TREATMENT METHOD FOR MICROSTRUCTURE AND MECHANICAL PROPERTIES OF AISI 4340 STEEL

• Main Author: Gendis Mawardani, Alief
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/38935
• Institution: Institut Teknologi Bandung

AISI 4340 steel is one of high strength steel with chromium, nickel and molybdenum as alloy element. Many industries use this steel as one of their material, such as in aircraft,automotive, automobile and in manufacture as tool steel. For application in industries, improvement of mechanical such as toughness, hardness and wear resistance charateristics is needed. Toughness improvement can be done with grain refirement as result from double quenching tempering method. For hardness and wear resistance improvent can be done by added one of heat treatment after conventional is called deep cryogenic treatment. Combination of the two method may produce better mechanical improvement for AISI 4340 steel. There are three heat treatment method that used in this research, there are CHT, DQT and combination of DQT-DCT. This experiment started by steel heating in 1000C for 60 minutes, then followed by oil quenching for CHT method. For DQT and DQT-DCT method, steel is reheating again in 950C for 15,30 and 60 minutes. And then followed by tempering in 300C for 60 minutes. In DQT-DCT method next process is soaked in liquid nitrogen for 48 hours that called DCT. After that, tempering that steel in 300C for 60 minutes. Each of tempering process is finished by oil quenching. At the end of the experiment, examination of steel is doing to check the effect of time in second austenization and comparison for the heat treatment method. The examination that used is impact, hardness, OM,XRD and SEM. From the experiment, more longer retention of second austenization make grain refirement. Smallest grain size is 11,99 µm in variation of 60 minutes second austenization. Increasing toughness is impact from grain refirement. The highest toughness is 35,272 J for 30 minutes of second austenization. For DQT and DQT_DCT method have a higher toughness than CHT. The highest hardness is 564,4 HV for 15 minutes of austenization. DQT method increase hardness about 24% and DQT-DCT method increase hardness about 28% than CHT. For the cleavage of impact test, in CHT method its have bigger cleavage facet than others method DQT-DCT method have most of rivers pattern.