I have quenched steel rebar in different mediums (liquid soap, automotive radiator antifreeze, and soda solution) but despite that, the hardness increased in comparison to normalized sample the strength of all quenched specimen reduced. why? is that due to corrosive effects of these mediums or there are other reasons
I did not understand the purpose of quenching rebar in liquid soap, automotive radiator antifreeze or soda solution. Is it for fun or a real study.
Is it TMT rebar or Tor Steel?
Did you heat the rebar before quenching? If yes, upto what temperature?
Dear Dr.vinod
This heat treatment is conducted inorder to investigate the effect of chemical solution on the mechanical properties of medium carbon steel(0.3 carbon content) and whether it is possible to use these mediums as quenchant. The process started first by normalizing the steel at 900C for 2hr to remove the effect of previous heat treatment of produced company then after the samples reheated to 900C for 2hr before quenching in these solutions. The hardness in all samples and compared to normalized case improved but the strength reduced so what is the reason?
Dear Mr. Taifor
Kindly note that TMT rebar is produced through high temperature rolling followed by intense but short duration water quenching. In the process, surface of the hot rolled rebar gets quenched and transforms to martensite whereas inside remains at high temperature austenite. Once the rebar comes out of water quenching line heat from the core tempers the hard martensite at the surface. This results in an excellent combination of high strength and high ductility.
As said earlier, you may further note that high strength is achieved due to hard rim and high ductility is achieved through soft ferrite+pearlite/ bainite core. Hardness in the rim (usually 1-3 mm depending upon grade and diameter) is very high whereas it is quite low in core.
You may further note that hardness is measured at a point and it varies from surface to centre whereas strength is a single value representing entire cross-section.
If you are quenching rebar after heating to 900C for 2 hrs in different media, obviously hardness increases in the centre whereas strength decreases because the quenching is as intense as observed during actual production.
The fast quench of steel, leads the grain to rebuilds its self in a different way than normal cooling. The grain shape build in dendritic shape towards the cooling media. This shape gives the steel new properties like more brittle, and increase in strength value. The degree of increase of strength depends on the size and shape of the grains which effected by how much cooling temperature be the quenching procedure.
Dear Mr. Taifor
Mr. Vinod Kumar very nicely explained difference between the quenching you performed in your experiment and technological process using in production of the rebar steel that includes thermo-mechanical treatment (TMT). Differences in mentioned mechanical properties are result of the fact that in your experimen whole voumen of your sample is quenched while in TMT process relatively small portion of sample volume at the surface is quenched.
For better understanding of TMT technological process of rebar steel production I suggest the next article.
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