The effect of the rebar rolling mills cooling after rolling can be divided into two categories according to the rebar before rolling, quick cold deformation austenite recrystallization state:
One is the deformation of austenite is fully recrystallization, deformation caused by the dislocation or substructure reinforcement has been eliminated, the deformation strengthening effect weakened or eliminated, thus improved only by phase transformation is complete, comprehensive mechanical properties increase is not much, but high-stress corrosion stability.
The other is that the austenite does not recrystallize or only partially recrystallizes before rapid cooling after rolling.
The strengthening effect of retained deformation or partially retained deformation on austenite can improve the comprehensive mechanical properties of rebar, but the stress corrosion cracking tendency is larger.
Generally, there are two ways to control the cooling of rebar rolling mills after rolling :
The first is to cool it immediately after rolling, to cool it rapidly to the specified temperature in the cooling medium, or to stop the fast cooling after cooling in the cooling device for a certain period of time, and then to air cooling and self-tempering. This cooling method is suitable for producing small section rebar.
The second is to supercool the surface of the rebar in the high-speed cooling device for a very short time to form martensite below the martensite transition point, and immediately stop the fast cooling, air cooling for a period of time, so that the surface layer of martensite tempering, the formation of tempering sinite!
Then, the second fast cooling is carried out for a certain time, and the fast cooling is interrupted again for air cooling so that the threaded steel core can obtain soxite structure, bainite and iron| somatic tissue. The tensile strength and yield strength of the threaded rebar obtained by this cooling method are slightly lower, the elongation is almost the same, and the corrosion resistance is stable!
At the same time, for large section steel, it can also reduce the internal and external temperature difference.
