JFE TECHNICAL REPORT
No.15 Special Issue on "Steel Bar and Wire Rod"
The forced air cooling process such as 'STELMOR' cooling bed is generally used for a cooling method of the rolled wire rod. The strength and ductility of high carbon steel wire rods can be controlled by online process in the rolling line with this process. However, because forced cooling is performed with an air blast, the cooling capacity of the forced air cooling process is inadequate. As a result, the strength and ductility of wire rods produced by the forced air-cooling process are low in comparison with wire rods produced by lead patenting, in which the material is reheated and immersed in a lead bath by a secondary processor. Mist cooling makes it possible to secure the same cooling capacity as lead patenting, and thereby enables transformation at low temperatures. Therefore, JFE Bars & Shapes commercialized the mist cooling process for wire and rods that led the world. The company also developed the new high tensile steel wire rods by utilizing this process.
Mist cooling has the following advantages in comparison with the conventional methods.
(1) Because water droplets which have been atomized with air are blown on the material at high speed, the heat transfer coefficient is large.
(2) Because the process uses fine water droplets, uniform cooling is possible.
(3) The cooling capacity can be controlled over a wide range.
(4) The process can be installed in combination with existing forced air-cooling lines and used in combination with the existing operation.
(5) The process contributes to improvement of the global environment by making it possible to omit the lead patenting process performed by secondary manufacturers.
In order to quench wire rod material that has been coiled at a specified temperature, a mist spraying device was installed above the conveyor in the first cooling zone of the forced air-cooling process, which is located adjacent to the coiling equipment. The mist flow rate is controlled corresponding to the diameter of the wire rod material and steel grade while measuring the material online with a thermometer.
The following high tensile steel wire rods have been developed by applying the mist cooling process. However, due to space limitations, only (1) and (2) will be introduced in this report.
(1) High strength, high ductility high carbon steel wire rods: 'TMP wire rods' (prior austenite grain refining, Pearlite lamellar refining)
(2) Low carbon high tensile steel wire rods: 'TNH® wire rods' (satisfaction of both strength and weldability by utilizing high cooling capacity)
(3) Non heat treated medium carbon steel wire rods (omission of heat treatment processes by utilizing high cooling capacity)
Read full technical paper at http://www.jfe-steel.co.jp/en/research/report/015/pdf/015-07.pdf
(Source - JFE)