In steel, the two most damaging impurities are Sulphur (S) and Phosphorous (P). Extreme levels of sulphur can cause ‘hot shortness’ in steel, a condition that causes the steel’s melting point to decline thereby reducing its strength under high temperature. Similarly, extreme levels of phosphorous can cause what is called as ‘cold shortness’ which causes the steel to become brittle under extreme cold conditions.
For manufacturing the best quality TMT steel bars, it is vital to ensure that the proportion of Sulphur and Phosphorous are controlled within manageable limits. In case, they are present in higher proportion, the chemicals will reduce the ductility of steel and produce illusions. This will badly affect the quality of steel bars eventually leading to steel bars being produced with damaging imperfections.
Thankfully, lower levels of Sulphur & Phosphorous can be achieved through advanced steel making technology.
This advanced steel making technology is LRF (Ladle Refining Furnace) technology.
WHAT IS LRF & LRF TECHNOLOGY?
During steel making process, once the steel is made in the basic oxygen furnace, arc furnace, or induction furnace, it gets transferred into the ladle for further refining, chemistry adjustment, inclusion modifications, etc. All of these treatments occur in the ladle.
To carry out these treatment operations, additional heat is required. This is why the ladle is provided with a heat source which heats the liquid metal and compensates for thermal losses. The furnace in which the liquid steel’s quality is enhanced through refining and heating is called a Ladle Refining Furnace (LRF).
LRF technology on the other hand is termed as a state-of-the-art technology that produces construction grade steel using iron ore as the raw material.
The quality of liquid steel is improved in LRF (Ladle Refining Furnace) where the temperature is raised resulting in a more refined grade of steel.
HOW IT ACHIEVES THE SAME?
The technology refines the steel by floating inclusions in them and then removing dissolved gases. Later ferro alloys are added to the steel to obtain the specified chemistry and the liquid steel is sent to the caster. In the caster, the refined steel is casted into billets of specific sizes in closed environment. This will ensure better control of any remnant gases and other inclusions. End-result, is higher quality 500D or 550D TMT steel bars.
500D and 550D grade TMT steel bars are majorly used in big scale infrastructure projects like airports, bridges, canals, dams, flyovers, malls, industrial structures, ports, skyscrapers, tech parks, tunnels, and all such infrastructure works that require steel bars that can ensure high quality, heavy-load bearing capacity. These bars are also extensively used in seismic area construction works that are prone to frequent earthquakes and other natural calamities, and pose a threat to lives and properties.
HOW IT HELPS IMPROVE QUALITY?
LRF technology ensures steel
- Gets desulphurised and dephosperised. While desulphurization improves transverse ductility and weldability, desphosphorization improves ductility.
- Becomes cleaner through removal of oxide inclusions. Subsequently the lower carbon level results in excellent ductility and weldability.
- Gets degassed through purging of inert gas. This will result in low gas (hydrogen, nitrogen, & oxygen) content.
In addition to the above, LRF technology also facilitates
- Gentle stirring by the ladle. This results in homogenization of the temperature and also the composition of molten steel.
- Better recovery and maintenance of composition in narrow range. This results in ample saving of ferro alloys consumption.
- Improvement of grain refinement in the microstructure.
- Lowering of temperature. This results in increase in productivity with the melting furnace getting emptied faster.
LRF also acts as a buffer by holding molten steel for sequencing on the CCM. This enables the steel to maintain higher resistance to failure. Without LRFs, lot of heat losses occur during refining with conventional ladles as a result of which the steel making furnaces are required to provide higher tap temperatures.
LRF technology has been hailed as a proven technology for producing high-quality steel by all GST registered TMT bar manufacturing companies. Currently, it is regarded as the most effective technology for producing high quality ‘D’ grade TMT steel bars in line with IS: 1786 norms. Through the induction route, it is even more so especially when iron ore is used as raw material.
In India, the best TMT steel bars are produced using LRF (Ladle Refining Furnace) technology, as per the norms of IS: 1786 which indicates exact chemical composition and associated physical properties required for manufacturing construction grade steel bars.