Hot Metal

Hot Metal Hot metal (HM) is the output of a blast furnace (BF). It is liquid iron which is produced by the reduction of descending ore burden (iron ore lump, sinter, and pellet) by the ascending reducing gases. HM gets collected in the hearth of the BF. From the hearth, the HM is tapped from the taphole of the BF after an interval of time. Normally in large BFs, HM tapping rates of 7 ton/min and liquid tapping velocities of 5 m/sec, in tap holes of 70 mm diameter and 3.5 m long, are typically encountered. The tapping rate of HM is strongly influenced by the taphole condition and taphole length. Generally the temperature of tapped HM varies in the range of 1420 deg C to 1480 deg C. The tapped HM is handled in the two stages namely (i) handling of the HM in the cast house i.e. from taphole to the hot metal ladles (open top or torpedo), and (ii) transport of HM ladles to the point of HM consumption. Presently most of the HM is consumed within integrated steel plants for steel making. The HM is transferred to the steel melting shop for making of steel. The HM which is not sent for steel making is cast into pig iron in pig casting machine for use in steel making later as cold charge or is sold to foundries or to mini steel plants having induction furnaces as merchant pig iron. HM can also be granulated by a process which is known as ‘Granshot’ process. Presently the Granshot plants for the production of GPI are working at six places namely (i) Uddeholm, Sweden, (ii) SSAB Lulea, Sweden, (iii) Voest Alpine, Donawitz, (iv) Saldanha steel, South Africa, (v) SSAB Oxelosund, Sweden, and (vi)...

Manganese in Steels

Manganese in Steels  Manganese (Mn) (atomic number 25 and atomic weight 54.93) has density of 7.44 gm/cc. Melting point of Mn is 1244 deg C and boiling point is 2095 deg C. The phase diagram of the Fe-Mn binary system is at Fig 1. Fig 1 Fe-Mn phase diagram  Mn is present in most commercially made steels. Mn plays a key role in steel because of its two important properties namely (i) its ability to combine with sulphur (S), and (ii) its powerful deoxidation capacity. Mn is undoubtedly the most prevalent alloying agent in steels, after carbon (C). Mn is intentionally present in many grades of steel and is a residual constituent of virtually all others. Mn has played a key role in the development of various steel making processes and its continuing importance is indicated by the fact that about 85 % to 90 % of all Mn consumed in the world annually goes into iron and steel making as well as in steel as an alloying element. No satisfactory substitute for Mn in steel has been identified which combines its relatively low price with outstanding technical benefits. Available forms Mn is used in steel industry in an extensive variety of product forms. These can be classified into three major groups namely (i) ferro-manganese (Fe-Mn), (ii) silico-manganese (Si-Mn), and (iii) Mn ore. There are several standard grades within each group. Fe-Mn and Si-Mn are used mainly during steel making while Mn ore is mainly used in iron making. Types of Fe-Mn and Si-Mn produced are given in article having link http://ispatguru.com/717/. High density Mn containing 96 % or 97 % Mn, depending on grade and Iron (Fe) as the principal impurity, is also used as a desirable addition agent for super alloys, stainless...

Deoxidation of Steel Sep03

Deoxidation of Steel

Deoxidation of Steel  Steel making process consists of refining of hot metal to steel which is done under oxidizing atmosphere. During refining process oxygen get dissolve in steel. The following are the main sources of oxygen in steel. Oxygen blowing Use of oxidizing slags and iron ore during the steel making processes Picking of atmospheric oxygen by the liquid steel during the teeming operation Oxidizing refractories of the lining Rusted and wet scrap. Deoxidation is the last stage in steelmaking. During making of steel, the steel bath at the time of tapping contains 400 to 800 ppm activity of oxygen. Deoxidation is carried out during tapping by adding into the teeming ladle appropriate amounts of ferro alloys or other special deoxidizers. If at the end of the blow the carbon content of the steel is below specifications, the liquid steel is also recarburized in the teeming ladle. However, large additions in the teeming ladle have the adverse effect on the temperature of the liquid steel. Solubility of oxygen in steel is negligibly small. During solidification of molten steel, excess oxygen is rejected by the solidifying steel. Solubility of oxygen in liquid steel is 0.23 % at 1700 deg C. It decreases during cooling down process and then drops sharply during the solidification of liquid steel reaching 0.003 % in solid steel. The excess oxygen liberated from the solid solution oxidizes the components of steel such as C, Fe, and alloying elements resulting into blowholes and non metallic inclusions entrapped within the cast steel structure. Both blowholes and inclusions have considerable effect on the mechanical properties and impact adversely the steel quality. In order to prevent oxidizing of steel components during solidification the oxygen content of liquid steel need to be reduced. This is done by deoxidation of steel which...