This article is literally my homework. However, during doing this assignment, I found some difficulties because the materials were not prepared on our lecture slides. I hope this article would benefit materials engineering students who want to do their homework faster.
Home Exercise Iron and Steelmaking
Lecturer : Sungging Pintowantoro, PhD
OpenBook, 120 minutes
26 May 2017
- What are different alternative iron making processes? Explain the alternative process suitable with iron ore in Indonesia.
ANSWER: There are several alternatives for iron making process. Iron could be processed either by Direct Reduction Iron (DRI) process and Smelting Reduction of Iron (SRI) process.
A. DRI process is the one that is applied in Indonesia. The example is Blast Furnace technology that is widely applied in several provinces.
B. SRI process has been developed in several countries such as Japan, Korea, Germany, and so on. The technology that is operated commercially nowadays is COREX, FINEX, and HISMELT. However, due to limited access, human resource, political issue, and the policy applied nowadays in Indonesia, these option has not ever been applied in any mining corporation.
Concerning about the profile of Indonesia’s iron ore, the blast furnace process is one option that is suitable and has been applied for years. However, Finex and Hismelt technology are also suitable for Indonesia’s iron ore because finex used low-grade iron profile. In 2015, Indonesia has signed MoU with Posco, Korea to use develop this technology in Indonesia. However, this far, this technology has not been applied widely yet.
- What is steelmaking?
ANSWER: Steelmaking is the process for producing steel from iron ore and scrap. In this process, impurities such as nitrogen, silicon, phosphorus, and sulfur and excess carbon are removed from the raw iron. Alloying elements such as manganese, nickel, chromium and vanadium are added to produce different grades of steel.
- Differentiate between pig iron, cast iron, and steel.
– Pig iron is the iron that is obtained from blast furnace. It contains 4% carbon and many impurities such as S, P, Si, Mn in a smaller amount.
– Cast iron is obtained by melting pig iron using hot air blast and given some coke to remove some of its impurities. Cast iron contains a lower amount of carbon (3%) than pig iron. Cast iron is also extremely hard and brittle.
-Steel is an alloy of iron and other additional materials. The primary content of steel is carbon. This material is the most important engineering and construction material because it has high strength and a cost.
- Why big ingots with circular cross section are not cast?
ANSWER: Casting large ingot is mean to minimize the tendency of the ingot to crack on cooling and solidifying. However, if the ingots are big and having circular cross section area, the ration of the perimeter to cross section area of the ingot would be minimum. It means there is no excess surface metal to draw upon as the outer portion of the ingots tends to cool and corrugated uniformly against its still molten interior. The perimeter is greatly increased in relation to the cross-sectional area. As the circular cross section ingots cool, it might contract initially at the outer vertical of the corrugation or fluting and it would eliminate any tendency to crack.
- What is the mechanism of decrease in viscosity of pure liquid silica on addition of CaO
ANSWER: Silicate is known having a high viscosity (105P). At the corner of silicate cristal, it bonds strongly to all direction in a wide range networking area. When CaO is added, two bonds of silicate would open the chain because it bonds with oxygen to form CaO. The driving force od the silicate bond separation is the attraction of oxygen and silicon. The content of CaO/SiO2 would change the flux and decrease the viscosity. This process happens when the temperature is heated.
6. Define basicity of slag from ionic slag model
ANSWER: The basicity of slag from Ionic slag model is defined by the number of an excess of 02- It can be understood from ionic or from molecular nature of slag. The ionic nature of slag assumes slag to consist of ions. It also could be calculated by differentiating the percent weight of CaO and the percent weight of SiO2.
7. Why is it necessary to have excess lime in slag in converter steelmaking?
ANSWER: It is important to have excess lime in slag to assure the protection to the converter refractories. The lime would also dissolve in lower temperature producing flux by the addition of FeO. The lime is very critical in steelmaking because it interacts with various components formed during the steelmaking process. Removing phosphorus from the steel lime and oxygen is needed to produce the product of P2O5.CaO to trap in the slag. For the removal of the phosphorus, slag is to be removed by deslagging of the converter in the middle of blow and in this process it is important to have excess lime to blow the heat down more (oxygen activity) and to keep it cooler
7. Explain the role of a basic oxidizing slag in steelmaking.
ANSWER: Oxidation is to refine the high carbon hot metal (HM) to low carbon liquid steel. Oxidizing slag is also aimed to obtain desired physiochemical properties of slag like melting point, basicity, viscosity, and etc. A strongly oxidizing slag is favorable for oxidation reactions. However, it also acts as a sink for impurities during refining of steel, controls oxidizing and reducing the potential of the bath during refining through FeO content. It also helps dephosphorization and absorbs some sulfur. It absorbs oxide /sulfide inclusion, provides protection to the liquid steel from re-oxidation and emulsifies the hot metal and promotes carbon oxidation.
8. Carry-over of the basic oxidizing slag from the converter is undesirable to the transfer ladle. Why? How is it possible to minimize the carry-over of slag?
ANSWER: It is possible to minimize the carry over slag is by designing various slag stoppers in conjunction with melter’s eyeballs, which remain the dominant control device. Slag in the ladle results in phosphorus reverion, retarded desulfurization and possibly dirty steel.
9. What are the functions of argon gas in R-H degassing processes
ANSWER: In R-H degassing process, Argon gas acts as a lifter gas to increase the molten steel velocity which is entering into the inlet snorkel.
10. Is electric steelmaking autogenous? Explain in brief
ANSWER: Electric Steelmaking is not an autogenous process like oxygen furnace because this furnace is basically melting the furnace in which charge material is melted. The required energy depends on the energy given from the outside instead of from its oxidation like in BOF.
11. What are conditions of producing rimming steel ingots
ANSWER: To produce rimming steel ingots is by molding to a height not greater than or not exceeding 75 inches height. It also not given deoxidizing agent added during casting. The carbon is less than 0.1%
12. Give parameters to judge quality of sponge iron for its usage in electric steelmaking
ANSWER: It is primarily evaluated by percentage of its metallic iron content. Typically Fe total is 90-92, Fe metallic 81-84, Sulphur 0.03, phosphorus 0,05 and carbon is 0,01. The size ranges from 5mm to 12mm.
13. How does preheating of scrap decrease electric consumption in electric steelmaking
ANSWER: Pre-heating the scrap make the process of melting it much easier so the EAF does not have to heat the scrap from zero temperature. In addition, pre-heating the scrap is also using hot waste gasses from the furnace that means that the energy is used well.
14. Why is it necessary to inject carbon in electric steelmaking?
ANSWER: Injection of carbon in Electric Steelmaking is important because the carbon would consume the excess oxygen in the melt down period.