What is the difference between carbon steels and “killed , semi killed ,rimmed and capped Steels”?
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Killed steel is steel that has been completely deoxidized by the addition of an agent before casting such that there is practically no evolution of gas during solidification. It is characterized by a high degree of chemical homogeneity and freedom from gas porosities. The steel is said to be "killedRead more
Killed steel is steel that has been completely deoxidized by the addition of an agent before casting such that there is practically no evolution of gas during solidification. It is characterized by a high degree of chemical homogeneity and freedom from gas porosities. The steel is said to be “killed” because it will quietly solidify in the mould, with no gas bubbling out. It is marked with a “K” for identification purposes.
The main disadvantage of killed steel is that it suffers from deep pipe shrinkage defects. To minimize the amount of metal that must be discarded because of the shrinkage, a large vertical mold is used with a hot top. Typical killed-steel ingots have a yield of 80% by weight.
Commonly killed steels include alloy steels, stainless steels, heat resisting steels, steels with a carbon content greater than 0.25%, steels used for forgings, structural steels with a carbon content between 0.15 and 0.25%, and some special steels in the lower carbon ranges. It is also used for any steel castings.
Semi-killed steel is mostly deoxidized steel, but the carbon monoxide leaves blowhole type porosity distributed throughout the ingot. The porosity eliminates the pipe found in killed steel and increases the yield to approximately 90% by weight. Semi-killed steel is commonly used for structural steel with a carbon content between 0.15 and 0.25% carbon, because it is rolled, which closes the porosity. It is also used for drawing applications.
Characteristics of SEMI KILLED steels.
Structural steels containing 0.15 to 0.25% carbon are generally semi-killed.
In semi-killed steel, the aim is to produce metal free from surface blowhole and pipe.
The surface should have a sound skin of considerable thickness.
They are used for general structural applications.
During solidification of semi-killed steel, gas is evolved in the body of the ingot, tending to compensate in part or entirely for the shrinkage accompanying solidification.
Since pipe cavities are minimized, semi-killed steels are usually cast in big-end -down molds without hot-tops.
This type of steel is suitable for drawing operation (except severe drawing).
Rimmed steel, also known as drawing quality steel, has little to no deoxidizing agent added to it during casting which causes carbon monoxide to evolve rapidly from the ingot. This causes small blow holes in the surface that are later closed up in the hot rolling process. Another result is the segregation of elements; almost all of the carbon, phosphorus, and sulfur move to the center of the ingot, leaving an almost perfect “rim” of pure iron on the outside of the ingot. This gives the ingot an excellent surface finish because of this iron rim, but also form the most segregated composition. Most rimmed steel has a carbon content below 0.25% carbon, a manganese content below 0.6%, and is not alloyed with aluminum, silicon, and titanium. This type of steel is commonly used for cold-bending, cold-forming, cold-heading and, as the name implies, drawing. Due to the non-uniformity of alloying elements it is not recommended for hot-working applications.
Capped steel starts as rimmed steel but part way through the solidification the ingot is capped. This can be done by literally covering the ingot mold or by adding a deoxidizing agent. The top of the ingot then forms into a solid layer of steel, but the rim of the rest of the ingot is thinner than in a rimmed steel. Also there is less segregation of impurities.
The yield of rimmed and capped steel is slightly better than that of semi-killed steel. These types of steels are commonly used for sheet and strip metal because of their excellent surface condition. It is also used in most cold-working applications.
Due to production processes, as the carbon content of rimmed and capped steel increases above 0.08%, the cleanliness decreases.
See lessYes they are steels and classified on basis of deoxidation in this. Killed steels are those which is heavily deoxidised during steelmaking so that no Oxygen is left there. Powerful deoxidised like Al are used here. Due to no dissolved O it lacks porosity and often has piping problems associated. SemRead more
Yes they are steels and classified on basis of deoxidation in this.
Killed steels are those which is heavily deoxidised during steelmaking so that no Oxygen is left there. Powerful deoxidised like Al are used here.
Due to no dissolved O it lacks porosity and often has piping problems associated.
Semi killed steels are those which are less deoxidised. Due to some Oxygen is still dissolved and during operation (solidification) they form CO gas bubbles which gives porosity to them and thus avoiding piping problems.
Rimming steels are those in which least or no deoxidation has been done. Due to this it has large amount of CO gas bubbles which rises up and the lower portion is very clean and taken out( called rimming action).
Capped steels are same as rimming steels where almost no deoxidation is there with adequate amount Oxygen. This usually differs in Operation where the rimming action is allowed for sometime then it is capped using metal or other caps so that top layer forms solid steel layer and lower rim part is thinner.
You can refer Ingot Casting or steelmaking book for further clarification.
See lessCarbon steel that is cast into ingots can be classified into four types: killed steel; semi-killed steel; rimmed steel and capped steel. Each type depends on the method of deoxidation during steel making, or the amount of gas evolved from the reaction of carbon with iron oxide during solidification.Read more
Carbon steel that is cast into ingots can be classified into four types: killed steel; semi-killed steel; rimmed steel and capped steel. Each type depends on the method of deoxidation during steel making, or the amount of gas evolved from the reaction of carbon with iron oxide during solidification. For continuous casting, only killed steel is used.
1.Killed steel- is characterised by more uniform composition and properties in comparison with the other types. The steel is fully deoxidised (killed) before casting by the addition usually of silicon, manganese and aluminium, but also sometimes vanadium, titanium and zirconium. There is virtually no gas evolution during solidification, and therefore the ingot contains very few, if any gas voids. However, this means that a shrinkage pipe forms at the top of the ingot, thus the amount of useful metal is reduced. Typically, killed steels are used for alloy steels, forging steels and steels for carburising. A typical Si-killed steel from UK steel making practices would contain more than 0.1%Si (usually 0.15%-0.35%Si); less than about 0.005%Al; 0.01 to 0.03%O 2; MnS and silicate inclusions.
Aluminium is often added to Si-killed steels to control the growth of austenite grains in reheated steels. A typical Si-killed, Al-treated steel from UK steel making practice would contain more than 0.1%Si; more than 0.01 to 0.02%Al (usually 0.03% to 0.06%); less than 0.005% O2; Al2O3 inclusions, but no silicates.
2.Semi-killed Steel -is characterised by variable degrees of uniformity in composition, intermediate between killed and rimmed steels. Typically, more gas is evolved in semi-killed steel than in killed steel, but less than in rimmed or capped steel, and there is a pronounced tendency for chemical segregation to occur at the top of the ingot. A typical semi-killed steel from UK steel making practices would contain less than about 0.1%Si (typically 0.03%, but possibly as low as 0.01%); less than about 0.005%Al; upwards of about 0.02% O2; MnS and silicate inclusions.
3.Rimmed Steel -is characterised by marked differences in chemical composition across the section and from top to bottom of the ingot. The steel from which the ingots are made is not fully deoxidised before casting. It is observed that the concentration of carbon, sulphur and phosphorus is lower than the average for the ingot in the outer rim, and higher in the central core. This pronounced segregation is due to greater gas evolution from the outer rim during solidification and the concentration of elements in the liquid portion increasing. Typically, rimmed steels are best suited for the production of steel sheets and plates, as the structural pattern persists through the rolling processes. After solidification of the outer rim, fine gas bubbles form in the body of the ingot and help to counteract the solidification shrinkage. Therefore no pipe forms and the yield of good quality metal is improved. The internal voids close up during rolling and forging, but the clean outer rim remains, and enhances the quality of the steel surface. Typically, rimmed steels contain 200-400ppm O2, <0.01%Si and 0.01%Al.
4.Capped Steel- has characteristics between those of semi-killed and rimmed steel. The addition of some deoxidising elements controls the rimming action by limiting the time for gas evolution from the outer layers of the ingot. The gas evolved inside the ingot is in excess of that required to counteract solidification shrinkage, hence the ingot has a tendency to expand. The capping operation limits the formation of an excessive number of gas voids in the body of the ingot. This is achieved either mechanically or chemically. The mechanical technique involves a heavy metal top being placed on the ingot mould to restrict the expansion of the ingot. For the chemical technique, aluminium or ferrosilicon is added to the top of the ingot so that the top surface solidifies rapidly and, again restricts the expansion of the ingot. This top portion is discarded before further processing. Capped steel typically contains more than 0.15% carbon, and is used for sheet, strip, wire and bars.
See lessKilled steel is produced by use of deoxidizing agent like Al,MN,Si used Semikilled steel C range 0.15-0.30% Less segregation than rimmed steel Rimmed steel ingot are pure iron it is used to be manufacturing process like plate sheet wire tubes it has good surface finishing and ductility Capped steelRead more
Killed steel is produced by use of deoxidizing agent like Al,MN,Si used
Semikilled steel C range 0.15-0.30%
Less segregation than rimmed steel
Rimmed steel ingot are pure iron it is used to be manufacturing process like plate sheet wire tubes it has good surface finishing and ductility
Capped steel are between rimmed and killed steel types. The capping operation reduces the number of gas voids inside the ingot.
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