Killed Steel

let's find for ASME code SA-20 para 3.1.6 killed steel

Thanks for your response, but what actualy I do not need the defination, I know it, I need How we can confirm that the SA-516 GR 70 steel is killed steel if the certificate/test report does not mentioned that in direct words?

What is the paragraph in ASME Code can help us? we need a formal and clear paragraph like the paragraph of (the fine austenitic grain size in SA-20 that says:

When aluminum is used as the grain refining element, the fine austenitic grain size requirement shall be deemed to be fulfilled if, on heat analysis, the aluminum content is not less than 0.020% total aluminum

or, alternately, 0.015% acid soluble aluminum.) so if the certificate/test report does not mentioned that in direct words we can confirm by the aluminum %.

killed steel —steel deoxidized, either by addition of strong deoxidizing agents or by vacuum treatment, to reduce the oxygen content to such a level that no reaction occurs between carbon and oxygen during solidification.

and I know more such as :

In practice, when a carbon steel contains a residual content of 0.10 Silicon in the chemical composition, it is considered as a Killed carbon steel. Examples are ASTM specifications A 516 Gr. 60, 70 (Plates),; A 106 Gr. B, A 333 Gr. 6 (Pipe); A 105, A 350 Gr. LF2 (forgings) etc.

When killed steel is made, a material such as aluminum, silicon, or manganese is added to the steel before it is poured into the molds. This deoxidizes the steel, forcing the oxygen out of the steel so that by the time it hits the mold, most if not all of the oxygen is gone. Some people say that the "killed" is a reference to the fact that the steel does not bubble in the mold once it is poured.

Killed steel has a very even grain and texture as a result of the absence of carbon monoxide bubbles. It is also very dense, lacking the small holes found in steel which has not been killed, which makes it heavier than pieces of steel of the same size which have not been subjected to this process. Killed steel is sometimes subject to shrinkage because of the density, which can be a concern in certain casting applications. This steel product's strength and durability are increased by deoxidation, although factors can influence the qualities of a finished steel product.

Killed steel is steel that has been completely deoxidized by the addition of an agent before casting, so that there is practically no evolution of gas during solidification. They are characterized by a high degree of chemical homogeneity and freedom from gas porosity. 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.^[3]

Common deoxidizing agents include aluminium, ferrosilicon and manganese. Aluminium reacts with the dissolved gas to form aluminium oxide. Aluminium also has the added benefit of forming pin grain boundaries, which prevent grain growth during heat treatments. For steels of the same grade a killed steel will be harder than rimmed steel.^[4]

Rimmed steel, also known as drawing quality steel, has little^[8] 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.

Rimmed and capped steels are not deoxidized; the only silicon present is the residual amount left from scrap or raw materials, typically less than 0.05% Si. Specifications and orders for these steels customarily indicate that the steel must be made rimmed or capped, as required by the purchaser, restrictions on silicon content are not usually given.

The extent of rimming action during the solidification of semikilled steel ingots must be carefully controlled by matching the amount of deoxidizer with the oxygen content of the molten steel. The amount of silicon required for deoxidation may vary from heat to heat. Thus, the silicon content of the solid metal can also vary slightly from heat to heat. A maximum silicon content of 0.10% is sometimes specified for semikilled steel, but this requirement is not very restrictive; for certain heats, a silicon addition sufficient to leave a residue of 0.10% may be enough of an addition to kill the steel.

Killed steels are fully deoxidized during their manufacture; deoxidation can be accomplished by additions of silicon, aluminum, or both, or by vacuum treatment of the molten steel. Because it is the least costly of these methods, silicon deoxidation is frequently used. For silicon-killed steels, a range of 0.15 to 0.30% Si is often specified, providing the manufacturer with adequate flexibility to compensate for variations in the steelmaking process and ensuring a steel acceptable for most applications.

Aluminum-killed or vacuum-deoxidized steels require no silicon; a requirement for minimum silicon content in such steel is unnecessary. A maximum permissible silicon content is appropriate for all killed plain carbon steels; a minimum silicon content implies a restriction that the steel must be silicon killed. Silicon is intentionally added to some alloy steels, for which it serves as both a deoxidizer and an alloying element to modify the properties of the steel. An acceptable range of silicon content would be appropriate for these steels.

Rimmed and capped steels are not deoxidized; the only silicon present is the residual amount left from scrap or raw materials, typically less than 0.05% Si. Specifications and orders for these steels customarily indicate that the steel must be made rimmed or capped, as required by the purchaser, restrictions on silicon content are not usually given.

The extent of rimming action during the solidification of semikilled steel ingots must be carefully controlled by matching the amount of deoxidizer with the oxygen content of the molten steel. The amount of silicon required for deoxidation may vary from heat to heat. Thus, the silicon content of the solid metal can also vary slightly from heat to heat. A maximum silicon content of 0.10% is sometimes specified for semikilled steel, but this requirement is not very restrictive; for certain heats, a silicon addition sufficient to leave a residue of 0.10% may be enough of an addition to kill the steel.

Killed steels are fully deoxidized during their manufacture; deoxidation can be accomplished by additions of silicon, aluminum, or both, or by vacuum treatment of the molten steel. Because it is the least costly of these methods, silicon deoxidation is frequently used. For silicon-killed steels, a range of 0.15 to 0.30% Si is often specified, providing the manufacturer with adequate flexibility to compensate for variations in the steelmaking process and ensuring a steel acceptable for most applications.

Aluminum-killed or vacuum-deoxidized steels require no silicon; a requirement for minimum silicon content in such steel is unnecessary. A maximum permissible silicon content is appropriate for all killed plain carbon steels; a minimum silicon content implies a restriction that the steel must be silicon killed. Silicon is intentionally added to some alloy steels, for which it serves as both a deoxidizer and an alloying element to modify the properties of the steel. An acceptable range of silicon content would be appropriate for these steels.

Killed steel is a type of steel from which there is only a slight evolution of gases during solidification of the metal after pouring. Killed steels are characterized by more uniform chemical composition and properties as compared to the other types.

Alloy steels, forging steels, and steels for carburizing are generally killed.

Killed steel is produced by various steel-melting practices involving the use of certain deoxidizing elements which act with varying intensities. The most common of these are silicon and aluminum; however, vanadium, titanium, and zirconium are sometimes used. Deoxidation practices in the manufacture of killed steels are normally left to the discretion of the producer.

Semikilled steel is a type of steel wherein there is a greater degree of gas evolution than in killed steel but less than in capped or rimmed steel. The amount of deoxidizer used (customarily silicon or aluminum) will determine the amount of gas evolved. Semikilled steels generally have a carbon content within the range of 0.15 to 0.30%; they are used for a wide range of structural shape applications.

Semikilled steels are characterized by variable degrees of uniformity in composition, which are intermediate between those of killed and rimmed steels. Semikilled steel has a pronounced tendency for positive chemical segregation at the top-center of the ingot (Fig. 2 ).

Rimmed Steels. In the production of rimmed steels, no deoxidizing agents are added in the furnace. These steels are characterized by marked differences in chemical composition across the section and from the top to the bottom of the ingot (Fig. 2 ). They have an outer rim that is lower in carbon, phosphorus, and sulfur than the average composition of the whole ingot, and an inner portion, or core, that has higher levels than the average of those elements. The typical structure of the rimmed steel ingot results from a marked gas evolution during solidification of the outer rim.

During the solidification of the rim, the concentration of certain elements increases in the liquid portion of the ingot. During solidification of the core, some increase in segregation occurs in the upper and central portions of the ingot. The structural pattern of the ingot persists through the rolling process to the final product (rimmed ingots are best suited for steel sheets).

The technology of manufacturing rimmed steels limits the maximum content of carbon and manganese, and those maximums vary among producers. Rimmed steels do not retain any significant percentages of highly oxidizable elements such as aluminum, silicon, or titanium.

Capped steels have characteristics similar to those of rimmed steels but to a degree intermediate between those of rimmed and semikilled steels. A deoxidizer may be added to effect a controlled rimming action when the ingot is cast. The gas entrapped during solidification is in excess of that needed to counteract normal shrinkage, resulting in a tendency for the steel to rise in the

mold. The capping operation limits the time of gas evolution and prevents the formation of an excessive number of gas voids within the ingot.

Mechanically capped steel is cast in bottle-top molds using a heavy metal cap.

Chemically capped steel is cast in open-top molds. The capping is accomplished by adding aluminum or ferrosilicon to the top

of the ingot, causing the steel at the top surface to solidify rapidly. The top portion of the ingot is discarded.

The capped ingot practice is usually applied to steel with carbon contents greater than 0.15% that is used for sheet, strip, wire, and bars.

Silicon is one of the principal deoxidizers used in steelmaking; therefore, the amount of silicon present is related to the type of steel. Rimmed and capped steels contain no significant amounts of silicon. Semikilled steels may contain moderate amounts of silicon, although there is a definite maximum amount that can be tolerated in such steels. Killed carbon steels may contain any amount of silicon up to 0.60% maximum.

Silicon is somewhat less effective than manganese in increasing as-rolled strength and hardness. Silicon has only a slight tendency to segregate. In low-carbon steels, silicon is usually detrimental to surface quality, and this condition is more pronounced in low-carbon resulfurized grades.

Aluminum is widely used as a deoxidizer and for control of grain size. When added to steel in specified amounts, it controls austenite grain growth in reheated steels. Of all the alloying elements, aluminum is the most effective in controlling grain growth prior to quenching. Titanium, zirconium, and vanadium are also effective grain growth inhibitors; however, for structural grades that are heat treated (quenched and tempered), these three elements may have adverse effects on hardenability because their carbides are quite stable and difficult to dissolve in austenite prior to quenching.

Titanium and Zirconium. The effects of titanium are similar to those of vanadium and niobium, but it is only useful in fully killed (aluminum-deoxidized) steels because of its strong deoxidizing effects.

Zirconium can also be added to killed high-strength low-alloy steels to obtain improvements in inclusion characteristics, particularly sulfide inclusions where changes in inclusion shape improve ductility in transverse bending.

When silicon-killed steel is specified, a range of 0.15−0.30% Si shall be supplied. Source: Ref 1

Steelmaking Practices

Steel plate is produced from continuously cast slabs or individually cast ingots or slabs. Preparing these steel slabs or ingots for subsequent forming into plates may involve requirements regarding deoxidation practices, austenite grain size, and/or secondary melting practices.

Deoxidation Practices. During the steelmaking process, segregation of carbon can occur when carbon reacts with the dissolved oxygen in the molten steel (a reaction that is favored thermodynamically at lower temperatures). Therefore, the practice of controlling dissolved oxygen in the molten metal before and during casting is an important factor in improving the internal soundness and chemical homogeneity of cast steel. Deoxidation is also important in lowering the impact transition temperatures.

Deoxidation can be achieved by vacuum processing or by adding deoxidizing elements such as aluminum or silicon.

Steels are classified by their level of deoxidation: killed steel, semikilled steel, capped steel, and rimmed steel. The steel used for plates is usually either killed or semikilled. Semikilled steel is commonly used for casting ingots because it is more economical than killed steel. Continuously cast steels are normally fully killed to assure internal soundness.

Killed steel is fully deoxidized, and from the viewpoint of minimum chemical segregation and uniform mechanical properties, killed steel represents the best quality available. Therefore, killed steel is generally specified when homogeneous structure and internal soundness of the plate are required or when improved low-temperature impact properties are desired. Killed steel can be produced either fine or coarse grained without adversely affecting soundness, surface, or cleanliness. Generally, heavy-gage plate

(thicker than 38 mm, or 11=2in.) is produced from killed steel to provide improved internal homogeneity.

Semikilled steel is deoxidized to a lesser extent that killed steel and therefore does not have the same degree of chemical uniformity or freedom from surface imperfections as killed steel. This type of steel is used primarily on lighter-gage plate, for which high reductions from ingot to plate thicknesses minimize the structural and chemical variations found in the as-cast ingot.

Austenitic Grain Size. Steel plate specifications for structural and pressure vessel applications may require a steelmaking process that produces a fine austenitic grain size. When a fine austenitic grain size is specified, grain-refining elements are added during steelmaking.

Aluminum is effective in retarding austenitic grain growth, resulting in improved toughness for heat-treated (normalized or quenched and tempered) steels. Steels used in high-temperature service normally contain only very small quantities of aluminum because aluminum may affect strain-aging characteristics and graphitization. However, the addition of aluminum may be necessary for some high-temperature steels (as well as most low-temperature steels) requiring good toughness. Other grain-refining elements, such as niobium, vanadium, and titanium, are used in high-strength low-alloy (HSLA) steels for grain

refinement during rolling (see the article "High-Strength Structural and High-Strength Low-Alloy Steels" in this Volume).

Melting Practices. The steel for plate products can be produced by the following primary steelmaking processes: open hearth, basic oxygen, or electric furnace. In addition, the steel can be further refined by secondary processes such as vacuum degassing or various ladle treatments for deoxidation or desulfurization.

Vacuum degassing is used to remove dissolved oxygen and hydrogen from steel, thus reducing the number and size of indigenous nonmetallic inclusions. It also reduces the likelihood of internal fissures or flakes caused when hydrogen content is higher than desired. A small cost premium is associated with the specification of vacuum degassing.

Desulfurization. By combining steel refining with the addition of ladle desulfurizing agents (for example, calcium or rare earth additions) immediately before casting or teeming, final plate steel sulfur content can be reduced to less than 0.005%. Lower sulfur content improves plate through-thickness properties and impact properties, but adds to the cost of the steel.

Aluminum is added to steel to kill the rimming action and thus produce a very clean steel known as an aluminum-killed, or special-killed, steel. Aluminum combines with both the oxygen and nitrogen to stop the outgassing of the molten steel when it is added to the ladle or mold. Aluminum also aids the development of preferred grain orientations to attain high r values in cold-rolled and annealed steel sheet. Elongated grains of an approximate ASTM 7 size are found in most well-processed aluminum-killed steels. Because the aluminum combines with the nitrogen, the steel is not subject to strain aging.

Aluminum-killed steels are deoxidized with aluminum and, possibly, with silicon. As already mentioned, use of aluminum results in a very clean steel, known as aluminum-killed or drawing-quality special-killed steel. Exceptional resistance to thinning through the sheet thickness (as measured by the plastic strain ratio, r) can be developed through the controlled processing of these steels. Because the pure iron skin characteristic of rimmed steel does not exist in aluminum-killed steel, surface imperfections may occasionally be encountered on aluminum-killed sheet. Both class 1 and class 2 drawing-quality aluminum-killed steels are produced. It should be noted that some aluminum-killed steels that cannot meet the formability requirements for drawing-quality sheet are sold as commercial-quality steel.

Thanks for your help