Non-metallic inclusions
5298137
219464923
2008-06-15T10:40:14Z
Jpedant
7310114
/* Classification of non-metallic inclusions */ typo
{{Orphan|date=November 2006}}
'''Non-metallic inclusions''' are [[chemical compound]]s of [[metal]] with [[nonmetal]] which are present in [[steel]] and [[alloy]]s like separated parts.
== Sources of inclusions formation ==
Non-metallic inclusions arise because of many physical-chemical effects which proceed in molten and consolidated metal during its production.
Non-metallic inclusions which arise because of different [[Chemical reaction|reactions]] during metal production are called natural. They include [[oxide]]s, [[sulfide]]s, [[nitride]]s and [[phosphide]]s.
Apart from natural inclusions there are also parts of [[slag]], [[Refractory|refractories]], material of a casting mould (the material which the metal contacts during production) in the metal. Such non-metallic inclusions are called foreign or accidental.
Most inclusions in the reduction smelting of metal are inclusions which were formed because of admixture dissolubility decreasing during cooling and consolidation.
The present-day level of steel production technology allows the elimination of most natural and foreign inclusions from the metal. However its general content in different steels can vary between wide limits and has a big influence on the metal properties.
== Classification of non-metallic inclusions ==
Non-metallic inclusions, the presence of which defines purity of steel, are classified by chemical and mineralogical content, by stability and by origin. By chemical content non-metallic inclusions are divided into the following groups:
#[[oxide]]s (simple — FeO, MnO, Cr<sub>2</sub>O<sub>3</sub>, SiO<sub>2</sub>, Al<sub>2</sub>O<sub>3</sub>, TiO<sub>2</sub> and others; compound — FeO·Fe<sub>2</sub>O<sub>3</sub>, FeO·Al<sub>2</sub>O<sub>3</sub>, FeO·Cr<sub>2</sub>O<sub>3</sub>, MgO·Al<sub>2</sub>O<sub>3</sub>, 2FeO·SiO<sub>2</sub> and others;
#[[sulfide]]s (simple — FeS, MnS, Al<sub>2</sub>S<sub>3</sub>, CaS, MgS, Zr<sub>2</sub>S<sub>3</sub> and others; compound — FeS·FeO, MnS·MnO and others);
#[[nitride]]s (simple — ZrN, TiN, AlN, CeN and others; compound — Nb(C, N), V(c, N) and others), which can be found in alloyed [[steel]] and has strong nitride-generative elements in its content: [[titanium]], [[aluminium]], [[vanadium]], [[cerium]] and others;
#[[phosphide]]s (Fe<sub>3</sub>P, Fe<sub>2</sub>P and others)
The majority of inclusions in metals are [[oxide]]s and [[sulfide]]s since the content of [[phosphorus]] is very small. Usually [[nitride]]s present in special steels which has an [[Chemical element|element]] with a high relationship to [[nitrogen]] in its content<!-- This sentence doesn't make sense. Perhaps it should be "Usually [[nitride]]s are present in special steels which contain an [[Chemical element|element]] with a high affinity to [[nitrogen]] -->.
By mineralogical content, oxygen inclusions are divided into the following main groups:
#free [[oxide]]s — FeO, MnO, Cr<sub>2</sub>O<sub>3</sub>, SiO<sub>2</sub> ([[quartz]]), Al<sub>2</sub>O<sub>3</sub> ([[corundum]]) and others;
#[[spinel]]s — compound [[oxide]]s which are formed by bi and trivalent elements. Ferrites, chromites and aluminates are in this group.
#[[silicate]]s which are present in steel like a [[glass]] <!-- "which are present in steel like a glass" should perhaps be "which are present in steel, such as glass"-->formed with pure SiO<sub>2</sub> or SiO<sub>2</sub> with admixture of iron, manganese, chromium, aluminium and tungsten oxides and also crystalline silicates. Silicates are the biggest group among non-metallic inclusions. In liquid steel non-metallic inclusions are in solid or liquid condition. It depends on the melting temperature.
By stability, non-metallic inclusions are either stable or unstable. Unstable inclusions are those which dissolve in dilute [[acid]]s (less than 10%concentration). Unstable<!-- Should this be "Stable"?. If not, this sentence could flow more smoothly from the previous, eg "...and include iron and manganese sulfides..." --> inclusions are iron and manganese sulfides and also some free oxides.
Present-day levels of steel production allow to move off from the metal different inclusions<!-- "allow to move off from the metal different inclusions" does not make sense and could mean a number of things. -->. However in general the content of inclusions in different steels varies within wide limits and has a big influence on the metal properties.
== Influence of non-metallic inclusions to the properties of steel and alloys ==
Present-day methods of steel and [[alloy]] production are unable to attain completely pure metal without any non-metallic inclusions. Inclusions are present in any steel to a greater or lesser extent according to the mixture and conditions of production. Usually the amount of non-metallic inclusions in steel is not higher than 0,1%. However, the number of inclusions in metal is very high because of their extremely small size.
Non-metallic inclusions in steel are foreign substances. They disrupt the homogeneity of structure, so their influence on the mechanical and other properties can be considerable. During deformation which occur in the process of flatting, [[Forge|forging]] and [[Stamping (metalworking)|stamping]] non-metallic inclusions can lead to cracks and to [[Fatigue (material)|fatigue failure]] of steel.
When investigating the influence of non-metallic inclusions on the quality of steel, of great importance are the properties of these inclusions: size, shape, chemical and physical characteristics. All these properties depend on the chemical composition of steel, method of [[smelting]] and for certain steel grade<!-- 'for certain steel grade' does not make sense and could mean a number of things. -->. These properties can change within wide limits even within the same mode of production.
Different methods for analysis of non-metallic inclusions have been developed and are now in use. These make it possible to determine content, structure and amount of non-metallic inclusions in steel and alloys with high accuracy.
==External links==
*[http://www.iss.org/ Association for Iron & Steel Technology]
*[http://www.naukaspb.ru/Demo%20Metall/ Metals and alloys: Reference-book (Russian)]
*[http://www.zeiss.de/nmi Software for non-metallic inclusions analysis]
[[Category:Metallurgy]]
[[Category:Organometallic chemistry]]
[[ru:Неметаллические включения]]
[[uk:Неметалічні включення]]