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Trecho da ASTM F2282-03

Quality Assurance Requirements for Carbon and Alloy SteelWire, Rods, and Bars for Mechanical Fasteners1

X4. SILICON AND ALUMINUM

X4.1 Silicon and aluminum act as somewhat similar elements with respect to their behavior when added

during the steel making process. They both have a high affinity for oxygen and are, therefore, used to

deoxidie or !kill" the steel.

#eoxidation or !killing" is a process by which a strong deoxidiing element is added to the steel to react

with the remaining oxygen in the bath to prevent any further reaction between carbon and oxygen. $hen

carbon and oxygen react in the bath a violent boiling action occurs which removes carbon from the steel.

$hen the bath or heat reaches the desired carbon content for the grade being produced, the carbonoxygen

reaction must be stopped %uickly to prevent further elimination of carbon. This addition is accomplished by

the addition of deoxidiers such as silicon and aluminum which have a greater affinity for oxygen than does

carbon. This effectively removes oxygen, eliminating the !carbon boil" and killing the heat. &lements otherthan silicon and aluminum can be used, but these are the most common.

X4.' Silicon and aluminum can be added together or individually. This is determined by the type of steel

desired. () silicon only is added, that particular batch of steel is referred to as a silicon killed coarse grain

 practice grade because silicon acts as a deoxidier without the formation of fine precipitates allowing the

formation of large or coarse austenitic grains.

X4.' sil*cio e alum*nio podem ser adicionados em con+unto ou individualmente. (sto determinado pelo

tipo de a-o dese+ado. Se s sil*cio adicionado, desse lote particular de a-o conhecido como acalmado em

sil*cio para granula-/o grosseira, por%ue o sil*cio atua como um desoxidante, sem a forma-/o de

 precipitados finos, permitindo a forma-/o de gr/os austen*ticos grandes ou grosseiros.

0ustenitic grain sie is not usually a factor for consideration in cold forming, but has a significant effect in

subse%uent fastener heat treatment. 0luminum, on the other hand, not only deoxidies the steel, but also

refines the grain sie. ike silicon, aluminum removes oxygen from the bath, effectively killing the heat.

0luminum also reacts with nitrogen in the steel to form aluminum nitride particles which precipitate both at

the grain boundaries and within the austenitic grains thus restricting the sie of the grains2 even when the

steel is reheated for carburiing or neutral hardening, hence the term fine grain.

Tamanho de 3r/o 0usten*tico n/o geralmente um fator a considerar na conforma-/o a frio, mas tem um

efeito significativo no tratamento trmico subse%uente do elementos de fixa-/o. alum*nio, por outro lado,

n/o s deoxida o a-o, mas tambm refina o tamanho de gr/o. Tal como sil*cio, alum*nio remove oxig5nio a

 partir do banho, acalmando eficamente o calor. alum*nio tambm reage com o nitrog5nio no a-o, para

formar part*culas de nitreto de alum*nio, %ue precipitam tanto nas fronteiras de gr/o e dentro dos gr/os

austen*ticos restringindo, assim, o tamanho dos gr/os, mesmo %uando o a-o rea%uecido para a cementa-/o

de endurecimento ou neutro, e da* o termo gr/o fino.

$hen aluminum only is added, the steel is referred to as aluminum killed, fine grain. 0 third group of steels

are referred to as silicon killed, fine grain. (n steels of this type, silicon is added as the deoxidier followed

 by the addition of aluminum for grain sie control.

6uando somente o alum*nio adicionado, o a-o referido como acalmado em alum*nio, de gr/o fino. 7m

terceiro grupo de a-os s/o referidos como acalmado em sil*cio, de gr/o fino. &m a-os deste tipo, o sil*cio

adicionado como desoxidante, seguido pela adi-/o de alum*nio para controle do tamanho de gr/o.

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X4.8 (n the two types where silicon is added, the silicon content can have several ranges with the most

common being 9.1: ; to 9.89 ;. $hen aluminum is added to these steels for grain sie control, the

aluminum content is generally in the 9.91: ; to 9.989 ; range. The aluminum content in fully aluminum

killed steels is generally 9.91: ; to 9.9:: ;, somewhat higher on average since the aluminum must both

deoxidie and control grain sie at the same time.

X4.8 <os dois tipos em %ue o sil*cio adicionado, o teor de sil*cio pode ter v=rios intervalos, sendo o mais

comum, 9,1:; a 9,89;. 6uando o alum*nio adicionado a estes a-os para controlar o tamanho de gr/os, o

teor de alum*nio geralmente na gama de 9,91:; a 9,989;. teor de alum*nio em a-os acalmados

integralmente de alum*nio geralmente de 9,91:; para 9,9::;, um pouco mais elevado, em mdia, uma

ve %ue o alum*nio tem a fun-/o tanto de desoxidar como a de controlar o tamanho do gr/o, ao mesmo

tempo.

X4.4 (n selecting the type of deoxidation practice for a particular carbon grade of steel to be used in fastener

manufacturing, a number of factors should be considered, such as, heat treated property re%uirements, heat

treat conditions, fastener sie, and steel availability, to name a few. Silicon acts as a ferrite strengthener and,

therefore, in the absence of aluminum, has somewhat greater hardenability. )or the same carbon grade and

heat treat conditions with and without aluminum, complete transformation of the fastener core during heat

treatment can take place in a larger section using a coarse grain steel. The disadvantage of silicon killed

steels can be reflected in reduced ductility and tool life during cold heading because of its ferritestrengthening characteristic. 0luminum killed steels are usually more formable and hence provide

somewhat improved tool life but reduced heat treatment response during heading, particularly in larger sie

fasteners. )or this reason, the recommended maximum diameter for oil %uenched aluminum killed carbon

grades is typically 9.1>9 in.

X4.4 <a sele-/o do tipo de desoxida-/o de uma grade espec*fica de a-o carbono para ser utiliado na

fabrica-/o de elementos de fixa-/o, um certo n?mero de fatores %ue devem ser considerados, tais como,

tratamento trmico re%uisitos de propriedades, das condi-@es de tratamento trmico, tamanho do elemento

de fixa-/o, e disponibilidade do a-o , para nomear apenas alguns. Sil*cio atua como um fortalecedor da

ferrita e, por conseguinte, na aus5ncia de alum*nio, tem um pouco maior de temperabilidade. Aara o mesmo

grau de carbono e as condi-@es de tratamento trmico com ou sem alum*nio, a transforma-/o completa do

n?cleo do item de fixa-/o durante o tratamento trmico pode ter lugar numa se-/o maior usando um a-o degr/o grosseiro. 0 desvantagem de a-os acalmados em sil*cio pode ser refletido na ductilidade reduida e

vida ?til da ferramenta durante o trabalho a frio por causa de sua caracter*stica de fortalecimento da ferrita.

0-os mortos alum*nio s/o geralmente mais mold=vel e, conse%uentemente, proporcionar um pouco melhor

a vida da ferramenta, mas reduida resposta a tratamento trmico durante dirigindo, especialmente em

grandes elementos de fixa-/o. Aor esta ra/o, o diBmetro m=ximo recomendado para a-os carbono

acalmados em alum*nio e temperados em leo tipicamente 9,1>9 polegadas.