Note: Descriptions are shown in the official language in which they were submitted.
5 1 5
BACKGROUND OF THE I:NVENTION
This invention relates to aluminum-treated
steel products, i.e. non-rimming steels to which aluminum
has been added for killing or grain refinement, or both,
and which nevertheless are not seriously characterized by
the surface defect problems often caused by the presence
of aluminum at or near the surface of an ingot, bloom,
slab or the like. As will be understood, such problems
chiefly arise from inclusions constituted of aluminum
oxides or nitrides, but in any case, the present invention
reduces or avoids significant aluminum content in the skin
of the ingot (which is wholly non-rimmed, both skin and
core) while maintaining adequa~e concentration for
desired purposes in the main body or core of steel and of
1~ products rolled from such ingot~
As~noted above, the invention is chiefly con-
cerned with steels of non-rimming character, particularly
compositions outside the usual rimming range, as by inclu-
sion of higher amounts of carbon or manganese, or both,
as well as possibly other elements, e.g. silicon, nickel,
chromium, which might also interfere with rimming action.
In particular, having regard to the fact that steels basi-
cally cannot exhibit the effervescent rimming action when
containing substantially more than or even as much as 0.15%
~5 carbon or substantially more than about 0.65~ manganese,
the invention is primarily related to non~rimming steel,
and in one preferred aspect urther contemplates that the
base composition, in unkilled state as first melted, should
be such, as to deoxidation, that formation of blow holes
at or near the surface of the ingot is inhibited. In
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1 ~ 655 1 5
1 any case, the invention provides a new product and a rela-
tively simple and effective way of making such product, to
achieve the conditions and c:ircumstances noted above,
especially for steels to be processed into bar products,
for which there is great concern in regard to ingot or
bloom defects.
Prior art has been noted that describes the
production of steel having an outer skin of rimmed steel
and a core which is killed with aluminum. Such products
tO have been attained by taking a melt of rimming steel,
pouring each ingot mold partly full, allowing the metal
to ri~ while a skin solidifies next to the mold wall,
and thereafter completing the fill o the mold with the
same molten steel, while adding aluminum. This final or
back-filling step mixes into the molten core, the ultimate
result being an ingot that has a skin of rimmed steel and
a core of killed steel w~ich otherwise has the same compo-
sition.
Some more recent inventions in this area have
2C related to addition of other and special alloying materials,
at the time of back-filling, so that the core becomes
characterized not only b~ a killed state, but by greater
strength, toughness or the like, as may be contributed by
the alloying elements. In general, these other developments,
wherein the core has bee~ killed by aluminum addition, have
contemplated the attainment of a rimmed steel skin surround-
ing the core, it being conceived that such type of skin is
necessary in order to achieve significant avoidance of skin
defects, and indeed such nature of the skin has been
especially desirable where the steel was processed, by
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~ ~65515
1 ultimate cold rolling and annealing, to achieve a true
deep-drawing grade.
The foregoing prior or other developments have
included not only disclosures in prior patents, but also
some presently developed inventions which are the subject
of other patent applications. Attention has also been
given to U.S. Patent No. 3,590,476, Bernard S. Levy et al.,
issued July 6, 1971, which describes a method, and result-
ing steel products, wherein addition of tellurium or
equivalent element for increasing machinability, is
injected into the molten core of a freshly poured ingot
after a surrounding steel skin has solidified. This patent
purports to deal with various kinds of steel, including
those with too much manganese to rim, and contemplates one
method in which the ingot mold is partly filled, then left
to solidify the non-rimming skin; thereafter, filling is
complet~d while adding the desired tellurium or equivalent.
The sole purpose of the described method and constitution
of the product is to avoid a surface defect (after hot
rolling) caused by tellurium and known as "surface check-
ing", said to be manifested by a large number of small
surface cracks, which rendèr the article commercially
unacceptable. The only concern of the Levy et al, method
and product is to avoid this surface checking on the hot
~5 rolled product, i.e. in the special si~uation of addition
of tellurium, selenium or lead, which may cause the
trouble; no other compositions or problems are considered
or discussed.
The present invention is directed to different
3U areas from the foregoing prior art, especially in making
~ 36~15
1 steel, for bar stock, which is basically non-rimming,
while the process and product are nevertheless such as
to involve relatively superior surface conditions of
the ingot or the immediately rolled articles. The chief
aim of the product is to achieve an aluminum-treated
composition, i.e. to provide a fully aluminum-killed
steel or an aluminum-grain refined steel, or both,
while avoiding certain common defects resulting from
the addition of aluminum. Moreover, the products of the
1U invention, for example by reason of suitable compositional
control, are preferably devoid of so-called blow holes,
as sometimes undesirably occur at or near the surface cr
skin of a rimmed or otherwise non~deoxidized ingot.
SUMMARY OF THE INVENTION
To the foregoing and other ends, it has been
discovered that improved, rolled steel products, especi-
ally bar products (whether round, s~uare or other cross-
sectional shape) made by hot rolling, or corresponding
billet or bloom stock appropriate for rolling to bar
shapes, can be produced by a method in which a base melt
is first prepared, as in open hearth or preferably basic
oxygen type furnaces, such melt being of non-rimming
character, but nevertheless not killed as by the inclusion
of sufficient aluminum, silicon or the like. Thus, such
a base melt of steel may contain 0.15% or more carbon,
i.e. 0.15 to 0.9% C, and 0.3 to 1.75~ manganese, with
customary limits of phosphorus and sulfur as in corres-
ponding standard steels, e.g. 0.04 max. ~ ~ and 0.045
max. % S. In addition, other elements such as nickel,
chromium and molybdenun may or may not be included as
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~ ~6~515
1 in percentages in the ranges up to 0.~ to 2.0%
I'he melt of steel so composed is then teemed into
the ingot molds, i.e. small molds conventionally suitable Eor
ingots to make bar products, for example molds on the order of 6 to
5 l0 tons capacity having horizontal dimensions of less -than
about 36 lnches (less than 9 sq. ft. in section). In each
case, the mold is first filled to about 80% to 95%, a skin
or shell of steel being allowed or caused to solidify next to
the mold wall. Although teeming may be interrupted, even for
10 one to five minutes, to insure solidification of such a skin,
it is found that with the non-rimming steel and especi~lly in
the small ingot molds appropriate for bar stock, a su~ficient,
solid shell or skin has been formed by the time the mold is
80 to 95% full so that no actual interruption of teeming is
1~ needed. In either case, teéming is continued with the same
molten steel, but with simultaneous addition of aluminum, as
by directing the latter into the falling stream of steel;
such additional material may not only be specifically aluminum,
but may also consist of one or more other elements, such as
20 silicon, sulfur, copper, boron, columbium, vanadium, titanium,
phosphorus and rare earths. As a result, the ingot mold is
filled and the core, still molten, contains the desired amount
of aluminum, plus such other elements as may be wanted.
Ordinarily, the aluminum, added so that the amount in the core
2~ will represent 0~2 to 0.5%, will have functioned -to kill the
steel throughout the core. It may also be sufficient to have
a grain-refining function if desired.
A further aspect of the invention is a preferred com-
positional adjustment or control of the base melt, i.e. in the
30 furnace or otherwise prior to pouring from the ladle (and before
the above addition of aluminum) such that so-called blow holes
do not foxm at or near the skin of the ingot. In particular,
1 ~)S5~5
1 this result may be accomplished by prsviding enough deoxidation
in the base melt for such purpose while the deoxidation is kept
insufficient for killing the steel. Thus, iE the silicon con-
tent is adjusted to be in the range of 0.03 to 0.15~ or the
5 aluminum in the range of 0.005 to 0.01%, the deoxidation is
ordinarily sufficient to inhibit formation of blow holes at
or near the ingot surface.
As will be understood, the completed ingot, with the
aluminum-treated and presumably aluminum-killed core, is pro-
cessed in conventional manner for killed steel. After solidifi-
cation, it is rolled to bloom or other shape and ultimately to
the desired products in this invention, although the steel could
conceivably be used for other hot rolled materials such as hot
rolled strip or plate.
The products, having a defined base composition
stated hereinabove, together with the core having an
aluminum content sufficient to constitute the product
as killed or grain refined, or both, are new, especially
in that the skin covering the principal surface of bars
of various cross-sectional shapes contains little or no
aluminum, or other additions (as of elements mentioned
above or possible inclusion during back-fi1ling) that
might produce surface defect problems. At the same time,
the non-killed steel is preferably sufficiently deoxidized
so that formation of blow holes at the surface is avoided.
The allowable surface defects on a Einished bar product
are dictated by specification, which is ordinarily met
by conditioning, l.e. grinding or scarfing the bloom or
billet material, from which the bar is rolled, to remove
3D surface defects before production of the finished hot
rolled bar. If the defects are too severe to be removed
,
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~6~l5
1 economically, the entire bloom or billet is scrapped.
This invention reduces the amount and/or severity of de-
fects in the bloom, billet or slab, m:inimizing rejections
and reduci.ng the conditioniny required; hence the yield of
final bar product per ton of melted steel is increased
and the cost of conditioning is reduced.
Further description of the invention and of various
specific features will appear in the following detailed
description.
DETAILED DESCRIPTION
As explained above, the basis for the present steel
may be a steel melt prepared in a conventional manner, e.g.
in a furnace process of the basic oxygen type, with various
elements added in the furnace or ladle according to the custo-
mary techniques. For example, the following are some of themany example~ of standard steel compositions that are suitable,
in weight percent (as elsewhere herein):
TABLE 1
Grade No. C Mn Si Ni Cr Mo
8620 0.18-0.23 0.7-0.g 0.2-0.35 0.4-0.70.~-0.6 0.15-0.25
20 4118 0.18-0.23 0.7-0.9 0.2-0.35 -- 0.4-0.6 0.08-0.15
4340 0.3g-0.43 0.65-0.85 0.2-0.35 1.65-2.0 0.7-0.9 0.2 -0.3
1023 0.2 -0.25 0.3-0.6 -- -- -- --
For this invention, the silicon content of the base
melt is kept at or below 0.15%, and the remainder where
desired ~as in some of the above compositions) is added
: specially at a later stage.
None of the foregoing, or indeed any steel within
the general composition ranges stated elsewhere herein, is
a rimming steel; i.e. it cannot be rimmed, in the sense of
3~ the effervescence or gas-releasing function that occurs in
3 lB5515
1 the molten metal when it is Eirst poured into an in~ot
mold. The chief characteristic responsible for the
non-rimming state is the carbon content, e.g. 0.15% or
more, although the melt, desirably for some purposes
of the present products, may also contain too much
manganese, as in the range upwards of 0.8%, e.g. 0.8%
to 1.75~ Mn. As will be unders~ood, the present inven-
tion is concerned with improvement in steels in which
these higher concentrations of carbon, and also manganese,
may be required for strength, toughness, hardness or
other properties, and which may also be desired to
include substantial contents of alloying elements such
as Ni, Cr, Mo, and perhaps lesser amounts of other addi-
tions, for instance, one or more of Si, B, Cb, V, Ti, P
and rare earths, and particularly ~1, the elements of
this last-mentioned group being incorporated in a
special manner (not in the base melt) pursuant to the
invention.
Although the base melt is neither rimmed nor
2n killed, it is preferably so treated or adjusted in compo-
sition that blow holes near the surface of the solidified
ingot are inhibited or avoided. This result can be
achieved by limited deoxidation with silicon or aluminum,
preferably by addition to or adjustment in the ladle, as
in amounts of 0.03 to 0.15~ Si or 0.005 to 0.01% Al.
Alternatively, bcth elements may be included, eOg. in
appropriately lesser ~uantities, or deoxidation may be
obtained with other elements such as calcium ~in limited
amount for this purpose, as will be known) or by inclu-
sion of sufficient carbon or manganese, e.g. as using the
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5 ~ 1 5
1 higher portion of the total general ranges of one orhoth of these elements as given herein. The steel, at
least after it reaches the ladle or is first poured, is
thus in partially killed state because of having sufficient
deoxidation to prevent formation of b:low holes ~e.g. at
or in the skin) but insufficient to be fully killed.
Such condition, and modes of obtaining it, can be con-
sidered to be well known or understood in the art, and is
amply defined by the term partially killed or by specifying
deoxidation produced by or equivalent to a content of 0.03
to 0.15% Si or 0.005 to 0.01% Al.
Stated more explicitly, the general ranges of
elements constituted essentially in a base steel suitable
for the invention, as well as certain presently preferre~
ranges by way of example, are as follows (with exceptions
noted below), the balance in each case being iron and
incidental elements, all in weight percent:
TABLE 2
C Mn Ni Cr Mo S P
-
20 Broad
range 0.15-0.9 0.3-1.750-2.0 0-1.0 0-0.5 a.o4s max. o.a4 max.
Special
range
as
example 0.18-0.450.3-0.9 0-2.0 0-1.0 0-0.25 0.045 max. 0.04 max.
As explained above, the composition as poured is preferably
in partially killed state, e.g. with inclusion of silicon or
aluminum in t~e li~ited ranges mentioned. It will also be
understood that except regarding present preference for
the above example, there is no particular correlation
between the quantities of carbon and manganese, i.e. only
_g_
1 ~$5~5
1 as practice may dictate; for instance, a steel having
selected suitabillty may need a higher Mn content (say,
l.0 to l.75%) with carbon below 0O45~l or the requirement
for a steel of 0.5 to 0.9% C may utilize manganese in the
lower range, as 0.3 to 0.6%. In general, selection of
speciEic compositions can follow standard or recognized
criteria for particular uses, especially as desired for
steel bars.
In making the ultimate product, the base molten
steel as described above, advantageously partially killed,
is teemed from the ladle into the ingot mold. Each mold is
first filled about 80 to 95% full (e.g. 90%) under circun-
stances (either by allowing the mold to stand, up to a few
minutes or more, or preferably without so doing) such that
a skin or shell solidifies against the inside wall of the
mold. Thereupon teeming of the same molten steel is con-
tinued to fill the mold completelY (i.eO back-filling) while
additional elements are added as desired. As will be under-
stood, if necessarv a plurality of molds can be partly
filIed in rapid succession, and the ladle can be returned for
the back-filling step to the same molds.
During the back-filling, i.e. completion of filling,
aluminum is added to the molten core in the mold, advanta-
geously adding it as metallic aluminum or ferro-aluminum,
in divided, solid form ~e.g. pieces not bigger than abol1t
l/4 inch~ to the stream descending from the ladle. Such
injection into the molten steel stream may begin with the
completion stage and be arranged to be finished just before
the end of all filling. There should he sufficient aluminum
added to make the ~otal amount in the completed ingot,
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5 1 5
1 i.e. in its core metal, of a desired value. Ordinarily,
the resulting steel of the core thus becomes fully
killed (aluminum killed), and further desired effects
such as grain refinement may also be achieved, in
accordance with known practices and ~unctions of aluminum
in steel. At the same time as the aluminum is added,
other elements may be incorporated in the molten core, for
example for strengthening purposes (silicon, columbium,
vanadium, titanium, boron), avoidance of directionality
in mechanical properties (rare earths such as cerium,
lanthanum and the like), corrosion resistance (copper)
and miscellaneous functions (sulfur/ phosphorus). These
elements are preferably injected into the falling stream
of steel in the same way, as solid pieces, either of the
selected element or of ferro-alloys or other compositions
of such elements or mixtures, as may be suitable.
Thus, elements so added during back-filling may
be such and in such amount as to provide the core with
the following total content, including any amounts
already present in the basic melt, inweight percent:
TABL _
Rare
Al Si Cu B Cb V Ti Earthc
0.02-0.5 0-0.5 0-2.0 0-0.05 0-0.15 0-0.3 0-0.4 0-0.0'
Max. % S P
0.40 0 to 0.2
For killed steel, an aluminum content of 0.02-0.2% usually
suffices, and for many steels silicon will be in a range
up to 0.2%, and there will be 0.045 max. % S and 0.035 max.
3D % P. In all cases f the ultimate solid product will have
~ :~ 8~51 ~
1 a skin or surface zone as defined in and with Table 2,
and a core as further defined (i.e. modifying the base
steel of the skin) in Table 3.
It will be understood that t:echniques and
devices are available for ~eeding particles, granules
or other pieces of the added metals, compounds or
alloys into the falling stream of molten metal, or
alternatively, directly into the metal in the mold as
and preferably where the steel is teemed in.
The metal filling the ingot mold, after the
above back-filling, is allowed to solidify and is
thereafter processed in manner suitable for killed steel,
and may be reduced by hot rolliny, e.g. to blooms and
billets, and ultimately to the desired shapes, which
are here contemplated to be bars (round, rectangular
or other), or of course can be hot rolled strip or plate
if the composition is suitable. Conditions for all such
hot rolling may be as known or readily determinable for
steels of the nature and composition finally attained in
the ingot core. As will now be appreciated, the rolled
products attain the unusual and highly desirable results
described above, having a non-rimmed and at most only
partially killed skin (e.g. of about l/2 to 4 inches
thickness around the ingot and about O.OOl to O.lO0 inch
around the bar or other products), which provides very
good surface properties, while the steel is functionally
and usefully equal to that of the core, with advantages
of fully killed condition and further properties attribut-
able to such content o~ alloying or other useful additives
as it may have. The steel is specially characteri~ed by
5 ~ ~ 5
1 absence of surface or near-surface difficulties (whether
of inclusions, blow holes or other nature), that are
normally of concern in ingots, blooms and billets to
be used in the manufacture of bar prc,ducts.
As a further example oF the invention,
experimental commercial-size ingots were cast in 6-ton
molds, 25 inches x 27 inches in cross-section, follow-
ing the above descrlbed practice, i.e. first filling
each mold about 85~ full, allowing it to stand about
one minute to solidify a skin, and then adding aluminum
to the teeming stream of steel during back-filling.
The ladle analysis of the base heat (balance iron) was
(%)0.22 C, 0.37-0.40 Mn, 0.03-0.04 Si, 0.03 Ni, 0.06 Cr,
0.01 Mo, 0.04 Cu, 0.007 Sn, 0.016-0.020 P, 0.016 S. During
back-filling, 6 lbs. aluminum was added into the core of
some molds, ~.2 lbs. Al in the core of othersj and 15.6
lbs. of ferro-aluminum in the core of still others,
respectively yielding core average aluminum contents (%)
of 0.042, 0.041 and 0.063. The skin in each case contained
less than 0.01% Al. All ingots were found to have excep-
tional surface properties, and as represented by the core
metal, constituted killed steel having the mechanical,
working and other properties of the base composition
when killed. Billets from these ingots required very
little surface conditioning and were successfully hot
rolled to bar products.
Although the foregoing has primarily described
the pro~uction of hot rolled bars (including rods), e.g.
rectangular, round or other, the steel of the invention
is also eminently suitable for bar products, likewise of
~ ~ 65~5
1 a variety of shapes, produced by cold reduction, Specifi-
cation as to surface character is likewise in such case
met by conditioning of the original hot rolled billet or
the like, and the invention is equally advantageous in re-
ducing the needed extent of such treatment. As will beunderstood, for example, cold drawn bar ~roducts are
usually ~roduced from hot rolled bar products, e.g. a
hot rolled bar or rod, by known, conventional procedure,
so that the surface requirements of the cold reduced pro-
ducts are expected to be satisfied by the hot rolled start-
ing products and therefore in turn by the state of the
original bloom or billet. In all cases, the principal
surfaces of product bars, meaning the chief and usually
all longitudinal bar surfaces, are in excellent condition.
~5 Respecting the above example, later tests showed the delay
before back-filling to be unnecessary.
It is explained that for the purpose of this
invention, steel containing 0.15% carbon or more is
considered non-rimming, especially having regard to the
~ further condition of the bar steel herein as partially
killed, i.e. sufficiently deoxidized to inhibit formation
of blow holes. Thus, even though in other circumstances
of molten steel, carbon in the neighborhood of 0.15% may
not be sufficient of itself to preclude the effervescent
action of rimming~ the carbon content is significant and
the situation of the melt can be such that at 0.15~ C,
notably at levels above such value, and most definitely
at 0.18~ C or more, the steel is non-rimming.
It is to be understood that the invention is
not limited to the specific compositions and steps herein-
-14-
1 1 ~5~;15
1 above set forth but may be carried out in other way~
without departure from its spirit.
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