CA1048306A - High strength low alloy steel - Google Patents

Abstract

HIGH STRENGTH LOW ALLOY STEEL

ABSTRACT OF THE DISCLOSURE

A low alloy steel having a composition containing columbium, vanadium and silicon, advantageously in specified ranges of content, has demonstrated superior mechanical pro-perties, comprising yield strength above 80 ksi, excellent toughness including good impact strength at low temperatures, and good formability evidenced by a suitably high percent elongation. The steel in its preferred embodiments includes a significant amount of manganese, and is economically pro-ducible in as-hot-rolled state to achieve the stated proper-ties, subject to attainment of even higher strength by an aging treatment.

Description

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B~CKGROUND OF rl'HE INVEN'~'IOI~ ;

This invention relates to high strengthl low alloy steels, particularly Or low carbon category, having ~eld strength of at least about 80 ksi (80 thousand pounds per 5 square inch), and very prererably superlor toughness, especi- -~
ally at low temperatures. More particularly, the invention is concerned with steel products achieved by hbt deformation, e.g.
by hot rolling to desired thicknesses and shapés, including sheet, strip or the like, wherein the desired properties of yield strength, toughness and also ad~antageously ductility, ~atigue resistance and weldability are attalned with an economy of alloying ingredients.
Considerable demand exists for hot rolled steel products of the sort described above, which can be ~ormed readily in a variety of fabricating operations such as in the automotive and other industries. Steels designed to serve - these purposes, and having yield strength Or the value noted above, have been proposed or made available, but to the extent ;
~hat they have avoided an expensive content of alloying ele-ments and have not required heat tr-~tments that add to the ~ost or complexity of processing, such 80 ksi or like steels appear to have been somewhat deficient in respect to proper-ties such as toughness and ductility.
Accordingly, an important aim of the present inven- i 25 tion is to provide a new steel product which is Or low alloy ~;
-~ype and which not only has the basic properties Or stren~th described above, but is characterlzed by improved ductility and greater toughness, notably improyed impact strength at temperatures ~Jell below 0F, such improvements being considered j~
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in relation to prior stecl products which mi~ht be considered approximately comparable in some other respects. Very ~ood rormability and exceptional toughness at very low ternperatures are special ob~ects of the lnvention, ~or correspondingly greater utility as to kinds Or articles that may ~ ~abri-cated ~rom the steel, and greater latitude in their circum-stances of use.

SUMMARY OF THF. I~IENTION
To the above and other ends, and especially ror economical attainment of high-strength steel products o~ the character described, an important aspect of the invention em-braces the discovery o~ a specialg low-alloy compositlon, that affords novel results in production and use. A composition which is unusually e~fective has been ~ound to comprise columbium, vanadium, and sllicon, in a manganese-containing steel ~at has a relatively low carbon content, e.g. not over about 0.1%. With this composltion, and very advantageously by the employment o~ preferred ranges for the stated elements as explained below, ste-el has been produced with the desired yi`eld stren~th of 80 ksi or above and with very good tough-- ness as well, particularly including high impact strength at low temperatures, even down to -100F. Steel products having these characteristics have been made, from ingot-derived slab or the like, by hot rolling and suitable cooling procedure, conveniently without requiri.ng any special heat treatment or the like in order to develop the properties Or strength. Un-llke some prlor steels Or this class, moreover, the composi-tions of the present in~ention do not appear to be sensitlve to minor chan~es in processlng" e.g. ~s ln hot rolllng, cooling, 1~

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~ 4~ 6 and the like, so that therc is no special dirriculty in pro-ction control to achieve the desired properties uniformly through successive heats and rolllng operations.
A rurther advantage Or the steels is that they ap-pear to have good ductility, e.g. as measured by conventional determinations of elongation, and also may have suitable weldability. Although for many purposes the products are abundantly use~ul in the as-hot-rolled condition, for example ln a~fording yield strengths upwards of 80 ksi when converted to desired product form by hot rolling or other hot de~orma-! ~ion (e.g. to a thickness reduction of at least about ~Og), it is found that these compositions can be age-hardened, in a .
simple manner, to provide still higher yield strengths, e.g.
o~ the nature 90-ksi and above. -Presently preferred compositions of the invention, now found to achieve very satisractory realization of all of the objects, include a columbium content somewhat higher than the amount employed in many previous alloys, i.e. a content -j~ above 0.05%, and advantageously in the range o~ 0. o6 to 0.15%.
- 20 A significant amount of vanadium is included, as ~rom 0.04%
to 0.1%, it being speci~ically ~ound that in these composi-tions of the invention, columbium and vanadium are not to be considered as alternatlves, i.e. they are not interchangeable as has sometimes been indicated ~or prior alloys. A content of silicon has been found important, and indeed requisite, for the speclal results described above, advantageously a content -Or 0.4% and above, being greater than mlght in some circum-stances be considered an incidental or ordinary amount; desirably the silicon content is 0.2~ or greater, and can userully be over .

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~and indeed substantially over) 0.3%. A presently prererr~d range for silicon ls 0.4% and above, and indeed quite prefer-ably 0.5 to o.6%.
The improvement in properties by the descrlbed combination o~ alloying elements appears to be unusual and quite dirferent ~rom the erfects that might have been e~pected by past experience wlth the indlvidual elements, and in fact ' different from the results of trials involving addition of certain elements separately. Thus~ ln one set of tests when .. . . .
vanadium was added to a columbium steel, i.e. a steel relying essentially on columblum for strength properties and having no special content of silicon~ there was an increase in yield 'strength, but there was also a reduction in'toughness. It is known, moreover, that the addition of sil'icon, e.g. in slg- ' '~
nificant amounts, has generally been found to reduce tough-ness even though it may have effects in improving hardness or - some other aspect of strength.
In the complete comblnation Or alloying ingredients, which represents a special feature o~ the invention, it has now been discovered that the addition of vanadium and sllicon ' together (in steel having the defined content o~ manganese and columbium)'avoids significant reduction of toughness, and ' ' that the resulting alloy, instead Or showing p-oor values of toughness or-ductility at the desired high levels Or yield strength, shows excellent toughness or impact strength as ~lell as good ductility as measured by high total elongation. In-deed, it appears that there is an unexpected synergistic effect amon~ the alloy constituents, presumably involving synergism ;
among va~adium~ sllicon and columbium, pre~erably as employed ', .

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~4~306 in the manganese-containing composition, ~or attainment Or ~oughness and ductility.
In consequence, the steel products are not only de-sirably strong but tough and excellently formable and thus have a wide utllity. Indeed, their economic value ls especi-ally high, because they are relatively inexpensive to produce and are capable o~ ernployment in clrcumstances where more costly products or heavier gauges o~ other products might have otherwise been required.
The steels are preferably made with a suitable sul-~lde shape control agent, being one Or more o~ the additions hereto~ore kn~wn for control of sul~lde shape in s*eels o~ this general class. That is to say, sulfide inclusions that are unavoidably or even ~or some purposes desirably present, not-1~ ably manganese sulfides, usually appear as globular or oval in shape be~orehot rolling. A~ter hot rolling, the sulfides tend to be abnormally elongated, in the rolling direction. This f adversely affects the transverse ductility and toughness properties of the produck. By addition, however, Or certain shape conkrol agents (which presumably reduce the plaskicity orthe inclusions), the sulfides can be kept in oval configura-~ion, with corresponding preservation of ductility and tough- i ness properties in transverse as well as longikudinal direc- ~ -tions. This shape conkrol agent, conveniently so designated 25 even though it may in ract be plural, can be one or more ele- !:
ments selected from the group consisting Or the rare earth --metals (e.g. cerium, lanthanum, or others as known)g æirconium, and in some cases se~enium or tellurium. The runction of such azents is well recognized.

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As indicated, an important, cooperatlny element in the compositions is manganese, usefully present in moderate rather than very low amount, e.g. 0.3~ and above, and advantage-ously a range over 0.4%, i.e. 0.8 to 1.65%. It also appears ;-desirable to have a small content of nitrogen, for example ;
up to 0.03%, it being thought that the effect of columbium and vanadium is in part achieved by a kind of precipitation hard-ening including the deposition of carbonitrides of these ele-ments. As noted, the carbon content is advantageously low and indeed can presumably be very low, but it appears that for satisfactory results, in general, expensive procedure to ~;
bring carbon down to extremely small values is unnecessary.
For instance, it is understood that a carbon content as low as 0.03% is readily obtainable in good electric furnace prac~
tice or the like, and indeed excellent results have been achieved in the present invention with carbon in the range of 0.05 to 0.1%. `~ ;
The invention is directed to a high strength steel product produced by hot rolling to a reduction of at least 50%, ~ `
and having a yield strength of at least 80 ksi longitudinally and transversely, the steel consisting essentially, in weight percent, of 0.05 to 0.10% C, 0.5 to 1.65% Mn, 0.2 to 0.8% Si, 0.08 to 0.15% Cb, 0.05 to 0.15% V, 0 to 0.2% of sulfide shape control agent, and from 0 to the following maximum percentages of the following elements, 0.03 max. P, 0.03 max. S, 0.03 max.
N, 0.09 max. Al, balance iron and normal impurities and residual elements.
The invention is also directed to a steel product as defined above which contains 0.8 to 1.65% Mn. The steel product may also contain 0.08 to 0.12% Cb.

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The steel product described may be produced by hot rolling to a finish temperature in the range of about 1500~F
to 1850F, cooling to a temperature in the range of about 900F to 1300F and collecting, at the temperature to which the hot-rolled steel is cooled, by coiling or piling, the steel being aluminum killed.
The steel produced may contain 0.8 to 1.65% Mn, 0.08 to 0.12% Cb, and 0.05 to 0.15% V.
The invention is also directed to high strength steel product having a yield strength of at least 80 ksi longitudinally and transversely and produced by hot deformation to a reduction of at least 50%, the steel consisting essentially, in weight percent, of 0.03 to 0.10% C, 0.3 to 1.65% Mn, 0.2 to 0.8% Si, 0.08 to ;
0.15% Cb, 0.05 to 0.20% V, 0 to 0.2% of sulfide shape control agent, and from 0 to the following maximùm percentages of the following elements, 0.03 max. P, 0.03 max. S, 0.03 max. N, 0.09 max. Al, balance iron and normal impurities and residual elements.
The steel product may contain 0.8 to 1.65% Mn, 0.08 - ;
to 0.12% Cb, and 0.05 to 0.15% V. `
The steel product produced may be aluminum killed and may be produced by hot rolling to the reduction, and may contain 0.05 to 0.10% C. ~ -The steel product produced may contain 0.5 to 1.65% Mn, and may also contain 1.25 to 1.60% Mn.

DETAILED DESCRIPTION
As indicated above, the steels of this invention, conveniently produced in economical manner without special heat treatment or the like, are characterized by yield strengths upwards of 80 ksi, ultimate tensile strength upwards of 90 ksi, `~

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ductility as measured by percent elongation (2 inches) in excess of 20%, and superior low temperature toughness. In particular, as measured by half-size Charpy V-notch specimens, in conventional manner, the steel showed impact strength of at least about 20 foot-pounds in the longitudinal direction and 10 foot-pounds in the transverse direction, at -100F.
The steel is also preferably characterized, - 7b -.:: ~ .' , .
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3~6 in the preferred compositlons~ by superior transverse and longitudinal rormability, good fatigue reslstance, and good weldability. All Or the foregoing properties are achieved ln the as-hot rolled condition, i.e. being the steel as directly resultlng rrom suitable hot rolling and cooling procedures.
The steel is prepared in an essentially conventional way, e.g. ror making a relatively low carbon, low alloy steel, following known practices for producing a clean steel, with good control of desired contents Or small percentages of al-loying elements. Thus the basic melt is achieved in a usualmanner, as in a standard electric or basic oxygen furnace~ ap-propriate attention being paid to the desired low carbon content, whether by conventional deca~burization if necessary, or otherwise. It is understood that carbon levels as low as -0.03% are effectively obtainable without special treatment of - the melt after tapping, and indeed present results have been very good with steels having a carbon range Or o. o6 to 0.1p, which pose no special problem in melting practice.
Additions of the several required elements to the basic charge of scrap, iron, and the like are made in the manner appropriate ~or such materials, the manganese being - added in the ~urnace and/or ladle, e.g. as rerromanganese.
Very preferably, the minor, special alloying additions, being columbium and vanadium, are e~fected by adding appropriate material (for example, as ~erroalloys) to the melt in ~e ladle after tapping. Sllicon, unless present in su~ficient amount by selection o~ materials or the original charge, can be added .. . ..
to the rurnace and/or ladle to the extent necessary~ e.g. as rerrosilicon. A desired nitrogen level above about 0.01% can , ..
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'~' 483()6 be achleved by the addltion o~ high' ni~ro~en bearln~ rerro-alloys, the manner Or adJusting the propor tion o~ nitrogen in steel, within the ranges noted elsew}~e herein, being ~ell known ln practice.
T}le steel compos~tion o~ thls inventlon must be fully deoxidized. Deoxidation is very preferably achieved by addition Or àluminum, e.g. to the ladle. Although conceivably other deoxidation practice may be followed, it is presently deemed desirable to reduce oxygen to very low values, i.e.
les~ than 0,005%
Another ladle and/or mold addition may preferably be

2 sulfide shape control agent which, as explained above, is selected ~rom the elements known ror such runction. The rare earth elements are presently conventional and effective ~or this purpose, and are suitable ~or the compositlons o~ the ~invention. Thus one or more Or the elements such as cerium, lanthanum, or others~as well known may be employed.' Por ex-am~e, compositions consisting primarily of cerium and lan-thanum æe commercially avaiIable for use as additions to steel' melts, and serve eff`ectively. Alternatively, when the level . o~ nitrogen is low, addition of zirconium may be employed, and in some instances addition o~ substances such as selenium or tellurium. `
A~ter pouring the steel of the melt, which has been ' suitablY controlled as to content of the several required ele-ments, the resulting ingots are handled in conventional way, being reduced to slab or the like, for rinal reduction by appro-priate hot de~ormation. For most purposes 9 thiS ~'s er~ected by ' hot rolling, for example through the requislte number o~ passes, '30 to a selected finish temperature~ for instance in the range o~
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3~6 about 1~500~l to 1,850F. The desired product~ e.g. sheet, strlp, or other shape delivered by the hot mill at the de-sired temperature, is appropriately cooled, for example at rates in the range Or about 15 to 135~ per second (with alr, or ~ith water spray or Jet if needed), down to a selected temperature, as in the range of about 900 to 1,300~. The strip or sheets or other products are then collected by coiling or plling at the last-mentioned temperature, and therea~ter allo~ed, in usual fashion, to cool very slowly as so collected.
The improved high streng~h, low alloy steels can be produced, as hot rolled product, in a usefully wide variety of gages, for instance ~rom about 0.05 to 0O~ inch, particularly o.o8 inch and upwards; a thickness range Or special utility, 15 economically realiæing all of the superior properties of yield strength, toughness, ductillty and formability, is from about 0.09 to about 0.35 inch. In all cases, the desired yield strength Or 80 ksi or better is readily achieved.
It is found, moreover, that sig~lificant increase in such strength to 90 ksi or higher is obtainable (without substan-tially impairing toughness or other properties), where desired, by a slmple aging treatment o~ the coiled or other finished hot rolled product; such treatment can be o~ a sort otherwise known ror aging, as by heating to a suitable temperature, e.g. 1000 to 1300F for a required time, such as 5 minutes to three hours. Thus aging for one half hour at 1100F has been found ~ery ef~ective, i.e. attaining the stated results on tests with steel from hot-rolled coils in the examples below. .
One example of a heat made to have the new.composi-tlon yielded hot rolled product with the rollowing analysls . . _ .... .
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all cases the balance being iron, and incidental elements e.g.
such as noted, or in trace amounts): 0.07~ ~, 1.538% Mn, I
0.574% Si, 0.037% Al, 0.117% Cb, 0.089% V, 0.018% ~, with (rare earths for sulfiAe sha~e control) 0.018Z Ce and 0.007 La, and low values Or phosphoru s, sulfur and oxygen, i.e.
0.008% P, 0.007% S and 0.001% oxygen. This heat was prepared ln the manner described above, a particularly satisfactory rolling sequence used in this and other preferred heats de- . .
scribed herein, being hot rolling to finish gage at a finish temperature of 1550 to 1650F or a little higher, cooling rather rapidly (in the range of rates mentioned above), with water ~ets i~ necessary~ to a temperature in the range of 1000to 1225F (or slightly above) for coiling or stacking.
Thus among other (and equally good) products of ~-his heat, ~ive hot rolled coils o~ gage about 0 09 inch were . ~-satisfactorily produced at finish temperatures varying from 1600 to 1700F, with coiling temperatures varying (in random relation to ~inish values) from 1020 to 1160F. These showed excellent properties, with very good unlformity, viz. upwards of 86 ksi yield strength (here and elsewhere herein determined at 0.2% ofrset) in various directions and various parts of the coil, and upwards o~ 100 ksi ultimate tensile strength simi- .
larly measured. Similar uniformity of results, among different 25 heats and among dlrferent coils from each heat and different :
locations in each coil was observed ln products from a number Or ~ke heats (mentioned below) with finish temperatures from 1550 to 1680 and coiling temperatures from 1160 to 1260, i.eO yield strength upwards of 83 ks1 and ultimate tensile Or ' ', .

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~#;~6 94 ksl and above. Average elongations (2 lnches) for the ~arious coils ranged rrom about 21% to 26% or hi~her.
As mentloned, other examples of products having the desired composition were produced with comparably superior .
5 results. Considering the above product and rour ~ther heats as .
representative, the variation Or individual element-contents .
(balance iron) in welght percent was: carbon 0.058 to 0.094 , manganese 1.347 to 1.538 3 silicon 0.495 to 0.574, aluminum . ~.018 to 0.054, columbium 0.093 to 0.130 ? vanadium 0.078 to . .
10 o.o89, nitrogen 0.016 to 0.024, cerium 0.015 to 0.027 and .
lanthanum 0.004 to 0.009. Phosphorus and su].fur maxima were 0.01%, oxygen 0.002%. The average or these compositions, wherein the variations were random relative to each other, was . (in percent) 0.078 C, 1.48 Mn, 0.554 Si, 0.034 Al, 0.114 Cb, :~
0.084 V, 0.019 Ce, 0.007 La~ 0.018 N, o.oo8 P, 0.007 S and - 0.001 oxygen. . . . . :
. From measurements of hot rolled products Or the above . heats, Or selected thicknesses from 0.09 to 0.22-inch, the .
average yield strength was 87.1 ksl, longitudinal, and 91.1 .
20 ksi3 transverse, with average ultimate tensile 103 ksi, longi- .
tudinal, and 105 ksi, transverse. The average percent elonga-tions (2 inches~ were 24.8 longitudinal and 23.6 transverse, .
being generally 20 or more and thus indicating good ductility. .
The toughness prope~ies were excellent; Charpy V-notch tests, :~
measured with half-size specimens.(at temperatures determined ~n degrees F.3, on products of the same heats, showed average :
impact values on specimens taken in the longitudinal dlrection (directlon of rolling), measured in root-pounds, of 43.8 at ~70~, 40.2 at ~20~ 37.1 at -20, 34.2 at -60, and.30.5 at :.
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33~36 -100. On transverse specirnens, the averaGe impact values in root-pounds were 30.2 at ~70, 28.ll at ~20, 26.8 at -20, 23.8 at -60, and 21.1 at -100. Deviations from these values ln individual caseswere not large lndlcating that the improved steels are capable o~ substantially exceeding values o~ 20 ~oot-pounds, longitudinal, and 10 ~oot-pounds, transverse, at -100F, representing superior low temperature toughness.
As explained above, it appears that the addition Or both ~anadlum and silicon in these steels ar~ords an unusual result, indicatlve o~ a synerglsm that is not expllcable by the known properties of these elements. Thus in one series o~
tests, Charpy V-notch determinations were ~irst made on columbium-containing steels which had low carbon compositions (including man~anese and columbium) that were generally similar to products of the above examples, but lacking vanadium and having no significant silicon content, i.e. ~rom 0.012 to 0.025 Si. Then similar steels were produced with addltions of ~anadium, e.g. 0.03 to 0.055%. In all cases, the latter co~n-positions showed a definite decrease in toughness (Charpy im~
pact values), bein~ marked at low temperatures e.g. -60 and -100F. The increase in yield strength was relatively modest.
Although additions of silicon (o~ the extent employed in the new products) are normally characterized by substantial decrease in toughness, with relatively moderate improvement in yield strength, the combination of vanadium and silicon con-tents in the present steels was found to afrord a very signifi-cant and uniform increase in yieldstren~th, with little or no decrease in tou~hness as compared with the basic steels con taining only columbium as special alloying element. Indeed, ~ .' , - , .

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tests sho~/ed that the C~arpy impact valucs werc relatively Ull-affected, or were even improved.
Specirically a steel contalning only 0.02 Si, and high Cb (0.094), wi.th no vanadium~ revealed yield strengths Or .
76 ksi longi~udinal and 79 ksi transverse and corr~sponding lmpact values Or 40 and 22 foot-pounds at-40F. A like com- .
position ~ith 0.05% vanadium added exhibited yield stren~ths Or 80 and 85 ksi and impact values of 37 and 21 (-40F), similarly measured. In marked contrast, the steel of the first example above, containing both vanadium and silicon (0.57%) as well as columbium, had markedly higher yield strengths o~ 87 and 92 Icsi and impact values of 37 and 26 (at -40F), whereas such addition o~ silicon alone would have been expected to have a lesser ef- -¦
fect on yield strength and a detrimental ef~ect on toughness.
It should be noted that ln all these tests the steels were otherwise comparable, for example as to low carbon content and as to a man~anese cont.ent in the range of 1.25 to 1.6%. :.
With reference to the above examples an.d to good re-liability of attainment of desired results ~of strength, tough-ness, ductility) regardless of variables in processing, it pre-sently appears that for products which have been, for example, hot-deformed to a reduction of at least 50%, particularly suit l.
able compositions are characterized by the followingcontents of significant elements (balance iron and incldentals): 0 to 0.1% C
25 (conveniently 0.03 to 0.1% C), 0.3 to 1.65% Mn, 0.2 ~ordinarily preferably from 0.4) to o.6% Si~ 0.06 to 0.15% Cb, 0.03 to 0.2% ,.
V; the composltion may also, indeed prererably, include a sul-~ide shape control agent, as in known, customary amount, thus de~inable as up to 0.2% o~ sulride shape control agent. Such , I .
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3~3 agent ~Ihen desired is includ2d ln an ef~ective amoun~ in a range above 0.01~, for example up to 0.1% beinG usually suffl cient for rare earth addition and up to 0.2% ror zirconlum.
~s will be understood, the steel is preferably aluminum-killed.
The product can be further defined as including from zero to the following maximum percentages of the ~ollowing elements, 0.03 max. P, 0.03 max. S, 0.03 max. N, 0.09 max. Al.
Mention of oxygen is omitted as in effect an incidental ele-ment~ being usually not more than 0.003%, o~ten only about 0.001%. Compositions within the ranges (as to all elements) given last above appear to exhibit fully the synergistic ef- ~-~
~ects that have been noted, i.e. including along with hlgh yield strength (well above 80 ksi), superior toughness (especi-ally in subzero condition), high total elongation and thus 15 improved formability. -A presently preferred range of compositions, for -economy and assurance of results, comprises 0. to 0.1% C (again, conveniently upwards Or 0.03%), o.8 to 1.65% Mn, 0.4 to o.6%
Si, 0.07 to 0.14~ Cb, 0.05 to 0.15% V, and other elements as noted in connection with the above somewhat wider ranges, but preferably including up to 0.025% (e.g. at least about 0.005) nitrogen, 0.01 to o.o6 Al, and an effective amount of sulfide shape control agent, e.g. up to 0.2%. The nature of such agents has been explained above; an especially useful agent consists of one or more elements of the olass consistlng o~ the rare earths and, with low nitrogen levels, zlrconium.
As will now be appreciated from all of ~he foregoing, a number of variations and selections, as to individual alloy-ing elements, i.e. each considered by itselr, are illustrative Or ~eneral aspects of the composition. ~hus for some purposes, - l5 ~

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~ 483~6 columblurn can be as ~ow as 0~0~1% (or possibly down to 0.03%), prererably at least 0.05%, but with special advanta~e for more thar~ o.o8%, prererably a range of 0.09~ and above, e.g. to 0.14%. Llkewise manganese can be varied independently of other elements, l.e. withln ranges elsewhere given herein, a very useful range being 0.8 to l.6%. While it ls conceivable thatin some cases a low silicon content can be employed, e.g.
down to 0.2%, especially (though perhaps not necessarily) ln s~tuations of the preferred contents of carbon, columbium and vanadium, it ls contemplated that superior results require a - signi~icant content o~ silicon, e.g. 0.4% or more, usually not above 0.6% although it is conceivable that silicon could sometimes - be as much-as 0.8%. Vanadium, another important element con-sidered independently o~ the others, may broadly lié in the 15 range o~ 0.03% (preferably at least 0.04%) and above, and even up to 0.2%, a greater preferred range is 0.05% to 0.1%.
A speci~ic example Or a steel, according to the in-vention, that is capable o~ higher strength in as-hot~rolled !
conditior., e.g. qulte substantially higher than 80 ksij is the - 20 following approximate composition as to elem~nts Or principal significance; 0.07% C max., 1.50% Mn, 0.60% Si, 0.15% V, .10% Cb, 0.017% nitrogen.
As will now be seen, the invention afrords new high strength, low alloy steels that attain excellent tensile pro-perties, toughness, ductility and rormability, that are economi-cal to make and use, and that can be produced with good reli--ability as to attainment o~ desired results.
It is to be understood that the invention is not llmited to the specific embodiments herein described but may be carriéd out in other ways without departure rrom its spirit.
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Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A high strength steel product produced by hot rolling to a reduction of at least 50%, and having yield strength of at least 80 ksi longitudinally and transversely, said steel consisting essentially, in weight percent, of 0.05 to 0.10% C, 0.5 to 1.65% Mn, 0.2 to 0.8% Si, 0.08 to 0.15% Cb, 0.05 to 0.15% V, 0 to 0.2% of sulfide shape control agent, and from 0 to the following maximum percentages of the following elements, 0.03 max. P, 0.03 max. S, 0.03 max.
N, 0.09 max. Al, balance iron and normal impurities and residual elements.

2. A steel product as defined in claim 1, which contains 0.8 to 1.65% Mn.

3. A steel product as defined in claim 1, which contains 0.08 to 0.12% Cb.

4. A steel product as defined in claim 1, which is produced by hot rolling to a finish temperature in the range of about 1500°F to 1850°F, cooling to a temperature in the range of about 900°F to 1300°F and collecting, at said tempera-ture to which the hot-rolled steel is cooled, by coiling or piling, said steel being aluminum killed.

5. A steel product as defined in claim 4, which contains 0.8 to 1.65% Mn, 0.08 to 0.12% Cb, and 0.05 to 0.15% V.

6. A high strength steel product having yield strength of at least 80 ksi longitudinally and transversely and produced by hot deformation to a reduction of at least 50%, said steel consisting essentially, in weight percent, of 0.03 to 0.10%
C, 0.3 to 1.65% Mn, 0.2 to 0.8% Si, 0.08 to 0.15% Cb, 0.05 to 0.20% V, 0 to 0.2% of sulfide shape control agent, and from 0 to the following maximum percentages of the following elements, 0.03 max. P, 0.03 max. S, 0.03 max. N, 0.09 max.

A1, balance iron and normal impurities and residual elements.

7. A steel product as defined in claim 6, which con-tains 0.8 to 1.65% Mn, 0.08 to 0.12% Cb, and 0.05 to 0.15% V.

8. A steel product as defined in claim 6, which is aluminum killed and is produced by hot rolling to said reduction, and which contains 0.05 to 0.10% C.

9. A steel product as defined in claim 6, which con-tains 0.5 to 1.65% Mn.

10. A steel product as defined in claim 9, which con-tains 1.25 to 1.60% Mn.