US2280283A - Deep-hardening boron steels - Google Patents

Description

- Patented Apr. 21, 1942 OFFICE DEEP-HARDENING BORON STEELS Walter Crafts, Niagara Falls, N. Y., assignor to Electro Metallurgical Company, a. corporation of West Virginia No Drawing.

Application January 5, 1940, Serial N0. 312,491

Claims. (Cl. 759123) This invention relates to steels, and more specifically to steels the hardness of which may be increased by rapid cooling from temperatures within or above the critical range. For the sake of simplicity of presentation, the application of the inventionwill be described herein principally as it may be applied to carbon steels containing 0.1% to 1% carbon, up to about 2% manganese,

and up to about 1% 81110011; but as the description proceeds it will be evident that the invenable steels.

When hardening steels by rapid cooling from taken into solid solution in steel at high temperatures, for instance boron, silicon, molybdenum,

, tungsten, chromium, or nickel. These hardening tion may be applied to a wide variety of hardenhigh temperatures, it is often-desired to produce a deep or thick zone of'hardened material rather than a thin or shallow hardened case. The depth to which a piece of steel will harden, at a given rate of heat extraction, is different in difierent steels. The property of the steel which involves this relative susceptibility to mass effect in hardening seems to be inherent, and for convenience it will be termed herein deep-hardenability.

An accepted, convenient measure of deephardenability is afforded by the Jominy" test, described in detail in A Hardenability Test for Carburizing Steel by W. E. Jominy and A. L.

Boegehold, Trans. Am. Soc. for Metals, vol. 26,

p. 574 (1938). To summarize briefly, the test is made on a small bar of steel of standardized shape and dimensions. and comprises heating the entire bar to the desired hardening temperature, quickly extracting heat through one end face of the bar, grinding off superficial scale and decarburized skin and producing a flat surface suit able for making a, hardness test, and measuring the Rockwell C hardnessalong the length of the bar. As a means for readily expressing the relation between the hardness and distance from the hardened end, the distance from the hard-' ened end at which the hardness becomes less than Rockwell C" 50 is used and is referred to herein as the Jominy depth. If the 'same hardening temperature and cooling conditions be used for a series of steels, the relative depths of the hardened zones indicate the relative deephardenability of the steels of that series, each to the others.

An object of this invention is to improve the deep-hardenability of hardenable steels generally, and of plain carbon and low alloy (less than 5% inthe aggregate of elements other than iron and carbon) steels especially.

The deep-hardenability of steel may be en hanced in some degree by. adding in suitable percentages any one of the elements which can be above-listed elements may be used to impart an even further enhanced deep-hardenability without substantial sacrifice of other. desirable properties of the steel. I have further observed that combinations of'certain ofthese elements with suitable percentages of one or'more of the alkali metals; alkaline earth metals, beryllium, aluminum, titanium, zirconium, uranium, cerium, thorium, vanadium, columbium, and tantalum, considerably enhance the effect of the combination on deep-hardenability.

In the course of my research on this subject I have discovered, that a few of these combinations of elements are particularly effective in imparting deep-hardenability, and the present invention is based on this discovery.

A particularly eiiective combination is boron and silicon, preferably with one or more of the further elements aluminum, beryllium, magnesium, calcium, barium, strontium, the alkali metals, titanium, zirconium, cerium, hafnium, thorium, vanadium, columbium, tantalum, uranium, in a suitable proportion greater than that required for grain refinement.

In accordance with the present invention, boron may be present in a percentage between 0.0005% and 0.05%, but should tween about 0.001% and 0.015%. The silicon contentmay suitably be between 0.1% and 1% or 2%, and will usually be between 0.15% and 0.35%. The minimum total proportion of said further element or elements to be'added is any proportion greater than that required for grain refinement, and preferably up to several times that required for grain refinement. The percentage required for grain refinement will depend on the kind of steel, the steel-making conditions, and the kind and number of deoxidizing and grain-refining elements used, and may be determined empirically by the methods now in common use by metallurgists' and steelmakers. In most instances the total percentage of such further elements to be added will be between 0.03% and 0.5% or 1%, and a preferred range is between 0.05% and 0.3%.

ordinarily .be beawunmswnmmmwmaamsmmn manmmmewamaunumnme J'ominy we ma d u N kUmw m m gt... eaeeceostmwwmmm Qnw0 nw m opmppmmm mmmmmmmmmmm I an e a a a a e e no 0 Q00 000000000 Q0 I TableC 0 mg... m o o o o tungsten, molybdenum,

mmmmmm emwmm Table D mm msmesemg Percentage 01 elements added Percentage oi elements added Percent Percent Percent Percent Percent Percent Percent Percent Percent Percent depth Table D is similar to Tables :e and 0, except that the relative eflfects of various combinations ,0! three, four, and live elements of the group aluminum. calcium, zirconium, vanadium, and

titanium are indicated.

For each element and each combination oi elements there appea s to be an optimum perlIardenabilit depth Percent Percent The relatively great emcacy of combinations of 7 boron and silicon maybe appreciated irom an 15 Each of the steels in Table A containsa total proportion of the elements aluminum, zirconium, 5 and .vanadiumslightlv above that required for centage .which imparts a maximum depth of hardenability and a frequent result oi an increase in percentage beyond the optimum is a de- 5 I crease of deep-hardenability below that imparted by the optimum. For reasons of economy, or to; obtain a steel having a certain desired co'mbina tion of physical properties, it will'often beds sired to add either lessor more of the elements than will impart a maximum depth or hardening. Hence, the invention is notlimited to the use of the optimum percentages.

inspection of the figures, derived from test data. in Table A whichindicat'e the relative Jominy hardenability depths, in hundredths of an inch, of steels containing about 0.45% carbon, 1.5% manganese, the indicated added percentage oi other elements, and the remainder iron.

Percent Percent Percent mess remmmm mswmmmw 0 0 0 & 0 0 G0 0"0 &0 0 0 0 grain refinement. It will be observed that neither 0.25% silicon nor 0.01% boron alone has any substantial effect on the deep-hardenability of the fine-grained steel; but that the addition of both silicon and boronincreasesthe deep-hardenability to a remarkable extent. 1

The respective and relative eflects. of additions of the single elements aluminum, zirconium, vanadium, and titanium on the deep-hardenability 45. of steels containing about 1.6% Mm-0.25% Si, 0.45% to 0.55% carbon, and 0.01%-added boron, are indicated by the figures in Table 18, derived from test data. The carbon contents of the None.

' The fact that considerable deep-hardenability is impartedbv-any of a large number o1'combi-' nations 0! elements is an important one, because the latitude in'choice or elements aflords an through selections! appropriate combinations. f In general, the deep-hardening steel of best qual- .o.oo 0.025 0.05 0.10 0.15 00 ityior mostpurposes-wlll be obtained by the ad ments" described above,zwit hin the range 0! per-' suggested herein; 'Ifhis generalization holds true not only for the steels oi the 8. All. 85 ,iaifi type (medium manganese oil hardening) g j chosen for purposesot exempliflcation in Tables 4 -B C, and D, but for low-alloy steels oiiall types,

including those containing one or more ot'the opportunity to control the cleanness, rain size, tensile streng h, and toughness oi. the steel dition of more 'two'ot the "further clenot to beunderstood that all properties neces- -sarily improve in a consistent procession as the number and percentage of added elements .in-

elements chromium, nickel, phosphorus, sulfur, etc.- However, it is Table C is similar to Table B, except that it indicates the relative effect of the addition of varicreases. .It must be borne in mind that the rel- J5 ative effectiveness 01 different elements is not the I rected) Iominy hardness depth (coraluminum, calcium, zirconium, vanadium, and

steels used in such tests rangedtrom 0.42% to 50 I Elementadded.

Alumlnmn .--.e--.. Titanium.. Zlrconium- Vanadium......;.

\ '"Not determined.

and the percentages of are the percentages added to the steel just before Rockwell 50.

by test data of the physical properties oi several representative steels after forging,

from 850 C., and drawing at 400, C. for one hour. In Table E, the indicated percentages 01" carbon and manganese are by analysis, the percentage of silicon in all steels is 0.25%, nominal, the remaining elements casting. In Table F, the yield point (Y. P.) and tensile strength (T. S.) of the steels of Table E are given in thousands of pounds per square inch; a two inch initial gage length, and per cent R. A. designates percentage reduction in area, upon fracture of the 0.505 inch diameter standam (A. S. T. M.) tensile test specimens. Under Izod are given the Izod impact test results, in foot-pounds, using. a standard specimen onecentimeter square with standard V notch one mm. deep. The Jominy Hardness Depth is that actually measured, in hundredths of an inch, to

Table E Composition of steels (rest substantially iron and 0.25% Si) Steel Per- Per- Per- Per- Per- Per- Per- Per- Percent cent cent cent cent cent cent cent cent C Mn B A] Ca V Zr Ti Cr 1 L 0A 51 7 (101 0.50 1.7 0.01 0.15 g) 0.50 1.6 0.01 0.07 0.07 0.51 1. 6 0.01 0.07 0.07 0.49 1.7 0.01 0.07 0.07 g) 0.49 1.6 0. 01 0.07 0.07 v() 0.46 1. 6 0.01 0.07 0. 07 0.50 1.6 0.01- 0.035 0.035 0.49 1. 7 0.01 0.025 0.025 0.025 0.49 1. 7 0.01 0.035 0.035 0.035 0.49 1. 7 0.01 0.035 0.035 0.035 0.035 0.51 1.6 0. 01 0.035 0.035 0. 035 .0. 035 0.50 1. 7 0. 01 0.025 0.025 0.025 0.025 0.025 0.48 .74 0.035 5') 0.035 0.035 1.0 0.50 .75 0.01 0.035 0.035 0.035 1.0

:None

Table F Properties of steels of Table E Steel N0. t P t I d J ercen ercen zo ominy 8 El 11. A. depth -In all of the Jominy hardness tests used as the bases of figures used in the tables herein, the same hardening temperature and cooling conditions were used.

As described in applications filed jointly by Walter Crafts and James H. Critchett, Serial El. designates percentage elongation in.

quenching I 3 Numbers 201,931 (Patent 2,221,781) 7 and 201,932

(Patent No. 2,221,782), both filed April 14, 1938;

and Serial Numbers.243,324(Patent No. 2,221,783) and 243,325 (Patent No. 2,269,407) both filed Debarium, strontium, boron, aluminum; (2) titanium, zirconium, cerium, hafnium, thorium; (3)

yanadium, columbium, tantalum, elements from at least two groups being presenteach in an amount preferably at least3%; or (B) at least 3% of each of at least two elements selected from the group titanium, zirconium, cerium, hafnium, and thorium. In general, it is preferred that the sumof the elements other than iron and silicon be between 10% and.20%, and not exceed at the most 25% plus an additional percentage which equals 5% multiplied by the number oi. elements in excess of two. For grain refinement, it is not ordinarily necessary to add more of the complex deoxidizing agent than enough to increase the silicon content of the steel by 0.25%. Thus, the maximum percentage that is really necessary for these purposes will not ordinarily exceed 1% of the iron or steel.

. The complex deoxidizing agents described'in the saidprior applications are admirably suited for use in accordance with the present invention, provided they. are used in a proportion greater than that required for grain refinement.

Such hardening agents as for instance boron I may be introduced into the steel with the deoxidizing andgrain refining agent, for instance as an ingredient of, one of the above-described complex deoxidizing agents, or it may be separately introduced into the molten steel either before, during, or after the addition of the deoxidizing and grain refining agent. Boron, for example, may be added to molten steel as borax, calcium borate, boron carbide or ferro-boron, i. e. in almost any convenient form.

The advantages of the invention may be expointed in any of several ways. For instance, the cheaper steels among those described above may be used instead of more expensive, more highly alloyed steels heretofore used to obtain the desired strength. Or, present high strength steels may be even further strengthened by applying the principles of the invention, either by deeper hardening to a lower average hardness or by deeper hardening to the same or even higher hardness. Among the various steels described, there is a wide range of choice in respect to such factors as cost, grain size control, ductility, strength, toughness, and types of inclusions. Thus, the invention is capable of a wide field of application, which will be apparent to metallurgists and steelmakers. Therefore, although numerous specific examples have been given herein to illustrate the principles of the invention, it will be understood that such examples are merely illustrative and do not restrict the invention beyond the requiremen of the claims and the state of the art.

I claim:

1. Method of imparting increased deep-hardenability to a hardenable steel which comprises adding to such steel while it is molten between and between 0.03% and 1%.

grain refining element in a total percentage greater than that required for grain refinement 2. 'In the method'deflned in claim 1, provement which comprises maintaining the boron content or the steel between 0.001% and 0.015%,- the siliconcontent between 0.15% and 1%, and the amount or grain-refiningelement added is between 0.03% and 1%.

. .3. Method of imparting improved deep-hardenability to a hardenable steel which comprises adding boron and silicon thereto and adjusting the proportions of such elements in said steel to at least 0.0005% but materially less than 0.05% boron and between about 0.50% and 2% silicon.

4. Method as "defined in claim 3, wherein the proportion of boron is between 0.001% and 0.015%and the proportion of silicon is between about 0.50% and 1.00%.

5'. In' a hardenable steel,'at least 0.0005% but materially less than 0.05% boron and about 0.50% to 2% silicon which boron and silicon impart improved deep-hardenability to said steel,

7 remainder iron and incidental impurities.

6. In a hardenable steel, 0.0005% to 0.015% boron; 0.1% to 1% silicon; and at least one further element chosen from each of the groups consisting of (1) aluminum, magnesium, calcium,

, barium, strontium, the alkali metals, and (2) titanium, zirconium, :cerium, hafnium, thorium,

the im- 0.1% and of silicon, at least 0.001% but mate'- .boron; between rially less than 0.05% boron, and at least one,

i v 0.1% and 2%- silicon; at least one further element of the group consist- 1115.0: aluminum, magnesium, calcium, barium, strontium, and' the alkali metals. in a total percentage greater than that required for grain reilnement and between about 0.03% and 1%.

8. Method of imparting improved deep-hardenability toahardenable steel which comprises adding thereto between 0.0005%' and 0.05%-

boron; between 0.1% and 2% silicon; and at least one further element otjthe group consisting of titanium, cerium, hafnium, thorium, vanadium, columbium, tantalum,- and uranium, in a total percentage greater than that required for grain refinement and between about 0.03%,and

9. Method of imparting improved deep-hardenability to a hardenable steel-which comprises addin thereto between 0.0005%' and 0.05%

boron; between 0.1% and 2% silicon; and at least one further element irom each of the groups consisting respectively of (1) aluminum, magflnesium, calcium? barium, strontium, and the vanadium, columbium, tantalum, and uranium,

. in a total percentage'greater than that required for grain refinement and between 0.03% and 1%, which boron, silicon, and further elements impart improved deep-'harden'ability to said steel;

alkali. metals, and (2) titanium, cerium, hafnium,

thorium, vanadium, columbium, tantalum, d uranium; the total percentage of such further elements being greater than that required for grain refinement and being between about 0.03% and 1%.

10. Method of treating molten steeloi a hardenable type to improve its dwp-hardenability when solidified, which comprises adding thereto 0.0005% to 0.05% boron'and an amount, greater than that required for grain refinement but less 0.01% to 1% carbon; manganese in a substantial proportion not over 2%; remainder iron.

'7. Method of imparting improved deep-hardeenability to a hardenablesteel which comprises adding 'thereto between 0.0005% and 0.015%

than 5%, of a composition of matter containing iron, 25% to silicon, and at least two iur= 'ther elements selected from the group titanium,

zirconium, cerium, hafnium, thorium, vanadium, columbium, tantalum, and uranium, the total amount of said further elements being between about 3% and about 20%.