US1279533A - Heat treatment of castings of special steels. - Google Patents

Description

15. Zing strmlg thermic hysteresis end chsrecte.

varying composition, so their anydoubt; arise as to wl'iether an ill advisable or not, praclicel e g STATES PATENT i rnnmco em mm or roam, ITALY, ASSIGNOB 'ro soomri ANONIMLA rmmsus can, ANSALDQ co, or GENOA, ITALY.

new TREATMENT or", cills'rmos 0F SPECIAL STEELS.

In "Drawing.

Steels, of which the following a specificat'ion. 10 The proc harming the object, of [this in, ventioll con 1s of a special heel: treatment to be spilled to on... legs made of special steels belt. ging to that well-lamewn. class of these metals which con'lliirise steels possess- I based by the great frequency of the centers of scciiimlcry or tellize1o11s $teels of the character mzhlziomnl form a very vest class comprising 1.

be, possible to mimic them all sepm'etcly.

I '1 he class of steels in one on is, however, well-known and, perlectly delu'mijl by the above [mentioned charactenstics; nor can steel or determined composition. belongs to said class or not. H

The heat treemncnl; :lomhing the ob ecl of the invel'iticm (jfiflllSlSllS. chiefly of the follow ihg operations to be eppliciil in the order stated to the cast.ing mmle' of a L iecml. steel havin thechemcteristics above mentioned:

1e steel casting, carefully cleansed and the scale removed, is submitted first to a.

i heat of about 800 C. hallowed by slow cool ing in the furnace. This first operetiop s performed with the principal ob ecti ot clumnatingthe ililtcrnel tension of the steel. It

dbes nof play on absolutely essentiiel part in 40 the attainment; of the hnel meohenltul properties which ibis desu cl to impart to the ,stcel by means of the complexive beet treebment, and can sometimes be on'iitited without. any drawback to the final result. Tl'llS on y "he 'verycol'ivcniently omitted, though only for economical reasons in treating certain types of steel and especially for those c011 timning a high percentage of carbon and n'mnganese. lioi'vh h lab. (emission 1s "re ience will be a, sullicienl; guide in each particular case,

The casting is brought graduelly as' min-m Spccificelion of Letters Palent.

Patented Sept. 24, 1918.

Application filed lune 4, nm'. Serial m1, 172,5?0.

and, a. Il'llLXlIlllllIl corresponding to about i 200 (l. above the same point A0,. Such temperature maintainergl within the limits above indicated for a length of time which 'vari s greatly with the variation of the di-.

mensions (and above all of the thicknesses),- of the pieces treated. Thus, for pieces weighing only a fewkilos having thicknesses of about a centimeter, the tame'm question may be lessthanm half an hour, while for "in all its pei.-ts-'---the temperature abovementioned, it removed from the furnace and pieces weighing several tons with c'lh'ick submitted to the most rapid cooling possible;

compatible with the necessity of preventing cracks. i i

This last condition depends, as is well known on the compositirm of the steel, on the way iri which the piecelms been cast, and on the dimensions and form of the piece itself.

The cooling medium..will thus have to be selected according to the above conditions of facts following the well known practical rules. 5 i I I Tl'ius, pieces of simple form and of relatively small dimensions formed of steel of average hardness will be left tocool in a currerit of cold air either natural or produced artificially.

' The large pieces of a very complicalted form. or with thin parts and formed of hard steels, will be left to'cool in n closed space. The small pieces or those of simpleform and those formed of steel with a: small percentego of carbon, of manganese and of chromium, may be cooled by immersing them parent:

in molten lead at just above its melting point, or in hotor cold oil, or in hot Water. 5. The plece treated as aboi'e is submitted to a uniform annealing.

The temperature at which this annealing should carried out depends on the final mechanical properties (particularly the ultimate resistance and the elastic limit) which are desired in the material of the piece submitted-to' treatment. 'The conditions of this annealing (aboveall as regards time and temperature) will, thus be determined for each particular case for each type of steel, by means of some preliminary tests made on the material submitted to the above mentioned treatment and followed by mechanical tests.

In. case the treatihent by the first'four steps (paragraphs 1, 2, 3 and 4) produces a product having the desired elastic limit, the annealing stepv may be omitted. I

It is, however, always advisable (and especially when a product of great tenacity and resiliency is wanted) to choose the material and to perform the treatment in such a way that the elastic limit of the steel after the treatment described in No. 4gwill be above the required value so as) to finally, bring this down to the desired point by efficient annealing. p i

It may happen in some cases that practical experience will show that it isadvlsable to repeat twice-or more,one, or cven several of the treatments described in the five preceding paragraphs. I

The application of the whole of the op erations above described, (performed under the prcscribed conditions' and in the order indicated) to steels having the characteristic properties specified at the beginning of this specification, permits one to obtain the fol lowing results, the novelty and technical importance of which are in themselies ap- A. Increase of the tenacity and resiliency of thc stcel simply cast to the approximate values, and sometimes also greater than those 'Which it is generally possible to obtain only in forged and treated steels. Such results appear above all evident in the endurance and bending; tests.

ii. The attainment of the values of the elastic limitand reduction of area, before breaking, nndcr tensile stress, such asare "generally attained only with forged and treated steels.

(7. Total climination'ot' thecharacteristic crystalline str' ctnrc ot' the cast steels. Such structure. always a sifzn (rift-agility, is sub-. stitnted (in the above mentioned steels sub- *mittcd to the described trratnwnt) by a fibrous structure similar to that which is (llfil'at'tl'ristiu of Forged steels.

l n order to be entirely clear. as to the (1) The first heating and cooling (first step of the process) is not necessary with this type of steel.

(2) The highesttemperature for the comhination in the second step of the tltermic treatment is 950 C.

(3) The heating in the third step must be maintained at about 720 C. A

(4) The cooling (in the fourth step) is effected in a cnrrent of cooled air.'

'(5) The annealing is effected at 500 C.

tem le II.-+-O0mpositz'on of the steel.

Carbon 0.09%

Silicon 0.25% Manganese": ..-0.70% 'Niokel 1.00% g Vanadium 0.28%

For this steel:

iii)

(1) The first heating (first step of the process) must be to a'temperature of about 800 C.. with this type of steel.

(2) The highest temperature for the combination in thesecond step of the thermic treatment is 1000 C.

3) The heating in the third step must be maintained at about 800 C.

(4) The cooling (in the fourth step) is best done in oil at C. I

(5) Annealing is not necessary.

Carbon 0.47% Silicon 0.20%

Manganese/suns, 0.75% Chromium -L 1.70% Vanadium 0.30% Molybdenum 0.20%

, For this steel:

(I) The first heating (first step) must be to about 800 with this type of steel.

(2') The highest temperature for the combination in the second step of the thermic treatment is 850 C.

(3) The heating in the third be maintained at about 680 (4.) The cooling (in the fourth ste is made in the atmospheric air in an inc osed space. (5) The annealing is performed at 550 C.

The position of point A0 for a casting of a given steel varies considerably with the step. mast onmtlitidm' of hpmogeneivty that Said flee presents immedmtely afixarthe of cm-3t ing and the follnwing solidificaimmn A130 slush coud twn of homogenmty a u e examples 5 suilerably wlththe WHY/1T1 wing, it; giwm Mmm, Hm lg to 0011dit l' melted whee]. (lm'ing the with the nature of the mat m molds in which the steel is v .molds, dry 'smld mnlda, 111

etc.)

The poillt Am, 'uannol; be 21% precisely determixmril, siy'mw 1T0 to it, the demnnining Mansfmmat of them ,tvhatserves m de'lserrnim it b, a, well gi'aduawd clefm-z'nmzimi not pflli'ffl localimd. From this it 5011mm 1611211; Hm (1m telmlilmtion of point Am, according; to Hm I constitution, may 0111;}; k" :b' 5K, in

Ltimi of alimony; 5

limmcnpg 91m?) I (claim; 5'

1. A. pmcess of. treating cast steely having stmnp; 1-1101?! 11 (mm, which comprises sldwly lwatnmg it-n. shed to a mn'lpemture of want flflfl" U, to 300? (I1 abnw the wignt 11d wminm ngl fllefifii ld steel. at Said tJlnpQFLH],

mpproxin."

0f album; 100 30150 C. and then rapidly c001 hrmf treatljnent te,

memt, send s ggmewd. great. portance of the hm"- Which ma pmdmwvariatio k: in mm From m such p( size and menb.

This said,;-- 1:n (milw 1; .1

' n 1, fiinllowed by an m ham l'mereauuto. signed.

m of 100mm l in pram 11135 than rziim'lingslowly