US2895860A - Pressure chill-castings of iron - Google Patents

Description

United grates Patent 21 .58.69 PREs li E QFhYP-QAS NGS 9F 13-91? ucien 'P ras, Billawwrt, ra ce, s ene t R e Natiou a le des Usines Renault, Billancourt, France, French works No Drawing. Application July SerialNo. 599,906

C aim P i t P t-$9 Fram Au us 5 5 Claims. c1. 14 -3 No. 336,188, filed February 10, 1953 and applicants oo-pending patent application Nof555ji285, filed December 27, 1955.

Thus, as stated in said application Serial No. 336,188 7 the combination of the processes of chill-casting, diecasting,'and g'raphiti zatio 'n' with pretreatment for the nuclear formation, leads industrially to new products of h h q l y, hi h output at tnassp es pa t pr e ien and good surface qualit es on t e n s, hi

st eng h of th east iron and. regu ar y o p duc ien- In fa th die-cas ing o i on in eh llm s is r at a i a e co pa ed w th steel, by t e at stabi i y of the me a ath in the stora e vfu nace, y h lowerin of the casting temperature, and by the considerable reduction in the effects ofhot erosion on the chill-mold.

Thus, 'white iron can be cast without microeshrinkagecracks or blow-holes, thanks to the pressure'le'xerted during the solidification. Cracks are avoided by stripping immediately after the solidification is finished.

Due to the chill-casting, the iron can have a relatively high silicon content which lowers the tapping temperature while preserving a white structure in the rough-cast pieces. Thus the normal contents in malleable cast irons can be considerably exceeded, reaching values of between 1.5 and 2%. Moreover, higher carbon contents of 2.6 to 3% can be allowed for the same reasons.

In order to obtain the optimum efiect, it is preferable, according to the invention, to use irons containing copper though without that being an absolute necessity. Copper acts as a constituent to improve the casting qualities, as an agent for the nuclear formation of the graphite, and as an additive with a view to suitability for the hardening and tempering heat-treatment.

In order for the process to have its full effect, it is necessary, according to the invention, to carry out the triple treatment of hardening, nuclear formation and graphitization. The hardening treatment can be carried out, starting from the casting heat, by stripping fairly hot, above 810 and quenching directly in a salt-bath, for example at 180 for 1 minute, then cooling in still air, which makes it possible to obtain chilled castings without the risk of cracks or shrinkage cracks. If the casting comprises narrow parts which have been overcooled, it can, after being stripped, be immersed in a stabilizing bath at 810 one minute, after being salthardened at 180. The casting is then subjected to nuclear formation treatment, for example 48 hours at 450, then, with or without intermediate cooling, the casting is subjected to graphitization of the primary cementite; in order for the graphitization to be absolutely complete; it is necessary to maintain it at 875 for 2 to 6 hours, but this time can be reduced to between 40 minutes and two hours by annealing at 900.

The following table gives the number N per mm. of fine spherules of graphite having an average diameter of 2,895,860 i entesl July 3101.95?

N0. of Casting l 0 per- -Si vMn Cu N/mm 1 I an I In order for the process to attain its full effectiveness, it is preferable tolallow the piece to .cool on leaving the matrix and to reheatit for austenization at 810 for minutesffor example, and hardening in stages, at for 1 minute for examplef The castings are then 'subjected tonuclear formation .trleatmentrfor example .48 hours at 450?, cooled'then'r'elreated to 875 for example, just lqng'enoughfor ,theg'raphitization of the primary cementite, then 'cooledfin still air, failing which, if th'e time ta en is too long, thegraphite undei'goes a coalesc'ence with a redujc oii inlthehumber of" spherules and lowering of the'iriechanical properties. This is' shown by the following ,table'which gives the number of spherules f ai t pe mha n a d m te ess tha 2 In each case, the quantity of cementite is nil, so that the annealing for 1 hours at 875 is sufiicient. It will be seen that here the best result is obtained with the cast iron containing 1.2% copper, which has 40,000 spherules of graphite per mm.

These chill-cast irons, reheated 810/ 30 minutes, hardened in salt at 180 for 1 minute, cooled in still air, reheated to 450 for 48 hours, cooled in still air then reheated at 875 for 1 hour, and cooled in still air, are lamellar pearlitic and have the following characteristics in test-pieces 4 mm. in diameter, machined from pieces 20 mm. thick:

N o. of Casting Ou, Per- E Kg./ R Kg./ A, Percent mm) mm. cent After this treatment, a piece of casting 2162 was reheated to 835, hardened in oil, tempered at 700; it then showed: E=80, R=82, A=2.5% in a machined test-piece 4 mm. in diameter.

It is also possible, after this last tempering at 700, to stop this by oil-hardening and temper it for 2 hours at 500 to induce the structural hardening of the copper.

Finally, it is possible to modify the compositions and properties of these cast irons by alloys such as: Ni, Mo, Ti, Al, Zr and the like. The machinability, after graphitization, with or without hardening and tempering, is particularly easy, due to the graphite.

According to the two aforesaid patent applications, white iron castings are obtained by chill casting predetermined compositions under pressure in suitably determined casting conditions. These castings are subjected to a graphitisation treatment comprising three phases:

(1) Bainite or rather ma'itensite staged prequench;

(2) Germination ofthe-graphiteat temperatures contained between '400 and 500 and for periods contained between 5 and 100 hours; I

(3) Graphitisation of the primary cementite, at temperatures contained between 850 and 900 contained between minutes and 12 hours.

Recent progress has rendered it possible to reduce the period of the germination treatment, as disclosed in the aforesaid co-pending application Serial No. 336,188 appreciably. This application relates to this latter improvement.

Said treatment may be reduced to periods varying. between a few minutes and 5 hours if the castings:

(a) -Are thin (less than about 10 m.);

(b) Contain elements favouring the martensite quench, such as Ni (0.4 to 2%), Mn (brought to 1.5%), or favouring the formation of germs of graphite, such as Al (between 0.03% to 0.05%).

With these special provisions (thin castings, elements favouring the martensite quench), the reduction of the period of the germination treatment in relation to that indica'tedin the patent application Serial No. 336,188 is not accompanied by any reduction in the exceptional mechanical properties which the method of treatment in three phases enables there to be obtained.

I claim:

1. A method of obtaining malleable iron of pearlitic structure containing diffused fine particles of graphite which comprises die casting in a chill mold an iron suitable for the formation of pearlitic malleable iron, stripping the casting from the mold while hot, and above 810 C., quenching the casting in a salt bath at a temperature of about 180 C. for about 1 minute, cooling the casting in still air, subjecting the casting to a temperature between 400 to 500 C. for a period of time up and forperiods U to 5 hours, suificient for effecting formation of graphite nuclei, subjecting the casting to graphitization of the primary cementite with heat at a temperature between 850 and 900 C. for 2 to'6 hours.

2. A method of obtaining malleable iron of pearlitic structure containing diffused fine particles of graphite which comprises die casting in a chill mold an iron suitable for the formation of pearlitic malleable iron, stripping the casting from the mold while hot, and above 810 C., quenching the casting in a salt bath at a temperature of about 180 C. for about 1 minute, cooling the casting in still air, subjecting the casting to a temperature between 400 to 500 C. for a period of time up 1 to 5 hours, sufiicient for effecting formation of graphite 7 Materials and Methods, vol. 32, Issue No. 6, December nuclei, cooling the casting in still air, subjecting the casting to graphitization of the primary cementite with heat at a temperature between 850 and 900 C. for 2 to 6 hours.

3. A method as defined in claim 1, wherein the iron treated contains 0.4% to 2% nickel and 1.5% manganese.

4. A method as defined in claim 2, wherein the iron treated contains 0.4% to 2% nickel and 1.5 manganese.

5. A method as defined in claim 1, wherein the iron treated contains a small amount'of aluminum.

References Cited in the file of this patent UNITED STATES PATENTS 1,498,128 Sowers June 17, 1924 2,185,894 Hultgren Ian. 2, 1940 2,331,886 Boegehold Oct. 19, 1943 2,501,059 Kluijtmans Mar. 21, 1950 2,564,885 Sternberg Aug. 21, 1951 2,651,570 Heine Sept. 8, 1953 OTHER REFERENCES

Claims (1)

1. A METHOD OF OBTAINING MALLEABLE IRON OF PEARLITIC STRUCTURE CONTAINING DIFFUSED FINE PARTICLES OF GRAPHITE WHICH COMPRISE DIE CASTING IN A CHILL MOLD AN IRON SUITABLE FOR THE FORMATION OF PEARLITIC MALLEABLE IRON, STRIPPING THE CASTING FROM THE MOLD WHILE HOT, AND ABOVE 810*C. QUENCHING THE CASTING IN A SALT BATH AT TEMPERATURE OF ABOUT 180* C. FOR A PERIOD OF TIME UP THE CASTING IN STILL AIR, SUBJECTING THE CASTING TO A TEMPERATURE BETWEEN 400* TO 500* C. FOR A PERIOD OF TIME UP TO 5 HOURS SUFFICENT FOR EFFECTING FORMATION OF GRAPHITE NUCLIE SUBJECTING THE CASTING TO GRAPHITZATION OF THE PRIMARY CEMENTITE WITH HEAT AT A TEMPERATURE BETWEEN 850* AND 900*C. FOR 2 TO 6 HOURS.