US1692842A - Method of manufacturing black-heart malleable cast iron from white cast iron - Google Patents

Description

Patented Nov. 27, 1928.

UNITED STATES PATENT OFFICE. 4

TABTO KIKUTA, OF TOBATA CITY, F UKUOKA KEN, JAPAN, ASSIGNOR TO TOBATA IMONO KABUSHIKI KAISHA, F TOBATA CITY, IUKUOKA KEN, JAPAN, A COB- roRA'rroN or JAPAN.

METHOD OF MANUFACTURING BLACK-HEART MALLEABLE CAST IRON FROM WHITE 'CAS'J. IRON. I v

No' Drawing.

I exposing same in the open air. The object of the invention is to spare packing material which has hitherto been necessary for the annealing process and also to shorten the anneal-- ing time. Moreover, this invention does not only produce castings of a uniform and superior quality, but also entirely prevents the black heart malleable cast iron from becoming brittle under heat treatment like hot alvanizing or sherardizing as when the or inary 2 process-of annealing is used and also, the superior quality of=iron obtained by th1s invention will remain unaffected by a temperature below the freezing point of water.

To obtain black heart malleable cast iron '25 by annealing white cast iron, it is common to fill an annealing pot with white cast iron together with sand, a mixture of sand and iron oxides, air furnace slag,or 'ash; charge an annealing furnace with same; and heat it, with coal, coal gas, fuel oil or electric current at a temperature ranging from 850 C. to 920 C.

for 7 0 to 100 hours. Then the pot is allowed to a cool very slowly in the furnace. It being possible by this method to maintain a high temperatur'e for a considerable length of time, it is possible to complete the graphitization of free cementite., but since the eutectoid cement- 'to produced at Ar, transformation point is Eraphitized only during the cooling period 40 of the furnace, the graphitization cannot be completed by the ordinary method when the quantities of carbon, silicon, and other elements contained in white cast iron are little,

or the capacity of the furnace is small. As

I regards the quality of black heart malleable cast iron produced, the perfect graphitization of this eutectoid cementite, as well as that of Application filed September 29, 1926. Serial No. 13 8,575.

the above free cementite, is of vital importance.

In an annealing according to my invention, the packing material indispensable in the method hitherto known can be dispensed with. The proper temperature between 850 and 950. is kept up constantly for 15 to 60 hours in order to graphitize free cementite. Then, the temperature is lowered to between 730 and 650 C., and after the temperature is maintained within this limit for 20 to 50 hours, the pot is taken out of the furnace and cooled in the open air. When a muflle furnace 15 used, the product is either taken out and cooled in the open air or quenched in water. The temperatures and length of time to be thus constantly maintained should be selected and properly kept within a given limit according to the chemical composition of the white cast iron.

Thus, accordingto my method it ispossible to prevent the imperfect graphitization of entect'oid cementite due to the shortage of car'- bon or silicon or the excess of the other elements contained in white cast iron such as manganese, sulphur and chromium which occurs in the method hitherto known. Besides, it is possible to shorten the time required for heating andcooling the furnace, because I do not use the packing material indispensable in the old method which adds tothe' slowness of the'cooling of a furnace due to its poor conductivity after the fire is extinguished, so that the time of one cycle of annealing can be reduced considerably, for example, by nearly 3 or days ina lO-ton furnace. Further, as

non-conductors of heat such as sand, iron oxide, slag, etc. are unnecessary, the operation is very much simplified, the annealing reduced, and the product obtained is of a superiorand more uniform uality.

The black heat malleab le cast iron manufactured by ordinary annealing methods becomes very brittle as a rule, when subjected to a heat treatment such as hot galvanizing or sherardizing; that is to say, when heatedat a ;temperature of 300 to 550 C. and then immersed in cold or boiling water. However, the product made according to my inventlon retains its original quality permanently, even if subjected to a violent heat treatment. In

fact, it may be heated to any temperature below Ar transformation point and then directly quenched in cold or boiling water or exposed to a temperature below the freezmg point of the water.

To show a manner of carrying out the present invention in practice, I give below ex-' amples of annealing process with the annealing furnaces heated by pulverlzed coal (1) and electricity (2) respectlvely.

Annealing furnaces used.

(1) Is charged with about 10 tons of the product.

(2) Is charged with about 600'kilograms of the product.

Method of charging.

Method of annealing.

In.(1), the furnace was heated at 900 C. for 40 hours to complete the first stage of aphitization (mainly of free cementite). or the second stage of graphitization (chiefly of eutectoid cementite) a temperature of 700 C. was' maintained for 40 hours. Soon after the fire was extinguished, the pots were taken out of the furnace and cooled in the open air as they are.

In (2), so as to carry out the first stage of graphitization the furnace was heated at 920 C. for 28 hours. Then, to complete the second sta e of graphitization a temperature of 710 was maintained for 35 hours. After that, the product was taken out of the furnace. Then a part of it wasquenched in cold water and the rest exposed in the open air to effect rapid cooling.

Result of annealing.

As a means of test, first a part of the product was broken and the fracture examined.

' Then, tensile and bending tests were conducted with tensile and bending test pieces made of the same melt, which has been annealed in the same furnace withthe products, and it was found out that it had been perfectly annealed, the fracture presenting a velvet-like grey color.

The following are the results ofthe tens1on and bending tests Tension test.

' Bend- Treetment after the comple- No. of Eloningtest tion of the second stage of test Tensile gatiou (inner graphitization. piece. strength in radius (kg./ (gauge 35mm.) mmJ) length= 50 mm) 995 A 36. 50 16.0 180 Agegrliiollgdplptroducts in the an B 3160 16 5 180 as at: a Air cooled products taken out 996 B 36. 90 15. 5 180 of the pot. 8g 2 g g 5 2 Qu'enched in-the water, prod- 997 B 1 1 n .85 15.5 180 ucts aken out of the pot. 997 0 3a 18 m 0 180 The tension test pieces used in the above test were inch in diameter, and thebending test pieces had a section of inch in thickness and inch in breadth.

Next, the black heart malleable cast iron manufactured by the annealing method of my invention and the malleable cast iron manufactured by an ordinary process were subjected to a heat treatment similar to those required for hot galvanizing or shera'rdizing; that is to say, heated at a temperature of 450 C. for 20 in the cold water. After being thoroughly cooled, the were subjected to an impact test, and the fo lowing results were obtained (the same result was obtained with boiling water instead of cold water, and therefore, that result is omitted) l.

minutes; and then immersed Black heart malleable cast iron manufactured by annealing according to the present invention. Black heart malleable cast iron 11191111180 Cooled in the Cooled in the Cooled in the li by air in a pot after air outside a cold water after ordmm anneal the completion not after the the completion l of the second completion of of the second stage of graphthe second stage stage of graphltlzation. of graphitization itizatlon.

Before After Before After Before After Before After the the the the the the the the heat heat heat heat heat heat heat heat treattreattreattreat treat: treattreattreat ment. ment. ment. ment ment. meat. ment. meat.

For the above impact test, a Char y impact testing machme and the standar notched bars were used and the meter-kilogram system was adopted asunits.

From the above it will be seen that the black heart malleable cast iron manufactured according tofthemethods of annealing of this invention undergoes no change in the quality under a heat treatment such as is used for hot galvanizing or sherardizing.

Thev above is more] one example of the annealing done accord ing to this invention,

and although the temperature and the time of heating should receive due consideration according to the size of a furnace and the method of heating it, etc., the essential point is to cool rapidly the product after carrying out the complete graphitization of the combined carbon contained in the white cast iron in two stages.

I claim- 1. A method of manufacturing black heart malleable cast iron from white cast iron without using packing material which comprises first maintaining the white cast iron at a temperature between 850 and 950 C. for 15 to 60 hours, then cooling the iron to a temperature between 730 and 650 0., and then maintaining the iron at the latter temperature for to 50 hours.

2. A method of manufacturing black heart malleable cast iron from white cast iron without usin packing material which comprises first maintaining the white cast iron at a temperature between 850 and 950 C for 15 to 60 hours, then cooling the iron to a temperature between 730 and 650 C., then maintaining the iron at thelatter temperature for 20 to 50 hours, and then removing iron from the furnace and cooling it rapn testimony whereof I have aflixed my signature.

v TARIO KIKUTA.