US2139939A - Method of producing an iron alloy - Google Patents

Description

Patented Dec. 13, 1938 UNITED STATES PATENT OFFICE 2,139,939 IHETHOD OF PRODUCING AN IRON ALLOY of New York No Drawing. Application May 15, 1936 Serial No. 79,922

3Claims.

This invention relates to the production of a cast-iron alloy of such nature that when used to form objects that are subjected to frequent and considerable heat such objects will not substan- 5 tially and permanently increase in size, change in shape or undergo undue cracking from repeated heating. An illustration of some of such objects are those parts of a cast-iron warmair furnace, stove or the like, that are subjected to the i0 direct and repeated actions of the heat such as the firepots, fire domes, grates and the like. These examples are to be understood as illustrative only and not as limiting the scope of our invention, as many other illustrations might be cited as being equally applicable.

' It has been the history of cast-iron warm air furnaces and stoves, that certain parts will frequently crack or burn out when operating under certain unfavorable conditions such as over-firing of the furnace, the use of certain types of coal, insuflicient air supply to the-heater, and other conditions. The need has long been felt of being able to develop some kind of cast-iron which would have properties that would more greatly resist and these conditions.

Upon high heating, prior to the present invention, the castings subjected to the direct and repeated actions of the heat would expand, and when allowed to cool would contract This repeated expansion and contraction has a wearing and tearing action upon the fibre of the castiron. Under each reheating they would expand more and more and never eventually return to their original or true dimensions. .They would 5 generally warp out of shape irregularly and unevenly. In doing this they would frequently carry this warpage into adjoining castings which are fitted to them. Damage is thus also done to other castings which are not under the same ,0 stress of high temperature and which ordinarily would not expand out of shape to such a great extent.

For the purposes of this specification we term this failure of such castings to return, after repeated expansions, to their original or true dimensions, as growt In other words, they eventually grow or increase in size, and sufier'an undue permanent deformation. This "growth continues with repeated expansions, with its destructive action, until the very body of the castiron begins to tear apart and cracks appear in the castings.

After these cracks are once started, deteriorating elements in the combustion of the fuel are able to penetrate intr these cracks and help add to the destructive action. taking place. These cracks eventually enlarge to such an extent that finally a direct break will occur and a hole be gradually burned through the casting.

After careful investigations and study we have found that when chromium is introduced into cast-iron, it refines the grain of the casting, delays the breaking up of that constituent, or those constituents, which promote the general tensile strength of gray iron castings, and stops or substantially stops growth and cracking in the casting.

In our experiments and developments we have discovered that the above mentioned defects and disadvantages can be substantially eliminated by adding to the molten cast-iron from 1 to 1.5 percent of chromium, the molten cast-iron being raised, prior to the addition of the chromium, to a temperature somewhat higher than that used in customary gray iron practice, and the molten iron, after the addition of the chromium, being more quickly transferred to the mold and poured immediately to avoid undue cooling of the iron.

Among the objects of our invention are the overcoming of the disadvantages and the gaining of the advantages pointed out above.

A further object is the prevention of substantial growth in cast-iron parts subjected to considerable and frequent heating.

Another object is the prevention of substantial cracking in cast-iron parts subjected to considerable and frequent heating.

A still further object is the provision of novel steps in handling the cast-iron in melting it and adding chromium thereto in proper proportions.

A further object is the addition of the chromium to the molten cast-iron at the proper time and place, the heating of the iron to a higher temperature, and the quick handling of the molten iron after the chromium is added.

Another object is the production of a new iron alloy for the purposes stated.

Other objects, advantages and capabilities inherent in our invention will later more fully appear.

The growth or permanent substantial deformation of the usual cast-iron parts subjected to considerable heat causes considerable difiiculty when it is necessary to replace an old permanently deformed part with a new part that is required to correctly interfit with another part that is likewise permanently deformed. The new part in suchinstances does not properly interfit with the old part because of the new part having the correct original dimensions while the original di- An instance of this is found in cast-iron warm air furnaces and stoves which have been in use for some time and in which it is found necessary to replace one of the parts, such as in the firepot, fire dome, .grates, etc., these being the parts subjected to the most heat and consequent deformation. When such new part does not interfit with the cooperating old part it is generally necessary to have to also order another new part to take the place of the old part, thus involving additional delay as well as further expense.

By our present invention this delay and additional expense is avoided, thus affording the purchasing public the advantageof economy as well as saving in time. Many other instances than the specific parts of heating furnaces and stoves mentioned above could be cited, but these serve as passing illustrations of the value to the general public of the present invention. With cast-iron parts made in accordance with the present invention such repairs or replacement will be necessary much less frequently, and even should they, in greater length of time, be needed the expense and delay would be very much less.

In the production of the alloy of the present invention we add chromium to the molten castiron, either in the cupola or preferably as it runs from the cupola orbther melting device, in an amount approximately between 1 to 2 percent. Among the compositions or mixtures of the castiron to which we have found it especially advantageous' to add the chromium, and preferably from 1 to 1.50 percent, is:

Carbon 3.00 to 4.00 percent Silicon 2.25 to 2.75 percent Sulphur .05 percent and under Phosphorous .50 to .80 percent Manganese .50 to 1.00 percent the balance being approximately pure iron. Materials of other and varying contents may be similarly treated to advantage with a similar content of chromium. Where we add the chromium to the molten metal in the cupola, we prefer to have the chromium in the form of briquettes.

The chromium we preferably obtain'in the form of what is commercially called ferro chrome, which contains from to percent chromium,

3 to 4 percent silicon and 4 to 5 percent carbon.

Carbon 3.00 to 4.00 percent Silicon; 2.25 to 2.75 percent Sulphur .05 percent and under, Phosphorous .50 to .80 percent Manganese .50 to 1.00 percent Chromium"; 1.00 to 2.00 percent Pure iron 92.70 to 89.45 percent In the carrying out of our improved method for the production of our new alloy, the castiron, which is preferably a mixture of scrap and pig iron, is melted in a cupola or the like to a temperature somewhat higher than that employed in the usual gray iron practice. The

chromium is preferably added after the molten iron emerges from the tap hole in the breast of the cupola, the addition of the chromium occurring intermediate the tap hole and the receiving ladle. In our particular practice the molten iron flows from the tap hole down an inclined. stationary spout and into a tiltable spout that can be tilted to either side in order to conduct the flowing stream of molten iron into a receiving ladle on either side of the front of the cupola.

We have found it good practice to introduce the chromium into the flowing stream of molten iron at the point where the stream passes from the stationary spout of the cupola into the tilting spout for conducting it to the ladle. The chromium may be in the form known commercially as ferro chrome. The desired amount of this ferro chrome may be placed in a container positioned just above the point of delivery of chromium to the molten iron, which container may be open at the top and provided on its bottom with a downwardly extending spout of such size in cross-section as to deliver the ferro chrome into the molten stream of iron at such speed that the period of flow of the desired amount of chromium will be from the time that about the first fifty pounds of molten iron is accumulated in say, for example, a one thousand pound ladle, up to shortly before the ladle is filled to its intended capacity. Just the intended amount for the size of the ladle being used may be dumped into the container so that within the time just enumerated this amount will flow through the spout of the container and the container be emptied at the desired time prior to the filling of the ladle; or, if desired, a greater amount of the ferro chrome may be placed in a container having a spout that will give a certain rate of flow, and

the opening of the spout be opened and closed at the desired times, the amount of chromium added,

being determined by the length of the time of fiow.

Assuming the receiving ladle to hold one thousand pounds of molten iron, about fifty pounds of molten iron may be run into the bottom of the ladle and the stream of ferro chrome then started and continued, as pointed out, up to shortly before the ladle is filled to its intended capacity,

when the stream of chromium will either have stopped of its own accord if the container holds only the desired amount for one ladle full of iron, or the stream will be cut off at that time shortly before the ladle is filled to its intended capacity if the amount of chromium is being regulated by rate of flow. As the percentage of chromium in pounds (11.55 lbs.) of chromium to one thousand pounds of molten iron or, in other words, would add from approximately 1 to 2 percent of chromium to the iron. This exact proportion may be somewhat varied but we find it to be satisfactory when the percentage of chromium runs some-- where between 1 to 2 percent.

While we have stated the exact point of the flowing stream of molten iron at which we prefer to add the chromium, this point may be varied within reasonable limits. The chromium will be partially mixed with the stream of molten iron as it flows along the spout and into the ladle,

which mixing will be completed inthe ladle by the ebullition or boiling action of the molten iron is filled to its intended capacity, and transportwithin the ladle.

As soon as the ladle is filled to its intended capacity with the mixture of molten iron and chromium, the transporting of the ladle to the mold or to such other ladle as the molten iron may be transferred to, and the pouring of the mold, is to be accomplished in a shorter time than is usual in the customary gray iron practice, as the addition of the chromium to the molten iron creates a tendency for it to solidify quicker than would such iron without chromium being added thereto. L

No mechanical mixing is necessary as the action of the flowing stream of molten iron, together with the boiling action of the molten iron in the ladle, is sufiicient to thoroughly mix the chromium with the molten iron. 4 I

Some of the articles made from the iron alloyand by the method disclosed herein are set forth and claimed in the copending application of William J. Doyle, Serial No. 41,283, 'flled September While the percentages of ingredients of the iron alloy given above may be varied, the limits stated herein are considered as giving satisfactory results.

Having now described our invention, we

claim:

1. The method of producing an iron alloy that will not suffer undue permanent growth or crack ing from high heating, which consists in melting ing the molten iron to and pouring it into a mold more quickly than is customary in gray iron practice.

2. That step in the method of producing a cast-iron alloy that will not sufier undue perma nent growth or cracking from heating, which consists in adding from 1 to 1.50 percent of chromium'to the flowing stream of molten iron as it flows from a cupola or the like, the chromium being granular and added in a flowing stream to the flowing stream of molten iron at a point intermediate the ladle and the cupola tap hole.

3. The method of producing an iron alloy that will not sufier ,undue substantial growth, deformation or cracking from heating, which consists in melting cast-iron in a cupola, or the like, at a temperature higher than that used in customary gray iron practice, measuring out such quantity of ferro chrome in granular form of approximately percent chromium content that will add from between 1 to 2 percent of chromium to the molten iron when the ladle is filled to its intended capacity, placing said ferro chrome in a container having a spout and supported alcovev the cupola spout between the tap hole and the ladle, flowing the molten iron in astream from the cupola to a ladle until a small amount of molten iron is accumulated in the ladle, then causing the granular ferro chrome to flow in a pacity, and transporting the molten iron to and pouring it into a mold more quickly than is customary in gray iron practice.

1!]; '1 J. DOYLE. JUS'I'US J. 3: