US2880303A - Process for resistance-welding of cast iron - Google Patents

Description

M. V. BERG March 31, 1959 PROCESS FOR RESISTANCE-WELDING OF CAST IRON Filed June 4, 1957 2 Sheets-Sheet 1 FIG)! FIG.2

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19r- T'OPNE/S March 31, 1959 M. V. BERG PROCESS FOR RESISTANCE-WELDIN Filed June 4, 1957 G OF CAST IRON 2 Sheets-Sheet 2 FIGA IN VE/VrOR Hemp/e50 BERG flrroRA/irs United PROCESS FOR RESISTANCE-WELDING OF CAST IRON This invention relates to resistance-welding; in particular it is directed to a process of resistance-welding of cast iron.

The resistance-welding of metals has been described by Thomson (U.S. Patent 455,420) and Schmidt (US. Patent 1,117,916). Rehse in two [1.8. Patents No. 2,193,- 490 and No. 2,243,488, dealing with resistance-flash, welding mentions briefly that his machines may be used for the flash welding of cast iron without giving any details as to the composition of the cast iron.

The only specification mentioned by Rehse as to details of handling cast iron as contrasted with steel, is that the final impacting pressure should be at a minimum as contrasted with steel. Rehse implies that the impacting operation, in the case of steel, may be regarded as a forging process; and the avoidance of the impacting in the case of cast iron is based on the fact that, as is known, cast iron is not a forgible material. Rehse also implies that all types of cast iron can be resistancewelded. Despite Rehses statement that cast iron can be successfully resistance-welded, technical experts throughout the world, including the United States, are of the opinion that cast iron cannot be resistance-welded to produce durable and reliable weldings.

So far as I am aware, in the more than fifteen years that have elapsed since the second of the aforesaid patents to Rehse was issued (May 27, 1941), no resistance-welded radiators or pipes of cast iron have appeared in any market, American or foreign.

Furthermore, during the time since the aforesaid patents were granted to Rehse, technologists and scientists working in this field have specifically reported and stated that cast iron cannot be resistance-welded. The following are illustrative of such reports and statements:

(1) Dipl. Ing. W. Brunst: Das elektrische Widerstandsschweissen. Gusseisen-praktisch nicht angewendet.

(2) Prof. Dr. Friedrich Erdman-Iesnitzer: Werkstoff und Schweissung, Berlin, 1951, page 436. Gusseisen lasst sich nicht abbrennstumpfschweissen.

(3) Dr. Ing. Erich Sudasch: Schweisstechnik. Karl Hanser Verlag. Munchen, 1950, page 206. Gusseisen ist nicht widerstandsschweissbar.

(4) Recommended Practices for Automotive Flash- Butt Welding (Tentative). American Welding Society, 1946, page 8. 108. Metals Not Recommended for Flash-Butt Welding: Cast Iron.

(5) Dr. Ing. W. Fahrenbach: Widerstandsschweissen. Heft 73. Second edition. Berlin, 1949, page 27, picture 48: Gusseisen-nicht moglich oder nicht versucht.

(6) Oskar Gonner: Die elektrische Widerstandsschweissung und ihre praktische Anwendung. Munchen, 1942, page 146: Grauguss lasst sich nicht stumpfschweissen.

I have discovered that it is possible to resistance-weld cast iron, provided that the composition thereof be such that the constituents fall within critical ranges.

It is to be noted that a union of two pieces of cast Patent "ice iron cannot be considered as satisfactory if the strength of the welding zone amounts only to about 60-70% of the strength of the surrounding basic material; or if the material bursts when the welding zone is cooled or the bursting takes place immediately thereafter. With respect to cast iron which has no appreciable elasticity, such a weak section can undergo rupture under rather insignificant dynamic stresses which take place, for example during transportation, in handling etc.

Before proceeding to discuss the critical factors that influence the result of resistance-welding which I discovered during my investigations, I have set forth a brief metallurgical survey of the composition of cast iron, its constituents, the influence of said constituents on the physical properties of the material, and finally the influence of those constituents and the changes in structure caused by the high temperature in the welding zone, on the resistance-flash weldability of cast iron.

Carbon Alloys of iron and carbon wherein the carbon content exceeds 1.7% are denominated as cast iron. Where the carbon content in cast iron ranges from 1.7 to 4.3%, the cast iron is called under eutectic. Where the carbon content is above 4.3% the cast iron is called over eutectic or hyper eutectic. An alloy in which cast iron has a carbon content of 4.3% is eutectic. An eutectic alloy has the lowest melting temperature (1139 C.). it is composed of uniform crystals and melts at a constant temperature like chemically pure metals. The eutectic structure metallographically is called ledeburite. For most technical uses under eutectic cast iron is used since hyper eutectic cast iron as a rule has the low strength.

In solid condition the cast iron contains free carbon (graphite) and a chemical compound of iron and carbon, ferrocarbide (Fe c) which metallographically is called cementite. Depending upon the chemical composition and the speed of cooling, other structures can be attained in cast iron such as perlite, ferrite, mixed structures, etc. with greater or smaller amounts of separated graphite. The graphite can be separated in diiferent forms such as coarse lamellar, lamellar, finely grained, temper carbon, spheroidal graphite and kish.

All of the aforesaid cast iron structures, like the different forms of separation of the graphite, also influence the resistance-Welding thereof. 1 have found in consequence thereof that to effectuate the welding of cast iron, certain structures should be aimed for in the welding zone.

Silicon As a rule graphite separates if the cast iron contains at least 2.5% of carbon, and even more if it contains a suitable amount of silicon, preferably not less than about 1.0 to 1.3%. if silicon is not present in the alloy, no separation of graphite will take place. The strength of cast iron decreases within certain limits with increasing amounts of graphite in the cast iron. The bending strength as well as the tensile strength decreases with increasing amounts of graphite in relation to the chemically bound carbon without taking the amount of silicon into consideration. Silicon itself has but little influence on the strength of cast iron. Accordingly, changes in the strength of the cast iron must be due to the graphite, the amount and form thereof.

As has been stated above, silicon does have an influence on the separation of the graphite. When the amount of silicon increases the separation of graphite also increases. According to scientific investigations the separation of graphite is at its maximum when the amount of silicon in cast iron lies between 3.0 and 3.5%.

In carrying out centrifugal casting of cast iron in ro- *1). and 8 are regarded as finely dispersed graphite. Also separation of graphite of nest-like form (temper-carbon tating, Water-cooled steel or cast iron chills whereby the molten iron on rapid cooling solidifies with a mixed structure, it is necessary to have a silicon content of between 2.3 and 2.7%. Such silicon content is necessary: in order to equalize the stresses in the mostly thin-wall casting; in order to facilitate, at the normalization carried. on afterwards, the separation of graphite necessary for workability. Silicon in an amount of over 2.6% has a detrimental influence on the weldability. This may be explained by the fact that at high temperatures in the melt silicic acid (SiO is formed which is difficult to press out of the weld seam during the upsetting operation. In such cases when there is a failure to take into consideration the formation of SiO there will be found lustrous non-united spots in the surface of a fracture of the weld seam which, to substantial extent, reduces the strength of the weld.

I have found that the amount of silicon in centrifugal cast tubes which are to be welded should lie between 2.0 and 2.6%; and in sand cast tubes or other sand casting, the silicon content should lie between 1.5 and 2.0%.

I have found that the formation of the Si may be counter-acted to the greatest extent possible by adding manganese in an amount of between 0.5 and 1.0% in order to render the cast iron weldable. In such case an iron-manganese silicate slag with a low viscosity is formed in the weld zone which is readily pressed out of the weld seam during the upsetting operation.

A still further factor has an influence on the separation of the graphite, namely, the speed at which the melt cools. The more slowly an iron-carbon alloy containing silicon cools, the more graphite separates from the melt. I have discovered that the form of the graphite and the amount thereof as it occurs, not only in the cast iron but also in the weld zone are of decisive significance in resistance welding of cast iron.

Graphite interrupts the continuity in the metallic basic mass by forming hollows in the cast iron. A particularly unfavorable form of graphite is the coarse lamellar form which should not be persent in cast iron that is to be resistance-welded. If graphite separates in lamellar form it should be finely dispersed. By finely dispersed graphite I mean that the graphite separations are such that, in a microscopic image of unetched mateiral under 'a magnification of 100 the length of the lamellas does not exceed 3-6 mm. (in American Foundryrnens Assn., A.S.T.M. Designation A.247 of 1942 Standards, Part In these standard tables, graphite sizes Nos. 6, 7

form) or spheroidal graphite is suitable for resistancewelding.

I have also discovered that certain practical changes are achieved in resistance-welding of cast iron containing more bound carbon than free graphite. It is particularly practical to apply this alternative when casting in chills or casting centrifugally and is to be normalization annealed. In such a case I have found the welding is carried out before the normalization annealing so that the stresses arising in the weld zone are eliminated through the annealing operation. The annealing is carried out for about 30-45 minutes at a temperature of 920-940 C.

The modulus of elasticity of the cast iron depends greatly on the distribution and the form of graphite in the cast iron. Short and compressed veins of graphite or veins of rounded form or temper-carbon-like (nest form) have less diverting effect on the course of the stresses in a metallic basic mass than long leaves of graphite coarse-lamellar graphite. These hollows in the basic mass obstruct the direction of the stresses axially (for example, along a cylindrical object). The stress lines are crowded in narrower metallic sections caused by these greater stress units of graphite and can surpass locally the tensile strength vof the metallic portion. This 4 also applies to heat stresses in the cast iron caused by the local high temperature in the weld zone. The heat is conducted away from the weld zone along the material through the metallic basic mass past the graphite lamellas (the relative heat conducting ratio i= graphite 1 and therefore in analogy with earlier mentioned force stresses (tension or pressure) there will be a crowding of stress lines in the metallic basic mass which has thus been reduced by the growth of the graphite grains. If these heat stresses are accumulated to an order of magnitude beyond what the strength of the material (the carbon-free steel) permits, there will be formation of cracks or rupture in the casting.

That the heat conductivity of the cast iron increases with increase in the amount of graphite is not to be regarded as an increased condition for the weldability of the cast iron. For example, cast iron having more chem ically bound carbon than free carbon has less heat con ductivity than cast iron with coarse lamellar graphite. Nevertheless, I have discovered, the former material is easily weldable, whereas the latter, on the other hand, is not. A possible explanation is that the stresses in the mixed cast iron are not diverted through their rectilinear direction through hollows in the metallic basic mass caused by coarser pieces of graphite, the graphite being chemically bound with the iron and thus being evenly distributed in the whole section.

Phosphorus A phosphorus content amounting up to 0.35 increases the strength of cast iron. A content above 0.35% results in a decrease in the strength as the phosphorus content increases. In the molten state, phosphorus in the melt reduces the viscosity. In the solid state brittleness of the cast iron increases. For example, when the phosphorus content of cast iron is 1.15% the impact resistance can be reduced by about 5 060% Iron phosphide, Fe P, consists of very brittle and hard crystals. They are undesirable in the cast iron structure for, like coarse lamellar graphite, they cause impairment in the strength of the cast iron. The mixed crystals (austenite) are saturated with phosphorus if they have received in the solution about 0.25% of phosphorus (at 1150 C.).

In cast iron, 50-85% of phosphorus is present as a rule in the form of phosphides. The finer these phosphides are with regard to structure, and the more evenly they are distributed in the cast iron, the higher can be the limiting amount of permissible phosphorus, before the phosphides begin to impair the mechanical and par ticularly the static properties of the cast iron. If the cast iron is caused to solidify ferritically or if ferritic structure is obtained through annealing, phosphorus penetrates, through diffusion, at high temperature more and more into the portions with the ferritic structure. Therefore, if cast iron details are produced which, after annealing, should show toughness in the material, the amount of the phosphorus should be reduced to a minimum. For example, in the case of centrifugally cast tubes which are to be resistance welded, the amount of the phosphorus should preferably not exceed 0.25 and for spherolithic cast iron, the amount of the phosphorus should not ex ceed 0.1%.

Phosphorus in cast iron will tend to gather in the border area round the graphite. As the graphite itself, as stated above, forms hollows in the cast iron, the phosphorus thus reduces to a still greater extent the continuity in the metallic basic mass. The discontinuity or interruption in the metallic basic mass thus increases with increasing amount of graphite, and the most unsuitable form of the graphite is coarse lamellar graphite (also kish), and. the condition is still more impaired through the amount of phosphorus which deposits in the ferrite round the graphite.

Therefore, of utmost importance in providing a cast iron which can be welded, is the control of the total amount of carbon, the separation of the graphite and the amount of the phosphorus. Accordingly, the resistance weldability of cast iron is characterized by the sum of the carbon plus the phosphorus content (C-l-P), whereby, depending upon the amounts of these components, the manner of their occurrence in the cast iron, the variation in the amount of the carbon, upwards or downwards, a greater influence is exerted on weldability than is exerted by corresponding variations in the amount of the phosphorus.

I have discovered that, insofar as the amount of carbon is concerned, the critical upper limit is 3.6%, above which reliable weldability ceases, and insofar as the amount of phosphorus is concerned, the upper limit is 0.25%, at which point the strength decreases abruptly in relation to the adjacent'values of the strength of the basic material. Furthermore, the graphite should be finely dispersed or for the greater part, in chemically bound form.

If the presence of greater amounts of phosphorus (up to 0.7 to 0.8% or higher) are unavoidable, as for example in the case of continental or English types of pig iron, the disadvantages in respect of the weldability of such cast iron can be counteracted by reducing the amount of the carbon in the alloy, as by adding suitable amounts of scrap steel to the charge.

Investigations have established that such can be accomplished. and also that the weldability of cast iron containing not more than 0.25% of phosphorus is most advantageous. The resistance values in the weld or the welding zone are equal to or substantially equal to the resistance values in the basic material.

When the amount of phosphorus exceeds 0.25%, the strength of the weld decreases suddenly to an extent of from 20 to 30%. Thus, if the carbon content is reduced, for example, from 3.53.6% to 3.15%, when the amount of the phosphorus is 0.60.7%, the strength of the weld is increased. This finding is in accord with the general explanation set forth above.

It is evident from results in carrying out welding tests that, when the carbon content is greater than 3.6%, the strength of the welds decrease in relation to the basic material in a manner which clearly indicates that weldability is not technically acceptable. The percentage of welds having low strength are too great, and therefore mass production of such welded objects is commercially unfeasible.

When the casting is carried out in stationary chills or centrifugally, it is difficult to effectuate the production of satisfactory castings from melts in which the amount of carbon is lower than 3%. The reason therefor is that cast iron in the molten condition, when the amount of carbon is so low, has a tendency rapidly to solidify, whereby casting in stationary or rotary watercooled chills is either completely impossible or substantially impossible, particularly with respect to the production of thin-walled and lengthy objects, such as pipes or the like.

Change of the degree of saturation of the cast iron: S =1 (entecticum) due to elements other than C In the binary system Fe-l-C eutecticum is at 4.3% C and then the degree of saturation 5 :1. In the ternary system Fe+C+Si silicon influences the ability of iron to absorb carbon in the solution, and therefore change of eutecticum goes to the left in the iron-carbon diagram. Eutecticum may for example be attained when the amount of silicon is 2.4%, only when the amount of carbon is about 3.5%. Likewise, other alloying substances, such as phosphorus, manganese, nickel etc. have influence on the degree .of saturation S Tobias and Brinkman have developed aformula for establishing the degree of saturation S in respect of the alloying substance Si, P, and Mn, which always occur in cast iron. This formula is as follows:

Percent C 4.3 0.312Si-O.33P+0.066Mn Si, P and Mn indicating the percental amount of these substances in the cast iron. If S l the cast iron is undereutectic, if S =1 it is eutectic, and if S 1 it is overeutectic.

Thus, the cast iron need not necessarily be undereutectic, if the percentage of carbon is for example 3.7. It should be noted, that, if one here speaks of weldability dependent on the degree of saturation (undereutectic, eutectic or overeutectic), this applies to cast iron of a composiiton according to the abovemeutioned formula.

As already mentioned undereutectic cast iron, S l, is most fit for use technically.

Where a cast iron has a composition such that in the iron-carbon diagram (as shown in Fig. 2) the carbon content is less than that of the eutectic, the more there will be present in the structure, primary graphite-less mixed crystals (austenite), rich in iron, before it passes over to eutectic crystallization. As these mixed crystals have higher strengths than crystals in the eutectic zone, the weldability of the cast iron will be more dependable, the greater the cast iron is under eutectic. Such characteristic may be expressed by the statement that the weldability of the cast iron increases with the degree of saturation S In other words, weldability of cast iron increases as saturation S decreases. I have found that a formula can be used for calculating the decrease in the amount of carbon in the melt should the cast iron prove to be over-eutectic in consequence of high values of alloying substances, as for example, when phosphorus is present in an amount of nearly or more than 1% (English pig iron). In such cases steel scrap can be added in the melting furnace so that the material passes into the under eutectic range.

In order to establish quickly where the eutectic amount of carbon is located, if the amounts of silicon and phosphorus cannot be varied, a simplified formula may be applied in which the amount for example of manganese is disregarded. Such a formula is:

As a result of investigations I have carried out, I find that satisfactory results can be obtained from compositions in which S =1.04. When the values of S exceed 1.04, the possibilities of obtaining reliable welding bonds cease. As a result of my investigations, it has been established that cast iron is resistance-weldable when the degree of saturation falls within the range of S =0.80 to 1.04, the most reliable results being obtained if the upper limit within this range is not in excess of 1.0. If the highest strengths of the weld zone are desired, the upper limit preferably should not exceed 0.95.

I have also found that the sum of carbon and phosphorus (C-i-P) should not exceed 3.9%; and that the separation of graphite in the pieces of cast iron that are to be resistance-welded with respect to the form and amount thereof, is in conformity to that stated above.

From the foregoing description of my discovery, I can set forth the following rule with respect to the resist ance-weldability of cast iron in consequence of its chemical composition and the form of the graphite:

(a) Cast iron can be resistance-welded in view of the degree of saturation S within the range wherein S =0.80 to 1.04

(b) The sum of carbon and phosphorus (C+P) should be kept within a range of from 3.0 to 3.9%, preferably between 3.0 and 3.5%, the amount of the phosphorus being kept, preferably, as far as possible, between 0.0 and 0.25%.

(c) The carbon in the cast iron should preferablybe present mostly in the form of chemically bound iron or if such is not the case, the graphite should be of such structure that it is either finely dispersed, temper carbonlike, or spheroidal, in order that the metallic basic mass shall be maintained in uninterrupted structure to the greatest extent possible.

(d) Structures in the basic material'suitable for welding are:

(l) Perlite or perlite-j-ferrite with finely dispersed graphite (sand casting).

(2) Mixed structure with mostly chemically bound carbon, for example unannealed chilled casting or unannealed centrifugally cast tubes cast in watercooled chill molds, or ditto objects.

(3) Ferritic or mostly ferritic structure with finely dispersed or temper carbon-like graphite (normalization annealed for about 0.5-0.75 hour at 920940 C.).

(4) Perlite with the graphite separated in spheroidal form (spherolithic cast iron).

After the welding tensionless annealing is preferred in order to eliminate the stresses caused in, and close to, the welding zone by the resistance flash welding.

Objects having a basic structure according to (d)2 should be normalization annealed after the welding for about 0.5-0.75 hour at 920-950 0., possibly about 2 hours at 900 C. dependent on the chemical composition of the material.

Welding of tubes according to this alternative (d)2 has given the best and most reliable results of resistance flash welding of cast iron.

The welding operation, upsetting Processes of resistance-welding metals are already known, and therefore, in this case, when cast iron is concerned, only a short account is required. In the drawing:

Fig. 1 shows diagrammatically a device for carrying out the method according to the invention.

Fig. 2 shows an iron-carbon diagram.

Fig. 3 shows a plurality of pipes disposed in arrangement suitable for welding them together.

K Fig. 4 shows a pipe obtained by the welding of the several pipes shown in Fig. 3.

The objects A to be welded, which are clamped between the contact jaws E of the flash welding machine, lie in the secondary circuit of a transformer (see Fig. l), the voltage in the welding circuit being low, 7-18 v., the current intensity, on the other hand, high, varying from 30,000 to 100,000 amperes, depending on the welding area. Generally, it may be said that the consumption of power per mm. of welding area is about 0.08 kva./mm. for tubular castings and about 0.06 kva./mm. for massive castings.

As cast iron has substantially greater electric resistance than, for instance, steel, the choice of electric power should be carefully considered. The choice of transformer stages in the machine should first be determined by tests before production is started on a large scale. Then the composition of the cast iron with regard to carbon and phosphorus should be considered, and it should be noted that the electric resistance of the cast iron increases with increasing amount of phosphorus.

The welding machine can be regulated to higher transformer stages or the clamping length can be reduced. As a rule both are adjusted after some test weldings.

This course of action cannot be generally described, as every welding machine has its typical peculiarities, and should be determined through tests on each machine by the operator, and values for transformer stages and clamping lengths for different materials and welding areas should be established.

After the work pieces, in respect of the necessary power, have been clamped in the machine in a suitable .manner, the desired lengths for preheating and flashing 8 and the length of upsetting motion are adjusted on corresponding scales.

When the current is switched on, before the welding operation is started, the upsetting slide moves one cast iron piece into contact with the other one, whereby a short-circuit occurs. This short-circuit ceases immediately by return of the slide. The current, which during a fraction of a second has passed through the work pieces in the moment of contact, now heats the latter near the spot where the contact was most effective. This procedure is repeated several times during the preheating period. During the pauses between the short-circuits some of the contacted material is flung out. On that spot, in the contact areas small hollows are formed, and the next time there will be short-circuit on another spot in the circumference. Thus, during the period of preheating the short-circuit travels over the whole area and thereby develops a heating zone evenly distributed round the whole welding area. This takes place during 30-120 seconds depending on the size of the welding area and the power supplied.

On a fully automatic resistance flash welding machine the consumption of material during this period can be exactly adjusted on the corresponding scale before the process is started; likewise the extent of the flash.

The next operation is the flashing, during which, for a short period, the welding surfaces are at a standstill close to each other, and the distance between them is so established that a loose contact occurs between the work pieces. Then, if the current flowing through the points of contact is sufficiently powerful, the joints are heated rapidly to melting condition, and also to partial vaporization.

Now the fluid material which contains slag and impurities, is flung out of the weld seam with a violent scintillation. Surrounding the weld scam the vaporized material (metal vapor), forms a vaporous-casing protecting against oxidation which lasts as long as the ejection of molten particles takes place, and the slide is moved forward as quickly as the ejected material disappears from the weld joint. Thereafter, when the preheating plus the flashing have attained the number of millimeters adjusted on the scale, the upsetting takes place. It is carried out vigorously by impact in order to fill up the hollows formed in the weld joints and in order to produce a good union between the welding surfaces.

As cast iron is not plastic at high temperature, the upsetting operation should be carefully carried out. If, during the upsetting operation, the slide is carried forwards with a great force and, if the length of travel of the slide is not restricted, there is risk that the material in the weld joint will be deformed and that the union will not be satisfactory.

Practical tests have shown that the upsetting should be carried out rapidly with great force as per above, with the restriction that the length of upsetting be preferably 23 mm. These values may vary somewhat, depending on the dimensions of the welding areas, when tubular objects are concerned, the thickness of the castings in relation to the diameter, et cetera. Generally, the limitation of the upsetting length to 2.5 mm. is most satisfactory.

With such procedure a good binding is obtained over the whole welding area and the risk of formation of cracks in the joints is eliminated.

After finishing the upsetting, the work piece should remain between the water-cooled electrode jaws in order that the heat accumulated in the welding zone may be quickly removed. Thus, as soon as the machine has been automatically disconnected, the greatly red-coloured welding zone quickly assumes the normal colour which the workpiece usually has at about 500 C. Thereafter, the contact jaws should be immediately disconnected and the work piece .taken out of the machine. Thereby, the

welding zone rapidly cools from about 1150 C. to about 500 C. and thereafter the cooling is carried out inair pmm Percent Percent. Perm, at normal room temperature. B1 Mn P B +P 8.

The purpose of this rapid cooling is that, in the welding zone more chemically bound carbon than free graphite 347 0.57 0-035 19 should befobtaiiied toht h?l (gireatesttposlslible extent 0;, that 312% g3;- 3 812: @822 gig fig amount 0 grap lite w 1c uringt e s ort period 0 coo- 5 4 4. 1.13 ring has clltad time {)0 separate willhbe (if finelyhdispersid 2;; 91 2:) 2%; orm an at east e not coarsert ant e grap ite int c 7 3.44 2. 3s 0. 30 0.0 0.030 4.30 1.08 hh" h 1. b 1 d 1. 1 2-3 8-33 1-3 i3.

is rapt coo ing s on e app ie to a m t 0. 5 .0 structures. As regards alternative d1 the weld seam M88 L047 ought to be afterheated in the machine in a suitable mannot by letting the current flow through the weld seam 50% of these weldeq'plpes broke dunng the transpoht 3-4 times for some seconds each time, before the work about 25% broke whlle betng worked to F bars m piece is taken out of the machine lathes and the rest had a tensile strength varying from 13 According to the above. mentioned principles, with to 16 ltgjrnm. across the weld scam, the tens1le strength regard ot the composition of the material structures, the of the has; mammal bemg an average & form of the graphite et cetera and mechanical treatment, In E h the Cast Iron has a ftbcmlcal composi- Such as upsetting Pressure cooling speed after heating 20 tion l ying outs de the above stated conditions for resistance and a suitable choice of welding effect, flawless welds wemmg" and 1f 1t Should not posslble reduce the have been massproduced with, values of strength above amount of carbon (for example producnon on a large 30 kg./mm. in the welding zone and tube welds, which scalenwhere only a Small of the .mtany prodiwed have been test pressed with a pressure of up to 200 atmosmen 15 used for the prqducnon of detalls 9 weldmg) pheres above atmospheric pressure and which have proved molybdenum andfilrommm can be alloyed mm the melt to be entirely. tight. so as to convert it into weldable mater al.

The f ll i are typical analyses of materials n Such added substances affect the cast iron in the follow centrifugally cast) which have been successfully welded mg manner: together to produce extremely good welds (except the Moll! 1n 05% to 11% Causes sixth test i which C+P=3.98%). compression of the graphite lamellas and forces the Percent Percent Percent Percent Percent Percent Sn 1 2 0 Si Mn P s 0+? 3.15 2.3 0.56 0. 21 0. 06 3.36 0.91 23.9 29.1 3.17 2.15 0. 3s 0. 24 0. 07 3. 41 0. 00 29. s 31. 5 3. 41 2. 20 0. 34 0.35 0. 07 3.76 0. 99 22. s 32. 4 3. 2. 20 0. 34 0. 39 0.01 3. 84 1.00 2-1.9 33.5 3. 11 2. 1s 0. 2s 0. 32 0. 0s 3. 73 0. 92 23. 7 30. 6 3. 63 2. 42 0. 33 0. 35 0.07 3. 9s 1. 07 18.8 32.1 3. 43 2.60 0. 29 0. 23 0. 09 3. 71 1.02 23. 0 31. 0

1=tenslle strength across the weld in kg./mrn. 2=tens1le strength in the basic material in kgJmm.=

It is to be noted that values of tensile strength below 20 kg./mm.- in the weld zone are not accepted, for example, by Angpannekontrollanter (Steam Boiler Controllers, Sweden, Lloyds Register of Shipping Det Norske Veritas, Norwegian Veritas) et cetera.

Resistance welding of cast iron makes it possible to manufacture, inter alia, centrifugally cast double-flanged tubes or double-mufied tubes, which hitherto only have been manufactured by casting in sand molds and which are of inferior quality and are more expensive and timewasting, the result being a smaller production.

Thus, it is possible to cast in a centrifugal casting machine tubes with one flange or a muff; and to weld such tubes together at the ends which have no flange or mufi (see Figs. 3 and 4) with or without the use of intermediate tube lengths having no flange or muff-in order to obtain necessary lengths.

At the same time it is pointed out that the conditions stated for successful welding of cast iron as to the degree of saturation S =0.80 to 1.04 and C+P=3.9% are not sufiicient as other conditions limit the carbon range. Besides, it is to be noted that, if the amount of phosphorus in cast iron is 0.6%, the amount of carbon shall be within a range of maximum 3.3%, and that an amount of phosphorus up to 0.7-0.9% often occurs in the production of castings particularly in the production of pipes.

An examination of the following typical analyses from two of the greatest tube foundries of Europe with which material (centrifugally cast) extensive tests of welding have been made, it will be noted that these lie outside the above-stated conditions of welding and no positive results of the welding have been obtained.

graphite to separate in granular form, that is the graphite separates in the form of short and compact leaves. Chromium is inclined to alloy with the carbon not yet separated and forms chromium carbide and iron-chromium carbides.

By adding a combination of about 0.5 to 1.0% of molybdenum and 0.4 to 0.5% of chromium, possibilities are thereby created for allowing the greater amounts of phosphorus to be present which arises in the resistancewelding of certain continental or English types of cast iron. Thus, in this way, it is possible to broaden the previously established conditions for resistance-welding of cast iron, to wit: S =1.04 and C+P=3.9 and thereby to use a cast iron according to the formula zLl and C+P=4.S it molybdenum and chromium as above described are added in accordance with the above described formulation.

Thus, the alloying of molybdenum and chromium as above described in the cast iron produces the same effect, of making it possible to resistance-weld the cast iron, as does the reduction in the amount of the carbon with a simultaneous increase in the amount of the phosphorus.

In consequence of the foregoing, it will be evident that the technical use of cast iron can be much more extensively applied, since the resistance-welding of cast iron increases the possibilities of using this material for difierent purposes in addition to the production of centrifugally cast double-flange or double-muff tubes set forth in the foregoing description.

This application is a continuation in part of my pending application Serial No. 447,919, filed August 4, 1954, now abandoned which was a continuation in part of my pre now Patent No. 2,834,871, dated May 13, 1958.

It will be understood that the foregoing description of the invention is merely illustrative of the principles thereof. Accordingly, the appended claims are to be con-- the full spirit and.

strued as defining the invention within scope thereof. 5 I claim:

1. A process of producing welded cast iron articles which comprises: effecting electric current flow through cast iron pieces by flash welding means, the said pieces of cast iron having a composition wherein the degree of saturation S is in the range of 0.8 to 1.04, and the sum of carbon and phosphorus (C-l-P) is in the range of from 3% to 3.9%, the upsetting in'the flash welding means being carried out with great force and with a length of travel in the upsetting'action of between 2 and 3 millimeters, rapidly coolingthe weld to a temperature of about 500 C. and slowly cooling the weld from said temperature of about 500 C. to room temperature.

2. A process in accordance with claim '1 wherein the length of travel in the upsetting action is 2.5 millimeters. 3. A process in accordance with claim l-wherein the flash Weldingis carried out at 0.08 kva./mm. of welding area for tubular castings, and the voltage in the welding circuit is maintained in the range of from 7 to 18 volts. "4. A process in accordance with claim 1 wherein the flash welding is carried out at 0.06 kvaJmm. of welding area for massive castings, and the voltage in the welding circuit is maintained in the range of from 7 to 18 volts.

5. A process for resistance-welding of tubular or masiron having a composition wherein the degree of saturation- S is in the range of. 0.8 to 1.04, and the sum of carbon and phosphorus (C+P) is in the range of from 6. A process in accordance with claim 1, wherein the degree of saturation S is in the range of 0.8 to 1.0.

f 7. A process in accordance with claim 1, wherein the degree of saturation S is in the range of 0.8 to 0.95. 8. A process in accordance with claim 1, wherein the cast iron contains more chemically bound carbon than free graphite. t Y I I 9. A process in accordance with claim 1, wherein the cast ironcontains saturated graphite in finely dispersed form.

r 10. A process in accordance with claim 1, wherein the cast iron contains separated graphite in temper-carbon form.

11. A process in accordance with claim 1, wherein the cast iron contains separated graphite in spheroidal form.

References Cited in the file of this patent UNITED STATES PATENTS 455,420 Thomson July 7, 1891 2,193,490 Rehse Mar. 12, 1940 2,243,488 Rehse May 27,1941

FOREIGN PATENTS 727,675 Great Britain Apr. 6, 1955

Claims (1)

1. A PROCESS OF PRODUCING WELDED CAST IRON ARTICLES WHICH COMPRISES: EFFECTING ELECTRIC CURRENT FLOW THROUGH CAST IRON PIECES BY FLASH WELDING MEANS, THE SAID PIECES OF CAST IRON HAVING A COMPOSITION WHEREIN THE DEGREE OF SATURATION SC IS IN THE RANGE OF 0.8 TO 1.04, AND THE SUM OF CARBON AND PHOSPHORUS (C+P) IS IN THE RANGE OF FROM 3% TO 3.9%, THE UPSETTING IN THE FLASH WELDING MEANS BEING CARRIED OUT WITH GREAT FORCE AND WITH A LENGTH OF TRAVEL IN THE UPSETTING ACTION OF BETWEEN 2 AND 3 MILLIMETERS, RAPIDLY COOLING THE WELD TO A TEMPERATURE OF ABOUT 500* C. AND SLOWLY COOLING THE WELD FROM SAID TEMPERATURE OF ABOUT 500* C. TO ROOM TEMPERATURE.

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