F·Oote Foundry Facts

F·OOTE FOUNDRY FACTS

PUBLISHED BY FOOTE MINERAL COMPANY, EXTON, PENNA. 19341 NUMBER 3 "WISE USE OF INOCULANTS CAN IMPROVE PROPERTIES OF GRAY CAST IRON; SAVE MONEY," SAYS PATTERSON

I s your gray cast iron too tired to·nucleate? Are you troubled with chiU, which causes machining problems? Is the graph Typical Compositions of Standard Graphitizing lnoculants ite structure of the wrong type, thus causing lower mechani Inoculant %Si %Ca % AI %Fe cal properties? If so, inoculation may be the key in solving 50% Ferrosilicon 47.50 0.20 1.30 balance these problems. 75% Ferrosilicon 76.50 0.82• 1.30 balance When an iron is lazy, or too tired to nucleate, under· 85% Ferrosilicon 86.00 1.01• 1.40 balance cooling results with subsequent chill and the formation of Calcium Silicide 62.50 32.0 1.10 balance the usually undesirable types B and D graphite flakes. Such an iron needs help-help of the type furnished by inoculants. • Available as 0.50% and 1.50% min. grades. Gray cast irons with carbon equiv Fifty percent ferrosilicon is not widely used by itself as alents varying from as low as 3.4% a means of controlling the graphite structure in cast iron. to as high as 4.5% ca.n benefit However, with the proper amounts of calcium and aluminum it can function very effectively for that purpose. To be more from inoculation. effective as a nucleating agent. the calcium ahould be over Inoculants for gray cast iron 0.50%, and, preferably, between 0.80 and 1.25%. are of two general types: graphitiz Seventy-five and eighty-five percent ferrosilicons a.re ing and stabilizing. available in two calcium ranges, 0.50% minimum and 1.50% minimum. It has been claimed that at inoculating tempera· The graphitizing type is added tures in excess of 2650°F, the higher calcium levels increase VERNON H. PATTERSON to gray cast iron to promote the the holding power of the inoculant. However, excessive cal formation of small, uniformly dis cium can increase the slag, or dross, on the metal. Hence it persed type A graphite flakes. This type of inoculant also is good pra.ctice to use the lower calcium level (0.50% minimizes chilling tendencies (thus enhancing machinabil minimum) whenever possible. This is especially true when ity) and decreases section sensitivity. fairly large quantities of inoculants are required (such as 8 lbs. or more per ton of metal) . The stabilizing type is added to gray cast iron to increase Work done at the Foote Research Laboratory has dem its strength and hardness without appreciably increasing the onstrated that at the same rate of addition to cast iron, 75% chilling tendencies of the iron. It does this by promoting a ferrosilicon is as effective in chill reduction and the control pearlitic matrix along with small uniformly dispersed type of graphite structure as 85% ferrosilicon. Since the latter A graphite Rakes. The stabilizing inoculants actually decrease material ordinarily Costs more on a contained silicon basis, there is usually an economic advantage to the use of 75% the section sensitivity of gray iron castings to a greater ferrosilicon. extent than the graphitizing type. ·In other words, they The calcium silicide composition shown in Table I has promote uniformity between thick and thin sections in the been used for many years as an inoculant for gray cast iron. same castings. However, its use has declined considerably because the high calcium content causes excessive slag which often becomes entrapped in the castings. Such castings are inferior in GRAPHITIZING I~OCULANTS mechanical properties as compared to sound, slag-free cast Graphitizing inoculants can be divided into two groups: ings of the same analyses. In addition, there have been the standard inoculants and the proprietary inoculants. Some objections to the flash and smoke which develop as a reau1t typical "standard" inoculants are listed in Table I. of its use. PAGE 2 FOOTE FOUNDRY FACTS

PROPRIETARY INOCULANTS type D graphite with a predominantly ferritic matrix. The Table II lists the compositions of a number of propri· addition of Graphidox transformed the graphite to type A, et.ary inoculants used for the graphitization of gray cast iron. small flakes, and allowed the matrix to transform to pearlite during solid state cooling. This accounts for the drastic TABLE II increase in tensile strength. From the above, it can be concluded that Graphidox Typical Compositions of Proprietary Graphitizing Inoculants should perform well in highly oxidized iron, made from %Other Inoculant %Si %Ca %AI % Fe charges high in rusty scrap. It also performs well in reducing Calsiloy 56.00 15.00 1.00 balance the chill and modifying the structure of thin section gray Craphidox 52.50 6.00 1.10 9.50Ti balance cast iron. lnoculoy 63 is an alloy of silicon, manganese, calcium Ioocu1oy63 62.50 2.75 1.10 10.00 Mo, 5.00 Ba balance and barium. The prime "nucleants" in this inoculant are CSFlO 38.00 0.50 0.50 12.00 Ce, other calcium and barium. The combination of these two elements R.E.3.00 balance helps to resist fading in the use of. the aiJoy. Thennoail 61.0 0.50 1.10 lO.ONaNO., Work carried out in the Foote Mineral Research Depart· 2.50Mg balance ment indicates that barium is very beneficial as a nucleating agent in an inoculant when added to cast iron at tempera· Calsiloy differs from standard calcium silicide in that it tures in excess of 2700°F. At temperatures ranging from has less calcium. This greatly reduces the volume of slag 2500° to 2650°F, however, calcium appears to be slightly produced, compared to the standard calcium silicon alloy more effective. The combination of barium and calcium in used for inoculating purposes. Flash and smoke are also an inoculant makes it more effective over a wider tempera reduced. Furthermore, the selling price of Calsiloy is less ture range. than that of standard calcium-silicide, even though, pound The advantages of lnoculoy 63 as an inoculant, com· for pound, it is equally effective. pared with calcium bearing 85% IerrosiJicon are illustrated in Figures 3 through 7. Figures 3 and 4 'compare the inocu· Graphidox, primarily a calcium·silicon-titanium alloy, !ants with respect to chill recluctions in gray ca.st irons of has been on the market for a number of years and has per· different carbon equivalents, 4.23% and 3.8% respectively. formed very weiJ. Although the calcium and titanium con Figure 5 shows the effects of the inoculants on the trans· tents of this alloy appear to be substantial, only small quan· verse strength of gray cast iron with a carbon equivalent of tities of Graphidox, such as 2-5 lbs. per ton, are required. 3.8%. Figure 6 compares the two inoculants with respect to The calcium functions as a deoxidizer, as well as a nucleating deflection in the 3.8% carbon equivalent iron. Figure 7 agent. The titanium also assists in the deoxidation of the shows the effects of the two inoculants on the tensile strength iron. In addition, it combines with excessive nitrogen in the of the same iron. iron to form tiny, harmless titanium nitrides, thus preventing CSF 10 is an alloy of cerium and silicon. This alloy is nitrogen porosity. a relatively new product originally developed as a graphitiz Figure 1 compares Graphidox and 75% ferrosilicon ing inoculant for gray cast iron. SmaH amounts of this alloy with respect to chill reduction of hypoeutectic cast iron. In appear to be very effective in reducing chill. However, tests this particular iron, it will be seen that 4 lbs. per ton of indicate that CSF 10 is a slow starter, requiring about 2 Graphidox are equivalent in chill reduction characteristics minutes at 2700°F to achieve its maximum chill reducing to 10 lbs. per ton of ferrosilicon. results. In recent tests, comparing 75% ferrosilicon, lnoculoy 63 Figure 2 shows the effect of increasing Graphidox and CSF 10 as chill reducing inoculants, the CSF 10 showed additions on the tensile strength of bypoeutectic cast iron. up best two minutes after inoculation and continued in the These results were obtained in a thin section casting having number one spot for the duration of the test. The l noculoy an approximate analysis of 3.15% T.C., and 1.60% Si. As 63 and 75% ferrosilicon were instantaneous in completely cast, uninoculated, the structure of this iron consisted of eliminating chill in Ys" chill plates. After 10 minutes, the

FIGURE 1 FIGURE 2 40.000 ChiU Reducing Ch4racter~tic$ Effect o/ lncreasin& Craphido:c ! o/ Graphidox vtr$U$ 75% Additions on Tensile Strength ~ JSOOO '-) F e"osilicon. of Gray Cast Iron. 3.9% Carbon Equivalent..- 3.7% Carbon Eqiuvalent 1)0 000 5/16" Chill Block W' Costin& Section FOOTE FOUNDRY FACTS PAGE 3

"\noculating effect of 75% ferrosilicon had faded very signifi· cantJy as compared to either InocuJo y 63 and CSF 10. Actual chill measurements on the YIJ" chill plates 10 minutes alter inoculation showed the following results: FIGURE~ ' CSF 10 5/32" Effect of Inoculation on. Chill lnoculoy63 6/32" Depth of Gray CtUt Iron. 4.23% Carbon Equioolent 75% Ferrosilicon 8/32" It is interesting to note that three minutes after inocula· tion, at the time that CSF 10 produced its maximum chill reduction, the eutectic cell number was less in iron treated with CSF 10 than in the irons inoculated with either 75% ferrosilicon or Inoculoy 63. Thermosil is an exothermic ferrosilicon. This inoculant is unique in that it contains magnesium, which in small FIGURE 4 quantities, enhances the nucleating action of inocuJants. i t4 Effect ofln.oculotion. on. Chill ! Thermosil is an inex,pensive inoculant designed to dissolve Depth of Gray Cast Iron.. ! .. readily in iron, even though the temperature may be as low 3.8% Car.bon Equioolen.t as 2250°F. Being exothermic, it does not lower the tempera· ture of the iron to which it is added. It is excellent for adding to hand ladles in small quantities to overcome any fading of inoculants added previously in the transfer ladles. For gray cast iron the proprietary graphitizing inocu· WIOC---.LkiT• !ants have distinct advantages "'over the standard ferrosilicon i'noculants. The two outstanding advantages are: FIGURE 5 ) 1. Less additive is needed in the case of proprietary EDect of Inoculation on inoculants to achieve the desired results. Generally, Tran.sverse S1rength of from 2 to 4 lhs. per ton of the proprietary inoculants Gray CtUt Iron. are required to do what 6 to 10 lbs. per ton of either 1 .2" Diameter T e.st Bar 75 to 85% ferrosilicons will do. 3.8% Carbon. Equioolent 2. The cost for inoculation is considerably less with

the proprietary inocuJants compared to the ferro· lltroc~Utlf.,. silicon inoculants...... ,...._ STABILIZING INOCULANTS o•o Table III lists the compositions of stabilizing inocuJants FIGURE 6 / :: • 0)0 which control the matrix structure as well as the graphite i Effect of Inoculation. on / .,, ,.. ,.... flake type in gray cast iron. Deflection. of Gray CtUt Iron. I oto l ./ 1.2" Diameter Test Bar v · TABLE lli 3.8% Carbon Equioolent 010 ., .. cr.,,, Typical Compositions of Stabilizing lnocuJants

Inoculant %Cr %Si % Mn %Other %Fe ~·- ..... ,,. Y·5 Foundry 41.03 16.0 9.26 0.80 Ca, 0.20 AI, Alloy 0.75Ti balance ...ooo -·\ .~ : : Blocking Grade 58.59 15.00 4.93 C, 0.10 AI balance Ferrochromium FIGURE 7 ...ooo ; Ferrochrome- 40.92 42.11 O.OSC (max.), Tensile Strength of I' n,ooo Silicon 0.10 Al balance Gray CtUt Iron.. IlL 1.2" Diameter Test Bar 1 >0,000 HS-Chrome-50 54.73 10.94 6.90 5.98C balance ) 3.8% Carbon. Equivalent ••.ooo :)) ~o-.-cc._,,, In most instances, the maximum improvement in strength from the use of stabilizing inoculants in gray cast

~~'""' '• PAGE 4 FOOTE FOUNDRY FACTS

iroru will be in the range of 4.0% to 4.5% carbon equiva· A regular grade of chrome·silicide, or ferrochrome· Ients. When used in gray cut irons with carbon equivalents silicon, is normall y only used for small chromium additions, in the range of 3.4% to 4.0%, it is recommended that a amall such as 10 to 15 points of chromium. amount of a proprietary graphitizing inoculant, such as HS.Chrome·50 is generally used in introducing up to Graphidox or Inoculoy 63, be used to insure minimum under· 0.20% Cr. It dissolves more readily in gray cast iron than cooling. This is especially true in gray cast irons with section either the blocking grade chromium, or chrome-silicide. Its thickn~ of %" and under. rate of solution in gray cast iron is about the same as V-5. For example, in a gray cast iron with a carbon equiva· However, since it does not contain so much silicon, calcium lent of 3.5% we would expect a minimum tensile strength or titanium as V-5, its nucleating power is not so great as of 45,000 psi in a .section size of Y2" if the gTapbite is present that of V-5. For this reason, it is recommended that a as type A flake. However, in an iron of this composition, proprietary graphitizing inoculant be used in conjunction excessive undercooling normally occurs unless the iron is with HS.Chrome-50, when the latter is used as a stabilizing inoculated. This would result in an iron of lower strength inoculant in gray cast iron. than expected. If a stabilizing inoculant were used alone, it Figures 8 and 9 show the effects of a 3 lb. per ton addi· is possible that too much underooo}jng might still result. Ten· lion of Inoculoy 63, a graphitizing inoculant, to a gray cast aile strength, irutead o£ being around 45,000 psi minimum, iron of 4.0% carbon equivalent. Figure 8 is the uas.cast" migHt be as low as 38,000 psi. Through the use of a pro structure ( Y2" section). Figure 9 shows the structure of the prietary graphitizing inocuJant (for example, 4 lhs. per ton same gray cast iron after inoculation. on Inoculoy 63), the tensile strength can be brought up to 45,000 psi minimum through the minimization of under· flCURE 8 cooling. However, i{ a 1% addition of a stabilizing inocu· "AJ.C4Jl"' Structure - Gray C4Jt Iron . 100 X Mo1. 4JJC/o lant, plus about 2 lbs. per ton of a proprietary graphitizing Corlx>n EquiiiiJient. *• C4J1· inoculant were used, the teruile strength could he raised to in1 SutU>n- Not IMculDted. a minimum value of 48,000 psi. Note Untlercoolin1 4J Eui· Another point to remember when using stabilizing denccd br Prucnce of Tr~ D inoculant. is that they are more efftttive in increasing the Graphite. teruiJe strengths of the weaker base gray cast irons rather 9 than the stronger base gray irons. For example, the addi· ncuR£ So!M Iron 01 Fi1urc 8-lrwc· tion of 1% of a stabilizing inoculant, such as V-5, to a gray ulotu w:itla 3 lbs. ~' ton o/ cast iron having a tensile strength of 30,000 psi in a Y2" lnoculor 63. Note Tr~ A section thickness, would be expected to increase the strength Groplaite-Denotin1 ElimiM· of this gray cast iron to 35,000 psi. The same addition to a tion of UnJercoolin1. gray cast iron with a base tensiJe strength of 40,000 psi, would raise the tensile strength only to about 43,500 psi. SUMMARY Normally, the most effective results from using V-5 will A broad range of inoculants is available to the foundry· be realized from using it in amounts varying from Y2 to man which can improve the properties of gray cast iron. 11 1Y2%. Smaller additions are not nearly so effective. Larger While standard" alloys may be employed, proprietary alloys additioru generally introduce too much silicon. are available which offer far greater efficiency and hence High silicon blocking grade ferrocbromium is normalJy reduced costs. The development of proper inoculation tech· uaed as a stabilizing inoculant for adding up to 0.20% niques is indisperuible to efficient foundry operations. chromium. In order to achieve maximum benefits from this Next issue we'll discuss post inoculanta for ductile cast stahili%ing inoculant, it is recommended that one to two iron. pounds per ton of a proprietary graphitizing inoculant he added with it to control the degree of undercooling. This is espeeialJy true for gray cast irons with section sUe8 under %" thickness.