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ISSN 09670912, Steel in Translation, 2012, Vol. 42, No. 7, pp. 572576. Allerton Press, Inc., 2012.Original Russian Text D.V. Rutskii, N.A. Zyuban, A.N. Galkin, S.B. Gamanyuk, 2012, published in Izvestiya VUZ. Chernaya Metallurgiya, 2012, No. 7, pp. 3137.

572

The growing requirements on heavy machinerydemand highquality forgings. Large forgings, such asships propeller shafts, turbine rotors, and housing andpipe blanks for power units, are manufactured fromingots whose weight is twice that of the final part.Increase in ingot mass leads to intense shrinkage and

liquation and hence to increased physical and chemical nonuniformity, as well as other uncontrollabledefects arising in the solidification of large metalmasses [1]. The ingots employed are mainly intendedfor the production of a dense axial zone, and hencehave a large deadhead (20% on average) and are characterized by differences in H/Dand the taper [2, 3].The large deadhead limits the scope for effectivereduction in wastage on forging. Another worryingproblem is the intense chemical liquation over theingot height (especially for carbon), which may lead torejection of the forgings produced.

Manufacturing enterprises in the transportation

and power industries produce a wide range of forgings.Up to 80% are hollow (rotor shafts of turbogenerators,wheels, thinwalled pipe, casings, housing components, etc.) [3]. In that case, to reduce forging wastes,the trend is to use long ingots with no deadhead. However, in view of the diversity of blank designs, suchapproaches are not always successful. To improveproduct quality and production economics, it is ofinterest to use ingots with a chilled upper section[4, 5]. Instead of a classic deadhead, a cooling attachment is employed (relative volume 4%), as illustratedin Fig. 1. In that case, compensation of the shrinkage

within the ingot continues until the solidificationfronts moving horizontally from the side walls of the

mold are close enough together to ensure a narrowshrinkage cavity in the axial zone. The metal in thecenter of the ingot with traces of shrinkage porosity isremoved in subsequent piercing or drilling.

Tables 1 and 2 present the chemical composition ofthe metal and the geometric and technical parametersof casting.

Tables 3 and 4 present the macrostructure and thephysical and chemical inhomogeneity of 38XH3MA

steel ingots cast with regular heating attachments andwith cooling attachments.

We see that, in the experimental ingot, the diameterand length of the axial cavity are almost half those ofthe conventional ingot. This may be attributed toshrinkage of the obstructedsupply zone in the final

stage of solidification and hence to better conditionsof liquidmetal delivery.

The shrinkage cavity in the experimental ingot isconcentrated in the axial region, with a small width(23.1% of the mean diameter); its height is considerable (50.4% of the height of the ingot body), as we seein Table 3. Accordingly, the shrinkage cavity is practically completely removed in ingot deformation andthe production of a hollow forging.

Analysis of the chemical inhomogeneity (Table 4)shows that it is considerably less pronounced in the

Influence of IngotSolidification Conditions

on Forging Structure and Quality

D. V. Rutskii, N. A. Zyuban, A. N. Galkin, and S. B. GamanyukVolgograd State Technical University

Received April 23, 2012

DOI: 10.3103/S0967091212070091

1

2

3

4

(a) (b)

Fig. 1. Casting ingots with heating (a) and cooling (b)attachments: (1) pan; (2) mold; (3) attachment; (4) castingladle.

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STEEL IN TRANSLATION Vol. 42 No. 7 2012

INFLUENCE OF INGOTSOLIDIFICATION CONDITIONS 573

Table 1. Chemical composition of forged steel samples

Ingot min, tContent, %

C Mn Si S P Cr Ni Cu Mo V

Conventional 4.50 0.41 0.52 0.39 0.015 0.017 0.11 0.15 0.15

Experimental 1.53 0.34 0.48 0.33 0.014 0.008 1.42 3.25 0.10 0.38 0.11

Table 2. Geometric dimensions of ingots and casting parametersIngot min, t H/D kbo,* % Vde, % Tfi, C Tca, C body, min de, min

Conventional 4.5 2.16 1.5 16.67 1665 1570 2.70 1.30

Experimental 1.53 1.99 6.1 4.00 1640 1570 1.55 1.10

* Throughout, values of the taper on both sides are given.

Table 3. Structural parameters of ingots

Parameter Ingot with heating attachment Ingot with cooling attachment

Crust zone:

mean width of zone, mm 15 10.5

relative area of axial section, % 5.7 3.0

Zone of columnar dendrites:

mean width of zone, mm 55 96.1


mean crystal size, mm 49 42

mean inclination to horizontal, deg 22 14

Zone of large disoriented dendrites:


mean crystal size, mm 9.1 8.6

mean inclination, deg 41.7 57

Shrinkage cone:

height, mm 685 204

proportion of ingotbody height, % 43.1 20.8

maximum diameter, mm 487 158

proportion of mean ingotbody diameter, % 76.1 34.3

relative area of ingot bodys axial section, % 26.7 3.5

mean crystal size, mm 5.1 3.6

mean inclination, deg 53.2 62

Zone of axial porosity:

extent, mm 720 391

proportion of ingotbody height, % 52.2 39.9

maximum diameter, mm 100 37

proportion of mean ingot diameter, % 15.6 8.0

relative area of ingot bodys axial section, % 6.6 1.7mean crystal size, mm 5.7 12.5

mean inclination, deg 54 53

Shrinkage porosity:

extent, mm 220 494

proportion of ingotbody height, % 50.4

relative area of ingot bodys axial section, % 7.2

maximum diameter in ingot body, mm 111.4

proportion of mean ingotbody diameter, % 23.1

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experimental ingot. That may be attributed to themore uniform distribution of strongly liquating elements (C, S, P, etc.) over the ingot height.

Less pronounced redistribution of the liquatingelements and development of chemical inhomogene

ity may be explained in that solidification is more rapidin the experimental ingot on account of the coolingeffect of the pan at the bottom and the cooling attachment at the top. To better understand ingot solidification with the cooling attachment, physical modeling

of ingot casting and solidification at different rates wasundertaken in laboratory conditions on twodimensional models of the molds in [6].

Table 5 presents the calculated scales of the process. We conclude that the solidification of liquid38XH3MA steel in the mold is comparable with thesolidification of the model liquid (hyposulfite) in thelaboratory model.

In the experiments, the moving solidification frontis divided into two components: the horizontal frontcorresponds to solid phase growing from the side wallsto the center of the mold; the vertical front corresponds to solid phase growing from the bottom to the

center of the mold.The modeling results show that the speed of the

horizontal solidification front is much greater in theexperimental ingot than in the conventional ingot(Fig. 2). At the end of solidification, when impurityredistribution is most developed, this difference is100% or more.

Thus, intense solidification tends to suppress theliquation and equalize the chemical composition ofthe metal over the ingot height and cross section.

The results show that ingots with a cooled uppersection may be used to produce hollow forgings. Thenarrow shrinkage cavity in the axial zone and uppersection of the ingots will certainly be removed in forging the ingots and boring out the forgings produced.

To confirm the modeling results, we consider theindustrial casting of 15X2MA steel ingots (mass13.56 and 12.14 t), for which the geometric and casting parameters are summarized in Table 6.

Forging of the given ingots yields hollow blanks,from which samples are taken for chemical analysisand mechanical testing, in accordance with Fig. 3.

100

80

60

40

20

0 135104734210

Time, min

Solidphase,

% 1

2

(a) (b)100

80

60

40

20

0 135104734210

Time, min

Solidphase,

%

1

2

Fig. 2.Progress of vertical (a) and horizontal (b) solidification fronts for ingots with cooling (1) and heating (2) attachments.

Table 4. Chemical Inhomogeneity of ingots

ParameterIngot with heating

attachmentIngot with cooling

attachment

Positive liquation, %:

carbon +10.8 +3.0

sulfur +18.8 +7.1

phosphorus +18.0 0

Negative liquation, %:

carbon 8.1 3.0

sulfur 6.3 14.3

phosphorus 9.1 11.1

Total liquation, %:carbon 18.9 6.0

sulfur 25.1 21.4

phosphorus 27.1 11.1

Table 5. Modeling scales for ingot solidification with bentbottom section

Parameter Symbol Value

Time scale 0.67

Linear scale e 4.28

Scale for heattransfer rate a 1.12

Scale for temperature differences 3.65

Scale for heat fluxes q 4.09Scale for dynamic intensity E 4.98

Table 6. Geometric and technological factors in ingot casting

min, t H/Dkbo,%

Vde, % Tfi, CTca,C

body,min

de,min

13.56 2.05 9.0 17.6 1655 1570 5.10 3.80

12.14 2.05 9.0 4.0 1655 1570 5.15 2.35

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INFLUENCE OF INGOTSOLIDIFICATION CONDITIONS 575

The carbon distribution in the initial experimentalingot (mass 12.14 t) and conventional ingot (mass13.56 t) is shown in Fig. 4.

The lower part of the conventional ingot is charac

terized by reduced carbon content (Fig. 4a). In thedeadhead region, the carbon content is greater. Thatcorresponds to the conventional notion of liquation inlarge forged ingots. The carbon distribution is moreuniform in the experimental ingot (Fig. 4b).

Accumulations of liquating impurities are less pronounced in the experimental ingot and concentratedin the central part of the ingot, which is removed. Theuseful part of the forging is characterized by uniformchemical composition. Negative liquation is observedin both the lower and upper parts of the experimentalingot. This difference in the distribution of elements

within the conventional and experimental ingots isdue to differences in the solidification process. In the

conventional ingot, the head is the last to solidify.Therefore, the maximum quantity of liquating elements displaced in solidification is concentrated thereand in the deadhead. In the experimental ingot, thelast portion of metal to solidify, which is rich in liquating elements, is within the narrow central region of theingot. The upper and lower levels are practically identical in chemical composition.

Calculation of the total carbon liquation shows thatit is 46.3% in the conventional ingot and 6.3% in theexperimental ingot. That indicates significant suppression of chemical inhomogeneity.

The final hollow components undergo routine tests

in accordance with the relevant standards. The metalquality in hollow forgings is investigated on samplesfrom rings of thickness 20 mm (Fig. 3). Two rings areconsidered, one at each end of the forging (corresponding to the bottom and top of the ingot).

Monitoring of the macrostructure and the liquational inhomogeneity for the end disks does not revealany discrepancies. All the components manufacturedfrom the experimental ingots comply with the requirements. Tables 7 and 8 compare the mechanical prop

erties of the conventional ingot and the experimental

ingot. Mean test data for several forgings are com

pared.

Analysis of Table 7 shows that the strength and rel

ative elongation of the ingots are the same. In Table 8,

we see that the nonuniformity of the distribution of the

mechanical properties at the ends of the forgings is

1.44.7 less in the case of the experimental ingots than

for the conventional ingots. This is associated with the

more uniform distribution of the liquating elements

over the length of the forgings, which, in turn, may be

attributed to the faster solidification in the experimen

tal ingot. When the chemical composition of the forg

ing is more uniform, it is simpler to select the temper

FS

IeIIe

F

S

SS

50C

50C

(a) (b)

Ie IIe

6900

460

30

515

50

375 460

Fig. 3.Selection of samples in end disks (a) and samples for determining the mechanical properties (b) in forgings from 13.56tand 12.14t ingots: Ie, end of forging that corresponds to bottom of ingot; IIe, end of forging that corresponds to deadhead;S, shocktesting samples; F, failuretesting samples.

(+33.3%) (6.7%)

(13%)(13%)

0.160.19

0.20

0.15

0.13

0.12

0.15

0.150.180.19

0.14

0.18

0.18

0.17

0.15

0.13

0.16

0.15

0.14

0.16

0.14

0.15

0.13 0.15

0.140.13

0.15

0.14

0.17

0.15

(a) (b)

Fig. 4.Carbon distribution over the height and cross section of 13.56t conventional ingot (a) and 12.14t experimental ingot (b).

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ature in the final heat treatment, since there is no needfor differential heat treatment.

This indicates that hollow forgings obtained fromthe experimental ingots are of higher quality, whichmeans that their production is more technologicallyand economically expedient.

CONCLUSIONS

The change in the solidification conditions ofingots with an upper cooling attachment favors thehorizontal motion of the front and accelerates solidification in the head of the ingot.

Comparison shows that ingots with rapid solidification in the head are characterized by improvedstructural and chemical homogeneity and by rational

shape optimal location of the shrinkage cavity, whichmay be entirely removed in the subsequent productionof hollow components.

Our results show that the distribution of themechanical properties over the volume is significantlymore uniform for forgings made from 12.14t ingots

with a cooled upper section than from 13.56t conventional forgings, on account of the suppression of liquation and the more uniform chemical composition inthe initial ingot.

ACKNOWLEDGMENTS

Funding was provided within the framework of

project no. MK4034.2012.8 for the improvement oflarge powerindustry components.

REFERENCES

1. Zhulev, S.I. and Zyuban, N.A., Proizvodstvo i problemykachestva kuznechnogo slitka(Production and Qualityof Forged Ingots), VolgGTU, RPK Politekhnik, 2003.

2. Durynin, V.A. and Solntsev, Yu.P., Issledovanie i sovershenstvovanie tekhnologii proizvodstva s tselyu povysheniyaresursa stalnykh izdelii iz krupnykh pokovok otvetstvennogo naznacheniya(Improvements in Production Technology to Extend the Life of Steel Parts Made fromLarge Critical Forgings), Siberia: Khimizdat, 2006.

3. Dub, V.S. and Dub, A.V., Elektrometallurgiya, 2006,no. 11, pp. 1822.

4. Zhulev, S.I., Optimizing the Production of Ingots forCritical Forgings on the Basis of CAD Technology,Doctoral Dissertation, Volgograd, 1991.

5. Skoblo, S.Ya. and Kazachkov, E.A., Slitki dlya krupnykh pokovok (Ingots for Large Forgings), Moscow:Metallurgiya, 1973.

6. Shamrei, V.A. and Zhulev, S.I., Metallurg, 2001,no. 11, pp. 4954.

Table 7. Mechanical properties at the ends of the forgings made from the experimental ingot and the conventional ingot

Type of forgingNumber

of forgings

y,

MPa

B,

MPa , % , %

Fracture

KCU,

kJ/m2HB

Macrostructure

Pipe forging (experimental) 15 653 745 20.3 74.3 C 246 236 D

Pipe forging (conventional) 10 637 728 19.7 73.4 C 239 222 D

Absolute change in mechanical properties 16 17 0.6 0.9 7 13.5

Relative change in mechanical properties, % of conventional value

2.5 2.3 3 1.2 2.8 5.7

Moldtype forging (experimental) 2 430 629 18.0 44.0 C 241 216 D

Moldtype forging (conventional) 7 415 634 17.9 43.2 C 233 211 D

Absolute change in mechanical properties 15 5 0.1 0.8 8 5

Relative change in mechanical properties,% of conventional value

3.4 0.7 0.6 1.8 3.3 2.3

Table 8. Nonuniformity of the mechanical properties of forgings made from the experimental ingot and the conventional ingot

Mechanical properties y, MPa B, MPa , % , % KCU, kJ/m2

Experimen

tal ingot

Difference between maximum

and minimum values

2.3 5.3 2.2 6.5 14

Nonuniformity of mechanicalproperties, %

4.8 3.3 11.4 9.6 5.7

Conventional ingot

Difference between maximumand minimum values

129 117.5 4.5 9.2 26.9

Nonuniformity of mechanicalproperties, %

19.1 15.3 23.4 13.6 11

Factor by which spread is reduced 4 4.7 2 1.4 1.9

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