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TitleSteel Casting Metallurgy
TagsMaterials Science Building Engineering Metals Phase (Matter) Crystal Structure
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STEEL CASTING METALLURGY

Edited by
Dr. John M. Svoboda

Technical & Research Director
and

Raymond W. Monroe
Research Manager

© Steel Founders’ Society of America, 1984
Cast Metals Federation Building

455 State Street, Des Plaines, Illinois 60016

Printed in the United States of America

Page 129

and vacuum spectrometers, or direct reading instruments for carbon,
silicon, sulfur, hydrogen, nitrogen, and total oxygen. Temperature is
preferably measured with immersion thermocouples (Pt-Pt l0% Rh or
Pt-Pt l3% Rh).

Summary

To summarize the process of producing a heat, a heat log of a Cr-Ni-Mo
steel is illustrated in Figure 2. Although many variations to the proce-
dures discussed do exist, they represent a normal practice as used by
the majority of steel foundries.

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BASIC MELTING PRACTICE

The basic electric melting process will be discussed in terms of operat-
ing practices and controls. Since many aspects of the basic practice
are the same as those in the acid practice, only the differences will be
pointed out and discussed. The term "basic practice" implies that the
bath is contained in a basic refractory hearth, and that the slags used
are generally basic in chemical characteristics. The principal reason
for the use of the basic practice, rather than the acid practice, is that
sulfur and phosphorus may be removed from the steel. This is required
for the production of steels to specifications requiring low sulfur and
phosphorus for improved impact properties. In some cases, the basic
practice can be more economical for plain carbon grades where lower
quality scrap may be upgraded. The basic practice is almost universally
used for high alloy and stainless steels as well as manganese steel.

The Charge
The comments concerning charging practices in the acid furnace given
previously also pertain to the basic operation. The charge generally
consists of 20 to 50 percent foundry returns. The charge is generally
limited to 0.10 percent phosphorus and 0.08 percent sulfur; and fre-
quently will run at lower levels. If the charge is low in carbon, pig iron
may be added to give a sufficient melt down carbon. Limestone or lime
may be added to assist in the formation of a basic slag. A typical charge
may consist of:

Foundry return scrap 30-50 %

Purchased scrap 30-50 %

Basic pig iron 5-15%

Limestone 6%

The choice of the use of limestone or lime is subject to many consider-
ations. Popp2 describes the advantages and disadvantages of the two
materials as follows:

Lime

1. Accurate CaO content

2. Low SiO2 content

3. Absorbs water

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Page 257

Austenitic materials are also severely degraded in corrosion fatigue
strength under conditions conducive to pitting, such as in seawater.
However, they are easily cathodically protected without fear of hydro-
gen embrittlement and perform well in fresh waters.

Duplex alloys have not been widely studied.

Stress Corrosion:
Stress corrosion susceptibility is similarly specific tothe alloy, environ-
ment and conditions of exposure. As a general rule, the high strength
martensitic steels have displayed sensitivity to stress corrosion as have
the austenitic alloys. Duplex stainless steels are an improvement over
single phase alloys.

Figure 18 indicates the relative performance of several duplex alloys.
The test conditions involved a relatively short exposure to a sodium
chloride solution at 400°F. While the trends suggested are complex, it is
apparent that resistance generally increases with ferrite content. Large
improvements appear possible through control of alloy composition.

244

Page 258

REFERENCES

1. Steel Castings Handbook, Fifth Edition, SFSA, 1980, P.F.Weiser, Ed.
2. Schaeffler, A. "Constitution Diagram for Stainless Steel Weld Metal",
3. Schneider, H., Foundry Trade J., 1960,108, 562.
4. Schoefer, E., Appendix to "Mossbauer-Effect Examination of Ferrite in Stainless

Steel Welds and Castings," Welding Journal, Research Supplement, 39, Jan. 1974,
p. 10-S.

5. Beck, F.,Schoefer, E., Flowers, Jr., and Fontana, M., "New Cast Higher Strength Al-
loys Grades by Structure Control" ASTM STP 369, 1965, p, 159-174.

6, Landerrnan, E.I., and Barnford, W., "Fracture Toughness and Fatigue Characteris-
tics of Centrifugally Cast Type 316, Stainless Steel Pipe after Simulated Thermal
Service Conditions", MPC-8, Ductility and Toughness Considerations in Elevated
Temperature Service, ASME, 1978.

7. Uddeholm Corrosion Control Information, NUCCI, No. 1-81,
8. Michels, H.T, and Hoxie, E.C.,"Some Insights Into Corrosion in SO2 Exhaust Sch-

rubbers", ASM Conference on Materials Reliability Problems in Fossil Fired Power
Plants, Knoxville, TN, Nov. 9, 1977.

9. Larson, J.A., "High Alloy Specifications-ATale of New Materials", SFSA, T&O Con-
ference, Nov. 1983, pp. 213-224.

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