摘要:

An examination of the unsteady-state heat balanced of an ESR furnace during a power interruption has been made. The results of this study show that the ingot heat balance during an electrode change may be characterized by a single term, the volume fraction of liquid solidified during the interruption. The application of this term to ESR and VAR practice is demonstrated. The structure and composition of ingot metal solidified during this change can be related to the local temperature gradients and solidification rate during the change. In turn, this may be related to the steady-state liquidus isotherm and the volume fraction solidified. The role of the local segregation coefficient in determining the maximum tolerable electrode change time is clearly demonstrated by the above parameters. The general relation of the above mechanisms to the electrode-change method is discussed for some practical cases. The engineering and economic problems associated with electrode-change practice are detailed. It is concluded that although there are many instances where a properly engineered electrode-change method may be used with no adverse effects in the ingot, the general applicability of the method is in doubt.

ISSN:0022-5355    

DOI:10.1116/1.1317026

出版商:American Vacuum Society    

年代:1972

数据来源: AIP

摘要:

Changing technology patterns, coupled with growing demands for high product reliability at low cost, will result in a pronounced growth in the preparation of alloy grades subject to some form of vacuum melting of iron, nickel, and cobalt base alloys in the next 10 years. It is predicted thatallgrades slated for high reliability and/or performance products will see some form of vacuum processing, whether degassing or primary melting. A trend towards duplexing of various melting methods into “melting systems” consisting of two or more melting methods is also developing for the same reason. The paper describes various iron, nickel, and cobalt base alloy systems and several product applications along with the characteristic problems thereof. A complete description of all known melting schemes is presented along with their specific characteristics relating to charge material, tendency for contamination, and applications to a full range of prevalent forms. The paper further describes unique combinations (duplexing) of these various methods in such a way as to result in optimized quality and melting cost. Application to specific problems known in the melting industry will be discussed. Recommendations for maximizing productivity at lowest cost through duplexing will be made.

ISSN:0022-5355    

DOI:10.1116/1.1317027

出版商:American Vacuum Society    

年代:1972

数据来源: AIP

摘要:

In vacuum consumable arc remelting, control over the ingot solidification rate is of paramount importance to optimum product quality. In general, solidification rate is very dependent upon ingot size and melting current which help to define the general characteristics of the molten pool geometry and that of the advancing freezing front within the ingot. However, control of these parameters is achieved by precisely monitoring arc gap throughout the melting operation. By having a close control over the arc gap, the vacuum melter can eliminate variations in solidification rate which can cause localized harmful segregates. There are several types of controls used in the vacuum melting industry today and these are discussed, including the hash control used at Special Metals Corporation. The important features of the control are outlined with respect to their influence on arc gap, including speed of feed, voltage limitation, and basic hash/arc gap relationships. The importance of controlling the arc gap in Udimet 718 is shown by illustrating the effect of intentional controlled variations in arc gap at several melting currents on the formation of several types of segregates. The method of programming arc melt cycles to gain the most control over arc gap to ensure a reproducible, high quality product is discussed.

ISSN:0022-5355    

DOI:10.1116/1.1317028

出版商:American Vacuum Society    

年代:1972

数据来源: AIP

摘要:

The reactions of titanium and silicon with slags of the system alumina-calcium oxide-fluorspar were calculated. The calculations were confirmed by melts in a laboratory induction furnace and also through statistical calculations of 320 heats of 500 mm □ (3,6 ton) ingots for theTi–Al2O3reaction and of 100 ESR heats of the same ingot size for theSi–Al2O3reaction. By statistical evaluation of all heats the dependence of the aluminum and titanium or silicon contents for differentTiO2orSiO2contents of the slags were determined. By application of these data the losses of Ti or Si by a reaction with alumina can be prevented.

ISSN:0022-5355    

DOI:10.1116/1.1317029

出版商:American Vacuum Society    

年代:1972

数据来源: AIP

摘要:

Presented by C. W. FinklA. Finkl and Sons Company, subsidiary Republic Steel CompanyThe vacuum decarburization of high chromium heats called VOD in North America and LD–VAC in the rest of the world has revolutionized the melting practice of stainless steel. Since production trials started at the end of the last decade, a world production capacity of 1 720 000 tons annually has been built or is under construction. This paper deals with the latest design of the Vacuum Decarburizing Unit, and of the basic-lined slide gate ladles. It sequentially describes operating procedures giving time, chemistry, and temperatures related to the separate steps of the process. Multicombinations of melting and vacuum decarburizing facilities are explained along with cost and furnace time savings. Equipment descriptions cover cost and type of ladle refractories, vacuum pumping curve, inherent fume control, and end-point determination. Latest metallurgical developments and short cycle desulfurization in direct combination with decarburization outside the premelting furnace are also discussed, as is the advantage of vacuum ladle degassing in the VOD/LD–VAC unit.

ISSN:0022-5355    

DOI:10.1116/1.1317030

出版商:American Vacuum Society    

年代:1972

数据来源: AIP

摘要:

The effect that C and N contents have on the toughness of Fe–Cr–Mo alloys has been known for some time, but only recently have vacuum melting and inert-gas or inert-gas-vacuum combination refining process between developed to the point where low interstitial ferritic stainless steels are commercially attractive engineering materials. This paper reviews the effects of C and N contents on various properties of Fe–Cr–Mo alloys in which the interstitial level varies over the range 50–1000 ppm. The alloys are divided into two classes: 25Cr–Mo and 18Cr–Mo. The properties studied included toughness, welded ductility, resistance to intergranular corrosion, and resistance to pitting corrosion. Some of the higher Mo alloys presented interesting problems since heat treatments used to negate the effects of carbide and nitride precipitation produced undesirable phases. This problem could be avoided in the higher purity alloys by using high temperature annealing treatments. The amount of C and N that can be tolerated before these ferritic stainless steels become susceptible to intergranular corrosion after welding is a function of their Mo and Cr contents with the more highly alloyed material having the higher limits. Both Ti and Nb can be used to stabilize less pure steels against intergranular corrosion, but both C and N must be considered in determining the proper addition. Although stabilizing additions appear to improve the as-welded ductility of less pure Fe-Cr-Mo alloys, they do not improve theirannealedtoughness. Generally speaking, purer alloys have better resistance to pitting corrosion.

ISSN:0022-5355    

DOI:10.1116/1.1317031

出版商:American Vacuum Society    

年代:1972

数据来源: AIP

摘要:

The feasibility of producing electroslag remelted hollows is shown. In this work electroslag hollows of two superalloys, Hastelloy alloy X and Haynes alloy No. 718 were produced. The microstructure of the as-cast hollows was significantly finer than that of a comparable ESR solid ingot. The segregation ratio defined as the maximum concentration of an element divided by the minimum concentration of the element was 1.16 and 1.33 for molybdenum for the ESR hollow and solid ingot, respectively. Mechanical property results from ring rolled and cross rolled specimens indicated that wrought properties were achieved in both alloys when total reductions exceeded 43%–50%. An acceptable although not optimum microstructure was obtained, and the reasons for this are discussed.

ISSN:0022-5355    

DOI:10.1116/1.1317033

出版商:American Vacuum Society    

年代:1972

数据来源: AIP

摘要:

The relationship between quantity and type of nonmetallic inclusions and critical mechanical properties was determined for the high-strength steels 4340 and 300M. Quantitative television microscope scanning data and various petrographic and microprobe methods were used to study the inclusions. Inclusion statistics showed that improved cleanliness was obtained in ascending order of (1) electric furnace air melted, (2) Dortmund–Horder degassed, (3) vacuum-arc–remelted and (4) electron beam hearth refined steels. Studies in the electron beam melted material were made on 1000 lb heats, whereas the remaining data were obtained on large-scale production heats. The properties for both 4340 and 300M improved in a similar manner with cleanliness. Transverse reduction of area was the property most influencd by inclusion content. Fatigue and impact properties were also affected, though to a lesser degree. Plane strain fracture toughness was relatively little affected by inclusion content and, in fact, longitudinal and transverse properties were substantially the same in direct contrast to reduction of area, impact, and fatigue properties.KIcis thus not a meaningful parameter for quality control measurement in these high-strength structural steels. While we realize that other factors, such as microsegregation, affect properties, we conclude that for steels processed according to specified practices, the inclusion content is the most important variable influencing critical mechanical properties.

ISSN:0022-5355    

DOI:10.1116/1.1317034

出版商:American Vacuum Society    

年代:1972

数据来源: AIP

摘要:

The authors show that at high tensile strength fracture toughness is insensitive to steel cleanliness, and reduction of area is very sensitive to steel cleanliness. These conclusions are generally substantiated by work conducted at U. S. Steel. The U. S. Steel work amplifies that reported in the subject paper by examining the effect of residual elements (cleanliness) on the reduction of area and fracture toughness of 18Ni maraging steels and the effect of prior-austenite grain size and residual-element content on the reduction of area and fracture toughness of high-strength quenched and tempered alloy steels. The U. S. Steel work shows that for the maraging and alloy steels studied, reduction-of-area values are very sensitive to residual-element level but not affected much by tensile-strength levels in the range 230–300 ksi. The fracture toughness of the maraging steels shows a sensitivity to residual-element level that decreases as the strength is raised. The steels appear to reach a point of complete insensitivity to residual-element level at a tensile strength of 310 ksi. At this strength, the fracture toughness approaches aKIcvalue of50 ksi( in.)12. The fracture toughness of the alloy steels is insensitive to residual-element level throughout the tensile-strength range 230–320 ksi, but is sensitive to prior-austenite grain size. The grain-size sensitivity decreases as the strength level increases and appears to reach a point of complete insensitivity at a tensile strength of about 310 ksi. Again, the fracture toughness of the steels at a tensile strength of 310 ksi approaches aKIcvalue of approximately50 ksi in.12. It is concluded that lowering residual-element levels by vacuum melting should improve the fracture toughness of maraging steels at tensile strengths below 310 ksi but will probably not improve the fracture toughness of quenched and tempered alloy steel at tensile strengths in the range 230 ksi and higher. Lowering residual elements by vacuum melting improves the ductility, as measured by reduction of area, of both maraging and alloy steels over the entire range of strengths studied. Reduction of area is not very sensitive to tensile strength in the range studied.

ISSN:0022-5355    

DOI:10.1116/1.1317035

出版商:American Vacuum Society    

年代:1972

数据来源: AIP

摘要:

Designs of plasma arc melting and plasma arc remelting systems available for metal refining, scrap recycling, cast structure improvement, and, in general, for the manufacture of very high quality ferrous and nonferrous metal alloys are reviewed. The advantages of plasma melting and remelting techniques in comparison to the various primary and secondary melting techniques are discussed. Data relative to the materials produced by this special melting technique are provided.

ISSN:0022-5355    

DOI:10.1116/1.1317036

出版商:American Vacuum Society    

年代:1972

数据来源: AIP