US3574605A

US3574605A - Weldable,nonmagnetic austenitic manganese steel

Info

Publication number: US3574605A
Application number: US739305A
Authority: US
Inventors: Albert M Hall; Donald B Roach; Dimon A Roberts; Frank A Pimentel
Original assignee: ALBERT M HALL; DIMON A ROBERTS; DONALD B ROACH; FRANK A PIMENTEL
Current assignee: ALBERT M HALL; DIMON A ROBERTS; DONALD B ROACH; FRANK A PIMENTEL
Priority date: 1968-06-24
Filing date: 1968-06-24
Publication date: 1971-04-13
Anticipated expiration: 1988-04-13

Abstract

A WELDABLE, NONMAGNETIC AUSTENITIC MANGANESE STEEL OF THE HADFIELD TYPE AND COMPATIBLE WELD METAL WHICH WILL REMAIN NONMAGNETIC AND TOUGH AS WELDED AND WITHOUT THE REQUIREMENT OF POST-WELD HEAT TREATMENT COMPRISING .3% CARBON, 13% MANGANESE, 5% NICKEL, 3 TO 5% CHROMIUM, 1% MOLYBDENUM AND .5% VANADIUM.

Description

April 13, 1971 TRUE STRESS, I000 psi ENGINEERING STRESS, IOOOpsi A. M. HALL ETAL WELDABLE, NONMAGNETIC AUSTENITIC MANGANESE STEEL Filed June 24, 1968 2 Sheets-Sheet 1 I25 X-'-)" X X -X"X/ I00 STRAIN, INCH PER INCH X X/ I50 X/ x/ x I00 x TRUE STRAIN INVENTORS ALBERTM. HALL F/ 2 D/MO/V A. ROBE/7 rs 6. DONALD B.R0A0H FRANK 4. P/MEN TEL v WELDABLE, NONMAGNETIC AUSTENITIC MANGANESE STEEL Filed June 24, 1968 71 A. M. HALL. ETAL ApriI 13, E

2 Sheets-Sheet 2 X M. X

STRAIN, INCH PER INCH E509 wmmmtw MS;

TRUE STRAIN INVENTORS ALBERTM. HALL 00mm 9. mac/1 D/MON 4.9055 i' g F/6 4 FRA/wmP/MEir Wm B N R m T A United States Patent C Filed June 24, 1968, Ser. No. 739,305 Int. Cl. C22c 39/20 U.S. Cl. 75-428 3 Claims ABSTRACT OF THE DISCLGSURE A weldable, nonmagnetic austenitic manganese steel of the Hadfield type and compatible weld metal which will remain nonmagnetic and tough as welded and without the requirement of post-weld heat treatment comprising 3% carbon, 13% manganese, 5% nickel, 3 to 5% chromium, 1% molybdenum and .5 vanadium.

BACKGROUND OF THE INVENTION The present invention relates to manganese steel of the Hadfield type and more particularly to a weldable, nonmagnetic austenitic manganese steel and compatible weld metal to replace Hadfields manganese steel in certain marine applications.

Austenitic manganese steel of the Hadfield type, containing about 12 to 14% manganese and 1.2% carbon, is used in a number of important naval applications. These steels are employed as cast and as wrought products and as a general rule are placed in service in the annealed condition which is achieved by water quenching from 1850 F. and above. In this condition they are nonmagnetic and exhibit excellent toughness and the capability to resist battering and abrasion resulting from heavy impacting.

The austenitic manganese steels have found wide usage in many applications characterized by heavy impacting, wear, and abrasion in the handling of bulk materials, e.g. balls for grinding mills. Another application is for helmets and body armor for military personnel. Still other applications of the austenitic manganese steels hinge on their nonmagnetic quality. In this category are parts for minesweepers, parts for lifting magnets, and special electrical equipment.

Hadfields steel, however, does have certain deficiencies which detract from its usefulness and service performance. The steel must be properly annealed (Water quenched from about 1900 F.) to exhibit high-toughness characteristics; plate or bar stock slow cooled from the annealing temperature will exhibit significantly reduced impact properties (Charpy V-notch valves as low as 20 ft.-lb.). The reduction in impact strength can be attributed to continuous grain-boundary carbide precipitation occurring in the temperature range from about 1600 to 600 or 700 F. Grain-boundary carbide precipitation is also equally detrimental in welding; Weld-heat-afiected zones frequently exhibit Charpy V-notch impact values in the order of ft.-lb. or less.

The grain-boundary carbide precipitation resulting from exposure to moderate temperatures can be attributed directly to the high carbon content of the steel, however, reductions in the carbon content reduce the amount and severity of the intergranular carbide precipitation that may occur. However, drastic reductions in carbon content (to perhaps 0.10% or less) are required to eliminate the thermally induced embrittlement in weld-heat-affected zones and in slow-cooled plate and bar. Because carbon is a potent strengthener and austenite stabilizer in these high-manganese austenitic steels, reductions in carbon content suflicient to result in acceptable resistance to thermally induced embrittlement in weldments are accompanied by a magnetic response in the steel at room temperatures. In reducing the carbon content of the steel, the temperature at which martensite starts to form on cooling from high temperatures (the M temperature) increases from cryogenic temperatures to temperatures approaching room temperature. At low carbon contents, the 12 to 14 percent manganese steel may have an M temperature approaching or above room temperature. The presence of martensite, of course, produces a magnetic response in the steel. In addition, martensite formation also reduces the toughness of the steel.

Thus, while Hadfields steel is an excellent material for applications requiring completely nonmagnetic characteristics and a high level of toughness, the steel does not retain these characteristics when welded. Weld deposits and weld-heat-afiected zones exhibit toughness properties considerably inferior to those of annealed material. Efforts to improve the toughness of Welded joints through the addition of alloying elements such as nickel, chromium and molybdenum have not been successful. However, it has been found that by adding nickel and reducing the carbon content of Hadfields manganese steel, alloys more resistant to thermally induced embrittlement can be obtained. For example, welding electrodes containing about 12 percent manganese, 2.75 to 5.0 percent nickel and 0.50 to 0.90 percent carbon are commercially available and can be employed to produce multipass Weld deposits with improved toughness. Of course, the electrode employed to join Hadfields steel does not affect the development of brittleness in parent metal heat-efiected zones.

The best prior art means to insure the characteristic toughness of austenitic manganese steel is to employ a postweld annealing treatment at 1850 F. or above, followed by Water quenching. Such postweld heat treatment is troublesome, impractical and often not feasible.

SUMMARY The general purpose of this invention is to provide an alloy that has all the advantages of Hadfields steel and none of the above-described disadvantages. The alloys of this invention possessing the properties indicated above, fall within the following composition ranges, in percent,

Iron-Balance plus incidental impurities.

Typical properties of the alloy of this invention, in the annealed condition, are as follows:

Yield strength45,000 p.s.i.

Tensile strength-115,000 p.s.i. Elongation% Impact strength (annealed)l55 ft.-lb.

Impact strength (sensitized at 1200 F. for 1 hour)- ft.-1b.

Accordingly, it is an object of the invention to provide a nonmagnetic steel of the austenitic manganese type.

A further object of the invention is to provide a non magnetic steel of the austenitic manganese type which can be welded by standard arc-welding processes without developing weld-heat-affected zones.

A still further object of the invention is to provide a steel which is resistant to general attack in seawater and resistant to stress-corrosion cracking in seawater when employed at yield-10a stresses.

Another object of the invention is to provide a compatible weld metal.

Still another object is to provide a compatible weld metal that will remain nonmagnetic and tough as welded and without the requirement of postweld heat treatment.

BRIEF DESCRIPTION OF THE DRAWINGS The exact nature of this invention as well as other objects and advantages thereof will be readily apparent from consideration of the following specification relating to the annexed drawing in which:

FIGS. 1 and 2 are graphical representations of Engineering Stress-Strain and True Stress-Strain curves for 0.505 inch diameter tensile specimens machined from annealed bar stock of an alloy of this invention.

FIGS. 3 and 4 are graphical representations of Engineering StressStrain and True Stress-Strain curves for All-Weld-Metal Tensile specimen machined from MIG Weld deposit of an alloy of this invention.

DESCRIPTION OF THE PREFFERED EMBODIMENT The invention is illustrated, but not limited, by the following specific examples of the preparation of a nonmagnetic steel and a compatible weld metal. Wherever possible, alternate modes of preparation are discussed but it will be recognized that various additional modifications can be made without deviating from the scope of the invention.

The excellent mechanical and physical properties of the alloys of this invention are obtained by the careful balance of the alloying elements (carbon, nickel, vanadium and chromium) to maintain nonmagnetic structure, the desired degree of thermal stability, and the desired strength properties. Vanadium should be restricted to a maximum of 0.5%. Chromium in amounts up to 5% is advantageous. Carbon should be restricted to the range from 0.25% to 0.40%. At lower carbon content, a magnetic response will be noted in deformed material, and at higher carbon contents, thermal stability is lacking. Nickel is required to maintain the austenitic structure at the carbon content specified. Increasing nickel above about 6% reduces strength, whereas less than 3.5% nickel results in an unstable austenitic structure. Molybdenum has little definite effect, however, a 1.0% addition appears to strengthen and maintain an austenitic structure.

While the composition ranges specified above will provide alloys having the above mentioned properties, a typical alloy embodying this invention is as follows:

Percent Carbon 0.30 Manganese 13.0 Nickel 5.0 Vanadium 0.5 Chromium 5.0 Molybdenum 1.0

To prepare suflicient material for subsequent welding tests, a 500 pound heat of the above composition was melted, fabricated into bar and plate, and evaluated in mechanical tests. A charge consisting of Armco iron and electrolytic nickel was melted in a magnesia lined induction furnace. After meltdown, ferromolybdenum, ferrovanadium, and ferrochromium were added, followed by the required ferromanganese. The melt was then deoxidized with ferrosilicon and poured into 100-pound ingot molds. The analysis of drillings taken from the ingot hot top was as follows:

The ingots were heated to 1950 F. and forged into 3-inch square bars for rolling into rounds, and into 3- by S-inch slabs for rolling into plate. The forged bars were hot rolled to 1 /8 inch diameter rounds, while the flats were hot rolled into /2 and inch thick plate. The rounds and plate were then annealed at 1900 F. and water quenched.

Specimens for mechanical and magnetic permeability tests were machined from the 1% inch diameter round material. Tensile tests were conducted on duplicate 0.505 inch diameter specimens, employing a strain rate of 0.005 inch per minute up to the yield load and a head speed of 0.10 inch per minute thereafter. By measuring the load after each 0.10 inch increment in elongation, a complete load-deformation curve was obtained. True-stress truestrain curves were constructed for each tensile test. Engineering Stress-Strain and True-Stress True-Strain curves for this material are shown in FIGS. 1 and 2. The results of the tensile tests were as follows:

Earl Bar2 Specimens machined from annealed rounds had impact strengths of 151, 157 and 156 ft.-1bs. Magnetic-permeability tests indicated that the material was nonmagnetic (permeability of 1.003 or less). Moreover, hand magnet tests revealed no evidence of a magnetic response in the fractured areas of the tensile or impact bars.

In preparing base metal and electrode wire for subsequent welding tests, a sample alloy was taken from the 500 pound heat mentioned above. Plate material /2 inch and inch thick, from this heat, were annealed at 1900 F. and water quenched. The plate was grit blasted and cleaned in acetone prior to welding tests.

In producing filler wire, a quantity of 1% inch round bar stock was hot rolled at 1900 F. to inch diameter rod, which was then centerless ground to remove any surface defects and subsequently annealed at 1900 F. The rod was then cold drawn into 0.035 inch diameter wire, cleaned, and spooled for welding tests. The rod work-hardened rapidly during drawing operations. In gages above 0.090 inch, it was necessary to anneal the rod after every 30 percent cold reduction. In sizes smaller than 0.090 inch, the wire could be cold reduced 50 percent between anneal processes. Annealing was performed at 1900 F. in an argon atmosphere retort and cooled in the retort. After final annealing, the wire was drawn through one die for straightening purposes, cleaned and spooled.

All gas metal-arc (MIG) welds were made in the flat position employing automatic welding equipment and a 0.035 inch diameter electrode produced from an alloy of this invention. Single-V butt joints were made in /2 and inch plate of this alloy. The joints were evaluated by means of the following tests:

(1) Transverse weld-metal tension tests (2) All weld-metal tension tests (3) Transverse-weld side bend tests (4) Transverse-weld Charpy V-notch impact tests Hatch-Hartbower type, weld-metal heat-affected-zone impact tests (6) Battelle variable restraint cracking tests.

Tensile tests-Transverse weld specimens The results of tensile tests on the round (0.505 inch) and rectangular /2 x A? inch) specimens were as follows:

1 Specimens broke in the grips where the extension tabs had been welded.

All 0.505-inch-diameter specimens failed in the weld deposit indicating that the heat-aifected zones were stronger than the weld deposit. The yield strengths of these transverse weld specimens were significantly higher (about 8,000 to 10,000 p.s.i.) than that of annealed plate material of this alloy. The tensile strengths of the weld specimens were slightly below that of the annealed wrought material. However, the transverse weld specimens exhibited less than half the ductility of the annealed wrought material. Nevertheless, a tensile elongation of 25 percent is considered acceptable.

Tensile tests-All-weld-metal specimens The results of tensile tests were as follows:

Ultimate 0.2% ofiset yield tensile Elongation Bar strength, p.s.i. strength, p.s.i. percent in 2 in.

Side-bend tests Transverse-weld side-bend tests were conducted on specimens 6 inches long by inch wide by inch thick, machined from welds in inch plate so that the width of the specimen represented the complete Weld thickness. The results showed that all three specimens could be bent around a die having a radius of inch without cracking in the heat-affected zone or at the fusion line. Some slight tearing of the weld metal was noted in bending over the inch radius. This tearing was manifested by small fissures less than A inch long near the center of the weld.

Impact tests The results of Charpy V-notch impact tests made in transverse weld specimens and on Hatch-Hartbower type specimens were as follows:

Specimen type: Impact valve, ft.-lb. Transverse weld 67, 54, 52 Hatch-Hartbower 125, 123, 123, 131, 123

In addition, measurements were made of the expansion occurring beneath the notch in the Hatch-Hartbower specimens. This expansion is indicative of the ductility of the material in the presence of a V-notch and under impacttest loading conditions. These measurements showed an average expansion of 0.0276 inch for the weld-metal portion and 0.0303 inch for the heat-aifected-zone portion of the specimens. In comparison, similar measurements made on broken impact specimens of annealed material of this alloy revealed an average expansion of 0.0357 inch. (This annealed material had shown an impact strength of about 150 ft.-lb.)

These results indicate that, in the welded specimens, the heat-affected zones had higher impact strengths than did the weld deposit and that the annealed wrought material had a higher impact strength than did the heatatfected zone and the weld deposit.

Variable-restraint weld tests Tests indicated that weld deposits and heat-affected zones of welded joints in the alloy of this invention are not susceptible to weld-metal or heat-atfected-zone cracking when under conditions of high restraint. No cracking or fissuring was observed even in areas of maximum restraint.

Metallographic examination Sections of welded joints made in inch plate were prepared for metallographic examination. Careful examination revealed fine discontinuous grain-boundary carbides in the weld-heat-affected zones. At relatively low power (250X), the grain-boundary carbides could not be clearly resolved in the areas adjacent to the fusion line. At very high power (1500X the fine discontinous nature of the carbide precipitation could be observed. These carbides are not considered embrittling-the heatalfected zone had shown high impact strength.

Magnetic characteristics Qualitative tests with a strong hand magnet did not reveal any evidence of a magnetic response in any of the welded joints. Furthermore, failed tensile and impact specimens also did not exhibit evidence of magnetic response in heavily deformed areas adjacent to the fractures.

From the foregoing it is apparent that the alloys of this invention provide a nonmagnetic steel of the austenitic manganese type which can be welded by standard arc-welding processes without developing weld-heat-affected zones and which are resistant to general attack in seawater and resistant to stress-corrosion cracking in seawater when employed at yield-load stresses.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A weldable, nonmagnetic, austenitic manganese steel consisting essentially of:

Iron-Balance plus incidental impurities.

2. A weldable, nonmagnetic, austenitic manganese steel consisting essentially of:

Percent Carbon 0.20-0.30 Manganese 12.0- Nickel 4.0-6.0 Chromium 3.0-5.0 Molybdenum 0.75-1.50 Vanadium 0.20-0.50

IronBalance plus incidental impurities.

3. A weldable, nonmagnetic, austenitic manganese steel consisting essentially of:

Percent Carbon 0.30 Manganese 13.0 Nickel 5.0 Vanadium 0.5 Chromium 5. Molybdenum 1.0

with the balance iron.

References Cited UNITED STATES PATENTS 2,026,468 12/1935 Hall 75128A 2,156,299 5/1939 Leitner 75128A 5 2,865,740 12/1958 Heger 75-128 HYLAND BIZOT, Primary Examiner US. Cl. X.'R. 7s 12s