ASTM A848
This specification covers the standard requirements for wrought low-carbon iron having a carbon content of 0.015% or less with the remainder of the analysis being substantially iron. Two alloy types are covered: Type 1 is a low-phosphorus grade and Type 2 contains a phosphorus addition to improve machinability. The alloy specimens shall conform to the required chemical compositions of carbon, manganese, silicon, phosphorus, sulfur, chromium, nickel, vanadium, titanium, aluminum and iron. The alloys shall be produced in a wide variety of forms and conditions namely: forging billet; hot-rolled product; cold-finished bars; strip; wire; and relay condition. The alloy materials shall undergo heat treatment. Magnetic testing shall also be performed wherein the alloys shall conform to the required values of the coercive field strength.
1.1 This specification covers the requirements for wrought low-carbon iron typically having a carbon content of 0.015 % or less with the remainder of the chemical composition being substantially iron.
1.1.1 Two alloy types are covered: Type 1 is a low-phosphorous grade and Type 2 contains a phosphorous addition to improve machinability.
1.2 This specification also covers alloys supplied by a producer or converter in the form and condition suitable for fabrication into parts which will be subsequently heat treated to create the desired magnetic characteristics. It covers alloys supplied in the form of forging billets, hot-rolled products, and cold-finished bar, wire, and strip.
1.3 This specification does not cover iron powders capable of being processed into magnetic components. Please refer to the following ASTM Standards for information regarding powdered metal materials and magnetic components: Specifications A811, A839, and A904.
1.4 This specification does not cover flat-rolled, low-carbon electrical steels. Please refer to Specification A726 for information regarding these materials.
Soft Magnetic Core Iron is a low carbon magnetic iron produced using vacuum induction melting and vacuum arc re-melting processes.
Other elements commonly found in low carbon irons are held as low as possible to ensure good DC magnetic properties. The double melting technique keeps the distribution of non-metallic inclusions to a minimum length and frequency so that thin wall sections will not contain leaks due to internal discontinuities.
Applications
Used in components where vacuum integrity is needed, such as power tubes and microwave devices
Relays, solenoids, magnetic pole pieces for scientific instruments
This product has an Iron content of 99.85% Min, without the addition of alloy elements. All natural impurities have been largely removed.
Pure iron undergoes pacification after melting by means of vacuum degassing following solidification. It therefore has a homogenous composition with regard to distribution of the accompanying elements, a very low oxygen content, and due to the low Carbon content, the micro structure consists of pure ferrite.
This material supports excellent magnetic properties and resistance against corrosion and oxidation. It has good cold forming capabilities and is well suited to welding.
Applications
Aviation construction
Nuclear technology
Magnet production
Automotive construction
Power station construction
Gaskets in the chemical and petrochemical industries
Magnetic shielding
Welding rods and fuse wire
An anti-corrosion anode
SPECIALTY PRODUCTS
Specialty Products:
Ultra-low Carbon Magnetic Iron Strip & Sheet per ASTM A-848-01
Ultra-low Carbon Magnetic Iron Precision Cold Rolled Foil
Ultra-low Carbon Magnetic Iron Hot-Rolled Pickled and Oiled Sheet
Magnetic Core Iron Cold Drawn Rod and Bar per ASTM A-848-01
Open Die Forgings for Magnetic Applications
Hot Rolled Bars per ASTM A-848-01
Magnetic materials are broadly classified into two groups with either hard or soft magnetic characteristics. Soft magnetic behavior is essential in any application involving changing electromagnetic induction such as solenoids, relays, motors, generators, transformers, and magnetic shielding. This Article provides a description on ferromagnetic properties, the effect of impurities, alloying additions, heat treatment, residual stress, and grain size on magnetic properties. It also describes the alloy classification and magnetic testing methods of soft magnetic materials, which include high-purity iron, low-carbon steels, silicon steels, iron-aluminum alloys, nickel-iron alloys, iron-cobalt alloys, ferrites, and stainless steels. The Article discusses the corrosion resistance of soft magnetic materials, and provides information on selection of alloys for power generation applications, including motors, generators and transformers. It concludes with a short note on design and fabrication of magnetic cores.
ASTM A848Type1 ASTM A848 Mechanical
The main mechanical properties are elasticity, plasticity, stiffness, aging sensitivity, strength, hardness, impact toughness, fatigue strength and fracture toughness.
Elasticity: Metal material deforms when it is subjected to external force. When the external force is removed, it can restore its original shape.
Plasticity: The ability of ASTM A848Type1 ASTM A848 to produce permanent deformation without causing damage under external forces.
Stiffness: The ability of ASTM A848Type1 ASTM A848 to resist elastic deformation under stress.
Strength: The ability of ASTM A848Type1 ASTM A848 to resist deformation and fracture under external forces.
Hardness: The ability of ASTM A848Type1 ASTM A848 to resist the pressure of a harder object into it.
Impact toughness: The ability of ASTM A848Type1 ASTM A848 to resist fracture under impact loading.
Fatigue strength: The maximum stress that does not cause fracture when ASTM A848Type1 ASTM A848 is subjected to numerous repeated or alternating loads.
Fracture toughness: a performance index used to reflect ASTM A848Type1 ASTM A848 is ability to resist crack instability and expansion
Scope Description:
Electric propulsion for space applications has demonstrated tremendous benefit to a variety of NASA, military, and commercial missions. Critical NASA electric propulsion needs have been identified in the scope areas detailed below. Proposals outside the described scope shall not be considered. Proposers are expected to show an understanding of the current state of the art (SOA) and quantitatively (not just qualitatively) describe anticipated improvements over relevant SOA materials, processes, and technologies that substantiate NASA investment.
To shape the magnetic fields needed for operations, Hall-effect thrusters utilize a magnetic circuit that also forms the thruster structure. The magnetic circuit components direct magnetic flux (typically produced by electromagnetic coils) and may experience operational temperatures in excess of 500 °C due to coil self-heating and the close proximity of plasma-wetted surfaces. Both low-carbon magnetic iron and cobalt-iron (Co-Fe) soft ferromagnetic alloys have been traditionally used in the role; low-carbon magnetic iron is typically cheaper with larger billet size availability, whereas Co-Fe soft ferromagnetic alloys are attractive due to high magnetic saturation and Curie temperature properties. As Hall-effect thrusters become larger to support future high-power applications, thruster components also experience and must survive increased inertial launch loads. To address this issue, prospective magnetic circuit materials are desired with improved structural strength compared to SOA options while retaining comparable or better magnetic and thermal properties. Prospective materials capable of being produced in machinable, large-diameter (i.e., >400 mm) solid billets—or that can be additively manufactured to achieve comparable sizes—are of particular interest. This solicitation seeks such prospective magnetic circuit materials suitable for Hall-effect thruster applications with the following properties:
Mechanical: Meets or exceeds yield stress properties in Table X2.4 of ASTM Standard A801-14.
Magnetic: Meets or exceeds properties in Appendix X1 of ASTM Standard A848-17.
Thermal: Meets or exceeds Curie temperature of 770 °C.
Method and apparatus for radial elecromagnetic power arrays
Abstract
Multiple arrays of linear motors and generators are combined in a radial configuration to provide high mechanical efficiency to deliver power in a single plane of motion to a common crankshaft. Magnet core assemblies for the motors and generators use powerful rare earth magnets positioned within an outer flux containment shell comprising a highly-magnetically-permeable ferrous-alloy to provide high power density. The motor magnet stack is attached directly to a link rod that connects to the crankshaft. Pulsed power is provided to electromagnetic coils by microcomputer control, and coil energy is recovered at the ends of the linear stroke. A controller energizes the coils in certain combinations of coil location and polarity in order to produce bi-directional mechanical motion. Energy that is released when coils are switched off is harvested as voltage pulses returned to standby batteries or capacitors, or the electrochemical cells.
DETAILED DESCRIPTION – Linear Actuators
As described below, improved linear actuators may be used in motors, generators, prime movers, and systems. ferrous properties and flux containment
A magnetic circuit behaves in a similar fashion to an ordinary electrical circuit in that magnetic elements can have “magnetic conductivity” or magnetic resistance, and there are limits to how much magnetic current a structure can carry before saturation. When Weodymium magnets are used in a device, it’s not uncommon to experience magnet induced flux densities near 1.5 Tesla. Most common materials like ferrites and carbon steels saturate at less than a third of this flux density- between 0.2 to 0.5 Tesla. In applicant’s experience, properly annealed ASTM A848 metal provides the highest commercially available flux density. As improved materials become available, those materials may be used for containment structures in linear elements.
Specifying ASTM A848 metal and invoking an appropriate annealing process gives the linear elements significant magnetic performance enhancements over other materials. The results are increased shaft power and decreased waste heat. Only a few suppliers provide the preferred raw metal for high- performance magnetics. These metals chemically meet or exceed ASTM A848 raw alloy standards. By “raw” it is meant that it is the user’s responsibility to anneal the raw materials so as to enhance and maximize the raw metal’s latent magnetic properties.
Performance is largely a function of the time-temperature history of the metal and its chemical composition. For example, annealing special ferrous metals, when properly performed, will maximize the magnetic permeability and saturation flux density of the outer shell flux containment canisters in linear elements. Optimum magnetic flux path performance is critical to achieve the aforementioned performance enhancements – in short, a far superior embodiment of magnetic principles over
conventional approaches is ensured by selecting the correct material and annealing it correctly. Rather than shun the use of ferrous metal in a reciprocating magnetic motor that uses Neodymium magnets, applicants embrace the use of ferrous material because the quality of ferrous material and the location of components circumvent the problems encountered in conventional systems when the designers attempt to combine Neodymium magnets in the near presence of ferrous structures.
Example annealing process
In an example annealing process, the sample is placed in a stainless steel bag such as provided by SenPak to eliminate oxygen exposure to the sample. The sealed bag placed in a muffle furnace or other suitable annealing furnace of 0- 1000 deg Centigrade range or greater. An annealing is performed by ramping the oven temperature from ambient to 845 degrees C at a ramp rate not to exceed 2 degrees C/minute; the oven temperature is held at 845 deg C for 2 hours; the oven temperature is ramped from 845 degrees C to 500 degrees C at a ramp rate not to exceed 1 degrees C/minute; and the oven temperature is ramped from 500 degrees C to ambient at a ramp rate not to exceed 2.5 degrees C/minute.
Shell fabrication methods
The flux canisters shown in the figures above are solid, metal cylinders made of ASTM A848 magnetic metal stock which provided approximately a 1 OX improvement over the floral wire wound shell. The parts were deliberately over sized in terms of wall thickness so as to avoid magnetic saturation of the parts during system operation. Air gaps in a magnetic assembly cause loss in magnetic flux capability and can lead to flux saturation. Air gaps, such as between th&magnet stacks and motor shell liners, could be decreased via tighter tolerances that may be obtainable with a lamination process and more precise machining
Ferrous magnetic flux structures such as flux containment shells, end caps, spacer washers, etc., can be fabricated from multiple layers of thin material. A shell made of laminations where the individual lamination layer is coated with a non-electrically conductive material such as thin plastic or shellac stops eddy currents from forming and thus reduces or eliminates magnetically- induced heating in the shell.
Thin sheets of 0.025 inch ASTM A848 metal are available for use in making laminations. In this example, the containment shell for a motor would require about 330 layers of magnetic
metal, possibly coated with shellac, and bolted together.
One type of lamination is a washer embedded in a NIB magnet stack. Washers or spacers help to reduce the magnetic NIB material required to make a magnet stack. For example, just one or two NIB magnets may be used, with the rest of the magnet stack using thin laminations of
properly-annealed ASTM A848.
Standard Specification for Low-Carbon Magnetic Iron
- Scope
1.1 This specification covers the requirements for wrought
low-carbon iron having a carbon content of 0.015 % or less
with the remainder of the analysis being substantially iron.
1.1.1 Two alloy types are covered: Type 1 is a lowphosphorous grade and Type 2 contains a phosphorous addition
to improve machinability.
1.2 This specification also covers alloys supplied by a
producer or converter in the form and condition suitable for
fabrication into parts which will be subsequently heat treated to
create the desired magnetic characteristics. It covers alloys
supplied in the form of forging billets, hot-rolled products, and
cold-finished bar, wire, and strip.
1.3 This specification does not cover iron powders capable
of being processed into magnetic components.
1.4 This specification does not cover flat-rolled, low-carbon
electrical steels.
1.5 The values stated in customary (cgs-emu and inchpound) units are to be regarded as standard. The values given
in parentheses are mathematical conversions to SI units which
are provided for information only and are not considered
standard. - Form and Condition
5.1 These two alloys are capable of being produced in a
wide variety of forms and conditions for fabrication into
magnetic components. The desired form and condition shall be
discussed with the producer to assure receiving the correct
product. Available forms and conditions are:
5.1.1 Forging Billet—Hot worked and surface conditioned
by grinding.
5.1.2 Hot-Rolled Product—Hot rolled; hot rolled and acid
cleaned; hot rolled and annealed; hot rolled, annealed, and acid
cleaned; hot rolled and mechanically cleaned; mechanical
properties as specified.
5.1.3 Cold-Finished Bars—Cold drawn, centerless ground,
mechanical properties as specified; or relay condition.
5.1.3.1 Relay condition applies to 1 in. (25.4 mm) round and
less in diameter and certain shapes supplied in the cold-worked
condition having up to 25 % reduction in area and capable of
meeting Class 2 magnetic property requirements as defined in
6.5.
5.1.4 Strip—Cold rolled, cold rolled and annealed, deep
draw quality, mechanical properties as specified; or relay
condition.
5.1.4.1 Relay condition applies to cold-rolled strip 0.020 to
0.200 in. (0.51 to 5.1 mm) thick having up to 25 % reduction
in thickness and capable of meeting Class 2 magnetic property
requirements as defined in 6.5.
5.1.4.2 Ordering information for strip must include edge
condition and mechanical property requirements.
5.1.5 Wire—Cold drawn, annealed, mechanical properties as
specified or relay condition.
5.1.5.1 Relay condition applies to cold-drawn wire when
capable of being supplied having up to 25 % reduction in area
and capable of meeting Class 2 magnetic property requirements as defined in 6.5. - Magnetic Property Requirements
6.1 Density—The density for test purposes is
7.86 g ⁄cm3 (7860 kg/m3
).
6.2 Test Specimen—Whenever possible, test specimen size
and shape shall conform to Practice A34/A34M. Shapes such
as ring laminations, solid rings, Epstein specimens, or straight
lengths having a uniform cross section are preferred. If,
however, it is impossible to prepare a preferred test specimen
shape from the product, specimen shape and size shall be
mutually agreed upon by the user and the producer.
6.3 Heat Treatment—It is recommended that the user
specify the desired heat treatment method to be applied to the
test specimens.
6.3.1 When relay condition is specified, the test specimen
shall be heat treated in a dry forming gas atmosphere (5 to
15 % hydrogen in nitrogen with a dew point less than −40°C)
at a temperature of 845°C for 1 h at temperature and cooled at
a rate from 55 to 100°C/h to 500°C and cooled at any rate
thereafter.
6.3.2 If relay condition is not specified and no heat-treating
procedure is specified by the user, the producer is free to
choose a heat treatment procedure. Refer to Appendix X3 for
heat treatment recommendations.
6.4 Test Method—Magnetic testing shall be conducted in
accordance with Test Methods A341/A341M, A596/A596M,
or A773/A773M or by use of a coercimeter. Under this
specification only the coercive field strength (Hc) must be
measured.
6.5 Requirements—The coercive field strength (Hc) measured from a maximum magnetic flux density of 15 kG (1.5 T)
or higher must meet the maximum values listed in Table 2
when the test specimen is heat treated in accordance with 6.3.1.
6.5.1 When a coercimeter is used, the supplier must be able
to demonstrate that the flux density in the test specimen reaches
at least 15 kG (1.5 T) during the magnetization cycle. In
addition, the test equipment and method should conform to
those specified in IEC Publication 60404-7. - Keywords
9.1 coercive field strength; magnetic iron; relay steel
X3. HEAT TREATMENT OF LOW-CARBON MAGNETIC IRON
X3.1 Magnetic test specimens shall be heat treated in
accordance with the procedure listed in 6.3.1 for qualifying
material to meet this specification.
X3.2 Parts fabricated from magnetic iron can be heat treated
in several different manners depending on the application and
the heat-treating equipment available. General comments regarding the heat treatment procedure are as follows:
X3.2.1 Atmosphere—Decarburizing atmospheres typically
result in the lowest coercivity material. The following atmospheres are listed in order of decreasing effectiveness of
decarburization:
X3.2.1.1 Wet Hydrogen—(dew point from −20 to 5°C) do
not use at temperatures greater than 950°C.
X3.2.1.2 Wet Forming Gas(5 to 15 % hydrogen balance
nitrogen)—do not use at temperatures greater than 950°C.
X3.2.1.3 Dry Hydrogen—(dew point less than −40°C) can
be used at all temperatures.
X3.2.1.4 Dry Forming Gas—can be used at all temperatures.
X3.2.1.5 Vacuum—can be used at all temperatures.
X3.2.1.6 Endothermic Atmospheres—carburizing potential
is inversely proportional to dew point.
X3.3 Temperature:
X3.3.1 The lowest suggested heat treatment temperature is
700°C. These alloys are ferritic up to a temperature of about
890°C. Above this temperature austenite forms. Decarburization is most readily obtained in the ferritic state.
X3.3.2 Heat treatment in the austenite phase (at temperatures above 890°C) will result in grain size refinement upon
cooling through the austenite to ferrite transformation.
Conversely, heat treatment at very high temperature followed
by slow cooling through the transformation will maximize the
ferrite grain size thus improving the magnetic properties.
X3.3.2.1 A suggested high temperature heat treatment procedure is: heat to and hold at 850 6 25°C for 4 h in wet
hydrogen, purge out wet hydrogen with dry hydrogen and heat
to 1120°C and hold at temperature for 4 h then cool at a rate of
55 to 100°C per hour to a temperature of 550°C followed by
cooling at any convenient rate.
X4.1 Trace amounts of carbon and especially nitrogen
present either in the as-melted material or introduced during
processing such as heat treatment in atmospheres containing
nascent or atomic nitrogen can cause time-dependent changes
in magnetic behavior termed magnetic aging. These changes
may occur over a period of weeks or even months at room
temperature and are due to the precipitation of nitrides and
carbides.
X4.2 Magnetic aging typically impairs magnetic
performance, especially in relays. The magnetic properties
most subject to aging include low-induction permeability and
coercive field strength. High-induction properties and magnetic
saturation are not measurably affected by magnetic aging.
X4.3 Magnetic aging can be effectively eliminated by use of
iron containing trace additions of strong nitride formers such as
vanadium, titanium, and aluminum. Vanadium and titanium are
also strong carbide formers and will suppress aging caused by
carbon.
X4.4 Magnetic aging can also be reduced or eliminated by
annealing in wet hydrogen to reduce the carbon and nitrogen
content and by slow cooling after the anneal.
X4.5 A procedure for determination of the potential for
magnetic aging is to measure the coercive field strength of a
freshly heat-treated specimen, heat at 100°C for a period of
eight days to accelerate the aging process and remeasure the
coercive field strength.
X4.6 The magnetic behavior of parts can be stabilized by
heating to 175 to 260°C for several hours to cause overaging.
Note that the magnetic properties will be inferior to freshly
heat-treated parts, but the time dependency will be largely
eliminated.
ROLEX METAL DISTRIBUTORS
57-A Khatargalli
Thakurdwar
Mumbai – 400 002 India
0091-22-23858802
0091-22-23823963
marketing@rolexmetals.com
www.rolexmetals.com