professional factory provide AISI 4340 Steel | 36CrNiMo4 | 1.6511 | EN24 | 817M40 | SNCM439 in Lesotho
AISI 4340 steel is a medium carbon, low alloy steel known for its toughness andstrength in relatively large sections. AISI 4340 is also one kind ofnickel chromium molybdenum steels. 4340 alloy steel is generallysupplied hardened and tempered in the tensile range of 930 – 1080 Mpa.Pre hardened and tempered 4340 steels can be further surface hardened by flame or induction hardening and by nitriding. The 4340 steel has goodshock and impact resistance as well as wear and abrasion resistanc...
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is a medium carbon, low alloy steel known for its toughness and
strength in relatively large sections. AISI 4340 is also one kind of
nickel chromium molybdenum steels. 4340 alloy steel is generally
supplied hardened and tempered in the tensile range of 930 – 1080 Mpa.
Pre hardened and tempered 4340 steels can be further surface hardened by
flame or induction hardening and by nitriding. The 4340 steel has good
shock and impact resistance as well as wear and abrasion resistance in
the hardened condition. AISI 4340 steel properties offer good ductility
in the annealed condition, allowing it to be bent or formed. Fusion and
resistance welding is also possible with our 4340 alloy steel. ASTM 4340
material is often utilized where other alloy steels do not have the
hardenability to give the strength required. For highly stressed parts
it is excellent choice. AISI 4340 alloy steel can also be machined by
all customary methods.
Due to availability the ASTM 4340 grade steel is often substituted
with European based standards 817M40/EN24 and 1.6511/36CrNiMo4 or Japan
based SNCM439 steel. You have the detailed data of 4340 steel below.
1. AISI 4340 Steel Specification and Relevant Standards
|Standard||EN 10250||JIS G4103|
2. ASTM 4340 Steels And Equilvalents Chemical Composition
|JIS G4103||SNCM 439/SNCM8||0.36-0.43||0.60-0.90||0.030||0.030||0.15-0.35||1.60-2.00||0.60-1.00||0.15-0.30|
3. AISI Alloy 4140 Steel Mechanical Properties
(Heat Treated Condition )
|Tensile Strength MPa||Yield Strength
|Thermal expansion co-efficient (20°C/68°F, specimen oil hardened, 600°C (1110°F) temper||12.3 µm/m°C||6.83 µin/in°F|
|Thermal conductivity (typical steel)||44.5 W/mK||309 BTU in/hr.ft².°F|
4. Forging of 4340 Alloy Steel
the steel 4340 first, heat up to 1150°C – 1200°C maximum for forging,
hold until temperature is uniform throughout the section.
Do not forge
below 850 °C. 4340 has good forging characteristics but care must be
taken when cooling as the steel shows susceptibility to cracking.
Following forging operation the work piece should be cooled as slowly as
possible. And cooling in in sand or dry lime is recommended etc.
5. AISI 4340 Steel Grade Heat Treatment
pre-hardened steel stress relieving is achieved by heating steel 4340
to between 500 to 550°C. Heat to 600 °C – 650 °C, hold until temperature
is uniform throughout the section, soak for 1 hour per 25 mm section,
and cool in still air.
full anneal may be done at 844°C (1550 F) followed by controlled
(furnace) cooling at a rate not faster than 10°C (50 F) per hour down to
315°C (600 F). From 315°C 600 F it may be air cooled.
4340 alloy steel should be in the heat treated or normalized and heat
treated condition before tempering. The tempering temperature for
depends upon the strength level desired. For strength levels in the 260 –
280 ksi range temper at 232°C (450 F). For strength in the 125 – 200
ksi range temper at 510°C (950 F). And don’t temper the 4340 steels if
it is in the 220 – 260 ksi strength range as tempering can result in
degradation of impact resistance for this level of strength.
Tempering should be avoided if possible within the range 250 °C – 450 °C due to temper brittleness.
Flame or Induction Hardening
As mentioned above, pre-hardened and tempered 4340 steel bars or plates can be further surface hardened by either the flame or induction hardening
methods resulting in a case hardness in excess of Rc 50. AISI 4340
steel parts should be heated as quickly as possible to the austenitic
temperature range (830 °C – 860 °C) and required case depth followed by
an immediate oil or water quenching, depending upon hardness required,
workpiece size/shape and quenching arrangements.
quenching to hand warm, tempering at 150°C – 200°C will reduce stresses
in the case with minimal effect on its hardness.
All de-carburised surface material must first be removed to ensure best results.
and tempered 4340 alloy steel can also be nitrided, giving a surface
hardness of up to Rc 60. Heat to 500°C – 530°C and hold for sufficient
time (from 10 to 60 hours) to develop the depth of case. Nitriding
should be followed by slow cooling (no quench) reducing the problem of
distortion. The nitrided grade 4340 materials can therefore be machined
to near final size, leaving a small grinding allowance only. The tensile
strength of the 4340 steel material core is usually not affected since
the nitriding temperature range is generally below the original
tempering temperature employed.
Surface hardness achievable is 600 to 650HV.
is best done with the alloy steel 4340 in the annealed or normalized
and tempered condition. It can be readily machined by all conventional
methods such as sawing, turning, drilling etc. However in the high
strength conditions of 200 ksi or greater the machinability is only from
25% to 10% that of the alloy in the annealed condition.
of steel 4340 in the hardened and tempered condition (as normally
supplied), is not recommended and should be avoided if at all possible,
because of the danger of quench cracking, as the mechanical properties
will be altered within the weld heat affected zone.
must be carried out, pre-heat to 200 to 300°C and maintain this while
welding. Immediately after welding stress relieve at 550 to 650°C, prior
to hardening and tempering.
If welding in the hardened and
tempered condition is really necessary, then the work piece, immediately
on cooling to hand warm, should be if possible stress relieved at 15 °C
below the original tempering temperature.
8. Application of 4340 Steel
4340 steel is used in most industry sectors for applications requiring
higher tensile/yield strength than 4140 steel can provide.
Some typical applications such as:
Aircraft Landing Gear
Oil and Gas Drilling,
Warm and Cold Forming,
Transfer Systems, like power transmission gears and shafts.
engineering industries and structural use applications, such as: heavy
duty shafts, gears, axles, spindles, couplings, pins, chucks, molds etc.
Check us out at http://www.tutorvista.com/content/physics/physics-iii/solids-and-fluids/amorphous-solids.php
Crystalline and Amorphous Solids
The process of forming a crystalline structure from a fluid or from materials dissolved in the fluid is often referred to as crystallization. In the old example referenced by the root meaning of the word crystal, water being cooled undergoes a phase change from liquid to solid beginning with small ice crystals that grow until they fuse, forming a polycrystalline structure. The physical properties of the ice depend on the size and arrangement of the individual crystals, or grains, and the same may be said of metals solidifying from a molten state.
Which crystal structure the fluid will form depends on the chemistry of the fluid, the conditions under which it is being solidified, and also on the ambient pressure. While the cooling process usually results in the generation of a crystalline material, under certain conditions, the fluid may be frozen in a noncrystalline state. In most cases, this involves cooling the fluid so rapidly that atoms cannot travel to their lattice sites before they lose mobility. A noncrystalline material, which has no long-range order, is called an amorphous, vitreous, or glassy material. It is also often referred to as an amorphous solid, although there are distinct differences between crystalline solids and amorphous solids: most notably, the process of forming a glass does not release the latent heat of fusion.
Crystalline structures occur in all classes of materials, with all types of chemical bonds. Almost all metal exists in a polycrystalline state; amorphous or single-crystal metals must be produced synthetically, often with great difficulty. Ionically bonded crystals can form upon solidification of salts, either from a molten fluid or upon crystallization from a solution. Covalently bonded crystals are also very common, notable examples being diamond, silica, and graphite. Polymer materials generally will form crystalline regions, but the lengths of the molecules usually prevent complete crystallization. Weak van der Waals forces can also play a role in a crystal structure; for example, this type of bonding loosely holds together the hexagonal-patterned sheets in graphite.
Most crystalline materials have a variety of crystallographic defects. The types and structures of these defects can contain a profound effect on the properties of the materials.
An “amorphous solid” is a solid in which there is no long-range order of the positions of the atoms. (Solids in which there is long-range atomic order are called crystallines or morphous). Most classes of solid materials can be found or prepared in an amorphous form. For instance, common window glass is an amorphous solid, many polymers (such as polystyrene) are amorphous, and even foods such as cotton candy are amorphous solids.
In principle, given a sufficiently high cooling rate, any liquid can be made into an amorphous solid. Cooling reduces molecular mobility. If the cooling rate is faster than the rate at which molecules can organize into a more thermodynamically favorable crystalline state, then an amorphous solid will be formed. Because of entropy considerations, many polymers can be made amorphous solids by cooling even at slow rates. In contrast, if molecules have sufficient time to organize into a structure with two- or three-dimensional order, then a crystalline (or semi-crystalline) solid will be formed. Water is one example. Because of its small molecular size and ability to quickly rearrange, it cannot be made amorphous without resorting to specialized hyperquenching techniques.
Amorphous materials can also be produced by additives which interfere with the ability of the primary constituent to crystallize. For example, addition of soda to silicon dioxide results in window glass, and the addition of glycols to water results in a vitrified solid.
Some materials, such as metals, are difficult to prepare in an amorphous state. Unless a material has a high melting temperature (as ceramics do) or a low crystallization energy (as polymers tend to), cooling must be done extremely rapidly. As the cooling is performed, the material changes from a supercooled liquid, with properties one would expect from a liquid state material, to a solid. The temperature at which this transition occurs is called the glass transition temperature or Tg.
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