27 Years Factory AISI 4340 Steel | 36CrNiMo4 | 1.6511 | EN24 | 817M40 | SNCM439 Factory in Vietnam

27 Years Factory
 AISI 4340 Steel | 36CrNiMo4 | 1.6511 | EN24 | 817M40 | SNCM439 Factory in Vietnam

Short Description:

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...

  • Length: 3-5.8mm or Customization
  • Surface: black, peeled, or rough turned
  • Heat treatment: air-cooling, normalized, annealed, Q&T
  • Smelting process: EAF+LF+VD
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    AISI 4340 steel
    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

    Country USA Britain Britain Japan
    Standard ASTM A29 EN 10250 BS 970 JIS G4103
    Grades 4340 36CrNiMo4/
    EN24/817M40 SNCM 439/SNCM8

    2. ASTM 4340 Steels And Equilvalents Chemical Composition

    Standard Grade C Mn P S Si Ni Cr Mo
    ASTM A29 4340 0.38-0.43 0.60-0.80 0.035 0.040 0.15-0.35 1.65-2.00 0.70-0.90 0.20-0.30
    EN 10250 36CrNiMo4/
    0.32-0.40 0.50-0.80 0.035 0.035 ≦0.40 0.90-1.20 0.90-1.2 0.15-0.30
    BS 970 EN24/817M40 0.36-0.44 0.45-0.70 0.035 0.040 0.1-0.40 1.00-1.40 0.20-0.35
    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

    Mechannical Properties

    (Heat Treated Condition )

    Condition Ruling section
    Tensile Strength MPa Yield Strength
    Izod Impact
    T 250 850-1000 635 13 40 248-302
    T 150 850-1000 665 13 54 248-302
    U 100 930-1080 740 12 47 269-331
    V 63 1000-1150 835 12 47 293-352
    W 30 1080-1230 925 11 41 311-375
    X 30 1150-1300 1005 10 34 341-401
    Y 30 1230-1380 1080 10 24 363-429
    Z 30 1555- 1125 5 10 444-

    Thermal Properties

    Properties Metric Imperial
    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

    • Stress Relieving

    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.

    • Annealing

    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.

    • Tempering

    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.

    • Nitriding

    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.

    6. Machinability

    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.

    7. Welding

    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.

    If welding
    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

    • Automotive,

    • Oil and Gas Drilling,

    • Forging,

    • Warm and Cold Forming,

    • Machine Building,

    • Transfer Systems, like power transmission gears and shafts.

    • General
      engineering industries and structural use applications, such as: heavy
      duty shafts, gears, axles, spindles, couplings, pins, chucks, molds etc.

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    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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