How to quenching and tempering of 4140 alloy steel

     How to quenching and tempering of 4140 alloy steel?
     The quenched and tempered of 4140 alloy steel production process: electric furnace smelting (EBT), LF refining, ingot casting, hot delivery, soaking pit, rolling, slow cooling, the surface peeled, quenching, tempering, steel straightening, cleaning inspection and turned over.
     4140 alloy steel rolling process:
     Use Rolling mill will steel ingot rolled into Φ180mm ~ Φ310mm. Since 4140 steel containing Mn and S, for the steel ingot of hot delivery use the soaking temperature 1260 ℃ in the production process, soaking time 3h, so you can make the steel ingot was burn-through, the steel rolling uniform deformation. Then the steel into the slow cooling pit slow cooling 60h, and then peeled surface treatment, and then quenched and tempered.
     4140 alloy steel quenched and tempered process:
     Before quenching, need to check whether there are cracks in the surface of the AISI 4140 steel, to prevent the quenching process since the steel surface crack lead to quenching crack.
     Steel quenching in bell-type furnace, installed furnace capacity controlled at about 20t, uniform heating to (890 ± 10) ℃, average temperature, heat preservation. Before quenching, tank filled with water and maintain a certain flow rate, water temperature is 10 ~ 40 ℃. From the baked to enter the water time is controlled within 10min. Steel was hanging out from the water every 2min, and then into the water. The quenching time a total of 30min, When leave the water, the steel surface temperature at 200 ℃. Steel after quenching, tempering as soon as possible. Tempering temperature of 580 ℃, the average temperature insulation 6 ~ 8h. After baked, in the sink fast cooling to 400 ℃, and then air cooling.
   

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The composition and properties of aisi 4130 alloy steel

The chemical composition of the aisi 4130 alloy steel:
Carbon (C):0.28 ~ 0.33
Silicon (Si): 0.15 ~ 0.35
Manganese (Mn): 0.40 ~ 0.60
Sulfur (S): allows the residual content is less than or equal to 0.040
Phosphorus (P): allows the residual content is less than or equal to 0.035
Chromium (Cr): 0.80 ~ 1.10
Nickel (Ni): allows the residual content is less than or equal to 0.030
Copper (Cu): allows the residual content is less than or equal to 0.030
Molybdenum (Mo): 0.15 ~ 0.25
The mechanical properties of alloy steel 4130:
Tensile strength σb (MPa): ≥930 (95)
Yield strength σs (MPa): ≥785 (80)
Elongation δ5 (%): ≥12
Section shrinkage ψ (%): ≥50
Impact energy Akv (J): ≥63
Impact toughness αkv (J / cm2): ≥78 (8)
Hardness: ≤229HB
Sample size: Sample size is 25mm rough
Heat treatment specifications: quenching 880 ℃, water cooling, oil cooling; tempering 540 ℃, water cooling, oil cooling.
   

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AISI 4340 steel heat treatment guide

     Performance: the AISI 4340 steel is a high hardenability steel, AISI 4340 steel heat treatment hardenability than any kind of steel in the AISI standard of the higher. When the elements are concentrated, hardenability is within the allowable range, the upper curve of hardenability essentially become a straight line, this indicates that the AISI 4340 steel need air quenching in thinner area. In accordance with the precise carbon content, when hardening, Rockwell hardness in the 54-59 range. Due to high hardenability, AISI 4340 steel using traditional welding methods are not suitable, although it can use this old methods, such as electron beam welding. AISI 4340 steel can be forged effortlessly, although its thermal performance than carbon or low-alloy steel is higher, the need to use high power forging machine. The mechanical processing is not very good.
     Forging: heated to 1230℃. After the temperature dropped to 900℃ to stop forging. Cool slowly to prevent cracks.
     Recommended AISI 4340 steel heat treatment operations:
     Normalizing: heating to 870℃. Cooling in air to 565 degrees; or heated to 830 degrees, rapidly cooled to 650 ℃, and hold 8 hours. In order to get the ball structure and heated to 750℃, rapidly cooled to 705℃, and then at a rate of not more than 3℃ per hour was cooled to 650℃, and hold 12 hours. Ball organizational structure is usually easy machining and heat treatment.
     Quenching: 845 degrees at the time, the steel organization becomes austenitic, then oil quenched. In the casting the thin area can be air quenching.
     Tempering: with all high hardenability steel the same, alloy steel 4340 will produce quenching cracks. In the casting to ambient temperature before (38-50℃), they should be placed in tempering furnace. Tempering temperature depends on the desired hardness or comprehensive mechanical properties.
     Nitriding: through nitriding to produce high surface hardness and enhance the anti fatigue performance.
 

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D2 steel heat treatment process

    D2 steel heat treatment methods:
    Stress relief annealing: the workpiece after rough machining, heating to 600~650 ℃, thermal insulation for 2 hours, with the furnace cooling to 500 ℃, followed by air cooling.
    Quenching: for the first time preheating, slowly warming the workpiece to 600 ℃, heat 20 minutes. After temperature uniformity, the second time preheating temperature was raised to 850 ℃, incubated for 30 minutes. Finally heated to 1020 ~ 1040 ℃, heat 25 to 40 minutes, followed by air cooling.
    Tempering: immediately tempering after quenching, and tempering at least twice, each holding time is not less than 2 hours.
    D2 steel heat treatment matters needing attention:
    After quenching, should be timely tempering, prevent cracking, and to prevent surface decarburization, for the manufacture of high precision die and gauge of D2 steel should be cryogenic treatment (-70 ℃), and the use of high-temperature tempering, To reduce the workpiece deformation, high temperature tempering temperature 500 ~ 560 ℃, hardness greater than 58HRC.
   

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