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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What are the methods of DIN 1.2379 steel heat treatment

    Thermal processing of DIN 1.2379 steel:
Start temperature 1050 °C, end temperature 850 °C, furnace cooling.
    Softening annealing treatment:
In the protection of gas, heating to 800~850 °C, then by 10 °C /h speed cooling to 600 °C, then the air cooling, the hardness is less than or equal to 250HBw.
    To eliminate stress treatment:
If want to eliminate the residual stress generated after rough machining, mold should be heated to 650 °C, heat 2h, and then with the furnace cooling to 500 °C, then followed by air cooling.
    DIN 1.2379 steel quenching and tempering:
The first preheating temperature 550 ~ 600 °C, maintained at about 30min per 25mm; the second preheating temperature 800 ~ 850 °C, maintained at about 30min per 25mm; austenitizing temperature 975 ~ 1040 °C, maintained at about 30min per 25mm , oil cooling (40 ~ 70 °C) or gas cooling, cooled to 50 ~ 70mm immediately tempered.
1) low-temperature tempering: tempering temperature 150 ~ 200 °C, each 25mm for about 60min above, air cooling, hardness ≥61HRC. Tempering should choose a lower austenitizing temperature 975 ~ 1025 °C.
2) high-temperature tempering: tempering temperature 480 ~ 540 °C, each 25mm for about 60min or more, air cooling, more than twice tempered, hardness ≥58HRC. Tempering should use a higher austenitizing temperature 1000 ~ 1040 °C.
    Cryogenic treatment of 1.2379 steel:
After hardening, the workpiece is immediately cooled to between -80℃~ -70 °C, maintaining 3 ~ 4h, then tempering. Cryogenic treatment can improve the hardness 1 ~ 3HRC.
    The aging treatment:
Temperature of 110 ~ 140 °C, thermal insulation 25 ~ 100h, in order to ensure that the workpiece size and stability during use.

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How to perform the heat treatment of 1.2344 mould steel

     1.2344 steel as a martensitic hot work die steel, with high toughness and resistance to thermal fatigue performance, moderate resistance to temper softening ability and resistance to melting loss and other comprehensive performance, belongs to medium heat resistant ductile steel, it‘s a kind of ideal hot work die steel. Currently, widely used in manufacturing aluminum die-casting mold many of them are made of 1.2344 mould steel, its not prone to fatigue cracking, even if there is also thin and short fatigue crack is not easy to expand. And anti-strong bond, and the interaction between the molten metal is small, thus ensuring casting can get better visual quality. Because of this the steel also has a high hot hardness, and commonly used in the hot extrusion processing.
     After annealing 1.2344 steel microstructure is mainly pearlite and a small amount of undissolved carbides, very stable supercooled austenite in the pearlite transformation zone. 1.2344 mould steel for containing high chromium steel and has good hardenability, more than 1% of the molybdenum contained in the steel, the steel hardenability it also plays an important role. Since vanadium can form stable carbides in the steel, actually reduces the steel hardenability. A 100mm diameter steel bars in air cooling quenching can also complete quenching. Size is larger than the 100mm mold adopts oil quenching.

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How to heat treatment of P20 plastic die steel

    Improve P20 plastic die steel hardness treatment:
    In order to improve die life up to 80 million times or more, can quenching and tempering way to achieve the implementation of pre-hardened steel. Quenching preheated at 500-600 ℃ 2-4 hours and then at 850-880 ℃ holding a certain time (for at least 2 hours), into the oil cooled to 50-100 ℃ oil cooled, quenched hardness of up to 50 -52HRC. Immediately carried out 200 ℃ low-temperature tempering treatment in order to prevent cracking. After tempering, the hardness can be maintained over 48HRC.
    P20 plastic die steel nitriding treatment:
    Nitrided surface tissue can be obtained with high hardness, surface hardness after nitriding reached 650-700HV (57-60HRC) die life can reach more than one million times, the nitride layer has a dense, smooth characteristics. Improve the mold release properties, P20 steel is improved in the moist air and alkali corrosion resistance.
(Nitriding treatment: refers to a certain temperature under nitrogen atoms penetrate certain media manipulation chemical heat treatment process of the workpiece surface.
After nitriding treatment products with excellent wear resistance, fatigue resistance, corrosion resistance and high temperature properties. Common liquid nitriding, gas nitriding, ion nitriding. Nitriding treatment, also known as diffusion nitriding. Gas nitriding by the Germans Fry in 1923 for the first time to research and development and industrialization. Nitrided article has excellent wear resistance, fatigue resistance, corrosion resistance and high temperature, gradually expanding its scope of application.)

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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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Introduction of structural steel 4130 steel

    The structural steel 4130 steel with high strength and toughness, high hardenability. In the oil, the critical quenching diameter 15 ~ 70mm. The structural steel 4130 steel hot strength is also good, at below 500 ℃ with a sufficiently high temperature strength, But the strength was significantly decreased at 550 ℃. When the lower limit of the content of alloying elements, the welding is quite good, but the content of alloying elements is close to the upper limit, the welding performance medium.  And the need to preheat to 175 ℃ above before welding. Good machinability of the 4130 steel, cold deformation plasticity medium. When the heat treatment, has a first temper brittleness in the range of 300 ~ 350 ℃, may form white spots.
    The structural steel 4130 steel is typically used in quenched and tempered condition. In medium-sized machinery manufacturing industry mainly for the manufacture of large cross-section, parts working under high stress conditions, such as shafts, spindles and steering wheel to withstand high loads, bolts, studs, and other gear. In the chemical industry for the manufacture of welded parts, welded structure consisting of plates and pipes. For the manufacture high-pressure pipe at containing nitrogen and hydrogen media work and the temperature does not exceed 250 ℃. Fasteners used in steam turbines, boilers manufactured manufacturing work below 450 ℃, below 500 ℃ under high pressure flange and flange cover.

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The performance of the 1.2738 mould steel

    The 1.2738 mould steel is manufactured in accordance with German DIN standard, with relatively superior mechanical properties in similar grades of steel, and good processability, mainly used for the production of hot work die processing, where the most common of plastic mold. In addition, special pre the steel hard treatment make it in the factory when has better hardness, can remove the mold production and processing in the heat treatment of links, improve economic benefits.
    The main performance of the 1.2738 mould steel: Material uniform hardness; excellent polishing performance; excellent machining performance; pre-hardened plastic mold steel; may be subjected to nitriding; suitable surface treatment, such as: plated Cr.
    The physical properties of the 1.2738 steel (Sample Hardness: 340HBW, at room temperature and high temperature conditions):
1) Temperature: 20℃ / 200℃ / 400℃, a density 7.8g/cm, 7.75g/cm, 7.7g/cm.
2) Temperature: 20 ~ 200℃ / 20 ~ 400℃, linear expansion coefficient 12.6×10K / 13.5×10K.
3) Temperature: 20℃ / 200℃ / 400℃, the thermal conductivity 29W·(m·K) / 29.5W·(m·K) / 31W·(m·K).
4) Temperature: 20℃ / 200℃ / 400℃, the elastic modulus 205000MPa / 200000MPa / 185000MPa.
    The mechanical properties of the 1.2738 mould steel (sample hardness 340HBW):
1) Temperature: 20℃ / 200℃ / 400℃, tensile strength 1100MPa / 1050MP8 / 850MPa.
2) Temperature: 20℃ / 200℃ / 400℃, conditions yield strength 980MPa / 925MPa / 770MPa.
3) Temperature: 20℃ / 200℃ / 400℃, section shrinkage rate 49% / 51% / 52%.
4) Temperature: 20℃ / 200℃ / 400℃, an elongation 13% / 14% / 16%.
5) Temperature: 20℃ / 200℃ / 400℃, impact toughness (≥) 20J/cm, 32J/cm, 42J/cm.

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