Heat treatment standard of 4140 forged steel

    One, the steps and conditions in the heat treatment of 4140 forged steel:
A, normalizing:
Normalizing temperature at 858 °C ~ 912 °C, and maintain the temperature within the specified time. Cooling in air.
B, quenching:
1, temperature Requirements: heated to 816 °C ~ 871 °C, and maintain the temperature within the specified time.
2, the cooling medium requirements: generally uses oil cooling.
C, tempering:
Tempering temperature is not lower than 552 °C, and maintain the temperature within the specified time. The holding time according to the following method to calculate.
1. If the material size less than 2 inches: heat preservation time is not lower than 60 minutes.
2. The material of size greater than two inches: at least 30 minutes per inch (or at least 12 minutes per centimeter) to calculate the holding time. (Material size according to the maximum cross-sectional dimension calculation)
To record the detailed process of heat treatment of 4140 steel (including heating time, heating rate, graphs and charts, furnace type, heat preservation time, cooling mode and other related information), and written the heat treatment report, furnace No. of heat treatment should also be recorded in the material identification certificate.
    Two, ultrasonic testing:
After heat treatment of 4140 forged steel, the removal of the epidermis by mechanical processing way, and then subjected to ultrasonic testing, ultrasonic testing surface roughness of the surface is not more than Ra6.3. Ultrasonic testing equipment, personnel and detection methods, refer to ASTM SA 388-2004 edition, a single defect is less than Φ3.2mm, multiple defects is less than Φ1.6mm. Defects allowed in a non-machined surface, machined surfaces must not have any flaws.
    Three, hardness test:
1, the hardness testing methods and requirements in accordance with ASTM E10 and ASTM E18 requirements.
2, hardness test results must be recorded in the test report, and noted in the material identification certificate.

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The structure and properties of 1.2379 die steel

     1, The characteristics of 1.2379 die steel
     1.2379 steel by conventional smelting, organizational structure is precision, is cold work tool steel, high wear resistance, good stability, good hardenability and hardness, good compressive strength and good toughness.
     2, Typical chemical composition (mass fraction,%)
     C1.50 ~ 1.60, Cr11.00 ~ 12.00, Mn0.15 ~ 0.45, Si0.20 ~ 0.60, P≤0.030, S≤0.030, Mo0.70 ~ 0.90, V0.90 ~ 1.10.
     3, Refer to the corresponding steel No.
     China GB standard steel No. Cr12Mo1V1, American AISI / ASTM standard steel No. D2, Japan JIS standard steel No. SKD11, German DIN standard steel No. X155CrVMo121, German DIN standard material number 1.2379 steel.
     4, The physical Properties of 1.2379 die steel
     Temperature 20 ~ 100 °C / 20 ~ 200 °C / 20 ~ 300 °C / 20 ~ 400 °C / 20 ~ 500 °C, coefficient of linear expansion 10.5 × 10-6K-1 / 11.0 × 10-6K-1 / 11.0 × 10- 6K-1 / 11.5 × 10-6K-112.0 × 10-6K-1.
     5, Temperature 20 °C / 350 °C / 700 ℃, thermal conductivity 16.7 [W / (mK)] / 20.5 [W / (mK)] / 4.2 [W / (mK)].
Quenching, tempering specification
The quenching temperature 980 ~ 1000 °C, gas cooling / oil cooling / 500 °C nitrate cooling.
The quenching temperature 1020 ~ 1040 °C, gas cooling / oil cooling / 500 °C nitrate cooling.
The quenching temperature 1060 ~ 1080 °C, gas cooling / oil cooling / 500 °C nitrate cooling.
Tempering temperature 180 ~ 300 °C / 500 ~ 570 °C, tempering time 1h / 20mm, at least 2 hours, still air cooling.
Typical application: suitable for making mold, extrusion mold stamping die.

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The casting properties of mould steel 1.2344

     Since the mould steel 1.2344 is a kind of multi element composite medium carbon alloy steel, it's contains more alloy elements Mo、V、Cr, make the solidification temperature of liquid alloy decreased, resulting in the crystallization temperature range increases, the casting performance is poorer. The following two tables are the mobility and linear shrinkage of 1.2344 steel. Tests showed, 1.2344 steel pouring temperature control in 1 530 ~ 1 630 ℃ is appropriate, its linear shrinkage be similar to ordinary carbon steel. By the electroslag remelting process can decrease the solidification temperature interval, improve the inner quality of 1.2344 mould steel, improve the toughness of casting mould.

Mobility
Casting type	Pouring temperature/°C	Overheating temperature/°C	Helix length/mm
Sand mold	1530	70	260
Sand mold	1588	128	350
Sand mold	1670	210	475
Sand mold	1700	240	760

Linear shrinkage(%)
Projeck	Parameter
Free shrinkage	1.68
Blocked shrinkage	1.29

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Can 40Cr replace the P20 mould steel

     P20 steel is a kind of plastic mold steel. P20 steel is mainly used in plastic mold and die casting mold material of low melting point metal. The purity of P20 mould steel is high, with good machinability and mirror grinding performance, made of high precision mold, never deformation, high tenacity.
     40Cr is a commonly used alloy structural steel, the tensile strength, yield strength and hardenability is higher than 1040 steel, but its welding is limited, may crack formation.  It can be made of quenched and tempered parts. After surface quenching, 40Cr can be made a part of load and wear resistance are high and impact force is small, such as gears, sleeves, shafts, crankshafts, etc..
     40Cr also belongs to the nitrided steel, it contains beneficial elements to nitriding. After nitrogen treatment, surface hardness of 40Cr is high, the highest reached 72 ~ 78HRA (43 ~ 55HRC).
     If the P20 mould steel nitriding treatment, its surface microstructure is high hardness. After nitriding surface hardness reaches 650-700HV (57-60HRC), the service life of the die can reach more than one million times, the characteristics of the nitride layer has dense structure, smooth, mold release properties and the anti wet air and salty liquid corrosion performance can be improved.
     Previously, most of the APG die is used 40Cr, and then gradually being replaced by P20 steel. From the processing performance for P20 steel processing performance is better than the 40Cr. From the service life of the die, the frequency of use of P20 steel is 5~10 million times, and the frequency of use of 40Cr is 50000 times.

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The important elements of 4130 alloy structural steel

     4130 alloy structural steel is a low alloy heat-resistant steel, with good mechanical properties and resistance to hydrogen at room temperature and high temperature. The main alloy elements in steel are molybdenum, chromium, vanadium, silicon, boron ect.
     Alloying element molybdenum is very important in 4130 steel , it greatly improve the thermo strength of the steel, maintaining sufficient strength at high temperature, and can refine the grain and prevent overheating tendencies of 4130 steel.
     However, if only containing molybdenum in steel, the carbon will gather into the graphite and precipitation in the long-term high temperature, the performance deterioration. In order to eliminate this kind of tendency, often while adding chromium in 4130 alloy structural steel.
     Chromium can enhance thermo strength, high temperature oxidation resistance and corrosion resistance of 4130 steel. Because the chromium can be formed oxide film of dense and strong adhesion on the surface of the steel, preventing the internal metal continued to be oxidation or corrosion. In steel the chromium content is higher, then oxide film more dense , antioxidant and corrosion resistance is better.

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How to prevent cracking of 1.2738 plastic mould steel

    In order to prevent excessive stress cracking of caused by the mold, should be performed 150 ~ 200 ℃ tempering. After the flame hardening, surface hardness can reach 45 ~ 50HRC. Note that, before the flame hardening treatment, 150 ~ 200 ℃ preheating of mould to prevent cracking of the mould.
    1.2738 plastic mould steel is the German DIN standard, vacuum degassing and ESR, steel pure quality, the thickness ≥500mm, its hardness is still evenly; sulfur and gas content is very low (S≤0.005%), mirror-polished performance is excellent, etch and EDM processing performance is good; the pre hardened state supply, do not need to reheat treatment can be directly processing; has excellent processing performance, easy cutting and polishing, stress relief annealing and surface nitriding treatment, size and hardness change little.
    You can use oxygen-acetylene flame heating method perform local hardening for 1.2738 plastic mould steel. The need to hardened parts, heating to light red (850 ~ 950 ℃), and then cooled in the air.
    1.2738 steel surface nitriding can improve the hardness of the surface organization. Nitriding surface is smooth and compact. It has good corrosion resistance. Conducive to product demould and improve production efficiency.

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