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 AISI D2 tool steel

     The wear resistance of AISI D2 tool steel is high, small deformation, the carbon content as high as 1.5%, chromium content up to 11.5%. After heat treatment, the hardness of D2 steel is up to 60HRC, but its ductility, toughness, resistance to rust ability are relatively weak, steel surface to mirror polished is not easy.
     Along with the cold stamping products to the development of high precision and high efficiency, multi species, requirement of die steel has good abrasion resistance and toughness. Compared with Cr12MoV steel, the D2 steel has increased by Mo and V in chemical composition, changing the cast structure of steel, improve the morphology of ledeburite, its strength and toughness and wear resistance is better than that of Cr12MoV steel, improve the service life of mould.
     The yield point and plastic deformation resistance of AISI D2 tool steel is higher than Cr12MoV steel, so the forging properties and thermal plastic forming is slightly worse than Cr12MoV. Cr12MolV, American D2, Japan SKD11, three although the same chemical composition, but the performance difference is very big. After heat treatment, Cr12MolV color slightly orange red, deformation is very large, prone to fatigue fracture at actual use; D2 steel is cold white color, hardness higher than SKD11, the toughness is lower than SKD11, high stress is easy to appear the tiny gap; SKD11 bright luster and the best overall performance.

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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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The characteristics of alloy structure steel 4340

     Alloy structure steel 4340 has high strength, high toughness and good hardenability. When hardened reaches half martensite hardness (HRC45), water quenching critical quenching diameter for Φ ≥100mm, critical quenching oil quenching diameter for Φ ≥75mm; when hardened to 90% martensite, water quenched critical diameter for Φ 80 ~ 90mm, oil quenched critical diameter for Φ 55 ~ 66mm. AISI 4340 alloy steel has anti-overheating and stability, but the white spot high sensitivity, temper brittleness, poor welding, high temperature preheating before welding, eliminate stress after welding.
     The main purpose of alloy structure steel 4340: manufacture of turbine gears, gear ring, the whole forging rotor. Engine connecting rods, valve. High strength, high toughness, a greater cross-sectional size forgings such as forged part of wind generator, drive eccentric shaft of horizontal type forging machine, crankshaft of forging machine etc.. Automobile, airplane special wear-resistant parts etc..

 


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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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