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Are you struggling to decide what steel alloy you should pick out of 4140 and 8620 for your project?
This confusion can result in reduced product quality as well as project delays if an unsuitable material is used. Therefore in this blogpost we will cover top 10 differences between 4140 and 8620 as well as their pros and cons so you can pick the best steel alloy for your particular needs.
What is 4140 Steel?
4140 steel is a low alloy steel which contains molybdenum and chromium. It provides high tensile strength and outstanding hardness. Moreover its good torsional and fatigue strength make it perfect for high stress applications. For example aerospace, manufacturing and automotive industries.
What is 8620 Steel?
8620 steel is basically a low carbon steel which is well known for its extraordinary core strength and toughness. This steel is broadly used in carburized applications like shafts, gears, bushings etc. Such components require ductile core and hard surface to assure durability under friction and high stress.
Top 10 Key Differences between 4140 vs 8620 Steel
1. Chemical Composition
4140 steel is a chromium-molybdenum alloy steel with balanced composition. It contains molybdenum (0.15-0.25%), manganese (0.75-1.00%), chromium (0.80-1.10%) and manganese (0.75-1.00%).
In contrast, 8620 steel is a nickel-chromium-molybdenum alloy. This alloy is composed of 0.4 to 0.7% nickel, 0.7 to 0.9 % manganese , 0.4 to 0.6% chromium and 0.15 to 0.25% molybdenum.
2. Carbon Content
4140 steel has relatively high carbon content ranging from 0.38% to 0.43%. This high carbon content increases its hardness as well as wear resistance and strength. Hence it is suitable for high stress applications that require outstanding mechanical properties.
In comparison 8620 steel has low carbon content which is in between 0.18 % -0.23%. Due to this low carbon level, it provides effective support in case hardening by creating hard surface & tough core.
3. Mechanical Properties
Tensile strength
4140 steel has higher tensile strength ranging from 690 to 1080 MPa whereas 8620 steel provides lower tensile strength ranging between 520-690 MPa.
Ductility
8620 steel shows higher ductility levels that range between 13 % to 31 %. Thus it is suitable for applications requiring flexibility of material without breaking.
4140, on the other hand, shows moderate ductility with values ranging from 11% to 26 %.
Impact resistance
8640 steel has low impact resistance and is used mostly in toughness focused operations. On the opposite, 4041 steel has greater impact resistance of 63J. So it is better for high stress applications.
4. Heat Treatment Procedures
4140 steel undergoes different treatments—annealing, quenching and tempering. Quenching process to increase its strength and tempering to decrease brittleness. This in turn makes it suitable for high-stress applications such as axles & bolts. Moreover its grain structure can be refined using normalizing to improve fatigue resistance and machinability.
8620 Steel, in contrast, depends primarily on carburizing. This particular process creates a hard surface along with maintaining a tough core inside. So as a result it works best for parts like shafts & gear where internal impact resistance and surface wear resistance are needed.
5. Hardness
4140 steel has greater Brinell hardness in range of 197 to 117 HB in its standard condition. But it is capable of reaching hardness level of 240 to 350 HB through heat treatment. In comparison, 8620 steel has lower Brinell hardness in its annealed state which is around 149 HB.
The hardness properties of both steels change a lot after heat treatment. 4140 steel has through hardening capability that helps it obtain greater hardness throughout its cross section. On the other side, 8620 steel achieves surface hardness through case hardening.
6. Machinability & Weldability
8620 steel has better machinability than 4140 steel. This is because of its soft core as well as low carbon content which make it easier to cut and shape in its annealed state. In contrast, 4140 steel is difficult to machine due to its higher hardness in hardened state. So special hard tools and low operating speed are required to machine 4140 steel.
8620 steel is easy to weld because of its low carbon content which decreases the risk of cracking during welding. In contrast, 4140 steel which has higher carbon content, requires preheating & post-weld stress relief to guarantee joint integrity and prevent cracking.
7. Corrosion Resistance
4140 steel contains molybdenum and chromium which form a protective oxide layer. This layer provides moderate corrosion resistance. But without surface treatments such as coating and plating, it is prone to rusting in harsh corrosive environments.
On the contrary, 8620 steel provides outstanding corrosion resistance due to high nickel and chromium content. In harsh conditions such as marine & industrial settings, these elements greatly improve its durability. Besides that 8620 steel resists aqueous and atmospheric corrosion well. This in turn makes it suitable for marine and outdoor applications.
8. Availability & Supply Chain
4140 steel is more easily available in the world than 8620 steel. Its widespread use in different industries such as automotive & aerospace guarantees strong supply chain globally. In contrast, 8620 steel is readily available too. But has relatively low market presence due to its specialized use in carburized components like shafts.
4140 steel has multiple distributors around the world. So it has well established supply chain. But its production time can increase due to heat treatment procedures. 8620 steel, on the other hand, has shorter lead times for standard shapes. But it needs additional processes like carburizing which might disrupt their distribution.
9. Cost Comparison
4140 steel has higher alloy content and additional processing requirements such as thorough hardening. So it is relatively more expensive than 8620 steel. Furthermore its outstanding wear resistance and strength provide reliable performance and longevity, thereby justifying its greater cost.
On the opposite, 8640 steel has lower initial cost which makes it perfect for low cost projects. Its lower carbon content as well as alloying elements decrease material cost. But their total production cost may increase due to additional processes like carburizing.
10. Applications
4140 steel is broadly used in industries that require great strength and wear resistance. In automobile industry, it is used to make different components due to its fatigue resistance & toughness. Such components are crankshaft suspension control arms, camshafts etc. In heavy machinery, it is used to make hydraulic machinery, torsion bars and shafts.
In contrast, 8620 steels are mostly used in applications where hard surfaces with tough cores are required. In automotive industry, it is commonly used to make pinions and gears. This material is used in industrial machinery to make parts such as bushings & sleeves that undergo rotating motion or sliding.
Pros & Cons of 4140 and 8620 Steel
Pros of 4140 Steel
- 4140 steel has impressive fatigue strength which helps it withstand cyclic loading without failure. Hence this steel is perfect for components like axles as well as crankshafts that undergo repeated stress.
- 4140 Steel shows outstanding resistance against twisting forces. Its chromium molybdenum composition creates microstructure. This structure not only resists deformation from rotational stress but assures reliability in power transmission applications too.
- 4140 Steel can be recycled repeatedly without losing its mechanical properties. This property lowers material cost as well as environmental impact and supports sustainable manufacturing practices.
Cons of 4140 Steel
- 4140 Steel does not have inherent corrosion resistance which is why it rusts in salt water or humid environments despite having molybdenum and chromium content.
- 4140 steel generates high tool wear as it has great strength & hardness. Therefore during its machining cutting tools need to be changed several times particularly at high speeds.
Pros of 8620 Steel
- 8620 steel has outstanding machinability which decreases tool wear and production time during manufacturing process. Moreover its low carbon content permits complicated components to be manufactured with better surface finishes & tight tolerances.
- 8620 steel has high chromium content that provides great oxidation resistance at temperatures up to 650°F. This chromium forms protective oxide layer on the surface that prevents underlying metal from degradation.
- 8620 steel gives extraordinary durability in demanding applications because it has distinct case hardened structure. Its tough core and hard surface layer provide protection against fatigue failure and resistance to wear respectively.
Cons of 8620 Steel
- 8620 Steel needs carburizing process in order to obtain good fatigue resistance. It performs very poorly under cyclic loading in its annealed state which makes proper heat treatment important.
- After carburizing 8620 steel becomes challenging to machine. Its hard surface limits secondary machining which then requires special techniques and tools. This increases manufacturing complexity as well as production costs.
4140 vs 8620 Steel – Which One You Should Choose?
The right option depends on your particular application needs. If you want better fatigue resistance, tensile strength and uniform hardness for high stress components such as crankshafts and axles, then 4140 steel is best.
8620 steel is perfect for use cases if you need case hardened parts with tough core & wear resistant surface. For example in camshafts and gears.
8620 steel provides good welding and machinability capability whereas 4140 gives better impact resistance and strength.
To Sum Up
In short both 8620 and 4140 have their own valuable qualities in different applications. 4140 steel is good in high stress conditions whereas 8620 steel has outstanding case hardening attributes. But the final choice depends on processing capabilities and special project needs.
If you need CNC machining services for either of these alloys – 4140 or 8620-, then RICHCONN is best option. You can contact us anytime.
Related Question
Can 8620 steel be nitrided to improve surface hardness?
Yes you can nitride it in order to improve surface hardness. 8620 steel responds well to nitriding and obtains surface hardness of 60 RC when it is suitably hardened and tempered (uncarburized).
Can 8620 Steel vs 4140 Steel be used in low-temperature environments?
Yes both can be used in low temperature environments. But the ductility of 8620 steel is greater compared to 4140. Thus it is slightly more suitable for applications where toughness is needed at lower temperatures.
What surface treatments are commonly applied to 8620 steel?
Some common surface treatments are normalizing, carburizing, hardening, tempering, nitriding etc. These treatments improve surface hardness and resistance to wear.
Can 4140 steel be used for manufacturing cutting tools?
Yes 4140 steel is perfect for making cutting tools such as milling cutters, saw blades and lathe tools.
Is stress relieving necessary after machining 4140 steel?
Yes stress relieving is necessary to avoid distortion, warpage and cracking. Stress relieving removes residual stress which occurs from manufacturing process.
