Medium Carbon Steel


  • EN8
  • EN8D
  • EN43B
  • C40
  • C45
  • CK45
  • 40C8
  • 45C8
  • S40C

EN8 (080M40)

EN8 is an unalloyed medium carbon steel which is used in applications where better properties than mild steel are required but where the costs do not justify the purchase of a steel alloy. EN8 can be heat treated to provide a good surface hardness and moderate wear resistance by flame or induction hardening processes. From the automotive trade to wider general engineering applications, EN8 is popular steel in industry.

Key Features:

EN8 Engineering Steel is an unalloyed carbon steel with reasonable tensile strength. It can be Flame or induction hardened and is a readily Machine able material. When heat treated, EN8 offers moderate wear resistance.

Typical Applications:

Automotive parts

Connecting rods

Studs, bolts

Axles, spindles

General engineering components.


EN8/EN8D is a very popular grade of through-hardening medium carbon steel, which is readily Machine able in any condition. EN8/EN8D is suitable for the manufacture of parts such as general-purpose axles and shafts, gears, bolts and studs.  It can be further surface-hardened typically to 50-55 HRC by induction processes, producing components with enhanced wear resistance. For such applications the use of EN8D is advisable. It is also available in a free-machining version, EN8M.It is therefore recommended that larger sizes of EN8/EN8D are supplied in the untreated condition, and that any heat treatment is carried out after initial stock removal.  This should achieve better mechanical properties towards the core.







Crane wheels,

Nuts, and Machine,


Textile Machinery parts.


General purpose medium carbon steel delivered in as rolled condition. It can be further heat treated to achieve specific mechanical properties. The 0.45% carbon content is not favourable for welding. However, it can be weld with appropriate pre and post weld heat treatment. Surface hardness of 57~62 HRC can be achieved with cast hardening to a depth of approximately 1mm. Used for most transmission and motor parts of medium strength. Case hardened parts such as camshafts, gears, rocking levers etc. Simple hand tools and various types of fasteners and fixtures, machinery parts and components with medium stress.

Hot work and heat treatment temperatures

Forging 1100~850*

Normalization 840~880

Subcritical annealing   650~700*

Isothermal annealing 820~860   600x1h*

Hardening    820~860 water

Tempering    550~660.


40c8 actually gives you the carbon and manganese value in the steel. This designation is mostly Used for plain carbon steels. Even though they are plain carbon they do contain some amount of Manganese to improve the harden ability of these steels. 40/100 = 0.4% this stands for carbon 8/10 = 0.8% manganese.

Heat treatment is process of heating and cooling of material. It is possible to obtain the desirable mechanical properties for steel or alloys by heat treatment. In heat Treatment temperature variation with time is basic parameter to alter mechanical property of the Component. If this variation is proper so that phase transformation is according to part Application requirement, because the basic requirement of mechanical properties is different for Different environment. In this paper a grade of steel 45C8 has been taken for experiment Purpose in highly stressed application and number of heat treatment processes has been Carried out which impart the optimum value of mechanical properties. In these heat treatment Processes a variation is made over temperature and time and optimum value has been Selected. The most important heat treatments are Stress relieving, Annealing, Normalising.


S40C steel is carbon (non-alloy) steel formulated for primary forming into wrought products. 1040 is the designation in both the SAE and AISI systems for this material. G10400 is the UNS number. The properties of SAE-AISI 1040 steel include two common variations. This page shows summary ranges across both of them. For more specific values, follow the links immediately below. The graph bars on the material properties cards further below compare SAE-AISI 1040 steel to: wrought carbon or non-alloy steels (top), all iron alloys (middle), and the entire database (bottom). A full bar means this is the highest value in the relevant set. A half-full bar means it’s 50% of the highest, and so on.


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