Two carbon steels separated by about 0.10% carbon: 45C8 at roughly 0.45% and 55C8 at roughly 0.55%. That difference shifts the balance between toughness and hardness, and decides which parts each grade suits.
45C8 carries about 0.45% carbon; 55C8 carries about 0.55%. The higher carbon makes 55C8 harder and more wear-resistant, and it can be heat-treated to a spring temper — at the cost of ductility and weldability. 45C8 is the better all-round shaft and machine-part steel, tougher and easier to machine. Pick 55C8 for springs, washers, wear surfaces and parts that need high hardness; pick 45C8 for general shafts, axles, gears and components that must balance strength with toughness.
| Property | 45C8 | 55C8 |
|---|---|---|
| Type | Medium-carbon (~0.45% C) | Higher-carbon (~0.55% C) |
| Carbon (C) | 0.40–0.50% | 0.50–0.60% |
| Manganese (Mn) | 0.60–0.90% | 0.60–0.90% |
| Silicon (Si) | 0.10–0.35% | 0.10–0.35% |
| Sulphur (S) | 0.050% max | 0.050% max |
| Phosphorus (P) | 0.050% max | 0.050% max |
| Tensile (normalised) | 620–720 MPa | 660–800 MPa |
| Yield (normalised) | 340–460 MPa | 370–520 MPa |
| Elongation | 15–20% | 12–16% |
| Hardness (normalised) | 180–230 HB | 200–250 HB |
| Max hardness after hardening | High | Higher — more carbon |
| Ductility & toughness | Higher — more forgiving | Lower — more brittle |
| Spring temper | Not typical | Yes — used for springs and washers |
| Weldability | Fair — preheat needed | Poor — preheat and post-weld treatment essential |
| Equivalents | 1045, C45 (1.0503), S45C, 080M46 | 1055, C55 (1.0535), S55C, 070M55 |
| Typical applications | Shafts, axles, spindles, gears, forgings | Springs, washers, wear plates, hand tools |
Both grades are supplied with a heat-wise mill test certificate stating the actual chemistry and properties for the heat you receive.
45C8 is the easier of the two to machine and fabricate. The higher carbon of 55C8 makes it harder in the as-rolled state, so it is more abrasive on tooling and less forgiving when bent or formed cold. Both cut best in the normalised or annealed condition, and bright cold-drawn or polished bar gives a cleaner finish and tighter tolerance than hot-rolled black bar. For 55C8, annealing before heavy machining is worth the extra step on harder heats.
Neither grade is a free-cutting steel; where chip control and turning speed matter most, a sulphurised grade such as EN1A machines faster. Choose 45C8 or 55C8 when the finished part needs the strength, hardness or spring temper that a free-cutting steel cannot provide.
Both grades through-harden, but 55C8 reaches a higher hardness because it carries more carbon. 45C8 normalises at 850–880 °C and is quenched from the same range and tempered at 550–660 °C for general machine parts. 55C8 is hardened and tempered to a higher hardness for wear surfaces, and to a spring temper for flat springs and washers, where a lower tempering temperature retains more strength and elasticity.
Hardenability is limited in both because they are plain-carbon steels, so hardness is deepest in small sections and falls in larger bar. 55C8's higher carbon also makes it more crack-sensitive on quenching, so oil or a milder medium is preferred and intricate shapes need care. Temper immediately after quenching. For a hard, uniform core in a large or heavily stressed part, an alloy grade such as EN19 is the better route than either carbon grade.
Ambhe Ferro rolls and finishes carbon steels including both grades as rounds (23.5–80 mm diameter), bright bars (21–63.5 mm), hexagons (23.5–52.5 mm across flats) and RCS (55, 63 and 75 mm). Standard length is 5–6 m, with custom cut lengths to order. Supply conditions cover hot rolled, annealed, normalised and bright (cold drawn or polished).
The minimum order quantity is 5 MT per size, and non-standard sizes are often available make-to-order against tonnage. Whichever grade the drawing calls for, every dispatch carries a heat-wise mill test certificate confirming the chemistry and mechanical properties of that heat, with third-party inspection on request.
Both grades are available from Indian re-rollers and priced similarly; form, size, finish and tonnage move the price more than the grade choice. They are not interchangeable, though: 45C8 will not reach the hardness 55C8 gives a spring or wear part, and 55C8 is too brittle to replace 45C8 in a shaft that sees impact. State the exact grade on the purchase order and confirm it against the mill test certificate before machining or heat treatment.
Ambhe Ferro is an engineering-steel manufacturer with two factories in MIDC Murbad, near Kalyan — about 80 km from Mumbai Port and JNPT. We roll and finish 45C8 and 55C8 steel at our units and dispatch quickly across the Mumbai–Pune–Nashik corridor and pan-India. Regular dispatches go to buyers in Mumbai, Navi Mumbai, Thane, Vasai–Virar, Pune, Pimpri-Chinchwad, Chakan, Nashik, Ahmednagar, Aurangabad, Kolhapur, Nagpur, Rajkot, Ahmedabad and Bengaluru; exports are arranged on request. Order as hot-rolled rounds, bright bars, hexagons or RCS against your size and tonnage, with a heat-wise mill test certificate on every dispatch.
MOQ is 5 MT per size. Send the grade, form, size and tonnage and we will respond with pricing, availability and lead time.
Tell us the grade, form, size, and tonnage. Ambhe Ferro responds with pricing, availability, and lead time — and a mill test certificate on every heat.
