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1055 C55 S55C Carbon Steel

S55C tool steel boasts elevated strength, excellent wear resistance and reliable hardening response, perfectly suited for heavy-duty gears, high-wear mold plates and precision machine spindles.

Standard: AISI 1055, DIN C55, JIS S55C, GB 55#
Technique: EAF + LF + VD, forged or hot-rolled, multi-directional forging ratio ≥4, normalized or annealed as required
Shape: Round, Flat, Plates, Blocks
Heat treatment: Supplied in normalized condition, hardness ≤241 HBW typical; quenched and tempered (QT) to 26–34 HRC available on request
Surface Treatment: Turned, milled / ground, sawn ends. Black (hot-rolled / forged surface) available for large sections
Tolerance: flat bars & plates thickness: +0.5/-0.0 mm (turned); forged blocks: ±0.2 mm
MOQ: 1 Ton

We supply AISI 1055 in various custom sizes

Chemical Composition (%)

Grade	C	Si	Mn	P (≤)	S (≤)	Cr (≤)	Ni (≤)	Cu (≤)	Mo (≤)
1055	0.50–0.60	0.15–0.35	0.60–0.90	0.040	0.050	0.20	0.20	0.35	0.06
C55	0.52–0.60	≤0.40	0.60–0.90	0.045	0.045	0.40	0.40	0.30	0.10
S55C	0.52–0.58	0.15–0.35	0.60–0.90	0.030	0.030	0.20	0.20	0.30	—
55#	0.52–0.60	0.17–0.37	0.50–0.80	0.030	0.030	0.25	0.25	0.25	—

Main characteristics of S55C tool steel

Elevated strength & surface hardness – stronger load-bearing capacity than lower carbon steel grades
Excellent wear resistance – withstands prolonged friction and reduces abrasion under cyclic operation
Reliable hardening response – delivers uniform hardness via standard heat treatment
High cost efficiency – a practical medium-high carbon option for heavy-duty structural and die parts

1055 | C55 | S55C tool steel applications

S55C steel for Heavy-Duty Gear & Spline Shaft

High surface hardness after induction hardening and good core toughness provide reliable fatigue resistance and wear life in heavy-duty power transmission.

S55C steel for High-Wear Mold Plate & Bolster

Higher carbon content than S50C gives S55C enhanced wear resistance, making it ideal for mold clamping plates and bolsters under high contact stress.

S55C steel for Precision Machine Spindle & Mandrel

Good dimensional stability and balanced strength after QT enable S55C to maintain machining accuracy in precision spindles and mandrels.

Our Production Technology For S55C (AISI 1055 / DIN C55) Medium Carbon Structural Steel

EAF
LF
VD
Fully Killed Steel
Hot Rolled or Hot Extruded
Forged (as required)
Annealed / Normalized / Quenched and Tempered (as specified)
Black surface or Machined surface / Peeled

mechanical properties & heat treatment of S55C steel

Heat temperature	Start forging temperature	Finish forging temperature	Cooling method
1100 – 1150 °C	1100 – 1050 °C	≥ 850 °C	Pit, sand, or furnace cooling

Annealing

Annealing temperature: 650 – 700°C
Hold at temperature for sufficient time (minimum 1 hour per 25mm of section thickness)
Cool slowly in the furnace
Hardness after annealing: max. 229 HB
Annealing in a protective atmosphere is recommended to reduce decarburization and surface scaling

Hardening

S55C is a medium carbon steel with poor hardenability. Quenching can cause deformation and cracking, making heat treatment control critical. Quenching is typically performed in water for maximum hardness
Pre-heating (recommended): Preheat to 600 – 650°C to reduce thermal shock during austenitizing
Austenitizing temperature: 805 – 845°C
Holding time: At least 30 minutes per 25mm of section thickness
Quenching media:
Water (preferred) — provides maximum hardness but increases distortion and crack risk
Oil — for reduced distortion, but lower hardness
Hardness after quenching (before tempering) : 56 – 63 HRC (water quenched)

Stress relieving

Perform after rough machining, heavy stock removal, or welding to reduce residual stresses
Heat carefully to 600 – 650°C (below the tempering temperature)
Hold at temperature for 1 hour per 25mm of section thickness (minimum 2 hours)
Air cool after holding
This operation reduces the risk of distortion during final heat treatment and improves dimensional stability

Tempering

Temper immediately after quenching when the workpiece cools to hand-warm temperature (approx. 50–70°C). Delayed tempering may cause cracking
Number of tempers: Minimum 1 time for standard applications; 2 times recommended for critical components
Holding time: 1 hour per 25mm of section thickness (minimum 2 hours)
Cooling method: Rapid cooling (out-of-furnace quenching) is required after tempering to avoid temper brittleness
Tempering temperature range: 550 – 660°C

Normalizing

Normalizing temperature: 825 – 865°C
Hold at temperature until uniformly heated (approx. 30 minutes per 25mm of section thickness)
Cool in still ai
Hardness after normalizing: 143 – 235 HB
Purpose: Refine grain structure, produce a more uniform ferrite-pearlite distribution, eliminate forging stresses, and prepare for final heat treatment

Why Choose NSPM as Your S55C Tool Steel Supplier

Source Direct

Direct mill cooperation ensures stable supply, competitive pricing, and consistent quality. Global resource integration and strong supply chain management guarantee reliable material sourcing and long-term availability.

Stock Ready

50,000+ tons inventory across 11 warehouses enables fast delivery. Flexible cutting, short lead times, and ready stock support urgent demands and improve customers’ production efficiency.

Expert Team

600+ professionals, including R&D specialists and technical engineers, provide application-driven support. Fast response and deep tooling knowledge ensure accurate solutions for diverse industrial needs.

Fully Inspected

Strict quality control system with full traceability, UT testing, and heat treatment records. Certified standards (ISO, CE) ensure every material meets high-performance and reliability requirements.

Full-Chain Machining

From steel supply to precision machining, heat treatment, and equipment manufacturing, NSPM offers integrated solutions that enhance accuracy, efficiency, and overall tooling performance.