Carbon Steel Grades: Complete Comparison of Low, Medium & High Carbon Steels
AISI/SAE, ASTM A36/A572/A516, EN 10025 · Published: 2026-07-25 · Updated: August 2026
Carbon steel grades are classified by carbon content into three categories: low carbon (mild steel, 0.04-0.30% C), medium carbon (0.30-0.60% C), and high carbon (0.60-1.50% C). Higher carbon increases strength and hardness but reduces ductility,...
Carbon steel grades are classified by carbon content into three categories: low carbon (mild steel, 0.04-0.30% C), medium carbon (0.30-0.60% C), and high carbon (0.60-1.50% C). Higher carbon increases strength and hardness but reduces ductility, weldability, and machinability. Low carbon steels are the workhorse of structural and general fabrication: a36-steel/">ASTM A36 (250 MPa yield) for buildings and bridges, a572-steel/">A572 Gr 50 (345 MPa) for high-strength structural, s355-steel/">S355 (355 MPa) for European construction, AISI 1018 (machining and shafting), and steel pipe grades like ASTM A53 and API 5L X52. Low carbon steels are readily weldable, formable, and low-cost—accounting for ~90% of all steel produced. Medium carbon steels (AISI 1035, 1040, aisi-1045/">1045, c45-carbon-steel/">C45) contain 0.30-0.60% carbon and respond to quenching and tempering, achieving yield strengths of 400-700 MPa after heat treatment. Used for shafts, gears, axles, couplings, and machinery components requiring wear resistance. Medium carbon steels require preheat for welding and are more challenging to form than low carbon. High carbon steels (AISI 1060, 1070, 1080, 1095) contain 0.60-1.50% carbon and achieve the highest strength and hardness (up to 65 HRC) of any unalloyed steel. Used for springs (music wire, valve springs), cutting tools, knives, chisels, and high-strength wire. High carbon steels have poor weldability, limited ductility, and require careful heat treatment. Carbon steel castings (ASTM A216 WCB, WCC) are used for valve bodies and pump casings. Pressure vessel grades include a516-gr70/">A516 Gr 70 and p355gh/">P355GH for boilers and pressure vessels. For a complete cross-grade comparison with stainless and alloy steels, see our Steel Grade Comparison Guide.
Quick Facts
| Category | Carbon Steel |
| Standard | AISI/SAE, ASTM A36/A572/A516, EN 10025 |
| Density | 7.85 g/cm³ |
| Yield Strength | 170-1000 MPa (grade- and condition-dependent) |
| Tensile Strength | 320-2000 MPa (grade- and condition-dependent) |
Detailed Mechanical Properties
| Yield Strength Range | 170 MPa (low C, annealed) - 1000+ MPa (high C, hardened) |
| Elongation Range | 5% (high C hardened) - 25% (low C annealed) |
| Hardness Range | 120 HB (low C) - 65 HRC (high C hardened) |
Physical Properties
| Density Range | 7.85 g/cm³ (all carbon steels) |
| Thermal Conductivity | 50-52 W/m·K at 20°C |
| Electrical Resistivity | 0.0000168-0.0000200 Ω·cm |
| Specific Heat | 486 J/kg·K |
Global Equivalents & Cross-Reference
| Alternative Standard / Grade | Action |
|---|---|
| AISI 1018 | Compare |
| AISI 1045 | Compare |
| AISI 1095 | Compare |
| ASTM A36 | Compare |
| A572 Gr 50 | Compare |
| S355 | Compare |
| C45 | Compare |
Heat Treatment & Processing
| Note | Low carbon steels cannot be hardened by heat treatment (strength by cold work only). Medium carbon steels respond to quench-and-temper (400-700 MPa yield). High carbon steels harden to 60-65 HRC by quenching. Carburizing (case hardening) adds carbon to surface of low-carbon steel for wear resistance. |
Welding & Fabrication
| Note | Low carbon steels (A36, 1018) have excellent weldability with no preheat for thin sections. Medium carbon steels (1045) require preheat 50-200°C. High carbon steels (1095) require 150-300°C preheat, low-hydrogen electrodes, and post-weld stress relief. Carbon equivalent >0.45 requires increasing preheat per AWS D1.1. |
Related Materials
🧮 Material Weight Calculator
Calculate the weight based on this material's density: 7.85 g/cm³
Frequently Asked Questions
What is the most common carbon steel grade?
ASTM A36 (250 MPa / 36 ksi yield) is the most common carbon steel grade in North America, used as the default structural steel for buildings, bridges, and general fabrication. AISI 1018 is the most common low-carbon grade for machining and shafting. Globally, S235JR and S275JR (European) and Q235B (Chinese) are the equivalent default structural grades.
What is the difference between low, medium, and high carbon steel?
Carbon content. Low carbon (mild) steel: 0.04-0.30% C—ductile, weldable, low strength, used for structures and sheet. Medium carbon: 0.30-0.60% C—heat-treatable, used for shafts and machinery. High carbon: 0.60-1.50% C—very hard, used for springs, tools, and knives. Higher carbon = more strength and hardness but less ductility and weldability.
What is the difference between A36 and A572 carbon steel?
A36 has 250 MPa (36 ksi) minimum yield; A572 Grade 50 has 345 MPa (50 ksi)—38% stronger. A572 achieves higher strength through micro-alloying (Nb, V) while keeping carbon low, preserving weldability. A572 Gr 50 is increasingly the default for new construction; A36 remains common for repair and simple structures. See <a href="/materials/a36-steel/">A36 steel</a> and <a href="/materials/a572-steel/">A572 steel</a> for full properties.
Can high carbon steel be welded?
High carbon steels (0.60%+ C) have poor weldability and require careful preheat (150-300°C), low-hydrogen electrodes, slow cooling, and post-weld stress relief to avoid cracking. For welded structural applications, use low- or medium-carbon grades. If high hardness is required in a weldment, consider an alloy steel (4140, 4340) with proper heat treatment instead.
What is the strongest carbon steel grade?
High-carbon spring steels like AISI 1095 achieve tensile strengths over 2000 MPa (290 ksi) in the quenched-and-tempered condition, comparable to some alloy steels. However, this comes with very low ductility (5-10% elongation) and poor weldability. For structural strength with ductility and weldability, medium-carbon AISI 1045 (700 MPa quenched) or A572 Gr 65 (450 MPa yield) are practical upper limits.
References & International Standards
- ASTM International. Standard Specifications for Steel & Metal Alloys. astm.org
- International Organization for Standardization (ISO). Metallic Materials — Cross-Reference Database. iso.org
- American Iron and Steel Institute (AISI). Steel Grade Designations & Equivalents. steel.org
- European Committee for Standardization (CEN). EN Steel Standards & Numbering System. cencenelec.eu
Structural & Carbon Steel — Engineering Reference
Structural steels are the backbone of construction and heavy industry. Grades in this category are specified primarily by their yield strength, tensile strength, and weldability — the three properties that determine whether a building stands or a bridge holds.
ASTM A36/A572/A516, EN 10025, JIS G3101/G3106, GB/T 700/1591
Building frames, bridges, pressure vessels, shipbuilding, offshore platforms, pipelines
When selecting a structural grade, match the required yield strength to the design load, but also verify Charpy impact values if the structure will operate below freezing — many structural steels undergo a ductile-to-brittle transition at low temperatures.