What is Mild Steel?
Mild steel, also known as carbon steel, is the most common type of steel. In ASTM standards, “mild steel” typically refers to low carbon steel, which usually has a carbon content ranging from 0.05% to 0.25%.
- Carbon Content: Mild steel has a carbon content typically between 0.05% and 0.25%, which gives it good plasticity and weldability.
- Iron (Fe): Iron is the main component of mild steel, usually comprising over 99% of the material.
- Manganese (Mn): Usually present in the range of 0.30% to 0.60%, manganese enhances the steel’s strength, hardness, and weldability.
- Silicon (Si): Present in small amounts, silicon increases the steel’s elasticity and resistance to oxidation.
- Phosphorus (P) and Sulfur (S): The phosphorus and sulfur content in mild steel is typically low, as these elements can reduce the material’s plasticity and toughness.
Mild steel is widely used due to its excellent machinability, weldability, and relatively low cost. Although it has poor corrosion resistance, its service life can be improved with coatings or corrosion protection measures. Its good ductility and formability make it popular in structural components, machinery, and everyday products.
Common Mild Steel Flange
Common mild steel flange materials include ASTM A105 FLANGE and ASTM A350 LF2 FLANGE:
ASTM A105 – Carbon Steel Flange
Application: Used for normal temperature and pressure pipeline connections, widely used in the oil, chemical, and other industries.
Mild steel grade: A105 is a typical low carbon steel, commonly used for flanges, fittings, and valves in normal temperature and pressure conditions, with a maximum carbon content of approximately 0.35%, falling under the mild steel category.
ASTM A350 – Low Temperature Pressure Pipeline Carbon Steel Flange (Low Temperature Service)
Application: Used for low-temperature pipeline systems, typically applied in cooling systems and low-temperature gas pipelines.
Mild steel grade: A350 LF2 is low carbon steel, offering good low-temperature toughness and crack resistance. It is suitable for low-temperature service environments and is categorized as mild steel.
Chemical Composition, Physical and Mechanical Properties of ASTM A105 and ASTM A350 LF2
| Item | ASTM A105 | ASTM A350 LF2 |
| Chemical Composition | ||
| C (Carbon) | ≤ 0.35% | ≤ 0.26% |
| Mn (Manganese) | 0.60% – 1.05% | 0.60% – 1.35% |
| P (Phosphorus) | ≤ 0.04% | ≤ 0.035% |
| S (Sulfur) | ≤ 0.05% | ≤ 0.035% |
| Si (Silicon) | 0.10% – 0.35% | 0.15% – 0.40% |
| Cr (Chromium) | – | – |
| Ni (Nickel) | – | – |
| Cu (Copper) | – | Max 0.20% |
| Fe (Iron) | Balance | Balance |
| Mechanical Properties | ||
| Yield Strength | Min 250 MPa (36 ksi) | Min 205 MPa (30 ksi) |
| Tensile Strength | 485-620 MPa (70-90 ksi) | 485-620 MPa (70-90 ksi) |
| Elongation | ≥ 20% (over 8 inches or 200mm) | ≥ 20% (over 8 inches or 200mm) |
| Hardness | Max 187 HB | – |
| Impact Toughness | – | Min 27 Joules (20 ft-lb) at -50°C |
| Physical Properties | ||
| Density | 7.85 g/cm³ | 7.85 g/cm³ |
| Thermal Expansion | 11.0 × 10⁻⁶ /°C | 11.0 × 10⁻⁶ /°C |
| Melting Point | 1425°C – 1538°C (2597°F – 2800°F) | 1450°C – 1550°C (2642°F – 2822°F) |
| Applications | General environment flanges, suitable for oil, gas, and chemical industries | Low-temperature pipeline systems, suitable for low-temperature liquid and gas pipelines |
ASTM Standards for Carbon Steel, Alloy Steel & Stainless Steel
Additionally, we need to mention other ASTM standards for carbon steel, alloy steel, stainless steel, and their relationship with mild steel. The following are common low-carbon steel (mild steel) related materials:
ASTM A516 – Low Temperature Pressure Vessel Carbon Steel Plates (Common in Boilers and Pressure Vessels)
Application: Used for making boilers and pressure vessels, especially in medium to low temperature environments.
Mild steel grade: A516 is primarily low carbon steel (maximum carbon content around 0.26%), commonly used for applications requiring good weldability and moderate strength.
ASTM A694 – High Strength Carbon Steel Flanges and Fittings
Application: Mainly used in the oil and gas industry for flanges and fittings in high-pressure environments.
Mild steel grade: Although A694 includes high-strength grades (such as F42, F46, F52), which generally do not fall under mild steel, the lower strength grades of A694 can be considered lower carbon steel, but they usually have higher carbon content and are suitable for high-pressure and harsh environments.
ASTM A182 – Forged Flanges and Fittings
Application: Used for flanges and fittings in high-temperature and high-pressure environments, commonly found in the oil, chemical, and power industries.
Mild steel grade: A182 includes a variety of steel grades, including low carbon steel (mild steel) as well as alloy steels. For instance, A182 F304 and A182 F316 are not considered mild steel, as they are stainless steels. However, some grades in A182, such as A182 F1 (a low carbon steel alloy), are suitable for regular service.
ASTM A694 and ASTM A182 contain some grades that are not considered mild steel, especially the high-strength grades or alloy steels.
These materials have different strengths and suitable environments, allowing for the selection of the appropriate steel type based on specific engineering requirements.
More resources：
Materials for Flanges and Flanged Fittings in ASME B16.5
