Steel Density Analysis: Core Differences between Mild and Medium Carbon Steels and Industrial Applications

June 20, 2025
BLOGS

The density of steel is one of the key parameters that determine its physical properties and industrial applications. Theoretical state of steel density of 7.85 g/cm³, but the actual density with the carbon content changes: Low-carbon steel about 7.85 g/cm³, medium-carbon steel down to 7.82 g/cm³, high-carbon steel is further reduced to 7.81 g/cm³. The higher the carbon content, the larger the crystal structure gaps, resulting in a lower density instead.

Low-carbon vs. medium-carbon steels: correlation between carbon content and properties

The core difference between the two types of steel lies in the carbon content and the mechanical properties derived from it:

1. Range of carbon content:

– Low carbon steel: 0.05%-0.25% carbon content, crystal structure dominated by ferrite, good plasticity.

– Medium carbon steel: carbon content of 0.25%-0.60%, the formation of more pearlite, hardness significantly increased.

2. Mechanical Properties Comparison:

Performance indicators	Low-carbon steel	Medium-carbon steel
yield strength	250-350 MPa	350-500 MPa
Tensile strength	400-500 MPa	500-650 MPa
Elongation	High (>25%）	Medium (15-25%)
Typical Applications	Automotive Body, Piping	Gears, Bearings, Tools

Medium carbon steels are suitable for load-bearing components due to their higher strength, but are less ductile than low carbon steels and are prone to cracking when welded.

Straight seam submerged arc welded pipe (LSAW STEEL PIPE): material selection and industry applications

LSAW pipes are rolled from a single sheet of medium-thickness plate and then welded by double-sided submerged arc welding. Its core advantages lie in high pressure-bearing capacity, precise dimensional control (e.g., diameter 457-1450 mm, wall thickness 8-45 mm), and excellent low-temperature corrosion resistance.

Material Suitability:

– Mild steel applications: more than 60%, mainly used for low-pressure fluid transportation (e.g., water pipes, structural building pipes) due to its excellent formability and weldability.

– Medium carbon steel applications: used for high-pressure oil and gas pipelines (e.g., grades X70 and above), with wall thicknesses up to 26.4 mm, to meet the needs of harsh environments, such as alpine and deep-sea environments.

Market Data & Technology Trends:

The global LSAW pipe market reached USD 8,792 million in 2023, with China accounting for 20.82% (USD 1,830 million). The production process is dominated by JCOE molding (88.36% share in 2022) due to its low tooling cost and adaptability, while the UOE process is suitable for high-quality thick-walled pipes but with higher investment.

Distribution of LSAW pipes by application fields in 2023

Applications	Market Size (USD Billion)	Percentage	Main Material Type
Oil & Gas	55.65	63.29%	Medium Carbon Alloy Steel
Construction	24.62	28.23%	Mild Carbon Steel
Machinery Manufacturing	7.65	8.48%	Medium Carbon Steel

In the future, the industry will move towards Green Manufacturing (reduction of CO₂emissions) and Intelligent (laser seam tracking system to increase welding speed by 10 m/min).

III. Synergistic evolution of material selection and industrial needs

In the field of energy and infrastructure, material selection needs to strictly match the working conditions:

– Mild carbon steel pipes : dominate the city gas network, building scaffolding, relying on its economy and ease of welding.

– Medium carbon steel thick-walled pipes : used in submarine pipelines (e.g. API 5L L450N PSL2 steel pipe), which are stress relieved by the cold expansion process, guaranteeing 50 years of service safety.

Leading enterprises such as ALLLAND STEEL PIPE (revenue of 1.5 billion yuan in 2023) have achieved an annual production capacity of 150,000 tons of thick-walled pipes through the optimization of the JCOE process, confirming the irreplaceability of medium-carbon alloy steel in high-performance pipes.

Conclusion: The Material Logic Behind Density

From the density difference (7.85→7.82 g/cm³) to the carbon content grading, the microstructure of steel determines the division of macro applications. LSAW pipes, as the key carrier, with its low carbon steel accounting for over 60% of the current situation, and the high growth of medium carbon steel in the energy sector (compound annual growth rate of 1.51%), together reflect the industrial scene of the precise demand for material performance. In the future, with the popularization of green metallurgy and intelligent welding technology, the two types of steel will promote the innovation of pipeline industry in a finer dimension.