AASHTO M270 and ASTM A709 are two different types of steel plate that are typically used in bridge building applications, as these materials have mechanical and physical properties ideal for withstanding harsh weather conditions and stresses.

While these steel plate materials are similar to one another, there are some differences between M270 and A709 grades that could impact a plate buyer’s choice on which material to use in their bridge construction project. This article will examine those similarities and differences.

AASHTO vs. ASTM

M270 and A709 steel materials are each produced to meet standards set by their regulatory bodies. The American Association of State Highway and Transportation Officials (AASHTO) oversees the specifications of M270 steel plate, while ASTM oversees the specifications of A709 steel plate.

AASHTO

AASHTO is a USA-based organization that sets and oversees standards for the design and construction of infrastructure used in various transportation modes, including highway, rail, air, water and public transportation.

Representing highway and transportation departments across the 50 states, District of Columbia and Puerto Rico, AASHTO typically regulates material standards for local or state government infrastructure projects.

ASTM

ASTM is an international organization that develops standards for products across various industries, including steel, petroleum and medical devices. These material standards may be regulated in both government and private business projects.

Dual Certification

Steel plate must be certified to specific standards to be labeled as M270 or A709 grades. However, steel plate can be dual-certified to meet the specifications of both AASHTO and ASTM.

For example, if a steel plate buyer is using A709 for a bridge construction project requiring materials to meet AASHTO standards, they can request A709 plate dual-certified in AASHTO specifications from plate suppliers like Leeco® Steel.

Bridge Manufacturing Considerations

When sourcing plate for bridge building applications, buyers must consider which materials would best suit the type of bridge being constructed and the climate where the bridge will be built.

Since M270 is certified to meet standards specifically for highway and transportation projects, it is primarily used in the construction of road bridges. A709, however, may be used to construct a variety of bridges, including railroad, road and pedestrian.

In particularly cold climates, plate used in bridges must be able to endure harsh conditions without corroding or breaking. Both M270 and A709 have weathering grades – represented by a “W,” as with A709 Grade 50W – which contain additional alloys that help them better endure extreme weather conditions.

A709 also has high-performance standard (HPS) grades, which offer a balance of strength, weldability, corrosion resistance and ductility. With their enhanced properties, HPS and weathering grades are typically better suited for harsher environmental conditions than standard M270 and A709 grades.

M270 & A709 Specifications

The chemical composition and mechanical properties of M270 and A709 grades both fall under ASTM specifications for A709 steel. These specifications designate the addition of chemical alloys that enhance properties important for materials used in bridge manufacturing, including the following.

Strength

To increase the yield and tensile strength of M270 and A709 steel materials, elements such as phosphorus, silicon and vanadium are added. The addition of strengthening elements ensures that steel used to construct bridges can withstand high energy and stress without breaking.

Hardness

To increase the wear resistance of M270 and A709 steel materials, elements such as manganese, phosphorus and silicon are added. The addition of hardening elements helps prevent steel from denting or wearing out when exposed to strong forces or elements.

Corrosion Resistance

To increase the corrosion resistance of M270 and A709 steel materials, elements such as phosphorus, chromium and nickel are added to weathering and HPS grades. The addition of corrosion resistant elements gives these particular grades enhanced abilities to withstand strong atmospheric forces.

Chemical Composition of AASHTO M270 & ASTM A709 Grades

M270 Chemical Composition

M270 Grade 50 (Max 4” Thick)

M270 Grade 50W Type A

M270 Grade 50W Type B

Carbon

0.23% MAX

0.19% MAX

0.20% MAX

Manganese

1.35% MAX

0.80-1.25%

0.75-1.35%

Phosphorus

0.030% MAX

0.030% MAX

0.030% MAX

Sulfur

0.030% MAX

0.030% MAX

0.030% MAX

Silicon

0.15-0.40%

0.30-0.65%

0.015-0.50%

Columbium

0.005-0.15%

N/A

N/A

Vanadium

0.01-0.15%

0.02-0.10%

0.01-0.10%

Nickel

N/A

0.40% MAX

0.50% MAX

Chromium

N/A

0.40-0.65%

0.40-0.70%

Copper

N/A

0.25-0.40%

0.20-0.40%

 

 

A709 Chemical Composition

A709 Grade 50 (Max 4” Thick)

A709 Grade 50W Type A

A709 Grade 50W Type B

A709 Grades HPS 50W & HPS 70W

Carbon

0.23%

0.19% MAX

0.20% MAX

0.11% MAX

Manganese

1.35%

0.80-1.25%

0.75-1.35%

1.10-1.50%

Phosphorus

0.030%

0.030% MAX

0.030% MAX

0.020% MAX

Sulfur

0.030%

0.030% MAX

0.030% MAX

0.006% MAX

Silicon

0.15-0.40%

0.30-0.65%

0.015-0.50%

0.30-0.50%

Columbium

0.005-0.15%

N/A

N/A

N/A

Vanadium

0.01-0.15%

0.02-0.10%

0.01-0.10%

0.04-0.08%

Nickel

N/A

0.40% MAX

0.50% MAX

0.25-0.40%

Chromium

N/A

0.40-0.65%

0.40-0.70%

0.45-0.70%

Copper

N/A

0.25-0.40%

0.20-0.40%

0.25-0.40%

Molybdenum

N/A

N/A

N/A

0.02-0.08%

Aluminum

N/A

N/A

N/A

0.010-0.040%

Nitrogen

N/A

N/A

N/A

0.015% MAX

 

 

The presence of these chemical alloys contributes to the relatively high yield and tensile points of M270 and A709 grades, which allow the plate to withstand the great forces that bridges face.

Mechanical Properties of AASHTO M270 & ASTM A709 Grades

Grade

Yield Point

Tensile

M270 Grade 50

50 ksi

65 ksi

M270 Grade 50W

50 ksi

70 ksi

A709 Grade 36

36 ksi

58-80 ksi

A709 Grade 50

50 ksi

65 ksi

A709 Grade 50W

50 ksi

70 ksi

A709 Grade HPS 50W

50 ksi

70 ksi

A709 Grade HPS 70W

70 ksi

85-110 ksi

 

M270 and A709 plate buyers may also request a Charpy impact test for steel materials used to construct bridges in cold climates. Charpy testing measures the ability that materials have to absorb impact at a variety of temperatures and ensures that steel is tough enough to withstand extremely harsh temperatures without fracturing.

Sourcing M270 & A709 Steel Plate For Bridge Manufacturing

Before choosing a supplier for M270 or A709 steel plate, buyers should consider several factors to ensure they are getting high-quality materials and service, such as:

  • Detailed paperwork, including mill test reports and invoices, to easily check that the material you are sourcing meets all necessary specifications
  • A quality management system, such as one that is ISO 9001 certified, to ensure you are sourcing high-quality steel plate
  • Distribution centers that have a variety of M270 and A709 grades and sizes, to ensure the material you need is in-stock

 With an ISO 9001 certified quality management system that verifies order accuracy in every step of the order fulfillment process, Leeco Steel ensures that customers receive high quality plate products that meet the specifications needed for their project. Leeco also has 11 distribution centers located throughout North America stocked with a wide variety of plate grades and sizes so customers get the plate they need, when they need it.

Contact Leeco or request a quote today to learn more about our M270 and A709 bridge construction grades.