TECHBRIEF Improved CorrosionResistant Steel for

Highway Bridge Construction 

FHWA Publication No.: FHWA-HRT-11-061

FHWA Contact: Paul Virmani, HRDI-60, (202) 493-3052, 

paul.virmani@dot.gov

This document is a technical summary of the Federal Highway 

Administration report, Improved Corrosion-Resistant Steel for Highway 

Bridge Construction (FHWA-HRT-11-062).

Introduction

Plate girder bridges are usually fabricated from painted carbon 

steels or unpainted weathering steels. Weathering steels, including 

the modern high-performance steels, offer the lowest life-cycle cost 

(LCC) over the design life of the bridge because, in most service 

environments, ongoing maintenance due to steel deterioration is 

not necessary. However, where the bridge is subject to high timeof-wetness or high chloride exposures—coastal areas and areas that 

use large quantities of deicing salt—weathering steels are not effective because the protective patina does not develop and the steel has 

a high corrosion rate.(1) In these conditions, structural stainless steel 

ASTM A1010 (UNS S41003) provides sufficient corrosion protection 

so that painting is not necessary and the bridge structure is maintenance free over its design life.(2) The initial cost of stainless steel is 

more than twice the cost of carbon or weathering steel. Reducing the 

cost of stainless steel would improve the LCC of bridges in severe 

corrosion service conditions. This study identifies steels with lower 

potential cost than ASTM A1010 that could be candidates for bridge 

construction while still providing low corrosion rates.

Approach

The alloy steel design selected to reduce the cost of ASTM A1010—that 

contains 11 percent chromium (Cr)—was to reduce the Cr content to

9, 7, and 5 percent. To compensate for the diminished corrosion resistance from lower Cr, additions of 2 percent silicon (Si), 

2 percent aluminum (Al), or a combination of 2   percent Si plus 

2 percent Al were made in the lower Cr experimental steels. After 

making and hot rolling the steels, the resulting plates were heat treated. 

These were tested for strength and impact resistance to determine 

which steels can meet the steel specifications for steel bridges.(3) The 

corrosion resistance of the alloyed steels was studied in the laboratory 

using accelerated test methods. In addition to measuring the corrosion 

rates, the corrosion products that developed on each of the steels were 

identified. Several steels were studied further by exposing them for 

1 year on an existing weathering steel bridge that has a high corrosion 

rate due to deicing salt use.

Additionally, a LCC analysis was conducted to examine the benefits of 

using maintenance-free, corrosion-resistant steel in place of regularly 

repainting conventional steel. Both deterministic and probabilistic LCC 

Research, Development, and 

Technology

Turner-Fairbank Highway 

Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

http://www.fhwa.dot.gov/

research/
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analyses were conducted for a bridge intended to 

have a 125-year service life.

Results

Experimental Steels

Melting of six experimental steels was performed in 

an induction furnace under vacuum. The aim compositions of all heats was 0.015 percent carbon (C), 

1.29 percent manganese (Mn), 0.022 percent phosphorus (P), 0.004 percent sulfur (S), 0.08 percent 

copper (Cu), 0.43 percent nickel (Ni), 0.24 percent 

molybdenum (Mo), 0.020 percent vanadium (V), and 

0.0150 percent nitrogen (N). Table 1 shows the nominal compositions of each experimental steel.

Heats weighing 100 lb (45 kg) were poured into iron 

molds. The resulting ingots measured approximately 

5 x 5 x 13 inches (125 x 125 x 350 mm). The ingots 

were heated one at a time in an electric furnace 

to 2,300 oF (1,260 oC) and hot rolled to 0.5625-inch 

(14.3-mm)-thick plates. These plates were normalized 

by heating to 1,650 oF (900 oC) and then cooling in air.

Mechanical Properties

The results of standard Brinell hardness tests on 

the as-normalized plates are presented in table 2. 

Most of the experimental steels exhibited the desired 

dual-phase or martensite microstructure, but the two 

Al-containing steels had an all ferrite microstructure, 

and they were relatively soft.

In the as-normalized condition, martensitic and 

dual-phase steels exhibited relatively high hardness, tensile strength, and yield strength. It was 

necessary to determine the temperature at which 

each steel needed to be tempered to achieve the 

two targeted yield strength levels of 50 to 65 ksi 

(344.5 to 447.9 MPa) and 70 to 85 ksi (482.3 to 

585.7 MPa). This was accomplished by systematic 

heat treatment studies for each experimental 

steel using hardness testing and tensile testing. 

All the steels could be normalized and tempered 

to achieve the targeted 50 to 65 ksi (344.5 to 

447.9 MPa) yield strength range representative of 

ASTM A709 50W, except 5Cr2Si2Al. All the steels 

could be normalized and tempered to achieve the 

ASTM A709 70W target yield strength of 70 ksi 

to 85 ksi (482.3 to 585.7 MPa), except 5Cr2Si2Al 

and 7Cr2Al. 

The Charpy V-notch (CVN) impact test is specified 

for bridge steels.(3) Figure 1 presents the results of 

this test for the experimental steels. At the 50 ksi 

(344.5 MPa) strength level, only 11Cr, representing 

the ASTM A1010 steel, exhibited sufficient impact 

toughness to be a candidate for bridge construction. Similar behavior was observed for the 70 to 

85 ksi (482.3 to 585.7 MPa) yield strength plates. 

The impact toughness results for the experimental 

steels are disappointing, but they may be explained 

by the optimum dual-phase microstructure of 11Cr 

with fine grain size compared to the other steels.

Laboratory Corrosion Evaluation

The atmospheric corrosion of bare structural bridge 

steels in chloride environments was simulated with 

the standard SAE J2334 cyclic corrosion test, consisting of 1-day cycles for 100 days.(4) Sets of coupons 

were run with a 5 percent sodium chloride (NaCl) 

spray solution, and another set of coupons was run 

with 3 percent NaCl solution to determine if a less 

severe chloride content in the spray solution might 

change the thickness loss rates from corrosion for 

any of the steels.(5) Thickness loss of test coupons 

and x-ray spectroscopic analysis of the corrosion 

products were both determined. Conventional ASTM 

A588 steel coupons representative of ASTM A709 

50W bridge steel and ASTM A1010 coupons were 

tested along with the experimental steels.

The effect of yield strength on the thickness loss was 

measured for the 11Cr, 9Cr2Si, and 7Cr2Si steels. 

There was no significant difference in thickness loss 

for the two different yield strengths of the three 

steels. It was concluded that the corrosion behavior 

of these steels was not influenced by the steel yield 

strength. 

The comparative corrosion behavior of the steels is 

presented in figure 2. As the number of corrosion 

cycles increased, the total thickness loss increased 

Table 2. As-normalized hardness and microstructures.

Steel

(Wt Percent) HBW Microstructure

11Cr (ASTM 

A1010)

285 Dual-phase ferrite plus 

martensite

9Cr 313 All martensite

9Cr2Si 256 Dual-phase—more ferrite 

than 11 percent Cr

7Cr2Si 258 Dual-phase—more ferrite 

than 11 percent Cr

7Cr2Al 154 All ferrite

5Cr2Si2Al 200 All ferrite

HBW = Brinell hardness number (ASTM recognized).

Table 1. Compositions of experimental steels.

Steel

(Wt Percent) Cr Si Al

11Cr (ASTM A1010) 11.4 0.5 —

9Cr 9.0 0.5 —

9Cr2Si 9.0 2.0 —

7Cr2Al 7.0 0.5 2.0

7Cr2Si 7.0 2.0 —

5Cr2Al2Si 5.0 2.0 2.0

— No (zero) aluminum present in these steels.
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for all the steels. The experimental steels, as well as 

the control ASTM A588 weathering steel, experienced 

thickness loss at a relatively constant rate per cycle. 

This behavior demonstrates that the protective patina 

responsible for providing reduced corrosion rates 

for weathering steels does not form when the test is 

conducted with 5 percent NaCl. Similar behavior was 

observed using 3 percent NaCl. 

All the reduced Cr experimental steels had significantly less corrosion resistance than the ASTM A1010 

control sample and its laboratory analog, the 11Cr 

steel. As the Cr content of the experimental steels 

decreased from 11 to 5 percent Cr, the corrosion 

rate (thickness loss) increased. However, all the 

experimental steels exhibited better corrosion resistance than the ASTM A588 control sample. Adding 

2 percent Si to the 9 and 7 percent Cr steels was 

detrimental to corrosion resistance. This is shown 

in figure 2 by comparing 9Cr to 9Cr2Si. Substituting 

2 percent Al for 2 percent Si in the 7 percent Cr steel 

had a strong positive effect on the corrosion rate. 

Figure 2 shows that the 7Cr2Al steel had the same 

corrosion performance as the 9Cr steel, suggesting 

that 2 percent Al is equivalent to 2 percent Cr for 

cyclic corrosion resistance. 

Since the corrosion rates in the cyclic corrosion tests 

appear to be linear, a regression equation was calculated for thickness loss as a function of cycles for 

each steel. The results of this analysis are presented in 

table 3. The values for the coefficient of determination 

(R2

) were all greater than 0.97, confirming that the 

corrosion rates of all the steels are linear with cycle 

number.

Under the conditions of the 5 percent NaCl cyclic 

corrosion tests, the corrosion rate of the ASTM A1010 

steel is one-tenth that of ASTM A588, implying it will 

take 10 times longer for the same amount of thickness loss from ASTM A1010 as from ASTM A588.

Field Corrosion

In a field corrosion test site on the Moore Drive Bridge 

over I-394S in Rochester, NY, various steel coupons 

were exposed on racks mounted to the lower flange of 

the bridge.(6) The Moore Drive Bridge is in a location 

of high deicing salt use on interstate highway I-394S 

passing beneath the bridge. Following 4 years of 

exposure, ASTM A588 coupons experienced thickness 

loss of 10 mil (254 μm) or a rate of 2.5 mil per 

year (mpy) (60 μm per year), 10 times the generally 

accepted maximum rate for weathering steel of less 

than 0.25 mpy (less than 6 μm per year). At the same 

time, ASTM A1010 stainless steel coupons exposed 

for 2 years showed a corrosion rate of 0.58 mpy 

(14.7 μm per year). 

The experimental steels selected for exposure on the 

Moore Drive Bridge were 9Cr, 7Cr2Si, and 7Cr2Al. 

After 329 days of exposure on the bridge, thickness 

loss of the steels was determined. The corrosion 

rate of each of the three developmental steels was 

1.07, 1.11, and 1.20 mpy (27, 28, and 30 μm per year), 

respectively. These rates are less than one-half the 

2.5 mpy (64 μm per years) of ASTM A588 weathering 

steel. The rust composition was similar for all three 

of the experimental steels: Akaganeite was the most 

abundant oxyhydroxide, followed by goethite and 

Figure 2. Summary of 5 percent NaCl cyclic 

corrosion test results.

1 mil = 25.4 μm

Figure 1. Average CVN absorbed energy values 

for experimental steels tempered to achieve yield 

strength greater than 50 ksi (344.5 MPa). 

5*(F-32)/9 oF = oC 

FC = Fracture Critical; NFC = Non-Fracture Critical

Table 3. Linear regression equations for thickness 

loss in 5 percent NaCl cyclic corrosion tests.

Steel

Coefficient,

Mil Per

Cycle

Predicted

Life Versus 

ASTM A588

ASTM A1010 0.050 10.4

11Cr 0.056 9.3

9Cr 0.147 3.5

9Cr2Si 0.197 2.6

7Cr2Si 0.304 1.7

7Cr2Al 0.152 3.4

5Cr2Si2Al 0.275 1.9

ASTM A588 0.519 1.0

1 mil = 25.4 μm
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lepidocrocite. Notably absent was maghemite, which 

was abundant on the cyclic corrosion test coupons. It 

was concluded that the cyclic corrosion test protocols 

used in this study were fundamentally different for 

Cr-containing steels than actual field environments 

for bridges exposed to deicing salts. It is likely the 

high time-of-wetness of the cyclic corrosion test 

promotes the formation of maghemite.

LCC Analysis

A LCC analysis examined the benefits of using a 

maintenance-free, corrosion-resistant steel in 

place of regularly repainting conventional steel. 

Deterministic LCC comparisons for a 125-year 

life span bridge girder made of painted carbon 

steel versus ASTM A1010 steel showed ASTM 

A1010 was more economical. Probabilistic LCC 

analysis determined that starting in about year 12

the probability that an ASTM A1010 steel girder costs 

less than a painted steel girder increases rapidly; 

the 50 percent probability occurs at year 15. By year 

20 of service, the probability is over 90 percent that 

the ASTM A1010 steel girder is less expensive, and 

it becomes certain that the ASTM A1010 steel girder 

is less expensive than a painted conventional steel 

girder after year 40.

Summary

The efforts to develop a less costly but equally

corrosion-resistant bridge steel than currently available ASTM A1010 were unsuccessful because the 

combination of strength and impact toughness 

required for steel bridge members could not be 

achieved with the lower Cr steels. The experimental steels were more corrosion resistant than ASTM 

A588. However, because ASTM A588 and other 

weathering steels do not develop a protective rust 

patina in the presence of high-salt exposure, bridges 

made from weathering steels or carbon steel must 

be painted and maintained by repainting at certain 

intervals for those service environments. Its corrosion resistance makes ASTM A1010 capable of lasting 

in structures for long periods of time—125 years, 

as considered in this study—without the need for 

initial painting or maintenance (i.e., repainting). 

Accordingly, the economic benefit of ASTM A1010 

is gauged on its lower LCC compared to that of a 

conventional painted bridge steel.

References

1. Federal Highway Administration. (1989). 

Uncoated Weathering Steel in Structures, 

Technical Advisory T4140.22, U.S. Department of 

Transportation, Washington, DC.

2. ASTM A1010/A1010M. 01. (2009). “Standard 

Specification for Higher-Strength Martensitic 

Stainless Steel Plate, Sheet, and Strip,” Annual 

Book of ASTM Standards, Volume 01.03, ASTM 

International, West Conshohocken, PA.

3. ASTM A709/A709M. (2010). “10 Standard 

Specification for Structural Steel for Bridges,” 

Annual Book of ASTM Standards, Volume 01.04, 

ASTM International, West Conshohocken, PA.

4. SAE J2334. (1998). Lab Cosmetic Corrosion Test, 

SAE International, Warrendale, PA.

5. Townsend, H.E., Davidson, D.D., and Ostermiller, 

M.R. (1998). Development of Laboratory Corrosion 

Tests by the Automotive and Steel Industries of 

North America, 659–666, Proceedings of the Fourth 

International Conference on Zinc and Zinc-Alloy 

Coated Steel Sheet, Iron and Steel Institute of Japan, 

Tokyo, Japan.

6. Cook, D.C. (2010). Moore Drive Bridge: Coupon 

Exposure Tests, AISI Corrosion Advisory Group 

Meeting, Washington, DC.

Researchers—This study was performed by ArcelorMittal in conjunction with Old Dominion University and Lehigh 

University.

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Key Words—Corrosion, Steel, Weathering steel, and Life-cycle cost.

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JULY 2011 FHWA-HRT-11-061

HRDi-60/07-11(600)E