Forged Steel Steering Knuckle Superior in Life Cycle Analysis Study

Detroit, MI, July 23, 2008 – A professor-student team at the Missouri University of Science & Technology recently performed a Life Cycle Assessment (LCA) study on the greenhouse gas emissions associated with the manufacturing of three steering knuckles.    The team found that the forged steel steering knuckle had significantly lower greenhouse gas emissions than either the cast aluminum or cast iron steering knuckle over their respective life cycles, which were divided into the manufacturing, use and end-of-life phases.

“As the steel industry and steel customers seek to lighten their environmental footprint, it is important to consider the entire life cycle in assessing the environmental impact,” said David Anderson, Director of Long Products at the American Iron and Steel Institute (AISI).  “While CAFE standards emphasize the use phase, a more important consideration is the environmental impact over the entire life cycle of the component or vehicle.” 

Students at Missouri University of Science & Technology (formerly University of Missouri-Rolla) were awarded a Ferrous Metallurgy Education Today (FeMET) Design Grant from the Association for Iron and Steel Technology (AIST) and AISI, based on their proposal to compare the greenhouse gas emissions produced over the life cycles of the steering knuckles.  The students worked under Professor Kent Peaslee, who holds a doctorate in Metallurgical Engineering and is the Associate Chair of the Materials Science & Engineering Department at the university.   The FeMET grant program is designed to seek innovative designs and solutions to industry-related issues. 

Testing Details

The forged steel steering knuckle came from the rear suspension of a 4-cylinder sedan and weighed 2.4 kg.  The cast aluminum steering knuckle came from the front suspension of a 6-cylinder minivan and weighed 2.4 kg.  The cast iron steering knuckle was from the front suspension of a 4-cylinder sedan and weighed 4.7 kg. 


Three components compared (left to right):  the forged steel steering knuckle, the cast aluminum steering knuckle, and the cast iron steering knuckle.

As the manufacturing processes vary for the different steering knuckles, software was used to analyze energy inputs and emissions for that particular steering knuckle’s method of production.  The team used GaBi 4 Software, developed by the University of Stuttgart to make the assessments, as well as the International Organization for Standardization (ISO) 14000 family classification, which includes life-cycle assessments and inventories.

Further Study Results

The team found that the forged steel steering knuckle produced the least amount of greenhouse gases throughout all the phases when compared with its cast aluminum and cast iron counterparts.  Being relatively lightweight, the forged steel component did not consume a large amount of fuel in either the use or end-of-life phases. 

Further, in producing the forged steel steering knuckle more recycled material was used than in producing the other steering knuckles.  According to the U.S. Environmental Protection Agency, more steel is recycled each year than all other materials combined, including aluminum, glass and paper.   This recycled iron and steel saves the nation 74 percent of the energy that would have been needed to make new steel.  

In analyzing the emissions from the cast aluminum steering knuckle, the team found that the total climate change potential of the aluminum component to be three times that of the forged steel steering knuckle.  Results of the LCA study showed that the material manufacturing processes produced high levels of greenhouse gases. For instance, the production of aluminum requires large amounts of electricity and therefore emitted the most greenhouse gases. 

The environmental impact of the cast iron steering knuckle was determined to be two times that of the forged steel component.  Overall, the aluminum and cast iron steering knuckles had more factors contributing to emissions than the forged steel steering knuckle. The cast iron steering knuckle weighed the most, contributing to higher emission levels in the use and end-of-life phases in transporting the component to landfills or recycling facilities. 

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Through the support of the American Iron and Steel Institute, the Long Products Market Development Group is growing the market for value-added steel bar and rod products. With seven member companies and two task forces--Automotive/Heavy Equipment and Construction/Infrastructure--the group is committed to developing innovative solutions to the challenges facing their clients and the steel industry.
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AISI’s Long Product Market Development Group Member Companies:

  • ArcelorMittal
  • Gerdau Ameristeel Corporation
  • Gerdau MACSTEEL
  • Nucor Corporation
  • Republic Engineered Products, Inc.
  • Steel Dynamics, Inc.
  • The Timken Company