Pitt researchers develop lead-free "green" steel

International consortium to market product

provided by University of Pittsburgh


n what could be one of the most important innovations in steel making in the past 30 years, researchers at the University of Pittsburgh's School of Engineering have developed a lead-free alternative to 12L14, a free-machining steel commonly used throughout the world. The new steel resulted from research by Anthony J. DeArdo and C. Isaac Garcia, professors of materials science and engineering at Pitt. According to DeArdo and Garcia, their new steel is not only more environmentally friendly, but potentially can be machined more easily than leaded steel.

DeArdo and Garcia used tin to replace the highly toxic lead, which is added to steel to make it easier to machine. The new product, which they term "green steel," not only eliminates an undesirable environmental hazard, but it may also offer cost savings.

A patent for the new lead-free steel was filed by the University of Pittsburgh and is expected to issue this month. The University, through the Office of Technology Management, created an international consortium of steel producers and manufacturers to commercialize the technology.

A test of the final product, completed recently at USS/Kobe Steel Company, found that a 220-ton heat of the new steel performed well. The new steel is presently being tested, and Milton Harris, chairman and CEO of Harris Steel, said the company is encouraged by the test results to date. The market for 12L14 steel is between two and three million tons per year, and at approximately $500 per ton, the worldwide potential market is $1 billion-plus for the lead-free steel.

Not only is the lead environmentally undesirable, but it adds production costs as companies need to implement environmental controls to the manufacturing process. Arthur A. Boni, Pitt's director of technology management, estimates that the "green" steel has the potential to save on environmental and machining costs.

"Ever since governments began asking steel manufacturers to reduce their use of lead, researchers have been trying to come up with alternatives," said DeArdo. And the major users of free machining steel are also interested. The most common use for the steel is in automobile parts, and Harris noted that major automakers in the United States and Germany have indicated a desire to use lead-free steel if it were competitively available.

While other researchers have experimented with different steel alloys, DeArdo and Garcia used another tack. "The key was asking the right question. We started with the scientific approach, asking, 'What does the lead do, on an atomic level, that makes the steel more machinable?'," DeArdo said.

The researchers studied leaded steel using an atom probe field ion microscope to examine the ferrite grain boundaries. "Once we saw what the lead did, the answer was obvious to us," DeArdo said.

The researchers decided that tin would be the most suitable replacement for the lead, then experimented with different ratios of tin in the steel before coming up with their new product. They found that too much tin made the steel too brittle; too little tin made it harder to machine. The final tin content chosen not only makes the steel more machinable than the existing leaded steel, but also could permit a substantial reduction in the machining cost of final components.

  Contact: Ken Service, (412) 624-4238; kpspitt.edu or John Fedele, (412) 624-4148; fedeleuniv-relations.pitt.edu.