Lead-free ‘green’ steel developed

The researchers claim the new steel is not only more environmentally friendly than 12L14, but can be machined more easily.

Anthony J. DeArdo and C. Isaac Garcia, professors of materials science and engineering at Pitt used tin to replace lead, which is added to steel to make it easier to machine. Not only is lead environmentally undesirable, but it adds production costs as companies need to implement environmental controls to the manufacturing process.

The resulting ‘green steel,’ not only eliminates an undesirable environmental hazard, but it may also offer cost savings, the researchers claim. “Ever since governments began asking steel manufacturers to reduce their use of lead, researchers have been trying to come up with alternatives,” said DeArdo.

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.

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 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.

The researchers’ work was conducted through the Basic Metals Processing Research Institute (BAMPRI), which is affiliated with the School of Engineering’s Department of Materials Science and Engineering.

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. The University also signed a technology licensing agreement with the consortium, which is officially organized as a limited liability company (LLC) of steel producers – the Nonleaded Free Machining Steel Consortium, LLC.

The producer members of the LLC will produce the lead-free steel commercially, and may sublicense to others as market demand increases.