From the mid-1960s through 2006, the Steelers had just four starting centers: Ray Mansfield, Mike Webster, Dermontti Dawson and Jeff Hartings.
In 2008, however, it appears the Steelers could have their third starting center in the past three seasons.
A report on the NFL Network revealed the Steelers agreed to a two-year contract with former Carolina center Justin Hartwig.
The deal is reportedly worth $4 million, including a $975,000 bonus.
Hartwig, 29, released by Carolina last week in a salary cap-related move, will compete with 2007 starter Sean Mahan and second-year pro Darnell Stapleton for the center position.
Mahan was a disappointment last season after joining the Steelers as a free agent from Tampa Bay as a replacement for Hartings, who retired.
The 6-4, 312-pound Hartwig is entering his seventh NFL season after joining the league as a sixth-round draft pick of the Tennessee Titans in 2002.
He was a three-year starter at center for the Titans before Carolina signed him to a five-year, $17-million contract in 2006.
Hartwig, however, was limited to two games that season after being placed on injured reserve with a groin injury.
He made 15 starts for the Panthers in 2007 before a knee injury ended his season. He has appeared in 67 career games, starting 63 of them, all at center.
Hartwig visited the Steelers Friday, leaving to also make a visit with Kansas City.
He is the third free agent to sign with the Steelers, joining running back Mewelde Moore and linebacker Keyaron Fox.
The Steelers have lost one free agent in guard Alan Faneca.
In other news Tuesday, guard Chris Kemoeatu and offensive tackle Trai Essex, a pair of restricted free agents, signed tender offers with the Steelers.