PITTSBURGH — The United Steelworkers union has reached a tentative four-year agreement with Allegheny Technologies Inc. after 2,200 workers were locked out more than six months ago.

A spokesman for the Pittsburgh-based specialty metals firm declined to comment beyond confirming the agreement, but union President Leo Gerard called it “a tremendous victory for a very brave group of workers.”

Union members are expected to vote on the contract later this week and details of the agreement were not going to be released until the union members are briefed and vote on the contract.

The last contract expired June 30, and ATI locked out the workers at 12 plants in Pennsylvania and five other states on Aug. 15. The lockout was especially felt in Western Pennsylvania, where about 1,500 union members work at plants in Harrison, Gilpin and Canton Townships, and Latrobe, Midland and Vandergrift.

It is unclear is what will happen to nearly 270 union workers at the Midland plant, which the company had continued to operate with management and temporary employees before idling it last month. The company has said the plant could remain idled for months until it can turn an acceptable profit, and ATI had similarly announced plans to idle the Gilpin Township plant in April.