49ers’ Ian Williams keeping nose to the ground

After finishing the previous two seasons on injured reserve, Ian Williams is finishing 2015 with a flourish.

The 49ers (4-11) are limping to the finish, but their nose guard is dominating down the stretch; Williams is a major reason the 49ers have allowed 77.5 rushing yards and 2.4 yards a carry in their past two games.

Williams will be an unrestricted free agent after the season and figures to receive a substantial raise after earning a $1 million base salary this season.

The 49ers haven’t engaged in serious extension talks with Williams’ agent, Drew Rosenhaus, during the season, which Williams viewed as possible nod to his medical file.

Williams finished 2013 and 2014 on the shelf with leg fractures that forced him to miss 21 of 32 games.

Despite his scant experience, Williams, 26, who had played in 15 games in his first four years, was named one the team’s four defensive captains before the season.

Defensive coordinator Eric Mangini recently touched on some of the qualities that have made Williams a respected locker-room presence, citing his work ethic, consistency and willingness to receive instruction.

Head coach Jim Tomsula was Williams’ position coach for his first four seasons and they have formed a close connection.