The Tin Woodman of Oz (Oz Series, Book 12)

The Tin Woodman of Oz: A Faithful Story of the Astonishing Adventure Undertaken by the Tin Woodman, Assisted by Woot the Wanderer, the Scarecrow of Oz, and Polychrome, the Rainbow's Daughter is the twelfth book in the Oz series written by L. Frank Baum and was originally published on May 13, 1918. The Tin Woodman is reunited with his Munchkin sweetheart Nimmie Amee from the days when he was flesh and blood. This was a backstory from Baum's 1900 novel, The Wonderful Wizard of Oz. It was followed by The Magic of Oz (1919).
The Tin Woodman and the Scarecrow are regaling each other with tales at the Woodman's palace in the Winkie Country when a Gillikin boy named Woot wanders in. After he is fed and rested, Woot asks the Woodman how he came to be made of tin.