Katchin (カッチン; pronounced "Cat-cheen") is a material said to be one of the strongest metals in the universe. In the English translation of the Dragon Ball manga, it is called Klangite or Kattin steel.
During the Majin Buu Saga, Shin used his powers of Magic Materialization to summon a block of Katchin to test the Z Sword. As Goku hurled the cube at Gohan, the Z Sword proved no match for the cube of Katchin, and thus the sacred Z Sword was broken, becoming no more than a dagger and releasing Old Kai.
In the future, Shin summoned a block of Katchin to finalize Trunks' training in preparation for Babidi's arrival on Earth. As Shin about to toss Trunks the block, Kibito sensed Babidi's movements so the Katchin was not used.
In the "Future" Trunks Saga, the conflict between Goku and Fused Zamas, Fused Zamas is able to summon a block of Katchin and hurls it towards Goku, then proceed to spawn 4 more Katchins, which greatly damaged Goku. After Vegito greatly pummeled Fused Zamas and was about to finish him off with a Final Kamehameha before defusing, Fused Zamas hurls a block of Katchin at him, before following up with several more blocks of Katchins.
Video game appearances
In Dragon Ball Z: Buu's Fury, there is a wall made of Katchin in the Cave of the Ancients on Grand Kai's planet. Unable to break it even with a kamehameha, Goku uses Instant Transmission to pass the wall and get the ancient artifact hidden inside. Later in the game, Shin makes a block of Katchin appear in order to test the Z Sword like he did in the manga/anime.
In the Budokai series, one of the Shin's special attacks involves him summoning a block of Katchin and throwing it at his opponent (technique called Supernatural Abilities in Budokai 3). In the Budokai Tenkaichi series, the block is used in the basic rush of Shin. In Dragon Ball Z: Budokai Tenkaichi 3, Shin's downward hypersmash is hitting the opponent with a block of Katchin.