12L13 12L14 12L15 are free cutting structural steel. Free cutting steel is a type of steel that is easy to cut (such as turning, milling, pulling, planing, drilling, etc.), also known as automatic machine tool processing steel, abbreviated as automatic steel. is easy cutting structural steel, easy cutting steel is easy to be (turning, milling, drawing, planing, drilling, etc.) cutting processing steel, also known as automatic machine tool processing steel, referred to as automatic steel. It is produced to adapt to machining automation and flow line production.