In an announcement Friday, the company said the appointments are effective 1 January 2020, the day Topalian is set to take on his new duties. 

"Leon and John have made outstanding contributions over their many years of service to Nucor. This is the culmination of many years of thoughtful succession planning, and I have full confidence in their leadership," said outgoing chairman and chief executive John J. Ferriola, who is retiring at the end of the year. 

Walker has more than 35 years of experience in metal-related manufacturing and fabricating industries and has served as a member of Nucor's board since 2008. He has been the lead director since 2017. 

He also served as chief executive officer of Global Brass and Copper from 2007 to 2014 and had been both executive chairman and non-executive chairman of that company from 2013 to 2019. In addition, he is a Weirton Steel Corp. alumnus, having joined the company in 1988. He went on to lead Weirton Steel and president and chief executive officer. 

"I am honored to have been chosen by my fellow directors to serve as non-executive chairman and enthusiastically welcome Leon to the board," Walker said. "I look forward to continuing to work with him, the rest of the board and all of our teammates at Nucor in this new role."

Topalian has been with Nucor since 1996 and currently serves as president and chief operating officer. His promotion to CEO was announced in September.  

“It is incredibly humbling to be asked to join the board of directors, and I look forward to working with John Walker and the rest of the board to lead Nucor," he said.