Peter O'Brien, a 51-year-old married father of six, from Llanishen, Cardiff, and Mark Sim, 41, from Caldicot, Monmouthshire, were killed in the blast in the basement of the rod and bar mill at Celsa Steel in Splott.
Five men were also injured.
The company is working with the Health and Safety Executive (HSE) and police to determine the cause of the blast.
Search dogs were seen being taken to the site on Thursday while specialist search teams have also been involved.
The alarm was raised at about 10:30 GMT on Wednesday and dozens of emergency services vehicles were sent to the scene.
Firefighters tackled an "extremely difficult" fire in the basement of the building, where five people were injured.
One was treated at the scene and four were taken to the University Hospital of Wales, Cardiff.
Three of them have since been discharged.
Searches are continuing for the bodies of two men who died in an explosion at a Cardiff steelworks on Wednesday.