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.

Wilson, Blues attack coach Matt Sherratt and Scarlets backs coach Stephen Jones will join tour head coach Robin McBryde in Tonga and Samoa.
"It's a great opportunity and I think we [Sherratt and I] will both come back as better coaches," said Wilson.
"[It] will hopefully benefit Cardiff Blues as well."
Wilson continued: "It was an honour to be asked. I'm not thinking about anything at the moment other than doing my job here at Cardiff Blues and at the end of the season I'll start thinking about the tour and the opportunity that presents."
Former Wales Under-20s head coach Wilson joined Cardiff Blues from Bristol in 2015 having previously worked with Scarlets and Newport Gwent Dragons.
Wilson admits he had to think hard before accepting the role.
"It was more a discussion with my wife than anything else because it falls during our time off when we're away from Cardiff Blues, but it's a great opportunity for me," he added.
"We'll also be organising pre-season so it'll be a busy time. But for me personally, with where I am with my career, it was a great opportunity I wanted to take with both hands, and also I hope I'll come back to Cardiff Blues better for the experience."
Formerly a scrum coach, Wilson is expecting to primarily to work with Wales' forwards in Tonga and Samoa.
"Obviously my area is set-piece and forward play and that will be a heavy part of the role," he said.
"It's all happened quite quickly and we've had the rough discussions around it, but they're ongoing."
Searches are continuing for the bodies of two men who died in an explosion at a Cardiff steelworks on Wednesday.
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Cardiff Blues head coach Danny Wilson says his experience with Wales on next summer's two-Test tour of the Pacific Islands will improve him as a coach.