A plan is being put together by workers to save the Orb steelworks in Newport.
The proposal is based on a new "Wales-only supply chain" using steel from Port Talbot instead of the Netherlands.
Tata Steel announced last month it was closing the site after failing to find a buyer, putting 380 jobs at risk.
Workers marched through Newport on Saturday to protest against the closure, which Tata Steel has blamed on upgrade costs - saying it would cost £50m to make it competitive.
Steel union Community worked with consultants Syndex to create an outline business plan which would require £30m of Welsh or UK government funding.
It calls for more automation and a new annealing line to treat the steel, allowing the business to produce steel for electric vehicle motors.
It proposes a new model where the site would produce two types of steel instead of one - grain-oriented and non-oriented.
The union said Port Talbot steelworks would need new facilities to supply Orb, which would "take a few years" to build.
Orb's future would be funded by the sale of another business it owns and the money set aside to close the site, according to the union plan, leaving the shortfall for the governments to pick up.
Tata Steel previously said continuing to fund substantial losses at the site was "not sustainable" and has been asked to comment on the proposals, as has the UK government.
A Welsh Government spokesman said: "We will continue to work with Tata, its loyal and dedicated workforce and steel unions at all sites in Wales, including Orb, to do everything in our power to keep steel production and steel jobs here in Wales.
"But the UK Government needs to step up to the plate too - they have done precious little so far to safeguard our steel sector and we again call on them to urgently back the industry and to invest in its protection and its future."
Community said the plan was "robust and credible".
Mark Spencer, who has worked at the site for 38 years, said: "There's a future for the company, my son now works there and I want something there for the future for my younger generations."
Cheryl Hider, whose daughter's partner works at Orb, added: "It's been part of our history since day one, it's part of Newport and we're part of Newport and we need to save Newport jobs."
Tata Steel said it was "committed to building a long-term sustainable future in Europe" but needed to focus on its core business.
"While we recognise how difficult this news was for all those affected, we continue to work very hard to support them."
A UK government spokesman said while it was a "commercial decision for Tata Steel Europe, we remain in regular contact with the company, unions and other partners throughout this process".