Steel giant Liberty House is to create 300 jobs and make multimillion-pound investments to secure the future of five plants.
The announcement was made as Liberty formally completed a £100 million deal to acquire the Speciality Steels division of Tata Steel UK.
The news protects the jobs of 1,700 existing staff at three major sites at Rotherham, Stocksbridge and Brinsworth in South Yorkshire, smaller sites in Bolton, Lancashire, and Wednesbury in the West Midlands, and two distribution centres in China.
The company announced expansion plans expected to generate an additional 300 production jobs in the business.
Liberty said it will invest up to £20 million in new plant and equipment in the next year to boost competitiveness and secure international market leadership for the business, which produces a range of high-value steels used in the manufacture of vehicles, aircraft, industrial machinery and equipment for the oil and gas industry.
The business will increase output substantially at the electric arc furnaces, casting shop and bar mill in Rotherham, with bigger plans across the wider business in the years ahead.
Production from the arc furnaces is expected to rise to more than one million tonnes a year.
Sanjeev Gupta, executive chairman of Liberty House, said: "The Speciality Steels business is a global leader in its field, with a highly skilled and well-motivated workforce and we are eager to invest so it can grow and achieve its full potential.
"Today marks a step change for the Liberty House Group because we are taking on strategically important capacity that will drive expansion in the years ahead.
"It will help us achieve our 'greensteel' vision and facilitate investment in engineering products, thereby reducing the supply chain gaps in the UK, especially in automotive and aerospace sectors.
"By investing to acquire Speciality Steels we are casting a big vote of confidence in the future of British industry.
"With the right business model and an innovative approach, the UK steel and engineering sectors can recover and thrive.
"The Government is now pursuing a new post-Brexit industrial strategy and steel must be at the heart of that strategy."
The acquisition will make Liberty one of the largest steel and engineering employers in the UK, with more than 4,500 workers.
Bimlendra Jha, chief executive of Tata Steel UK, said: "As a responsible owner, Tata Steel in the last couple of years has undertaken a transformation plan at Speciality Steels, including investing in a state-of-the-art vacuum induction melting furnace, to ensure the business can have a sustainable future.
"We thank the employees, trade unions and management of Speciality Steels for their diligent hard work in the journey to turn around the business in difficult times and we wish them a successful future under new ownership."
Roy Rickhuss, general secretary of the Community trade union, said: "The completion of the sale will bring some welcome certainty to a workforce that has faced a tough time over recent months and years.
"It's testament to the skills and commitment of the steelworkers and the trade union leadership within the business that Liberty has taken on Speciality Steels and given it new hope.
"To support and guarantee the success of the business, all parties in the General Election must demonstrate a commitment to a joined-up industrial strategy, which will create the environment where Speciality Steels and other steel businesses can thrive."