The financing was led by Piva Capital, BHP Ventures, and Devonshire Investors, the private investment firm affiliated with FMR, the parent company of Fidelity Investments.
Existing investors Breakthrough Energy Ventures, Prelude Ventures, OGCI Climate Investments, and The Engine also participated in the round.
The funding will allow Boston Metal to accelerate industrial-scale deployments of its molten oxide electrolysis (MOE) technology towards emissions-free steel.
"Boston Metal is ushering in a new era of metallurgy," chairman and CEO Tadeu Carneiro said.
"Steel production has relied on the same basic formula for millennia, and revolutionising such an industry requires a rare combination of team, technology, and partners.
"With this new round of funding, Boston Metal has brought together all of these elements and is positioned to deliver a future where steel production is efficient, modular and clean."
Boston Metal's MOE technology uses electricity to transform metals from a raw oxide form into high-purity molten metal products, facilitating CO2 emissions-free steel production from a wide array of iron ores in a potentially more efficient, less costly and more sustainable approach.
The funding will allow Boston Metal to validate its patented inert anode technology at industrial-scale, further expand its world-class team, and begin to deploy its MOE technology with customers, starting with high-value ferroalloy production as it advances toward steel applications.
"Unfortunately, the production of steel is responsible for more than 8% of global carbon dioxide emissions, and the time is now to identify a more sustainable and cost-effective solution," Piva partner Bennett Cohen said.
"Boston Metal's team of remarkable entrepreneurs, scientists and engineers will completely transform the steel industry by delivering a truly world-changing technology for producing emissions-free steel."
BHP Ventures is the internal venture capital unit within BHP, which is seeking to solve critical global challenges through its investments.
"Our investment in Boston Metal complements the initiatives and partnerships we have underway to support decarbonisation options across our value chain and help drive long-term growth and profitability for BHP and its customers," BHP Ventures head Mark Frayman said.
In November, BHP signed a memorandum of understanding with steelmaker China Baowu to invest up to $35 million and share technical knowledge to help address the challenge of reducing greenhouse gas emissions facing the global steel industry.
BHP and other big miners have come under pressure for not doing more on Scope 3 emissions, or the emissions emitted by its steel-making customers.