When a lieutenant to Warren E. Buffett first invested in Precision Castparts three years ago, the billionaire had hardly heard of the metal parts manufacturer.

Now Mr. Buffett has bought the company in his biggest takeover ever.

Berkshire Hathaway, his $354 billion industrial empire, said on Monday that it would buy Precision Castparts for $32 billion. The move will help move Mr. Buffett’s company — which includes earlier acquisitions ranging from the Burlington Northern Santa Fe railroad to Fruit of the Loom underwear — further into the industrial sector. Including debt, the transaction is worth $37.2 billion.

Not only is the acquisition Mr. Buffett’s most ambitious — just weeks from his 85th birthday — but it is also a standout in what has been a banner year for mergers, with more than $2.7 trillion in deals already announced.

It is also a bet that Precision Castparts — whose turbine airfoils and valves are used by companies like Boeing and Airbus — will benefit from growing numbers in airline travel, and more demand from aircraft manufacturers.