William Justin Kroll

Luxembourgish metallurgist best known for inventing the Kroll process in 1940, which is used commercially to extract metallic titanium from ore.

Working in Germany, in 1918, Kroll invented a very efficient bearing alloy based on lead, commercialized under the name Lurgi metal, and he was awarded various metallurgy related patents. In Austria in 1922, he developed alloys known as Alusil and Alsia used primarily for cast-aluminum pistons. In 1923, Kroll returned to Luxembourg and set up a private laboratory. Kroll invented precipitation hardening (PH) stainless steel in 1929, when he added a small amount of titanium to stainless steel and strengthened it by thermally precipitating TiC particles. In the 1930s he began focusing on the study of titanium and its alloys.

As the Nazi cloud began to spread over Germany in 1940 Wilhelm J. Kroll elected to emigrate to the United States. He arrived in New York on 22 February 1940. On 25 June 1940, the United States Patent and Trademark Office awarded patent 2,205,854 for Kroll's method of manufacturing titanium and alloys thereof, filed on 6 July 1938. On 4 December 1940, Kroll applied for US citizenship. He worked as a consulting engineer for Union Carbide Research Laboratories at Niagara Falls, New York.

William J. Kroll returned to Europe in 1961 where he died in Brussels on 30 March 1973 at age 83.