See also German classic philologist, Wilhelm Kroll (philologist) (1869–1939). William Justin Kroll (born Guillaume Justin Kroll; November 24, 1889 – March 30, 1973) was a Luxembourgish metallurgist. He is best known for inventing the Kroll process in 1940, which is used commercially to extract metallic titanium from ore. Biography In 1909, Wilhelm Kroll graduated from Luxembourg's Athenaeum High School, and in 1910, he registered at the faculty of metallurgy at the Technische Hochschule Charlottenburg in Berlin, graduating in 1914. He spent the next four years there to complete his doctoral thesis under the guidance of legendary professor K. A. Hofmann. 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. Before Kroll, titanium as a metal was a laboratory curiosity. In 1938, titanium was machined for the first time at the Cerametal factory in Bereldange, Luxembourg. William Kroll visited the US, arriving in New York aboard the SS Queen Mary from Cherbourg, France on October 18, 1938. He called on various US non-ferrous industries, showing his titanium samples, but there was little to no interest in titanium at the time. Disappointed, he returned to Luxembourg. 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 February 22, 1940, having sailed from Rotterdam, The Netherlands, aboard the on February 10, 1940. On May 10, 1940, German troops invaded Luxembourg, occupying the country for the next four years. On June 25, 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 July 6, 1938. On December 4, 1940, Kroll applied for US citizenship. He worked as a consulting engineer for Union Carbide Research Laboratories at Niagara Falls, New York. As the US declared war on the Axis nations in December 1941, Kroll's patent