Mitsubishi Corp., the remaining corporate defendant in a U.S. price-fixing investigation that led to convictions of six companies and more than $300 million in criminal fines, goes on trial this week on charges that it helped organize the global graphite-electrode cartel. Since 1998, the Justice Department investigation has netted convictions of the world's two leading manufacturers of graphite electrodes--UCAR International Inc. and Germany's SGL Carbon. Both companies pleaded guilty to participating in the conspiracy to fix the price of the product that is used to heat scrap metal at high temperatures to make steel in mini-mills. They paid fines totaling $245 million. Four other Japanese companies or their U.S. units also have pleaded guilty and paid fines totaling more than $40 million. Mitsubishi maintains it is innocent. "We believe the government's case lacks merit and we intend to contest those charges very vigorously," said Kris Lathan, a Mitsubishi spokeswoman. "We expect to be fully exonerated." The Mitsubishi trial, in federal court in Philadelphia, will feature the testimony of former UCAR Chairman Robert Krass, who is completing a 17-month prison term for his guilty plea, and SGL Chairman Robert Koehler, fined $10 million for his role in the conspiracy, according to court papers. The government said the presentation of testimony would take about a month.