May_June_AMP_Digital

5 A D V A N C E D M A T E R I A L S & P R O C E S S E S | M A Y / J U N E 2 0 1 9 A GAME OF INCHES With regard to the comments from D. Vukovich in the April issue, I’m a bit puzzled. In his letter, he states that “…the surfaces of the plate were pack or gas carburized to depths up to about five inches.” Wow! I was active in the metallurgy business for over 50 years and it was rare when I encountered a requirement for a carburized case depth of as much as 0.100 in. Vukov- ich is talking about something that is 50 times as much. Am I missing something? Bill Glater, P.E. MEA CULPA I thank Mr. Glater for his comments about gas carburized case depths in steel. In my experience, case depths usually ranged from 0.025 to 0.050 in. The report of a 5-in. carburized case depth in naval armor steel came as a re- sult of casually plucking a number from the literature. Going back to the original inqui- ry by Mr. Vander Voort, the literature states that nickel and chromium al- loy additions were used in naval armor plate steel as early as 1876. In 1890, the Harvey United Steel Co. produced “Harveyized” armor with a claimed 1-in. case depth having 1 to 1.1% surface carbon when pack carburized at 1700°F for two to three weeks. After pack car- burizing, the armor plate was heat- ed, forged to refine grain size, held at temperature to diffuse the carbon for a deeper case, then spray quenched on the carburized side. This resulted in a total hardened depth of 30-40% of the plate thickness, including the carbu- rized case depth. A reference to the Harris carbon diffusion equation and the gas carburiz- ing depth equation where d = K t 5 gives a carburized depth of 0.46 in. at 1700°F for three weeks. Carburizing at 1900°F We welcome all comments and suggestions. Send letters to frances.richards@asminternational.org. RESEARCH TRACKS LIFT ANNOUNCES NEW JOINING PROJECT Lightweight Innovations For To- morrow (LIFT), Detroit, a national manufacturing innovation institute operated by the American Light- weight Materials Manufacturing In- novation Institute, announces a new project with the Center for Automo- tive Research (CAR) to test and evalu- ate mixed-material joining technolo- gies. The new project, part of LIFT’s Fast Forge program, is led by LIFT and CAR, and partners include CAR’s Coalition for Lightweighting Materials working group and LIFT members. The teamwill test various joining technologies and recommend the most optimal choic- es for specific material combinations. Results will include a detailed catalog containing information on innovative mixed-material joining technologies, including selection criteria, comput- er-aided engineering results, physical testing data for various combinations, and application-specific recommen- dations for the industry. The project, valued at $500,000, will take place in three phases to be completed by October 31. www.lift.technology/lift- fast-forge. for three weeks should produce a 0.72-in. case depth. As reported in the literature, pack carburizing will gener- ally produce a deeper case and higher surface carbon than gas carburizing for a given time at temperature. It is amus- ing to discover that a gas carburized case depth of 5 in. would take 4 1/2 years to complete. Mea culpa! It would be interesting to hear comments from people at United States Steel, Bethlehem Steel, and Krupp (now part of ThyssenKrupp AG) about any reference in their archives to the case depths used for naval armor plate circa 1900-1935. Dennis T. Vukovich View of the USS Arizona fromNew York’s Manhattan Bridge. FEEDBACK