Despite the growth of alloy steels and special means of surface hardening, the ancient art of carburizing steel remains one of the fundamental operations in the manufacture of machine parts. It retains its popularity because it enables the workman to start with a material that can be easily machined, and end with an excessively hard and desirable surface for resisting wear, retaining ductile metal underneath with sufficient strength and shock-resisting properties to stand up to severe duty.
As is well known, most carburizing is done by the time-honored method of packing the steel with carbonaceous materials in suitable containers, covering it in such a way as to prevent infiltration of furnace gases, then raising the temperature to a suitably high point, and holding it there for some hours, depending upon the depth and character of case desired. Carburizing by this means is dependent on a number of factors, many of which arise from the character and uniformity of the compound; great care must therefore be vised in handling the compound to obtain satisfactory results. At best, there are still many variables that are hard to control and results that are difficult to explain. It has been felt for many years that this metallurgical process is too cumbersome and dirty to fit in well with modern manufacturing practice. To those who have studied the matter, it seemed that the desired improvement could be had in a process for carburizing with an externally prepared gaseous atmosphere. Such an atmosphere could be clean, of uniform composition, easily controlled, always fresh and theoretically desirable.
