An 80-Year Legacy of Thermal Processing
An article entitled “Notes on the Evolution of Ferrous Metallurgy,” by Dr. Allan Bates in the October 1938 issue, gives us some insight into the early days of thermal-processing history. Actual excerpts follow:
“In the present sense of the term, the ‘steel industry’ began around the 1870s. Of metallurgical science there was likewise essentially none previous to that day. None was possible until the modern science of chemistry came into existence in the early decades of the 19th century. Quickly thereafter, chemical analysis became an important laboratory activity, and, by 1870, the major chemical components of cast iron and steel were generally recognized. It was realized that carbon was the somewhat inconsistent heroine of the play, phosphorus and sulfur the villains, silicon and manganese controlled the action, and oxygen furnished the suspense – all these working in complicated unison to develop the character of the hero, iron.
“It is almost a rule that advances in scientific thought originate in the development of new tools or technique of investigation. This has been the case with metallurgy. In 1863, the microscope was first used in the study of metals by an English geologist, who, when he turned his microscope on a piece of soft annealed steel, found a fascinating crystal structure. And when he looked at hard steel he still saw only crystals: hot-forged steel, cold-hammered steel, cast steel and iron, wrought iron, steel low and high in carbon – all were composed of crystals. This is possibly the first point in our pattern of fundamental concepts: all solid metals and alloys are crystalline and, after any given treatment, owe their engineering properties primarily to the nature and distribution of the crystals produced by that treatment.
“These, then, are the three basic points in the pattern of concept and fact, which today provide the metallurgist with some confidence in his prescriptions for steel treatment:
1. The laws of crystal formation, structure and properties
2. Constitutional relationships as expressed in the equilibrium diagram
3. Rates of crystal transformation as described by reaction rate curves.”
History RevisitedAround the turn of the 20th century, Andrew Carnegie sold out to J.P. Morgan, creating U.S. Steel Corp. The aircraft industry was born in 1903 when the Wright brothers made their historic first powered flight in Kitty Hawk, N.C. Heat-treatment studies in steel were well under way by the turn of the century, and a trend of specialized processing was beginning. Processes such as carburizing and nitriding were well known, and advances in equipment and processing were being made regularly.
World War IThe following decade of the 1910s brought more developments, such as the use of X-ray diffraction for determination of crystal structure in 1912. Also significant during this time was the development, at Princeton University, of the induction-melting process in 1915. As we see from the pages of Industrial Heating throughout the years, events of the time impacted technology and the economy.
The Roaring TwentiesFollowing WWI, the 1920s began with a renewed hope and enthusiasm for technological development but ended with a depression that would last many years. In 1923, Prof. Willibald Trinks of the Carnegie Institute of Technology published his book Industrial Furnaces, bringing much attention to the industrial heating industry. In 1924, a new electric vacuum furnace was reported to be the first furnace to combine high temperature and high vacuum with accurate temperature readings via an optical pyrometer.
Industrial Heating’s predecessor, Fuels & Furnaces, with Trinks as its technical advisor, began to document the details of many of these developments during this decade. From this point forward, we were a part of the history.
It's DepressingThe decade of the 1930s resulted in significant technological advances in spite of the economic disadvantages. The growth of the automotive and aircraft industries led to advancements such as the installation of the largest continuous electric roller-hearth furnace in the world (at that time), measuring 325 feet long for bright normalizing of automotive body stock. Centrifugal casting and infrared heating were also being utilized by the auto industry. The development of “superalloys” that began during this period was prompted by the need to improve the temperature capabilities of materials used in aircraft-engine turbosuperchargers and, subsequently, gas turbine engines for jet aircraft.
American metallurgists Bain and Davenport described the solid reaction rate curve (so-called “S-curve”) of high-carbon steel in 1930 following long, patient experimentation. Some of this experimentation was documented in the pages of Industrial Heating.
In the 1930s, Guinier and Preston verified the theories involving the precipitation hardening of aluminum alloys by discovering “GP zones” in aluminum-copper alloys using X-ray diffraction. Induction heat treating would see its first commercial application at the Packard Motor Car Co. to harden crankshafts used in the car company’s 1937 engine. Also proposed during this time was the use of optical pyrometers to measure temperature in rapidly moving objects such as sheets, rails, bars, billets, etc.
Two interesting and significant contributions to the thermal-processing industry were made in the late 1930s. The first “integrated” atmosphere furnace system was introduced, and, in 1939, a “vacuum electron bombardment” furnace would be introduced to Industrial Heating readers by Asst. Prof. Ralph Hultgren of Harvard University. Although this type of furnace had been used previously by physicists for the evaporation of thin films, this unit was reported to be the first of its type used for melting of high-temperature refractory alloys.
World War IIBy the start of World War II, many automated continuous electric furnaces with accurate time and temperature control were available in mesh-belt conveyor, plate conveyor, roller hearth, pusher, rotary hearth, monorail conveyor and rotary-drum types, with ratings varying from a few kilowatts to 2,000 kilowatts. New fibrous ceramic products such as board and blanket were being introduced as a more convenient form of insulation for industrial furnaces.
Massive heat-treating facilities were being installed and upgraded to meet production demands. It was during this decade that another interesting metallurgical event would occur, resulting in significant changes in the alloying and processing of steel. It was found that many ship hulls would fracture at weld seams when exposed to the frigid waters of the north Atlantic. Several ships literally broke in half while sitting at their docks. Post-war investigations soon led to the discovery of the ductile-to-brittle transition temperature of steel, improved welding methods and the development of fracture mechanics as an engineering science.
Happy DaysAround 1950, the first commercial mill products of titanium were being produced by the Titanium Metals Company of America. As the decade progressed, new steels and superalloys were constantly being developed, titanium was being utilized more frequently due to its high specific strength and corrosion resistance, and scientific investigations into intermetallic compounds such as nickel-aluminide began due to their potential for use in high-temperature applications. Electron-beam melting gained attention as a viable method for commercial production of specialty alloys.
With regard to the processing of steel and high-temperature alloys, two other significant events occurred in 1952. Vacuum arc remelting (VAR) was introduced, and the process is still recognized as one of the most important developments in the history of thermal processing. This same year, the basic oxygen process (BOP) of steelmaking was introduced at a plant in Donawitz, Austria. It’s interesting that a German “VAR” process was described in a 1930 edition of F&F – over 20 years earlier!
The Cold WarThe 1960s began with an air of apprehension. Russia and the U.S. were clearly driving aerospace technology to new levels with the rapid expansion of their space programs. By the end of the decade, man had landed on the Moon, and the pages of Industrial Heating were filled with articles relating to new materials and their applications in the aerospace industry.
With the rapid development of new materials, the thermal-processing industry took on new challenges in designing specialized heating systems. Oxide dispersion-strengthened alloys produced via powder-metallurgy (PM) technology began to attract attention for their potential as high-temperature structural materials, although publicity far outweighed actual utilization. In 1960, metal-bonded graphite was first reported to have potential as a dry-lubricated bearing material.
By the end of the decade, vacuum oil-quenching furnaces were being used commercially, and improvements in vacuum-coating and brazing processes were also being made. Computers also were beginning to play an important role in the thermal-processing industry.
Peace & LoveThe outgrowth of technology from the 1950s and 1960s resulted in many new concepts being implemented in the 1970s. By 1974, laser systems were being applied to surface hardening, welding and cutting operations. Solid-state induction-heating units and control systems entered the market to gain more control over furnace behavior during operation, and materials with higher-temperature capabilities were utilized to improve thermal efficiency. Ceramic-fiber modules became more common as an improved insulation product for industrial furnaces.
With energy conservation and rising utility costs becoming more important issues, the thermal-processing industry began to shift its focus slightly from designing new exotic pieces of equipment to improving the efficiency of existing systems. The fuel efficiency of combustion burners was receiving attention with work being done in control of excess air, flue-gas recuperation and oxygen enrichment.
In the PM field, hot isostatic pressing (HIP) became viable as a commercial process used to improve the properties of PM and cast materials. By the 1980s, the HIP process would be a standard requirement for PM and cast parts used in the aerospace industry.
The Disco EraThe introduction of personal computers in the late 1970s, and in particular the IBM Personal Computer in 1981, would begin to revolutionize the controls market in the early part of the decade. Computer-aided design (CAD) systems for the design of engineering production furnaces were becoming more common. Fiber optics began to appear in instrumentation such as infrared pyrometers and other line-of-sight instruments. In the area of sensors, oxygen probes began to appear for atmosphere monitoring in both research and production environments.
In vacuum processing, liquid-phase vacuum sintering followed by forging or HIPing was examined as a method to increase the density of PM parts. Interest in single- and multi-chamber vacuum furnaces with rapid gas-quenching capabilities was increasing as manufacturers looked for ways to harden tool steels without oil quenching and produce cleaner products. Ion nitriding, plasma carburizing and vacuum carburizing were gaining more acceptance as surface-treatment processes.
In other fields, rotating-electrode and plasma rotating-electrode processes were being used to produce high-quality powders from high-temperature exotic alloys. Improved brazing techniques were being examined for joining of dissimilar metals such as wrought aluminum to cast aluminum and titanium to stainless steel. Near-net-shape processing methods such as isothermal forging and hot-die forging were being implemented more readily based on cost effectiveness as compared to conventional hammer-press die forging. Advances in magnetic-field concentrators were made with the introduction of magnetodielectric materials as an alternative to laminations and carbonyl iron-powder materials.
Last Decade of the 20th CenturyDuring the decade of the 1990s, the thermal-processing industry was driven by the need to reduce costs and increase productivity while improving quality. The most significant advances in thermal processing occurred in the areas of process control, instrumentation and computer modeling. The implementation of Total Quality Management systems and quality certification programs required industrial heating equipment manufacturers to focus on more sophisticated control systems capable of programming, controlling, monitoring and re-cording furnace parameters during operation. In addition, automated furnace systems were integrated directly into production lines to accommodate “just-in-time” manufacturing philosophies.
Environmental and safety issues also influenced the design of thermal-processing systems. Quenchants and quenching systems received more attention in an effort to reduce the industry’s reliance on oil-based quenching processes. Water-based polymer quenchants and high-pressure gas-quenching systems were applied more frequently as environmentally friendly methods. The emission of combustion products such as SO2, CO2, CO and NOx also received more attention as burner manufacturers focused on improving combustion efficiency and developing low-NOx and other “low-emission” burners.
A New CenturyThe first decade of the 2000s brought an incorporation of more of the developed technologies as ROI improved and replacement equipment was needed. The focus was still on energy savings, and recuperative and regenerative burners became more common. Insulation options, such as microporous material, were incorporated as standard practice for new furnace systems and rebuilds. Vacuum carburizing incorporating high-pressure gas quenching (LPC + HPGQ) benefitted from its continuous improvement and became a more commonly used process.
Instrumentation might have been the biggest development in the past decade. Requirements such as Nadcap and CQI-9 imposed documentation that was most easily accomplished using paperless systems. Chart recorders continued to go the way of the buggy whip, and people also began incorporating some form of wireless technology, which continues to develop. Process modeling has also become more integrated with furnace control systems. These developments will help manufacturers decrease costs and increase productivity.