Midcentury-Modern Heat Treatment
This article summarizes heat treatment history from 1950 to the 1990s.
Around 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 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.
The 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 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.
During 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 recording 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.