- Corrosion Experts
- Technical Groups
With the Delhi Pillar (Delhi, India), improved corrosion resistance was achieved through alloy additions to the iron, but this was the result of luck with the ore used. It was not until the late Victorian era that scientific investigations produced the precursors to the modern corrosion-resistant steels in use today. The discovery in 1882 of Hadfield’s manganese steel with its remarkable wear-resisting properties probably started serious investigations into means of making major improvements in steel properties by controlled additions of alloys. However, attempts at improving the corrosion resistance of steel had commenced early in the 19th century. Michael Faraday carried out experiments alloying iron with noble metals such as platinum, although the results were disappointing.
Harry Brearley in Sheffield, United Kingdom is often considered to be the inventor of stainless steel (SS), but in fact there were important discoveries made before he prepared the first martensitic stainless in 1913. In 1911, Monnartz and Borchers in Germany discovered three important facts regarding SS. First, the correlation between chromium content and corrosion resistance; second, that a significant boost in corrosion resistance is achieved when the chromium content exceeds 10.5%; and finally, that molybdenum can have an important influence on corrosion resistance. Monnartz is also the first to use the term “passivity” to describe the improvement in corrosion resistance. Concurrently, Eduard Maurer and Benno Strauss at the Krupp works in Germany alloyed steel with both chromium and nickel to produce the first austenitic SS. However, it was Brearley who recognized the commercial significance of SS and developed the large-scale production of the metal, initially for cutlery. In the early 1920s, a whole variety of chromium and nickel combinations were tried, with the best known being the 18/8 or 304 SS (18% chromium, 8% nickel). The addition of nickel produced a SS that was more ductile, and more resistant to acid.
Most of the standard grades produced in these early years are still in use today. The first major use of SS in architecture, an example that arguably has not been surpassed, is the Chrysler Building, erected in New York City (New York, USA) in 1930. Walter Chrysler engaged architect William Van Alen to design the tallest building in the world, and at the same time produce a building that would promote his automobiles. A Krupp version of 18/8 stainless known as “Nirosta” was selected as the cladding metal. The gargoyles are supposed to represent Chrysler hood ornaments. The stainless-clad radiating arched crown in a sunburst pattern is the most impressive feature of the Art Deco masterpiece. When the spire was added in 1930, it was the tallest building in the world, but less than a year later it was overtaken by the nearby Empire State Building. The building was declared a National Historic Landmark in 1976, and is often first in polls of architects, engineers, historians, and builders as their favorite building in New York.
A committee was set up to inspect the condition of the building every five years as there was an obvious interest in the durability of SS in architectural applications. This committee was disbanded in 1960 because there had been virtually no deterioration of the panels. The top of the building has been cleaned manually only twice, in 1961 and 1995. During the 1995 cleaning, some dents and cracks were observed and repaired, and superficial pitting near an incinerator vent was detected. But the condition of the stainless was found to be excellent, looking like it had just been installed. As one commentator has noted, “With its stainless steel crown gleaming in the sun … the Chrysler building always looks like the future.”
Alloying to make steel corrosionresistant was effective, but most applications required something much cheaper. Therefore, putting a barrier between the steel and its environment, a protective coating, has become the single most important means for preventing corrosion. And, as we shall see next month, the most effective way is to apply a thin layer of zinc to the steel.