Corrosion-Resisting Ferrous Alloy, James A. Parsons, Jr., Patent No. 2,200,208
The patent by James A. Parsons, Jr. of Dayton, Ohio, assignor to The Duriron Company, Inc., describes a Corrosion-Resisting Ferrous Alloy (Patent No. 2,200,208), filed in 1935 and granted in 1940. This invention is a high-performance austenitic stainless steel—specifically a precursor to the famous Durimet 20 (now known as Alloy 20)—engineered to withstand the most drastic corrosive agents, such as hot sulfuric acid, while maintaining superior casting and hot-working properties.
The “Why”
In the mid-1930s, the chemical processing industry faced a severe pain point: alloys that were resistant to acid were notoriously difficult to manufacture. They often suffered from “hot shortness” (becoming brittle and cracking when forged) or produced “leaky” castings that failed under hydrostatic pressure. Furthermore, traditional alloys often lost over 50% of their material during rolling and forging due to waste. Parsons sought to create a “fortified” steel that was both chemically invincible and industrially “workable.”
Inventor Section: Engineering Philosophy
James A. Parsons, Jr. was a pathbreaking Black scientist and metallurgist who directed the research laboratory at Duriron. His engineering philosophy was rooted in elemental synergy and precision ratios. Parsons did not just add ingredients to a melt; he studied how elements like molybdenum and silicon interacted at the grain boundary. Operating at a time when industrial leadership was rarely open to African Americans, Parsons’ technical mastery was so undeniable that his alloy became the gold standard for the defense and chemical industries during World War II and beyond.
Key Systems Section
1. The Molybdenum-to-Silicon “Workability” Ratio
The core of Parsons’ discovery is a strict ratio between these two fortifying elements.
- Mechanical Principle: Parsons found that to prevent brittleness, the percentage of molybdenum (Mo) must always be substantially greater than that of silicon (Si)—ideally twice as great.
- Function: This ratio suppresses the precipitation of “ferrite” on the crystallographic planes, ensuring a homogeneous microstructure that can be bent cold without cracking.
2. Copper Fortification (The Sulfuric Defense)
Copper is the key to resisting sulfuric acid, but it normally makes steel impossible to forge.
- The Solution: By balancing the nickel content (at least 20% to 40%) and keeping carbon extremely low, Parsons “unlocked” the ability to use high copper levels (up to 5%).
- Modern Term: This is a high-nickel “super-alloy” technique that prevents “intercrystalline corrosion”—the “eating away” of the metal from the inside out.
3. Low-Carbon “Intergranular” Protection
Parsons pushed for carbon levels as low as 0.04% to 0.07%.
- Engineering Insight: High carbon leads to the formation of insoluble carbides at the grain boundaries. By keeping carbon near zero, Parsons ensured that the chromium remained distributed throughout the metal rather than “clumping,” which would leave “soft spots” for acid to attack.
4. Casting & Forging Yield Optimization
Standard alloys of the time had a 50% waste rate during fabrication.
- The Result: Parsons’ alloy achieved significantly higher yields because it was not “hot short.” This meant pump and valve parts could be cast thinner and lighter without the risk of porosity or “double-wall” effects (coring).
Comparison Table: Standard 1930s Stainless vs. Parsons’ Alloy
| Feature | Prior High-Cr/Ni Steels | The Parsons Alloy (Alloy 20 precursor) |
| Copper Content | Max 0.3% (due to brittleness). | Up to 5.0% (for max acid resistance). |
| Forging Yield | Less than 50% (high waste). | Far higher yield (economic fabrication). |
| Sulfuric Acid Resistance | Moderate/Low. | Extremely High (across all temps). |
| Ductility | Fails cold bend tests. | Withstands 90° to 180° cold bend. |
| Microstructure | Ferrite precipitation (brittle). | Homogeneous (stable austenite). |
Significance
James A. Parsons, Jr.’s work is a cornerstone of modern Materials Science:
- The “Alloy 20” Standard: This patent provided the chemical blueprint for what is now widely known as Alloy 20, a staple in the pharmaceutical, food, and nuclear industries.
- Industrial Workability: He proved that “extreme” chemical resistance did not have to come at the cost of manufacturing ease, revolutionizing the production of high-pressure valves.
- Black Excellence in STEM: Parsons’ legacy as a lead metallurgist and department head during the Jim Crow era remains one of the most significant achievements in American industrial history.
