José Apraiz Barreiro’s Tratamientos Térmicos de los Aceros is arguably the most authoritative Spanish-language reference on ferrous metallurgy and thermal processing. First published in the mid-20th century and revised multiple times, it remains a cornerstone for engineers, metallurgists, and technicians. This article distills its core principles, methods, and practical wisdom.
A major section of the book covers diffusion-based treatments that harden only the surface while leaving a tough core:
| Process | Diffusing element | Temperature | Case depth | Hardness after quench | Common applications | |---------|------------------|-------------|------------|----------------------|---------------------| | Carburizing (Cementación) | Carbon | 900–950°C | 0.5–2.5 mm | 58–62 HRC | Gears, cams, shafts | | Nitriding (Nitruración) | Nitrogen | 500–550°C | 0.1–0.6 mm | 60–70 HRC (no quench) | Cylinder liners, injectors | | Carbonitriding | C + N | 750–880°C | 0.1–0.8 mm | 58–63 HRC | Small precision parts | | Induction/Flame hardening | None (local heating + quench) | Surface melting point | 1–10 mm | 50–60 HRC | Rail heads, rolls |
Apraiz emphasizes that nitriding produces the highest surface hardness without subsequent quenching, but requires alloying elements (Al, Cr, Mo, V) to form stable nitrides.
Templado: Consiste en calentar el acero a una temperatura crítica y luego enfriarlo rápidamente (templar) en agua, aceite o aire forzado para obtener una microestructura dura y resistente al desgaste.
Revenido: Después del templado, el acero suele ser muy duro pero también muy frágil. El revenido implica calentar el acero templado a una temperatura por debajo de la crítica para reducir la dureza y aumentar la tenacidad. Deep Article: Heat Treatment of Steels – A
Normalización: El acero se calienta a una temperatura crítica y luego se enfría en aire tranquilo. Este proceso refina la estructura del grano y homogeneiza las propiedades mecánicas.
Recocido: El acero se calienta a una temperatura específica y luego se enfría lentamente. Este tratamiento reduce la dureza y aumenta la ductilidad, facilitando el mecanizado.
Endurecimiento por precipitación: Algunos aceros se endurecen mediante un tratamiento térmico que provoca la precipitación de partículas finas dentro de la microestructura.
Although digital simulation and vacuum furnaces have advanced since Apraiz’s early editions, his systematic, empirical approach remains invaluable. The book’s strength lies in:
Modern heat treaters still use Apraiz to diagnose quench cracks, select tempering colors, and avoid embrittlement. It is the Spanish-language equivalent of Grossmann’s Principles of Heat Treatment or ASM Handbooks. Templado : Consiste en calentar el acero a
The book includes an exhaustive list of real-world failures:
Testing methods covered: Hardness (Rockwell, Brinell, Vickers), microhardness (for case depth), tensile, impact (Charpy), metallographic microscopy, and Jominy test.
"I work in a heat treatment plant in Monterrey, Mexico. We have a tattered physical copy of Apraiz Barreiro in the break room. But I downloaded a best PDF version on my phone. Last week, I looked up how to avoid soft spots on a large gear. The solution was to increase agitation during oil quenching. That saved us a $5,000 part."
— Carlos M., Heat Treat Supervisor
"As a student in Spain, I couldn’t afford the 150€ physical book. A colleague shared a PDF. But it was an awful scan. I spent 10 hours cleaning it, adding bookmarks, and OCR. That’s now the ‘best’ version in my university. Everyone asks for the Apraiz Barreiro PDF from me."
— Elena G., Master’s in Materials Engineering
Apraiz Barreiro begins by establishing that the properties of steel (hardness, strength, ductility, toughness) are not intrinsic solely to its chemical composition but are determined by its microstructure. Heat treatment consists of controlled heating and cooling cycles to induce phase transformations. Revenido : Después del templado, el acero suele
Not all PDFs are created equal. When searching for the best digital copy of Apraiz Barreiro’s work, users encounter several versions:
| Quality Type | Characteristics | Best For | | :--- | :--- | :--- | | Poor (OCR scan) | Blurry images, missing tables, garbled text | Nothing – causes frustration | | Good (clean scan) | Legible text, complete pages, some margin notes | Reading on tablets | | Best (searchable OCR + bookmarks) | Fully searchable, interactive table of contents, high resolution figures | Professionals and students |
The best version allows you to:
Many users report that old library scans from the 1980s are difficult to read because the iron-carbon diagrams are nearly invisible. A high-quality, professionally digitized version is worth its weight in metallurgical gold.