Barreiro dedicates the initial chapters to the fundamental question: Why does heat change steel? He provides a clear, diagram-heavy explanation of the Iron-Carbon equilibrium diagram. He explains the critical temperatures (A1, A3, Acm) and the structural components: Ferrite, Austenite, Cementite, and Pearlite. Unlike dry physics texts, Barreiro connects these phases directly to machinability and toughness.
If you manage to locate the file (often a scanned PDF with handwritten notes from previous owners), here is the intellectual journey you will undertake.
A significant portion of the PDF covers treatments that change the surface chemistry, not just the structure:
In a famous chapter, Barreiro argues that water is for "savage" quenching (plain carbon steels) and oil is for "noble" quenching (alloy steels). He provides a specific pearl because many shops use water on oil-hardening steel to save money on quench oil. The result? Cracking. The PDF contains a stress chart showing that water quenching on a 4140-type steel creates tensile stresses 300% higher than oil quenching. Barreiro dedicates the initial chapters to the fundamental
While it is easy to find a scanned copy on academic sharing sites or forums, note that copyright status varies by country. If you are a student, check:
If you use a shared PDF, acknowledge Apraiz Barreiro’s legacy. Do not sell it; share the knowledge freely, as he intended to educate the industrial base.
Barreiro emphasizes that heat treatment is controlled by three variables: Temperature, Time, and Cooling rate. He provides a simple equation of thumb: Hardenability = (Temperature above A3) x (Soaking time) / (Section thickness). He warns that most failures occur because the operator increases temperature to "speed up" the soak time, which leads to grain growth and cracking. If you use a shared PDF, acknowledge Apraiz
Subject: 🛑 STOP struggling with TTT curves! Here is the ultimate resource.
If you are studying Materials Science or Metallurgy, you know how confusing heat treatment diagrams can be. If you haven't checked out "Tratamientos Térmicos de los Aceros" by José Apraiz Barreiro, you are missing out on the best explained resource in Spanish.
Here is what makes it a lifesaver for exams and projects: For the toolmaker
✅ Crystal Clear Diagrams: The book contains detailed Isothermal Transformation (TTT) and Continuous Cooling (CCT) diagrams that are easier to interpret than many modern handbooks. ✅ Process Breakdown: It separates processes clearly: Annealing, Normalizing, Hardening (Quenching), and Tempering. ✅ Steel Selection: It helps you understand which steel to choose based on the final hardness and toughness required.
It is dense, but it is the kind of book you keep on your desk, not on the shelf.
Pro Tip: Pay special attention to the chapters on the "Jominy test" – the explanation there is worth the price of the book alone!
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For the toolmaker, Barreiro provides a color-temperature chart for tempering based on oxide layer formation (straw, brown, purple, blue). He notes that a straw color (230°C) is for shears and lathe tools, while a blue color (300°C) is for springs and wrenches. This visual guide, easily printed from the PDF, is often taped to the side of toolshop ovens.