The Science of Heat Treatment for High Grades Fasteners
In the world of high-performance machinery and fasteners, “Quenching and Tempering” (often abbreviated as Q&T) is the gold standard for heat treatment. It is not a single step, but a dual-process combination designed to achieve the perfect balance of strength and toughness.
- Step 1: Quenching & The Role of “Neutral Hardening”
- Step 2: High-Temperature Tempering
- Why Choose Q&T Over Basic Hardening?
The Formula:
Quenching + High-Temperature Tempering = Q&T (Tempered Sorbitite Structure)
Result:
The resulting structure is called tempered sorbite, which is the ultimate goal of “tempering”—both strong and tough.
Step 1: Quenching & The Role of “Neutral Hardening”
Quenching involves heating the steel above its critical temperature (Austenitizing) and then cooling it rapidly in oil or water.
The Goal: To transform the internal structure into Martensite, which is extremely hard.
Quenching is divided into ordinary hardening and neutral hardening：
Normal quenching:
As long as it is cooled after heating, it counts, regardless of whether the surface carbon is lost or not.
Neutral hardening:
Quenching performed without altering the surface composition
When we talk about Neutral Hardening, we are referring to the quality of the heating environment-
By using a protective atmosphere, we ensure the steel surface neither loses carbon (Decarburization) nor gains carbon (Carburization). The fastener maintains consistent hardness from the very surface to the core.
Step 2: High-Temperature Tempering
As-quenched steel is “brittle like glass.” It contains massive internal stresses and can snap under the slightest impact.
The Process: Reheating the quenched part to 500°C – 650°C.
The Transformation: This step converts brittle Martensite into Tempered Sorbitite.
The Result: The part retains high tensile strength but gains the “give” or ductility needed to absorb energy without catastrophic failure.
Why Choose Q&T Over Basic Hardening?
Many buyers mistake “hardness” for “quality.” However, a part that is simply hardened (without proper tempering) is a liability.
- Safety: Q&T parts will bend before they break, providing a safety margin in structural applications.
- Fatigue Life: The uniform structure of Tempered Sorbitite significantly extends the service life of bolts and shafts under vibrating loads.
At Shanghai Screwtool, we prioritize standard Q&T for all Grade 8.8, 10.9, and 12.9 fasteners to ensure reliability in every thread. If you have fastener issue and require certain solution, welcom to contact by info@shscrewtool.com.
