1. The Nightmare: "It just snapped!"
Imagine this scenario: You bought high-quality S45C (AISI 1045) bars. You machined them into shafts and heat-treated them to make them hard.
But the next day, you find tiny cracks on the surface, or worse—the shaft snaps in half during assembly. Is the steel bad?
Probably not. In 90% of cases, the culprit is not the steel, but the "Cooling Method."
2. The Invisible Killer: Quenching Cracks
S45C contains 0.45% Carbon. When you heat it to 850°C and dip it into cold water (Quenching), the steel structure changes instantly to become hard (Martensite).
Water cools the steel too fast. The outside cools down while the inside is still hot. This creates massive internal stress, causing the steel to tear itself apart. This is called a "Quenching Crack."
3. How to Prevent Cracking (3 Tips)
Hardened steel is like glass—hard but brittle. You MUST reheat it to roughly 150°C~200°C (Tempering) immediately after quenching. This relieves the stress and gives the steel "toughness."
Stop using pure water. S45C is often called a "Water Hardening Steel," but for complex shapes, water is too aggressive. Use Polymer Quenchant or Oil to cool it down more gently.
Sharp corners concentrate stress. Add a Radius (Round Corner) to your shaft design. Sharp edges are where cracks always start.
If your S45C shafts keep cracking even with oil quenching, it's time to stop using S45C.
You need a better material: SCM440 (Chrome Moly Steel).
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NEXT STRATEGIC STEP ➤
[Machine #2] S45C vs SCM440: Smart Buyer's Guide
"S45C failed? Learn why SCM440 is the ultimate upgrade for heavy-duty shafts."