Cracks Appearing After Forging
Cracks that show up after a forging session — or ambush you during grinding — almost always trace back to temperature: steel worked too cold, corners burned too hot, or stress never relieved before the bar cooled. Here is how to find them, judge them, and stop making them.
Symptom
Visible cracks at bar edges, corners, or mid-face after forging; hairlines that appear as grinding progresses; or cracks that reveal themselves violently at the quench. Ends and corners are the most common sites.
Likely Causes
Forging below dull red (the number-one cause u2014 cold steel tears instead of flowing). Burnt spots from welding-heat corners (steel that sparkled in the fire is dead). Accumulated forging stress never relieved by normalizing. Drastic cooling (hot bar on cold concrete or an impatient dunk). Or the steel itself u2014 mystery scrap with fatigue history.
Quick Checks
Grind a clean window and etch it u2014 cracks show as sharp dark lines. Wipe with penetrating oil, wipe dry, and watch the crack weep it back out. A file dragged across a suspect line catches on a real crack. When in doubt, snap-test a coupon from the same bar and read the grain.
Fixes
End and corner checks: cut back to sound steel and continue u2014 this is routine, not failure. Cracks in the intended blade body: scrap it honestly. There is no fix that makes cracked steel trustworthy; steel is cheap and your name is not.
Prevention
Stop hammering at dull red, always. Watch corners and thin sections at high heat u2014 they overheat first. Normalize with descending thermal cycles after forging, cool in still air, and start from known steel. Most crack problems are the same three habits wearing different disguises.
When to Stop and Get Help
Any crack that survives grinding into the final blade envelope ends the blade u2014 and remember the quench multiplies whatever cracks you carry into it. Cut back or start over before heat treat, never after.