About 4140H|4140 with guaranteed hardenability band. Same relationship to 4140 as
4340H has to
4340. The 'H' designation means the steel meets a Jominy hardenability range per ASTM A304, giving engineers confidence that heat treatment will produce predictable results across different heats of steel. In practice, most 4140 from reputable mills will meet the H band anyway, but the certification matters for aerospace, oil and gas, and any application with a formal material spec. If your customer's drawing says 4140H, don't substitute standard 4140 without approval. Machines identically to regular 4140. Compare to 4140 (same material, less guaranteed hardenability) and 4340H (when you need more toughness or thicker section hardenability).
