Tempering Color Calculator

For 1084, O1, and W1, no -- those three share a Target-Use-driven temperature (Knife/Cutting Edge always tempers at 400°F regardless of which of those three you pick). 5160 Spring Steel is different: its Spring/Flex Tool temperature is 850°F (verified real spring-tempering practice, not the generic 500°F baseline) and its Knife/Cutting Edge temperature is 400°F but yields a much smaller hardness drop, since published 5160 blade-tempering data shows it barely loses hardness at that temperature compared to the other three steels.

Target Use has the larger swing once 5160's real tempering behavior is accounted for: the hardness drop from tempering now ranges from 1 point (5160 at a knife-blade temper) up to 14 points (5160 at a genuine spring temper) depending on Target Use, a wider effective swing than the as-quenched starting hardness spread across the four steels (60 to 66 HRC, 6 points). Both matter, but Target Use edges it out once steel-specific tempering response is modeled honestly.

Because the two uses want opposite trade-offs from the same steel. A genuine leaf or coil spring needs to survive millions of flex cycles without permanent set, so it is tempered hot (around 800°F) to sacrifice a large amount of hardness -- down to roughly 46-48 HRC -- in exchange for the ductility and fatigue resistance a spring needs. A 5160 knife blade instead wants to hold onto as much edge hardness as practical while still gaining toughness over the as-quenched state, so bladesmiths temper it much cooler, around 400°F, for roughly 58.5-59.5 HRC. Applying the spring temperature to a blade, or the blade temperature to a spring, would leave either one poorly suited to its job.

Because springs need more toughness and flex resistance than raw edge hardness, so this calculator tempers Spring/Flex Tool at a higher 500°F than Knife/Cutting Edge's 400°F -- the higher temperature trades away more hardness (a 10-point HRC drop versus 5 points) in exchange for the flexibility a spring needs to survive repeated bending.

Treat it as a rough field reference, not a substitute for measured temperature. Oxide color depends on more than just heat -- ambient lighting, how clean and polished the steel's surface is, and the specific alloy's composition all shift how a given temperature actually appears, so two blacksmiths tempering the same steel at the same temperature can disagree on what color they're looking at.