Here are my favorite steels to use in the shop that aren’t mild steel. This list and the uses I have listed are just how I use them. This by no means limits what these steels are good for.
S7 Tool Steel
Type: Shock-resisting tool steel (air hardening)
Typical Process Steps: Annealing → Preheat → Austenitizing (hardening) → Quench → Tempering (usually multiple cycles)
Heat Treatment Guidelines:
- Annealing (soften for machining): Heat to ~1500–1550°F (815–845°C), hold, then furnace-cool slowly.
- Preheating: ~1200°F (650°C) before hardening; hold to equalize temperature.
- Austenitizing (Hardening): ≈1725°F (940°C), hold ~1 hr/inch of thickness.
- Quenching: Air quench (still air) for most sections; larger sections may use interrupted oil to increase cooling rate.
- Tempering: Two cycles commonly at ~400–450°F (204–232°C) to reach desired balance of hardness and toughness; hold ~2 hrs/in.
Notes: S7 air hardens with reduced distortion compared with oil-quenched steels. S7 is my go to for punches and top tools.
4140 Steel
Type: Medium-alloy Cr-Mo steel, widely used as heat-treatable structural steel rather than a high-end tool steel
Typical Process Steps: Normalize (optional) → Austenitize → Quench → Temper
Heat Treatment Guidelines:
- Austenitizing (Hardening): ~1550–1600°F (845–870°C).
- Quench: Oil is common to achieve martensitic transformation.
- Tempering: Varies widely (≈200–650°C; ~400–1200°F) depending on the required toughness/hardness.
Notes: 4140 is often normalized first to refine grain, then hardened and tempered. It is not typically “tool steel” by classification but is heat-treatable. 4140 is my go too for hammers and top tools. it’s also a good choice for making hooks and other load bearing items.
440C Stainless Steel
Type: Martensitic stainless tool steel (high-carbon, high-chromium)
Typical Process Steps: Anneal → Preheat → Austenitize → Quench → Temper
Heat Treatment Guidelines:
- Annealing (soften for machining): ≈1560–1650°F (850–900°C), furnace cool.
- Preheating: ~1425°F (775°C) before austenitize recommended for larger parts.
- Austenitizing (Hardening): ≈1850–1950°F (1010–1066°C).
- Quench: Oil quench or air cool to ~125–150°F (50–65°C).
- Tempering: Often twice at ~300–500°F (149–260°C) to achieve a range of hardness (e.g., ~56–60 HRC).
Notes: Tempering above ~425°C (~800°F) can reduce impact strength and corrosion resistance; cryogenic treatment can reduce retained austenite before tempering. This is my main choice for kitchen knives as it’s dishwasher safe.
5160 Steel (Spring Steel)
Type: High-carbon chromium spring steel
Typical Process Steps: (Optional Normalize) → Austenitize → Oil Quench → Temper
Heat Treatment Guidelines:
- Austenitizing (Hardening): ~1500–1525°F (815–830°C).
- Quench: Oil quench (medium oil).
- Tempering: Typically two cycles at ~350–400°F (175–205°C) to reduce brittleness and achieve ~58–61 HRC in many applications.
Notes: Normalizing before hardening is a common optional step to refine grain and relieve stress. This is the most common type of steel in coil spring found in scrap yards, it’s also a common steel in leaf springs. This is my go too steel for things like pry bars and other tools that need some flex in them.
D2 Tool Steel
Type: High-carbon, high-chromium air-hardening tool steel
Typical Process Steps: Annealing → Preheat → Austenitize → Air Quench → Temper (often multiple cycles)
Heat Treatment Guidelines:
- Annealing: ~1200–1250°F (650–677°C) slow cool (or slower anneal at ~850°C).
- Preheating: ~1200–1250°F (650–677°C) before austenitizing.
- Austenitizing (Hardening): ≈1796–1877°F (980–1025°C).
- Quench: Air quench is typical, though larger sections may be oil or salt bath quenched to complete transformation.
- Tempering: Often double or triple tempers Hold for 2 hours per temper (e.g., ~200–500°F / ~150–260°C), 60-62 HRC
Notes: D2 is known for high wear resistance and minimal distortion due to air-hardening. Great for punches to work cold or hot.