Live Hardness Converter
Type a value into any field and all other scales update instantly. Or click any row in the table below to load those values here.
ⓘ Values are approximate equivalents for carbon and alloy steel per BS EN ISO 18265:2013. Always verify with direct measurement for critical applications. HRB scale is only reliable below approx. 20 HRC / 240 HV.
Full Conversion Table
Click any row to load its values into the live converter above. Sortable by any column. 39 data points from dead-soft annealed to maximum tool steel hardness. All values per BS EN ISO 18265:2013.
| HRC ↕ | HRB ↕ | HV ↕ | HB ↕ | Tensile N/mm² ↕ | Range | Typical Grade / Condition | Data Sheet |
|---|
Heat Treatment Processes
Heat treatment alters the microstructure of steel to achieve specific mechanical properties without changing its chemical composition. The six principal processes used in engineering steel are covered below.
Annealing
650–900°C — slow furnace coolAnnealing heats steel to a defined temperature, holds it until the temperature equalises throughout the section, then cools it very slowly inside the furnace. This slow cooling rate is what distinguishes annealing from all other processes — it allows the microstructure to transform fully into soft ferrite and pearlite, eliminating hardened structures, relieving internal stresses, and restoring ductility to cold-worked or previously hardened material.
Full annealing (850–900°C) produces maximum softness — used after heavy cold working or before precision machining. Process annealing (650–700°C) provides partial softening and stress relief without full re-austenitising. Spheroidise annealing (700–750°C, extended hold) converts carbides to a globular form — the standard supply condition for high-carbon bearing steels such as 100Cr6 to make them machinable before hardening.
Specify when: After cold drawing or heavy machining. Before hardening high-carbon grades. When softening purchased stock that is too hard to machine efficiently. When stress-relieving welded assemblies prior to finish machining.
Normalising
870–950°C — still air coolNormalising heats steel above its upper critical temperature then cools it in still air — faster than annealing but much slower than quenching. This produces a uniform, fine-grained pearlitic microstructure with moderate strength and good machinability. It is the most common conditioning treatment for engineering steel bar, frequently applied to refine the coarse grain structure left by hot rolling or forging and to produce a consistent, predictable starting condition across a batch.
Key distinction from annealing: Normalised steel is harder and stronger than fully annealed steel because the faster air cool suppresses complete carbide precipitation. However it is softer and tougher than as-rolled material because the grain structure has been refined and homogenised. EN8 (080M40) and EN19 (708M40) are both commonly supplied in the normalised condition as the standard bright bar supply state.
Specify when: To homogenise grain structure after forging or casting. To improve machinability of medium carbon steels. As a preliminary treatment before hardening. When a consistent, repeatable base condition is required across a production batch.
Hardening (Quenching)
820–870°C — oil or water quenchHardening heats steel above its upper critical temperature to form austenite, then quenches rapidly in oil or water to trap carbon in martensite — the hardest microstructure achievable in steel, and also the most brittle. Oil quenching cools more slowly than water, producing less distortion and cracking risk, and is the standard quench medium for alloy steels including EN19, EN24 and EN36. Water quenching gives higher hardness but significantly increases cracking risk, particularly in complex sections or higher alloy content steels.
Hardenability — the ability to achieve full martensite transformation through the section — varies significantly between grades. Plain carbon steels (EN3B, EN8) harden effectively only in sections up to about 40mm. Alloy steels (EN19, EN24T) harden throughout much larger cross-sections due to their chromium, molybdenum and nickel content retarding the austenite-to-pearlite transformation during cooling.
⚠ Critical: As-hardened steel is dangerously brittle and must be tempered immediately after quenching. Never use as-hardened steel in service.
Tempering
150–660°C — air cool after holdTempering is always carried out immediately after hardening. The as-hardened steel is reheated to a temperature well below the critical point, held for a defined period, then air cooled. This converts some of the brittle martensite into tougher structures, relieving internal stresses without excessively reducing hardness. The tempering temperature is the critical variable the heat treater controls to achieve the required specification:
• 150–200°C — maximum hardness retained (~60–64 HRC for tool steels). Cutting tools, dies, bearing steels.
• 200–400°C — moderate improvement in toughness, 50–58 HRC. Springs, high-wear components.
• 450–550°C — significant toughness, 40–50 HRC. High-tensile engineering — the typical range for EN19T and EN24T in the Q+T (T) condition.
• 550–660°C — maximum toughness, 25–35 HRC. Heavy impact applications where toughness is paramount.
The “T” suffix in grade designations (e.g. EN24T, 817M40T) denotes steel supplied in the quenched and tempered condition — ready to use without further heat treatment. This is the most common supply condition for bright bar alloy steel shafting grades.
Case Hardening (Carburising)
880–930°C carburise — then harden & temperCase hardening creates a hard, wear-resistant surface (the “case”) over a tough, impact-resistant core. It is used with low-carbon steels that cannot be through-hardened by conventional quenching because their carbon content is too low to form significant martensite.
Stage 1 — Carburising: The steel is held in a carbon-rich atmosphere (gas, liquid or solid) at 880–930°C. Carbon diffuses into the surface layer, raising the carbon content from ~0.15% to 0.8–1.0% over a depth of 0.3–2.0mm depending on time at temperature.
Stage 2 — Hardening & Tempering: The carburised steel is quenched to harden the carbon-enriched case to 58–64 HRC, while the low-carbon core remains soft and tough. This combination of hard case and tough core is what makes case hardening so effective for gears, camshafts and heavily stressed shafts.
Key grades: EN36 (655M13), EN36B, 8620 (805M20), EN32M (210M15). These grades are specifically designed to give a tough, ductile core whilst accepting a hardened carburised surface case.
Nitriding
480–530°C — 20–80 hours — no quenchNitriding diffuses nitrogen (rather than carbon) into the steel surface at relatively low temperature, producing an exceptionally hard surface layer without any quenching. This eliminates the distortion and cracking risk associated with conventional hardening, making nitriding the preferred choice for precision components that must maintain tight dimensional tolerances after surface treatment. Surface hardness of 700–1100 HV is achievable depending on grade and time.
Since the nitriding temperature (480–530°C) is well below the austenitising temperature, the steel’s core properties remain largely unaffected. The component must be in the correct Q+T condition before nitriding. Gas nitriding uses ammonia over 20–80 hours to produce a case depth of 0.15–0.6mm. Plasma (ion) nitriding gives more control over compound layer thickness and can be applied to stainless steels. The high chromium content of nitriding steels is essential — chromium nitrides form at the grain boundaries to provide the hardness.
Key grade: EN40B (722M24) — a 3% chromium-molybdenum steel designed specifically for gas nitriding. Supplied in the Q+T condition ready for machining and subsequent nitriding to achieve 700–850 HV surface hardness.
Advantage over carburising: Nitrided components show negligible dimensional change — critical for precision shafts, hydraulic cylinder rods and gear flanks where post-treatment grinding is not practical.
Process Comparison
Use this table to identify the right process for your application at a glance.
| Process | Softens? | Strengthens? | Surface Hard? | Distortion Risk | Applicable Grades | Typical Use Case |
|---|---|---|---|---|---|---|
| Annealing | ✓ Yes | ✕ No | ✕ No | Very Low | All grades | Restore machinability, stress relief, condition before hardening |
| Normalising | △ Partial | △ Moderate | ✕ No | Very Low | EN3B, EN8, EN19, S355 | Refine grain structure, consistent base condition, pre-hardening |
| Hardening + Tempering | ✕ No | ✓ Yes — high | △ Through section | Moderate | EN8, EN19, EN24T | High-tensile shafts, gears, tools — Q+T (T) condition |
| Case Hardening | ✕ No | △ Core only | ✓ 58–64 HRC surface | Moderate | EN36, 8620, EN32M | Gears, cams, shafts needing hard surface + tough core |
| Nitriding | ✕ No | ✕ Core unchanged | ✓ 700–1100 HV surface | Minimal | EN40B (722M24) | Precision shafts, hydraulic rods — no distortion |
Typical Hardness by Grade & Condition
Indicative hardness values for common Parkside Steel grades. Always verify against material test certificate and your heat treater's specific capabilities.
| Grade | BS 970 | As Drawn / Norm. HB | Q+T (T condition) HB | Max Hardened HRC | Case / Nitride | Data Sheet |
|---|---|---|---|---|---|---|
| EN1A | 230M07 | ~140–180 | N/A | — | ~58–62 case* | |
| EN3B | 070M20 | ~115–160 | N/A | — | ~58–62 case* | |
| EN8 | 080M40 | ~163–207 | ~225–269 | ~54–58 | — | |
| EN19 / 42CrMo4 | 708M40 | ~248 | ~295–352 | ~54–58 | — | |
| EN24T / 34CrNiMo6 | 817M40T | — | ~293–352 | ~56–60 | — | |
| EN36 / 14NiCr14 | 655M13 | ~170–210 | — | — | ~58–63 case | |
| EN40B / 31CrMo12 | 722M24 | — | ~248–302 | — | 700–850 HV nitrided | |
| 8620 / 20NiCrMo2 | 805M20 | ~160–200 | — | — | ~58–62 case | |
| S355 J2 | S355J2 | ~150–180 | N/A | — | — |
* Case hardened surface only — core remains soft. N/A = process not applicable. Values are guidance only.
Common Questions
The questions engineers and machinists ask most often about steel hardness and heat treatment.
40 HRC is approximately 371 HB (Brinell hardness), equivalent to approximately 392 HV (Vickers) and a tensile strength of around 1,280 N/mm² for carbon and alloy steel. This is a typical hardness for EN19 (708M40 / 42CrMo4) in the Q+T condition tempered at around 500–550°C. Use the live converter above to check any other HRC value instantly.
HRC (Rockwell C) uses a diamond cone indenter under a 150 kg load and is used for harder materials — generally above 20 HRC. It gives fast, small-footprint results and is widely used for hardened tool steels, case hardened surfaces and Q+T engineering steels. The small indent means it is less suitable for inhomogeneous materials like cast iron.
HB (Brinell) uses a 10mm steel or carbide ball under a 3000 kg load, producing a larger indent that is more representative for inhomogeneous materials such as cast iron and forgings. The Brinell scale becomes unreliable above about 450 HB because the ball begins to deform plastically. The two scales are related but not directly proportional — use the conversion table above for specific values.
EN19 (708M40 / 42CrMo4) in the T condition typically has a hardness of 295–352 HB, equivalent to approximately 31–38 HRC or 311–372 HV. This corresponds to a tensile strength of approximately 850–1100 N/mm². The T condition means the steel has been quenched and tempered at typically 540–620°C. For sections above 63mm the upper hardness range is reduced due to hardenability limits. Download the EN19 data sheet for full mechanical properties by section size.
EN24T (817M40T / 34CrNiMo6) in the T condition is supplied at 248–302 HB for sections up to 63mm, corresponding to approximately 24–32 HRC or 255–320 HV. Fully hardened (before tempering), EN24 can reach 56–60 HRC. In larger sections the upper hardness range is reduced. Download the EN24T data sheet for the full tensile and hardness ranges by condition and section size.
Both processes heat steel above a critical temperature to refine the microstructure, but the cooling method differs significantly:
Annealing cools very slowly inside the furnace — typically at a controlled rate of 10–30°C per hour. This produces maximum softness and ductility, used when the steel needs to be as easy to machine as possible or when complete stress relief is required.
Normalising cools in still air — faster than annealing but much slower than quenching. This produces a finer, more uniform grain structure with moderate strength and good machinability. Normalised steel is harder and stronger than annealed steel, but softer and tougher than as-rolled or as-forged material. It is the most common supply condition for bright engineering steel bar.
Yes — EN8 (080M40) can be hardened, though its hardenability is limited compared to alloy steels. EN8 through-hardens well in sections up to approximately 40–63mm when oil quenched, achieving a maximum surface hardness of typically 54–58 HRC. In larger sections, the core remains substantially softer. EN8 also responds well to flame and induction surface hardening, achieving 50–55 HRC on the treated surface with a tough core below. Download the EN8 data sheet for full hardening parameters and mechanical properties.
For applications requiring deeper hardening through large sections, specify EN19 (708M40 / 42CrMo4), which has significantly higher hardenability due to its chromium and molybdenum content.
Grey cast iron (EN-GJL-250 / BS 1452 Grade 250) typically has a hardness of 170–260 HB depending on section size and cooling rate during casting. This is approximately 86–27 HRB (Rockwell B — the C scale is not appropriate for cast iron in its as-cast condition). Vickers hardness is typically 175–270 HV. Note: standard steel hardness conversion tables are not accurate for cast iron — the tensile strength column in particular does not apply. Download the cast iron data sheet for full properties.
For carbon and alloy steel, a widely used approximation is: Tensile strength (N/mm²) ≈ HV × 3.3. This gives a reasonable estimate in the range 150–600 HV. For example, 300 HV ≈ 990 N/mm². Use the live converter above for a more precise interpolated value from the full data table.
This approximation does not apply to stainless steel, cast iron, aluminium, brass or other non-carbon steels — each requires a material-specific conversion. The relationship is also less reliable at very high hardness values (above 500 HV) where conversion errors increase. Per BS EN ISO 18265, conversions above 650 HV should be treated as approximate guidance only.