HRB to HRC Converter
Rockwell B to Rockwell C Hardness Conversion Calculator
Quick Conversions
Rockwell Hardness Scales Explained
Rockwell B (HRB)
- Uses 1/16 inch (1.588mm) steel ball indenter
- Applied load: 100 kg (980.7 N)
- Suitable for softer materials
- Range: 0-130 HRB
- Materials: Aluminum, brass, soft steel, annealed copper alloys
Rockwell C (HRC)
- Uses 120° diamond cone indenter (Brale)
- Applied load: 150 kg (1471 N)
- Suitable for harder materials
- Range: 20-70 HRC
- Materials: Hardened steel, hard alloys, case hardened materials
HRB to HRC Conversion Table
| Rockwell B (HRB) | Rockwell C (HRC) | Brinell (HB) | Vickers (HV) | Typical Application |
|---|---|---|---|---|
| 60 | – | 105 | 112 | Soft aluminum alloys |
| 70 | – | 127 | 127 | Annealed brass |
| 80 | – | 147 | 147 | Cold rolled steel |
| 90 | 9 | 185 | 180 | Medium carbon steel |
| 95 | 16 | 210 | 201 | Normalized steel |
| 100 | 20 | 240 | 227 | Quenched and tempered steel |
| 105 | 24 | 271 | 252 | Heat treated alloy steel |
| 110 | 27 | 301 | 277 | Hardened carbon steel |
| 115 | 30 | 332 | 302 | Spring steel |
| 120 | 35 | 362 | 327 | High strength steel |
Conversion Formula and Methods
Approximate Conversion Formula
For the overlap range (HRB ≥ 95), an approximate conversion can be calculated using empirical relationships:
HRC ≈ (HRB – 95) × 0.6 + 16
This formula is most accurate for HRB values between 95 and 120.
Conversion Examples
Example 1: Convert HRB 100 to HRC
HRC = (100 – 95) × 0.6 + 16 = 5 × 0.6 + 16 = 19 HRC
Example 2: Convert HRB 110 to HRC
HRC = (110 – 95) × 0.6 + 16 = 15 × 0.6 + 16 = 25 HRC
Example 3: Convert HRB 120 to HRC
HRC = (120 – 95) × 0.6 + 16 = 25 × 0.6 + 16 = 31 HRC
Popular Hardness Conversions
HRB to HB (Brinell)
Commonly used for softer metals and annealed steels. Brinell testing provides larger indentation areas for more representative hardness values.
HRB to HV (Vickers)
Vickers hardness is ideal for testing small parts, thin sections, and case-hardened surfaces with precise measurements.
HRC to HRB
Reverse conversion is needed when testing harder materials that may fall outside the HRB range but need softer scale reference.
HRB to Tensile Strength
Approximate tensile strength (N/mm²) can be estimated from hardness values for steel materials, useful for quality control.
| From Scale | To Scale | Conversion Range | Accuracy |
|---|---|---|---|
| HRB | HRC | 95-120 HRB → 16-35 HRC | Moderate |
| HRB | HB | 40-120 HRB → 100-400 HB | Good |
| HRB | HV | 40-120 HRB → 100-400 HV | Good |
| HRC | HRB | 0-25 HRC → 95-120 HRB | Moderate |
When to Use HRB vs HRC
| Material Type | Recommended Scale | Hardness Range | Reason |
|---|---|---|---|
| Aluminum alloys | HRB | 30-85 HRB | Too soft for HRC diamond indenter |
| Brass and bronze | HRB | 40-100 HRB | Steel ball suitable for these materials |
| Annealed steel | HRB | 60-110 HRB | Softer than heat-treated steel |
| Heat-treated steel | HRC | 25-65 HRC | Diamond cone provides accurate results |
| Hardened tool steel | HRC | 45-65 HRC | Too hard for steel ball indenter |
| Case-hardened parts | HRC | 50-63 HRC | Measures surface hardness effectively |
| Spring steel | HRC | 40-52 HRC | Optimal range for hardened springs |
| Stainless steel (annealed) | HRB | 80-95 HRB | Appropriate for softer stainless grades |
Frequently Asked Questions
What is the difference between Rockwell B and Rockwell C hardness scales?
Rockwell B (HRB) uses a 1/16″ steel ball indenter with a 100 kg load, designed for softer materials like aluminum, brass, and annealed steel. Rockwell C (HRC) uses a 120° diamond cone indenter with a 150 kg load, specifically for harder materials such as hardened steel, tool steel, and case-hardened components. The different indenters and loads make each scale optimal for specific hardness ranges.
Can all HRB values be converted to HRC?
No, only HRB values above approximately 95 have meaningful HRC equivalents. Below HRB 95, materials are too soft for accurate HRC measurement, as the diamond cone indenter would penetrate too deeply. The practical conversion range is HRB 95-120, corresponding to approximately HRC 16-35. Values outside this range should be measured directly using the appropriate scale.
How accurate are HRB to HRC conversions?
Conversions between different Rockwell scales are approximations with typical accuracy of ±3 units. The accuracy varies based on material type, composition, heat treatment, and surface condition. For critical applications requiring precise hardness measurements, direct testing using the appropriate scale is recommended rather than relying on conversions.
Why do conversion tables show different values?
Different conversion tables may show slight variations because they are based on empirical testing of different material samples. Factors like material composition, microstructure, heat treatment processes, and testing conditions all influence hardness relationships. Most reputable conversion tables are accurate within ±2-3 hardness units for steel materials.
What materials are tested with Rockwell B hardness?
Rockwell B hardness is ideal for aluminum alloys, copper alloys, brass, bronze, soft steel, annealed steel, normalized steel, mild steel, and other materials with hardness below approximately 100 HRB. These materials would be too soft for Rockwell C testing, which could damage the diamond indenter or produce inaccurate readings.
Can stainless steel be measured with both HRB and HRC?
Yes, depending on the stainless steel condition. Annealed austenitic stainless steels (like 304 or 316 in annealed state) typically measure 80-95 HRB. Heat-treated martensitic or precipitation-hardened stainless steels (like 410, 17-4 PH) measure in the HRC range, typically 25-45 HRC. The appropriate scale depends on the alloy type and heat treatment condition.
How does material thickness affect Rockwell hardness testing?
Material thickness must be at least 10 times the depth of indentation to prevent anvil effect. For Rockwell B, minimum thickness is approximately 1.5-2mm. For Rockwell C, minimum thickness is approximately 1mm. Thinner materials may show falsely high hardness readings due to substrate support. Very thin materials should be tested using Rockwell Superficial scales instead.
What is the relationship between hardness and tensile strength?
For steel materials, there is an approximate correlation between hardness and tensile strength. A rough approximation is: Tensile Strength (MPa) ≈ 3.4 × HB (for HB 175-450). For example, a material measuring 100 HRB (approximately 240 HB equivalent) would have estimated tensile strength around 800-850 MPa. However, this relationship varies with material type and should only be used for rough estimates.
Testing Procedures and Best Practices
Surface Preparation
Ensure test surface is clean, flat, smooth, and free from scale, oxides, or contaminants. Surface roughness should not exceed Ra 1.6μm for accurate readings. Grind or polish rough surfaces before testing.
Test Spacing
Maintain minimum distance of 3-5 times the indentation diameter between adjacent tests. For HRB, space tests at least 4-5mm apart. For HRC, minimum 3mm spacing prevents interaction between indentations.
Sample Support
Place samples on firm, rigid support to prevent movement during testing. Ensure sample doesn’t tilt or shift. For cylindrical parts, use appropriate V-block fixtures or adapters.
Load Application
Apply test load smoothly without shock or vibration. Allow adequate dwell time (typically 2-8 seconds) for material creep to stabilize. Follow ASTM E18 or ISO 6508 standards for timing.
Temperature Control
Perform tests at room temperature (18-28°C). Temperature variations affect hardness readings. Allow test pieces to stabilize to room temperature before testing if they’ve been stored differently.
Multiple Readings
Take at least 3-5 readings per test location and average the results. Discard outliers that differ significantly. Report both average value and range or standard deviation.
Common Materials Hardness Reference
| Material | Condition | HRB Range | HRC Equivalent | Application |
|---|---|---|---|---|
| 1018 Carbon Steel | Hot rolled | 70-85 HRB | – | General fabrication |
| 1045 Carbon Steel | Annealed | 80-95 HRB | – | Machinery parts |
| 1045 Carbon Steel | Normalized | 95-105 HRB | 16-24 HRC | Shafts, gears |
| 4140 Alloy Steel | Annealed | 85-95 HRB | – | Before heat treatment |
| 4140 Alloy Steel | Q&T 850°F | – | 28-32 HRC | High strength parts |
| 304 Stainless | Annealed | 80-90 HRB | – | Corrosion resistant parts |
| 17-4 PH Stainless | H900 condition | – | 40-44 HRC | Aerospace components |
| Aluminum 6061 | T6 temper | 60-70 HRB | – | Structural applications |
| Brass C360 | Half hard | 65-80 HRB | – | Fittings, fasteners |
| O1 Tool Steel | Annealed | 90-100 HRB | – | Before hardening |
| O1 Tool Steel | Hardened | – | 58-64 HRC | Cutting tools, dies |
| A36 Structural Steel | As rolled | 60-75 HRB | – | Construction, beams |
References
- ASTM E18-20, “Standard Test Methods for Rockwell Hardness of Metallic Materials,” ASTM International, West Conshohocken, PA, 2020.
- ISO 6508-1:2016, “Metallic materials – Rockwell hardness test – Part 1: Test method,” International Organization for Standardization, Geneva, Switzerland, 2016.
- Chandler, H., “Hardness Testing, 2nd Edition,” ASM International, Materials Park, OH, 1999.
- Davis, J.R., “Metals Handbook Desk Edition, 2nd Edition,” ASM International, Materials Park, OH, 1998.
- ASTM E140-12B(2019), “Standard Hardness Conversion Tables for Metals Relationship Among Brinell Hardness, Vickers Hardness, Rockwell Hardness, Superficial Hardness, Knoop Hardness, Scleroscope Hardness, and Leeb Hardness,” ASTM International, West Conshohocken, PA, 2019.