Intro
The hardness of nickel alloys is a crucial property that significantly impacts their performance. Nickel alloys are indispensable materials in various industries due to their superior resistance to heat, corrosion, and wear. Hardness refers to a material’s resistance to surface deformation such as indentation or scratching.
This article will cover the basics of nickel alloys, the importance of hardness in their applications, different hardness testing methods, techniques for improving hardness, and a comparison of hardness values across several popular nickel alloy families, including Alloy 200/201, Monel, Inconel, Incoloy, and Hastelloy.
Additionally, we will delve into hardness conversion, providing insights into HV vs. HRC, and exploring how to use a hardness conversion chart effectively.
1. What Are Nickel Alloys?
Nickel alloys are metal alloys that contain nickel as the primary element, combined with other elements like chromium, molybdenum, iron, and copper. These alloys are known for their excellent performance in high-temperature, high-pressure, and corrosive environments. Popular nickel alloy families include:
1.1 Alloy 200/201:
Primarily made of pure nickel, offering excellent corrosion resistance in chemical processing.
1.2 Monel:
A nickel-copper alloy known for exceptional corrosion resistance, particularly in marine environments.
1.3 Inconel:
A nickel-chromium alloy designed for high-heat applications, commonly used in jet engines and turbines.
1.4 Incoloy:
A nickel-iron-chromium alloy known for its strength at high temperatures and resistance to acidic environments.
1.5 Hastelloy:
A nickel-molybdenum alloy offering superb resistance to a wide variety of corrosive substances.
2. The Importance of Hardness in Nickel Alloys
Hardness is critical when selecting a nickel alloy for a specific application, as it influences a material’s ability to resist wear, indentation, and deformation. Hardness plays a key role in several applications:
2.1 Aerospace:
High-hardness alloys like Inconel are preferred for turbine blades, which must withstand extreme heat and pressure.
2.2 Chemical Processing:
Alloys such as Hastelloy, which are both hard and corrosion-resistant, are used in chemical reactors and other aggressive environments.
2.3 Marine and Offshore:
Monel alloys are ideal for applications requiring both hardness and resistance to seawater corrosion, such as propellers and pumps.
3. Hardness Testing Methods and Units
There are various methods for measuring hardness, each suitable for different materials and applications. The most commonly used hardness scales are:
3.1 Brinell Hardness (HB):
Measures the size of the indentation created by a hardened steel ball. This is especially useful for coarse-grained materials. For example, converting BHN to HRC is often needed when comparing Brinell hardness to Rockwell hardness values.
3.2 Rockwell Hardness (HR):
Measures the depth of penetration of an indenter under a fixed load.
The Rockwell C scale (HRC) is the most commonly used for harder materials, and HRC hardness values are often cited for alloys like Inconel and Monel.
3.2 Rockwell Hardness (HR):
Measures the depth of penetration of an indenter under a fixed load.
The Rockwell C scale (HRC) is the most commonly used for harder materials, and HRC hardness values are often cited for alloys like Inconel and Monel.
3.3 Vickers Hardness (HV):
Uses a diamond pyramid indenter and is suitable for very small materials. It’s often used for nickel alloys in thin-walled sections.
3.4 Knoop Hardness (HK):
Similar to Vickers but uses a rhombic-based diamond indenter, useful for brittle materials or small sample sizes.
If you’re comparing different methods, hardness conversion charts come in handy. For example, Vickers hardness to Rockwell C conversion (Vickers to HRC) is a common conversion that can be easily achieved with a hardness conversion calculator.
3.5 What is 30-35 HRC?
An HRC value between 30 and 35 is often considered moderate hardness, which is typical for many stainless steels and tool steels.
Hardness conversions help engineers and material scientists find equivalences between different scales (e.g., HV to HRC or BHN to Rockwell).
3.6 Conversion Chart
BRINELL | ROCKWELL -C [HRC] | ROCKWELL -B [HRB] | VICKERS [HV] | Strength [N/mm^2] |
| 800 | 72 | |||
| 780 | 71 | |||
| 760 | 70 | |||
| 752 | 69 | |||
| 745 | 68 | |||
| 746 | 67 | |||
| 735 | 66 | |||
| 711 | 65 | |||
| 695 | 64 | |||
| 681 | 63 | |||
| 658 | 62 | |||
| 642 | 61 | |||
| 627 | 60 | |||
| 613 | 59 | |||
| 601 | 58 | 746 | ||
| 592 | 57 | 727 | ||
| 572 | 56 | 694 | ||
| 552 | 55 | 649 | ||
| 534 | 54 | 120 | 589 | |
| 513 | 53 | 119 | 567 | |
| 504 | 52 | 118 | 549 | |
| 486 | 51 | 118 | 531 | |
| 469 | 50 | 117 | 505 | |
| 468 | 49 | 117 | 497 | |
| 456 | 48 | 116 | 490 | 1569 |
| 445 | 47 | 115 | 474 | 1520 |
| 430 | 46 | 115 | 458 | 1471 |
| 419 | 45 | 114 | 448 | 1447 |
| 415 | 44 | 114 | 438 | 1422 |
| 402 | 43 | 114 | 424 | 1390 |
| 388 | 42 | 113 | 406 | 1363 |
| 375 | 41 | 112 | 393 | 1314 |
| 373 | 40 | 111 | 388 | 1265 |
| 360 | 39 | 111 | 376 | 1236 |
| 348 | 38 | 110 | 361 | 1187 |
| 341 | 37 | 109 | 351 | 1157 |
| 331 | 36 | 109 | 342 | 1118 |
| 322 | 35 | 108 | 332 | 1089 |
| 314 | 34 | 108 | 320 | 1049 |
| 308 | 33 | 107 | 311 | 1035 |
| 300 | 32 | 107 | 303 | 1020 |
| 290 | 31 | 106 | 292 | 990 |
| 277 | 30 | 105 | 285 | 971 |
| 271 | 29 | 104 | 277 | 941 |
| 264 | 28 | 103 | 271 | 892 |
| 262 | 27 | 103 | 262 | 880 |
| 255 | 26 | 102 | 258 | 870 |
| 250 | 25 | 101 | 255 | 853 |
| 245 | 24 | 100 | 252 | 838 |
| 240 | 23 | 100 | 247 | 824 |
| 233 | 22 | 99 | 241 | 794 |
| 229 | 21 | 98 | 235 | 775 |
| 223 | 20 | 97 | 227 | 755 |
| 216 | 19 | 96 | 222 | 716 |
| 212 | 18 | 95 | 218 | 706 |
| 208 | 17 | 95 | 210 | 696 |
| 203 | 16 | 94 | 201 | 680 |
| 199 | 15 | 93 | 199 | 667 |
| 191 | 14 | 92 | 197 | 657 |
| 190 | 13 | 92 | 186 | 648 |
| 186 | 12 | 91 | 184 | 637 |
| 183 | 11 | 90 | 183 | 617 |
| 180 | 10 | 89 | 180 | 608 |
| 175 | 9 | 88 | 178 | 685 |
| 170 | 7 | 87 | 175 | 559 |
| 167 | 6 | 86 | 172 | 555 |
| 166 | 5 | 86 | 168 | 549 |
| 163 | 4 | 85 | 162 | 539 |
| 160 | 3 | 84 | 160 | 535 |
| 156 | 2 | 83 | 158 | 530 |
| 154 | 1 | 82 | 152 | 515 |
| 149 | 81 | 149 | 500 | |
| 147 | 80 | 147 | 490 | |
| 143 | 79 | 146 | 482 | |
| 141 | 78 | 144 | 481 | |
| 139 | 77 | 142 | 480 | |
| 137 | 76 | 140 | 475 | |
| 135 | 75 | 137 | 467 | |
| 131 | 74 | 134 | 461 | |
| 127 | 72 | 129 | 451 | |
| 121 | 70 | 127 | 431 | |
| 116 | 68 | 124 | 422 | |
| 114 | 67 | 121 | 412 | |
| 111 | 66 | 118 | 402 | |
| 107 | 64 | 115 | 382 | |
| 105 | 62 | 112 | 378 | |
| 103 | 61 | 108 | 373 | |
| 95 | 56 | 104 | ||
| 90 | 52 | 95 | ||
| 81 | 41 | 85 | ||
| 76 | 37 | 80 |
3.7 Hardness and Scale Conversion:
30-35 HRC is a common Rockwell C scale range, where HRC (Rockwell C) indicates hardness for hard materials. Converting from Rockwell hardness to Vickers (or HV to HRC) is common in alloy selection.
To convert 82 HRA to HRC, you’d need to reference a hardness conversion calculator or hardness conversion chart. These tools help to convert from Rockwell A (HRA) to Rockwell C (HRC), or from Vickers (HV) to Rockwell C for an accurate comparison.
4. Methods to Improve Hardness of Nickel Alloys
Several techniques can improve the hardness of nickel alloys, making them more suitable for demanding applications:
4.1 Alloying:
Adding elements like chromium or molybdenum enhances hardness. For example, adding chromium increases the hardness of Incoloy and Inconel alloys.
4.2 Heat Treatment:
Techniques like annealing, quenching, and tempering can alter the microstructure of the alloy, thereby increasing its hardness. For example, rockwell hardness scale charts often show the results of various heat treatments for nickel alloys.
4.3 Surface Treatments:
Methods like nitriding and carburizing can harden the surface of the alloy, making it more resistant to wear while maintaining the core’s ductility.
4.4 Work Hardening:
Cold working processes such as rolling and forging can increase the hardness of nickel alloys by inducing dislocations in the material’s crystal structure, which strengthens the material.
5. Hardness Comparison of Popular Nickel Alloys
The hardness of different nickel alloys can vary significantly based on their composition and processing methods. Here’s a comparison of the hardness values of some commonly used nickel alloys:
5.1 Comparison Table of the Hardness
| Test Method | Brinell (HB) | Rockwell C (HRC) | Vickers (HV) | Knoop (HK) |
|---|---|---|---|---|
| Alloy 200/201 | 70-90 | 40-45 | 160-190 | 140-170 |
| Monel | 120-170 | 55-60 | 200-250 | 160-210 |
| Inconel 625 | 220-270 | 85-90 | 350-420 | 300-380 |
| Incoloy 800 | 170-220 | 70-75 | 200-250 | 170-220 |
5.2 Explanation of the able
As shown in the table, Inconel 625 has a significantly higher Rockwell C (HRC) value compared to Alloy 200/201, which is softer. This means Inconel is more suitable for high-temperature, high-stress applications.
For those looking to convert Brinell to Rockwell C, a hardness conversion chart or calculator can be very helpful. The BHN to HRC conversion is often required when comparing softer alloys like Alloy 200/201 (which has a low HRC value) with harder alloys like Inconel (which has a high HRC value).
6. Conclusion
Understanding hardness is crucial when selecting nickel alloys for specific applications, as it directly influences the material’s resistance to wear, deformation, and environmental factors. Whether you’re designing components for aerospace or chemical processing, selecting the right nickel alloy based on its hardness is essential.
When working with nickel alloys, it’s important to use the appropriate hardness scale, whether Rockwell, Vickers, or Brinell. Hardness conversion tools like conversion calculators and conversion charts allow for easier comparison between hardness scales such as HRC to Vickers or Brinell to Rockwell C. For example, the conversion from BHN to HRC or from HV to HRC is often done using a hardness conversion calculator.
By understanding these hardness values, along with conversion tables such as the Rockwell C hardness chart or the Vickers hardness to Rockwell C chart, engineers can make better decisions
