What are Differences Between Hardness of HRC, HB and HV

Hardness is a crucial indicator of a material’s mechanical properties, reflecting its resistance to penetration by an external object. In engineering and scientific research, hardness measurement is widely applied for material selection, quality control, and performance evaluation. HRC (Rockwell Hardness), HV (Vickers Hardness), and HB (Brinell Hardness) are three of the most used measurement methods, each with distinct characteristics and application scopes. The differences between these three methods are detailed below.

HRC (Rockwell Hardness)

Rockwell hardness is a measurement method proposed by S.P. Rockwell in 1921. It represents the hardness value of a metallic material determined using a Rockwell hardness tester. This value is unitless, represented simply by the symbol “HR” and is usually followed by C to indicate that the measurement was obtained using a diamond cone indenter.

Principle

Rockwell hardness is determined based on the depth of the indentation’s plastic deformation. Under a specified major load, a diamond cone indenter is pressed vertically into the surface of the test material, creating an indentation. After the load is released, the Rockwell hardness value is calculated using the formula HR = (K-H)/C, where K is a constant, H is the net indentation depth of the indenter, and C is a constant related to the indenter geometry and the material scale.

Application

Rockwell hardness testing is typically used for materials with high hardness, such as quenched and alloy steels. This is because the hardness of these materials increases significantly after quenching, and other measurement methods might not yield accurate or reliable values. Furthermore, Rockwell hardness measurement is widely used in industrial production due to its advantages, including simple operation, fast measurement speed, and a wide measurement range.

When using a Rockwell hardness tester, the following points should be noted:

• Ensure the test material surface is flat, clean, and free of contaminants like oil or scale.
• Select the appropriate load and indenter based on the material’s hardness and thickness.
• Maintain the perpendicularity of the indenter to the material surface during the test to avoid measurement errors.

HV (Vickers Hardness)

Vickers hardness employs a square-based pyramid-shaped diamond indenter for measurement. Compared to Rockwell hardness, Vickers hardness is considered more precise and is particularly well-suited for measuring a material’s surface hardness.

Principle

Vickers hardness is also determined based on the plastic deformation of the indentation. Under a specified load, the square-based pyramid-shaped diamond indenter is pressed into the test material’s surface, creating a square pyramidal indentation. By measuring the length of the indentation’s diagonals, the area of the impression can be calculated, which then allows for the determination of the hardness value. Vickers hardness is fundamentally expressed as the normal pressure per unit area, with units such as Pascal (Pa) or Megapascal (MPa), although in practice, a unitless hardness number is often used.

Application

Vickers hardness is suitable for measuring the hardness of material surfaces, especially surface-treated materials like those that have been nitrided, or coated. This is because the surface hardness and bulk hardness of these materials can differ significantly, and other methods might not provide an accurate surface hardness value. Additionally, Vickers hardness testing is suitable for thin plates, small parts, and materials that are difficult to measure using alternative hardness tests.

When using a Vickers hardness tester, the following points should be noted:

• Ensure the test material surface is flat, smooth, and free of defects like scratches or cracks.
• Select the appropriate test force (load) and indenter based on the material’s hardness and thickness.
• Maintain the perpendicularity of the indenter to the material surface and strictly control the dwell time (measurement time) to minimize errors.

HB (Brinell Hardness)

Brinell hardness uses a hardened steel ball as the indenter. It is suitable for measuring softer metallic materials, such as annealed steel and cast iron.

Principle

Brinell hardness is determined based on the area of the indentation. Under a specified load, a hardened steel ball of a certain diameter is pressed into the test material’s surface, held for a specified dwell time, and then unloaded. By measuring the impression diameter, the indentation area can be calculated, allowing determination of the hardness value. Brinell hardness is expressed as the normal pressure per unit area, with common units being Megapascal (MPa), though a unitless hardness number is often cited in practical applications.

Application

Brinell hardness testing is primarily suited for measuring softer metallic materials, such as annealed steel and cast iron. Since these materials’ hardness generally decreases after annealing, other methods might not yield accurate hardness values. Furthermore, Brinell hardness measurement is widely used in the research and quality control of metallic materials due to its simple operation and wide measurement range.

When using a Brinell hardness tester, the following points should be noted:

• Ensure the test material surface is flat, clean, and free of contaminants like oil or scale.
• Select the appropriate load and steel ball size based on the material’s hardness and thickness.
• Maintain the steel ball’s perpendicularity to the material surface and strictly control the dwell time to avoid measurement errors.

Conversion Relationship

A section explaining the conversion relationship between the three scales would typically be included here.

Conversion between Rockwell hardness and Vickers hardness：

Conversion between Rockwell hardness and Brinell hardness：

Conversion between Vickers hardness and Brinell hardness：

Table 1: Cross-border table of HV, HB, and HRC hardness

HB	HRC	HV	HB	HRC	HV
	68.0	940	415	44.5	440
	67.5	920	401	43.1	425
767	66.4	880	388	41.8	410
757	65.9	860	375	40.4	396
745	65.3	840	363	39.1	383
733	64.7	920	352	37.9	372
722	64.0	900	341	36.6	360
710	63.3	780	331	35.5	350
698	62.5	760	311	33.1	328
684	61.8	740	302	32.1	319
682	61.7	737	293	30.9	309
670	61.0	720	285	29.9	301
656	60.1	700	277	28.8	292
653	60.0	697	269	27.6	284
647	59.7	690	262	26.6	276
638	59.2	680	255	25.4	269
630	58.8	670	248	24.2	261
627	58.7	667	241	22.8	253
620	58.3	660	235	21.7	247
601	57.3	640	229	20.5	241
578	56.0	615	223		234
	55.6	607	217		228
555	54.7	591	212		222
	54.0	579	207		218
534	53.5	569	201		212
	52.5	553	197		207
514	52.1	547	192		202
	51.6	539	187		296
	51.1	530	183		192
495	51.0	528	179		188
	50.3	516	174		183
477	49.6	508	170		178
461	48.8	495	167		175
	48.5	491	163		171
	47.2	474	156		163
444	47.1	472	149		156
429	45.7	455	143		150

Summary

HRC, HV, and HB are three widely used hardness measurement methods, each possessing unique characteristics and specific applications:

• Rockwell Hardness (HRC) is suitable for measuring materials with higher hardness, such as quenched steel.
• Vickers Hardness (HV) is ideal for measuring surface hardness, especially on surface-treated parts.
• Brinell Hardness (HB) is best suited for measuring softer metallic materials, such as annealed steel.

When selecting a hardness measurement method, you must comprehensively consider factors such as the nature of the test material, its intended application, and measurement requirements to ensure the accuracy and reliability of the results. Concurrently, when using any hardness tester, close attention must be paid to the effects of factors such as operating procedures and measurement conditions on the results to minimize measurement errors.