What's the difference between HRC, HV, HB, HRB hardness units?
These are scales from different test methods: HRC is Rockwell C scale (diamond indenter + 150kgf total load), most common for hardened/tempered steel; HV is Vickers (diamond square pyramid + selectable 1~120kgf load), best universal coverage from soft to hard; HB is Brinell (cemented carbide ball + 3000kgf load), for cast iron/cast steel/soft metals/non-ferrous metals; HRB is Rockwell B scale (1.588mm steel ball + 100kgf), for mild steel/annealed steel/copper-aluminum alloys.
Can hardness be converted precisely like length? Why are they approximate values?
No, they cannot be precisely converted because: (1) Different test principles—Brinell/Rockwell/Vickers use different indenter shapes and loads, different indentation depth/area measurement methods; (2) Indentation size and plastic deformation mechanisms differ, different materials have different strain hardening behavior; (3) Standards only establish empirical comparison tables for specific materials (like carbon/low-alloy steel) in specific hardness ranges; (4) The same hardness value on different materials may correspond to different strengths. All cross-scale conversions are empirical approximations—engineering allows ±1~2HRC or ±10~20HV error. Quality arbitration must test directly on the target scale.
What does HRC60 mean? What's the hardness of common steels?
HRC60 is very high hardness, typical of quenched high-carbon/tool/bearing steel—can cut ordinary steel but is more brittle. Common material hardness reference: Pure copper/aluminum annealed<HRB50; Low-carbon steel annealed≈HRB60~70(HRC<20 unmeasurable); 45 steel quenched & tempered≈HRC28~32; 40Cr Q&T≈HRC32~38; Bearing steel GCr15 quenched≈HRC61~65; High-speed steel W18Cr4V quenched≈HRC63~66; Cemented carbide YG8≈HRA89~91(HRC off scale); Stainless steel 304 annealed≈HRB80~90.
What does HRC55-60 on a drawing mean? What test method is needed?
HRC55~60 means Rockwell C scale hardness between 55~60, typically quenched + low-temperature tempered high-hardness parts (like gears, punches, die inserts). This hardness should be tested directly with a Rockwell hardness tester C scale (diamond cone + 150kgf)—determining pass/fail from converted HV/HB is not recommended. Portable Leeb hardness testers can do quick screening on the shop floor, but final acceptance should use a bench Rockwell tester.
What's the relationship between Leeb hardness (HLD) and Rockwell HRC?
Leeb hardness (HL, Leeb) is a dynamic rebound hardness—an impact body strikes the specimen surface, hardness calculated from ratio of rebound velocity to impact velocity (HLD uses D-type impact device). Leeb's biggest advantage is portability, convenient for large parts on-site. HLD has empirical conversion to HRC (HLD500≈HRC20, HLD760≈HRC56, HLD830≈HRC64), but is strongly affected by workpiece weight, thickness, and surface roughness—only suitable for on-site rough measurement, not a substitute for bench testers for final determination.
Why are there two Brinell designations HBW and HBS?
HBS was the old standard using a hardened steel ball indenter; HBW is the new standard using a cemented carbide ball. ISO 6506 and ASTM E10 now use HBW (W for Wolfram cemented carbide) exclusively; HBS is obsolete. HBW indenters commonly use 10mm diameter (large parts), 5mm/2.5mm/1mm (small parts/thin sections), with loads selected at 30D²/10D²/5D²/2.5D² ratios. HB in this tool refers to HBW (cemented carbide ball).
Is higher HV number harder? What's the difference between HV1, HV10, HV30?
Yes, higher HV means harder material. The number after HV is test force in kgf: HV1 (1kgf, thin layers/small parts), HV5, HV10, HV30 (30kgf, standard). Ideally, a uniform material should have consistent HV at different loads, but in practice surface hardening/decarburization/size effects cause differences. Micro Vickers (HV0.1/HV0.05) is for thin layers, coatings, weld zones.
Is there a relationship between hardness and tensile strength? Can HB estimate σb?
For carbon/low-alloy steel in a certain range there's an empirical relationship: σb(MPa)≈3.45~3.5×HB (or≈3.2~3.5×HV). For example: 45 steel normalized HB210≈σb≈735MPa; 40Cr Q&T HB280≈σb≈980MPa. But this relationship only roughly holds for carbon/low-alloy steel—errors are larger for high-alloy steels, stainless steel, non-ferrous metals, and cast iron. Use only for material selection/estimation, not a substitute for tensile testing.
What is Mohs hardness? How does it correspond to metal hardness HRC?
Mohs hardness is relative scratch resistance of minerals, rated 1~10 (extended to 15): 1 talc, 2 gypsum, 3 calcite, …, 7 quartz, 8 topaz, 9 corundum, 10 diamond. Mohs is scratch hardness—completely different physical principle from metal indentation hardness (HRC/HV/HB), so there is no strict conversion. Reference correspondence: Fingernail≈2.5, Copper coin≈3.5, Knife blade≈5.5, Window glass≈5.5~6, Steel file≈6.5. Hardened steel HRC60≈Mohs 5.5~6.5 (quartz level), cemented carbide≈Mohs 9.
What is Shore HS (Scleroscope)? Is it the same as rubber Shore A/D?
No, be careful to distinguish: Shore HS (Shore Scleroscope) is rebound hardness for metals—diamond hammer dropped from fixed height, rebound height measured, HS20~100, traditionally used for rolls/large castings; Shore A/D (Shore Durometer) is for rubber/plastics—A for soft rubber(30~95A), D for hard plastic/hard rubber. Both are called 'Shore' but test objects and methods are completely different—do not confuse them.
Why is HRC below 20 inaccurate?
Rockwell C scale (HRC) uses 150kgf major load + diamond indenter. When material hardness is below ~HRC20, indentation depth is too great, potentially causing inappropriate plastic deformation readings from the diamond indenter, plus unclear indentation boundaries leading to large errors. Switch to Rockwell B scale (HRB, steel ball, 100kgf) or Brinell HBW/Vickers HV. General rule: mild steel/annealed use HRB/HB; quenched + medium-high temper use HRC25~45; quenched + low temper use HRC50~65.
Can aluminum alloys and stainless steel use this converter?
Stainless steel (martensitic/ferritic/austenitic): Martensitic stainless (like 2Cr13/440C) in quenched state can reference this tool for HRC; Austenitic stainless (304/316) usually<HRB100, HRC conversion should not be used. Aluminum alloys: Typical aluminum alloy hardness≈HB60~150(HRB20~70), hardness-strength relationship differs from steel—this tool's carbon steel tables cannot be directly used for aluminum alloys, only rough HV/HRB/HB mutual reference. Copper alloys similar. For non-ferrous metals, test directly on target scale rather than relying on conversion.
