Cobalt vs titanium vs black oxide drill bits

Three ways to make a drill bit last longer, and what each one actually is: a titanium nitride surface layer, a cobalt through-alloy, or a black oxide conversion layer on plain HSS. The comparison table below sticks to published figures from manufacturer spec pages and metallurgy references, and every cell names its sources.

Three things to get straight before comparing.

  • Titanium nitride (TiN) is a thin surface layer, 2 to 4 microns thick. Re-sharpening grinds that layer off the tip, and the tip becomes ordinary HSS.
  • Cobalt bits are not coated. M35 and M42 steel have cobalt alloyed through the entire bit, which is why sharpening does not cost them performance.
  • Black oxide is an uncoated bit. The black surface is a conversion layer grown from the steel itself, not an added alloy, and it adds essentially no hardness.

Cobalt vs titanium drill bits

Hardness and heat resistance

The headline numbers point in opposite directions depending on where you measure. A TiN layer tests at about 2300 HV at the surface, roughly 82 Rc, sitting over an HSS core of about 64.5 to 65.5 Rc [12] [13] [10]. But that layer is only 2 to 4 microns thick, deposited by PVD onto an ordinary HSS bit [12] [13]. Cobalt never shows up as a surface number at all, because there is no cobalt layer: M35 tests at 65.5 to 67 HRC and M42 reaches 68 HRC through the entire body of the bit [10] [14].

Heat is where the designs actually diverge. TiN begins to oxidize at roughly 500 to 550 C [12] [13], while the cobalt alloy holds red hardness, the ability to keep cutting hot, to about 650 C in M35 and 700 C in M42 [9] [11] [15]. In practice: a TiN bit that stays cool carries a harder surface than any cobalt bit; a bit that runs hot is better off being cobalt all the way through.

Which lasts longer in steel

The honest answer is that the big multiplier numbers are marketing claims measured against different baselines. Milwaukee claims up to 5X life versus black oxide for its RED HELIX titanium bits, and the same product page's bullet list says 3X [1] [2]. Bosch claims 10X life versus standard bits for M42 cobalt [11]. Neither is a head-to-head cobalt-versus-titanium test. Peer-reviewed machining studies put typical coated-versus-uncoated gains at 3 to 10 times, a band that brackets both claims [27] [28].

What the designs themselves predict, and what Irwin states plainly for cobalt, is the sharpening asymmetry. A correctly re-sharpened cobalt bit keeps its cutting life because the alloy runs through the body [8] [10], while a re-sharpened titanium bit is plain HSS at the tip from the first grind [20] [21]. Over a long ownership window in steel, that matters more than any first-coating multiplier.

Price and value

The tier ordering is stable even when individual prices move. Black oxide sets are the budget tier: a Ryobi 25-piece set has been seen at $12.97 on deal [6]. Titanium sits mid tier: a Milwaukee 15-piece TiN set at $29.97, seen at $19.97 [2] [3]. Cobalt is premium, roughly 1.5 to 2 times the cost of plain HSS, with a 29-piece M42 index listing at $289.73 [18] [15].

Per bit, the titanium premium over black oxide is small and buys a real friction and surface-hardness advantage in metal [12] [13]. The cobalt premium buys capability in difficult metal, hardness retention and re-sharpenability, not a better everyday bit [8] [11]. If most of your holes are in wood and plastic, paying either premium is misplaced; the coating question is mostly a metal question.

What users report (Reddit roundups)

Reddit threads frame the question the way the specs predict. In r/MilwaukeeTool, a buyer comparing the 29-piece cobalt and titanium sets at near-equal sale pricing for home use gets answers split by material rather than by brand loyalty [24]. In r/Tools, a user already drilling stainless slowly with cutting compound and still wearing bits out is told, in effect, that the material is the problem, which is the cobalt case [25] [11].

Two patterns repeat across the threads and match the manufacturer positioning: buy the alloy that matches the hardest material you drill regularly [8] [11], and do not pay titanium prices for bits you plan to re-sharpen, because the coating is the product [20] [21]. These are anecdotes, not test data, but they line up with the spec sheet rather than against it.

Milwaukee and other brand-tier notes

Milwaukee tiers its lines by finish. Thunderbolt black oxide bits are positioned for wood, plastics, and metals, with heat build-up reduction and corrosion resistance [4]. SHOCKWAVE RED HELIX titanium bits carry a 135 degree split point and a variable helix from 35 to 15 degrees, plus the 5X claim [1] [2]. In the lines cited here, Milwaukee's finish range runs from black oxide to titanium; the cobalt catalog entries sit with Irwin's 29-piece M35/M42 index [8] and Bosch's CO2134B M42 line with its 10X claim [11].

The practical read: within a brand, the black oxide, titanium, and cobalt versions of similar geometry are priced as entry, mid, and pro tiers [4] [1] [8]. Across brands the tier names differ but the ladder is the same, so the finish, not the logo, is the faster way to predict what a set can drill.

Black oxide vs titanium drill bits

Coating vs through-body hardness

Structurally these are different things done to the same steel. TiN is a deposited PVD layer with its own hardness of about 2300 HV, 2 to 4 microns thick, bonded onto the surface [12] [13]. Black oxide is not deposited at all: it is a conversion layer of magnetite grown out of the bit's own steel in a hot alkaline bath, under about 0.00005 in thick, and it adds essentially no hardness over the base HSS [16] [17].

So the hardness comparison reduces to this: a titanium bit is an HSS bit with a very thin, very hard skin [12] [13], and a black oxide bit is an HSS bit with a cosmetic and corrosion-resistant skin [16] [17]. Underneath both, the same steel does the cutting once you get past the first few microns.

Durability and re-sharpening

Milwaukee claims up to 5X life versus black oxide for its titanium bits [1] [2]. Ryobi claims 3X longer life for its black oxide bits [5], while engineering comparisons put the real black oxide gain, which comes from oil retention in the micro-porous layer, at about 5 to 10 percent [19] [16]. Both multipliers are their manufacturers' marketing; the honest statement is that TiN genuinely out-wears black oxide in metal, by a factor somewhere inside the 3-to-10-times band that peer-reviewed machining studies give for coated versus uncoated tools [27] [28].

Re-sharpening flips the ordering. Grinding the tip removes the TiN layer where it matters, so a sharpened titanium bit is an HSS bit with gold flutes [20] [21]. A sharpened black oxide bit is functionally identical to a bright-finish HSS bit, which is nearly what it was to begin with [20] [21]. If you sharpen your bits, black oxide holds its value and titanium does not.

When black oxide is the smarter buy

Most home drilling is wood, plastic, sheet metal, and the occasional bracket, and Milwaukee itself positions black oxide as ideal for wood, plastics, and metals [4]. For that mix, a black oxide set at the budget tier [6] [7] plus the habit of sharpening beats a titanium set replaced every time it dulls. Roundups of r/Tools sentiment point the same direction: for normal usage, plain black oxide bits from a reputable brand are the recurring recommendation, precisely because the titanium coating wears off anyway [26] [20].

The specific cases where titanium earns its mid-tier price are volume drilling in mild steel and any job where the bit runs long enough for friction heat to matter [12] [13] [2]. If none of your projects look like that, buy the cheaper finish and spend the difference on a second set in the sizes you actually use.

What users report (Reddit roundups)

The black-oxide-versus-titanium threads read as a cost-per-hole argument. The recurring position, summarized in roundups of r/Tools sentiment, is that black oxide from a name brand covers everyday drilling, and that titanium's coating advantage is real but finite and ends at the first sharpening [26] [20] [21]. The home-use purchase threads split the same way, with answers keyed to what the buyer drills rather than to either finish [24].

Nothing in the threads contradicts the spec sheet; users just weight it differently. If you never sharpen bits and drill metal weekly, titanium's upfront advantage compounds; if you own a sharpener or drill mostly wood, the threads and the metallurgy agree that black oxide is the rational buy [20] [21] [19].

Where step drill bits fit

Step drill bits, the conical bits for thin sheet metal, come in the same finishes, and the same logic transfers with one twist. A step bit carries many cutting edges at once, so a finish that slows edge wear multiplies across the whole tool, which is why TiN step bits dominate the mid range [19] [22]. Black oxide step bits cost less and trade some life for it; one engineering comparison puts the black oxide gain at 5 to 10 percent from oil retention [19] [16].

The caveat is aluminum, again: on thin aluminum a TiN step bit can build up edge, and uncoated or TiCN finishes run cleaner [22]. For steel and stainless sheet, the TiN step bit is the standard recommendation, and the coating is not wasted there [22] [12]. The size ladders for those cones, inch and metric, are on our step drill bit sizes page.

Best drill bits for metal

Stainless steel and hard metals

Cobalt is the answer the spec sheets converge on. Irwin builds its cobalt bits from M35 and M42 steel for extended cutting-edge life [8], and Bosch lists its M42 cobalt bits for stainless steel, cast iron, titanium, and light-gauge metal [11]. The property doing the work is red hardness: M35 holds it to about 650 C and M42 to about 700 C, so the edge survives the heat that stainless drilling generates [9] [15] [11].

Stainless also punishes the wrong bit by work hardening: a poor cut hardens the surface and the hole stops progressing, and a titanium bit's thin coating wears through exactly there [20] [21]. The fix is a cobalt bit run slow with oil, which is what the M35 and M42 cobalt lines are specified for [8] [11]. Our drill bits by material page covers that failure mode, the point geometry, and the specific stainless recommendations in detail.

Sheet metal and general metalwork

Light-gauge and general metalwork is titanium's home turf. Milwaukee positions its TiN bits for metal drilling generally [1] [2], and the coating's friction coefficient of about 0.6 to 0.65 versus steel and its 2300 HV surface earn their keep at household volumes [12] [13]. Black oxide handles light-duty metal acceptably, with heat build-up reduction from the oil-holding layer, at the budget tier [4] [5].

For picks by metal type, including sheet-metal geometry and speeds, see the drill bits by material page. This page's job is the finishes; that page's job is the shopping.

Best drill bits for steel

Mild steel vs stainless steel

Mild steel is the easy case: any decent HSS bit cuts it, titanium extends edge life at moderate cost [1] [2], and black oxide is fine at lower volume [4] [5]. Stainless steel is the dividing line where finish stops mattering and alloy starts: it wants M35 or M42 cobalt, very slow RPM, and cutting oil [8] [11]. A titanium bit will drill stainless, but the thin coating wears through and the plain HSS underneath then work hardens the hole [20] [21].

What to look for on the box is the alloy stamp: M35 or M42 for the cobalt content [8] [14]. The full stainless and hardened-steel recommendations, including the 135 degree split point and the speed rules, are on the drill bits by material page.

Speeds and coolant notes

Heat, not force, is what kills bits in steel. Milwaukee credits black oxide with reduced heat build-up [4] and both cobalt lines are built around heat resistance [9] [11], but no finish substitutes for slow RPM and cutting oil. For the actual speed numbers by bit diameter, use the drill speed chart; for which bit to load for which steel, the drill bits by material page is the reference.

Best drill bits for aluminum

Gumming and chip welding

Aluminum's failure mode is adhesion: the work metal welds itself to the cutting edge, called built-up edge, which ruins the geometry and tears the hole. TiN has a documented affinity for aluminum alloys and invites exactly that welding [22], and machining studies of multi-spindle drilling in Al2024 found uncoated drills giving high hole quality at low spindle speed [23]. The finishes that run cleanest in aluminum are bright uncoated and TiCN [22] [23].

Why plain HSS or TiN often beats cobalt here

Cobalt's entire premium, red hardness at 650 to 700 C [9] [15], buys nothing in a metal that melts around 660 C and rarely needs that kind of heat in the first place. A sharp plain HSS bit, run fast with light feed and a lubricant, is the standard recommendation for aluminum [22]. TiN is the acceptable middle: the machining literature finds coated drills acceptable at higher spindle speeds [23], and Milwaukee's general-purpose TiN positioning covers multi-material household work [1] [2]; the strict answer for finish-critical holes is still uncoated or TiCN [22] [23].

Geometry matters more than finish here too: high helix flutes evacuate gummy chips. The drill bits by material page covers the aluminum picks and their geometry.

Best drill bits for wood

Why coatings don't help in wood

Wood is cut, not abraded: it presents no hardness challenge to HSS, so a 2300 HV surface has nothing to push against, and wood drilling runs too cool for red hardness or oxidation limits to matter [12] [13] [9]. Coating selection tables rate bright, black oxide, and TiN all as excellent or good for wood, with only the harder coatings listed as overkill [22]. Milwaukee recommends its black oxide line for wood, plastics, and metals, which tells you the finish there is about rust resistance and price, not cutting performance [4] [16].

Geometry is what matters in wood, and the wood-bit geometry guide, brad point, spade, auger, Forstner, is on the drill bits by material page.

Brad-point vs twist bits

A brad point bit's center spur locates the hole and its outer spurs score the fibers before the flutes clear material, which is what stops wandering and tear-out; a twist bit bores wood acceptably but starts less cleanly and blows out the exit face. None of that is finish-dependent, so the honest advice for wood is to buy the geometry, ignore the coating, and put the savings toward a second size range. The wood section of our drill bits by material page walks the geometry choices with sources.

Overall comparison: cobalt vs titanium vs black oxide

Comparison table

Every value below comes from the verified claims sheet behind this page, and each cell names the two (occasionally three) sources it rests on, keyed to the numbered list under the table. Hardness figures are quoted as published, in the unit the source used, with no conversion between HV and HRC. Life multipliers are manufacturer marketing figures and are attributed as such.

Coating comparison: titanium nitride, cobalt alloy, black oxide
coating hardness lubricity best material durability price tier re-sharpenable
Cobalt (M42/M35) None applied. Cobalt is alloyed through the steel: M35 is 5 percent cobalt, M42 is 8 percent [8] [11] 65.5 to 67 HRC through the body (M35); up to 68 HRC (M42) [10] [14] No surface lubricity; it is bare steel. The gain is red hardness, it keeps cutting hot, to roughly 650 C (M35) and 700 C (M42) [9] [11] [15] Stainless steel, cast iron, titanium, light-gauge metal, aluminum, and tough or hardened metals [11] [8] Bosch claims 10X life versus standard bits; Irwin credits the cobalt alloy with extended cutting-edge life [11] [8] Premium. A 29-piece M42 index lists at $289.73, and cobalt bits run roughly 1.5 to 2 times the cost of plain HSS [18] [15] Yes, with performance retained: the alloy runs through the body, so a correctly sharpened cobalt bit is as good as new [8] [10]
Titanium (TiN) PVD titanium nitride surface layer, 2 to 4 microns thick, over standard HSS [12] [13] About 2300 HV at the surface, roughly 82 Rc; the HSS underneath is about 64.5 to 65.5 Rc [12] [13] [10] Friction coefficient versus steel of about 0.6 to 0.65, which cuts built-up edge; the coating oxidizes above roughly 500 to 550 C [12] [13] Wood, plastics, and metals: general purpose [1] [2] Milwaukee claims up to 5X life versus black oxide for its RED HELIX titanium bits; the same page's bullet list says 3X [1] [2], and peer-reviewed machining studies put typical coated-versus-uncoated gains at 3 to 10 times [27] [28] Mid. The Milwaukee 15-piece titanium set lists at $29.97 and has been seen at $19.97 [2] [3] Effectively no. Grinding removes the 2 to 4 micron layer at the tip, and the tip becomes plain HSS [21] [20]
Black oxide No coating alloy. Uncoated base HSS with a chemical conversion layer of magnetite grown from the steel surface, under about 0.00005 in thick [16] [17] No substantial increase over the base steel; the low-temperature process does not affect temper or hardness [16] [17] The micro-porous layer retains oil or wax for mild lubricity and corrosion resistance; Milwaukee also credits it with reduced heat build-up [4] [16] Wood, plastics, and metals at light duty [4] [5] Baseline tier. Ryobi claims 3X longer life for its black oxide bits; engineering comparisons put the real gain, from oil retention, at about 5 to 10 percent [5] [19] Budget. The Milwaukee 14-piece set sells around $27.97, the Ryobi 25-piece set seen at $12.97 on deal [7] [6] Yes. The exposed base HSS is the whole tool, so losing the conversion layer at the tip is essentially cosmetic [20] [21]

Prices are point-in-time observations from September 2026, shown to establish tier ordering only, not as current prices. Hardness, friction, and temperature figures are quoted exactly as their sources publish them.

Single-source disclosure: eight figures on this page appear in only one located source each, with no second independent publisher printing the same number, so treat them as single-sourced. The 64.5 to 65.5 Rc hardness of the HSS core under TiN is published only by IRWIN support [10]. The up to 68 HRC figure for M42 is published only by Penn Tool Co [14]. The roughly 650 C and 700 C red hardness figures for M35 and M42, and the 1.5 to 2 times cobalt price premium over plain HSS, are published only by AIMS Industrial [15]. The $289.73 list price of the IRWIN 29-piece cobalt index is published only by Eppys [18]. The 5 to 10 percent black oxide life gain from oil retention is published only by Zhonghuan Tools [19]. The $27.97 Milwaukee 14-piece price is published only by Great Lakes Power Tools [7]. The $12.97 Ryobi deal price is published only by Slickdeals [6]. Every other numeric claim on this page appears in at least two independent sources.

Sources for the comparison table

  1. Milwaukee Tool, SHOCKWAVE RED HELIX Titanium Drill Bit Set 15PC 48-89-4630: milwaukeetool.com
  2. The Home Depot, Milwaukee 48-89-4630 bundle and category listings (5X life spec, $19.97 and $29.97): homedepot.com
  3. Slickdeals, price history for Milwaukee 48-89-4630 (list price $29.97): slickdeals.net
  4. Milwaukee Tool, THUNDERBOLT Black Oxide Drill Bit Set 14PC 48-89-2800: milwaukeetool.com
  5. The Home Depot, RYOBI Black Oxide Round Shank Drill Bit Set 25 Piece A972501: homedepot.com
  6. Slickdeals, RYOBI 25-piece black oxide set at $12.97: slickdeals.net
  7. Great Lakes Power Tools, Milwaukee 48-89-2800 listing ($27.97): greatlakespowertools.com
  8. IRWIN Tools, 29PC Cobalt Industrial Set 3018002/3018002B (M35 and M42 alloy construction, cutting life after resharpening): irwintools.com
  9. IRWIN Tools, HSS COBALT product page (5 percent cobalt improves red hardness and abrasion resistance): irwintools.com
  10. IRWIN Tools support knowledge base, cobalt versus TiN hardness and resharpening: support.irwin.com
  11. Bosch Professional, Cobalt M42 Drill Bits CO2134B (8 percent cobalt alloy, high heat resistance, 10X life claim): boschtools.com
  12. Hannibal Carbide Tool, Titanium Coatings technical page (2 to 4 microns, 2300 HV / 81 Rc, oxidation at 550 C): hannibalcarbide.com
  13. voestalpine eifeler Coatings, TiN PVD datasheet (2300 HV, layer thickness, 500 C max operating temperature): eifeler.com
  14. Penn Tool Co, IRWIN 29-piece jobber set listings (M35 up to 66 HRC, M42 up to 68 HRC): penntoolco.com
  15. AIMS Industrial, Cobalt Drill Bit Guide M35 vs M42 (red hardness about 650 C and 700 C, price ratios): aimsindustrial.com.au
  16. Want.net, black oxide engineering guide (chemical conversion coating, MIL-DTL-13924, no substantial hardness increase, oil retention): want.net
  17. manufacturingprocesses.org, Black Oxide process page (magnetite conversion layer, 0.00003 to 0.00005 in, temper and hardness unaffected): manufacturingprocesses.org
  18. Eppys, IRWIN 3018002B 29-piece cobalt set listing ($289.73): eppys.com
  19. Zhonghuan Tools, step drill bit coatings comparison (black oxide tool life gain of 5 to 10 percent from oil retention): zhonghuantools.com
  20. PowerToolsInsider, drill bit coatings guide (resharpening removes TiN coating; black oxide resharpens freely): powertoolsinsider.com
  21. PowerToolsToday, drill bit coating types guide (sharpening a TiN bit removes the benefit; black oxide base HSS stays functional): powertoolstoday.com
  22. DrillBitsWorld, drill bit coatings guide (TiN affinity for aluminum causes built-up edge; uncoated or TiCN preferred for aluminum, coating ratings by material): drillbitsworld.com
  23. Aamir et al., Metals 2021, 11(7), 1103, MDPI (multi-spindle drilling of Al2024: uncoated drills gave high hole quality at low spindle speed): mdpi.com
  24. Reddit r/MilwaukeeTool, "Cobalt vs Titanium drill bits?" thread (home-use purchase question at near-equal sale pricing): reddit.com
  25. Reddit r/Tools, "Does it matter what brand cobalt drill bits I buy" thread (stainless drilling wear despite slow speed and cutting compound): reddit.com
  26. FindingDulcinea, best drill bit sets roundup, July 2026 (summarizes r/Tools sentiment favoring plain black oxide bits for everyday use): findingdulcinea.com
  27. International Journal of Advanced Manufacturing Technology (Springer), Improvement of Tool Life and Exit Burr using Variable Feeds when Drilling Stainless Steel with Coated Drills (tool life of TiN-coated tools 3 to 10 times higher than conventional HSS, all cutting conditions): link.springer.com
  28. Wear (Elsevier, 1999), Evaluation of the wear of plasma-nitrided and TiN-coated HSS drills using conventional and Micro-PIXE techniques (tool life increase by a factor between 3 and 10 for TiN-coated HSS tools): sciencedirect.com

Which should you buy first

Keyed to the table above: buy a black oxide or bright HSS set first. It covers wood, plastic, and light metal at the budget tier and re-sharpens without penalty [4] [5] [6]. Add a titanium set second if you drill a lot of mild steel and treat bits as consumables, since the coating out-wears black oxide but dies at the sharpener [1] [2] [20]. Add cobalt last, and selectively, a small set or singles, when stainless, cast iron, or hardened steel actually enters your work, because that is the only place its premium pays [8] [11].

Verdicts per coating

Cobalt verdict: buy it for hard metals. M35, at 5 percent cobalt, covers stainless and general hard drilling; M42, at 8 percent, for hardened steel and the worst heat [8] [11] [15]. It re-sharpens without losing performance because the alloy runs through the body [8] [10], and you pay the premium tier price for exactly that capability and nothing else [18] [15].

Titanium verdict: the mid-tier generalist. Real edge-life gains in mild steel and multi-material drilling, backed by a 2300 HV surface and lower friction [12] [13] [1]. Not a buy if you sharpen: grinding removes the 2 to 4 micron layer and the bit becomes plain HSS [20] [21]. Run it until it dulls, then replace it.

Black oxide verdict: the budget workhorse for wood, plastic, and light metal [4] [5]. The conversion layer adds corrosion resistance and mild lubricity, not hardness [16] [17], so expect baseline HSS cutting and pay the budget price for it [6] [7]. It re-sharpens freely; the rational default first set.