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Case-Hardening Steel

Case-hardening (carburizing) steels are low-carbon alloy steels, 0.10–0.25 % C with chromium, manganese, nickel or molybdenum, designed to be carburized: the surface is saturated with carbon at 900–950 °C, quenched and lightly tempered to 58–62 HRC while the low-carbon core stays tough at 30–45 HRC and 800–1,200 MPa yield. That hard skin over a ductile body is what gear teeth, cams, pins and splines need to survive contact stress and shock, and it is the standard route for automotive and industrial gearing.

Popular case-hardening steel grades

Compare in the explorer
GradeYield, MPaTensile, MPaDensity, g/cm³MachinabilityWeldabilityBest for
16MnCr54006207.85GoodFairEN volume gear steel for small and medium teeth
20MnCr54607507.85GoodFairEN gear steel for larger teeth and shafts
18CrNiMo7-63706407.85GoodFairHeavy-duty Ni gearing; wind, mining, trucks
20CrMnTi4006207.8GoodFairGB gear steel on Chinese drawings
46203605707.85GoodGoodNi-Mo pins and camshafts, moderate loads
48204507007.86FairFairHigh-nickel deep-case gears and pinions
EN364507007.85FairPoorUK Ni-Cr gear and shaft steel

All 102 case-hardening steel grades

Choose case-hardening steel for

Gears, pinions, splines, sprockets, camshafts and cam followers, gudgeon and piston pins, universal-joint crosses, bearing races on shafts, rack teeth — any part where a 58–62 HRC surface must ride on a core that absorbs shock and resists tooth-root or shaft fatigue.

Look elsewhere when

The part needs uniform hardness through the section (4140, 4340 quench-and-tempered), the hard layer can be shallow and the geometry suits induction hardening (1045, 4140), maximum wear at 60+ HRC with no case-depth limit is required (52100 or D2), the part is welded after hardening (1018), or quench distortion is unacceptable — nitrided 4140 or 38CrMoAl gives a thinner but distortion-free case.

Yield strength against elongation at break, Case-hardening steel among every steel grade

No materials in view have both of these properties.

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Case-hardening steel by application

Automotive and industrial gears
16MnCr5 / 20MnCr5 or 8620 carburized to 0.6–1.2 mm effective case, 58–62 HRC surface, 30–40 HRC core; 20CrMnTi on GB drawings. Grind or hone the teeth after hardening and allow 0.1–0.2 mm distortion stock.
Heavy-duty and large gears
18CrNiMo7-6, 17CrNiMo6 or 4820 for modules above about 8 mm and case depths to 2 mm; the nickel keeps the core tough at 1,000+ MPa and resists tooth-root fatigue. EN36 and EN353 are the UK equivalents.
Pins, cams and followers
8620 or 4620 for gudgeon pins, cam lobes and rollers; 15B21 / 10B21 carbonitrided for lighter-duty pins, clips and fasteners where a 0.2–0.4 mm skin is enough.
Carburized shafts with splines
20MnCr5 or 8620 with the journals and threads masked or copper-plated where they must stay soft for machining after hardening; 25MnCr5 when the core strength must be higher.

Working with case-hardening steel

Machining
All machining is done before carburizing, in the normalized or annealed state — these are soft (150–200 HB) low-carbon steels that cut like 1020 with a slightly gummy chip; 16MnCrS5 / 20MnCrS5 and controlled-sulfur 8620 run cleaner. After hardening only grinding, honing or hard turning with CBN is possible. Leave 0.1–0.3 mm on critical surfaces for distortion.
Heat treatment
Carburize 900–950 °C in gas or vacuum (low-pressure carburizing) for a 0.5–2 mm effective case, direct or reheat quench in oil, temper 150–200 °C: surface 58–62 HRC, core 30–45 HRC depending on grade and section. Specify effective case depth (to 50 HRC), surface hardness and core hardness on the drawing. Carbonitriding at 820–870 °C gives a thinner, harder skin on the boron grades and on 1018.
Welding
Weldable before carburizing with mild-steel procedures (0.15–0.25 % C — light preheat for the Ni-Cr-Mo grades). After hardening the case cracks under the arc; mask the weld zone with copper plate or stop-off paint during carburizing if welding must follow, or design the joint elsewhere.
Finishing
Carburized surfaces are ground to finish and often shot-peened for fatigue (gear roots). Black oxide or phosphate for storage; hard chrome is not needed on a 60 HRC case. Do not plate before carburizing except as a deliberate stop-off.

Other steel series

Case-Hardening Steel — frequently asked

What is case-hardening steel?

Case-hardening (carburizing) steels are low-carbon alloy steels, 0.10–0.25 % C with chromium, manganese, nickel or molybdenum, designed to be carburized: the surface is saturated with carbon at 900–950 °C, quenched and lightly tempered to 58–62 HRC while the low-carbon core stays tough at 30–45 HRC and 800–1,200 MPa yield. That hard skin over a ductile body is what gear teeth, cams, pins and splines need to survive contact stress and shock, and it is the standard route for automotive and industrial gearing.

Which grade of case-hardening steel should I use?

8620 (SNCM220, 20NiCrMo2-2) is the North American general-purpose grade for gears, pins and shafts; 16MnCr5 and 20MnCr5 are its EN counterparts and the volume gearing steels in Europe and Asia, 20MnCr5 for larger teeth. 20CrMnTi is the GB equivalent found on Chinese gear drawings. 18CrNiMo7-6 (17CrNiMo6, EN36, 4820) is the heavy-duty nickel grade for wind-turbine, mining and truck gears where core strength above 1,000 MPa and deep cases are needed; 9310 is the aerospace version. 4615 / 4620 are the older nickel-molybdenum grades for camshafts and pins; 10B21 and 15B21 are low-cost boron grades for carburized or carbonitrided fasteners and clips. 16MnCrS5 / 20MnCrS5 are the sulfur-bearing versions that machine faster.

Which grade of case-hardening steel is the strongest?

18Cr2Ni4WA has the highest yield strength in the series at 1,150 MPa; 20Cr2Ni4A follows at 1,120 MPa. Values are for each grade's default condition.

Which grade of case-hardening steel is easiest to machine?

20MoCrS4 (machinability good, 66/100), then 20MoCr4 (63/100).

Is case-hardening steel heat-treatable?

Yes. These grades gain their strength from heat treatment; the conditions and their properties are listed on each grade page.

8620 or 16MnCr5 / 20MnCr5?

They do the same job: 8620 is the SAE Ni-Cr-Mo grade, 16MnCr5 and 20MnCr5 the EN Mn-Cr grades — 16MnCr5 for small gears and pins, 20MnCr5 for larger teeth where more core strength is needed. Carburized, all three reach 58–62 HRC on the surface with a 30–40 HRC core. Specify the one your drawing standard and your heat treater know; 20CrMnTi is the same idea on GB drawings.

Carburize or nitride?

Carburizing gives a deep case (0.5–2 mm) at 58–62 HRC and needs a quench, so parts distort and must be ground afterwards; it is the choice for gear teeth under heavy contact stress. Nitriding runs at 500–550 °C with no quench, so distortion is near zero, but the case is thin (0.1–0.5 mm) — used on finished 4140, 38CrMoAl or 31CrMoV9 parts where dimensional stability matters more than case depth.