20MC5 is a manganese-chromium case-hardening steel from the AFNOR system, equivalent to Wnr. 1.7147 / DIN 20MnCr5 — one of the most widely used carburizing grades in European gear and shaft manufacturing. Manganese and chromium together provide good hardenability for a relatively lean alloy content, letting the steel carburize to a hard wear-resistant case while keeping a tough, fine-grained core. It sits at the lighter-duty end of the case-hardening family, a step below heavier Ni-Cr-Mo grades like 18NCD6 in both alloy cost and section-thickness capability.
20MC5 is supplied and machined in the annealed or normalized condition, then carburized and case-hardened to develop its working surface hardness. It's a mainstay for medium-duty automotive and industrial gears, pinions, shafts, and camshafts — applications where a hard wearing surface and moderate core toughness are needed but the section sizes and load levels don't demand the deeper hardenability of the nickel-alloyed case-hardening grades.
| Standard | Designation |
|---|---|
| AFNOR | 20MC5 |
| Wnr. (Werkstoffnummer) | 1.7147 |
| DIN / EN | 20MnCr5 |
| SAE / AISI | ~5120 (closest approximate match) |
AISI 5120 is the closest practical cross-reference, not an exact match — national standards define slightly different manganese and chromium ranges for their case-hardening grades.
| Element | Content |
|---|---|
| Carbon (C) | 0.17 – 0.22% |
| Silicon (Si) | 0.10 – 0.35% |
| Manganese (Mn) | 1.10 – 1.40% |
| Chromium (Cr) | 1.00 – 1.30% |
Phosphorus and sulfur are each held below about 0.035% per EN 10084.
In its annealed or normalized delivery condition (typically around 163-217 HB), 20MC5 is one of the more approachable case-hardening steels to machine. The manganese-chromium alloy content keeps cutting forces moderate and abrasive tool wear manageable, without the gumminess that nickel-alloyed grades can show. Chip formation is generally favorable, producing manageable chips with standard chipbreaker geometries.
As with other carburizing steels, essentially all cutting work — turning, milling, gear hobbing, drilling — happens before heat treatment, while the part is still soft. Once carburized and case-hardened, the hardened surface is finished by grinding rather than further machining, so leaving appropriate stock for that operation is standard practice.
A coated carbide grade with balanced wear resistance and toughness, run at moderate feeds with a rigid setup, gets consistent results on this steel. Because the alloy content is modest, 20MC5 doesn't demand the more conservative parameters that heavier-alloyed case-hardening grades require.
| Operation | Vc (m/min) | Vc (SFM) |
|---|---|---|
| Turning | 230 – 310 | 750 – 1020 |
| Milling | 145 – 195 | 480 – 640 |
| Parting | 110 – 150 | 360 – 490 |
| Grooving | 130 – 175 | 430 – 570 |
| Drilling | 95 – 125 | 310 – 410 |
Values assume the annealed/normalized delivery condition (approx. 163-217 HB), before carburizing and case hardening. Adjust down for interrupted cuts, poor rigidity, or harder-than-nominal stock.
| Grade | Coating | ISO Application Range |
|---|---|---|
| FM2533 | CVD | P10 |
| FM2543 | CVD | P20 |
| FM324 | PVD | P20 – P30 |
| FM2553 | CVD | P30 |
| Grade | Coating | ISO Application Range |
|---|---|---|
| FM125 | PVD | P20 – P30 |
| FM199 | PVD | P30 |
| FM90 | DLC | P20 |
| FM20 | Uncoated | P10 |
| Grade | Coating | ISO Application Range |
|---|---|---|
| FM125 | PVD | P15 – P35 |
Ready to cut 20MC5? Shop FM Carbide inserts matched to this alloy's turning, parting, grooving, and milling requirements.
Shop Turning & Grooving Inserts Shop Milling Inserts| Parameter | Value |
|---|---|
| Honing Size | 0.05 – 0.08 mm / 0.002 – 0.003" |
| Rake Angle | 11° – 13° |
| Land Angle | Positive |
| Land Width | 0.20 – 0.30 mm / 0.008 – 0.012" |