The strongest structural member in a car body side — hot stamped from Al-Si coated 22MnB5+AS in the 1.2–2.0 mm range to a finished 1300–1500 MPa tensile strength.
If you cold-formed a 1500 MPa steel into a B-pillar, the die would not survive and the part would crack at the radii. Hot stamping sidesteps this: form the soft austenitic blank, then harden it in the die. The steel family that makes this practical is boron-alloyed 22MnB5, and the coating that makes it survive the air furnace is Al-Si.
Boron in the low-alloy range is the cheapest hardenability enhancer in steel. It lets a 1.2–2.0 mm blank harden fully to martensite in the die without expensive alloying — the reason 22MnB5 costs what it does and hardens like it does.
Boron is the enabler of low-cost, fully hardenable thin strip.Uncoated 22MnB5 would scale and decarburize in the ~900 °C air furnace, softening the surface and ruining the part. The Al-Si layer melts and forms a stable intermetallic barrier that protects the steel through heating, forming and quenching.
The +AS suffix is not optional for an air-furnace hot stamping line.Uncoated saves cost but needs furnace atmosphere control and shot blasting after. Zinc coatings risk liquid-metal embrittlement at hot stamping temperatures. Al-Si is the mainstream because it works in a standard roller-hearth furnace with no post-stamp descaling.
Al-Si is the production-standard coating for body structural hot stamping.Indicative values for B-pillar programs; the final spec is agreed at RFQ against your part design and OEM material standard.
| Parameter | Typical value | Why it matters |
|---|---|---|
| Strip thickness | 1.2 – 2.0 mm | Sets part mass and crash performance; thicker for lower-body reinforcement zones |
| Base grade | 22MnB5 (boron-alloyed) | Fully hardenable in the die; the press hardening family standard |
| Coating | Al-Si (+AS), intact on both sides | Prevents oxidation and decarburization during ~900 °C heating |
| Finished tensile | 1300 – 1500 MPa (after die quench) | Martensitic microstructure; the strength the crash structure is designed around |
| Finished hardness | ~ 450 – 500 HV (indicative) | Consistent with the tensile band; verified on parts, not on strip |
| Heating cycle compatibility | Furnace time/temperature per OEM spec | Coating must survive the full soak without cracking or losing protection |
| Width / coil form | Slit to blanking width; CTL blanks available | Blank nesting and heating-furnace indexing want exact widths |
| MTC | Chemistry + coating + mechanicals per heat | Traceability for PPAP and crash-simulation correlation |
Finished-part strength is validated by the stamper's mechanical testing per the OEM specification; the strip's contribution is consistent chemistry, coating and gauge so every part reproduces the crash-test result.
22MnB5+AS is the baseline; equivalents below map to the same material family under different OEM designations. All supplied with Al-Si coating, slit to blanking width.
| Grade | Strength class (hot stamped) | Why it is specified | Typical use |
|---|---|---|---|
| 22MnB5+AS | 1300 – 1500 MPa | Baseline boron steel, Al-Si coated; the most widely specified PHS grade | B-pillar reinforcements, roof rails, tunnel members |
| T1500HS+AS (OEM designation) | 1500 MPa class | OEM-spec 1500 MPa hot stamping steel under European OEM naming | Same parts, European OEM drawing standards |
| AC1500HS+AS | 1500 MPa class | Baosteel commercial 1500 MPa hot stamping designation | Same parts, Baosteel sourcing systems |
| SABC1470+AS | ~ 1470 MPa class | Higher-strength variant for ultra-high-load pillars | Heavy-duty and SUV B-pillar zones |
| CR950/1300HS+AS | 950/1300 MPa class | Ductility-tuned PHS for energy-absorbing zones in the same pillar | Tailored pillars with soft zones |
Strength classes are indicative of the hot-stamped condition; exact guaranteed values follow the governing OEM material standard and the latest revision of the relevant specification.
Hot stamping looks simple — heat, form, quench — but the failure modes are specific and expensive. These are the ones the strip can prevent.
Unprotected steel in a ~900 °C air furnace scales and softens at the surface. Fix: Al-Si coating that melts into a stable barrier — the +AS is the whole point of the grade.
Sheared edges can crack the coating; cracks propagate into the part surface during forming. Fix: clean slitting with controlled edge quality and coating-integrity checks on delivered blanks.
If boron and carbon wander, the die quench may not reach full martensite. Fix: documented chemistry per heat so the austenitizing window holds for the whole coil.
Gauge scatter shifts cooling rate and part geometry. Fix: tight thickness tolerance on the delivered strip keeps the die-quench response repeatable part to part.
The B-pillar is one part in a hot stamped body structure. Match your component below and confirm at RFQ.
22MnB5+AS and equivalents for hot stamped structural parts — the core of this page. Press hardening family →
For reinforcements that are cold stamped instead of hot — DP and MS steels in the 980–1180 MPa class. AHSS family →
For brackets and mounting plates around the pillar, blanked to net shape. Fine blanking range →
A typical sedan B-pillar reinforcement, described the way it runs.
The part is a B-pillar inner reinforcement about 1.1 m long, 1.4 mm thick, hat-shaped in section with a wide flange for spot welding to the outer panel. The coil is 22MnB5+AS, slit to 280 mm; blanks are laser-cut or die-blanked, then run through a roller-hearth furnace at ~900 °C for several minutes. The austenitic blank is transferred to a water-cooled die in under five seconds, formed and quenched in one stroke, and comes out fully martensitic at roughly 1400 MPa. Holes that cannot be formed are laser-cut after stamping — the 1500 MPa-class material is too hard to pierce cold.
The part then goes to E-coat and assembly. In the side-impact crash test, this single member carries a large share of the intrusion load; the cabin survival space depends on it. Every blank that went into the furnace was Al-Si coated, so the surface is clean and paintable; every heat had confirmed boron and carbon, so the die quench always reached martensite; every coil had uniform gauge, so the geometry reproduced. That reproducibility is the entire value of the strip — the crash test only has to pass once, but it has to pass in production.
If your pillar sits in the 1.2–2.0 mm PHS envelope, send the part drawing and OEM spec and we confirm grade, coating, width and a trial-blank plan.
Related reading: what the Al-Si coating does through the hot stamping cycle, and 22MnB5+AS — the press hardening material family explained.
These grade families share material, processing or application territory with the topic on this page.
DP / TRIP / HSLA grades (HC180YD, HC260LA, DP590) combining strength with formability for lightweighting.
SPHC / Q235 / Q345 scale-free coils with oil coating, cost-effective for structural and tube applications.
Send the part drawing, OEM material spec, thickness × width and quantity. Our engineers reply within one working day with grade match, coating confirmation and a trial-blank option.