Four steel families, one vehicle platform: 51CrV4 for the coil spring that compresses 500,000 times, 22MnB5+AS for the control arm hot-formed to 1500 MPa, SAPH440 for the subframe that welds and holds, and 65Mn for the stabilizer bar that twists with every corner.
A coil spring fails by fatigue crack at the surface. A control arm fails by buckling or intrusion in a crash. A subframe fails by weld fatigue. A stabilizer bar fails by torsional fatigue. Each failure mode demands a different steel: one that resists surface-initiated fatigue, one that hardens to 1500 MPa in a die, one that welds and forms, and one that twists a billion times. The four families below map directly to those four failure modes.
C 0.47–0.55%, Cr 0.90–1.20%, V 0.10–0.25%. Vanadium refines the grain and raises the elastic limit; chromium deepens hardenability so a 16 mm bar hardens through. After hot coiling, quenching and tempering, the spring lands 45–50 HRC with elastic limit ≥800 MPa and fatigue life ≥500,000 cycles. Supplied spheroidized-annealed with decarb ≤0.03 mm per side so the surface is not a crack origin.
Choose 51CrV4 for every coil spring, torsion bar and high-cycle elastic element.C 0.22%, B 0.002–0.005%, Al-Si coating 120–160 g/m². Boron gives through-hardening in a water-cooled die; the Al-Si coating prevents scale during austenitizing. After hot stamping at 900–950 °C and die quenching, tensile strength reaches 1300–1500 MPa. Control arms and crash parts run 2.0–4.0 mm thick — thinner than conventional chassis steel, cutting unsprung mass while meeting side-impact intrusion targets.
Choose 22MnB5+AS for control arms, lower arms and crash-reinforcement members.JIS G3113 hot-rolled pickled steel, 440 MPa min tensile, 305 MPa min yield. Good formability for complex subframe geometry, excellent weldability for MIG and spot welding, and fatigue resistance sufficient for chassis structural loads. Typical thickness 2.0–6.0 mm, supplied pickled and oiled. SAPH440 is the workhorse of chassis structures where the part does not see the extreme elastic or crash loads that demand spring or press-hardening steel.
Choose SAPH440 for subframes, crossmembers, brackets and trailing arms.C 0.62–0.73% (65Mn) or 0.72–0.85% (SAE1078), manganese for hardenability. Stabilizer bars are bent from bar or tube (3–6 mm wall), then induction-hardened in the torsion zone to 42–48 HRC. The bar twists with every suspension movement — torsional fatigue resistance and a consistent hardness band along the working length are the governing parameters. 65Mn is the GB standard; SAE1078 is the AISI equivalent for global platforms.
Choose 65Mn/SAE1078 for stabilizer bars, spring seats and chassis fasteners.Indicative values from production chassis programs; the final spec is agreed at RFQ against your part drawing, vehicle platform and governing standard (GB, JIS, AISI, EN).
| Component | Steel grade | Section / thickness | Key parameter |
|---|---|---|---|
| Coil spring (front suspension) | 51CrV4 / 50CrV4 | Wire Ø 8 – 16 mm | HRC 45–50, fatigue ≥500k cycles, free height 200–400 mm |
| Stabilizer bar (solid) | 65Mn / SAE1078 | Bar Ø 18 – 32 mm | Induction HRC 42–48 in torsion zone, torsional fatigue |
| Stabilizer bar (tubular) | SAE1078 | Wall 3 – 6 mm | HRC 42–48, weight reduction vs. solid bar |
| Control arm / lower arm | 22MnB5+AS | 2.0 – 4.0 mm | Hot-formed tensile 1300–1500 MPa, Al-Si coating |
| Subframe / crossmember | SAPH440 | 2.0 – 6.0 mm | Tensile ≥440 MPa, pickled & oiled, weldable |
| Shock absorber piston / rod guide | SAE1045 / 42CrMo | Bar Ø 12 – 30 mm | Surface HRC 55–60, core tough, chrome-plated OD |
| Spring seat / spring pad retainer | 65Mn | 2.0 – 4.0 mm | HRC 40–45, fatigue-resistant contact surface |
| Suspension bracket / trailing arm | SAPH440 | 3.0 – 5.0 mm | Formable, weldable, fatigue-rated |
Hardness, tensile strength and fatigue values are agreed per part and verified on the MTC. For 22MnB5+AS, the as-delivered tensile is approximately 600 MPa (ferrite-pearlite); the 1300–1500 MPa figure is after hot stamping and die quenching. Coating weight is confirmed per coil.
All grades supplied with confirmed chemistry and mechanicals per heat. Choose by load mode (elastic, crash, structural, torsional), manufacturing route (hot coil, hot stamp, cold stamp, induction harden) and drawing standard.
| Part type | Primary grade | Alternative grade | Selection criterion |
|---|---|---|---|
| Front / rear coil spring | 51CrV4 (EN) | 50CrV4 (GB) | Elastic limit + fatigue life ≥500k cycles |
| Heavy-duty / commercial spring | 50CrV4 | 55Cr3 (EN) | Higher load capacity, larger wire Ø |
| Stabilizer bar (solid) | 65Mn (GB) | SAE1078 (AISI) | Torsional fatigue + induction hardenability |
| Stabilizer bar (tubular) | SAE1078 | 51CrV4 | Weight reduction + high elastic limit |
| Control arm / lower arm | 22MnB5+AS | 22MnB5 (bare) | Hot-form tensile 1300–1500 MPa + coating |
| Crash reinforcement / B-pillar link | 22MnB5+AS | PHS 1500 | Intrusion resistance in side impact |
| Subframe / crossmember | SAPH440 (JIS) | SPH440 / QStE420TM | Formability + weldability + cost |
| Suspension bracket | SAPH440 | SPHC (structural) | Load rating + stamping complexity |
| Shock absorber piston rod | SAE1045 | 42CrMo | Surface hardness + core toughness |
| Spring washer / chassis fastener | 65Mn | SAE1078 | Elastic limit + HRC 42–50 |
Grade selection for hot-formed parts is driven by the target tensile after die quenching and the coating requirement (Al-Si coated for in-line hot stamping, bare for secondary blasting). Spring grade selection is driven by wire diameter, fatigue load spectrum and the governing standard (EN 10089, GB/T 1222, ASTM A229).
These are the failure modes that show up in chassis and suspension production, in the order chassis engineers care about them.
A coil spring with a decarburized surface layer under-hardens at the wire surface, creating a soft skin that becomes a fatigue crack origin after 100,000–200,000 cycles. Fix: 51CrV4/50CrV4 supplied with controlled-atmosphere spheroidizing and measured decarb ≤0.03 mm per side, reported on the MTC. The spring maker then shot-peens the surface to introduce compressive residual stress, closing any remaining surface defects.
A 22MnB5+AS control arm that does not reach full martensite after die quenching runs soft in thick sections or at die contact points, failing crash intrusion tests. Fix: confirm the boron content (0.002–0.005%) and hardenability band on the MTC, specify the Al-Si coating weight (120–160 g/m²), and validate the die-quench cooling rate on the first trial parts. We supply 22MnB5+AS with chemistry confirmed per heat and can support trial-coil stamping.
A stabilizer bar that fails at the bend radius after 200,000 cycles typically has a hardness drop or surface defect introduced during bending. Fix: 65Mn/SAE1078 bar with consistent through-hardening response, controlled surface finish (no seams or laps), and an induction-hardening cycle that covers the full torsion zone including the bend radius. We confirm the bar's surface quality and hardenability per heat.
A subframe that develops weld cracks at chassis bracket joints after durability testing usually has inadequate weld penetration or a heat-affected zone that is too soft. Fix: SAPH440 supplied with confirmed carbon equivalent (CEV ≤0.30%) for good weldability, pickled and oiled surface for consistent welding, and mechanicals within the JIS G3113 band. We confirm CEV and tensile per coil and can supply cut-to-length blanks for subframe stamping.
Chassis production draws on several steel families. Match your component below and confirm at RFQ.
51CrV4 / 50CrV4 / 65Mn spring steel for coil springs, stabilizer bars and chassis elastic elements at HRC 45–50 with controlled decarb. Spring steel family →
22MnB5+AS Al-Si coated press-hardening steel for hot-formed control arms, crash members and B-pillar reinforcements reaching 1300–1500 MPa. Press-hardening family →
SAPH440 / SPHC hot-rolled pickled steel for subframes, crossmembers, suspension brackets and trailing arms with weldability and formability. Hot-rolled pickled family →
42CrMo / SAE1045 alloy steel for shock absorber piston rods, steering components and high-strength chassis fasteners. Alloy structural family →
A typical C-segment passenger car front coil spring, described the way it runs.
The spring is a cylindrical coil with progressive pitch, 12.5 mm wire diameter, 96 mm mean coil diameter, 280 mm free height, and 6.5 active coils. The drawing calls 51CrV4 spring steel wire to EN 10089, spheroidized-annealed, decarb ≤0.03 mm per side, surface free of seams and laps. The wire is hot-coiled at 850–900 °C, quenched in oil, and tempered at 400–450 °C to land 46–48 HRC. After heat treatment, the spring is shot-peened to introduce compressive residual stress at the surface, then preset (compressed to solid height three times) to settle the material and eliminate permanent set in service.
The fatigue test is the moment of truth. The spring is loaded between its rated minimum and maximum heights at 2 Hz for 500,000 cycles. Any spring that fractures before 500,000 cycles is traced back to a surface defect — a seam, a decarburized patch, or a peening miss. That is why the incoming wire's surface condition and decarb limit are not optional: they are the difference between a 99% first-pass fatigue yield and a 75% yield with root-cause investigation. Our job is to make the 51CrV4 wire's chemistry, decarb and surface so repeatable that the spring line's variables (coiling temperature, quench rate, peening coverage) are the only variables left.
The same vehicle platform uses a 22MnB5+AS front lower control arm, 2.8 mm thick, hot-stamped and die-quenched to 1400 MPa tensile. The control arm's Al-Si coating prevents scale during austenitizing, so the part leaves the hot-stamping press ready for welding without shot blasting. And the rear subframe is stamped from SAPH440 pickled and oiled coil, 3.2 mm thick, MIG-welded to the suspension brackets and body mounts. If your chassis program needs 51CrV4 for springs, 22MnB5+AS for control arms, SAPH440 for structures, or 65Mn for stabilizer bars, send the drawing and we confirm grade, key parameters and a trial-coil plan. Our slitting and processing services cover exact-width coils, cut-to-length blanks and edge conditioning.
Related reading: how 51CrV4, 50CrV4 and 65Mn compare across EN, GB and AISI spring standards, and the 22MnB5+AS hot-stamping process from austenitizing to die quenching. For procurement context, see our precision steel strip buyer's handbook. Related application pages: press-hardening steel for automotive B-pillars and spring steel for clutch disc springs.
These grade families share material, processing or application territory with the topic on this page.
51CrV4 / 50CrV4 / 65Mn grades with high elastic limit and fatigue resistance for suspension components.
22MnB5+AS Al-Si coated grades reaching 1300–1500 MPa after die quenching.
SAPH440 / SPHC grades with weldability and formability for chassis structural members.
Send part drawing, section size, key parameter (HRC, tensile, fatigue), quantity and destination port. Our engineers reply within one working day with grade match and a trial-coil option.