Vehicle lightweighting and crash performance are now delivered through advanced high strength steel, and the designations are dense: DP, CP, MS, TRIP, TWIP, QP, PHS and the UHSS grades. Choosing among them is a matter of matching strength, formability and crash behaviour to the part, and the coating decision matters as much as the grade. This guide sets out the families, the specification axes and the sourcing checks.
The AHSS families
Dual phase, DP
DP grades such as DP600, DP780, DP980, DP1000 and DP1180 consist of a ferrite matrix with hard martensite islands. They offer a good strength and formability balance, a low yield to tensile ratio and high work hardening rate, which makes them the standard choice for structural and reinforcement parts across the body in white.
Complex phase, CP
CP grades such as CP800 and CP1000 add more hard phases plus micro alloying, giving higher yield strength and better hole expansion than DP for the same tensile strength. They suit parts where edge stretchability matters, such as suspension components and structural members. HC700/980CP is a typical hot rolled CP grade.
Martensitic, MS
MS grades such as MS1180, MS1300 and MS1500 are almost fully martensitic, delivering the highest strength in the AHSS family with limited elongation. They are used for anti intrusion parts where the forming is simple and the crash demand is high.
TRIP, TWIP and QP
TRIP steel uses retained austenite that transforms to martensite during forming, giving high work hardening and excellent elongation. TWIP steel relies on twinning for very high elongation and strength, and is used where the most demanding forming is combined with high strength. QP, quenching and partitioning, grades such as QP980 deliver a strong elongation and strength combination.
Press hardening steel, PHS
Usibor 1500 and 2000, and the boron grades 22MnB5 and 30MnB5, are formed and then hot stamped and quenched in the die, giving very high strength in complex shapes with limited springback. The aluminium silicon coating is a key part of the specification because it provides the surface for subsequent processing and plays a role in the heat treatment.
Lower strength but essential grades
IF steel for deep drawing, grades such as DC04 and DC06, bake hardening steel, and the conventional HSLA and structural grades are not AHSS but remain part of the same sourcing programme, and a complete programme covers them alongside the high strength grades.
Specification axes that decide whether a grade works
Coating type and coating weight
Specify whether the sheet is hot dip galvanised, galvannealed, zinc aluminium, or aluminium silicon for press hardening, and specify the coating weight per side. For hot stamped parts the coating determines whether the part can be laser cut and whether it needs to be shot blasted.
Formability measures beyond tensile strength
Total elongation and the hole expansion ratio describe whether the material will survive the actual forming operation, and they are not implied by tensile strength. For edge critical parts, specify the hole expansion requirement.
Surface quality and defects
Specify the surface class for exposed panels, and specify the acceptance level for defects such as scratches, roll marks and inclusions, since these show through paint on a class A surface.
Mechanical property range and variability
Grade standards permit a property range. For robust forming, specify the required strength and elongation range and require lot to lot consistency data, because a material at the top of the strength range may crack where a mid range material would not.
Hydrogen and delayed cracking
For the highest strength martensitic and press hardened grades, hydrogen embrittlement and delayed cracking are real concerns, and the specification should address coating, cutting and any subsequent processing that can introduce hydrogen.
Verification steps before releasing steel to production
- Confirm the grade and coating against the order, and verify coating weight per side rather than total coating weight.
- Measure yield and tensile strength and elongation on a sample per coil.
- Check the coating adhesion and surface condition after any forming trial.
- Run a forming trial on critical parts rather than relying on handbook formability values.
- Confirm the certificate of analysis and traceability per coil.
- Verify flatness and thickness tolerance for panels where these affect the forming or the assembly.
Common sourcing mistakes
- Selecting on tensile strength alone without considering hole expansion or elongation for the forming operation.
- Specifying coating type without coating weight per side.
- Ignoring the surface class for exposed parts, then finding defects after painting.
- Assuming a grade meets the property requirement exactly, when the standard permits a range.
- Overlooking hydrogen embrittlement risk for the highest strength press hardened parts.
Sourcing AHSS from Hunan and China
China is a major producer of automotive steel including AHSS, press hardening steel and coated automotive sheet, supported by integrated automotive steel lines and a large vehicle industry. Hunan hosts advanced steel suppliers within its advanced materials base, serving both domestic vehicle makers and export customers. LiiFoo maintains verified supplier profiles in the advanced steel materials cluster covering automotive and high strength steel.
For grade matched quotations, mill certificates and forming trial samples, see the cluster above or contact our sourcing team.
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