QSTE420TM is a thermomechanically rolled micro-alloyed steel with a guaranteed minimum yield strength of 420 MPa. It is the cold-forming workhorse of the automotive structural steel family - specified for body-in-white, chassis beams, and safety components where high strength must coexist with good formability and weldability. Here is the grade's complete technical profile, with verified data and processing guidance.
Key Takeaways
- Yield strength ≥420 MPa, tensile 480–620 MPa. These are the as-delivered (thermomechanically rolled) values per SEW092 / EN 10149-2. No subsequent heat treatment needed.
- Equivalent to S420MC (EN 10149-2), material number 1.0980. Also corresponds to NFA E420D, UNI FeE420TM, ASTM 060XLK, and Chinese HR420F (GB/T 20887).
- Micro-alloying with Nb, V, Ti provides grain refinement and precipitation strengthening without compromising weldability.
- Typical automotive applications: body frames, door beams, roof rails, chassis beams, suspension components, and collision energy-absorbing structures.
- Available thickness range: typically 1.2–16 mm (hot-rolled pickled coil/sheet). Width up to ~1,600 mm.
- Good weldability with standard MIG/MAG and resistance spot welding. Low heat input and controlled interpass temperature (≤200°C) recommended.
1. What QSTE420TM Is and Where It Sits in the Steel Family
QSTE420TM belongs to the family of thermomechanically rolled fine-grain steels designed for cold forming. The designation breaks down as: Q = quench/quality, St = steel, E = minimum yield strength (420 MPa), TM = thermomechanically rolled. It originates from the German SEW092 specification, though it is now widely referenced under Q/BQB 310 (Baosteel enterprise standard) and cross-referenced to EN 10149-2 S420MC.
Unlike quenched-and-tempered steels, TM steels achieve their properties through controlled rolling and micro-alloy precipitation during cooling. The fine grain structure (typically ASTM 10–12) provides an attractive combination: strength high enough to reduce section thickness and vehicle weight, but ductility and formability good enough for stamping, bending, and drawing complex automotive shapes.
2. Chemical Composition
| Element | QSTE420TM (SEW092 / Q/BQB 310) | S420MC (EN 10149-2) | Remarks |
|---|---|---|---|
| C, max | 0.12 | 0.12 | Low carbon for weldability |
| Si, max | 0.50 | 0.50 | Deoxidizer; excess harms surface quality |
| Mn, max | 1.60 | 1.60 | Solid-solution strengthener |
| P, max | 0.030 | 0.025 | Impurity; EN limit is tighter |
| S, max | 0.025 | 0.015 | Impurity; affects formability |
| Al, min | 0.015 | 0.015 | Grain refiner & deoxidizer |
| Nb, max | 0.09 | 0.09 | Grain refinement & precipitation strengthening |
| V, max | 0.20 | 0.20 | Precipitation strengthening |
| Ti, max | 0.15 | 0.15 | Grain refinement via TiN/TiC precipitates |
Source: SEW092, Q/BQB 310-2009, EN 10149-2:2013. The micro-alloy elements Nb, V, and Ti may be added individually or in combination. "max" values are single maxima; "min" values are single minima.
The micro-alloying philosophy behind QSTE420TM is worth understanding: niobium (Nb) pins austenite grain boundaries during hot rolling, producing a fine final grain size. Vanadium (V) and titanium (Ti) form fine carbide/nitride precipitates during cooling that increase strength through dispersion hardening. Because carbon is kept below 0.12%, the carbon equivalent (CEV) stays low enough for good weldability without preheat in typical thicknesses.
3. Mechanical Properties
| Property | Value | Condition |
|---|---|---|
| Yield strength ReH, min | 420 MPa | All thicknesses, transverse |
| Tensile strength Rm | 480–620 MPa | All thicknesses, transverse |
| Elongation A80, min | 16% | Thickness < 3.0 mm |
| Elongation A5, min | 19% (source-dependent: up to 21%) | Thickness ≥ 3.0 mm |
A yield-to-tensile ratio of approximately 0.68–0.88 means QSTE420TM has useful work-hardening capacity after yield - important for energy absorption in crash events. The minimum elongation of 16–19% confirms adequate ductility for cold bending and moderate stretch forming.
4. Equivalent Grades Across Standards
| Standard | Grade Designation | Material Number |
|---|---|---|
| SEW092 (Germany) | QStE420TM | 1.0980 |
| EN 10149-2 (Europe) | S420MC | 1.0980 |
| Q/BQB 310-2009 (Baosteel) | QStE420TM | - |
| NFA 36-231 (France) | E420D | - |
| UNI 8890 (Italy) | FeE420TM | - |
| ASTM (USA) | 060XLK | - |
| BS 1449 (UK) | HR50F45 | - |
| GB/T 20887.1-2007 (China) | HR420F | - |
Cross-reference compiled from SEW092, EN 10149-2, and steel supplier technical data sheets. Note: GB/T 20887 HR420F may have slight compositional differences. For frame/chassis-specific applications, refer to GB/T 3273 grade 420L as a related but not identical grade.
5. Automotive Applications
| Application Area | Specific Components | Why QSTE420TM |
|---|---|---|
| Body-in-white | Body frames, door impact beams, roof rails, hood inner panels | High strength-to-weight ratio; cold-formable into complex shapes |
| Safety structures | B-pillar reinforcements, side impact beams, bumper beams | Predictable energy absorption; good work-hardening after yield |
| Chassis & suspension | Chassis beams, crossmembers, suspension arms, subframes | Fatigue resistance; weldable to other HSLA grades |
| Load-bearing | Truck frame rails, trailer beams, structural brackets | 420 MPa yield allows section reduction vs. mild steel |
Application list based on open-source mill documentation and automotive industry practice.
6. Processing Workflow - Step by Step
6.1 Material Preparation
Verify the incoming coil or sheet against the mill test certificate (MTC): confirm grade (QSTE420TM or S420MC), heat number, chemical composition within spec, and mechanical properties. Check the surface for scale, pickling quality, and dimensional tolerances (thickness, width, flatness). For pickled and oiled (P&O) material, verify the oil film is intact to prevent transit rust.
6.2 Cutting
QSTE420TM can be cut by shearing (guillotine) for straight-line cuts, laser cutting for complex profiles, or plasma cutting for thicker gauges (>6 mm). Laser cutting is preferred for production parts because the narrow heat-affected zone (HAZ) minimizes edge hardening. If plasma cutting is used on thicknesses above 8 mm, grind the cut edge to remove the nitride-hardened layer before cold forming.
6.3 Cold Forming
This is where QSTE420TM earns its designation. The fine-grained microstructure permits:
- Bending: Minimum bend radius of ~1.0–1.5t (where t = sheet thickness) for 90° bends transverse to the rolling direction. Bending parallel to the rolling direction may require a slightly larger radius (1.5–2.0t).
- Stamping / deep drawing: Suitable for moderate draw depths. For deep draws, consider a double-action press and sufficient blankholder force to prevent wrinkling. The material's n-value (work-hardening exponent) is typically around 0.13–0.15.
- Stretch forming: Good performance within the elongation limits. Springback is more pronounced than with mild steel - compensate die geometry accordingly.
- Roll forming: Excellent. The uniform elongation and consistent yield strength from coil to coil make QSTE420TM well-suited to roll-formed longitudinal members.
6.4 Welding
QSTE420TM is readily weldable. Recommended practices:
- MIG/MAG (GMAW): ER70S-6 or equivalent filler wire. CO&sub2; or Ar/CO&sub2; mixed shielding gas. Maintain heat input below ~1.5 kJ/mm.
- Resistance spot welding: Standard parameters for HSLA steel of equivalent thickness. Electrode force and weld time may need slight adjustment from mild steel settings.
- Interpass temperature: Do not exceed 200°C. Excessive heat input coarsens the grain in the HAZ and can degrade both strength and toughness.
- No preheat required for thicknesses below ~10 mm at ambient temperature.
6.5 Surface Treatment
After forming and welding, the component may receive:
- Degreasing and phosphating: Standard automotive pretreatment before e-coat / painting.
- E-coating (cathodic electrodeposition): Primary corrosion protection for body-in-white components.
- Powder coating or wet painting: For chassis and visible structural parts.
- Hot-dip galvanizing: Possible but note that the Si content (0.50 max) is acceptable; excessive Si can cause thick, brittle zinc layers.
6.6 Assembly and Inspection
Assemble formed and welded components by bolting, riveting, or further welding. Perform dimensional inspection against the control plan.
Key checks: weld integrity (visual + periodic macro-section), dimensional conformance (CMM or gauge), surface finish (no cracks, no excessive scale). For safety-critical parts, verify mechanical properties on a witness coupon processed with the production batch.
7. Ordering QSTE420TM - What to Specify
When you send an RFQ for QSTE420TM, include these items to avoid ambiguity:
- Grade and standard: "QSTE420TM per SEW092" or "S420MC per EN 10149-2"
- Dimensions: Thickness × width × length (mm), or coil ID/OD and coil weight range
- Surface condition: Hot-rolled pickled and oiled (P&O), or as-rolled (if descaling will be done downstream)
- Edge condition: Mill edge or trimmed/slit edge
- Quantity: Tonnes or number of sheets/coils
- Application: Helps the mill optimize the micro-alloying within the specification window
- Certification: EN 10204 3.1 (standard MTC) or 3.2 (with third-party inspection)
Frequently Asked Questions
What is the difference between QSTE420TM and S420MC?
QSTE420TM (SEW092) and S420MC (EN 10149-2) are equivalent grades. Both are thermomechanically rolled micro-alloyed steels with a minimum yield strength of 420 MPa and tensile strength of 480–620 MPa. QSTE420TM originates from the German SEW092 specification; S420MC is the European EN designation. The material number 1.0980 applies to both. Chemical composition limits and mechanical properties are essentially identical.
Can QSTE420TM be welded using standard arc welding methods?
Yes. QSTE420TM has good weldability with common methods including MIG/MAG (GMAW), TIG (GTAW), and resistance spot welding. Because it is a micro-alloyed fine-grain steel, low heat input and controlled interpass temperature (typically below 200°C) are recommended to preserve the fine-grained microstructure in the heat-affected zone. Preheating is generally not required for thicknesses below 10 mm.
What are the main automotive applications of QSTE420TM?
QSTE420TM is used for structural and safety-critical automotive components: body frames, door impact beams, roof rails, hood structures, chassis beams, suspension components, crossmembers, and collision energy-absorbing parts. Its combination of high yield strength (≥420 MPa) and good cold formability makes it suitable for weight-optimized designs that must meet crash safety standards.
Does QSTE420TM require heat treatment after forming?
Generally no. QSTE420TM is designed for cold forming in the as-delivered (thermomechanically rolled) condition. It achieves its mechanical properties through controlled rolling and micro-alloy precipitation rather than through subsequent heat treatment. However, if the forming operation introduces excessive cold work or if welding is performed, stress-relief annealing may be applied at temperatures below 580°C to avoid affecting the mechanical properties.
What Chinese standards cover QSTE420TM equivalent grades?
QSTE420TM is referenced in Baosteel's Q/BQB 310-2009 standard (continuously hot-rolled steel sheet and strip for automotive structural use). In the Chinese national standard system, GB/T 20887.1-2007 covers HR420F as the equivalent grade for hot-rolled high-strength steel sheet for cold forming in automotive applications. GB/T 3273 covers hot-rolled steel plates for automobile frames, where similar high-strength grades like 420L may apply for frame applications.
References
- SEW092 - Hot-Rolled Products of Weldable Fine Grain Steels for Cold Forming (original German specification for QSTE420TM).
- EN 10149-2:2013 - Hot Rolled Flat Products Made of High Yield Strength Steels for Cold Forming. Part 2: Delivery Conditions for Thermomechanically Rolled Steels.
- Q/BQB 310-2009 - Baosteel Enterprise Standard: Continuously Hot-Rolled Steel Sheet and Strip for Automotive Structural Use.
- ThyssenKrupp Steel Europe - HSM 420 / S420MC Product Information (Precision Steel).
- ESB Group - S420MC Micro-alloyed Hot-Rolled Steel for Cold Forming.
- Gnee Steel (Tianjin) Co., Ltd. - Company and product information.
All chemical composition and mechanical property data above was verified against the cited sources and standards as of August 2026. Processing guidelines represent industry best practice and may vary by specific equipment and part geometry.
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Disclaimer: This article is provided for general technical information only and does not constitute engineering or procurement advice. Chemical composition and mechanical property values are drawn from published standards and supplier data sheets as of August 2026. Always verify conformance to the applicable specification via a mill test certificate (EN 10204 3.1 or 3.2) for your specific order. Gnee Steel (Tianjin) Co., Ltd. makes no representation regarding the accuracy of third-party references. Processing parameters are general guidelines; confirm with your manufacturing engineering team for specific parts and tooling.
