1. Core Mechanical Properties (Based on EN 10346)
Performance Parameters Typical Range Test Standard (e.g., ISO/ASTM) Description
Tensile Strength (TS) 270-350 MPa ISO 6892-1 Lower strength, focusing on formability
Yield Strength (YS) 140-260 MPa ISO 6892-1 Based on the lower yield point (ReL)
Elongation (A80) ≥30% ISO 6892-1 Gauge length 80mm, measures plastic deformation capability
n Value (Hardening Index) 0.18-0.22 ISO 10275 Higher values are more suitable for complex stamping
r Value (Plastic Strain Ratio) 1.4-2.0 ISO 10113 Higher values improve thinning resistance and deep drawing performance
2. Mechanical Properties Analysis
Low strength, high ductility:
Low carbon design (C ≤ 0.12%) and sufficient annealing make it suitable for Deep drawing and stretch forming are possible, but load-bearing capacity is limited.
Compared to high-strength steel (such as HX340LAD+Z), its tensile strength is approximately 30% lower, but its elongation is over 50% higher.
Anisotropy (r-value):
A high r-value indicates that the steel plate is more difficult to thin in the thickness direction, making it suitable for deep-drawn parts (such as automobile fuel tanks).
Hardening properties (n-value):
A higher n-value indicates that the material hardens more uniformly during deformation, reducing the risk of localized cracking.
3. Performance Comparison Under Different Standards
Standard Grade Tensile Strength (MPa) Yield Strength (MPa) Elongation (%)
EN 10346 DX57D+Z 270-350 140-260 ≥30
JIS G 3302 SGCC 270-380 120-260 ≥30
GB/T 2518 DC57D+Z 270-350 140-260 ≥30
Note: The strength range for SGCC in the JIS standard is slightly wider, but in actual production, steel mills typically control it to the lower and middle limits based on customer requirements.
4. Key Factors Affecting Mechanical Properties
Chemical Composition:
Low Carbon (C), Low Sulfur (S): Ensure high plasticity. The sulfur content should be ≤ 0.025% to reduce inclusions.
Manganese (Mn): A trace addition (0.2-0.5%) can improve strength, but excessive addition can reduce ductility.
Process Control:
Annealing Temperature: Full recrystallization annealing (700-800°C) optimizes ductility.
Cold Rolling Reduction: Typically controlled between 50-70%. Exceeding this level may result in increased strength and decreased ductility.
Effect of the Galvanizing Layer:
Hot-dip galvanizing (galvanizing temperature approximately 450°C) has minimal effect on the mechanical properties of the substrate, but the size of the zinc spangles may affect the surface friction coefficient.
5. Performance Considerations in Practical Applications
Stamping:
High elongation and n-value are suitable for complex parts (such as door inner panels and appliance housings), but excessive stretching that may cause localized necking should be avoided.
The die clearance is recommended to be 1.1-1.2 times the plate thickness.
Weldability:
The galvanized layer must be removed by grinding beforehand to prevent the formation of pores (zinc boiling point is only 907°C).
It is recommended to use a low-carbon steel welding rod (such as ER70S-6) and reduce the current by 10%-15%.
Corrosion Resistance and Mechanical Balance:
Thicker zinc layers (such as Z80) provide better corrosion resistance, but may increase frictional resistance during stamping.
6. FAQs
Q1: Can DX57D+Z improve its strength through heat treatment?
Heat treatment is generally not recommended for galvanized sheet, as high temperatures will damage the zinc layer. If higher strength is required, it is recommended to switch directly to a high-strength steel grade (such as DX58D+Z).
Q2: How should the sampling direction be selected for mechanical property testing?
For stamping parts, it is recommended to take samples in the transverse direction (perpendicular to the rolling direction) because actual deformation is mostly due to transverse forces, resulting in more conservative and reliable data.
Q3: Is an elongation of 30% sufficient for deep drawing?
Yes, but this requires a comprehensive evaluation based on the n value and r value. For example, automobile fuel tanks require an A80 of ≥32% and an r value of ≥1.8.
7. Material Selection Recommendations
Preferred Formability: DX57D+Z (suitable for deep drawing and stretching).
Mild Strength Requirements: DX58D+Z (Temperature Shock 340-420 MPa, A80 ≥ 26%).
High-Strength Corrosion Resistance: HX340LAD+Z (Temperature Shock ≥ 340 MPa, Z60 Galvanized Layer).