What Key Performance Indicators Need To Be Tested For 430 Stainless Steel Sheets?

As a typical representative of ferritic stainless steel, 430 stainless steel sheet is widely used in architectural decoration, home appliance manufacturing, automotive components, and other fields. The testing process must be tailored to the material's characteristics and application requirements, with a focus on verifying core indicators such as chemical composition, mechanical properties, and corrosion resistance. This article systematically outlines the key performance parameters and testing methods for 430 stainless steel sheet, providing a technical basis for quality control.

 

Chemical Composition Analysis

The chemical composition of 430 stainless steel directly affects the material's performance. A spectrometer must be used to verify that the chromium (Cr) content meets the standard range of 16–18%, while the carbon (C) content should be controlled below 0.12%. Additionally, the content of elements such as manganese (Mn), silicon (Si), phosphorus (P), and sulfur (S) must be tested; excessive levels of sulfur and phosphorus can significantly reduce the material's toughness. X-ray fluorescence spectroscopy (XRF) and inductively coupled plasma optical emission spectroscopy (ICP-OES) are commonly used testing methods.

 

Mechanical Property Testing

For tensile strength testing, the specimen must withstand a stress of ≥450 MPa on a tensile testing machine, and the yield strength must be ≥310 MPa. The elongation index is measured based on the gauge length and is typically required to be ≥20%. Hardness testing may be performed using a Rockwell hardness tester (HRB) or a Vickers hardness tester (HV), with standard ranges of HRB 85–95 and HV 170–200, respectively. These data reflect the material's deformation and fracture characteristics under load.

 

Corrosion Resistance Testing

Salt spray testing must be conducted in accordance with the ASTM B117 standard. Test specimens are placed in a salt spray environment formed by a 5% sodium chloride solution, and surface corrosion is observed after 48 hours. Nitric acid pitting corrosion testing uses a 65% nitric acid solution; specimens are immersed at 70°C for 48 hours, and the mass loss per unit area is measured. Intergranular corrosion testing must be performed in accordance with the GB/T 4334 standard, using a boiling sulfuric acid–copper sulfate solution test to determine the material's resistance to intergranular corrosion.

 

Metallographic Analysis

After preparation, grinding, and polishing, the test specimens are electrolytically etched using a 10% oxalic acid solution. Under an optical microscope, the uniformity of the ferrite grain size is observed; the average grain size should meet ASTM Grade 6–8. Particular attention must be paid to the presence of σ-phase precipitation; when temperatures fall within the 550–900°C range, a hard and brittle phase is prone to form, which significantly reduces the material's toughness. X-ray diffraction analysis can be used to confirm the phase composition.

 

Surface Quality Inspection

A 10x magnifying glass is used to inspect the surface for defects such as scratches, pits, and cracks. Roughness testing is performed using a contact profilometer; the 2B surface finish requirement is Ra ≤ 0.8 μm. The thickness of the oxide layer is measured using a magnetic thickness gauge; for cold-rolled sheets, the oxide layer should be ≤ 0.01 mm. For mirror-finished sheets, surface gloss must also be tested; the measured value at a 60-degree angle of incidence should be ≥ 600 GU.

 

Dimensional Tolerance Verification

Thickness measurement requires taking nine measurement points 20 mm from the edge using a micrometer; the allowable deviation is ±0.02 mm. Width tolerances are controlled in accordance with the JIS G4305 standard; a deviation of ±3 mm is permitted for a width of 1000 mm. For flatness testing, place the sheet on a testing platform and measure the maximum gap using a feeler gauge; the deviation over a 1-meter length must be ≤1.5 mm. Diagonal deviation must be controlled within 0.2% of the total length.

 

Welding Performance Testing

Prepare butt-weld test specimens and measure hardness variations in the weld zone. The hardness of the heat-affected zone must not exceed 120% of the base material's hardness. For the bending test, the specimen must not develop cracks after being bent 180 degrees. For the impact toughness test, use Charpy V-notch specimens; the impact energy of the welded joint at 0°C must be ≥27 J. Metallographic examination must confirm that the weld zone is free of defects such as lack of fusion and porosity.

 

High-Temperature Performance Evaluation

Place the test specimen in a muffle furnace for high-temperature oxidation testing. After holding at 800°C for 100 hours, the weight gain per unit area should be ≤2.0 g/m². For the creep test, apply a continuous load at 600°C and 100 MPa; the creep deformation after 100 hours should be ≤0.5%. Testing for the Coefficient of Thermal Expansion: Using a dilatometer, the linear coefficient of thermal expansion in the 20–600°C range should fall within 10.4 × 10⁻⁶/°C.