Hot-Forming Temperature Range
The optimal hot-forming temperature for Q235NH is 900–1100°C. Within this range, the steel's microstructure becomes austenitic, which significantly improves its ductility and formability, allowing for complex shaping operations (e.g., bending, stamping, forging) without causing surface or internal cracks. Temperatures below 900°C will lead to insufficient ductility, increasing the risk of deformation defects; temperatures above 1100°C may cause grain coarsening, which could slightly reduce the steel's toughness after cooling.
Impact on Corrosion Resistance and Mechanical Properties
Corrosion resistance: Hot-forming does not damage the alloy elements (Cu, Cr, Ni) that contribute to patina formation in Q235NH. After forming and cooling, the steel surface can still react with oxygen and moisture to form a dense, self-healing patina, with no loss of atmospheric corrosion resistance.
Mechanical properties: Proper hot-forming (with controlled heating and cooling rates) will not degrade Q235NH's core mechanical properties. Its minimum yield strength of 235 MPa and tensile strength of 375–500 MPa can still meet the requirements of general structural applications. If grain coarsening occurs due to overheating, a post-forming normalizing treatment (heating to 850–900°C and air-cooling) can refine the grains and restore toughness.
Key Processing Notes
Avoid rapid cooling after hot-forming (e.g., quenching in water), as this may cause excessive residual stress or hardening, increasing the risk of cracking during subsequent processing or use. Air-cooling is the preferred cooling method.
Protect the steel surface during heating (e.g., using anti-oxidation coatings) to reduce scale formation. Thick oxide scales may affect patina uniformity, but minor scales can be removed by shot blasting without impacting corrosion resistance.
For thick Q235NH plates (≥20 mm), ensure uniform heating throughout the material to prevent uneven deformation caused by temperature gradients.
