Q:What is the difference between the corrosion resistance of Q195 and Q235 in normal atmospheric environment?
A:Corrosion mechanism: Mainly affected by oxygen, water vapor and a small amount of dust, the corrosion rate is low (about 5-10μm/year).
Performance of galvanized layer:
Hot-dip galvanized layer (60-85μm): The corrosion resistance of Q195 and Q235 galvanized steel can reach 15-30 years, and the substrate will not begin to corrode until the zinc layer is consumed.
Electroplated zinc layer (8-15μm): The life span is only 5-10 years, suitable for short-term indoor use (such as home appliance shell).
Differences: There is no significant difference between the two. The corrosion resistance mainly depends on the thickness of the coating and has nothing to do with the strength of the substrate steel.
Q:What is the difference between the corrosion resistance of Q195 and Q235 in industrial atmospheric environments?
A:Corrosion mechanism: Acidic gases such as SO₂ and NOx form acid rain or acid mist, which accelerates the corrosion of the zinc layer (corrosion rate 10-20μm/year). • Performance of the galvanized layer: ◦ Hot-dip galvanizing (≥85μm): The service life of Q195 and Q235 galvanized steel can reach 10-20 years, and the integrity of the coating needs to be checked regularly (such as industrial plant buildings and chimney brackets). ◦ Electrogalvanizing (<15μm): The service life is less than 5 years, and "white rust" (zinc oxide corrosion product) is prone to occur, and paint needs to be applied.
Q:In a marine atmosphere environment (high corrosion), what is the difference between the corrosion resistance of Q195 and Q235?
A:Corrosion mechanism: Salt spray (NaCl particles) adsorbs on the surface of steel, forming an electrochemical corrosion cell with a corrosion rate of up to 20-50μm/year. • Performance of galvanized layer: ◦ Hot-dip galvanizing (≥100μm): The service life of Q195 and Q235 galvanized steel is about 8-15 years (such as coastal guardrails, port facilities), but the zinc layer needs to be repaired every 5-8 years (such as zinc spraying or coating with high chlorinated polyethylene paint). ◦ Electrogalvanizing (<20μm): Service life is <3 years, not recommended for marine environment. • Alternative: If long-term salt spray resistance is required, hot-dip galvanized aluminum-magnesium alloy coating (such as Zn-Al-Mg) can be selected, and the corrosion resistance is 3-5 times that of ordinary galvanized layer.
Q:In a freshwater environment (high corrosion), what is the difference between the corrosion resistance of Q195 and Q235?
A:Corrosion mechanism: Affected by dissolved oxygen, microorganisms and minerals (such as calcium and magnesium ions) in water, the corrosion rate is 5-15μm/year (static water corrodes more severely than flowing water). • Performance of galvanized layer: ◦ Hot-dip galvanizing (60-85μm): Both Q195 and Q235 galvanized steel can be used for a long time (such as water pipelines, reservoir gates), with a service life of more than 20 years. ◦ Note: If the water is acidic (pH < 6) or contains sulfides (such as hot spring water), the zinc layer will corrode faster, and stainless steel or epoxy-coated steel pipes need to be used instead.
Q:In seawater environment (high corrosion), what is the difference between the corrosion resistance of Q195 and Q235?
A:Corrosion mechanism: High concentration of Cl⁻ destroys the passivation film of the zinc layer, forming pitting, and the corrosion rate can reach 30-60μm/year. • Performance of galvanized layer: ◦ Hot-dip galvanizing (≥100μm): The service life is only 5-10 years (such as offshore bridge pile foundations and ship structures), and cathodic protection (such as sacrificial anodes) is required. ◦ Not recommended scenarios: Deep sea environment (>50 meters water depth) or long-term immersion parts, it is recommended to directly use weathering steel (such as Q355NH) or stainless steel (316L).