Martensitic Gost 4kh5mfs Steel Bar Corrosion Resistance Characteristics - China

GOST 4Х5МФС steel bar (≈ AISI H11 / DIN 1.2343 X38CrMoV5-1 / GB 4Cr5MoSiV) is a Cr-Mo-V series hot-work die steel, not a stainless steel.

Its "corrosion resistance" depends on the specific application scenario and should not be judged against stainless steel standards.

Corrosion characteristics determined by composition

• Cr content is 4.5–5.5%, which is below the 10.5% passivation threshold required for stainless steel; therefore, it cannot spontaneously passivate over the long term in an atmospheric environment.

• Contains 1.2–1.5% Mo and 0.3–0.5% V, offering better rust resistance than carbon tool steels or grades like 3Cr2W8V, yet it remains fundamentally an alloy tool steel prone to rusting.

- S and P ≤0.03%, residual Cu ≤0.3%, Ni ≤0.4%; no specific alloying elements added for corrosion resistance.

Actual performance in various environments (perspective based on bar stock)

• Dry indoor storage: Annealed bars (≤241 HBW) will not rust in the short term, but surface flash rust may appear if left exposed for several weeks; long-term storage requires anti-rust oil coating or PE film wrapping, especially for sawn end faces.

- Humid/marine climates (e.g., condensation in workshops, even in non-coastal regions like Hesse, Germany): Unprotected bars may develop pitting or edge corrosion; susceptibility to rusting increases after machining.

• High-temperature oxidation (service condition): In air at 500–600°C, it forms a relatively dense Cr₂O₃ film with a low oxidation rate (on the order of <0.1 mm/year).

This accounts for its "good oxidation resistance, " which is distinct from general "corrosion resistance.

" - Molten aluminum/zinc/magnesium erosion: Offers decent resistance to melt erosion and is not prone to sticking to the melt (die soldering); this makes it suitable for hot extrusion dies, though this property is unrelated to acid or alkali resistance.

• Acidic, alkaline, or chloride-ion-containing media: Not resistant.

Prolonged exposure to residues of hydrochloric acid, sulfuric acid, seawater spray, or cutting fluids can induce pitting and stress corrosion; the quenched-and-tempered state is more susceptible than the annealed state (due to residual stress and the martensitic matrix).

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• Posted By: Dongguan Songshun Mould Steel Co., Ltd.

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