HIGH-STRENGTH STEEL FOR CHAIN, RESISTANT TO CORROSION IN SEA WATER, CHAIN ​​AND METHOD OF ITS MANUFACTURING

Claims

1. A chain steel containing the following chemical elements in mass percentages: C: 0.25-0.35%, Si: 0.1-0.6%, Mn: 0.3-0.9%, Cr: 0.3-1.2%, Ni: 1.8-3.2%, preferably 1.8-2.95%, Mo: 0.39-1.0%, preferably 0.4-1.0%, more preferably 0.4-0.88%, Al: 0.02-0.05%, V: 0.08-0.30%, N: 0.009-0.02%, the rest is Fe and unavoidable impurities.

2. The chain steel according to claim 1, wherein the chain steel has a chemical composition satisfying the following ratio: 1.3*Ni+2*Cr+7*Mo+0.5*Si+V≥8, preferably 8≤1.3*Ni+2*Cr+7*Mo+0.5*Si+V≤10.22, where Ni, Cr, Mo, Si and V respectively represent numerical values ​​preceding the % symbol, denoting the mass percentage content of the corresponding elements.

3. The chain steel according to claim 1, wherein the unavoidable impurities include P, S and O, wherein P≤0.015%, S≤0.01% and O≤0.002%.

4. The chain steel according to claim 1, wherein the chain steel has a microstructure of acicular martensite.

5. Steel for chains according to item 1, wherein the steel for chains has the following properties: yield strength Rp 0,2 ≥1050 MPa, tensile strength R m ≥1100 MPa, relative elongation A≥14%, reduction in cross-sectional area Z≥50%, Charpy impact strength A kv at -20°C ≥ 60 J.

6. A chain comprising: chain steel according to any one of paragraphs 1-5 and a zinc coating applied to the chain steel.

7. The chain of claim 6, wherein the zinc coating has a thickness of 10-150 μm, preferably 40-150 μm; and / or the chain steel has a microstructure of acicular tempered martensite and dispersed carbides; preferably the size of the carbides is less than 300 nm.

8. A chain according to item 6 or 7, wherein the chain has the following properties: yield strength Rp 0,2 ≥1050 MPa, tensile strength R m ≥1100 MPa, relative elongation A≥14%, reduction in cross-sectional area Z≥50%, Charpy impact strength Akv at -20°C ≥ 60 J, corrosion rate ≤ 0.2 g / m 2 ⋅h after 120 h of corrosion testing in neutral salt spray with 5% NaCl.

9. A method for manufacturing a chain according to any one of paragraphs 6-8, comprising the following stages performed sequentially: S1, melting and casting molten steel to produce a cast slab; S2, heating and rolling the cast slab, wherein the reduction of the cast slab is ≥10; S3, ring forming and welding; S4, quenching, wherein the heating temperature during quenching is 840-980°C, preferably 850-950°C, the holding time is 1-4 hours, preferably 1-3 hours, and cooling during quenching is carried out with water; S5, pickling for chain steel; S6, hot-dip galvanizing, in which chain steel after pickling pretreatment is subjected to a preheat treatment followed by hot-dip galvanizing to obtain a chain comprising chain steel and a zinc coating formed on the surface of the chain steel; wherein the temperature difference between the preheating temperature for the preheat treatment and the temperature of the galvanizing bath used in hot-dip galvanizing is controlled in the range of -30 to 30°C.

10. The manufacturing method according to claim 9, wherein at step S1 the melting comprises melting in an electric furnace or converter, refining in a ladle furnace and vacuum degassing or circulating vacuuming; casting is carried out using a continuous casting process; preferably, vacuum degassing or circulating vacuuming is carried out for 10-20 minutes; during casting, the degree of superheating of the molten steel in the pouring ladle is controlled in the range of 15-40°C; in stage S2, during heating and rolling, the cast slab is heated to a temperature of ≥1150°C for 3-6 hours, the final rolling temperature is ≥850°C, and after rolling, air cooling or slow cooling is carried out; In the S6 stage, the preheating temperature is 400-550°C, and the preheating time is ≥0.5 h; the temperature of the galvanizing bath used in hot-dip galvanizing is 400-530°C.

11. The manufacturing method according to claim 9, wherein the zinc coating on the surface of the chain has a thickness of 10-150 μm, preferably 40-150 μm.

12. The manufacturing method according to claim 9, wherein the chain steel obtained in step S6 has a microstructure of acicular tempered martensite and dispersed carbides; preferably, the size of the carbides is less than 300 nm.

13. The manufacturing method according to claim 9, wherein the chain has the following properties: yield strength Rp 0,2 ≥1050 MPa, tensile strength R m ≥1100 MPa, relative elongation A≥14%, reduction in cross-sectional area Z≥50%, Charpy impact strength A kv at -20°C ≥ 60 J; corrosion rate less than 0.2 g / m 2 ⋅h after 120 h of corrosion testing in neutral salt spray with 5% NaCl.