High-strength steel for chains, high-corrosion-resistant chain for mining operations and its manufacturing method

Claims

1. Chain steel containing the following chemical elements in mass percentages: C: 0.20-0.30%, Si: 0.05-0.6%, preferably 0.15-0.6%, Mn: 1.0-1.8%, Cr: 0.4-0.8%, Ni: 0.6-1.2%, Mo: 0.5-0.9%, Ti: 0.01-0.03%, Al: 0.02-0.05%, B: 0.001-0.005%, N: 0.002-0.006%, and the balance is Fe and unavoidable impurities.

2. Steel for chains according to claim 1, the chemical composition of which satisfies the following ratio: 30000*B / (300*B+0.7*Ni+2*Cr+5*Mo)≥6, preferably 6≤30000*B / (300*B+0.7*Ni+2*Cr+5*Mo)≤24.43, where the symbols of the elements respectively represent the numerical values ​​before the symbol % of 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, where P≤0.015%, S≤0.01% and O≤0.002%.

4. The chain steel of claim 1, wherein said chain steel has a microstructure of acicular martensite.

5. Steel for chains according to item 1, having the following properties: yield strength Rp 0,2≥1050 MPa, tensile strength R m ≥1200 MPa, relative elongation A≥14%, reduction in cross-sectional area Z≥50% and Charpy impact strength A kv at -20°C≥60 J.

6. A chain comprising chain steel according to any one of claims 1 to 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 tempered martensite and carbides dispersed interlamellarly.

8. The chain according to item 6, wherein the chain has the following properties: yield strength Rp 0,2 ≥1050 MPa, tensile strength R m ≥1200 MPa, relative elongation A≥14%, reduction in cross-sectional area Z≥50%, Charpy impact strength A kv at -20°C≥60 J and 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, carrying out quenching, wherein the heating temperature during quenching is 840-980°C, preferably 850-950°C, and the holding time is 1-4 hours, preferably 1-3 hours, followed by cooling with water for quenching; S5, Carrying out pre-treatment by pickling to obtain 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, a continuous casting process is used for casting; 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; and / or in the S2 stage, during heating and rolling, the cast slab is heated at a heating temperature of ≥1150°C for 3-6 hours, and the final rolling temperature is ≥850°C; after rolling, air cooling or slow cooling is carried out; and / or at step S6, 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 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 tempered martensite and carbides dispersed interlamellarly.

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≥1200 MPa, relative elongation A≥14%, reduction in cross-sectional area Z≥50%, Charpy impact strength A kv at -20°C≥60 J; and the corrosion rate is less than 0.2 g / m 2 ⋅h after 120 h of corrosion testing in neutral salt spray with 5% NaCl.