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US-12618129-B2 - Steel with controlled yield ratio and manufacturing method therefor

US12618129B2US 12618129 B2US12618129 B2US 12618129B2US-12618129-B2

Abstract

Disclosed are a steel with controlled steel ratio and a manufacturing method therefor. The steel comprises the following components in percentage by mass: C: 0.245-0.365%, Si: 0.10-0.80%, Mn: 0.20-2.00%, P: ≤0.015%, S: ≤0.003%, Cr: 0.20-2.50%, Mo: 0.10-0.90%, Nb: 0-0.08%, Ni: 2.30-4.20%, Cu: 0-0.30%, V: 0.01-0.13%, B: 0-0.0020%, Al: 0.01-0.06%, Ti: 0-0.05%, Ca: ≤0.004%, H: ≤0.0002%, N: ≤0.013%, O: ≤0.0020%, and the balance of Fe and inevitable impurities, wherein the components satisfy (8.57*C+1.12*Ni)≥4.8% and 1.2%≤(1.08*Mn+2.13*Cr)≤5.6%. The steel has excellent low-temperature impact toughness and aging impact toughness at −20° C. and −40° C., a rationally controlled yield ratio, and ultra-high strength, ultra-high toughness, and ultra-high plasticity, which can be used in applications such as offshore platform mooring chains, mechanical structures, and automobiles that require high strength and toughness of the steel.

Inventors

  • Sixin Zhao
  • Zongze Huang
  • Jiaqiang Gao
  • Jun Zhang

Assignees

  • BAOSHAN IRON & STEEL CO., LTD.

Dates

Publication Date
20260505
Application Date
20210207
Priority Date
20200228

Claims (8)

  1. 1 . A steel with controlled yield ratio, comprising the following components in percentage by mass: C: 0.245-0.365%, Si: 0.10-0.80%, Mn: 0.20-2.00%, P: ≤0.015%, S: ≤0.003%, Cr: 0.20-2.50%, Mo: 0.10-0.90%, Nb: 0-0.08%, Ni: 2.30-4.20%, Cu: 0-0.30%, V: 0.01-0.13%, B: over 0 to 0.0020%, Al: 0.01-0.06%, Ti: 0-0.05%, Ca: ≤0.004%, H: ≤0.0002%, N: ≤0.013%, O: ≤0.0020%, and the balance of Fe and inevitable impurities, wherein the components satisfy (8.57*C+1.12*Ni)≥4.8% and 1.2%≤(1.08*Mn+2.13*Cr)≤5.6%; and the steel with controlled yield ratio has a yield ratio of 0.85-0.95, a tensile strength of 1,100 MPa or more, and a yield strength of 900 MPa or more.
  2. 2 . The steel with controlled yield ratio of claim 1 , wherein a microstructure of the steel with controlled yield ratio is tempered martensite+tempered bainite.
  3. 3 . The steel with controlled yield ratio of claim 2 , wherein the steel with controlled yield ratio has a Charpy impact energy A kv at −20° C. of 90 J or more, a Charpy impact energy A kv at −40° C. of 70 J or more, a Charpy impact energy A kv at −20° C. of 80 J or more after holding at a temperature of 100° C. for 1 h after 5% strain, a Charpy impact energy A kv at −40° C. of 60 J or more after holding at a temperature of 100° C. for 1 h after 5% strain, a yield ratio of 0.85-0.95, a tensile strength of 1,100 MPa or more, a yield strength of 900 MPa or more, an elongation rate of 15% or more, an area reduction of 50% or more, a strength toughness product (Tensile Strength*Charpy Impact Energy A kv at −20° C.) of 115 GPa*J or more, and a strength plasticity product (Tensile Strength*Elongation Rate) of 16 GPa* % or more.
  4. 4 . The steel with controlled yield ratio of claim 1 , wherein the steel with controlled yield ratio has a Charpy impact energy A kv at −20° C. of 90 J or more, a Charpy impact energy A kv at −40° C. of 70 J or more, a Charpy impact energy A kv at −20° C. of 80 J or more after holding at a temperature of 100° C. for 1 h after 5% strain, a Charpy impact energy A kv at −40° C. of 60 J or more after holding at a temperature of 100° C. for 1 h after 5% strain, a yield ratio of 0.85-0.95, a tensile strength of 1,100 MPa or more, a yield strength of 900 MPa or more, an elongation rate of 15% or more, an area reduction of 50% or more, a strength toughness product (Tensile Strength*Charpy Impact Energy A kv at −20° C.) of 115 GPa*J or more, and a strength plasticity product (Tensile Strength*Elongation Rate) of 16 GPa* % or more.
  5. 5 . A manufacturing method for the steel with controlled yield ratio according to claim 1 , comprising the following steps: S1: smelting and casting, wherein the smelting and casting are carried out according to the components in claim 1 to form a casting billet; S2: heating, wherein the casting billet is heated at a heating temperature of 1,010-1,280° C.; S3: rolling or forging, wherein a final rolling temperature is 720° C. or more or a final forging temperature is 720° C. or more; and performing air cooling, water cooling or retarded cooling after the rolling; S4: quenching heat treatment, wherein the quenching is performed at a quenching temperature of 830-1,060° C. using water quenching or oil quenching, and a ratio of the quenching time to the thickness or diameter of the steel is 0.25 min/mm or more; and S5: tempering heat treatment, wherein a tempering temperature is 490-660° C., a ratio of the tempering time to the thickness or diameter of the steel is 0.25 min/mm or more, and performing air cooling, retarded cooling or water cooling after the tempering.
  6. 6 . The manufacturing method for the steel with controlled yield ratio of claim 5 , wherein a microstructure of the steel with controlled yield ratio is tempered martensite+tempered bainite.
  7. 7 . The manufacturing method for the steel with controlled yield ratio of claim 6 , wherein the steel with controlled yield ratio has a Charpy impact energy A kv at −20° C. of 90 J or more, a Charpy impact energy A kv at −40° C. of 70 J or more, a Charpy impact energy A kv at −20° C. of 80 J or more after holding at a temperature of 100° C. for 1 h after 5% strain, a Charpy impact energy A kv at −40° C. of 60 J or more after holding at a temperature of 100° C. for 1 h after 5% strain, a yield ratio of 0.85-0.95, a tensile strength of 1,100 MPa or more, a yield strength of 900 MPa or more, an elongation rate of 15% or more, an area reduction of 50% or more, a strength toughness product (Tensile Strength*Charpy Impact Energy A kv at −20° C.) of 115 GPa*J or more, and a strength plasticity product (Tensile Strength*Elongation Rate) of 16 GPa* % or more.
  8. 8 . The manufacturing method for the steel with controlled yield ratio of claim 5 , wherein the steel with controlled yield ratio has a Charpy impact energy A kv at −20° C. of 90 J or more, a Charpy impact energy A kv at −40° C. of 70 J or more, a Charpy impact energy A kv at −20° C. of 80 J or more after holding at a temperature of 100° C. for 1 h after 5% strain, a Charpy impact energy A kv at −40° C. of 60 J or more after holding at a temperature of 100° C. for 1 h after 5% strain, a yield ratio of 0.85-0.95, a tensile strength of 1,100 MPa or more, a yield strength of 900 MPa or more, an elongation rate of 15% or more, an area reduction of 50% or more, a strength toughness product (Tensile Strength*Charpy Impact Energy A kv at −20° C.) of 115 GPa*J or more, and a strength plasticity product (Tensile Strength*Elongation Rate) of 1 GPa* % or more.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a U.S. national phase entry under 35 USC § 371 of Patent Cooperation Treaty Application No. PCT/CN202 1/075734 filed Feb. 7, 2021, which in turn claims priority from Chinese Patent Application 202010130904.1 filed Feb. 28, 2020. Each of the above described applications is hereby incorporated herein by reference in their entireties. TECHNICAL FIELD The present invention relates to a steel having high strength and toughness, in particular to a steel with controlled yield ratio having excellent low-temperature impact toughness and a manufacturing method therefor. BACKGROUND Steel having high strength and toughness, such as steel rods and plates having ultra-high strength and toughness, are applied in the fields of offshore platforms, huge mechanical structures, and high-strength sheets for automobiles. The strength grades of round steels for offshore platform mooring chains include a tensile strength 690 MPa grade R3, a tensile strength 770 MPa grade R3S, a tensile strength 860 MPa grade R4, a tensile strength 960 MPa grade R4S, a tensile strength 1,000 MPa grade R5, and a tensile strength 1,100 MPa grade R6. In the ship rules published by the DNV Classification Society in July 2018, R6 has been incorporated in the new ship rules. while technical indexes of R6 are stipulated in the factory certification outline, Approval of manufacturers DNVGL-CP-0237 Offshore mooring chain and accessories (Edition July 2018) and the chain link standard DNVGL-OS-E302 Offshore mooring chain (Edition July 2018), and the main technical indexes of R6 include a low temperature impact energy at −20° C. of 60J or more, a tensile strength of 1,100 MPa or more, a yield strength of 900 MPa or more, an elongation rate of 12% or more, an area reduction of 50% or more, an aging impact energy at −20° C. (holding at a temperature of 100° C. for 1 h after 5% strain) of 60J or more, a yield ratio of 0.85-0.95, etc. The mooring chain is used for fixing the offshore platform and has demands for ultra-high strength, high toughness, high corrosion resistance, and the like. In consideration of cases that the offshore platform needs to be constructed in sea areas at various latitudes and the cold climate in high-latitude sea area, the impact performance at an environment temperature of −40° C. needs to be considered simultaneously. If the yield ratio of the mooring chain is too high, easy fracture after deformation may occur, which is harmful to the safety of the offshore platform. The offshore platform mooring chain needs ultra-high strength, high toughness and high plasticity at the same time, and thus, the steel needs to have ultra-high strength, toughness and plasticity. The offshore platform mooring chain may deform during service and needs to have good low-temperature impact toughness if deformation occurs. Therefore, the aging impact energy is an important technical index for the offshore platform mooring chain. Many studies have been conducted on steel having ultra-high strength, toughness and plasticity all over the world. The steel having ultra-high strength and toughness usually adopts a microstructure of bainite, bainite+martensite, or martensite. The bainite or martensite structure contains supersaturated carbon atoms, which may change the lattice constant, inhibit the dislocation motion, and improve the tensile strength. A refined structure ensures that the steel can absorb more energy under stress so as to achieve higher tensile strength and impact toughness. Chinese patent CN102747303A discloses “a high strength steel plate with a yield strength of 1,100 MPa-grade and a manufacturing method thereof”. The high strength steel plate is a steel plate having ultra-high strength and toughness with a yield strength of 1,100 MPa and low temperature impact energy (−40° C.), and comprises the following components in percentage by mass: C: 0.15-0.25%, Si: 0.10-0.50%, Mn: 0.60-1.20%, P: ≤0.013%, S: ≤0.003%, Cr: 0.20-0.55%, Mo: 0.20-0.70%, Ni: 0.60-2.00%, Nb: 0-0.07%, V: 0-0.07%, B: 0.0006-0.0025%, Al: 0.01-0.08%, Ti: 0.003-0.06%, H: ≤0.00018%, N: ≤0.0040%, 0: ≤0.0030%, and the balance of Fe and inevitable impurities, wherein the carbon equivalent satisfies CEQ≤0.60%. The steel has a yield strength of 1,100 MPa or more, a tensile strength of 1,250 MPa or more, and a Charpy impact energy Akv (−40° C.) of 50J or more. The steel plate disclosed by the patent has ultra-high strength, but the impact performance at −40° C. cannot reach 70J stably, and has low elongation rate, while the aging impact performance and the yield ratio are not stipulated, either. Chinese patent CN103898406A discloses “a steel plate with a yield strength of 890 Mpa-grade and low welding crack sensitivity and a manufacturing method thereof”, which adopts heat-control mechanical rolling and cooling technology to obtain a steel having high strength toughness with a matrix structure of ultrafine bainite lath. The steel p