Thick, tough, high tensile strength steel plate and production method therefor

Patent metadata

Field	Value
Publication number	US-10000833-B2
Application number	US-201414770853-A
Country	US
Kind code	B2
Filing date	Mar 11, 2014
Priority date	Mar 15, 2013
Publication date	Jun 19, 2018
Grant date	Jun 19, 2018

Abstract

A thick, high-toughness high-strength steel plate has excellent strength and toughness in the central area through the plate thickness. The thick steel plate has a specific chemical composition and includes a microstructure having, throughout an entire region in the plate thickness direction, an average prior austenite grain size of not more than 50 μm and a martensite and/or bainite phase area fraction of not less than 80%. A continuously cast slab having the specific chemical composition is heated to 1200° C. to 1350° C., hot worked with a strain rate of not more than 3/s and a cumulative working reduction of not less than 15%, and thereafter hot rolled and heat treated.

First claim

The invention claimed is:

1. A thick, high-toughness high-strength steel plate having a plate thickness of not less than 100 mm, the steel plate comprising a microstructure having, throughout the plate thickness direction, an average prior austenite grain size of not more than 50 μm and a martensite and/or bainite phase area fraction of not less than 80%,
the yield strength of the steel plate is not less than 620 MPa,
a reduction of area after fracture in a tensile test in the direction of the plate thickness of the steel plate is not less than 25%,
an absorbed energy by Charpy impact test at −40° C. vE −40 of the steel plate is 70 J or more,
the steel plate includes by mass %, C: 0.08 to 0.20%, Si: not more than 0.40%, Mn: 0.5 to 5.0%, P: not more than 0.015%, S: not more than 0.0050%, Cr: not more than 3.0%, Ni: not more than 5.0%, Ti: 0.005% to 0.020%, Al: 0.010 to 0.080%, N: not more than 0.0070% and B: 0.0003 to 0.0030%, the balance being Fe and inevitable impurities, and
the steel plate satisfies the relationship represented by Expression (1)
Ceq IIW =C+Mn/6+(Cu+Ni)/15+(Cr+Mo+V)/5≥0.57  (1)

wherein the alloying element symbols indicate the respective contents (mass %) and are 0 when absent.

2. A method of manufacturing a thick, high-toughness high-strength steel plate having a plate thickness of not less than 100 mm, the steel plate including a microstructure having throughout an entire region in the plate thickness direction, an average prior austenite grain size of not more than 50 μm and a martensite and/or bainite phase area fraction of not less than 80%, the method comprising:
heating a continuously cast slab to 1200° C. to 1350° C.,
hot working the slab at not less than 1000° C. with a strain rate of not more than 3/s and a cumulative working reduction of not less than 15%, and
hot rolling, quench hardening and tempering the steel, the continuously cast slab including, by mass %, C: 0.08 to 0.20%, Si: not more than 0.40%, Mn: 0.5 to 5.0%, P: not more than 0.015%, S: not more than 0.0050%, Cr: not more than 3.0%, Ni: not more than 5.0%, Ti: 0.005% to 0.020%, Al: 0.010 to 0.080%, N: not more than 0.0070% and B: 0.0003 to 0.0030%, the balance being Fe and inevitable impurities, the continuously cast slab satisfying the relationship represented by Expression (1):
Ceq IIW =C+Mn/6+(Cu+Ni)/15+(Cr+Mo+V)/5≥0.57  (1)

wherein the alloying element symbols indicate the respective contents (mass %) and are 0 when absent, wherein the continuously cast slab is heated to 1200° C. to 1350° C., hot worked at not less than 1000° C. with a strain rate of not more than 3/s and a cumulative working reduction of not less than 15%, air cooled, heated again to Ac3 point to 1200° C., subjected to hot rolling including at least two or more passes with a rolling reduction per pass of not less than 4%, air cooled, heated to Ac3 point to 1050° C., quenched to 350° C. or below and tempered at 450° C. to 700° C., and wherein the yield strength is not less than 620 MPa.

3. The method according to claim 2 , wherein the slab further includes, by mass %, one, or two or more of Cu: not more than 0.50%, Mo: not more than 1.00% and V: not more than 0.200%.

4. The method according to claim 2 , wherein the slab further includes, by mass %, one or both of Ca: 0.0005 to 0.0050% and REM: 0.0005 to 0.0050%.

5. The method according to claim 2 , wherein the continuously cast slab is worked to reduce its width by not less than 100 mm before hot working and is thereafter hot worked with a strain rate of not more than 3/s and a cumulative working reduction of not less than 15%.

6. The method according to claim 3 , wherein the slab further includes, by mass %, one or both of Ca: 0.0005 to 0.0050% and REM: 0.0005 to 0.0050%.

7. The steel plate according to claim 1 , wherein steel plate further includes, by mass %, one, or two or more of Cu: not more than 0.50%, Mo: not more than 1.00% and V: not more than 0.200%.

8. The steel plate according to claim 1 , wherein steel plate further includes, by mass %, one or both of Ca: 0.0005 to 0.0050% and REM: 0.0005 to 0.0050%.

9. The steel plate according to claim 7 , wherein steel plate further includes, by mass %, one or both of Ca: 0.0005 to 0.0050% and REM: 0.0005 to 0.0050%.

Assignees

• Jfe Steel Corp

Inventors

• Kitsuya Shigeki
• Matsunaga Naoki
• Ichimiya Katsuyuki
• Hase Kazukuni
• Endo Shigeru

Classifications

• C21D8/02

  during manufacturing of plates or strips (C21D8/12 takes precedence) · CPC title

• C22C38/20

  with copper · CPC title

• C22C38/12

  containing tungsten, tantalum, molybdenum, vanadium, or niobium · CPC title

• C22C38/38

  with more than 1.5% by weight of manganese · CPC title

• C22C38/54

  with boron · CPC title