Hot rolled and steel sheet and a method of manufacturing thereof

Patent metadata

Field	Value
Publication number	US-12509740-B2
Application number	US-202017783926-A
Country	US
Kind code	B2
Filing date	Dec 15, 2020
Priority date	Dec 17, 2019
Publication date	Dec 30, 2025
Grant date	Dec 30, 2025

Abstract

A hot rolled steel sheet having a composition including the following elements, 0.18%≤Carbon≤0.3%, 1.8%≤Manganese≤4.5%. 0.8%≤Silicon≤2%, 0 001%≤Aluminum≤0.2%, 0.1%≤Molybdenum≤1%, 0.001%≤Titanium≤0.2%, 0.0001%≤Boron≤0.01%, 0%≤Phosphorus≤0.09%, 0%≤Sulfur≤0.09%, 0%≤Nitrogen≤0.09%, 0%≤Chromium≤0.5%, 0%≤Niobium≤0.1%, 0%≤Vanadium≤0.5%, 0%≤Nickel≤1%, 0%≤Copper≤1%, 0%≤Calcium≤0.005%, 0%≤Magnesium≤0.0010% the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of said steel sheet including in area fraction, of at least 70% martensite, 8% to 25% residual austenite, wherein the shape factor of the residual austenite is between 4 and 12.

First claim

What is claimed is:

1 . A hot rolled steel sheet having a composition comprising the following elements, expressed in percentage by weight:
0.18%≤carbon≤0.3% 1.8%≤manganese≤4.5% 0.8%≤silicon≤2% 0.001%≤aluminum≤0.2% 0.1%≤molybdenum≤1% 0.001%≤titanium≤0.2% 0%≤phosphorus≤0.09% 0%≤sulfur≤0.09% 0%≤nitrogen≤0.09% and optionally one or more of the following elements 0.0001%≤boron≤0.01% 0%≤chromium≤0.5% 0%≤niobium≤0.1% 0%≤vanadium≤0.5% 0%≤nickel≤1% 0%≤copper≤1% 0%≤calcium≤0.005% 0%≤magnesium≤0.0010% a remainder of the composition being composed of iron and unavoidable impurities caused by processing, a microstructure of the steel sheet comprising in area fraction, of at least 70% martensite, 8% to 25% residual austenite, wherein a shape factor of the residual austenite is between 4 and 12.

2 . The hot rolled steel sheet as recited in claim 1 , wherein the composition includes 0.9% to 1.9% of silicon.

3 . The hot rolled steel sheet as recited in claim 1 , wherein the composition includes 0.19% to 0.28% of carbon.

4 . The hot rolled steel sheet as recited in claim 3 , wherein the composition includes 0.001% to 0.15% of titanium.

5 . The hot rolled steel sheet as recited in claim 1 , wherein the composition includes 1.9% to 4.2% of manganese.

6 . The hot rolled steel sheet as recited in claim 1 , wherein the composition includes 0.15% to 0.7% of molybdenum.

7 . The hot rolled steel sheet as recited in claim 1 , wherein the composition includes 0.02% to 0.06% of aluminum.

8 . The hot rolled steel sheet as recited in claim 1 , wherein a cumulative presence of carbon and manganese is between 2.3% and 4.5%.

9 . The hot rolled steel sheet as recited in claim 1 , wherein the amount of residual austenite is between 8% and 22%.

10 . The hot rolled steel sheet as recited in claim 1 , wherein the steel sheet has a yield strength of 850 MPa or more, and a total elongation of 15% or more.

11 . The hot rolled steel sheet as recited in claim 10 , wherein said steel sheet has a yield strength of 880 MPa or more.

12 . The hot rolled steel sheet as recited in claim 1 , wherein the shape factor of the tempered martensite and residual austenite is between 5 and 11.

13 . A method of production of a hot rolled steel sheet comprising the following successive steps:
providing a semi-finished product having a composition comprising the following elements, expressed in percentage by weight:
0.18%≤carbon≤0.3%
1.8%≤manganese≤4.5%
0.8%≤silicon≤2%
0.001%≤aluminum≤0.2%
0.1%≤molybdenum≤1%
0.001%≤titanium≤0.2%
0%≤phosphorus≤0.09%
0%≤sulfur≤0.09%
0%≤nitrogen≤0.09%
and optionally one or more of the following elements
0.0001%≤boron≤0.01%
0%≤chromium≤0.5%
0%≤niobium≤0.1%
0%≤vanadium≤0.5%
0%≤nickel≤1%
0%≤copper≤1%
0%≤calcium≤0.005%
0%≤magnesium≤0.0010%
a remainder of the composition being composed of iron and unavoidable impurities caused by processing; reheating the semi-finished product to a temperature between Ac3+50° C. and 1300° C.; rolling the semi-finished product in the austenitic range wherein a hot rolling finishing temperature is at least Ac3 to obtain a hot rolled steel strip; optionally coiling the hot rolled steel strip at a coiling temperature range is between 200° C. and 450° C.; then cooling the hot rolled strip from the hot rolling finishing temperature to a temperature range between Ms and 20° C., with a cooling rate between 10° C./s and 200° C./s; then heating the hot rolled strip from a temperature range between Ms−50° C. and 20° C. to a temperature Tsoak between Ac3 and Ac3+250° C., with a heating rate HR1 of at least 1° C./s, and holding for 5 to 1000 seconds then cooling the hot rolled strip, wherein cooling starts from Tsoak to a cooling stop temperature T1 between Ms−10° C. and 50° C., with a cooling rate CR1 between 0.1° C./s and 150° C./s; then bringing the hot rolled strip from T1 to a partitioning temperature Tpartition between Ms−150° C. and Ms+150° C. wherein the hot rolled steel strip is held for 5 s to 1000 s; thereafter cooling the hot rolled steel strip to room temperature at a cooling rate CR2 between 0.1° C./s and 10° C./s to obtain the hot rolled steel sheet as recited in claim 1 .

14 . The method as recited in claim 13 , wherein the hot rolling finishing temperature is between 840° C. and 980° C.

15 . The method as recited in claim 13 , wherein the cooling rate for cooling after hot rolling is between 20° C./s and 180° C./s.

16 . The method as recited in claim 13 , wherein the Tpartition temperature is between Ms+100° C. and Ms−100° C.

17 . A method for the manufacture of a part of industrial machinery or green goods or yellow goods comprising performing the method as recited in claim 13 .

18 . A method for the manufacture of a part of industrial machinery or green goods or yellow goods comprising employing the steel sheet as recited in claim 1 .

Assignees

• Arcelormittal

Inventors

• De Knijf Dorien
• Duprez Lode
• Theuwissen Koenraad
• Waterschoot Tom

Classifications

• C22C38/60

  containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur · CPC title

• C22C38/14

  containing titanium or zirconium · CPC title

• C22C38/12

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

• C22C38/06

  containing aluminium · CPC title

• C22C38/04

  containing manganese · CPC title