High-formability and super-strength hot galvanizing steel plate and manufacturing method thereof

Patent metadata

Field	Value
Publication number	US-10100385-B2
Application number	US-201314442426-A
Country	US
Kind code	B2
Filing date	Feb 21, 2013
Priority date	Nov 15, 2012
Publication date	Oct 16, 2018
Grant date	Oct 16, 2018

Abstract

A high-formability, super-high-strength, hot-dip galvanized steel plate, the chemical composition of which comprises, based on weight percentage, C: 0.15-0.25 wt %, Si: 1.00-2.00 wt %, Mn: 1.50-3.00 wt %, P≤0.015 wt %, S≤0.012 wt %, Al: 0.03-0.06 wt %, N≤0.008 wt %, and the balance of iron and unavoidable impurities. The room temperature structure of the steel plate comprises 10-30% ferrite, 60-80% martensite and 5-15% residual austenite. The steel plate has a yield strength of 600-900 MPa, a tensile strength of 980-1200 MPa, and an elongation of 15-22%. Through an appropriate composition design, a super-high-strength, cold rolled, hot-dip galvanized steel plate is manufactured by continuous annealing, wherein no expensive alloy elements are added; instead, remarkable increase of strength along with good plasticity can be realized just by appropriate augment of Si, Mn contents in combination with suitable processes of annealing and furnace atmosphere control. In addition, the steel plate possesses good galvanization quality that meets the requirement of a super-high-strength, cold rolled, hot-dip galvanized steel plate for automobiles.

First claim

What is claimed is:

1. A high-formability, ultra-high-strength, hot-dip galvanized steel plate, consisting of:
a) 0.15˜0.25 wt % carbon (C)
b) 1.00˜2.00 wt % silicon (Si)
c) 1.50˜3.00 wt % manganese (Mn)
d) <0.015 wt % phosphorus (P)
e) <0.012 wt % sulfur (S)
f) 0.03˜0.06 wt % aluminum (Al)
g) <0.008 wt% nitrogen (N), and
h) a balance of iron (Fe) and unavoidable impurities;
wherein the steel plate structure at room temperature consists of 10˜30% ferrite, 60˜80% martensite, and 5˜15% residual austenite; and
wherein the steel plate exhibits a yield strength of 600˜900 MPa, a tensile strength of 980˜1200 MPa, and an elongation of 15˜22%.

2. The high-formability, ultra-high-strength, hot-dip galvanized steel plate of claim 1 , wherein carbon is present in an amount ranging from 0.18˜0.22 wt %.

3. The high-formability, ultra-high-strength, hot-dip galvanized steel plate of claim 1 , wherein silicon is present in an amount ranging from 1.4˜1.8 wt %.

4. The high-formability, ultra-high-strength, hot-dip galvanized steel plate of claim 1 , wherein manganese is present in an amount ranging from 1.8˜2.3 wt %.

5. The high-formability, ultra-high-strength, hot-dip galvanized steel plate of claim 1 , wherein phosphorus is present in an amount <0.012 wt % and sulfur is present in an amount <0.008 wt %.

6. A method for manufacturing the high-formability, ultra-high-strength, hot-dip galvanized steel plate of claim 1 , comprising the following steps:
a) smelting the raw materials according to the composition of the high-formability, ultra-high-strength, hot-dip galvanized steel plate of claim 1 ;
b) casting the raw materials of step a) into a plate blank;
c) heating the plate blank of step b) to 1170˜1230° C.;
d) hot rolling the plate blank of step c) at an end rolling temperature of 880±30° C., and a coiling temperature of 550˜650° C.;
e) acid pickling the steel of step d);
f) cold rolling the acid pickled steel of step e) to a reduction rate of 40-60%, wherein a steel strip is formed;
g) annealing the steel strip of step f) by (1) to (5), wherein the annealing is performed in a continuous mode using a two-stage heating procedure comprising a direct flame heating in an oxidative atmosphere and an irradiation heating in a reducing atmosphere,
(1) direct flame heating the steel strip to 680˜750° C. in an oxidative atmosphere, wherein the dew point in the continuous annealing furnace is controlled at a value higher than 35° C., and the heating time is 10-30 s;
(2) heating the steel strip to 840˜920° C. by irradiation in a reducing atmosphere and holding at this temperature for 48-80 s while the H content in the continuous annealing furnace being controlled at 8˜15%;
(3) cooling the steel strip at a cooling rate of 3˜10° C/s to 720˜800° C. so that a proportion of ferrite is generated in the material;
(4) cooling the steel strip to 260˜360° C. at a cooling rate >50° C/s so that part of austenite is converted into martensite;
(5) reheating the steel strip to 460˜470° C. and holding at this temperature for 60-120 s;
h) feeding the steel strip of step g) into a zinc pot to complete hot-dip galvanization, wherein carbon is distributed from martensite into austenite to make austenite rich in carbon and stabilized during the above course of reheating, holding and galvanization; and
i) cooling the steel strip to room temperature,
wherein, at room temperature, the structure of the steel plate consists of 10-30% ferrite, 60-80% martensite, and 5-15% residual austenite and the steel plate exhibits a yield strength of 600˜900 MPa, a tensile strength of 980˜1200 MPa, and an elongation of 15˜22%.

7. The method of claim 6 , wherein the plate blank of step c) is heated to 1170˜1200° C.

8. The method of claim 6 , wherein the coiling temperature of step d) is 550˜600° C.

9. The method of claim 6 , wherein the steel strip is heated to 680˜720° C. by direct flame in oxidative atmosphere in (1).

10. The method of claim 6 , wherein in (1), the dew point in the furnace is controlled at −30 to −20° C. during the direct flame heating in oxidative atmosphere.

11. The method of claim 6 , wherein the steel strip is further heated to 860˜890° C. by irradiation in reducing atmosphere in (2).

12. The method of claim 6 , wherein in (2), the hydrogen (H) content in the continuous annealing furnace is controlled at 10˜15% during the irradiation heating in reducing atmosphere.

13. The method of claim 6 , wherein in (4), the steel strip is cooled to 280˜320° C.

14. The method of claim 6 , wherein after cooling in (4), the steel strip is reheated to 460˜465° C. and held for 80˜110 s in (5).

15. The method of claim 6 , wherein the steel strip is cooled to 730˜760° C. in (3).

Assignees

• Baoshan Iron & Steel

Inventors

• Zhong Yong
• Wang Li
• Feng Weijun
• Zhang Liyang

Classifications

• C21D8/0263

  following hot rolling · CPC title

• C22C38/06

  containing aluminium · CPC title

• C22C38/001

  containing N · CPC title

• C21D1/52

  with flames · CPC title

• C21D2211/008

  Martensite · CPC title