WO2020030040A1

WO2020030040A1 - Production of twin-roll cast and hot rolled steel strip

Info

Publication number: WO2020030040A1
Application number: PCT/CN2019/099764
Authority: WO
Inventors: Hualong LI; Tingting Li; Aihua Chen; Yixin Shi; Jian Liu; Yi Ma; Dongsheng Zhou; Xinyuan Liu; Xia Li; Yihai ZHU
Original assignee: Zhangjiagang Zhongmei Ucs Technology Co Ltd; Jiangsu Shagang Group Co Ltd; Jiangsu Shagang Iron and Steel Research Institute Co Ltd
Current assignee: Zhangjiagang Zhongmei Ucs Technology Co Ltd; Jiangsu Shagang Group Co Ltd; Jiangsu Shagang Iron and Steel Research Institute Co Ltd
Priority date: 2018-08-08
Filing date: 2019-08-08
Publication date: 2020-02-13
Anticipated expiration: 2021-02-08
Also published as: CN109881085A

Abstract

A method of manufacturing an easy-to-weld twin roll cast and hot-rolled steel strip, such as a Q345 steel strip, having a chemical composition by mass percentage of: C: ≤0.05%; Si: 0.15～0.3%; Mn: ≤0.7%; Nb: ≤0.04%; P: ≤0.03%; S: ≤0.003%; N: ≤0.005%, and the balance being Fe and inevitable impurities is disclosed. The method comprises twin roll casting the molten steel and forming a cast strip having a thickness of 1.4-2.5 mm, hot rolling the cast strip and forming a hot-rolled strip having a thickness of 0.7-1.9 mm by means of a one pass hot rolling step, cooling the hot rolled strip to 400-600°C at a cooling rate of 30-80°C/s, and coiling the cooled hot rolled strip.

Description

PRODUCTION OF TWIN-ROLL CAST AND HOT ROLLED STEEL STRIP

Technical field

The invention relates to an easy-to-weld twin-roll cast and hot rolled steel strip and its manufacturing method.

The invention relates particularly, although by no means exclusively, to an easy-to-weld twin-roll cast and hot rolled Q345 steel strip and its manufacturing method.

Background

The following discussion of the invention focuses on steel production in China. However, it is noted that the relevance of the invention is not confined to China.

The discussion of the invention focuses on Q345 steel. However, it is noted that the invention is not confined to this steel composition.

The steel industry one of the pillars of the Chinese national economy and is developing rapidly. China's steel industry has always faced problems such as energy shortage, lack of resources, large investment, high cost and serious environmental pollution. The further development of the steel industry requires the development of a new generation of steel production processes that save energy resources, reduce environmental pollution, increase recycling, and are environmentally friendly in order to achieve sustainable development of the steel industry.

Twin-roll casting technology is a comparatively new technology that is an opportunity for sustainable development of the steel industry because it has a short process, low energy consumption, low capital and operating investment, and green environmental credentials.

In a twin roll caster, molten metal, typically steel, is introduced between a pair of counter-rotated casting rolls that are cooled so that metal shells solidify on the moving roll surfaces and are brought together at a nip between them. The term "nip" is used herein to refer to the general region at which the rolls are closest together. The molten metal may be delivered from a ladle into a smaller vessel or series of smaller vessels from which it flows through a metal delivery nozzle located above the nip, forming a casting pool of molten metal supported on the casting surfaces of the rolls immediately above the nip and extending along the length of the nip. As the metal shells are joined and pass through the nip between the casting rolls, a thin metal strip is cast downwardly from the nip.

The applicant has calculated that the energy consumption of the hot-rolled strip coil by a twin-roll casting process is 16%of the thick slab casting process, 32%of the thin slab casting process, 45.5%of the ESP process, and the CO ₂ emissions are 24.9%of the thick slab process, 44.4%of the thin slab process, 33.7%of the ESP process, the fuel consumption is reduced by 95%, the water consumption is reduced by 80%, and the energy saving and environmental protection effect is remarkable.

Steel Q345 is a typical low-alloy steel in China. It is the most widely and largely used structural steel in China. It needs to exhibit high and stable tensile strength and excellent welding performance to meet product specifications.

In order to effectively provide the required the mechanical strength of steel, the conventional Q345 steel strip manufacturing method is based on a medium-low carbon and high manganese steel composition, with a C content of between 0.1%and 0.2%, and a manganese content of between 0.75%and 1.2%.

Due to the high C content and C equivalent, the conventional Q345 steel strip has poor welding performance.

Summary

The invention provides an easy-to-weld hot-rolled steel strip, such as Q345 steel strip, produced by twin-roll casting Q345 steel strip and hot rolling the cast strip.

The easy-to-weld twin-rolled cast and hot-rolled steel strip, such as Q345 steel strip may have a chemical composition by mass percentage that includes:

C: ≤0.05%;

Si: 0.15～0.3%;

Mn: ≤0.7%;

Nb: ≤0.04%;

P: ≤0.03%;

S: ≤0.003%;

N: ≤0.005%;

and balance being Fe and inevitable impurities.

In order to improve the strength of the steel, an appropriate amount or amounts of one or more than one of alloying elements such as Cr, V, and Ti may be added to the steel composition, such as the Q345 steel composition, in a total amount by mass percentage that does not exceed 2%.

The steel composition may include other elements in addition to those mentioned above. The other elements may include any one or more of the elements Cu, Ni, and Mo.

In some situations, an element mentioned in the two preceding paragraphs may be an inevitable impurity and in other situations the same element may be a deliberate addition. This depends of factors such as the feed materials for the steel production step 1) and on the required mechanicla properties of the easy-to-weld twin-rolled cast and hot-rolled steel strip.

The steel composition, such as Q345 steel composition, may have a carbon equivalent Ceq value of less than 0.178 and a cold crack sensitivity index Pcm value of less than 0.095.

The invention also provides a method of manufacturing an easy-to-weld Q345 steel strip comprising the steps of:

1) producing molten steel according to the above-mentioned chemical composition and mass percentage;

2) twin roll casting the molten steel produced in step 1) and forming a cast strip;

3) hot rolling the cast strip in step 2) ;

4) cooling the hot rolled cast steel strip; and

5) coiling the cooled hot rolled cast steel strip.

The molten steel in steel production step 1) may be obtained by electric furnace steelmaking, vacuum tank degassing, and LF refining.

The pouring temperature of molten steel in twin roll casting step 2) may be 1500-1600℃.

The casting speed in twin roll casting step 2) may be 20-120m/min.

The molten steel may be twin roll cast in twin roll casting step 2) under inert gas protection.

The cast strip produced in twin roll casting step 2) may have a thickness of 1.4-2.5mm.

The hot rolling step 3) may be a one pass hot rolling step with a reduction of 10-50%.

The hot rolling temperature may be 850-1050℃.

The cooling step 4) cools the hot rolled cast strip to 400-600℃ at a cooling rate of 30-80℃/s. The cooling step may be carried out using any suitable cooling options, such as water sprays or water mist jets.

The coiling step 5) coils the cooled hot-rolled cast strip at a temperature of 400-600℃ and allows the cast strip to cool to room temperature in a coil.

The steel strip, such as Q345 steel strip, produced by the method may have a yield strength of ≥ 380MPa.

The steel strip, such as Q345 steel strip, produced by the method may have a tensile strength of ≥ 520 MPa, typically 520-590 MPa.

The steel strip, such as Q345 steel strip, produced by the method may have an elongation of ≥20%.

The composition of the steel strip, such as Q345 steel strip, may have a carbon equivalent Ceq value of less than 0.178.

The composition of the steel strip, such as Q345 steel strip, may have a cold crack sensitivity index Pcm value of less than 0.095.

It is noted that the carbon equivalent Ceq value is calculated in accordance with formula (1) below and the cold crack sensitivity index Pcm value is calculated in accordance with formula (2) below:

Ceq (%) = C + Mn/6 + (Cr + Mo + V) /5 + (Ni + Cu) /15

Pcm (%) = C + Si/30 + Mn/20 + Cu/20 + Ni/60 + Cr/20 + Mo/15 + V/10 + 5B

Beneficial technical effects

Compared with the prior art known to the applicant, the beneficial technical effects obtained by the invention include, for example:

1. The twin-roll casting and hot rolling method of the invention makes it possible to produce steel strip, such as Q345 steel strip, with few production steps, significantly reduced production cost and labor costs.

2. The steel strip, such as Q345 steel strip, of the invention has the advantages of thin thickness and high strength and can replace the traditional thick-type high-strength hot-rolled steel strip products, thereby achieving the effects of reducing cost, energy saving and environmental protection.

3. In the context of conventional Q345 steel strip, the steel strip of the invention has an ultra-low carbon and low-manganese steel composition and consequently has better welding performance. The main alloying elements in conventional Q345 steel strip are: C: 0.1-0.2%; Si: 0.15～0.5%; Mn: 0.75～1.2%. With this composition range, the carbon equivalent Ceq value is 0.23～0.33 and the cold crack sensitivity index Pcm value is 0.143-0.21. The carbon equivalent Ceq value of Q345 steel strip in a comparative example of the invention is no more than 0.178 and the cold crack sensitivity index Pcm value is no more than 0.095. It is clear from this data that the steel strip, such as Q345 steel strip, of the invention has better welding performance.

4. The composition of the steel strip, such as Q345 steel strip, of the invention may be modified to compensate for a reduction in strength due to the reduced content of manganese by adding Nb or any other suitable elements, typically in small concentrations to the steel composition. The addition of Nb may also have a beneficial impact of refining and homogenizing the steel strip, such as Q345 steel strip, and effectively improve the comprehensive mechanical properties of the steel strip as a consequence of Nb microalloy precipitates.

5. The microstructure of the steel strip, such as Q345 steel strip of the invention may be irregular equiaxed ferrite and acicular ferrite.

Brief description of the drawings

In order to explain the technical solutions of the embodiments of the present invention more clearly, a brief description about the drawings of the embodiments will be given below. Obviously, the drawings described below merely concern some of the embodiments of the present invention, rather than limitation to the present invention.

FIG. 1 is an elevational side view of an exemplary strip caster for use with the disclosed methods;

FIG. 2 is an enlarged partial sectional view of a portion of the twin roll caster of FIG. 1;

FIG. 2A is a schematic view of a portion of twin roll casters of FIG. 2; and

FIG. 3 is a photograph of the microstructure of Q345 steel strip obtained in embodiment 1 of the invention.

Detailed description

In order to make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, a clear and full description will be afforded below to the technical solutions of the embodiments of the present invention. The described embodiments are some of the embodiments of the invention, rather than all of the embodiments. All other embodiments obtained by the ordinary skilled in this art based on the described embodiments of invention without any creative endeavors fall into the protection scope of the invention.

Unless defined otherwise, the technical terms or scientific terminology as used in the present disclosure should take the meaning usually understood by the ordinary skilled in this art of invention.

In general terms, an embodiment of the invention is an easy-to-weld twin roll cast and hot-rolled steel strip, such as a Q345 steel strip, having a chemical composition by mass percentage that includes: C: ≤0.05%; Si: 0.15～0.3%; Mn: ≤0.7%; Nb: ≤0.04%; P: ≤0.03%; S: ≤0.003%; N: ≤0.005%; and balance being Fe and inevitable impurities.

The steel composition may include other elements in addition to those mentioned above. The other elements may include any one or more of the elements Cr, V, Ti, Cu, Ni, and Mo. In some situations, these other elements may be an inevitable impurity and in other situations the same element or elements may be a deliberate addition. This depends of factors such as the feed materials for the steel production step 1) and on the required mechanicla properties of the easy-to-weld twin-rolled cast and hot-rolled steel strip.

In general terms, an embodiment of the invention is a method of manufacturing an easy-to-weld steel strip, such as a Q345 steel strip, comprising the steps of:

1) producing molten steel according to the above-mentioned chemical composition;

2) twin roll casting the molten steel produced in steel production step 1) and forming a cast strip;

3) hot rolling the cast strip formed in step 2) and forming a hot rolled steel strip;

4) cooling the hot rolled steel strip; and

5) coiling the cooled hot rolled steel strip.

Embodiment 1

(1) Steel production. Molten steel having the following composition is obtained by electric furnace steelmaking, vacuum tank degassing, LF refining according to mass percentage: C: 0.024%; Si: 0.28%; Mn: 0.6%; Nb: 0.023%; P: 0.01%; S: 0.002%; N: 0.003%; and balance being Fe and inevitable impurities.

(2) Twin roll casting. The molten steel is cast into a cast strip in twin-roll casting equipment, with the pouring temperature of molten steel being 1510℃, with the casting speed being 45m/min, and with the molten steel is strip being cast under inert gas protection. A cast strip with a thickness of 2.2mm is obtained.

(3) Hot rolling. The cast strip is hot rolled into a strip with a thickness of 1.8mm by means of a one pass hot rolling stand with a reduction of 18%at a hot rolling temperature is 1050℃.

(4) Cooling and coiling. The hot-rolled strip is cooled to 600℃ at a cooling rate of 40℃/sand then coiled at temperature and allowed to cool to room temperature.

The mechanical properties of the cast strip produced by the above method are as follows in Table 1:

Table 1 Mechanical properties of Q345 steel strip obtained in Embodiment 1

FIG. 3 is a photograph of the metallographic structure of Q345 obtained in Embodiment 1. The microstructure shown in FIG 3 comprises irregular equiaxed ferrite and acicular ferrite.

Embodiment 2

(1) Steel production. Molten steel having the following composition is obtained by electric furnace steelmaking, vacuum tank degassing, LF refining according to mass percentage: C: 0.03%; Si: 0.23%; Mn: 0.52%; Nb: 0.025%; P: 0.012%; S: 0.0018%; N: 0.0038%; and balance being Fe and inevitable impurities.

(2) Twin roll casting. The molten steel is cast into a cast strip in twin-roll casting equipment, with the pouring temperature of molten steel being 1550℃, with the casting speed being 70m/min, and with the molten steel being strip cast under inert gas protection. A cast strip with a thickness of 1.8mm is obtained.

(3) Hot rolling. The cast strip is rolled into a strip with a thickness of 1.2mm by means of a one pass of hot rolling stand with a reduction of 33%and a hot rolling temperature of 950℃.

(4) Cooling and coiling. The hot-rolled strip is cooled to 500℃ at a cooling rate of 55℃/sand then coiled at temperature and allowed to cool to room temperature.

The mechanical properties of the cast strip produced by the above method are as follows in Table 2:

Table 2 Mechanical properties of Q345 steel strip obtained in Embodiment 2

Embodiment 3

(1) Steel production. Molten steel having the following composition is obtained by electric furnace steelmaking, vacuum tank degassing, LF refining according to mass percentage: C: 0.037%; Si: 0.18%; Mn: 0.35%; Nb: 0.032%; P: 0.008%; S: 0.001%; N: 0.0023%; and balance being Fe and inevitable impurities.

(2) Twin roll casting. The molten steel is cast into a cast strip in twin-roll casting equipment, with the pouring temperature of molten steel being 1570℃, with the casting speed being 100m/min, and with the molten steel being strip cast under inert gas protection. A cast strip with a thickness of 1.5mm is obtained.

(3) Hot rolling. The cast strip is rolled into a strip with a thickness of 0.8mm by means of a one pass of hot rolling stand with a reduction of 47%at a hot rolling temperature is 850℃.

(4) Cooling and coiling. The hot-rolled strip is cooled to 400℃ at a cooling rate of 65℃/sand then coiled at temperature and allowed to cool to room temperature.

The mechanical properties of the cast strip produced by the above method are as follows in Table 3:

Table 3 Mechanical properties of Q345 steel strip obtained in Embodiment 3

While it is appreciated that any twin roll strip caster may be employed for the invention, an exemplary thin strip caster is shown in FIGS. 1, 2, and 2A, the exemplary thin strip caster forming a twin roll caster. The twin roll caster has a main machine frame 10 standing up from the factory floor and supports a pair of counter-rotatable casting rolls 12 mounted in a module in a roll cassette 11. The casting rolls 12 are mounted in the roll cassette 11 for ease of operation and movement as described below. The roll cassette 11 facilitates rapid movement of the casting rolls 12 ready for casting from a setup position into an operative casting position as a unit in the caster, and ready removal of the casting rolls 12 from the casting position when the casting rolls 12 are to be replaced. There is no particular configuration of the roll cassette 11 that is desired, so long as it performs that function of facilitating movement and positioning of the casting rolls 12 as described herein.

With continued reference to FIGS. 1, 2, and 2A, the casting apparatus for continuously casting thin steel strip includes the pair of counter-rotatable casting rolls 12 having casting surfaces 12A laterally positioned to form a nip 18 there between. Molten metal is supplied from a ladle 13 through a metal delivery system to a metal delivery nozzle 17 (core nozzle) positioned between the casting rolls 12 above the nip 18. Molten metal thus delivered forms a casting pool 19 of molten metal above the nip 18 supported on the casting surfaces 12A of the casting rolls 12. This casting pool 19 is confined in the casting area at the ends of the casting rolls 12 by a pair of side closure plates, or side dams 20 (shown in dotted line in FIG. 2A) . The upper surface of the casting pool 19 (generally referred to as the "meniscus" level) may rise above the lower end of the delivery nozzle 17 so that the lower end of the delivery nozzle 17 is immersed within the casting pool 19. The casting area includes the addition of a protective atmosphere above the casting pool 19 to inhibit oxidation of the molten metal in the casting area. The casting rolls 12 are internally water cooled so that as the casting rolls 12 are counter-rotated, shells solidify on the casting surfaces 12A, as the casting surfaces 12A move into contact with and through the casting pool 19 with each revolution of the casting rolls 12. The shells are brought close together at the nip 18 between the casting rolls 12 to produce a thin cast strip product 21 delivered downwardly from the nip 18. The thin cast strip product 21 is formed from the shells at the nip 18 between the casting rolls 12 and delivered downwardly and moved downstream.

The ladle 13 of FIG. 1 may be of a conventional construction supported on a rotating turret 40. For metal delivery, the ladle 13 is positioned over a movable tundish 14 in the casting position to fill the tundish 14 with molten metal. The movable tundish 14 may be positioned on a tundish car 66 capable of transferring the tundish 14 from a heating station, where the tundish 14 is heated to near a casting temperature, to the casting position. A tundish guide, such as rails, may be positioned beneath the tundish car 66 to enable moving the movable tundish 14 from the heating station to the casting position. The movable tundish 14 may be fitted with a slide gate 25, actuable by a servo mechanism, to allow molten metal to flow from the tundish 14 through the slide gate 25, and then through a refractory outlet shroud 15 to a transition piece or distributor 16 in the casting position. From the distributor 16, the molten metal flows to the delivery nozzle 17 positioned between the casting rolls 12 above the nip 18.

The side dams 20 may be made from a refractory material such as zirconia graphite, graphite alumina, boron nitride, boron nitride zirconia, or other suitable composites. The side dams 20 have a face surface capable of physical contact with the casting rolls 12 and molten metal in the casting pool 19. The side dams 20 are mounted in side dam holders, which are movable by side dam actuators, such as a hydraulic or pneumatic cylinder, servo mechanism, or other actuator to bring the side dams 20 into engagement with the ends of the casting rolls 12. Additionally, the side dam actuators are capable of positioning the side dams 20 during casting. The side dams 20 form end closures for the molten pool of metal on the casting rolls 12 during the casting operation.

FIGS 1 and 2A show the twin roll caster producing the cast strip 21, which passes across a guide table 30 to a pinch roll stand 31, comprising pinch rolls 31A. Upon exiting the pinch roll stand 31, the thin cast strip 21 passes through a hot rolling mill 32, comprising a pair of work rolls 32A, and backup rolls 32B, forming a gap capable of hot rolling the cast strip 21 delivered from the casting rolls 12, where the cast strip 21 is hot rolled to reduce the strip to a desired thickness, improve the strip surface, and improve the strip flatness. The work rolls 32A have work surfaces relating to the desired strip profile across the work rolls 32A. The hot rolled cast strip 21 then passes onto a run-out table 33, where it may be cooled by contact with a coolant, such as water, supplied via water jets 90 or other suitable means, and by convection and radiation. In any event, the hot rolled cast strip 21 may then pass through a second pinch roll stand 91 having roller 91A to provide tension of the cast strip 21, and then to a coiler 92. The cast strip 21 may be 0.3 to 2.0 millimeters in thickness before hot rolling.

At the start of the casting operation, a short length of imperfect strip is typically produced as casting conditions stabilize. After continuous casting is established, the casting rolls 12 are moved apart slightly and then brought together again to cause this leading end of the cast strip 21 to break away forming a clean head end of the following cast strip 21. The imperfect material drops into a scrap receptacle 26, which is movable on a scrap receptacle guide. The scrap receptacle 26 is located in a scrap receiving position beneath the caster and forms part of a sealed enclosure 27 as described below. The enclosure 27 is typically water cooled. At this time, a water-cooled apron 28 that normally hangs downwardly from a pivot 29 to one side in the enclosure 27 is swung into position to guide the clean end of the cast strip 21 onto the guide table 30 that feeds it to the pinch roll stand 31. The apron 28 is then retracted back to its hanging position to allow the cast strip 21 to hang in a loop beneath the casting rolls 12 in enclosure 27 before it passes to the guide table 30 where it engages a succession of guide rollers.

An overflow container 38 may be provided beneath the movable tundish 14 to receive molten material that may spill from the tundish 14. As shown in FIG. 1, the overflow container 38 may be movable on rails 39 or another guide such that the overflow container 38 may be placed beneath the movable tundish 14 as desired in casting locations. Additionally, an optional overflow container may be provided for the distributor 16 adjacent the distributor 16.

The sealed enclosure 27 is formed by a number of separate wall sections that fit together at various seal connections to form a continuous enclosure wall that permits control of the atmosphere within the enclosure 27.

The enclosure 27 may include an upper collar portion 43 supporting a protective atmosphere immediately beneath the casting rolls 12 in the casting position. When the casting rolls 12 are in the casting position, the upper collar portion 43 is moved to the extended position closing the space between a housing portion 53 adjacent the casting rolls 12, as shown in FIG. 2, and the enclosure 27. The upper collar portion 43 may be provided within or adjacent the enclosure 27 and adjacent the casting rolls 12 and may be moved by a plurality of actuators such as servo-mechanisms, hydraulic mechanisms, pneumatic mechanisms, and rotating actuators.

The casting rolls 12 are internally water cooled as described below so that as the casting rolls 12 are counter-rotated, shells solidify on the casting surfaces 12A, as the casting surfaces 12A move into contact with and through the casting pool 19 with each revolution of the casting rolls 12. The shells are brought close together at the nip 18 between the casting rolls 12 to produce a thin cast strip product 21 delivered downwardly from the nip 18. The thin cast strip product 21 is formed from the shells at the nip 18 between the casting rolls 12 and delivered downwardly and moved downstream as described above.

It is clear form the above description of embodiments of the invention that the method and product of the invention are an effective alternative to conventional Q345 steel and Q345 steel strip production.

The above description is merely an exemplary embodiment of the present invention, and it should be noted that those skilled in the art can also make several improvements and modifications, which should also be the scope of protection of the present invention, without departing from the principle of the present invention.

Claims

A method of manufacturing an easy-to-weld steel strip, such as Q345 steel strip, comprising the following steps:

1) producing molten steel having the following chemical composition by mass percentage,

C: ≤0.05%;

Si: 0.15～0.3%;

Mn: ≤0.7%;

Nb: ≤0.04%;

P: ≤0.03%;

S: ≤0.003%;

N: ≤0.005%; and

the balance being Fe and inevitable impurities;

2) twin roll casting the molten steel produced in step 1) and forming a cast strip;

3) hot rolling the cast strip formed in step 2) and forming a hot rolled steel strip;

4) cooling the hot rolled steel strip; and

5) coiling the cooled hot rolled steel strip.
The method according to claim 1, wherein the molten steel composition produced in steel production step 1) further comprises any one or more than one of the elements Cr, V, and/or Ti having a mass percentage of no more than 2%of the molten steel.
The method according to claim 2, comprises producing the molten steel in step 1) by electric furnace steelmaking, vacuum tank degassing, and LF refining.
The method according to any one of claims 1-3, wherein twin roll casting step 2) comprises twin roll casting molten steel from steel production step 1) at a pouring temperature of 1500～1600℃.
The method according to any one of claims 1-4, wherein twin roll casting step 2) comprises twin roll casting molten steel from steel production step 1) at a casting speed is 20～120m/min.
The method according to any one of claims 1-5, wherein twin roll casting step 2) comprises twin roll casting molten steel from steel production step 1) under inert gas protection.
The method according to any one of claims 1-6, wherein the cast strip produced in twin roll casting step 2) has a thickness of 1.4-2.5mm and a width of 700-1700mm.
The method according to any one of claims 1-7, wherein hot rolling step 3) comprises hot rolling the cast strip form twin roll casting step 2) in a one pass hot rolling step with a reduction rate of 10-50%.
The according to claim 8, wherein the hot rolling temperature for the one pass of hot rolling step is 850-1050℃.
The method according to any one of claims 1-9, wherein the rate of cooling the hot-rolled steel strip in cooling step 4) is 30-80℃/s.
The method according to any one of claims 1-10, wherein the coiling temperature for the hot-rolled steel strip in coiling step 5) is 400-600℃.
The method according to any one of claims 1-11, wherein the hot-rolled steel strip produced in hot rolling step 3) has a thickness of 0.7-1.9mm and a width of 700-1700mm.
An easy-to-weld twin roll cast and hot-rolled steel strip, such as Q345 steel strip, produced by the method according to any one of claims 1-12.
The easy-to-weld twin roll cast and hot-rolled steel strip, such as Q345 steel strip, according to claim 13 having a carbon equivalent Ceq value of less than 0.178.
The easy-to-weld twin roll cast and hot-rolled steel strip, such as Q345 steel strip, according to claim 13 or claim 14 having a cold crack sensitivity index Pcm value of less than 0.095.
The easy-to-weld twin roll cast and hot-rolled steel strip, such as Q345 steel strip, according to any of claims 13 to 15 having a microstructure of irregular equiaxed ferrite and acicular ferrite.