CN109136754B - Cold-rolled low-alloy high-strength steel and production method thereof - Google Patents

Abstract

The invention discloses cold-rolled low-alloy high-strength steel and a production method thereof, wherein the high-strength steel comprises the following chemical components in percentage by mass: c: 0.06 to 0.08; si: 0.06 to 0.12; mn: 0.50 to 0.80; p is less than or equal to 0.015; s is less than or equal to 0.005; al is less than or equal to 0.040; nb: 0.020 to 0.035; ti: 0.015 to 0.0.025; n is less than or equal to 50 ppm; the balance of Fe and inevitable impurities. The cold-rolled low-alloy high-strength steel and the production method thereof have the advantages of easiness in processing and stamping, higher tensile strength, accordance with the development trend of reducing the overall weight of a vehicle, and further reduce the fuel consumption of the vehicle.

Description

Cold-rolled low-alloy high-strength steel and production method thereof

Technical Field

The invention relates to the field of metallurgical materials, in particular to cold-rolled low-alloy high-strength steel and a production method thereof.

Background

The cold-rolled low-alloy high-strength steel accounts for about 60-80% of the automobile structural member and the reinforcing plate, the strength and plasticity index of the cold-rolled low-alloy high-strength steel are improved, and the cold-rolled low-alloy high-strength steel plays a decisive role in the development of automobile lightweight, micro-alloy elements Nb and Ti are added into the cold-rolled low-alloy high-strength steel based on C-Mn or C-Si-Mn, and meanwhile, the cold-rolled low-alloy high-strength steel is combined with C, N to form carbide and nitride to play a reinforcing role, and finally, corresponding.

Chinese invention patent (application No. CN201410372216.0, application date 2014.7.31) discloses 340 MPa-grade cold-rolled low-alloy high-strength steel, which comprises the following chemical components in percentage by weight of 0.030-0.060 Wt%; less than or equal to 0.20 Wt% of [ Si ]; 0.075-0.095 Wt% of Mn; less than or equal to 0.015 Wt% of [ P ]; (S) less than or equal to 0.015 Wt%; (Als) 0.015-0.045 Wt%; less than or equal to 0.10 Wt% of Ti and Nb; the balance of Fe and inevitable trace elements. The process flow is as follows: blast furnace molten iron smelting → molten iron desulphurization pretreatment → converter molten steel smelting → LF molten steel refining treatment → CSP thin slab continuous casting and rolling → acid pickling cold continuous rolling → bell type furnace annealing → leveling → inspection and packaging for warehousing. The product has stable chemical components and mechanical properties, high strength, and good plasticity, toughness and formability. But its processing and punching properties are poor.

Disclosure of Invention

The invention aims to provide cold-rolled low-alloy high-strength steel and a production method thereof aiming at the defects of the prior art, and the cold-rolled low-alloy high-strength steel has the advantages of easiness in processing and stamping, and higher tensile strength, conforms to the development trend of reducing the overall weight of a vehicle, and further reduces the fuel consumption of the vehicle.

In order to achieve the above object, the present invention is achieved by the following technical solutions.

The cold-rolled low-alloy high-strength steel comprises the following chemical components in percentage by mass: c: 0.06 to 0.08; si: 0.06 to 0.12; mn: 0.50 to 0.80; p is less than or equal to 0.015; s is less than or equal to 0.005; al is less than or equal to 0.040; nb: 0.020 to 0.035; ti: 0.015 to 0.0.025; n is less than or equal to 50 ppm; the balance of Fe and inevitable impurities.

Further, the high-strength steel comprises the following chemical components in percentage by mass: c: 0.06 to 0.07; si: 0.08 to 0.10; mn: 0.67 to 0.69; p: 0.010 to 0.016; s: 0.002-0.004; al: 0.033 to 0.038; nb: 0.027-0.030; ti: 0.020 to 0.022; 0.008-0.015 percent of Ca; n is less than or equal to 50 ppm; the balance of Fe and inevitable impurities.

A production method of cold-rolled low-alloy high-strength steel sequentially comprises blast furnace molten iron, converter steelmaking, LF refining, slab continuous casting, hot rolling and acid cold rolling,

in the converter steelmaking process, the tapping temperature of converter tapping is 1600-1630 ℃, and in the molten steel tapped by the converter: the percentage by mass of P is less than or equal to 0.010 percent and the percentage by mass of S is less than or equal to 0.010 percent;

in the LF refining process, a whole-process argon blowing process is adopted;

in the slab continuous casting process, the temperature of molten steel entering a tundish is controlled to be 1545-1580 ℃, the continuous casting superheat degree delta T is less than or equal to 20-40 ℃, and the casting speed is controlled to be 0.90-1.10 m/min.

Further, the hot rolling process comprises: heating a plate blank, descaling by high-pressure water, fixing a width press, rolling by an E1R1 roughing mill, rolling by an E2R2 roughing mill, flying shears, descaling by high-pressure water, rolling by an F1-F7 finishing mill, cooling by dense laminar flow, coiling, transporting a tray system, sampling and inspecting,

in the slab heating process, a step-type heating furnace is adopted to heat the slab, and the slab heating temperature is 1180-1260 ℃; the heating time is more than or equal to 130 min; the soaking temperature is 1210-1260 ℃; soaking for 30-60 min, and discharging at 1200-1260 ℃;

in the rolling process of the E2R2 rough rolling mill, the rough rolling finishing temperature is 1000-1050 DEG C

In the rolling process of the F1-F7 finishing mill, the starting rolling temperature of finish rolling is 980-1020 ℃; the finish rolling temperature is 860-900 ℃;

in the coiling process, the coiling temperature is 550-600 ℃.

Further, the acid cold rolling process comprises the following steps: acid rolling uncoiling, welding, straightening, acid washing, rinsing, drying, trimming, cold rolling by a continuous rolling mill, slitting, coiling, off-line inspection, weighing, marking, bundling, packaging, warehousing, continuous annealing uncoiling, welding, cleaning, inlet loop, annealing furnace, outlet loop, leveling, loop inspection, trimming, surface inspection, oil coating, coiling, weighing, sampling and inspection,

a vertical continuous annealing furnace is adopted in the annealing process of the annealing furnace, and the outlet temperature of a heating and soaking section is 780-820 ℃; the outlet temperature of the slow cooling section is 620-670 ℃; the outlet temperature of the rapid cooling section is 380-450 ℃; the temperature of the overaging section is 200-350 ℃; the outlet temperature of the final cooling section is less than or equal to 150 ℃; the speed of the process section is 130-160 m/min;

in the leveling process, the elongation of the leveling machine is 1.0-1.6%.

Further, the thickness of the high-strength steel is 0.8-1.5 mm, the yield strength is 360-398 Mpa, the tensile strength is 460-483 Mpa, the elongation is 28-31%, and the yield ratio is 0.79-0.85.

The cold-rolled low-alloy high-strength steel and the production method thereof have the advantages of easiness in processing and stamping, high tensile strength and capability of meeting the development trend of reducing the overall weight of a vehicle and further reducing the fuel consumption of the vehicle.

Detailed Description

The present invention is further illustrated by the following examples, but is not limited to the details of the description.

A cold-rolled low-alloy high-strength steel comprises the following chemical components in percentage by mass: c: 0.06-0.08%; si: 0.06 to 0.12; mn: 0.50 to 0.80; p is less than or equal to 0.015; s is less than or equal to 0.005; al is less than or equal to 0.040; nb: 0.020 to 0.035; ti: 0.015 to 0.0.025; n is less than or equal to 50 ppm. The balance of Fe and inevitable impurities, and the mass fraction is 100 percent. Si is mainly used for improving the strength of the material through solid solution strengthening to ensure higher elongation after fracture, and Nb and Ti respectively improve the strength and toughness of the material through fine grain strengthening and precipitation strengthening.

The steel-making process comprises the following steps: molten iron → converter steelmaking → LF refining → slab continuous casting. KR pre-desulfurized molten iron, ferrosilicon, ferromanganese, ferroniobium and ferrotitanium alloy are adopted for deoxidation alloying in converter smelting, argon is blown and stirring is carried out on the molten steel in the whole process, and the continuous casting superheat degree delta T is less than or equal to 20-40 ℃.

The hot rolling process comprises the following steps: heating a plate blank → descaling with high pressure water → a constant width press → rolling with E1R1 roughing mill → rolling with E2R2 roughing mill → flying shear → descaling with high pressure water → rolling with F1-F7 finishing mill → cooling with dense laminar flow → coiling → a pallet transportation system → sampling and inspection. The heating temperature of the plate blank is 1200 plus or minus 20 ℃; the heating time is more than or equal to 130 min; the rough rolling mode adopts 3+ 3; the initial rolling temperature of finish rolling is 980-1020 ℃; the finish rolling temperature is 860-900 ℃, and the coiling temperature is 550-600 ℃.

The cold rolling process comprises the following steps: acid rolling and uncoiling → welding → straightening → acid pickling → drying → trimming → tandem cold rolling → splitting → coiling → off-line inspection → weighing → marking → bundling → packaging → warehousing → continuous uncoiling → welding → cleaning → inlet loop → annealing furnace → outlet loop → leveling → inspection loop → trimming → surface inspection → oiling → coiling → weighing → sampling and inspection. Annealing process parameters: the outlet temperature of the heating and soaking section is 780-820 ℃, the outlet temperature of the slow cooling section is 620-670 ℃, the outlet temperature of the fast cooling section is 380-450 ℃, the temperature of the overaging section is 200-350 ℃, the outlet temperature of the final cooling section is less than or equal to 150 ℃, and the elongation of the temper mill is 1.0-1.6%.

Some of these smelting processes are further described below.

1. Smelting process

1.1 converter smelting: the molten iron is pretreated and desulfurized to be smelted in a converter, oxygen blowing, decarbonization and temperature rising are carried out, ferrosilicon and ferromanganese are added for deoxidization and alloying in the later smelting period, P, S components are controlled, the molten steel is prevented from being peroxidated, the tapping temperature is 1600-1630 ℃, the tapping [ P ] of the converter is less than or equal to 0.010 percent, and the tapping [ S ] is less than or equal to 0.010 percent.

1.2 refining: and an LF whole-process argon blowing process is adopted, a good reducing atmosphere is kept in the refining process, Al wire deoxidation is adopted, ferromanganese and ferrocolumbium are added in the later stage of LF for alloying, and calcium treatment is carried out after the LF is finished.

1.3, continuous casting: the temperature of molten steel entering the ladle is controlled to be 1545-1580 ℃, the superheat degree is 25-40 ℃, and the pulling speed is controlled to be 0.90-1.10 m/min.

2 Hot rolling process

A stepping heating furnace is adopted to heat a casting blank (the heating process is shown in table 1), double-frame R1 and R2 are adopted for rough rolling to carry out reciprocating rolling, the adopted rough rolling mode is 3+3, the continuous rolling process from F1 to F7 is adopted for finish rolling, and the specific hot rolling process is shown in table 2.

TABLE 1 casting blank heating System

TABLE 2 Rolling Process

3 acid rolling process

The acid rolling adopts a continuous rolling process of F1-F5 frames, and the rolling schedule of different finished product thicknesses is shown in table 3.

TABLE 3 Rolling schedule by acid rolling

Finished product thickness (mm)	Thickness of raw material (mm)
		≥0.5～0.75	2.3
≥0.75～0.9	2.5
		≥0.9～1.05	3.0
≥1.05～1.30	3.5
		≥1.3～1.5	4.5

4 annealing process

The annealing adopts a vertical continuous annealing furnace, and the furnace is cooled by adopting a mixed protective atmosphere of reducing atmosphere and nitrogen and hydrogen. The control conditions of the outlet temperature of each section of the heating furnace are shown in a table 4, and the control conditions of different thicknesses of the elongation of the temper mill are shown in a table 5.

TABLE 4 annealing Process

TABLE 4 annealing Process

Finished product thickness mm (H)	Elongation percentage of temper mill%
		0.8≥H≥0.5	1.0
1.1＞H＞0.8	1.2
		1.5≥H≥1.1	1.5

5 analysis of examples

5.1 Steel making composition

The actual slab chemistry (mass percent) is shown in table 5 below, according to the above steelmaking process requirements.

Table 5 example chemical composition

5.2 Hot Rolling Properties

According to the design chemical components and the hot rolling process, the hot rolling thickness is 2.3-4.5 mm, the room temperature tensile property is shown in Table 6, and the test method refers to GB/T228.1 and GB/T229.

TABLE 6 Hot Rolling tensile Properties

5.3 Final Properties

Based on the hot rolling mechanical property, the finished product is produced according to the acid rolling process and the annealing process which are designed above, the room-temperature tensile mechanical property of the finished product is shown in Table 7, the metallographic structure is equiaxed ferrite and a small amount of pearlite, and the grain size is 10-11 grade.

TABLE 7 tensile Properties of the finished product

The chemical composition of the invention is designed to add Nb and Ti elements on the basis of S-Si-Mn, and the Nb content is reduced by adding Ti element, thereby reducing the alloy cost. The production process comprises smelting, 2250mm rolling mill, acid continuous rolling and continuous annealing process, and hot rolling and annealing core process are mainly designed, so that the performance of the finished product is in the front in the same industry, and the feedback is better after the user uses a plurality of parts.

The invention introduces a preparation process and a method of cold-rolled low-alloy high-strength steel HC340LA with high post-fracture elongation, which adopts a design idea of comprehensive action of microalloy and Si and controls a hot-rolling controlled cooling process, an acid rolling reduction and an annealing process. The elongation after fracture is more than or equal to 28 percent, the feedback is better through the batch use of users, the batch production is realized through the cold rolling at present, and the popularization value is better.

The cold-rolled low-alloy high-strength steel and the production method thereof have the advantages of easiness in processing and stamping, high tensile strength and capability of meeting the development trend of reducing the overall weight of a vehicle and further reducing the fuel consumption of the vehicle.

It should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. Not all embodiments are exhaustive. All obvious changes and modifications which are obvious to the technical scheme of the invention are covered by the protection scope of the invention.

Claims (1)

1. A cold-rolled low-alloy high-strength steel is characterized in that: the high-strength steel comprises the following chemical components in percentage by mass: c: 0.06 to 0.07; si: 0.08 to 0.10; mn: 0.67 to 0.69; p: 0.010 to 0.016; s: 0.002-0.004; al: 0.033 to 0.038; nb: 0.027-0.030; ti: 0.020 to 0.022; 0.008-0.015 percent of Ca; n is less than or equal to 50 ppm; the balance of Fe and inevitable impurities;

the metallographic structure of the cold-rolled low-alloy high-strength steel is equiaxed ferrite and a small amount of pearlite, and the grain size is 10-11 grades;

the production method of the cold-rolled low-alloy high-strength steel sequentially comprises the following steps of blast furnace molten iron, converter steelmaking, LF refining, slab continuous casting, hot rolling and acid cold rolling:

in the converter steelmaking process, the tapping temperature of converter tapping is 1600-1630 ℃, and in the molten steel tapped by the converter: the content of [ P ] is less than or equal to 0.010 percent, and the content of [ S ] is less than or equal to 0.010 percent;

in the LF refining process, a whole-process argon blowing process is adopted, a good reducing atmosphere is kept in the refining process, Al wires are adopted for deoxidation, ferromanganese and ferrocolumbium are added in the later stage of LF for alloying, and calcium treatment is carried out after the LF is finished;

in the slab continuous casting process, the temperature of molten steel entering a tundish is controlled to be 1545-1580 ℃, the continuous casting superheat degree delta T is less than or equal to 20-40 ℃, and the casting speed is controlled to be 0.90-1.10 m/min;

the hot rolling process comprises the following steps: heating a plate blank, descaling by high-pressure water, fixing a width press, rolling by an E1R1 roughing mill, rolling by an E2R2 roughing mill, flying shears, descaling by high-pressure water, rolling by an F1-F7 finishing mill, cooling by dense laminar flow, coiling, transporting a tray system, sampling and inspecting:

in the slab heating process, a step-type heating furnace is adopted to heat the slab, and the slab heating temperature is 1180-1260 ℃; the heating time is more than or equal to 130 min; the soaking temperature is 1210-1260 ℃; soaking for 30-60 min, and discharging at 1200-1260 ℃;

in the rolling process of the E2R2 rough rolling mill, the rough rolling finishing temperature is 1000-1050 ℃;

in the rolling process of the F1-F7 finishing mill, the starting rolling temperature of finish rolling is 980-1020 ℃; the finish rolling temperature is 860-900 ℃;

in the coiling process, the coiling temperature is 550-600 ℃;

the acid cold rolling process comprises the following steps: acid rolling uncoiling, welding, straightening, acid pickling, rinsing, drying, trimming, cold rolling by a continuous rolling mill, slitting, coiling, offline inspection, weighing, marking, bundling, packaging, warehousing, continuous annealing uncoiling, welding, cleaning, inlet loop, annealing furnace, outlet loop, leveling, loop inspection, trimming, surface inspection, oil coating, coiling, weighing, sampling and inspection:

a vertical continuous annealing furnace is adopted in the annealing process of the annealing furnace, and the outlet temperature of a heating and soaking section is 780-820 ℃; the outlet temperature of the slow cooling section is 620-670 ℃; the outlet temperature of the rapid cooling section is 380-450 ℃; the temperature of the overaging section is 200-350 ℃; the outlet temperature of the final cooling section is less than or equal to 150 ℃; the speed of the process section is 130-160 m/min;

in the leveling process, the elongation of the leveling machine is 1.0-1.6%;

the thickness of the high-strength steel is 0.8-1.5 mm, the yield strength is 360-398 MPa, the tensile strength is 460-483 MPa, the elongation is 28-31%, and the yield ratio is 0.79-0.85.