CN111172460B

CN111172460B - Steel wire rod for 600 MPa-level yield strength welding wire and production method thereof

Info

Publication number: CN111172460B
Application number: CN202010065035.9A
Authority: CN
Inventors: 董捷; 郑瑞; 王慧军; 王嘉伟; 薛虎东; 边影; 苏航; 赵桂英
Original assignee: Baotou Iron and Steel Group Co Ltd
Current assignee: Baotou Iron and Steel Group Co Ltd
Priority date: 2020-01-20
Filing date: 2020-01-20
Publication date: 2021-03-16
Anticipated expiration: 2040-01-20
Also published as: CN111172460A

Abstract

The invention discloses a steel wire rod for a 600 MPa-level yield strength welding wire and a production method thereof, wherein the steel wire rod for the 600 MPa-level yield strength welding wire comprises the following chemical components in percentage by mass: c: 0.06 to 0.12; si: 0.35 to 0.45; mn: 1.55-1.70; p is less than or equal to 0.020; s is less than or equal to 0.010; cr: 0.25 to 0.40; ni: 1.70-1.95; mo: 0.42 to 0.52; ti: 0.10 to 0.12; the balance being Fe and unavoidable impurities. The mechanical property of the provided steel wire rod for the welding wire meets the following requirements: the yield strength is more than or equal to 600MPa, the elongation is more than or equal to 25%, the reduction of area is more than or equal to 70%, and the method can be applied to the field of high-strength steel welding of coal mine machinery, containers, buildings, ships, bridges and the like.

Description

Steel wire rod for 600 MPa-level yield strength welding wire and production method thereof

Technical Field

The invention belongs to the technical field of metallurgy, and particularly relates to a steel wire rod for a 600 MPa-level yield strength welding wire and a production method thereof.

Background

With the rapid development of economy in China, steel materials gradually develop from a common level to a high-strength level; meanwhile, the market demand of the wire steel with high strength grade matched with the wire steel is also increasing. Most of domestic mature welding wires with yield strength of more than 600MPa need to be imported, and the requirement of the gas shielded welding of low-alloy high-strength steel which is growing day by day can not be met. This results in a serious weakness of the entire weld joint. Therefore, the research on welding materials also severely restricts the wide application of high-strength steel materials. Therefore, the development of corresponding high-strength welding materials to solve the problem of unmatched structure and performance of base metal and welding seam metal is imperative. The high-strength welding wire with the yield strength of more than 600MPa is mainly applied to welding high-strength steel structures of coal mine machinery, containers, buildings, ships, bridges, military vehicles and the like.

The welding wire with the yield strength of 600MPa has higher strength, the yield strength of the welding wire commonly used in China is 350-420 MPa, the content of manganese and silicon in the steel for the high-strength welding wire is higher, the CCT transformation curve is easy to move towards the lower right, and the Ni, Cr, Mo and Ti alloy is added to delay and prolong the transformation time, so that the cooling of the steel grade adopts delayed cooling, so that the wire rod generates a bainite structure under the condition of approximate isothermal transformation. The high alloy is added to enhance the strength of the wire rod and increase the sensitivity to the cooling speed, so that the CCT curve moves more to the lower right, abnormal structures such as martensite and the like are easily generated, the generation of the abnormal structures causes adverse effects on the drawing performance of a welding wire and the wire rod is easily brittle, and therefore, the difficulty in controlling the wire rod rolling process to obtain good target structures and good performance of the wire rod is high.

Disclosure of Invention

In view of one or more of the problems in the prior art, one aspect of the present invention provides a steel wire rod for a 600MPa grade yield strength welding wire, which comprises the following chemical components in percentage by mass: c: 0.06 to 0.12; si: 0.35 to 0.45; mn: 1.55-1.70; p is less than or equal to 0.020; s is less than or equal to 0.010; cr: 0.25 to 0.40; ni: 1.70-1.95; mo: 0.42 to 0.52; ti: 0.10 to 0.12; the balance being Fe and unavoidable impurities.

The mechanical properties of the steel wire rod for the 600 MPa-level yield strength welding wire meet the following requirements: the yield strength is more than or equal to 600MPa, the elongation is more than or equal to 25 percent, and the reduction of area is more than or equal to 70 percent.

The invention also provides a production method of the steel wire rod for the 600 MPa-level yield strength welding wire, which comprises the following steps of: blast furnace molten iron-molten iron pretreatment-converter top combined blown smelting-LF ladle furnace refining-billet continuous casting-heating furnace heating-high pressure water descaling-rolling-spinning-stelmor line delayed cooling-bundling-finished wire rod, wherein in the molten iron pretreatment procedure, the sulfur content in the molten iron is less than or equal to 0.06%; in the converter top combined blowing smelting process, the C content of the steel tapping is controlled to be 0.02-0.03%, the tapping temperature is 1631-; in the LF ladle furnace refining process, the in-position temperature is 1545-1572 ℃, the refining out-position temperature is 1595-1617 ℃, the refining treatment time is 28-65 min, Ar blowing operation is carried out in the whole process according to the refining rule, desulfurization, component fine adjustment and heating operation are carried out according to the components and the temperature of the molten steel of the converter, the content of [ O ] is less than or equal to 30ppm, the content of [ N ] is less than or equal to 60ppm, the content of [ H ] is less than or equal to 2.0ppm, titanium is increased by adopting low-aluminum ferrotitanium, a silicon-barium wire is adopted to replace a silicon-calcium wire in the final refining stage, meanwhile, argon is blown at; in the small square billet continuous casting process, the superheat degree is controlled to be between 25 and 30 ℃, and the drawing speed is between 1.9 and 2.2 m/min; the total heating time in the heating process of the heating furnace is more than or equal to 2.5 hours, wherein the temperature of the preheating section of the heating furnace is 720-: 1245 and 1260 ℃; the rolling comprises rough rolling, intermediate rolling and finish rolling, wherein the initial rolling temperature is controlled to be 970-990 ℃; the spinning temperature is 885-925 ℃.

According to the production method of the steel wire rod for the welding wire with the yield strength of 600MPa, provided by the technical scheme, the alloy elements such as Ni, Mo, Cr and Ti are added, the strength of the welding wire is improved by alloying the metal elements, and the wire rod enters the heat-insulating cover at a temperature slightly higher than the phase transition point and enters the phase transition region in advance by reducing the initial rolling temperature and the spinning temperature through reasonable rolling control and cooling control. And the slow cooling is carried out by adopting stelmor line delayed cooling to obtain a uniform and good structure, so that the generation of a martensite abnormal structure is avoided. The mechanical properties of the obtained steel wire rod for the welding wire with the yield strength of 600MPa grade meet the following requirements: the yield strength is more than or equal to 600MPa, the elongation is more than or equal to 25%, the reduction of area is more than or equal to 70%, the metallographic structure is a granular bainite structure with high strength, the welding wire manufactured by the method has less splashing and stable electric arc in the welding process, can be produced in large scale, has good popularization value, and can be applied to the high-strength steel welding field such as coal mine machinery, containers, buildings, ships, bridges and the like.

Drawings

FIG. 1 is a 500-fold metallographic picture of a steel wire rod for a 600MPa grade yield strength welding wire produced by the furnace 1 in the example.

Detailed Description

The invention provides a steel wire rod for a 600 MPa-grade yield strength welding wire, which comprises the following chemical components in percentage by mass: c: 0.06 to 0.12; si: 0.35 to 0.45; mn: 1.55-1.70; p is less than or equal to 0.020; s is less than or equal to 0.010; cr: 0.25 to 0.40; ni: 1.70-1.95; mo: 0.42 to 0.52; ti: 0.10 to 0.12; the balance being Fe and unavoidable impurities.

C can rapidly improve the strength of the welding seam, but can reduce the impact toughness and improve the ductile-brittle transition temperature, and the crack resistance is influenced. The high carbon content is the main reason for cold and hot cracks of the welding seam. When the content of C is high, the wire feeding is not smooth and the conductive nozzle is blocked, the deformation resistance is high in the drawing process, the rapid drawing is not facilitated, and the loss of the die is greatly influenced, so that the carbon with low content is adopted, and the content is preferably 0.06-0.12%.

Mn element is an effective element for strengthening the welding seam, and can improve the hardenability of the welding seam metal, inhibit the generation of eutectoid ferrite and promote the formation of acicular ferrite. Si element can prevent the oxidation of the welding line and stabilize the matrix to ensure the welding line strength, plays a role in deoxidation and weld line strengthening during welding, is used as a deoxidizer to supplement the burning loss in the welding process, prevents the generation of air holes, refines molten drops, stabilizes electric arc, and ensures the mechanical property of the welding line. However, the higher manganese and silicon contents also increase the segregation degree and the inclusion content in the steel, a banded structure appears, the higher manganese and silicon contents are not beneficial to drawing, the wear of a wire drawing die is aggravated, and the user cost is increased, so the invention adopts the lower silicon and manganese contents, wherein the silicon content is preferably 0.35-0.45%, and the manganese content is preferably 1.55-1.70%.

Phosphorus and sulfur are harmful elements in steel, the steel with high sulfur content is easy to cause hot brittleness during high-temperature processing, the phosphorus can obviously reduce the plasticity and toughness of the steel, and the steel is subjected to cold brittleness, wherein the lower the phosphorus is in a standard range, the better the phosphorus is.

The Ni element can improve the strength and toughness of steel, can improve the toughness of a ferrite matrix and promote the formation of ferrite, and when the content is high, the physical properties of the steel can be obviously changed, and the corrosion resistance of the steel is improved, wherein the content of Ni is preferably 1.70-1.95%.

Mo is a main element for obtaining high-strength weld metal, is used as a high-melting-point substance, has good effect on grain refinement, does not greatly damage plastic toughness while improving strength, and preferably has the content of 0.42-0.52%.

The Cr element is beneficial to improving the toughness of the welding seam and can form dispersed carbide with carbon to improve the strength of the welding seam, but the higher Cr element increases the hardenability of steel, so that the steel is sensitive to the change of the cooling speed in the rolling process, and the preferable content of the Cr element is 0.25-0.40%.

Ti is a microalloy strengthening element, and forms titanium nitride and titanium carbide points with N, C to achieve the purpose of refining grains, so that the comprehensive mechanical property of the weld metal is improved, and the content of Ti in the invention is preferably 0.10-0.12%.

The invention also provides a production method of the steel wire rod for the 600 MPa-level yield strength welding wire, which comprises the following steps: blast furnace molten iron-molten iron pretreatment-converter top combined blown smelting-LF ladle furnace refining-small square billet continuous casting-heating furnace heating-high pressure water descaling-rolling (rough rolling-medium rolling-finish rolling) -spinning-stelmor line delayed cooling-coil collecting-bundling-finished wire rod. During the production process, the non-metallic inclusion targets were controlled as in table 1 below.

Table 1: non-metallic inclusions (grades)

The present invention will be described in further detail with reference to examples.

The following disclosure provides many different embodiments, or examples, for implementing different aspects of the invention. The present invention provides examples of various specific processes and materials, but one of ordinary skill in the art may recognize the application of other processes and/or the use of other materials.

The present invention is described in detail below with reference to specific examples. The embodiments are implemented on the premise of the technical scheme of the invention, and detailed implementation modes and specific operation processes are given, but the disclosure of the invention is not limited to the following embodiments.

The methods used in the following examples are conventional methods unless otherwise specified.

In the examples, the production of steel wire rods for welding wire with yield strength of 600MPa grade in three furnaces (furnace 1, furnace 2 and furnace 3) was carried out, and the production method thereof comprises the following steps: blast furnace molten iron-molten iron pretreatment-converter top combined blown smelting-LF ladle furnace refining-small square billet continuous casting-heating furnace heating-high pressure water descaling-rough rolling-intermediate rolling-finish rolling-spinning-wire laying-stelmor line delayed cooling-coil collecting-bundling-finished wire rod.

The method specifically comprises the following steps:

1) pretreating molten iron: the sulfur content in the molten iron is less than or equal to 0.060 percent;

2) converter top combined blown smelting

Controlling the C content of the steel to be 0.02-0.03%, the steel tapping temperature to be 1631-; so that the phosphorus content is less than or equal to 0.13 percent and the sulfur content is less than or equal to 0.06 percent. Table 2 below shows the top-blown converter smelting in three heats.

Table 2: molten iron condition, deoxidizer and tapping condition

3) Refining in an LF ladle furnace: the in-place temperature is 1545-1572 ℃, the refining out-of-place temperature is 1595-1617 ℃, the refining treatment time is 28-65 min, the Ar blowing operation is carried out according to the refining rule in the whole process, and the operations of desulfurization, component fine adjustment and temperature rise are carried out according to the components and the temperature of the molten steel of the converter. [0] Less than or equal to 30ppm, less than or equal to 60ppm [ N ], and less than or equal to 2.0ppm [ H ]. The low-aluminum ferrotitanium is adopted to increase titanium, and the silicobarium wire is adopted to replace the silicocalcium wire in the final refining stage, so that the intake of calcium in the welding wire is reduced, and the influence on splashing is reduced. Meanwhile, argon is blown under high pressure for stirring, the soft blowing time is longer than 10min, the flow of molten steel is increased, impurities are removed after the impurities float sufficiently, and finally, the desulfurization and the deoxidation of the molten steel are realized. By utilizing the LF refining technology, the purity of the molten steel is improved, and the internal quality of the welding wire steel billet is improved. The kind of the wire feed, the argon gas consumption, the soft blowing time, the soft blowing flow rate, and the stage temperature are shown in Table 3.

Table 3: type of feed, soft blowing time, soft blowing flow rate, and temperature

4) Continuous casting of small square billets:

carrying out full-protection pouring, carrying out argon sealing on the long nozzle of the ladle, and filling argon into the tundish 2min before pouring; after the ladle is cast, the alkaline covering agent is put into the ladle to quickly cover the slag surface, and the argon blowing pipe can be withdrawn only after the slag surface completely covers the molten steel; the submerged nozzle is hung from the tundish to the crystallizer to prevent the secondary oxidation of molten steel and ensure the further control of the content of impurities.

The liquidus temperature TL is 1511 ℃, the superheat degree is not more than 35 ℃, the superheat degree is controlled to be 25-30 ℃ as much as possible, the constant drawing speed is adopted, the drawing speed is controlled to be 1.9-2.2 m/min, the continuous casting billet is timely taken off the line and slowly cooled after being cut, a cover type is paved on the lower part, the slow cooling time is more than 36 hours, the slow cooling is carried out to remove hydrogen, and the generation of internal casting billet stress is reduced.

5) Heating by a heating furnace: the preheating period is 25min, the temperature is 720-.

6) Rolling and laying

By reducing the initial rolling temperature, the temperature is reduced from 1000-1050 ℃ to 970-. The wire rod enters the heat-insulating cover at a temperature slightly higher than the phase-change point and enters the phase-change area in advance, the speed of the roller way is reduced from 0.2m/s to 0.1m/s, the time of the wire rod in the heat-insulating cover is prolonged, the wire rod of the welding wire is fully subjected to phase change, the generation of martensite abnormal structures is avoided, and the performances of the welding wire such as elongation, section shrinkage and the like are improved.

The steel wire rod for the welding wire with the yield strength of 600MPa grade is obtained through the procedures, and the chemical components and the mechanical properties of the finished steel are shown in the following tables 4 and 5.

Table 4: chemical composition of finished steel%

Table 5: mechanical property of finished steel

According to the data in the table 5, the steel wire rod for the welding wire with the yield strength of 600MPa for each heat has excellent mechanical properties, and meets the following requirements: the yield strength is more than or equal to 600MPa, the elongation is more than or equal to 25%, the reduction of area is more than or equal to 70%, the metallographic structure is uniform, the grain size is 11 grade, and no abnormal structure is generated. FIG. 1 shows a 500-fold metallographic of a steel wire rod for a 600MPa grade yield strength welding wire in a furnace 1, and it can be seen that the metallographic structure is a granular bainite structure having a high strength in its entirety. In addition, the high-strength welding wire produced by the steel wire rod for the 600 MPa-level yield strength welding wire produced by the invention has less splashing and stable electric arc in the welding process.

Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The steel wire rod for the 600 MPa-level yield strength welding wire is characterized by comprising the following chemical components in percentage by mass: c: 0.06 to 0.12; si: 0.35 to 0.45; mn: 1.55-1.70; p is less than or equal to 0.020; s is less than or equal to 0.010; cr: 0.25 to 0.40; ni: 1.70-1.95; mo: 0.42 to 0.52; ti: 0.10 to 0.12; the balance of Fe and inevitable impurities;

the mechanical properties of the steel wire rod for the 600 MPa-level yield strength welding wire meet the following requirements: the yield strength is more than or equal to 600MPa, the elongation is more than or equal to 25 percent, and the reduction of area is more than or equal to 70 percent;

the production method of the steel wire rod for the 600 MPa-level yield strength welding wire comprises the following steps of: blast furnace molten iron-molten iron pretreatment-converter top combined blown smelting-LF ladle furnace refining-billet continuous casting-heating furnace heating-high pressure water descaling-rolling-spinning-stelmor line delayed cooling-bundling-finished wire rod, wherein in the molten iron pretreatment process, the sulfur content in the molten iron is less than or equal to 0.06%; in the converter top combined blowing smelting process, the C content of the steel tapping is controlled to be 0.02-0.03%, the tapping temperature is 1631-; in the LF ladle furnace refining process, the in-position temperature is 1545-1572 ℃, the refining out-position temperature is 1595-1617 ℃, the refining treatment time is 28-65 min, Ar blowing operation is carried out in the whole process according to the refining rule, desulfurization, component fine adjustment and heating operation are carried out according to the components and the temperature of the molten steel of the converter, the content of [ O ] is less than or equal to 30ppm, the content of [ N ] is less than or equal to 60ppm, the content of [ H ] is less than or equal to 2.0ppm, titanium is increased by adopting low-aluminum ferrotitanium, a silicon-barium wire is adopted to replace a silicon-calcium wire in the final refining stage, meanwhile, argon is blown at; in the small square billet continuous casting process, the superheat degree is controlled to be between 25 and 30 ℃, and the drawing speed is between 1.9 and 2.2 m/min; the total heating time in the heating process of the heating furnace is more than or equal to 2.5 hours, wherein the temperature of the preheating section of the heating furnace is 720-: 1245 and 1260 ℃; the rolling comprises rough rolling, intermediate rolling and finish rolling, wherein the initial rolling temperature is controlled at 970-990 ℃; the spinning temperature is 885-925 ℃.