CN111876679B

CN111876679B - Chromium-vanadium hot-rolled steel wire rod and preparation method thereof, and preparation method of steel wire and hand tool

Info

Publication number: CN111876679B
Application number: CN202010683332.XA
Authority: CN
Inventors: 刘金源; 谢志雄; 丘文生; 钟寿军; 张志明; 刘春林; 李成良; 胡娟; 程羲
Original assignee: SGIS Songshan Co Ltd
Current assignee: SGIS Songshan Co Ltd
Priority date: 2020-07-15
Filing date: 2020-07-15
Publication date: 2021-06-25
Anticipated expiration: 2040-07-15
Also published as: CN111876679A

Abstract

The application provides a chromium-vanadium hot-rolled steel wire rod and a preparation method thereof, and a preparation method of a steel wire and a hand tool, belonging to the technical field of wire rod steel. The chromium-vanadium hot-rolled steel wire rod comprises Mn and Cr with the total content of 1.25-1.55 wt%, and is obtained by rolling a casting blank, wherein the alloy core segregation index Pcr of the casting blank is less than or equal to 1.10. The preparation method of the chromium-vanadium hot rolled steel wire rod comprises the steps of rolling a casting blank, spinning and cooling. The preparation method of the steel wire comprises the step of directly carrying out cold drawing treatment on the chromium-vanadium hot rolled steel wire rod without spheroidizing annealing treatment. The preparation method of the hand tool comprises the steps of directly carrying out blanking processing on the steel wire without intermediate annealing treatment, and then sequentially carrying out quenching treatment and tempering treatment. The wire rod can be directly cold-drawn to produce the steel wire without annealing, and the processing cost of the wire rod to produce the steel wire is greatly reduced.

Description

Chromium-vanadium hot-rolled steel wire rod and preparation method thereof, and preparation method of steel wire and hand tool

Technical Field

The application relates to the technical field of wire rod steel, in particular to a chromium-vanadium hot rolled steel wire rod and a preparation method thereof, and a preparation method of a steel wire and a hand tool.

Background

The chromium-vanadium hot-rolled alloy spring steel wire rod product has better toughness, not only can be used for producing springs, but also can be used for producing hand tools with high performance and high service life and quality requirements, such as wrenches, external hexagonal fasteners, screw blank heads and the like. Because the steel contains high-hardenability elements such as chromium, vanadium and the like, bainite and even martensite low-temperature phase transformation structures are easy to appear in the wire rod, and the wire breakage rate is high, so that the wire rod cannot be directly subjected to cold drawing processing. Therefore, when the spring steel wire rod is used by downstream users, the spheroidizing annealing pretreatment is needed to eliminate bainite and martensite structures in the steel, and then the cold drawing processing of the next procedure can be carried out.

Disclosure of Invention

The application aims to provide a chromium-vanadium hot-rolled steel wire rod, a preparation method thereof, a steel wire and a hand tool preparation method, the wire rod can be directly cold-drawn to produce the steel wire without spheroidizing annealing, and the processing cost of the steel wire produced by the wire rod is greatly reduced.

The embodiment of the application is realized as follows:

in a first aspect, embodiments of the present application provide a chromium-vanadium hot rolled steel wire rod comprising Mn and Cr in a total content of 1.25 to 1.55 wt%.

The chromium-vanadium hot rolled steel wire rod is obtained by rolling a casting blank, and the alloy core segregation index Pcr of the casting blank is shown as formula I:

the alloy core segregation index Pcr of the casting blank is less than or equal to 1.10.

In a second aspect, embodiments of the present application provide a method for preparing a chromium-vanadium hot-rolled steel wire rod provided in an embodiment of the first aspect, including: and rolling, spinning and cooling the casting blank.

In a third aspect, an embodiment of the present application provides a method for preparing a steel wire, including: the chromium-vanadium hot-rolled steel wire rod provided by the embodiment of the first aspect is directly subjected to cold drawing without spheroidizing annealing.

Or, the chromium-vanadium hot-rolled steel wire rod is prepared by the preparation method provided by the embodiment of the second aspect, and the chromium-vanadium hot-rolled steel wire rod is directly subjected to cold drawing treatment without spheroidizing annealing treatment.

In a fourth aspect, an embodiment of the present application provides a method for manufacturing a hand tool, including: the steel wire manufactured by the manufacturing method provided by the embodiment of the third aspect is directly subjected to blanking processing without intermediate annealing treatment, and then is subjected to quenching treatment and tempering treatment in sequence.

The inventor finds that the core of the existing chromium-vanadium hot-rolled alloy spring steel wire rod changes the C curve form of the core due to the segregation phenomenon of alloy element components such as carbon, manganese, chromium and the like, improves the hardenability of the core, leads to that bainite and even martensite structures are inevitably generated in the core even if a slow cooling process of a whole-course cover heat-insulating cover is adopted after the wire rod is spun, and seriously deteriorates the drawability of the wire rod. Therefore, when the conventional wire rod is used for preparing steel wires and hand tools, the wire rod must be treated by spheroidizing annealing to improve the drawing performance of the wire rod, and the process flow for preparing the hand tools is generally as follows: the wire rod is subjected to acid cleaning, phosphorization, spheroidizing annealing treatment, acid cleaning, phosphorization, cold drawing treatment to a specified wire diameter, intermediate annealing treatment, blanking processing, quenching treatment, tempering treatment and surface treatment to obtain a finished product, and the spheroidizing annealing treatment is carried out, so that the acid cleaning and the phosphorization treatment are carried out once more, and the processing cost is increased by about 800 yuan/ton.

The chromium-vanadium hot-rolled steel wire rod and the preparation method thereof and the preparation method of the steel wire and the hand tool provided by the embodiment of the application have the beneficial effects that:

mn is an effective strengthening element in steel, can improve the tensile strength and the wear resistance of the steel, and is also a deoxidizing element of the steel. Cr is a carbon binding element, forms alloy carbide with carbon, and improves the tensile strength and the wear resistance of the steel. The inventor researches and discovers that the carbon, manganese and chromium form a combined action when the eccentric aggregation of the center is serious, the local C curve form of the center can be obviously influenced, so that the C curve is shifted to the right, a bainite and even martensite low-temperature phase transformation structure is formed in the center under the slow cooling condition, and the drawing performance of the wire rod is deteriorated. In the embodiment of the application, the total content of Mn and Cr is controlled to be 1.25-1.55 wt%, the alloy core segregation index Pcr of Mn and Cr in a casting blank is reduced and controlled to be less than or equal to 1.10 while the strengthening effect on a hot rolled steel wire rod is ensured, the banded structure of the wire rod is effectively improved, the core segregation is reduced, and the core structure is ensured to be in a normal form of pearlite, ferrite and sorbite. When the wire rod is used for preparing the steel wire for processing the spring and the hand tool, the influence of bainite and even martensite low-temperature phase change structures can be effectively eliminated, the wire rod can be directly cold-drawn to produce the steel wire without spheroidizing annealing, the cost of spheroidizing annealing treatment and acid washing and phosphating treatment of subsequent procedures can be saved, and the processing cost of downstream users is effectively reduced by about 800 yuan/ton; the maximum reduction rate of the wire rod in cold drawing can reach more than 85 percent, and the cold drawing processing requirement of large deformation can be better met.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained from the drawings without inventive effort.

FIG. 1 is a metallographic microstructure of a chrome vanadium hot rolled steel wire rod provided in example 1 of the present application at a magnification of 100 ×;

FIG. 2 is a metallographic microstructure of a chromium vanadium hot rolled steel wire rod provided in example 1 of the present application at a magnification of 500 ×;

FIG. 3 is a metallographic microstructure of a chrome vanadium hot rolled steel wire rod provided in comparative example 1 of the present application at a magnification of 500 ×;

fig. 4 is a metallographic microstructure of a chromium vanadium hot rolled steel wire rod provided in comparative example 4 of the present application at a magnification of 500 ×.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

The chromium vanadium hot rolled steel wire rod and the method for producing the same, and the method for producing the steel wire and the hand tool according to the examples of the present application will be specifically described below.

It should be noted that "and/or" in the present application, such as "scheme a and/or scheme B" means that the three modes of scheme a alone, scheme B alone, scheme a plus scheme B may be used.

Mn is an effective strengthening element in steel, can improve the tensile strength and the wear resistance of the steel, and is also a deoxidizing element of the steel. Manganese shifts the C curve of the steel to the right, improves the stability of austenite, and improves the quenching performance of the product.

Researches show that the core segregation is easily formed by high-content manganese, an obvious longitudinal banded structure is formed, the local C curve form of the core is changed when carbon and manganese are seriously accumulated in the core, the C curve is shifted to the right, a bainite and even martensite low-temperature phase change structure can be formed under the slow cooling condition, and the drawing performance of the wire rod is deteriorated. Optionally, the content of Mn element in the chromium vanadium hot rolled steel wire rod is 0.65 to 0.90wt%, or 0.75 to 0.80 wt%, such as but not limited to any one of 0.65 wt%, 0.70wt%, 0.75 wt%, 0.80 wt%, 0.85 wt%, and 0.90wt%, or a range between any two. The content design of the manganese element can improve the tensile strength of the wire rod, improve the zonal structure of the wire rod and the eccentric center of the wire rod, and ensure the plasticity and drawing performance of the wire rod.

Cr is a carbon binding element, forms alloy carbide with carbon, and improves the tensile strength and the wear resistance of the steel. Chromium enables the C curve of the steel to move to the right, improves the stability of austenite, and improves the quenching performance of the product; the alloy carbide formed by carbon and chromium can prevent austenite grains from growing, refine grains and tissues and improve the toughness of the product. In the tempering process after quenching, fine alloy carbides are recovered and separated out, the tempering soft resistance is improved, the secondary hardening effect is achieved, the hardness and the wear resistance of steel are improved without making the steel brittle, and the hardness and the strength performance of the hand tool after high-temperature tempering can be ensured after the hand tool is processed.

Researches show that the core segregation is easily formed by high content of chromium, so that the core is easily formed into an abnormal structure. Optionally, the content of Cr element in the chromium vanadium hot rolled steel wire rod is 0.58 to 0.70wt%, such as but not limited to any one or a range between any two of 0.58 wt%, 0.60 wt%, 0.62 wt%, 0.64 wt%, 0.66 wt%, 0.68 wt% and 0.70 wt%. The content design of the chromium element can improve the tensile strength of the wire rod, improve the ribbon structure of the wire rod, reduce the eccentric center, and ensure the plasticity and drawing performance of the wire rod.

The inventor further researches and discovers that the carbon, manganese and chromium form a combined action when the eccentric aggregation of the center part is serious, the form of the local C curve of the center part can be obviously influenced, the C curve is shifted to the right, a bainite and even martensite low-temperature transformation structure is formed in the center part under the slow cooling condition, and the drawing performance of the wire rod is deteriorated.

In the embodiment of the application, the total content of Mn and Cr is controlled to be 1.25-1.55 wt%, the alloy core segregation index Pcr of Mn and Cr in a casting blank can be reduced and controlled to be less than or equal to 1.10 while the strengthening effect on a hot rolled steel wire rod is ensured, the banded structure of the wire rod is effectively improved, the core segregation is reduced, and the core structure is ensured to be in a normal form of pearlite, ferrite and sorbite. When the wire rod is used for preparing the steel wire for processing the spring and the hand tool, the influence of bainite and even martensite low-temperature phase change structures can be effectively eliminated, the wire rod can be directly cold-drawn to produce the steel wire without spheroidizing annealing, the cost of spheroidizing annealing treatment and acid washing and phosphating treatment of subsequent procedures can be saved, and the processing cost of downstream users is effectively reduced by about 800 yuan/ton; the maximum reduction rate of the wire rod in cold drawing can reach more than 85 percent, and the cold drawing processing requirement of large deformation can be better met.

In some possible embodiments, the chromium vanadium hot rolled steel wire rod comprises C in an amount of 0.43 to 0.47wt% and Cu in an amount of 0.10 to 0.15wt%, the content of C element is, for example and without limitation, in a range of any one or any two of 0.43 wt%, 0.44 wt%, 0.45 wt%, 0.46 wt% and 0.47wt%, and the content of Cu element is, for example and without limitation, in a range of any one or any two of 0.10 wt%, 0.11 wt%, 0.12 wt%, 0.13 wt%, 0.14 wt% and 0.15 wt%.

The C element is the most effective and economic strengthening element in the steel, plays a role in solid solution strengthening in the steel, forms alloy carbide with alloy elements such as chromium, vanadium and the like in the steel, and effectively improves the strength performance and the wear resistance of the product. However, carbon increases the strength of steel and deteriorates the plasticity and drawing properties of steel.

The Cu element is a beneficial alloy element in the chromium-vanadium hot rolled steel wire rod, and the copper with proper content can improve the stability of austenite, improve the hardenability of steel and improve the strength, toughness and wear resistance of the steel. In addition, a certain amount of copper is added into the steel, so that the atmospheric corrosion resistance of a steel part can be obviously improved, the corrosion and rust prevention capability of a hand tool obtained by processing a wire rod in the atmosphere can be improved, and the service life is prolonged. However, copper is a low-melting-point element, and too high a content of copper easily causes hot brittleness in high-temperature rolling.

The content design of the C element and the Cu element properly reduces the content of the C element, improves the decarburization condition of the wire rod, improves the wear resistance and the surface hardness of the wire rod, can reduce the strength of steel after carbon reduction, and properly improves the content of the Cu element, so that the beneficial effect of copper can be exerted, the hot brittleness phenomenon of high-temperature rolling can be prevented, the strength and the atmospheric corrosion resistance of the steel can be improved while the toughness of the steel is not reduced, and the hand tool obtained after the wire rod is processed has better service performance.

In some exemplary embodiments, the chromium vanadium based hot rolled steel wire rod comprises in weight percent: 0.43 to 0.47wt% of C, 0.10 to 0.15wt% of Cu, 0.16 to 0.34wt% of Si, 0.65 to 0.90wt% of Mn, 0.58 to 0.70wt% of Cr, 0.08 to 0.15wt% of V, 0.010 to 0.025wt% of Als, less than or equal to 0.015wt% of P, less than or equal to 0.010wt% of S, less than or equal to 0.15wt% of Ni, less than or equal to 0.01wt% of Mo, less than or equal to 0.040wt% of As, less than or equal to 0.03wt% of Sn, less than or equal to 0.0015wt% of O, and the balance of Fe and inevitable impurities.

Si element can strengthen the ferrite strength in steel and is also a deoxidizing element of steel. The content design of the silicon element can not only effectively strengthen but also avoid the cold processing performance of the wire rod from being deteriorated due to excessive silicon element.

The V element can obviously refine the grain structure of the steel and improve the strength/toughness and wear resistance of the steel. In the steel in the application, vanadium is a micro-strengthening alloy element which is a strong carbon bonding element and can form a compound with carbon, and a fine and dispersed vanadium-carbon compound is precipitated at low temperature, so that the strength of the material is improved, and the service life of the hand tool obtained by processing is prolonged. In addition, the vanadium can obviously improve the tempering stability of the steel and has strong secondary hardening effect, and the addition of the vanadium can properly improve the tempering temperature and improve the strength and the toughness of the hand tool obtained by processing. The vanadium is a noble alloy, and the content design of the vanadium element can not only effectively strengthen but also reasonably control the cost.

Als is a strong deoxidizing element in steel, and a certain content of acid-soluble aluminum can effectively refine austenite grain size and microstructure, and remarkably improve the plasticity and drawing performance of the wire rod. However, too high Als in steel tends to form alumina inclusions with high melting point, no deformation, and high hardness, and significantly affects not only the drawing performance of wire rods but also the castability of molten steel.

As element and Sn element are low-melting point elements, which form center segregation and are harmful elements, and the lower the content in the steel, the better. Considering the combined action mechanism of arsenic and tin and the cost control, the total content of arsenic and tin is less than or equal to 0.06 wt% optionally.

The P element is a harmful element in the steel of the present application, and a higher content of the phosphorus element deteriorates the plasticity and cold workability of the steel, so that the lower the content of phosphorus in the steel of the present application, the better. The content of the phosphorus element is designed, so that the influence of phosphorus on the steel can be effectively controlled.

The S element belongs to harmful elements in the steel grade of the application, and sulfide inclusions can be formed by the sulfur element with higher content, so that the plasticity and cold processing performance of the steel are influenced, and the lower the sulfur content in the steel is, the better the steel grade of the application is. The design of the content of the sulfur element can effectively control the influence of sulfur on steel.

The O element belongs to harmful elements in the steel grade of the application, forms deoxidized inclusions with elements such as silicon, manganese, iron and the like, has low oxygen content in the steel, is beneficial to controlling the content and the grade of the oxidized inclusions in the steel, and prolongs the service life of the hand tool obtained by processing. The design of the content of the oxygen element can effectively control the influence of oxygen on the steel.

Exemplarily, the chromium vanadium hot rolled steel wire rod provided by the embodiment of the present application:

regarding the microstructure: the microstructure is pearlite, ferrite and sorbite, and has no bainite and martensite, the austenite grain size is more than or equal to 11.0 grade, and the central carbon segregation is less than or equal to A1.5 grade.

And the content grade of impurities: class A is less than or equal to 1.5, class B is less than or equal to 1.5, class C is less than or equal to 0.5, class D is less than or equal to 1.0, and class DS is less than or equal to 1.0.

Regarding the decarburization index: no full decarburized layer is formed, and the ratio of the total decarburized layer is less than or equal to 0.5 percent. In the examples of the present application, the total decarburized layer ratio means a ratio of the thickness of the total decarburized layer to the total thickness of the steel material.

Regarding the mechanical properties: the tensile strength is 800-950 MPa, the elongation after fracture is more than or equal to 20%, and the reduction of area is more than or equal to 50%. The hardness of a finished product obtained by drawing the chromium-vanadium hot rolled steel wire rod after final quenching and tempering treatment can reach 51-54 HRC, or 52-54 HRC, such as 53 HRC.

In a second aspect, embodiments of the present application provide a method for preparing a chromium-vanadium hot-rolled steel wire rod provided in an embodiment of the first aspect, including: and rolling, spinning and cooling the casting blank with the standard alloy core segregation index.

Preparation of cast slab:

in some possible embodiments, the preparation operation of the cast slab includes converter smelting treatment, LF refining treatment, RH furnace vacuum treatment, billet protection continuous casting treatment, and cast slab heating treatment.

In the smelting treatment of the converter, exemplarily, the high-carbon-pulling tapping operation is adopted, the content of C element at the end point is required to be 0.10-0.35 wt%, and the content of the further C element is more than or equal to 0.12 wt%, so that the blowing frequency can be reduced, the oxygen content in molten steel is ensured to be lower when the converter taps, the pressure of removing oxide inclusions in the LF refining treatment process is reduced, and the reduction of inclusions in the steel is facilitated.

In LF refining treatment, illustratively, aluminum calcium carbon, Si-Fe powder, SiC and a composite deoxidizer are added for diffusion deoxidation, reducing slag is rapidly produced, and lime and synthetic slag are used for adjusting fluidity. The higher alkalinity is beneficial to further desulfurization in the LF refining process, optionally, the alkalinity of refining slag is controlled to be 3.0-6.0, the refining time is more than or equal to 40min, the low sulfur content in steel is ensured, and the level and the content of inclusions in steel are optimized.

In the RH furnace vacuum treatment, illustratively, the vacuum treatment time is more than or equal to 8min, and the pure degassing time is more than or equal to 8 min; feeding pure calcium wire 200-400 m, soft blowing time is not less than 8 min.

In the billet protection continuous casting process, for example, a 6-machine 6-flow billet continuous casting machine is adopted, an integral water gap tundish and an immersed large-diameter (for example, 38mm) integral water gap are used, the whole process is argon sealed to protect casting, and the section size of a continuous casting billet is 160mm by 160 mm; the casting powder is special casting powder for medium carbon steel, the superheat degree of a tundish is controlled to be 10-30 ℃, and secondary cooling water adopts a weak cooling system and adopts electromagnetic stirring and end electric stirring; the pulling speed is controlled to be 1.8-2.0 m/min, and further, the matching requirements of the pulling speed and the superheat degree are shown in table 1.

TABLE 1 matching requirement of pulling rate and superheat degree

Superheat degree of tundish	Pulling speed m/min
		Not less than 10 and not more than 20	2.0
Greater than 20 and less than or equal to 25	1.9
		More than 25 and less than or equal to 30	1.8

In the casting blank heating treatment, illustratively, the heating temperature of a heating section is 1100-1180 ℃, the heating temperature of a soaking section is 1100-1180 ℃, and a lower heating temperature is adopted to prevent high-temperature austenite from being coarse so as to obtain fine austenite grain size; meanwhile, the heating temperature is controlled to be more than 1100 ℃, so that vanadium carbide and the like in the steel can be completely dissolved in high-temperature austenite, the uniformity of the austenite is increased, the rolling uniformity of a casting blank is improved, the surface structure of the wire rod is improved, more finely and dispersedly distributed vanadium carbide precipitated phases can be precipitated after rolling, and the strength, toughness and drawing performance of the wire rod are improved. Furthermore, the total heating time of the casting blank in the heating section and the soaking section (high temperature section) is controlled to be 80-150 min, the head-tail temperature difference is less than or equal to 30 ℃, the residual oxygen content in the furnace is controlled to be less than or equal to 5%, and the depth of a decarburized layer on the surface of the wire rod is reduced. Because the decarburization of steel affects the surface hardness of the hand tool, the ratio of the total decarburized layer on the surface of the wire rod provided by the application is less than or equal to 0.5 percent, and a complete decarburized layer is not provided, so that the drawing performance of the wire rod and the surface hardness of a finished product of the hand tool processed by the wire rod are ensured.

Regarding the rolling treatment:

firstly, removing phosphorus by adopting high-pressure water to ensure that iron scales on the surface of a casting blank are completely removed, and then, carrying out rolling treatment, wherein the rolling treatment comprises primary rolling, pre-finish rolling and finish rolling in sequence. Illustratively, water tank cooling is adopted between rolling sections, and temperature rise caused by high-speed rolling is inhibited, so that fine austenite grains are obtained.

In some possible embodiments, the temperature of the blooming is 1000 to 1050 ℃, such as but not limited to being any one of 1000 ℃, 1010 ℃, 1020 ℃, 1030 ℃, 1040 ℃ and 1050 ℃ or a range between any two; the temperature of the pre-finish rolling (BGV inlet) is 1000-1030 ℃, and the temperature of the finish rolling (TMB inlet) is 1000-1030 ℃, both of which are, for example, but not limited to, any one of 1000 ℃, 1010 ℃, 1020 ℃ and 1030 ℃ or ranges between any two of them.

The chromium-vanadium hot rolled steel wire rod contains high content of chromium and vanadium alloy elements, forms alloying carbide of vanadium carbide and chromium carbide with carbon in steel, and is still in a single-phase austenite crystallization region when the rolling temperature is between 1000 and 1050 ℃. The rolling temperature is controlled according to the requirements, hard phase substances such as vanadium carbide, chromium carbide and the like are not separated out during rolling, the rolling uniformity of the wire rod is improved, and the surface quality of the wire rod and the uniformity of the performance of a finished product are improved.

Regarding the laying process:

in some possible embodiments, the spinning temperature of the spinning process is 900-930 ℃, 900-920 ℃, such as but not limited to, 900 ℃, 905 ℃, 910 ℃, 915 ℃, 920 ℃, 925 ℃ and 930 ℃, or a range between any two thereof.

The chromium-vanadium hot rolled steel wire rod contains high content of strong alloy elements such as carbon, chromium, vanadium, manganese and the like, and the higher spinning temperature is controlled according to the requirements, so that the austenite uniformity of the wire rod before the phase transformation of an air cooling roller way is improved, and the bainite or martensite structure in the center is effectively avoided in the subsequent structure cooling; on the other hand, the method is beneficial to reducing the strength performance of the wire rod at high temperature after spinning, improving the spinning uniformity, obtaining good coil shape, and improving the surface quality and the drawing performance of the wire rod.

Regarding the cooling treatment:

the chromium-vanadium hot-rolled steel wire rod contains high-content chromium and vanadium two elements with strong hardenability, after the wire rod is spun, exemplarily, the cooling speed in the cooling treatment after the wire rod is spun is controlled to be less than or equal to 3.0 ℃/s, a slow cooling process is adopted to be matched with the alloy core segregation index standard of a casting blank, and the low-temperature phase transformation structure of bainite and martensite of the wire rod is effectively avoided.

In a third aspect, an embodiment of the present application provides a method for preparing a steel wire, including: the chromium-vanadium hot-rolled steel wire rod provided by the embodiment of the first aspect is directly subjected to cold drawing without spheroidizing annealing. Or, the chromium-vanadium hot-rolled steel wire rod is prepared by the preparation method provided by the embodiment of the second aspect, and the chromium-vanadium hot-rolled steel wire rod is directly subjected to cold drawing treatment without spheroidizing annealing treatment. In the embodiments of the present application, the steel wire is, for example, in the form of a round filament or a hexagonal rod, and is used not only for producing a spring but also for producing a hand tool such as an external hexagonal fastener.

In a fourth aspect, an embodiment of the present application provides a method for manufacturing a hand tool, including: the steel wire manufactured by the manufacturing method provided by the embodiment of the third aspect is directly subjected to blanking processing without intermediate annealing treatment, and then is subjected to quenching treatment and tempering treatment in sequence. After cold drawing, proper quenching and tempering processes are adopted to ensure the strength performance and hardness index of the hand tool processed by the manufactured steel wire. The chromium-vanadium hot-rolled steel wire rod has better cold drawing processing performance, and is directly and sequentially subjected to quenching treatment and tempering treatment without intermediate annealing treatment after cold drawing treatment, so that the processing cost is further reduced. Illustratively, the preparation process flow of the hand tool is as follows: pickling or shot blasting of wire rods, phosphorization, cold drawing treatment to a specified wire diameter, blanking processing, quenching treatment, tempering treatment and surface treatment to obtain finished products.

In some possible embodiments, the heating temperature of the quenching treatment is 830 to 840 ℃, for example 835 ℃. On one hand, A of the steel grade provided by the embodiment of the application_c3The temperature is about 797 ℃, the heating temperature above 830 ℃ is selected to enable the steel to be completely austenitized, and alloy elements and compounds such as carbon, chromium, vanadium, manganese and the like in the steel are completely dissolved in high-temperature austenite, so that the uniformity of the austenite is improved, and the hardenability of the wire rod is improved; on the other hand, the heating temperature of not higher than 840 ℃ is selected to obtain fine prior austenite grain size, and fine uniform structure is obtained after quenching and cooling so as to improve the plasticity of the material.

Optionally, the medium for quenching treatment is oil. The steel grade provided by the embodiment of the application has good quenching performance, can be used for processing hand tools with edges and corners on some sections, can ensure full quenching of workpieces by using oil as a cooling medium, obtains uniform martensite structures on the whole sections, and does not generate quenching stress cracks.

In some possible embodiments, the heating temperature of the tempering treatment is 430-440 ℃, for example 425 ℃, so that the martensite structure in the steel is completely transformed into the troostite structure with good toughness property matching. Because the steel provided by the embodiment of the application contains higher carbon, chromium and vanadium, optionally, the medium for tempering is water, and a large amount of alloy compounds such as chromium carbide, vanadium carbide and the like can be precipitated in subsequent tempering, the strength, hardness and wear resistance of the processed hand tool can be improved, the torque performance of the hand tool can be improved, and the service life of the hand tool can be prolonged.

The features and properties of the present application are described in further detail below with reference to examples.

A preparation method of a chromium-vanadium hot-rolled steel wire rod comprises the following steps: smelting and continuously casting the raw materials to prepare a casting blank; heating the casting blank; then the casting blank is subjected to rolling treatment, spinning treatment and cooling treatment.

In each of the examples and comparative examples:

the alloy core segregation index of the casting blank, the specification of the chromium-vanadium hot rolled steel wire rod and the component content of the chromium-vanadium hot rolled steel wire rod are shown in table 2; the process parameters of smelting and continuous casting are shown in Table 3; the process parameters of the heat treatment are shown in table 4; the process parameters of the rolling treatment and the laying treatment are shown in table 5; the cooling speed of the cooling treatment after the wire rod spinning is less than or equal to 3.0 ℃/s, the temperature and the cooling speed of the wire rods with different specifications at each section of the air cooling roller bed are exemplified by small-specification wire rods, medium-specification wire rods and large-specification wire rods, which are specifically shown in table 6.

TABLE 2 core segregation of the ingot and coil gauge (mm) and composition (wt%)

TABLE 3 Heat treatment parameters

Note: in Table 3, the high temperature period refers to the total time of the heating period and the soaking period.

TABLE 4 smelting and continuous casting parameters

TABLE 5 Rolling treatment and laying treatment parameters

	The start rolling temperature is DEG C	BGV temperature deg.C	TMB temperature C	Spinning temperature DEG C
					Example 1	1045	1010	1010	903
Example 2	1050	1020	1015	912
					Example 3	1025	1000	1030	913
Example 4	1030	1010	1010	918
					Example 5	1040	1015	1020	920
Example 6	1050	1030	1000	928
					Example 7	1020	1025	1010	930
Example 8	1050	1005	1000	900
					Comparative example 1	1020	1050	1020	950
Comparative example 2	1010	990	1000	920
					Comparative example 3	1035	1030	1035	940
Comparative example 4	1020	1050	1025	930
					Comparative example 5	1010	1020	1000	910
Comparative example 6	1035	1040	1020	920

TABLE 6 temperature and cooling rate at each air-cooled roller table

The chromium vanadium hot rolled steel wire rods prepared in each example and comparative example were subjected to performance tests.

The mechanical properties of the chromium vanadium hot rolled steel wire rods obtained in each example and comparative example are shown in table 7.

TABLE 7 mechanical Properties of the wire rod

	Tensile strength MPa	Elongation after fracture%	Reduction of area%
				Example 1	830	24.0	62.5
Example 2	829	22.5	58.5
				Example 3	809	23.5	59.0
Example 4	821	23.0	56.5
				Example 5	815	22.5	57.5
Example 6	865	23.5	59.5
				Example 7	856	22.5	54.0
Example 8	860	22.0	58.5
				Comparative example 1	1020	10.5	28.0
Comparative example 2	960	9.5	25.0
				Comparative example 3	1050	8.5	20.0
Comparative example 4	930	12.5	24.0
				Comparative example 5	910	13.5	22.0
Comparative example 6	935	11.5	28.5

The metallographic microstructure of the chromium vanadium hot rolled steel wire rod obtained in example 1 is shown in fig. 1 and 2, and the metallographic microstructure of the chromium vanadium hot rolled steel wire rod obtained in comparative example 1 is shown in fig. 3. The microstructure of the chromium vanadium hot rolled steel wire rods obtained in each of the examples and comparative examples is shown in Table 8, and the decarburization condition and the inclusion grade of the wire rods are shown in Table 9.

TABLE 8 microstructure of the wire rod

	Microstructure of	Austenite grain size fraction	Class of central segregation
				Example 1	S + P + fine uniform F	11.5	A1.0
Example 2	S + P + fine uniform F	11.5	A1.0
				Example 3	S + P + fine uniform F	11.5	A1.5
Example 4	S + P + fine uniform F	11.5	A1.0
				Example 5	S + P + fine uniform F	11.5	A1.5
Example 6	S + P + fine uniform F	11.5	A1.0
				Example 7	S + P + fine uniform F	11.0	A1.0
Example 8	S + P + fine uniform F	11.0	A1.5
				Comparative example 1	S+P+B+M+F	12	A1.5
Comparative example 2	S+P+B+M+F	11.5	A1.5
				Comparative example 3	S+P+B+M+F	11.0	A1.5
Comparative example 1	S+P+B+M+F	11.0	A1.5
				Comparative example 2	S+P+B+M+F	11.0	A1.5
Comparative example 3	S+P+B+M+F	11.0	A1.5
				Comparative example 4	S+P+B+M+F	11.0	A1.5
Comparative example 5	S+P+B+M+F	11.0	A1.5
				Comparative example 6	S+P+B+M+F	11.0	A1.5

Note: in table 8, S represents sorbite, P represents pearlite, F represents ferrite, B represents bainite, and M represents martensite.

TABLE 9 decarburization of the wire rod and the grade of inclusions

A method of making a steel wire comprising: after pickling and phosphorizing the chrome vanadium hot rolled steel wire rod, directly cold drawing the chrome vanadium hot rolled steel wire rod to a specified wire diameter without spheroidizing annealing treatment.

In which the chromium-vanadium hot rolled steel wire rods obtained in examples 1 to 8 and comparative examples 1 to 6 were treated in the order corresponding to test examples 1 to 14. In each test example, the cold drawability of the steel wire was measured for 1.0t of coil in each drawing test, and the results are shown in Table 10.

TABLE 10 Cold drawability of the Steel wires

A method of making a hand tool comprising: after pickling and phosphorizing the chrome vanadium hot rolled steel wire rod, directly performing cold drawing treatment to a specified wire diameter without spheroidizing annealing treatment, then directly performing blanking processing without intermediate annealing treatment, and then sequentially performing quenching treatment and tempering treatment.

In each of the examples 1 to 8, the chromium-vanadium hot rolled steel wire rods were treated in the order corresponding to the test examples 1 to 8. In each test example, the diameter of the drawn steel wire, the process parameters of the quenching treatment and the tempering treatment, and the hardness of the finished product are shown in table 11.

TABLE 11 processing parameters and finished product Properties

As can be seen from Table 2, in the examples, the total amount of Mn and Cr is controlled within the range of 1.25-1.55 wt%, and the alloy core segregation index Pcr of the casting blank is effectively controlled within the range of less than or equal to 1.10; in the comparative example, the total amount of Mn and Cr exceeds 1.55wt%, and the alloy core segregation index Pcr of the casting blank is more than 1.10.

As can be seen from fig. 1 to 4 and tables 7 to 9, the microstructure of the chromium vanadium hot rolled steel wire rod prepared in the examples can be controlled to be free of bainite and martensite, and the microstructure of the chromium vanadium hot rolled steel wire rod prepared in the comparative examples has bainite and even martensite. Compared with the comparative example, in the embodiment, the total amount of Mn and Cr is controlled within the range of 1.25-1.55 wt%, the content of the element C is properly reduced, the content of the element Cu is properly increased, the ratio of the total decarburized layer can be effectively controlled to be less than or equal to 0.5%, and the post-fracture elongation and the reduction of area of the chromium-vanadium hot-rolled steel wire rod are remarkably improved while the chromium-vanadium hot-rolled steel wire rod has good tensile strength; in comparative example 4, only the content of C element was properly reduced, the total amount of Mn and Cr exceeded the range of 1.25 to 1.55wt%, the total decarburized layer ratio could be effectively controlled to 0.5% or less, and Pcr could not be effectively controlled to 1.10 or less; in comparative examples 5 and 6, the total amount of Mn and Cr exceeds the range of 1.25 to 1.55wt%, and the content of C element is relatively high, not only it is not possible to effectively control Pcr to be within the range of not more than 1.10, but also the total decarburized layer ratio is not more than 0.5%.

According to table 10, it can be seen that the chromium-vanadium hot rolled steel wire rod provided in the embodiment of the present application is directly cold drawn without spheroidizing annealing treatment, no wire break occurs in the middle, and the maximum total surface reduction rate reaches 85%. The chromium-vanadium hot-rolled steel wire rod provided by the application in the comparative example is directly subjected to cold drawing, the number of middle wire breakage times reaches about 10 or more, the total drawing area reduction rate can only reach about 20-30%, and the drawing strength and the end face shrinkage rate are obviously reduced compared with those of the embodiment.

As can be seen from table 11, the chromium-vanadium hot-rolled steel wire rod provided in the embodiment of the present application is directly cold-drawn without spheroidizing annealing, and then is quenched and tempered without intermediate annealing, so that the hardness can reach 51 to 54HRC, and the service life of the chromium-vanadium hot-rolled steel wire rod can be effectively prolonged when the chromium-vanadium hot-rolled steel wire rod is used as a hand tool.

The embodiments described above are some, but not all embodiments of the present application. The detailed description of the embodiments of the present application is not intended to limit the scope of the claimed application, but is merely representative of selected embodiments of the application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

Claims

1. A chromium-vanadium hot-rolled steel wire rod is characterized by comprising Mn and Cr, the total content of which is 1.25-1.55 wt%;

the chromium-vanadium hot rolled steel wire rod is obtained by rolling a casting blank, wherein the alloy core segregation index Pcr of the casting blank is shown as the formula I:

the alloy core segregation index Pcr of the casting blank is less than or equal to 1.10;

the chromium-vanadium hot-rolled steel wire rod comprises the following components in percentage by weight: 0.43-0.47 wt% of C, 0.10-0.15 wt% of Cu, 0.16-0.34 wt% of Si, 0.65-0.90 wt% of Mn, 0.58-0.70 wt% of Cr, 0.08-0.15 wt% of V, 0.010-0.025 wt% of Als, less than or equal to 0.015wt% of P, less than or equal to 0.010wt% of S, less than or equal to 0.15wt% of Ni, less than or equal to 0.01wt% of Mo, less than or equal to 0.040wt% of As, less than or equal to 0.03wt% of Sn, less than or equal to 0.0015wt% of O and the balance of Fe;

the microstructure of the chromium-vanadium hot rolled steel wire rod is pearlite, ferrite and sorbite, and bainite and martensite are not contained.

2. A method of producing a chromium vanadium hot rolled steel wire rod according to claim 1, comprising: and carrying out rolling treatment, spinning treatment and cooling treatment on the casting blank.

3. The method according to claim 2, wherein the cooling rate of the cooling treatment is 3.0 ℃/s or less.

4. The production method according to claim 2 or 3, wherein the laying temperature of the laying process is 900 to 930 ℃.

5. The production method according to claim 2 or 3, wherein the rolling treatment comprises a preliminary rolling at a temperature of 1000 to 1050 ℃, a preliminary finish rolling at a temperature of 1000 to 1030 ℃, and a finish rolling at a temperature of 1000 to 1030 ℃ in this order.

6. A method for preparing a steel wire, comprising: directly performing cold drawing treatment on the chromium-vanadium hot rolled steel wire rod of claim 1 without spheroidizing annealing treatment;

or, the chromium-vanadium hot-rolled steel wire rod is prepared by the preparation method according to any one of claims 2 to 5, and the chromium-vanadium hot-rolled steel wire rod is directly subjected to cold drawing without spheroidizing annealing treatment.

7. A method for manufacturing a hand tool, comprising subjecting the steel wire manufactured by the manufacturing method of claim 6 to blanking processing without intermediate annealing, and then to quenching processing and tempering processing in this order;

the heating temperature of the quenching treatment is 830-840 ℃; and/or the heating temperature of the tempering treatment is 430-440 ℃.

8. A method of making hand tools as claimed in claim 7, wherein the quenching medium is an oil.

9. A method of manufacturing a hand tool according to claim 7, characterised in that the tempering medium is water.