CN109402521B - Steel for cold-heading hollow rivet and preparation method thereof - Google Patents

Abstract

The invention relates to steel for cold heading hollow rivets and a preparation method thereof, wherein the steel comprises the following chemical components in percentage by weight: c is less than or equal to 0.01 percent, Si is less than or equal to 0.04 percent, Mn: 0.05-0.25%, P is less than or equal to 0.020%, S is less than or equal to 0.015%, Als: 0.025 to 0.06%, Ti: 0.06-0.12 percent of Cr, less than or equal to 0.04 percent of Ni, less than or equal to 0.02 percent of Cu, less than or equal to 0.015 percent of As and less than or equal to 0.015 percent of Sn; the balance being Fe and unavoidable impurities, copper equivalent (Cueq = Cu% +3 As% +8 Sn% -Ni%) in the steel; the method comprises the following steps: smelting, continuously casting into small square billets, cooling the billets in heaps, heating the billets, carrying out rough rolling and finish rolling on high lines, spinning, and carrying out sectional cooling to below 200 ℃ by adopting a stelmor air cooling line to cool to room temperature. The C, N compound of Ti is used for thinning and separating out particles for precipitation strengthening, and the strength of the ultra-low carbon cold heading steel can be ensured without adding noble metal.

Description

Steel for cold-heading hollow rivet and preparation method thereof

Technical Field

The invention belongs to the field of cold heading steel for fasteners, and relates to steel for a cold heading hollow rivet and a preparation method thereof.

Background

The rivet replaces bolt connection and welding in many fields, so that various structural components become compact, light, attractive in appearance, convenient to use, labor-saving and material-saving, and the rivet is widely applied to industries such as automobiles, machinery, electrical instruments, building decoration, cases and the like. The materials for manufacturing the rivet are gradually replacing expensive pure aluminum wires, aluminum-magnesium alloy wires, copper wires, stainless steel wires and the like with steel materials. The existing steel for producing the rivet is mainly ultra-low carbon cold forging steel which is close to industrial pure iron, is ultra-low carbon pure steel, has stable components, low harmful elements, high steel purity, high surface quality, high geometric dimension precision, certain strength and good toughness, can be punched into an extremely complex shape, and is mainly used for manufacturing hollow rivets with large deformation. However, because the ultra-low carbon cold heading steel is close to industrial pure iron, the problem that strength and plasticity matching cannot meet the requirements exists in some industries with higher requirements on rivet strength, such as the automobile industry, for example, the Chinese patent with the publication number of CN102268595A discloses a steel for copper clad steel and a production method thereof, the component design of the steel adopts ultra-low carbon, and the chemical components are C: less than or equal to 0.010 percent, Si: less than or equal to 0.009%, Mn: 0.05 to 0.12%, Als: 0.008-0.015%, P: less than or equal to 0.015%, S: less than or equal to 0.010 percent, and the balance of Fe and inevitable impurities. The rolling method comprises the steps of heating a continuous casting blank, wherein the rolling temperature is 1030-1090 ℃, the finish rolling inlet temperature is 895-925 ℃, the inlet temperature of a reducing and sizing unit is 890-910 ℃, the spinning temperature is 890-910 ℃, the Stelmor wire is cooled to 650-670 ℃ in a delayed manner, and the maximum tensile strength of a finished product is 297.5 MPa.

In order to improve the strength of the ultra-low carbon cold heading steel, the prior art generally adds a large amount of noble metals such as Cr, Ni and Cu, and the like, for example, Chinese patent with publication number CN103789636A discloses a method for preparing steel for a cold heading blind rivet, which comprises the following chemical components: 0.12 to 0.16%, Si: 0.30 to 0.50%, Mn: 0.40-0.60%, Cr: 1.20-1.60%, Ti: 0.02-0.08%, V: 0.10-0.20%, Als: 0.01-0.05%, P: less than or equal to 0.03%, S: less than or equal to 0.015 percent, and the balance of Fe and inevitable impurities, an electric furnace is adopted for smelting, common slow cooling is adopted for cooling after rolling, and the cooling speed is 1-3 ℃/s. Also, for example, Japanese patent (application No. JP19780104523[ P ]. 1980-03-05) discloses a steel having cold forgeability having a chemical composition of C.ltoreq.0.02%, Si.ltoreq.1.0%, Mn: 3.0-4.0%, P is less than or equal to 0.040%, S is less than or equal to 0.003%, Ni: 6.00-8.00%, Cr: 17.00-19.00%, Cu: 2.50-4.00%, N: 0.04-0.10 percent, the balance of Fe and inevitable impurities, and also contains expensive metals such as Cr, Ni, Cu and the like, which is not beneficial to reducing the production cost of enterprises. For example, the analysis on the defects of the ultra-low carbon cold heading steel hollow rivet on pages 60-63 of 2004, (11) describes the ultra-low carbon cold heading steel for manufacturing the hollow rivet, and the chemical components of the ultra-low carbon cold heading steel comprise C less than or equal to 0.008 percent, Si less than or equal to 0.08 percent, Mn: 0.15-0.25%, not more than 0.030% of P, not more than 0.030% of S, not less than 0.02% of Al, not less than 0.06% of Ti and the balance of Fe and inevitable impurities, the production process adopts electric furnace smelting, the produced large square billet is cogging through a secondary firing process to produce wire rod coils, the production cost is high, the quality is unstable, the processing hardening is obvious, the problem of upsetting cracking is more, and the downstream user needs to carry out annealing treatment during drawing.

In summary, in order to meet the requirement of strength and plasticity matching of steel for rivets, the prior art generally adopts a two-fire material forming process of adding a large amount of noble metals of Cr, Ni, Cu and the like to cause great increase of production cost, smelting adopts electric furnace smelting, casting into a bloom or die casting blank after smelting, and then cogging and rolling wire rods in a wire rod disk, so that the manufacturing cost is extremely high.

Disclosure of Invention

In order to overcome the technical defects, the invention provides the steel for the cold-heading hollow rivet and the preparation method thereof, and the steel has the characteristics of simple production process, high production efficiency, reasonable and balanced utilization of resources, adoption of one-step-heating material forming, energy conservation and reduction of production cost. The steel for the cold-heading hollow rivet produced by the method can meet the requirements of manufacturing of stamping parts, forging parts and special-shaped parts with large deformation quantity, such as the hollow rivet, the case hollow rivet and the like, and has proper strength and excellent cold processing performance.

In order to achieve the technical purpose, the technical scheme adopted by the invention is as follows:

the steel for the cold-heading hollow rivet comprises the following chemical components in percentage by weight: c is less than or equal to 0.01 percent, Si is less than or equal to 0.04 percent, Mn: 0.05-0.25%, P is less than or equal to 0.020%, S is less than or equal to 0.015%, Als: 0.025 to 0.06%, Ti: 0.06-0.12 percent of Cr, less than or equal to 0.04 percent of Ni, less than or equal to 0.02 percent of Cu, less than or equal to 0.015 percent of As and less than or equal to 0.015 percent of Sn; the balance being Fe and unavoidable impurities, copper equivalent (Cueq = Cu% +3 As% +8 Sn% -Ni%) in the steel.

The preparation method of the steel for the cold-heading hollow rivet comprises the following steps:

(1) molten iron pretreatment, converter smelting, LF refining, RH refining and continuous casting, wherein electromagnetic stirring and constant-temperature constant-speed steel drawing are adopted in the continuous casting process to ensure the internal quality and the surface quality of a casting blank, and a continuous casting billet with the section of 160 × 160mm is produced and is subjected to stack cooling;

(2) heating a casting blank: heating the cooled casting blank; the temperature of the heating section is controlled to be 1000-;

(3) rough rolling is carried out on the high speed wire, and the initial rolling temperature is 930-950 ℃;

(4) performing finish rolling on the altitude, controlling the inlet temperature of the finish rolling to be 930-950 ℃, and controlling the reducing and sizing temperature to be 930-950 ℃; the accumulated reduction rate of finish rolling is more than 60 percent;

(5) spinning, wherein the spinning temperature is controlled to be 900-920 ℃;

(6) different specifications and different finish rolling speeds, the finish rolling speed of the specification phi 6.5mm is 100m/s, the finish rolling speed of the specification phi 8mm is 91.5m/s, and the finish rolling speed of the specification phi 10mm is 58.6 m/s.

(7) And (3) carrying out sectional cooling by adopting a stelmor air cooling line, wherein the cooling speed is more than or equal to 5 ℃/s at the temperature of more than 630 ℃, the cooling speed is 0.1-3 ℃/s at the temperature of less than 630 ℃, and the air cooling is carried out to the room temperature below 200 ℃.

(8) And (6) collecting rolls and packaging.

The following specifically describes the technical scheme of the invention:

designing components: (1) the increase of the carbon content can improve the strength of the steel, but is not beneficial to cold heading performance, and the steel requires excellent cold processing property, so the carbon content in the steel is required to be less than or equal to 0.01 percent; (2) although the silicon can obviously improve the deformation resistance of the steel, the silicon is extremely unfavorable for cold heading and extrusion, so the lower the silicon content is, the better the silicon content is, and the silicon content is controlled to be less than or equal to 0.04 percent; (3) manganese has a good effect on the mechanical properties of carbon steel, and is present in the steel in a solid solution strengthening manner, so that the strength and hardness of hot-rolled carbon steel can be improved. Manganese is also added into steel as an element for deoxidizing and removing sulfur, so that the deoxidizing effect of aluminum and silicon can be improved, and manganese sulfide is formed by combining manganese with sulfur, so that the harmful effect of sulfur in steel is eliminated to a considerable extent, and the range of manganese is selected to be 0.05-0.25%; (4) aluminum and Als: aluminum is added to steel as a deoxidizing element, and the aluminum portion added to the molten steel combines with oxygen to form Al₂O₃Various impurities float up to slag to play a role in deoxidation, the rest part of the impurities is melted into solid iron, dispersed fine AlN second-phase particles are formed during heating and cooling, austenite grains are prevented from growing, the function of refining the austenite grains is played, and the Als range in the steel is selected to be 0.025-0.06%; (5) phosphorus is a harmful impurity element and is derived from steelmaking raw materials such as ores, pig iron and the like, the phosphorus can improve the strength of steel, but reduces the plasticity and the toughness, and sharply increases the brittle transition temperature of the steel, namely improves the cold brittleness (low-temperature brittleness) of the steel, so that the content of the phosphorus is controlled to be less than or equal to 0.020%; (6) sulfur is a harmful element and is mainly derived from sulfur dioxide generated by burning raw materials for pig iron, ores added during steel making, and fuels. The greatest hazard of sulfur is cracking during hot working, resulting in hot shortness. The sulfur content in steel is high, the sulfide inclusion content is increased, the plasticity and toughness of steel are reduced, the influence of sulfur on the mechanical property of steel is related to the sulfur content of steel, the size, the form and the distribution of the formed sulfide inclusion, and therefore, the sulfur content is controlled to be less than or equal to 0.015 percent. (7) Titanium element: the Ti element and C, N, S have stronger affinity, and on one hand, the Ti element and C, N, S are combined with C, N to form C, N compound, so that the fine-grain strengthening effect is generated, and the strength of the steel is obviously improved; on the other hand, the Ti can react with S to form spherical Ti with plasticity much lower than that of strip MnS₄C₂S₂MnS in the steel is gradually eliminated and becomes spherical inclusions which can improve the toughness and the formability of the material, thereby reducing the harmful effects of MnS and improving the transverse performance of the steel. Ti forms TiN in steel firstly, but only the fine TiN particles can refine the structure and play a role in strengthening. With the increase of Ti content, TiN particles are coarsened, the amount of fine TiC is increased, the strength of the steel is obviously improved along with the increase of the Ti content due to precipitation strengthening effect, but when the Ti content is too high, the amount of non-coherent precipitates is increased, the precipitation strengthening effect is weakened, and meanwhile, formed C, N compounds cause embrittlement of the steel. Therefore, the content of effective Ti in the steel mainly depends on the content of S, N, and the lower the S, N content is, the higher the content of effective Ti is, the precipitation strengthening effect of TiC particles can be shown. Therefore, the Ti content is controlled to be 0.06-0.12%. (8) Since Cu, As, Sn, etc. increase the copper equivalent, they are very easy to be segregated in the grain boundary, reduce the cohesion of the grain boundary, and have the influence on the macroscopic properties of reduced work of fracture and obviously reduced toughness, therefore, the content thereof should be particularly controlled appropriately.

Continuous casting billet production is adopted, so that the waste of energy and cost caused by secondary-fire cogging is reduced; heating the casting blank after the stack cooling, wherein the temperature of the heating section is controlled to be 1000-; rolling and cooling processes: a. roughly rolling and finely rolling the heated casting blank, and then controlling and cooling; b. roughly rolling and refining austenite grains in the austenite recrystallization region, wherein the rolling starting temperature is 930-950 ℃, and because the rolling deformation of the wire rod is large enough, dynamic recrystallization and static recrystallization are generated in the rolling process to refine the austenite grains; c. carrying out finish rolling on the high-speed wire, controlling the inlet temperature of the finish rolling to be 930-950 ℃, and controlling the reducing and sizing temperature to be 910-930 ℃; the target temperature is realized mainly by a cooling water system arranged between units; the accumulated reduction rate of finish rolling is more than 60%, the dislocation density is improved through large deformation, and meanwhile, titanium carbonitride is subjected to strain-induced precipitation at the dislocation, so that the movement of dislocation is pinned, and organization preparation is made for the next cooling process; d. controlling the spinning temperature to be 900-920 ℃, feeding the spun yarn into an air cooling line for controlled cooling, performing sectional cooling by adopting a stelmor air cooling line, rapidly cooling at the cooling speed of more than or equal to 5 ℃/s at the temperature of more than 630 ℃, slowly cooling at the cooling speed of 0.1-3 ℃/s at the temperature of less than 630 ℃, and cooling to room temperature at the temperature of below 200 ℃. The design of the finish rolling reduction rate and the control of the finish rolling temperature are mainly used for improving the precipitation strengthening effect of micro-alloy elements and ensuring the strength and the toughness of the ultra-low carbon steel.

The invention has the beneficial effects that: the C, N compound of Ti is used for thinning and separating out particles for precipitation strengthening, and the strength of the ultra-low carbon cold forging steel can be ensured without adding noble metal; continuous casting billet production is adopted, so that the waste of energy and cost caused by secondary-fire cogging is reduced; controlling the heating of the steel billet and controlling the rolling and cooling to obtain relatively uniform pure ferrite structure with the grain size of about 8 grades and R of the hot-rolled wire rod_mThe elongation is more than or equal to 48 percent and the Z is more than or equal to 90 percent under 330-350 MPa, so that the process cost is reduced while the strength and the toughness are ensured.

Drawings

FIG. 1 is a metallographic structure diagram of a disc with a diameter of 6.5mm according to an embodiment of the present invention;

FIG. 2 is a distribution diagram of titanium element scanned by the surface of a 6.5 mm-diameter disc-shaped electronic probe according to an embodiment of the present invention.

Detailed Description

The invention is described in more detail below with reference to the figures and examples. These examples are merely illustrative of the best mode of carrying out the invention and do not limit the scope of the invention in any way.

See fig. 1 and 2.

Example 1

The cold heading hollow rivet steel is characterized by being prepared from the following components in percentage by weight, wherein the cold heading hollow rivet steel is steel with the mark of CH 1T: c is less than or equal to 0.01 percent, Si is less than or equal to 0.04 percent, Mn: 0.05-0.25%, P is less than or equal to 0.020%, S is less than or equal to 0.015%, Als: 0.025 to 0.06%, Ti: 0.06-0.12 percent of Cr, less than or equal to 0.04 percent of Ni, less than or equal to 0.02 percent of Cu, less than or equal to 0.015 percent of As and less than or equal to 0.015 percent of Sn; the balance being Fe and unavoidable impurities.

The method for producing the steel CH1T for the cold heading hollow rivet by rolling comprises the following steps:

(1) controlling chemical components according to CH1T steel, smelting and continuously casting into a billet, wherein the section size of a small square billet is 160mm × 160 mm;

(2) heating the steel billet to 1010 ℃, preserving heat for 100 minutes, and ensuring that the time of the steel billet in a heating section and a soaking section is 100 minutes during production control; controlling the furnace temperature of the heating section at 1000-1120 ℃, and controlling the furnace temperature of the soaking section at 1000-1110 ℃;

(3) rough rolling is carried out on the high speed wire, and the initial rolling temperature is 930-950 ℃;

(4) performing finish rolling on the altitude, controlling the inlet temperature of the finish rolling to be 930-950 ℃, and controlling the reducing and sizing temperature to be 930-950 ℃;

(5) spinning, wherein the spinning temperature is controlled to be 900-920 ℃;

(6) different specifications and different finish rolling speeds, the finish rolling speed of the specification phi 6.5mm is 100m/s, the finish rolling speed of the specification phi 8mm is 91.5m/s, and the finish rolling speed of the specification phi 10mm is 58.6 m/s;

(7) carrying out sectional cooling by adopting a stelmor air cooling line, quickly cooling at a cooling speed of more than or equal to 5 ℃/s at the temperature of more than 630 ℃, slowly cooling at a cooling speed of 0.1-3 ℃/s at the temperature of less than 630 ℃, and cooling to room temperature by air cooling below 200 ℃;

(8) and (5) collecting rolls and packaging for later use.

The structure and the mechanical property of the wire rod are tested, the tissue picture of the wire rod with the diameter of 6.5mm is shown in figure 1, the structure is mainly ferrite, and the grain size of the structure at the radius of 1/2 is 8.5 grade. Through the surface scanning analysis of the electronic probe, Ti elements are dispersedly distributed in the wire rod body, which plays an important role in improving the strength of the wire rod, as shown in figure 2. The specification performance detection values of the wire rod phi 6.5mm, phi 8mm and phi 10mm are shown in table 1, and the wire rod tissue and mechanical properties meet the requirements of manufacturing rivets with large deformation and certain strength.

Table 1 statistical table of steel material coiling test detection results in the embodiment of the present invention

Wire rod specification	Yield strength p0.2(MPa)	Tensile strength Rm(MPa)	Elongation after Break (%)	Reduction of area (%)	Ferrite grain grade
						6.5mm	248	335	57	91	8.5
Φ8mm	245	333	50	90	8
						Φ10mm	243	333	48.5	90	8

As can be seen from Table 1, the yield strength of the steel CH1T for the cold-heading hollow rivet is more than or equal to 240MPa, the tensile strength is more than or equal to 330MPa, the plasticity index is extremely good, the elongation after fracture reaches about 50%, and the reduction of area is more than or equal to 90%.

Claims (1)

1. The steel for the cold-heading hollow rivet is characterized by comprising the following chemical components in percentage by weight: c is less than or equal to 0.01 percent, Si is less than or equal to 0.04 percent, Mn: 0.05-0.25%, P is less than or equal to 0.020%, S is less than or equal to 0.015%, Als: 0.025 to 0.06%, Ti: 0.06-0.12 percent of Cr, less than or equal to 0.04 percent of Ni, less than or equal to 0.02 percent of Cu, less than or equal to 0.015 percent of As and less than or equal to 0.015 percent of Sn; the balance being Fe and inevitable impurities, the equivalent of copper in the steel = Cu% +3 As% +8 Sn% -Ni%;

the preparation method of the steel for the cold-heading hollow rivet comprises the following steps:

(1) molten iron pretreatment, converter smelting, LF refining, RH refining and continuous casting, wherein electromagnetic stirring and constant-temperature constant-speed steel drawing are adopted in the continuous casting process to ensure the internal quality and the surface quality of a casting blank, and a continuous casting billet with the section of 160 × 160mm is produced and is subjected to stack cooling;

(2) heating a casting blank: heating the casting blank after the stack cooling, wherein the temperature of the heating section is controlled to be 1000-; the high-temperature section comprises a heating section and a soaking section;

(3) rough rolling is carried out on the high speed wire, and the initial rolling temperature is 930-950 ℃;

(4) performing finish rolling on the altitude, controlling the inlet temperature of the finish rolling to be 930-950 ℃, and controlling the reducing and sizing temperature to be 930-950 ℃; the accumulated reduction rate of finish rolling is more than 60 percent;

(5) spinning, wherein the spinning temperature is controlled to be 900-920 ℃;

(6) different specifications and different finish rolling speeds, the finish rolling speed of the specification phi 6.5mm is 100m/s, the finish rolling speed of the specification phi 8mm is 91.5m/s, and the finish rolling speed of the specification phi 10mm is 58.6 m/s;

(7) carrying out sectional cooling by adopting a stelmor air cooling line, quickly cooling at a cooling speed of more than or equal to 5 ℃/s at the temperature of more than 630 ℃, slowly cooling at a cooling speed of 0.1-3 ℃/s at the temperature of less than 630 ℃, and cooling to room temperature by air cooling below 200 ℃;

(8) and (6) collecting rolls and packaging.

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