CN1847439A - A guide roller for introducing steel billets into a high-speed wire rolling mill and its preparation method - Google Patents

Abstract

The present invention discloses one kind of guide and guard roller for guiding steel billet in high speed wire rolling machine and its making process. Chemically, the guide and guard roller has material comprising C 0.7-1.4 wt%, Wt% 7.0-10.0 wt%, V 0.8-1.5 wt%, Cr,5.0-10.0 wt%, B 1.2-2.5 wt%, Mo<1.5 wt%, Si<1.5 wt%, Mn<1.5 wt%, RE 0.08-0.18 wt%, Mg 0.05-0.15 wt%, Ti 0.08-0.20 wt%, S<0.05 wt%, and P<0.05 wt%, except Fe and inevitable impurity. The guide and guard roller is made through electric furnace smelting and precise wax mold casting or evanescent mold casting. It has high strength, high toughness, high wear resistance, high fatigue and oxidation resistance, high quick cooling and heating resistance, and use performance obviously higher than that of high Ni-Cr cast steel guide and guard roller.

Description

A guide roller for introducing steel billets into a high-speed wire rolling mill and its preparation method

Technical field

The invention belongs to the technical field of steel rolling, and relates to a guide roller and a preparation method thereof, in particular to a guide roller for introducing billets into various high-speed wire rolling mills and a preparation method thereof.

Background technique

For continuous bar and wire rolling mills, rolling guide devices are mostly used at the entrance and exit of intermediate and finishing mills. Due to the harsh operating environment, guide rollers have become the main vulnerable parts. In addition, since modern high-speed rolling mills have high requirements on the dimensional accuracy of the guide rollers, the consumption of the guide rollers is large. In high-line production, the rolling speed is generally above 50m/s, and the rotation speed of imported guide rollers is as high as 260r/s or above. During rolling, the guide rollers have to withstand high temperature (about 1000°C), sliding and rolling friction of high-speed running wires and bars, and abrasive wear of oxides. At the same time, when the material hardness of the guide roller is low, the working surface of the guide roller is rough and the installation accuracy is not high, the local force on the guide roller is too large during the working process, and iron oxide chips accumulate and adhere to the surface of the guide roller. Working surface, and stick to it to bite and fail. In addition, due to the forced water cooling of the guide rollers, the guide rollers are prone to thermal fatigue damage due to repeated exposure to alternating thermal stresses of hot and cold.

At present, most of the guide rollers used in China are made by precision casting with external dimensions and steel types provided by foreign countries. In order to ensure the safety and reliability of guide rollers under high-speed rolling, cobalt-based, nickel-based, tungsten-cobalt-based and high-chromium-iron-based casting alloys are mostly used in China to manufacture guide rollers. Chinese invention patent CN1609256 discloses a powder metallurgy steel rolling guide roller and a manufacturing method thereof. Through material optimization design and powder metallurgy liquid phase sintering technology, a steel rolling guide roll with excellent performance is obtained. The powder raw material composition of powder metallurgy rolling steel guide roller is: Cr, 8%-20%; Mo, 0.8%-3.6%; W, 0.5%-2%; Ni, Co and Cu are all 3.5%-7%; V , 0.3% to 1.2%; BN, 0.1% to 0.5%; C, 1.8% to 2.5%; amide wax powder 0.5%; surfactant 0.3% to 1%; the balance is iron powder. The manufacturing method of the powder metallurgy rolled steel guide roller basically includes the following steps: a. batching and mixing; b. pressing and forming; c. sintering; d. heat treatment; e. machining. The hardness of powder metallurgy rolling steel guide roller is HRC50~63, the bending strength is 1000~1300Mpa, the radial crushing strength is 1500~1800Mpa, the impact toughness is α _k 3.9~5J/cm ² , and the tensile strength _σb is 800~1200MPa. Continuously use 3 to 5 shifts. Although the wear resistance of this guide roller is very good, it is brittle and easily cracks during use, which affects the normal operation of the rolling equipment.

Chinese patent CN2552617 discloses a steel rolling rolling guide roller of composite structure, which is used to guide the centering of the rolled piece and enter the roll pass. It consists of a roll body and a rolling bearing installed inside it, and is characterized in that the roll body is composed of a cermet outer ring and an aluminum alloy inner ring, and a rolling bearing is installed in the inner ring, between the outer ring and the inner ring, the inner ring Static fit connection is adopted with the bearing. Due to the high hardness of the outer ring and the light weight and small moment of inertia of the inner ring, the wear-resistant life of the surface of the guide roller is comprehensively improved. However, the preparation process of this combination guide roller is complicated, and the production efficiency is low, and the working layer of the guide roller is a relatively brittle ceramic, which is prone to peeling during use, which affects the normal production of rolled steel.

Chinese patent CN2571515 discloses a rolling guide roll of a rolling mill. The rolling guide roll of a rolling mill is made by machining and cleaning the base body of the guide roll, and bonding the tungsten carbide sleeve and the base body together by using a bonding method. The hardness of the tungsten carbide sleeve of the rolling guide roll of this rolling mill is above HRA80, and it has high wear resistance and crack resistance. Its comprehensive service life is 10 to 15 times longer than that of forged alloy steel and alloy cast iron guide rolls. For wire, bar mills, bar mills and slit rolling. The guide roller has the disadvantages of complicated processing technology and the disadvantages that the tungsten carbide sleeve and the guide roller matrix are easy to fall off during use.

Chinese invention patent CN1693527 discloses a cobalt-free multi-component high-speed tool steel and its manufacturing method, which can be used to produce rolls, roll rings and guide rolls. The chemical composition (weight %) of the steel is C: 1.8-2.2; Si: 0.5-1; Mn: 0.5-1; S: <0.05; P: <0.05; Cr: 4-6; V: 4-6; Mo: 4-6; W: <2; Ni: 0.8-1.2; Nb : 0.2; Ti: 0.05-0.1; Mg: 0.005-0.01; RE: 0.05-0.1. The invention highlights high carbon, high molybdenum and high vanadium. At the same time, the rare and precious metal cobalt is removed from the material, which saves the cost of materials; the present invention adopts the intermediate frequency furnace for smelting and uses the yttrium-based heavy rare earth alloy for pre-furnace modification treatment, the material structure is fine and dense, and the dispersed distribution of the eutectic compound is realized, reducing the cost. tissue stress. However, the content of molybdenum in this material is too high, and the production cost is high, while the content of tungsten is too low, which reduces the high-temperature hardness and red hardness of the material, which is not conducive to improving the high-temperature wear resistance of the material.

European patent 726236-A discloses a ceramic guide roller for hot rolling steel, which is mainly made of Si ₃ N ₄ sintered at 1100-1300°C under the protection of nitrogen, and has excellent corrosion resistance and wear resistance , It is not easy to stick to steel, which improves the surface quality of rolled products. However, the preparation process of the ceramic guide roller is complicated, and the material is brittle, and the thermal fatigue performance is poor, and it is easy to be brittle and peeled off during the hot rolling process.

Contents of invention

The object of the present invention is to provide a guide roller for introducing billets into a high-speed wire rod mill and a preparation method thereof. The guide roller is smelted in an electric furnace and poured by wax mold precision casting or lost foam casting. Its main feature is that boron is added to the cobalt-free high-speed steel to improve the wear resistance of the material. In addition, it reduces the high price of high-speed steel. The amount of molybdenum and vanadium added, in order to ensure that the guide roller has excellent high temperature wear resistance, the content of tungsten should be increased appropriately. In addition, adding an appropriate amount of rare earth-magnesium-titanium composite modifier to the high-speed steel can refine the structure, especially to break and isolate the eutectic carbide, which is beneficial to the substantial improvement of the mechanical properties of the high-speed steel, which will eventually lead to Improvement of the performance of high-speed steel guide rollers.

In order to achieve the above object, the present invention is realized through the following technical measures:

A guide roll for high-speed wire rolling mills for introducing steel slabs, characterized in that the prepared guide roll mainly contains the following chemical components in weight percentages: C, 0.7-1.4; W, 7.0-10.0; V, 0.8-1.5; Cr , 5.0~10.0; B, 1.2~2.5; Mo<1.5; Si<1.5; Mn<1.5; RE, 0.08~0.18; Mg, 0.05~0.15; Ti, 0.08~0.20; S<0.05; P<0.05; The amount is Fe and undetectable trace impurities.

The above-mentioned preparation method of the guide roll for importing billets into the high-speed wire rod mill adopts ordinary electric furnace melting, and is characterized in that the process steps are:

1) Mix and heat ordinary steel scrap, pig iron, ferrotungsten, ferrovanadium, ferrochrome, ferroboron, ferromolybdenum, ferrosilicon and ferromanganese;

2) After the composition of the furnace is adjusted to pass, the temperature of the molten steel is raised to 1550 ° C ~ 1600 ° C, adding deoxidizer aluminum, and then out of the furnace;

3) Crush the magnesium-containing modifier, rare earth ferrosilicon and ferrotitanium into small pieces with a particle size of less than 18mm. After drying below 260°C, place them at the bottom of the ladle, and use the method of pouring into the ladle to carry out compound modification treatment on molten steel ;

4) The guide roller is poured by the wax mold precision casting method or the lost foam casting method, and the molten steel pouring temperature is 1400 ° C ~ 1450 ° C;

5) The poured guide roller is annealed after being polished and cleaned. The process is to keep warm at 880°C-950°C for 2h-4h, and then furnace cool to 550°C and then furnace cool or air cool;

6) After the guide roller is roughly processed, it is then subjected to isothermal quenching treatment. The process is to heat it in an electric furnace or a salt bath furnace to 1050 ° C ~ 1180 ° C, keep it warm for 1.5h ~ 3h, and then directly heat it at 280 ° C ~ 360 ° C Isothermal in the salt bath for 2h ~ 4h, then air cooling; then tempering treatment, the process is to keep warm at 500 ° C ~ 580 ° C for 3 h ~ 6 h, then furnace cooling or air cooling, tempering twice under the same process, and finally fine It can be processed to the specified size.

The performance of the alloy material is determined by the metallographic structure, and a certain structure depends on the chemical composition and heat treatment process. The chemical composition of the present invention is determined as follows:

Because high-speed steel contains a large amount of alloying elements such as tungsten, molybdenum, chromium, vanadium, etc., it has high normal temperature hardness, which is especially valuable; compared with ordinary materials, high-speed steel has excellent red hardness, and it still maintains HRC55 at 500 °C Above, it has excellent high-temperature wear resistance, so high-speed steel is used to make guide rollers.

In addition to more tungsten, chromium and other strong carbide-forming elements, high-speed steel guide rollers also contain high carbon content. Only when the carbide-forming elements and carbon content meet the proportional relationship in the alloy carbide molecular formula , the hardening effect of secondary carbides is the best, which ensures that high-speed steel has high red hardness and wear resistance. According to the working characteristics of the guide roller, the chromium content in the high-speed steel can be appropriately increased to 5% to 10%. Increasing the chromium content can improve the oxidation resistance of the high-speed steel and prevent the oxidation of the guide roller during use. Due to the high price of molybdenum and vanadium elements, the amount of molybdenum and vanadium added to the high-speed steel guide roller is relatively small. In order to improve the high-temperature wear resistance of the high-speed steel guide roller, the tungsten content is controlled at 7.0% to 10.0%. In addition, 1.2% to 2.5% boron is added to the high-speed steel. The solid solution of boron in the high-speed steel matrix is very low. Adding high-speed steel mainly forms high-hardness borides and boron-carbon compounds, which can significantly improve the high-speed steel. abrasion resistance. In addition, boron can also promote the disconnection and spheroidization of carbides in high-speed steel during heating, which is beneficial to the improvement of strength and toughness of high-speed steel.

Adding a proper amount of rare earth to the high-speed steel guide roller can reduce the content of S and O in molten steel, increase the supercooling degree of eutectic solidification, and refine the eutectic structure. The crystal growth front hinders the growth of austenite and refines the austenite dendrites. Due to the refinement of the austenite dendrites, the eutectic molten steel formed by segregation between the austenite dendrites melts in the later stage of solidification. The pool becomes smaller, which refines the eutectic carbides. Adding appropriate amount of titanium to the high-speed steel guide roller, TiC can be formed preferentially over MC carbides in the high-speed steel molten steel, and TiC can be used as an effective heterogeneous core for the nucleation of MC carbides to promote the refinement of MC carbides. A proper amount of magnesium is added to the high-speed steel guide roller. During the eutectic crystallization, the magnesium is selectively adsorbed on the surface of the eutectic carbide in the preferred growth direction, forming an adsorption film, which hinders the atomic growth of W, Mo, Cr, etc. in the molten steel. The addition of eutectic carbide crystals reduces the growth rate of the eutectic carbide in the preferred direction, and promotes the eutectic carbide from lamellar to spherical. Therefore, the addition of rare earth-magnesium-titanium in the guide roller of high-speed steel can refine the matrix structure, improve the morphology and distribution of carbides, and help improve the strength, toughness and wear resistance of high-speed steel.

The purpose of annealing the high-speed steel guide roller is to improve the processing performance. The salt bath quenching is used mainly to obtain a bainite structure with excellent toughness and wear resistance. The tempering is mainly to eliminate stress and stabilize the structure.

Compared with the prior art, the present invention has the following characteristics:

(1) The guide roller prepared by the invention has high hardness, good high-temperature wear resistance, and the service life is 3 to 5 times longer than that of commonly used alloy steel guide rollers.

(2) The guide roller of the present invention has high strength and toughness, and there is no phenomenon of fracture, chipping and peeling during use, and the guide roller of the present invention does not stick to steel, and the surface of the rolled material is smooth and clean.

(3) The guide roller of the present invention takes the abundant tungsten and boron in my country as the alloy elements mainly improving wear resistance, does not contain expensive cobalt, and the addition of molybdenum and vanadium elements with high price is also less, so the production cost is relatively low. Low.

(4) The guide roller of the present invention is formed by an ordinary casting method, the preparation process is simple, and the production efficiency is high.

Detailed ways

The present invention will be further described in detail below in conjunction with the examples given by the inventor.

Example 1:

The guide roller of the present embodiment is smelted in a 500kg intermediate frequency induction furnace, and its manufacturing process steps are:

(1) Mix common steel scrap, pig iron, ferrotungsten, ferrovanadium, ferrochrome, ferroboron, ferromolybdenum, ferrosilicon and ferromanganese by heating and melting.

(2) After the composition is adjusted before the furnace, the temperature is raised to 1590°C, and 0.12% of the total amount of molten steel is added for deoxidation, and then it is released from the furnace.

(3) Break the magnesium-containing modifier, rare earth ferrosilicon and ferrotitanium into small pieces with a particle size of less than 18mm, and after drying at 230°C, place it at the bottom of the ladle, and perform compound modification treatment on molten steel by pouring into the ladle .

(4) The guide roller is poured by the lost foam casting method, and the molten steel pouring temperature is 1440°C.

(5) After casting, the guide roller is annealed after grinding and cleaning. The process is to keep it at 930°C for 2.5h, then cool it in the furnace to 550°C and then air cool it.

(6) After rough machining, the guide roller is subjected to isothermal quenching treatment. The process is to heat it to 1150°C in an electric furnace, hold it for 2 hours, and then directly hold it in a salt bath at 330°C for 2.5 hours, and then air cool it; then temper it Treatment, the process is to keep warm at 550 ° C for 5 hours, then air-cool, temper twice under the same process, and finally finish machining to the specified size. The composition of the high-speed steel guide roller is shown in Table 1, and the mechanical properties are shown in Table 2.

Table 1 Composition of high-speed steel guide rollers (wt%) element C W V Cr B Mo Si mn RE Mg Ti S P Fe Element 1.33 7.74 1.48 6.99 1.51 1.08 1.17 0.82 0.13 0.07 0.15 0.028 0.037 margin

Table 2 Mechanical properties of high-speed steel guide rollers Hardness HRC Red hardness HRC at 600℃ Tensile strength MPa Impact toughness kJ/m ² Fracture toughness MPa.m ^1/2 65.8 60.5 905 153 30.7

Example 2:

The guide roller of the present embodiment is smelted in a 300kg intermediate frequency induction furnace, and its manufacturing process steps are:

(1) Mix common steel scrap, pig iron, ferrotungsten, ferrovanadium, ferrochrome, ferroboron, ferromolybdenum, ferrosilicon and ferromanganese by heating and melting.

(2) After the composition is adjusted before the furnace, the temperature is raised to 1570°C, and 0.10% of the total amount of molten steel is added for deoxidation, and then it is released from the furnace.

(3) Crush the magnesium-containing modifier, rare earth ferrosilicon and ferrotitanium into small pieces with a particle size of less than 18mm, and after drying at 240°C, place them at the bottom of the ladle, and perform compound modification treatment on molten steel by pouring into the ladle .

(4) The guide roller is poured by wax mold precision casting method, and the pouring temperature of molten steel is 1425°C.

(5) The guide roller is annealed after grinding and cleaning. The process is to keep the temperature at 900°C for 3 hours, and then cool it in the furnace.

(6) After the rough machining of the guide roller, it is subjected to isothermal quenching treatment. The process is to heat it to 1100°C in a salt bath furnace, keep it warm for 2.5h, and then directly place it in a salt bath at 300°C for 2.3h, and then air cool it; Tempering treatment, the process is to hold at 520 ° C for 5.5 hours, then cool in the furnace, temper twice under the same process, and finally finish machining to the specified size. The composition of the high-speed steel guide roller is shown in Table 3, and the mechanical properties are shown in Table 4.

Table 3 Composition of high-speed steel guide rollers (wt%) element C W V Cr B Mo Si mn RE Mg Ti S P Fe Element 1.01 8.30 0.97 7.51 1.85 1.13 1.22 0.75 0.09 0.14 0.10 0.031 0.036 margin

Table 4 Mechanical properties of high-speed steel guide rollers Hardness HRC Red hardness HRC at 600℃ Tensile strength MPa Impact toughness kJ/m ² Fracture toughness MPa.m ^1/2 66.2 60.7 894 150 30.9

The guide rollers prepared in the above examples were tested on the finishing mill of a high-speed wire rod rolling mill to roll φ5.5mm wire rods, the material is plain carbon steel, and the rolling speed was 120m/s. The test results show that the average steel passing capacity of the guide roller of the present invention is 3670 tons. Compared with other guide rollers, the high-speed steel guide roller of the present invention has high strength, good toughness, good wear resistance, excellent thermal fatigue resistance and oxidation resistance, good resistance to shock and heat, and is not brittle and cracked during use. No peeling, no cracking, no sticking to steel, etc., the service life is 3 to 5 times higher than that of high nickel-chromium alloy cast steel guide rollers, the service life is extended, and the time for shutdown treatment (replacement guide rollers) in production is reduced, and the average Shift output increased from 650 tons/shift to 675 tons/shift. The guide roller of the invention has simple production process, less precious alloy addition and low production cost. Using the guide roller of the invention can significantly increase the operating rate of the rolling mill, reduce the production cost of rolling materials, and has good economic benefits.

Claims (2)

1. A high-speed wire rod rolling mill imports a guide roller for billet, characterized in that the prepared guide roller mainly contains the following chemical components in weight percentage: C, 0.7～1.4; W, 7.0～10.0; V, 0.8～1.5 ; Cr, 5.0~10.0; B, 1.2~2.5; Mo<1.5, Si<1.5, Mn<1.5, RE, 0.08~0.18; Mg, 0.05~0.15; Ti, 0.08~0.20; S<0.05, P<0.05 , the balance is Fe and unavoidable trace impurities. 2. The preparation method of the guide roller for importing steel billet into a high-speed wire rod mill according to claim 1, which adopts an ordinary electric furnace for smelting, and is characterized in that the process steps are: 1) Mix and heat ordinary steel scrap, pig iron, ferrotungsten, ferrovanadium, ferrochrome, ferroboron, ferromolybdenum, ferrosilicon and ferromanganese; 2) After the composition of the furnace is adjusted to pass, the temperature of the molten steel is raised to 1550 ° C ~ 1600 ° C, adding deoxidizer aluminum, and then out of the furnace; 3) Crush the magnesium-containing modifier, rare earth ferrosilicon and ferrotitanium into small pieces with a particle size of less than 18mm. After drying below 260°C, place them at the bottom of the ladle, and use the method of pouring into the ladle to carry out compound modification treatment on molten steel ; 4) The guide roller is poured by the wax mold precision casting method or the lost foam casting method, and the molten steel pouring temperature is 1400 ° C ~ 1450 ° C; 5) The poured guide roller is annealed after being polished and cleaned. The process is to keep warm at 880°C-950°C for 2h-4h, and then furnace cool to 550°C and then furnace cool or air cool; 6) After the guide roller is roughly processed, it is then subjected to isothermal quenching treatment. The process is to heat it in an electric furnace or a salt bath furnace to 1050 ° C ~ 1180 ° C, keep it warm for 1.5h ~ 3h, and then directly heat it at 280 ° C ~ 360 ° C Isothermal in the salt bath for 2h ~ 4h, then air cooling; then tempering treatment, the process is to keep warm at 500 ° C ~ 580 ° C for 3 h ~ 6 h, then furnace cooling or air cooling, tempering twice under the same process, and finally fine It can be processed to the specified size.