High-speed wire rod pre-finishing rolling machine Anti-spalling roll material and heat treatment process

Abstract

A high-speed wire rod pre-finishing rolling machine anti-spalling roll material, and a heat treatment process. The chemical components of the high-wire pre-finishing rolling mill anti-spalling roll material comprise: C, Si, Mn, Cr, Ni, Mo, V, W, Nb, Fe and unavoidable impurities. The heat treatment process of the roll material comprises annealing and quenching-tempering, the quenching-tempering step comprising: first heating and holding, second heating and holding, third heating and holding, spray quenching, and high-temperature tempering. The resulting high-performance roll material addresses issues of short service life and frequent spalling of raw material rolls, improves production efficiency, reduces production costs, and has good prospects for widespread application.

Description

High-speed wire pre-precision rolling mill set anti-peeling roller material and heat treatment process TECHNICAL FIELD

[0001] The present application relates to the field of roller casting, more particularly to high-speed wire pre-precision rolling mill set anti-peeling roller material and heat treatment process. BACKGROUND

[0002] High-speed wire rod mill has the characteristics of high speed, high quality and high efficiency, which provides guarantee conditions for high yield and wide range of product specifications. In recent years, the wire rod production line adopts short stress line mill, and develops in the way of "high speed, no twist and no tension". The technologies of endless rolling and low temperature rolling are researched and developed. Due to the diversification of wire and bar product specifications, the increasing demand for small size products and the continuous improvement of mechanical properties, the mechanical properties of processing tools also need to be continuously improved. In addition, the high-speed wire production line realizes low-temperature discharge and low-temperature controlled rolling, and the microstructure, yield strength and toughness of the obtained products are improved at the same time.

[0003] At present, the roller used in the front section of high-speed wire pre-precision rolling is mainly traditional high-nickel chromium bainite nodular cast iron. The recent use shows that the anti-accident performance such as wear resistance and anti-peeling of the roller is poor, and the roller groove surface is not wear-resistant, peeling and dropping, and the single groove rolling quantity is low, and the roller changing frequency is frequent, which becomes the bottleneck for further improving the production capacity. With the development of rolling mill towards high speed and high quality, the service life of the roller made of the above-mentioned material is low due to the above defects, which affects the production efficiency of the production line. Therefore, it is required that the work layer of the pre-precision rolling mill roller has greatly improved anti-peeling and wear resistance, and the matrix has good strength and toughness.

[0004] The prior art CN91107234.9 discloses a vanadium-titanium infinite hard nodular cast iron roller and a casting method. The roller does not contain valuable alloy elements such as Ni, Cr, Mo and Cu. During casting, a mixed spheroidizing agent composed of rare earth magnesium and iron magnesium is used. The produced roller has the characteristics of low cost, high hardness, good wear resistance and high strength. However, the absence of valuable alloy elements such as Ni, Cr, Mo and Cu can reduce the cost, but it will have a negative impact on the mechanical properties of the roller, the amount of steel passing through, and the wear resistance. The prior art CN201410085918 discloses a manufacturing method of centrifugal casting easy-to-cut high-speed steel roller. The processing technology discloses degeneration, quenching and tempering process, heat treatment process, etc. However, the heat treatment process is complex, the heating speed is slow, and the production cycle is long, which affects the application range of the process.

[0005] The roller material of the rough rolling mill stand of the wire and bar mill and the section steel mill is generally selected from pearlite nodular cast iron. In the use process, there are phenomena such as deep rolling groove crack, large single steel passing amount, large turning amount and large hardness difference.

[0006] SUMMARY

[0007] To solve the above technical problems, the present application provides a high linear pre-precision rolling mill group anti-peeling roller material, the chemical composition of the roller material comprising: C, Si, Mn, Cr, Ni, Mo, V, W, Nb, Fe and inevitable impurities.

[0008] Preferably, the mass percentage of V, Mo and W satisfies: V+Mo+W / 2=1.9-4.5%.

[0009] Further preferably, the chemical composition of the roller material comprises, in mass percentage: 2.6-3.6% C, 1.3-2.0% Si, 0.5-0.8% Mn, 1.5-3.0% Cr, 1.0-2.5% Ni, 0.2-0.8% Mo, 1.5-3.2% V, 0.5-1.0% W, 0.12-0.25% Nb, the balance of Fe and inevitable impurities.

[0010] The roles of the elements in the roller are as follows:

[0011] C (carbon): C is the most basic element in the roller material alloy, and the content thereof determines the amount of carbide, the relative amount of M7C3 type carbide and total carbide, hardness, toughness and hardenability of the material, etc. Relevant test results show that the C content in the roller is preferably controlled in the range of 2.6-3.6 wt%.

[0012] Si (silicon): Silicon element can induce the nucleation of bainite in the alloy matrix of the roller material, and improve the nucleation rate. This is because Si can refine the eutectic group, increase the austenitizing temperature, increase the undercooling degree ΔT of austenite transformation, and the small nucleus embryo in the austenite can be used as the core of bainite or martensite; in the present application, the heat treatment process is improved according to the different dynamics of bainite and martensite nucleation, and the contents of bainite and martensite are controlled. Test results show that the Si element can better induce bainite phase change and refine the bainite structure, so that the hardness and toughness are improved. On the other hand, silicon is an element that strongly promotes graphitization and inhibits carbide precipitation. The increase of silicon content can fully inoculate spheroidal graphite, and a large number of fine and round graphite can be obtained, i.e. the eutectic group is refined, and the bainite structure is also refined. Therefore, the Si content is preferably controlled in the range of 1.3-2.0 wt%.

[0013] Mn (manganese) : when the amount of Si is constant, the appropriate reduction of Mn content can improve the comprehensive mechanical properties of bainite, which is mainly due to the fact that Mn is a positive segregation element, which can reduce the austenitizing temperature, increase the carbon content in austenite, reduce the activity of carbon, stabilize austenite and drag the transformation of bainite. Silicon is a negative segregation element, which can increase the austenitizing temperature, increase the activity of carbon and make the bainite transformation complete, thereby improving the performance. The research results show that after adding Mn, the matrix structure is fine needle bainite structure, but with the increase of Mn content, the segregation of Mn in the structure is more serious, the number of martensite at the grain boundary increases, and the carbide is distributed along the grain boundary, which will lead to the decrease of toughness. Therefore, the addition amount of Mn should be controlled below 0.8wt%, and the addition amount of Mn in the present application is preferably 0.5-0.8wt%.

[0014] Cr (chromium) : Cr is the most important element in the alloy of the roll material, because the higher the ratio of M7C3 carbide, the better the hardenability, and the Cr content needs to be controlled to obtain M7C3 carbide in the matrix. Experimental research shows that when the Cr content is greater than 1.5wt%, M7C3 carbide exists in the form of M7C3 carbide. However, with the increase of Cr content, the eutectic point moves to the left, at this time, the C content and the Cr content need to be considered comprehensively, so that the Cr element exists in the form of carbide, and less exists in the form of solid solution in the matrix. This is because of the particularity of the wire rod, the high alloy wire rod is often rich in Cr, when the Cr content dissolved in the roll matrix is too high, the phenomenon of sticking steel often occurs. Through a large number of experiments, it is found that when the Cr content in the roll is more than 3.0wt%, the phenomenon of sticking steel will occur. Therefore, the mass percentage of Cr in the present application is controlled as follows: 1.5wt% < Cr < 3.0wt%.

[0015] Ni (nickel) : nickel element can refine the matrix and enhance the hardening performance of steel. Experimental results show that the addition of nickel element in the roll matrix has obvious effect on improving the plasticity and toughness and thermal strength of steel. However, considering that nickel is a rare element, the addition amount is only controlled between 0.8-1.5%. When the mass content of Ni is less than 0.8%, the increase of plasticity and toughness and thermal strength of the roll at room temperature is not obvious. When the mass content of Ni is between 0.8-1.5%, the plasticity and toughness and thermal strength at room temperature increase with the increase of Ni content. When the mass content of Ni is greater than 1.5%, the increase of plasticity and toughness and thermal strength at room temperature is not consistent with the increase of cost, that is, the cost performance is not high.

[0016] V (vanadium) : within the research scope of the present application, with the increase of the addition amount of V, the bainite structure is obviously refined, the hardness of bainite ductile iron and the bainite transformation amount are increased, and the microhardness of austenite and bainite changes little. Experimental research shows that the optimal range of V content is 1.5-3.2wt%.

[0017] The mechanism of V refining the bainite structure can be attributed to two aspects. First, V is one of the elements that strengthen ferrite and austenite, which dissolves into austenite to form a solid solution, reduces the diffusion speed of carbon, and itself needs time to diffuse, thereby delaying the austenite transformation and prolonging the bainite transformation incubation period. Under the condition of continuous cooling in this test, this means that the bainite transformation will be carried out at a lower temperature. The increase of transformation undercooling degree will bring greater driving force for bainite nucleation. Second, during austenitization, the VC (vanadium-carbon) particles formed during solidification have a "pinning" effect, hindering the movement of grain boundaries and grain growth, thereby refining the austenite grains and providing more favorable nucleation sites for bainite. Due to the above two aspects, the bainite core increases greatly, the bainite structure is refined, and the amount of bainite transformation is increased.

[0018] Mo (molybdenum) and W (tungsten): in the technical solution of the present application, Mo acts as a strong carbide-forming element, improving the stability of austenite and the hardenability of the roll matrix, preventing the second type of temper brittleness, and using Mo and W to form M6C type carbide, which improves the stability of MC type carbide and the temper resistance of the matrix, and inhibits the generation of thermal cracks; therefore, in the technical solution of the present application, the mass percentage of Mo needs to be controlled between 0.2-0.8%, the mass percentage of W needs to be controlled between 0.5-1.0%, and (V+Mo+W / 2) = 1.9-4.5wt% needs to be satisfied.

[0019] Nb (niobium): in the present application, the role of Nb element is that it has strong affinity with carbon, nitrogen and oxygen, can form extremely stable compounds, and plays a role in refining grains, increasing grain coarsening temperature, hardenability and temper stability; in addition, as a hard element, Nb can improve the wear resistance of thickened dies; therefore, in the technical solution of the present application, the mass percentage of Nb element is controlled as follows: 0.12-0.25wt%.

[0020] The second application of the present application provides a heat treatment process for a high-line pre-finishing roll material, which comprises the following steps: annealing and quenching and tempering.

[0021] Preferably, the annealing step comprises: cooling the cast roll material to a temperature of 930-950℃, then performing 3-4h of in-furnace annealing treatment, then stopping heating, slowly cooling in the furnace to 600℃, taking out of the furnace, and air cooling to room temperature.

[0022] Preferably, the quenching and tempering step comprises:

[0023] S1, first temperature rising and holding;

[0024] S2, second temperature rising and holding;

[0025] S3, third temperature rising and holding;

[0026] S4, spray quenching;

[0027] S5, high temperature tempering.

[0028] Preferably, the first temperature rising and holding includes: heating the roll material treated in the annealing step at a temperature rising speed of 180-200 ℃ / h, and holding for 10-12 min at 700 ℃.

[0029] Preferably, the second temperature rising and holding includes: continuing to rise the temperature at a temperature rising speed of 180-200 ℃ / h on the basis of the step S1, and holding for 10-12 min at 900 ℃.

[0030] Preferably, the third temperature rising and holding includes: rising the temperature to 980-1100 ℃ on the basis of the step S2, holding for 30-40 min, and quenching out of the furnace.

[0031] Preferably, the spray quenching includes: spraying the flow rate of the spray cooling device to make the cooling speed of the roll body of the roll material be 2-4 ℃ / s on the basis of the step S3; after 245-550 s, blowing air to the roll body, the highest re-temperature of the blowing stage is 340-350 ℃, the roll temperature is 150-170 ℃, the blowing is stopped and air cooling is performed until the roll body temperature is stable at 150-170 ℃.

[0032] Preferably, the high temperature tempering step includes: preheating the tempering furnace to 100-150 ℃; then heating the roll material at a temperature rising speed of 180-200 ℃ / h on the basis of the step S4, holding for 90-120 min at 480-600 ℃, cooling to 150 ℃ in the furnace, and air cooling to room temperature out of the furnace; the high temperature tempering process is repeated for 2-3 times.

[0033] In the processing steps in the application, the temperature rising process needs to be held for multiple times, because when the temperature rising speed is fast and the quenching temperature is high, the short-time temperature holding can make the roll be heated uniformly; therefore, in the steps S1 and S2 of the technical scheme of the application, the temperature is held for 10-12 min at 700 ℃ and 900 ℃.

[0034] In the steps S3 and S4 of the processing technology in the application, the high temperature quenching is performed at 980-1100 ℃, the spray flow rate is reasonably controlled, the cooling speed of the roll body is controlled to be 2-4 ℃ / s, the microstructure is controlled to be bainite, a small amount of martensite, residual austenite and carbide. The spray cooling time is controlled to be 245-550 s, and the thickness of the working layer is appropriately controlled to be 35-40 mm.

[0035] High temperature quenching at 980-1100℃ is because the alloying elements in the roll material are optimized in the patent, and the high melting point carbides are increased. The carbide of MC with V is precipitated at eutectic transformation or from austenite, and the initial solid solution temperature is 1000-1150℃, the VC particles are fine and uniformly distributed. M6C is the carbide of W and Mo, which is solid-solved in austenite at 1050-1300℃, M6C is relatively stable and is not easy to aggregate and grow, which can increase the hardness and wear resistance of the die. M7C3 is the carbide of Cr, which is a primary eutectic carbide or a secondary carbide precipitated from austenite, which can dissolve into W, Mo, V and other elements to increase wear resistance and reduce friction coefficient. The secondary M7C3 is dissolved into austenite at 950-1150℃; M 23 C6 is another carbide of Cr, which starts to solid-solve at a temperature of 1000-1020℃, and completely solid-solves in austenite at a temperature of 1150-1200℃. Therefore, a higher quenching temperature of 980-1100℃ must be used to fully dissolve the carbide into the matrix.

[0036] In the high temperature tempering step of the processing process S5 in the application, high temperature quenching is used. Tests show that high temperature quenching, combined with a higher tempering temperature of 480-600℃, increases the thermal fatigue resistance of the roll iron roll, delays the initiation time of the roll surface thermal cracks during service, and reduces the crack propagation rate; this is because the austenitizing temperature is increased, more carbides are melted in the matrix, the solid solubility of matrix alloying elements and carbon is increased, the matrix is effectively strengthened, and the strength and toughness are improved; in addition, the higher tempering temperature improves the temper resistance of the roll body and the thermal cycle stability, effectively reducing the roll surface peeling and other failures during rolling. The tempering holding time is controlled within 120min to ensure that the hardness of the reducing diameter roll meets the requirements while having high strength and toughness. Advantages

[0037] (I) Compared with the traditional pearlitic material roll, the amount of steel passing through the roll material described in the application is increased by 1.5 times, the roll surface is free of peeling and micro-cracks after the machine, and the grinding amount is reduced by 20-30%. The comprehensive cost performance is improved by more than 2 times.

[0038] (II) The new material and heat treatment process of the high line pre-finishing roll in the application are designed to increase the strength and toughness of the roll matrix to meet the low temperature rolling requirements of high strength steel such as spring steel and cold heading steel.

[0039] (Three) at the same time, the application adopts a supporting heat treatment process, so that the normal temperature and high temperature mechanical properties of the new roller material are comprehensively improved, especially the high temperature strength and toughness, oxidation resistance and heat crack resistance are greatly improved, the problems of short single machine service life and frequent peeling are solved, the production efficiency is improved, and the production cost is reduced; at the same time, the microstructure of the roller treated by the heat treatment step is changed from original pearlite to bainite, and the anti-accident performance of the roller material matrix is further improved.

[0040] (Four) the normal temperature hardness of the high wire pre-finishing rolling mill roller developed by the application is 75-80HSD, and the tensile strength is 600-650MPa; at 600 DEG C, the hardness is 50-55HSD, and the tensile strength is 500-550MPa, and the use performance is excellent.

[0041] (Five) the application develops a bainite nodular cast iron roller special for rough rolling, strengthens and refines the matrix structure by adding special alloy elements, optimizes the chemical composition and heat treatment process, develops a bainite + martensite type roller material under the premise of not greatly increasing the cost, so that the roller has high matrix strength, and the anti-accident performance, wear resistance and single machine service life of the rough and medium rolling mill stand roller are improved. BRIEF DESCRIPTION OF DRAWINGS

[0042] Fig. 1 is a crystal phase diagram of the roller of example 1 after the heat treatment step (scale: 20 μm). DETAILED DESCRIPTION

[0043] Example 1

[0044] The first aspect of the example provides a high wire pre-finishing rolling mill anti-peeling roller material, and the chemical element components in the roller material are as follows in terms of mass percentage: 2.6% C, 1.3% Si, 0.5% Mn, 1.5% Cr, 1.0% Ni, 0.2% Mo, 1.5% V, 0.5% W, 0.12% Nb, the balance of Fe and inevitable impurities.

[0045] The second aspect of the example provides a heat treatment process for the high wire pre-finishing rolling mill anti-peeling roller material, which specifically comprises the following steps: annealing and quenching and tempering.

[0046] The annealing step comprises: cooling the cast roller material to 940 DEG C, and then performing 4h furnace holding annealing treatment, then stopping heating, furnace cooling to 600 DEG C, and air cooling to room temperature 25 DEG C.

[0047] The quenching and tempering step comprises:

[0048] S1, first temperature rising and holding: the roller material treated by the annealing step is heated at a temperature rising speed of 200 DEG C / h, and when the temperature is 700 DEG C, 10min isothermal holding is performed;

[0049] S2, second temperature rising and holding: on the basis of S1, continue to rise the temperature at a rate of 200°C / h, when the temperature rises to 900°C, carry out 10 min of temperature holding;

[0050] S3, third temperature rising and holding: on the basis of S2, rise the temperature to 1100°C, hold for 40 min, quenching after discharging;

[0051] S4, spray quenching: on the basis of S3, through the spray flow of the spray cooling device, the cooling speed of the roll body of the roll material is 2°C / s; blow air to the roll body for 475 s, the highest reheat temperature in the blowing stage is 350°C, until the roll temperature is 150°C, stop blowing and air cool until the roll body temperature stabilizes at 150°C;

[0052] S5, high temperature tempering: preheat the tempering furnace to 150°C, then on the basis of S4, heat the roll material to 600°C at a rate of 180°C / h, tempering for 120 min; cool down to 150°C with the furnace, and air cool to room temperature 25°C after discharging.

[0053] The step of high temperature tempering is repeated for 3 times.

[0054] The crystal phase diagram of the roll material after the heat treatment steps of Example 1 is shown in Figure 1.

[0055] Examples 2-5

[0056] The specific implementation of Examples 2-5 is the same as that of Example 1, except that the mass percentage of the chemical element components in the roll material is different, as shown in Table 1.

[0057] Table 1 Composition of Examples 1-5 (wt%)

[0058] Comparative Example 1

[0059] The first aspect of the present example provides a roll material, the chemical element components in the roll material are as follows in terms of mass percentage: 2.8% C, 0.7% Si, 0.6% Mn, 1.6% Cr, 1.0% Ni, 0.2% Mo, 1.5% V, the balance of Fe and unavoidable impurities.

[0060] The second aspect of the present example provides a heat treatment process for a roll material, which comprises the following steps: softening annealing the cast roll at 1000°C, then quenching at 960°C, tempering at 500°C, and air cooling to room temperature 25°C after discharging.

[0061] Performance test

[0062] I. Mechanical property test

[0063] Test object: the mechanical properties at room temperature (25 DEG C) and high temperature (test temperature: 600 DEG C) of the roll materials of examples 1-5, wherein the mechanical properties at room temperature refer to: GB / T228.1-2021; the high temperature mechanical properties refer to: GB / T228.2-2015, and the test results are shown in table 2.

[0064] Table 2 mechanical property test results table

[0065] According to the table 1 and table 2, the tensile strength R m of the new material roll in examples 1-5 is 600-650 MPa, the impact energy A KU2 is 3.6-5.0 J, the hardness HSD is 52-55; at 600 DEG C, the tensile strength is 510-548 MPa, and the hardness HSD is 51-55.

[0066] II. Mechanical property test

[0067] Test object: the roll described in examples 1 and comparative example 1, and the test results are shown in table 3.

[0068] Table 3 single machine average rolling amount comparison table

[0069] The test method or test standard of single machine average rolling amount: for conventional rolls, according to the use experience, there is a fixed rolling tonnage in the rolling procedure, and the rolling tonnage is changed to the roll.

[0070] The new material roll carried out in the application can be continuously used until the roll surface defects appear and the roll is changed, and at this time, the rolling tonnage is counted, that is, the single machine rolling tonnage of the new material roll.

[0071] The application adopts a new material and a heat treatment process to prepare a new material high-performance roll material, which has excellent strength and toughness, wear resistance and heat cracking resistance, solves the problems of short service life and frequent peeling of the raw material roll, improves the production efficiency, reduces the production cost, and has good popularization and application prospect.

Claims

1. A material for a high-speed wire pre-roughing mill roll characterized by comprising, The chemical composition of the roller material comprises, in percentage by mass: 2.6-3.6% C, 1.3-2.0% Si, 0.5-0.8% Mn, 1.5-3.0% Cr, 1.0-2.5% Ni, 0.2-0.8% Mo, 1.5-3.2% V, 0.5-1.0% W, 0.12-0.25% Nb, the balance of Fe and inevitable impurities; the mass percentage of V, Mo and W satisfies: V+Mo+W / 2=1.9-4.5%.

2. The process for heat treatment of the material of the roll for preventing spalling in a high-speed wire rod prefinishing mill train according to claim 1, characterized in that, The heat treatment process of the roller material comprises: an annealing step and a quenching and tempering step; The quenching and tempering step comprises: S1, first temperature rising and holding; S2, second temperature rising and holding; S3, third temperature rising and holding; S4, spray quenching; S5, high-temperature tempering.

3. The heat treatment process for the material of the striping roller of the high-speed wire rod pre-finishing mill train according to claim 2, characterized in that, The annealing step comprises: After casting, the roller material is cooled to a temperature of 930-950℃, and then is subjected to in-furnace holding annealing treatment for 3-4h, after which the heating is stopped, and the roller material is in-furnace slowly cooled to 600℃, and is air-cooled to room temperature after being discharged from the furnace.

4. The heat treatment process for the material of the striping roller of the high-speed wire rod pre-finishing mill train according to claim 2, characterized in that, The first temperature rising and holding comprises: The roller material subjected to the annealing step is heated at a temperature rising speed of 180-200℃ / h, and is subjected to temperature holding for 10-12min at 700℃.

5. The heat treatment process for the material of the striping roller of the high-speed wire rod pre-finishing mill train according to claim 2, characterized in that, The second temperature rising and holding comprises: On the basis of S1, the roller material is continuously heated at a temperature rising speed of 180-200℃ / h, and is subjected to temperature holding for 10-12min at 900℃.

6. The heat treatment process for the material of the striping roller of the high-speed wire rod pre-finishing mill train according to claim 2, characterized in that, The third temperature rising and holding comprises: On the basis of S2, the roller material is heated to 980-1100℃, and is held for 30-40min, and is quenched after being discharged from the furnace.

7. The heat treatment process for the material of the striping roller of the high-speed wire rod pre-finishing mill train according to claim 2, characterized in that, The spray quenching comprises: On the basis of S3, the roller material is cooled at a cooling speed of 2-4℃ / s by means of the spray flow of a spray cooling device; after 245-550s, air is blown to the roller body, the highest temperature of the air blowing stage is 340-350℃, and the roller temperature is 150-170℃, the air blowing is stopped and the roller body is air-cooled to a stable temperature of 150-170℃. The high-temperature tempering in S5 comprises:

8. The heat treatment process for the material of the strip mill's anti-flaking roll according to claim 2, characterized in that, A tempering furnace is preheated to 100-150℃, and then on the basis of S4, the roller material is heated in the tempering furnace at a temperature rising speed of 180-200℃ / h, and is heated to 480-600℃, and is held for 90-120min; the roller material is in-furnace cooled to 150℃, and is air-cooled to room temperature after being discharged from the furnace; the high-temperature tempering is repeated for 2-3 times. ​

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