A method for preparing a high compressive strength and high wear-resistant roughing vertical roll applicable to hot-rolled strip steel

Abstract

The present invention provides a method for preparing a high compressive strength and high wear-resistant roughing vertical roll applicable to hot-rolled strip steel, and strengthens the working surface of the alloy cast steel vertical roll by surfacing; the chemical composition and its weight percentage of the working surface of the roughing vertical roll after surfacing are as follows: C: 0.13% - 0.15%, Mn: 1.40% - 1.45%, Cr: 13.15% - 13.35%, Mo: 1.10% - 1.16%, Ni: 1.12% - 1.19%, V: 0.30% - 0.41%, W: 0.09% - 0.10%, and the rest is iron and inevitable impurities; the hardness of the working surface of the roughing vertical roll after surfacing is 53HSD - 56HSD. By adjusting the wire composition, welding method and heat treatment process, the present invention significantly improves the hardness, wear resistance and thermal crack resistance of the working surface of the vertical roll after surfacing, extends the rolling cycle by more than 225%, significantly increases the steel passing amount, has high wear resistance on the roll surface, ensures the wear degree of the welded layer and the quality of the strip steel edge, and effectively controls defects such as burrs, fine cracks, scale peeling and scratches on the strip steel edge.

Description

Technical Field

[0001] The present invention relates to the technical field of steel rolling, in particular to a method for preparing a high-pressure and wear-resistant rough rolling vertical roller suitable for hot-rolled strip steel. Background Art

[0002] During the rough rolling process of continuously cast slabs in hot-rolled strip production lines, vertical rollers are essential to control the strip width and ensure the flatness of the slab's sides. Vertical rollers are installed in pairs, with the slab passing between them. Both sides of the slab come into contact with the vertical rollers, where they are rolled to the desired width. In hot-rolling production, roughing vertical rollers must simultaneously meet three production requirements: stable rolling, width adjustment and precision control, and guaranteed surface quality.

[0003] The roughing rolls in a 1250mm hot rolling line are typically made of alloy cast steel. The main components, by weight, are: C: 0.55%-0.65%, Si: 0.25%-0.45%, Mn: 0.80%-1.00%, S≤0.020%, P≤0.025%, Cr: 0.80%-1.20%, and Mo: 0.20%-0.40%. The low Cr content in these roughing rolls results in poor overall wear resistance and insufficient thermal fatigue resistance. At the end of rolling, roll surface buildup, scarring, chipping, and severe wear are common. Defects such as burrs, fine cracks, warping, and scratches often appear on the strip edges, severely impacting the surface quality of the billet. Furthermore, because the billet often requires significant lateral pressure from the rolls during rolling, the rolls' hardness and wear resistance are key factors limiting their service life. Existing alloy cast steel rolls have a short service life, require frequent replacement, and are costly. Therefore, how to improve the hardness and wear resistance of the working surface of the rough rolling vertical roller to improve the rolling effect and extend the service life has become a major problem that needs to be solved urgently.

[0004] Currently, one approach to addressing this issue is to increase the Cr content in the vertical rolls. For example, Chinese Patent 200810203737.8 discloses a high-chromium cast iron vertical roll for a rolling mill stand. By increasing the C and Cr content in the vertical rolls, chromium and carbon form chromium-containing carbides, resulting in M7C3 carbides with high microhardness, thereby improving the wear resistance and thermal cracking resistance of the vertical roll surface. However, the excessive hardness of these vertical rolls makes them generally only suitable for finishing rolling and not for roughing rolling. Furthermore, the large number of scrapped roughing vertical rolls that are replaced within the mill presents a disposal challenge. The working surfaces of these roughing vertical rolls are often severely worn, with the cores even exposed. Therefore, reusing these scrapped roughing vertical rolls has become a research and development priority for steel companies. Summary of the Invention

[0005] To solve the above problems existing in the prior art, the purpose of the present invention is to provide a method for preparing a high-compression and high-wear-resistant roughing vertical roll applicable to hot-rolled strip steel.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a high-compression and high-wear-resistant roughing vertical roll applicable to hot-rolled strip steel, which is to strengthen the working surface of the alloy cast steel vertical roll by surfacing; the chemical composition and its weight percentage of the working surface of the roughing vertical roll after surfacing are as follows: C: 0.13% - 0.15%, Mn: 1.40% - 1.45%, Cr: 13.15% - 13.35%, Mo: 1.10% - 1.16%, Ni: 1.12% - 1.19%, V: 0.30% - 0.41%, W: 0.09% - 0.10%, and the rest is iron and inevitable impurities; the hardness of the working surface of the roughing vertical roll after surfacing is 53HSD - 56HSD.

[0008] The chemical composition of the alloy cast steel vertical roll includes: C: 0.55% - 0.65%, Si: 0.25% - 0.45%, Mn: 0.80% - 1.00%, S ≤ 0.020%, P ≤ 0.025%, Cr: 0.80% - 1.20%, Mo: 0.20% - 0.40%, and the rest is iron and inevitable impurities.

[0009] The surfacing process of the working surface of the alloy cast steel vertical roll includes the following steps:

[0010] S1. Preheating the working surface

[0011] Send the working surface of the vertical roll into a heating furnace for preheating, with the preheating temperature of 290°C - 330°C and the preheating holding time of 23h - 25h;

[0012] S2. Surfacing

[0013] Perform high-temperature surfacing on the preheated working surface of the vertical roll, using a combination of backing and capping. First, deposit a backing weld layer on the working surface of the vertical roll, and then deposit a capping weld layer on the backing weld layer; the thickness of the backing weld layer is 8mm - 13mm, and the thickness of the capping weld layer is 28mm - 35mm;

[0014] S3. Post-weld heat treatment

[0015] After surfacing, perform tempering at 520°C for 18h, slow cooling in the furnace, with the cooling rate ≤ 50°C / h, and take it out of the furnace for air cooling when the temperature drops to 60°C, thus obtaining a high-compression and high-wear-resistant roughing vertical roll.

[0016] In step S2, the compositions of the backing wire and the capping wire are different; the chemical composition and weight percentage content of the backing wire are: W C= 0.05%, W Mn = 1.0%, W Cr = 2.5%, W Mo = 0.7%, W Ni = 0.5%, the balance being iron and unavoidable impurities; the chemical composition of the capping welding wire and its weight percentage are: W C = 0.1%, W Mn = 1.2%, W Cr = 13.1%, W Mo = 0.7%, W Ni = 0.4%, W W = 0.1%, W V = 0.25%, the balance being iron and unavoidable impurities.

[0017] The hardness of the backing welding wire is 2 HSD - 4 HSD higher than that of the base material, and the hardness of the capping welding wire is 3 HSD - 5 HSD higher than that of the backing welding wire.

[0018] The deposition rate of the backing welding wire is controlled at 4.7 kg / h, and the deposition rate of the capping welding wire is controlled at 4.5 kg / h.

[0019] In the step S3, the surfacing welding method is uphill welding, the bead overlap is 60% - 70%, the current is 330 - 400 A, and the surfacing temperature is 270°C - 350°C.

[0020] In the step S3, multi-layer welding is used during surfacing, and the single-layer thickness of the weld layer is 2.0 mm - 2.2 mm.

[0021] Intermediate heat treatment is carried out once every two layers of surfacing. The intermediate heat treatment adopts stress relief treatment by tempering at 520°C × 16 h, and welding is continued after detecting the hardness of the weld layer.

[0022] Due to the adoption of the above technical solution, the technical progress achieved by the present invention is:

[0023] The present invention provides a method for preparing a high compressive strength and high wear-resistant roughing vertical roll applicable to hot-rolled strip steel. Surfacing is used to strengthen the working surface of a conventional alloy cast steel vertical roll. By adjusting the wire composition, welding method and heat treatment process, the hardness, wear resistance and thermal crack resistance of the working surface of the vertical roll after surfacing are significantly improved. The roll surface is not prone to tumor formation and wear, and the rolling cycle is effectively extended. According to on-site production practice, the high compressive strength and high wear-resistant roughing vertical roll of the present invention has good use effect, the rolling cycle is extended by more than 225%, the steel passing amount is significantly increased, the roll surface has high wear resistance, the wear degree of the weld layer and the quality of the strip steel edge are ensured, and defects such as burrs, fine cracks, peeling and scratches on the strip steel edge are effectively controlled. [[ID=$$]]

[0024] The present invention can not only strengthen the working surface of a brand-new conventional alloy cast steel vertical roll, endowing it with good hardness and wear resistance and improving its service life, but also re-reinforce the severely worn working surface of a waste alloy cast steel vertical roll, enabling it to be reused, which is environmentally friendly.

[0025] During surfacing of the present invention, a welding method combining backing welding and capping welding is adopted, and backing welding wires and capping welding wires with specific components and specific hardness are used. The hardness of the base material, backing welding wire, and capping welding wire increases gradually, enabling stable bonding between the weld layer and the base material and achieving good comprehensive performance.

[0026] The welding consumables of the present invention are selected from the Cr13-based stainless steel series, which belongs to martensitic heat-resistant steel. Appropriate amounts of Ni, Mo, V, and W are added on the basis of Cr13-based stainless steel to promote the transformation of martensite, refine grains, and improve welding performance. The metallographic structure of the rough rolling vertical roll after welding is martensite + ferrite, improving the toughness and plasticity of the weld layer structure. The carbon content is reasonably controlled, and the carbon content of the surfacing working surface is controlled within a relatively low range of 0.13% - 0.15%. It has both high hardness and good resistance to thermal and cold fatigue; an appropriate amount of Ni element is added for toughening treatment to improve the toughness of the surfacing working surface; an appropriate amount of W element is added, and W combines with C to form WC, which rapidly increases the hardness of the surfacing working surface and enhances wear resistance; a certain amount of V is added, and V combines with C to form VC. VC exists in the form of fine particles, inhibiting the movement of grain boundaries and the growth of grains, being not easily deformed and cracked, and also having the effect of inhibiting grain growth at high temperatures. The dispersed vanadium carbide can significantly increase the hardness and wear resistance of the surfacing layer and improve the crack resistance of the weld layer, playing a role of dispersion strengthening; during the process of stress relief by high-temperature tempering, various alloy carbides such as WC, VC, Mo2C, and Cr7C3 are precipitated, controlling the hardness of the final surfacing working surface within a reasonable range of 53HSD - 56HSD. This not only improves the wear resistance of the working surface, reduces wear, but also lowers the processing difficulty and improves the processing quality, with excellent comprehensive performance.

[0027] During surfacing of the present invention, an appropriate surfacing temperature is adopted, which can promote the complete transformation of martensite, refine grains, improve welding performance, and at the same time improve the uniformity of the structure, further enhancing the mechanical properties of the surfacing rough rolling vertical roll, endowing it with stronger oxidation resistance, wear resistance, and the toughness and plasticity of the weld layer structure. At the same time, the present invention adopts a form combining multiple intermediate heat treatments and post-weld heat treatment to further relax the welding residual stress, stabilize the shape and size of the structure, and reduce distortion; improve the performance of the base material and welding joint, including improving the plasticity of the weld metal, reducing the hardness of the heat-affected zone, increasing the fracture toughness, improving the fatigue strength, restoring or increasing the yield strength, and enhancing the ability to resist stress corrosion. It can further release harmful gases in the weld metal, especially hydrogen, prevent the occurrence of delayed cracks, and completely eliminate the residual stress during the surfacing process. Brief Description of the Drawings

[0028] Figure 1 This is a schematic structural view of the roughing vertical roll of the present invention;

[0029] In the figure, 1 - vertical roll body, 2 - working surface of the vertical roll, 3 - backing weld layer, 4 - capping weld layer. Embodiment

[0030] The present invention will be described in detail below.

[0031] A method for preparing a high - compressive - strength and high - wear - resistant roughing vertical roll applicable to hot - rolled strip steel is to strengthen the working surface of an alloy cast steel vertical roll by surfacing. The chemical composition and its weight percentage of the alloy cast steel vertical roll are as follows: C: 0.55% - 0.65%, Si: 0.25% - 0.45%, Mn: 0.80% - 1.00%, S ≤ 0.020%, P ≤ 0.025%, Cr: 0.80% - 1.20%, Mo: 0.20% - 0.40%, and the rest is iron and inevitable impurities.

[0032] The chemical composition and its weight percentage of the working surface of the roughing vertical roll after surfacing are as follows: C: 0.13% - 0.15%, Mn: 1.40% - 1.45%, Cr: 13.15% - 13.35%, Mo: 1.10% - 1.16%, Ni: 1.12% - 1.19%, V: 0.30% - 0.41%, W: 0.09% - 0.10%, and the rest is iron and inevitable impurities.

[0033] The hardness of the working surface of the roughing vertical roll after surfacing is 53HSD - 56HSD.

[0034] The surfacing process of the working surface of the alloy cast steel vertical roll includes the following steps:

[0035] S1. Pre - heating of the working surface

[0036] Feed the working surface of the vertical roll into a heating furnace for pre - heating. The pre - heating temperature is 290°C - 330°C, and the pre - heating holding time is 23h - 25h;

[0037] S2. Surfacing

[0038] Perform high - temperature surfacing on the pre - heated working surface of the vertical roll. Adopt a combination of backing and capping. First, deposit a backing weld layer on the working surface of the vertical roll, and then deposit a capping weld layer on the backing weld layer; the thickness of the backing weld layer is 8mm - 13mm, and the thickness of the capping weld layer is 28mm - 35mm.

[0039] S3. Post - weld heat treatment

[0040] After surfacing, temper at 520°C for 18 h, cool slowly in the furnace, with a cooling rate ≤ 50°C / h. When the temperature drops to 60°C, take it out of the furnace and air-cool to obtain a high compressive strength and wear-resistant rough rolling vertical roll.

[0041] In the said step S1,

[0042] The heating-up time of the vertical roll in the heating furnace is 3 h to 3.5 h, preferably 3 h, and then it enters the preheating and heat-preserving stage. By limiting the heating-up speed and the preheating and heat-preserving time, it is ensured that the working surface of the vertical roll is fully and comprehensively preheated.

[0043] In the said step S2,

[0044] The chemical compositions and hardness of the backing wire and the capping wire are different. Specifically,

[0045] The chemical composition and weight percentage of the said backing wire are: W C = 0.05%, W Mn = 1.0%, W Cr = 2.5%, W Mo = 0.7%, W Ni = 0.5%, and the rest is iron and inevitable impurities. The chemical composition and weight percentage of the said capping wire are: W C = 0.1%, W Mn = 1.2%, W Cr = 13.1%, W Mo = 0.7%, W Ni = 0.4%, W W = 0.1%, W V = 0.25%, and the rest is iron and inevitable impurities.

[0046] The hardness of the said backing wire is 2 HSD to 4 HSD higher than that of the base material, and the hardness of the said capping wire is 3 HSD to 5 HSD higher than that of the backing wire. Due to the gradual increase in the hardness of the wire, it is ensured that the welded surface is firmly bonded to the base material, providing the hardness and wear resistance of the working surface.

[0047] When strengthening the working surface of a new vertical roll, the hardness of the said base material is the hardness of the working surface of the vertical roll; but when refurbishing a used vertical roll, in order to ensure the hardness of the welded layer, generally the worn and peeled working surface is stripped, and surfacing is directly carried out on the roll core. At this time, the hardness of the said base material is the hardness of the roll core of the used vertical roll.

[0048] During welding, dilution rate = (melting area of base material / area of entire molten pool) * 100. The deposition rate of the backing wire is controlled at 4.7 kg / h, and the deposition rate of the capping wire is controlled at 4.5 kg / h. If the cladding speed is too slow, it is easy to cause the local temperature of the weld layer to be too high, resulting in burn-through of the weld layer and too many weld beads; if the cladding speed is too fast, it is easy to cause defects such as lack of fusion and inclusion of flux, resulting in a decrease in strength and a reduction in welding performance, affecting the reduction of the strength value. Therefore, the present invention defines a specific cladding speed based on the wire with specific components, ensuring the welding effect to the greatest extent.

[0049] The surfacing welding method uses uphill welding, the bead overlap is 60% - 70%, the current is 330 A - 400 A, and the surfacing temperature is 270 °C - 350 °C, preferably 320 °C.

[0050] Multi-layer welding is used during surfacing. The single-layer thickness of the weld layer is 2.0 mm - 2.2 mm. The total number of layers of the backing weld layer and the capping weld layer is 9 - 11 layers, that is, the total thickness on one side is 18 mm - 24.2 mm, and the total diameter thickness is twice the total thickness on one side, that is, 36 mm - 48.4 mm. Generally, the total number of layers of the backing weld layer is 2 - 3 layers, and the total number of layers of the capping weld layer is 7 - 8 layers.

[0051] During the surfacing process, to ensure the quality of the welding surface, intermediate heat treatment is carried out every two layers of surfacing (the thickness on one side is about 4.0 mm - 4.4 mm); the intermediate heat treatment uses tempering at 520 °C for 16 h to eliminate stress, and after detecting the hardness of the weld layer, welding continues.

[0052] Through the surfacing method, the present invention clads an alloy material with certain service performance on the surface of the roll body base material by means of a certain heat source, and improves the hardness and wear resistance of the new roll material through alloying and other means, extending the service life of the new roll. During the surfacing process, the welding method and the composition of the wire have a direct impact on the hardness and wear resistance of the weld layer. After long-term and multiple R & D, the present invention finally determines the wire composition, and by means of increasing hardness, adopts a welding method combining backing and capping, achieving better comprehensive performance, and controlling the carbon content of the surfacing working surface within a lower range of 0.13% - 0.15%, having both high hardness and good resistance to thermal and cold fatigue.

[0053] An appropriate amount of Ni element is added to the wire for toughening treatment, improving the toughness of the surfacing working surface, making the hardness of the surfacing working surface in the as-welded state above 47 HSD. During the process of stress relief by high-temperature tempering, various alloy carbides such as VC, Mo2C, and Cr7C3 are precipitated, playing a role of dispersion strengthening, and obtaining a surfacing working surface with excellent comprehensive performance and a hardness of 53 HSD - 56 HSD.

[0054] The present invention will be further described in detail below in combination with examples and comparative examples. Example

[0055] A method for preparing a high-pressure and wear-resistant rough rolling vertical roller suitable for hot-rolled strip steel is to strengthen the working surface of the alloy cast steel vertical roller by surfacing welding.

[0056] The chemical composition of the alloy cast steel roughing rolls is as follows by weight: C: 0.55%, Mn: 0.95%, Si: 0.40%, P: ≤ 0.025%, S: ≤ 0.020%, Cr: 1.20%, Mo: 0.25%, with the remainder being iron and unavoidable impurities. The hardness of the alloy cast steel roughing rolls is 46-48 HSD.

[0057] The surfacing process of the alloy cast steel vertical roller working surface comprises the following steps:

[0058] S1. Preheating of working surface

[0059] Send the working surface of the vertical roller into the heating furnace for preheating, the preheating temperature is 290℃~330℃, the preheating time is 3h, and the preheating holding time is 24h;

[0060] S2, surfacing

[0061] After preheating, high-temperature surfacing welding is performed on the working surface of the vertical roller. First, a 10mm thick base weld layer is applied, followed by a 20mm thick cover weld layer. Uphill welding is used, with a weld overlap of 60% to 70%, a current of 330A to 400A, and a temperature of 300°C. After every two layers (approximately 4.0mm to 4.4mm thick on one side), an intermediate heat treatment is performed, using an intermediate tempering treatment at 520°C for 16 hours to relieve stress. The weld layer hardness is then tested before continuing with welding.

[0062] Base welding wire composition W C =0.05%, W Mn = 1.0%, W Cr =2.5%, W Mo =0.7%, W Ni =0.5%, the rest is iron and unavoidable impurities. The hardness of the rooting wire is 48HSD~52HSD, and the deposition rate is 4.7kg / h.

[0063] Cover welding wire composition W C =0.1%, W Mn =1.2%, W Cr =13.1%, W Mo =0.7%, W Ni = 0.4%, W W =0.1%, W V= 0.25%, and the rest is iron and inevitable impurities. The hardness of the capping wire is 51HSD - 57HSD, and the deposition rate is 4.5 kg / h.

[0064] S3. Post-weld heat treatment

[0065] After surfacing, tempering is carried out at 520 °C for 18 h, followed by slow cooling in the furnace, with a cooling rate ≤ 50 °C / h. The furnace is unloaded and air-cooled when the temperature drops to 60 °C, thus obtaining the high compressive strength and wear-resistant rough rolling vertical roll.

[0066] The composition and hardness of the working surface of the obtained high compressive strength and wear-resistant rough rolling vertical roll are detected; after detection, the chemical composition weight percentages of the surfacing layer on the working surface of the rough rolling vertical roll are as follows: C: 0.14%, Mn: 1.45%, Cr: 13.35%, Mo: 1.16%, Ni: 1.19%, V: 0.41%, W: 0.10%, and the rest is iron and inevitable impurities.

[0067] Take the high compressive strength and wear-resistant rough rolling vertical roll after surfacing and the alloy cast steel vertical roll without surfacing, and respectively measure their hardness, metallographic structure, rolling cycle and the amount of steel passing through the cycle, and observe the surface conditions of the working surface of the vertical roll after rough rolling and the surface conditions of the strip steel. See the following table for details.

[0068] Example 2

[0069] A method for preparing a high compressive strength and wear-resistant rough rolling vertical roll applicable to hot-rolled strip steel is to strengthen the working surface of the alloy cast steel vertical roll by surfacing.

[0070] The chemical composition weight percentages of the alloy cast steel rough rolling vertical roll are as follows: C: 0.60%, Mn: 0.85%, Si: 0.35%, P ≤ 0.025%, S ≤ 0.020%, Cr: 1.10%, Mo: 0.30%, and the rest is iron and inevitable impurities. The hardness of the alloy cast steel rough rolling vertical roll is 46HSD - 48HSD.

[0071] The surfacing process of the working surface of the alloy cast steel vertical roll includes the following steps:

[0072] S1. Preheating of the working surface

[0073] Send the working surface of the vertical roll into the heating furnace for preheating. The preheating temperature is 280 °C - 310 °C, the preheating temperature rising time is 3 h, and the preheating holding time is 24 h;

[0074] S2. Surfacing

[0075] Perform high-temperature surfacing on the preheated working surface of the vertical roll. First, build a backing surfacing layer of 10 mm on the working surface of the vertical roll, and then build a capping surfacing layer of 20 mm on the backing surfacing layer. The surfacing is carried out with uphill welding, the bead overlap is 60% - 70%, the current is 330 A - 400 A, and the surfacing temperature is 300 °C. Conduct an intermediate heat treatment every two layers of surfacing (the unilateral thickness is about 4.0 mm - 4.4 mm), and carry out stress relief treatment by intermediate tempering at 520 °C × 16 h. After detecting the hardness of the surfacing layer, continue welding.

[0076] Composition of the backing welding wire W C = 0.05%, W Mn = 1.0%, W Cr = 2.5%, W Mo = 0.7%, W Ni = 0.5%, and the rest is iron and inevitable impurities. The hardness of the backing welding wire is 48 HSD - 52 HSD, and the deposition rate is 4.7 kg / h.

[0077] Composition of the capping welding wire W C = 0.1%, W Mn = 1.2%, W Cr = 13.1%, W Mo = 0.7%, W Ni = 0.4%, W W = 0.1%, W V = 0.25%, and the rest is iron and inevitable impurities. The hardness of the capping welding wire is 51 HSD - 57 HSD, and the deposition rate is 4.5 kg / h.

[0078] S3. Post-weld heat treatment

[0079] After the surfacing is completed, carry out tempering at 520 °C × 18 h, cool slowly in the furnace, the cooling rate ≤ 50 °C / h, and take it out of the furnace for air cooling when the temperature drops to 60 °C, then the high compressive strength and wear-resistant rough rolling vertical roll can be obtained.

[0080] Detect the composition and hardness of the working surface of the obtained high compressive strength and wear-resistant rough rolling vertical roll; after detection, the chemical composition weight percentages of the surfacing layer on the working surface of the rough rolling vertical roll are as follows: C: 0.13%, Mn: 1.42%, Cr: 13.17%, Mo: 1.12%, Ni: 1.15%, V: 0.35%, W: 0.09%, and the rest is iron and inevitable impurities.

[0081] Take the high compressive strength and wear-resistant rough rolling vertical roll after surfacing and the alloy cast steel vertical roll without surfacing, and measure the hardness, metallographic structure, rolling cycle and passing steel amount per cycle, and observe the surface conditions of the working surface of the vertical roll after rough rolling and the strip steel, as shown in the following table. From the comparison of the data in the above two embodiments, it can be seen that the roll surface hardness of the existing conventional alloy cast steel roughing vertical rolls is relatively low, the rolling cycle is short, only 10 - 12 days, the steel passing capacity is small, and defects are prone to appear on the roll surface of the vertical roll and the strip edge after taking off the machine. After surfacing strengthening, the strength of the working surface of the vertical roll is significantly improved, with strong wear resistance and thermal crack resistance, and the strip edge quality is good. The rolling cycle is increased to 39 - 44 days, which is 2.25 - 3 times that of the roughing vertical roll before surfacing; the steel passing capacity is increased to 313,000 - 347,000 tons, which is 1.85 - 3.34 times that of the roughing vertical roll before surfacing. The improvement effect is very obvious, fully meeting the use requirements of the existing rolling line.

[0082] The effects of the present invention will be further described below through comparative examples.

[0083] Comparative Examples 1 - 2 are the comparative examples of Example 1, used to compare the influence of surfacing temperature on the quality of the surfacing working surface.

[0084] Comparative Example 1

[0085] The difference between this comparative example and Example 1 is that the surfacing temperature is 250 °C, and the types of the remaining raw materials, control parameters, and heat treatment parameters are the same as those in Example 1.

[0086] The roughing vertical roll of this comparative example is taken for testing. The chemical composition weight percentages of the surfacing layer on the working surface of the roughing vertical roll are as follows: C: 0.13%, Mn: 1.42%, Cr: 13.15%, Mo: 1.12%, Ni: 1.15%, V: 0.35%, W: 0.09%, and the rest are iron and inevitable impurities. The hardness of the surfacing layer on the working surface of the roughing vertical roll is 48.2 HSD - 50.6 HSD.

[0087] The metallographic structure of the working surface of the prepared high compressive strength and wear-resistant roughing vertical roll is tested, which is tempered martensite + retained austenite + ferrite, and the structure is uneven.

[0088] The high compressive strength and wear-resistant roughing vertical roll is used for rough rolling of steel billets. The rolling cycle is 23 days, and the steel passing capacity per cycle is 226,000 tons. The working surface of the vertical roll after rough rolling: the upper part is flat, the lower part is severely worn, without tumor formation, but there are obvious cracks; the surface of the strip after rough rolling: smooth without defects; the edge of the strip after rough rolling: smooth without defects. Although the rolling cycle and steel passing capacity of the roughing vertical roll in Comparative Example 1 have been improved compared with those of the alloy cast steel vertical roll, its hardness is still relatively soft, and the uneven structure leads to poor wear resistance.

[0089] Comparative Example 2

[0090] The difference between this comparative example and Example 1 is that the surfacing temperature is 380 °C, and the types of the remaining raw materials, control parameters, and heat treatment parameters are the same as those in Example 1.

[0091] The surfacing layer of the roughing vertical roll in this comparative example was tested, and the chemical composition weight percentages of the surfacing layer on the working surface of the roughing vertical roll were as follows: C: 0.15%, Mn: 1.44%, Cr: 13.20%, Mo: 1.10%, Ni: 1.13%, V: 0.33%, W: 0.09%. The hardness of the surfacing layer on the working surface of the roughing vertical roll was 49.1 HSD - 50.8 HSD.

[0092] The metallographic structure of the working surface of the prepared high compressive strength and wear-resistant roughing vertical roll was tested, and it was tempered martensite + pearlite + carbide particles, with coarse grains.

[0093] This high compressive strength and wear-resistant roughing vertical roll was used for billet roughing. The rolling cycle was 19 days, and the steel passing volume in the cycle was 192,000 tons. On the working surface of the vertical roll after roughing: there were pits caused by impacts on the surface, and defects such as carbide particle shedding and looseness; on the surface of the strip after roughing: it was smooth without defects; on the edge of the strip after roughing: there were slight burr defects.

[0094] It can be seen from Comparative Example 1 and Comparative Example 2 that the surfacing temperature directly affects the hardness and wear resistance of the weld surface. When the surfacing temperature is lower than 270 °C, the martensite transformation is incomplete, the grain distribution is uneven, and the metallographic structure is mainly tempered martensite + retained austenite + ferrite, resulting in poor thermal crack resistance of the surfacing working surface; when the surfacing temperature is higher than 350 °C, the metallographic structure is mainly tempered martensite + pearlite + carbide particles, with coarse grains, resulting in poor mechanical properties of the surfacing working surface.

[0095] Comparative Example 3

[0096] This comparative example is the comparative example of Example 1. The difference between this comparative example and Example 1 is that the intermediate heat treatment step was cancelled during the surfacing process, and only the post-weld heat treatment step was retained; the types of other raw materials, control parameters, and heat treatment parameters were the same as those in Example 1.

[0097] The roughing vertical roll in this comparative example was tested. The chemical composition weight percentages of the surfacing layer on the working surface of the roughing vertical roll were as follows: C: 0.15%, Mn: 1.45%, Cr: 13.30%, Mo: 1.11%, Ni: 1.17%, V: 0.40%, W: 0.10%. The hardness of the surfacing layer on the working surface of the roughing vertical roll was 50.7 HSD - 54.1 HSD.

[0098] The metallographic structure of the working surface of the prepared high compressive strength and wear-resistant roughing vertical roll was tested, and it was tempered martensite + ferrite + dispersed carbides.

[0099] The high-pressure and wear-resistant roughing vertical roll is used for billet roughing. The rolling cycle is 15 days, and the steel passing volume in one cycle is 155,000 tons. After roughing, the working surface of the vertical roll: there are tumors and severe cracks. Through eddy current flaw detection, the crack depth penetrates the entire cover layer weld, detaching from the backing wire. As the rolling cycle extends, the cracks gradually expand and extend; the surface of the strip after roughing: is smooth and defect-free; the edge of the strip after roughing: has scratching and rubbing defects.

[0100] It can be seen from Comparative Example 3 that if intermediate heat treatment is not carried out during the surfacing process, there are still residual stresses in the weld surface that have not been eliminated, which will affect the connection strength between the weld layers, and then reduce the hardness and wear resistance of the weld surface; during roughing, tumors and cracks are likely to occur, and the steel passing volume is small. In Example 1, intermediate heat treatment is carried out multiple times during the surfacing process, which can timely eliminate the residual stresses during the surfacing process, enhance the connection tightness and strength between the weld layers, and effectively improve the strength and hardness of the weld surface; the working surface of the roughing roll has high hardness, is not easy to form tumors and deform, and has a large steel passing volume.

[0101] Comparative Examples 4 to 6 are comparative examples of Example 1, used to compare the influence of the wire rod composition on the quality of the surfacing working surface.

[0102] Comparative Example 4

[0103] The difference between this comparative example and Example 1 is that a single-wire acidic slag system flux-cored wire is used for surfacing, the powder filling coefficient is 13% - 16%, mainly rutile with a TiO2 content of more than 92% is selected, accounting for 35% - 55% of the powder weight, and iron powder accounts for 15% - 30% of the powder weight. An appropriate amount of SiO2, ZrO2, Al2O3, and MgO are added to form an appropriate molten slag, specifically a flux-cored submerged arc wire with extremely low carbon, chromium, manganese, and molybdenum; the types of other raw materials, control parameters, and heat treatment parameters are the same as those in Example 1.

[0104] Comparative Example 5

[0105] The difference between this comparative example and Example 1 is that a single-wire basic flux-cored wire is used for surfacing, specifically: the powder filling coefficient is 24% - 28%, and mainly CaF, CaCO3, part of SiO2 or an appropriate amount of TiO2 is selected as the basic slag system. The types of other raw materials, control parameters, and heat treatment parameters are the same as those in Example 1.

[0106] After testing, the hardness of the surfacing working surface of Comparative Example 4 is 32 HSD. The main characteristics of this slag system welding wire are stable arc, small spatter, and easy slag removal. The fine-diameter flux-cored wire is suitable for all-position welding. However, the slag itself has a relatively large oxidation property, and the low-temperature toughness of the weld metal is relatively low. It is generally used for the welding of carbon steel and some low-alloy steels; the hardness of the surfacing working surface of Comparative Example 5 is 56.2 HSD. The hardness of the surfacing working surface of Comparative Example 4 is too low, with poor wear resistance, an increase in the roll change time during shutdown, and the roll surface is easily worn into an irregular surface, which is prone to sticking steel and affecting the quality of the slab; the hardness of the surfacing working surface of Comparative Example 5 is too high, the weld has excellent low-temperature toughness, the difficulty of hole profiling and repair increases, and there is a phenomenon of chipping under the rolling force. It can be seen that too high or too low hardness is not conducive to the working performance of the roughing vertical roll.

[0107] Comparative Example 6

[0108] The difference between this comparative example and Example 1 is that a single type of welding wire is used for surfacing, specifically a flux-cored submerged arc welding wire of Cr13 stainless steel with high manganese, low nickel, low molybdenum, and low vanadium; the types of other raw materials, control parameters, and heat treatment parameters are the same as those in Example 1.

[0109] The flux-cored submerged arc welding wire of Cr13 stainless steel has the advantages of corrosion resistance, high temperature resistance, and high tensile strength, but its weldability is relatively poor, cracks are likely to appear during welding, the structure changes from pearlite + ferrite before optimization to ferrite + austenite, and the hardness of the working surface after welding is 32 HSD - 49 HSD.

[0110] Comparative Example 7

[0111] The difference between this comparative example and Example 1 is that the wire composition is different, C: 0.10%, Mn: 2.00%, Cr: 13.75%, Mo: 0.80%, Ni: 0.50%, V: 0.20%, W: 0.08%. The roughing vertical roll of this comparative example is tested. The chemical composition weight percentages of the surfacing layer on the working surface of the roughing vertical roll are as follows, C: 0.12%, Mn: 1.52%, Cr: 13.49%, Mo: 0.81%, Ni: 0.75%, V: 0.25%, W: 0.09%. The hardness of the surfacing layer on the working surface of the roughing vertical roll is 51.4 HSD - 55.9 HSD. The other control parameters and heat treatment parameters are the same as those in Example 1.

[0112] The metallographic structure of the working surface of the prepared high compressive strength and wear-resistant roughing vertical roll is tested, and it is tempered martensite + ferrite.

[0113] The high compressive strength and wear-resistant roughing vertical roll is used for the rough rolling of steel billets. The rolling cycle is 25 days, and the steel passing amount in the cycle is 232,000 tons. On the working surface of the roughing vertical roll after rolling: there are multiple serious cracks; on the surface of the rough-rolled strip steel: it is smooth and defect-free; on the edge of the rough-rolled strip steel: there are burrs and scratch defects.

[0114] It can be seen from Comparative Example 7 that the surfacing composition directly affects the hardness and hot crack resistance of the weld surface, resulting in poor hot crack resistance of the surfacing working surface.

[0115] From the data of Example 1 and Comparative Examples 4 to 7, it can be compared that the composition of the welding wire is directly related to the welding performance and the hardness of the working surface after welding. The Ni element dissolves in liquid iron and ferrite, promotes graphitization during eutectic, and its function is equivalent to 1 / 3 Si. It can lower the austenite transformation temperature, expand the austenite region, refine and increase pearlite, improve the strength of the alloy layer, and greatly improve the wear resistance of the roll. The Cr element has a medium-strong effect in the anti-graphitization effect and can stabilize pearlite during eutectoid transformation. Chromium is an element that shrinks the γ region. When the carbon content is the same, the material with gradually increasing chromium content has better thermal fatigue performance, but when chromium is higher, it will cause carbide particles to fall off. When Mo < 0.6%, the effect of stabilizing carbides is relatively mild, and its main function is to refine pearlite and also refine graphite. When Mo > 1.0%, the strengthening effect on the roll strength is greater. The V and W elements can improve the toughness and hardness of the roll. However, the hardness of the traditional alloy cast steel roughing vertical roll is between 46 HSD and 52 HSD. Due to the low content of alloying elements such as Cr and Mo, the roll hardness is low, and the lack of alloying elements such as Ni, V, and W results in insufficient overall wear resistance of the roll, thus increasing the roll roughness.

[0116] To ensure the surfacing effect and the quality of the working surface, it is required that the compositions of the backing welding wire and the capping welding wire be uniform. Cut off the head and tail, and only keep the middle part of the wire with uniform composition for welding.

[0117] Comparative Example 8

[0118] This comparative example is a comparative example of Example 1, and the difference lies in the different surfacing methods. In this comparative example, downhill welding is used for surfacing; the types of other raw materials, control parameters, and heat treatment parameters are the same as those in Example 1.

[0119] Upon observation, after using downhill welding, tiny cracks appeared in the weld layer. After testing, this problem was caused by uneven composition, and the harmful elements phosphorus and sulfur exceeded the standard. The weld microstructure was pearlite + retained austenite + a small amount of dispersed carbides, and the hardness reached 51.7 HSD, meeting the rolling requirements. However, after turning and layer-by-layer hardness inspection, a hardness drop occurred, and the lowest hardness was 35 HSD, which was not conducive to pressure rolling.

[0120] Comparative Example 9

[0121] This comparative example is a comparative example of Example 1, and the difference lies in the different surfacing shielding atmospheres. In this comparative example, CO2 gas shielded welding is used for the welding wire, and submerged arc welding is used for the welding wire in the example; the types of other raw materials, control parameters, and heat treatment parameters are the same as those in Example 1.

[0122] After detection, the hardness of the welded working surface is 47HSD - 50HSD, which is slightly lower. There are obvious pores after slag removal. After detection and analysis, it is found that the Mn content in the outer skin of the welding wire is relatively high, and the S and P components are unqualified.

[0123] Comparative Example 10

[0124] The difference between this comparative example and Example 1 is that instead of using a backing welding wire for transition, the capping welding wire is directly surfacing welded on the surface of the substrate, and other control parameters and heat treatment parameters remain unchanged.

[0125] After observation, the working layer mainly composed of the capping welding wire cracked and was directly scrapped and unusable. Moreover, due to the hardness difference, the working surface was directly separated from the substrate. In severe cases, the entire working surface chipped, causing scrap steel accidents and roll damage.

[0126] The above are only the preferred embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims

1. A method for preparing a high compressive strength and high wear-resistant roughing vertical roll applicable to hot-rolled strip steel, characterized in that: Strengthen the working surface of the alloy cast steel vertical roll by surfacing; the chemical composition and its weight percentage of the working surface of the rough rolling vertical roll after surfacing are as follows: C: 0.13% - 0.15%, Mn: 1.40% - 1.45%, Cr: 13.15% - 13.35%, Mo: 1.10% - 1.16%, Ni: 1.12% - 1.19%, V: 0.30% - 0.41%, W: 0.09% - 0.10%, and the rest is iron and inevitable impurities; the hardness of the working surface of the rough rolling vertical roll after surfacing is 53HSD - 56HSD; The surfacing process of the working surface of the alloy cast steel vertical roll includes the following steps: S1. Preheat the working surface Send the working surface of the vertical roll into the heating furnace for preheating, with the preheating temperature of 290°C - 330°C and the preheating holding time of 23h - 25h; S2. Surfacing Conduct high-temperature surfacing on the preheated working surface of the vertical roll, using a combination of backing and capping. First, deposit a backing weld layer on the working surface of the vertical roll, and then deposit a capping weld layer on the backing weld layer; the thickness of the backing weld layer is 8mm - 13mm, and the thickness of the capping weld layer is 28mm - 35mm; S3. Post-weld heat treatment After surfacing, temper at 5,20°C for 18h, cool slowly in the furnace, with the cooling rate ≤ 50°C / h, and take it out of the furnace for air cooling when the temperature drops to 60°C, then the high-compression and high-wear-resistant rough rolling vertical roll is obtained.

2. The preparation method of a high-compression and high-wear-resistant roughing vertical roll applicable to hot-rolled strip steel according to claim 1, wherein: The chemical composition of the alloy cast steel vertical roll includes: C: 0.55% - 0.65%, Si: 0.25% - 0.45%, Mn: 0.80% - 1.00%, S ≤ 0.020%, P ≤ 0.025%, Cr: 0.80% - 1.20%, Mo: 0.20% - 0.40%, and the rest is iron and inevitable impurities.

3. A method for preparing a high compressive strength and high wear-resistant roughing vertical roll applicable to hot-rolled strip steel according to claim 1, characterized in that: In S2, the chemical composition and weight percentage content of the backing welding wire are: C: 0.05%, Mn: 1.0%, Cr: 2.5%, Mo: 0.7%, Ni: 0.5%, and the rest is iron and inevitable impurities; the chemical composition and its weight percentage content of the capping welding wire are: C: 0.1%, Mn: 1.2%, Cr: 13.1%, Mo: 0.7%, Ni: 0.4%, W: 0.1%, V: 0.25%, and the rest is iron and inevitable impurities.

4. A method for preparing a high compressive strength and high wear-resistant roughing vertical roll applicable to hot-rolled strip steel according to claim 3, characterized in that: The hardness of the backing welding wire is 2HSD - 4HSD higher than that of the base material, and the hardness of the capping welding wire is 3HSD - 5HSD higher than that of the backing welding wire.

5. A method for preparing a high compressive strength and high wear-resistant roughing vertical roll applicable to hot-rolled strip steel according to claim 4, characterized in that: The deposition rate of the backing welding wire is controlled at 4.7kg / h, and the deposition rate of the capping welding wire is controlled at 4.5kg / h.

6. A method for preparing a high compressive strength and high wear-resistant roughing vertical roll applicable to hot-rolled strip steel according to claim 1, characterized in that: In S3, the welding method for surfacing is uphill welding, the bead overlap is 60% - 70%, the current is 330A - 400A, and the surfacing temperature is 270°C - 350°C.

7. A method for preparing a high compressive strength and wear-resistant roughing vertical roll for hot-rolled strip steel according to claim 1, characterized in that: In S3, multi-layer welding is used for surfacing, and the single-layer thickness of the weld layer is 2.0mm - 2.2mm.

8. A method for preparing a high compressive strength and high wear-resistant roughing vertical roll applicable to hot-rolled strip steel according to claim 7, characterized in that: During the surfacing process, intermediate heat treatment is carried out once every two layers of surfacing. The intermediate heat treatment uses 520°C × 16h intermediate tempering to eliminate stress, and continue welding after detecting the hardness of the weld layer.

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