Wear-resistant steel boiler suspender and heat treatment method thereof

Abstract

The invention discloses a corrosion-resistant and wear-resistant suspender and a heat treatment method thereof, and belongs to the field of boiler parts and metal heat treatment. In order to solve the problems that an existing suspender is insufficient in molten salt corrosion resistance and particle washing resistance, uneven in large section performance and short in service life, low alloy components with specific weight percentage are designed, the low alloy components comprise 0.18-0.28% of C, 3.00-5.00% of Cr, 0.80-2.00% of Ni, 0.15-0.35% of V, 0.0010-0.0035% of B and the like, normalizing, austenitizing at the temperature of 870-910 DEG C, salt bath isothermal quenching at the temperature of 360-410 DEG C and tempering at the temperature of 500-560 DEG C are adopted, and a complex-phase structure with lower bainite as the main part is obtained. The hanger rod is remarkably improved in corrosion resistance and wear resistance, uniform in large-section performance, capable of prolonging the service life to 8-12 years, less than or equal to 20% in cost increase, compatible with an existing production line, suitable for hanging a boiler heating surface tube bundle, and outstanding in economic benefit and environmental protection benefit.

Description

Technical Field

[0001] This invention belongs to the field of boiler component manufacturing and metal material heat treatment technology, specifically relating to a wear-resistant steel hanger suitable for boiler suspension and its heat treatment method. Background Technology

[0002] Alkali recovery boilers are core equipment in the paper industry for realizing the resource utilization of black liquor. Their core function is to recover alkali chemicals and heat energy by burning black liquor, achieving the dual goals of chemical recycling and waste heat power generation. This is crucial for the paper industry's environmental compliance and economic efficiency improvement. However, alkali recovery boilers operate in extremely harsh environments, with long-term stable operating temperatures of 500-650℃. The flue gas contains not only a large amount of suspended molten alkali salt deposits, mainly composed of Na2CO3, Na2S, NaOH, and Na2SO4, but also hard fly ash and molten salt particles such as SiO2 and Al2O3. As an indispensable load-bearing component inside the boiler, the hanger rod is directly exposed to this extreme environment. It must withstand the tensile load of the heated tube bank for a long time and also faces multiple threats of failure: high-temperature molten alkali salts can easily penetrate into the steel surface, react with the matrix to form low-melting-point compounds, destroy the integrity of the surface oxide film, and cause intergranular corrosion and uniform thinning; high-speed flowing hard particles continuously scour the hanger rod surface, accelerating the peeling off of surface materials; more importantly, corrosion weakens the protective ability of the surface passivation layer, while wear quickly peels off corrosion products, forming a vicious cycle of "corrosion-wear", which leads to a significant reduction in the service life of the hanger rod and becomes a weak link restricting the stable operation of the boiler.

[0003] Currently, the manufacturing and application of alkali recovery boiler hangers in the industry mainly follow T / CASME 1773—2025 "Manufacturing Process Specification for Hangers for Alkali Recovery Boilers". This standard was issued and implemented by the China Association of Small and Medium-sized Commercial Enterprises. It specifies in detail the requirements for the entire process, including hanger type, material selection, process flow, machining, welding, post-weld treatment, surface protection and finished product inspection, and represents the current conventional technical level in the industry. The recommended materials mainly include carbon steel (such as 20#, 25Mn, Q355B, etc.) and alloy steel (such as 15CrMo, 12Cr1MoV, 35CrMoA, etc.). Among them, the typical alloy steel 12Cr1MoV is characterized by low carbon, low Cr content, small amount of Mo and V, no Ni element and trace amount of B element. The heat treatment process is mainly normalizing + high temperature tempering, and finally obtains tempered sorbite or pearlite structure with a hardness of only about HB200-300. The core design goal is to eliminate processing stress and ensure basic mechanical properties. It does not strengthen the design for the corrosion and wear synergy conditions unique to alkali recovery boilers. The performance requirements also mainly focus on tensile strength, impact toughness and non-destructive testing qualification, without setting quantitative assessment indicators for corrosion resistance and wear resistance.

[0004] Although the standard specifies mature and reliable processes with low manufacturing costs, its shortcomings are fully exposed under extreme operating conditions of alkali recovery boilers: the low Cr content and Ni-free composition design prevent the formation of a stable and dense passivation protective film on the steel surface, making it easy for molten alkali salts to penetrate and corrode. In actual operation, the corrosion layer thickness can reach 80-120μm within 300 hours, and the corrosion rate remains high; the low hardness and lack of dispersed strengthening phases make the hanger rod prone to surface spalling under the scouring of hard particles, and the synergistic effect of corrosion and wear further exacerbates material loss; the limited hardenability of traditional steel means that for the commonly used φ80-120mm large-section hanger rods in industry, the core structure is prone to softening, making it impossible to achieve overall uniform strengthening; these problems ultimately result in the actual service life of existing hanger rods being only 3-5 years. Frequent replacement not only brings high maintenance costs but also causes long-term boiler shutdowns, resulting in huge economic losses for enterprises.

[0005] A search of existing technologies reveals that patented technologies for general-purpose wear-resistant steel, corrosion-resistant steel, or bainitic steel are mostly designed for conventional operating conditions such as room-temperature mechanical wear and acid corrosion, or are only applicable to small-section components. None of these technologies adequately consider the unique synergistic operating conditions of alkali recovery boilers involving "molten alkali salts + particle erosion," nor do they propose bainitic strengthening technologies suitable for large-section suspension rods. Therefore, existing technologies still fail to effectively address the industry pain points of insufficient corrosion and wear resistance, poor uniformity of performance across large sections, and short service life of alkali recovery boiler suspension rods, necessitating a targeted technological solution for breakthrough. Summary of the Invention

[0006] In view of this, the present invention proposes a wear-resistant steel boiler hanger and its heat treatment method, aiming to solve the core problems of insufficient corrosion resistance and wear resistance, poor uniformity of large cross-section performance, and short service life of boiler hangers under the combined environment of high-temperature molten alkali salt and particle erosion in the prior art. At the same time, it takes into account process compatibility and economy, and achieves a balanced optimization of corrosion resistance, wear resistance, mechanical properties and cost.

[0007] The technical solution of the present invention is achieved as follows: The present invention provides a wear-resistant steel boiler hanger rod, the main material of which is a specially designed low-alloy wear-resistant steel and is made by a specific heat treatment process; at the same time, it provides a heat treatment method for the wear-resistant steel boiler hanger rod, which releases the potential of material performance through deep matching of composition design and heat treatment process.

[0008] In some embodiments, the main body material of the boom is composed of the following chemical composition by weight percentage: C 0.18–0.28%, Si 0.20–0.60%, Mn 0.80–1.40%, Cr 3.00–5.00%, Mo 0.50–1.00%, Ni 0.80–2.00%, V 0.15–0.35%, B 0.0010–0.0035%, P ≤ 0.015%, S ≤ 0.010%, with Fe as the balance.

[0009] This compositional design breaks through the single-minded focus on low-cost heat resistance in existing technologies, constructing a synergistic system integrating corrosion resistance, wear resistance, hardenability, and toughness: Carbon (C) provides the necessary foundation for carbide formation, while the low carbon range of 0.18–0.28% effectively avoids stress corrosion cracking and matrix embrittlement under high-temperature molten alkali salt environments, solving the defect in existing technologies where carbon content design did not consider the risk of embrittlement under corrosive conditions; Cr, as the core corrosion-resistant element, with a high content of 3.00–5.00%, promotes the formation of a dense and stable Cr2O3 passivation film on the steel surface, significantly blocking the penetration and hot corrosion of molten alkali salts. Compared to the low Cr content of 0.9–1.2% in existing 12Cr1MoV steel, the protective capability represents a qualitative leap; the introduction of Ni is a targeted design for molten alkali salt (especially Na2S) corrosion, with a content of 0.80–2.00% acting synergistically with Cr to further stabilize the passivation film structure, compensating for the shortcomings of existing technologies in molten salt corrosion resistance due to the lack of Ni; Mo… A content of 0.50–1.00% can enhance the steel's resistance to pitting and crevice corrosion, and synergistically improve the stability and durability of the passivation film in extreme environments with Cr. A V content of 0.15–0.35% can promote the formation of fine VC carbides with a size of <1μm inside the steel. By pinning grain boundaries through dispersed distribution, it can significantly improve the material's resistance to particle erosion and wear, solving the problem of insufficient wear resistance caused by the lack of dispersed strengthening phase in existing technologies. A trace amount of B of 0.0010–0.0035% can greatly improve the hardenability of the steel, ensuring uniform transformation of the microstructure in the core and surface of large-section hangers, breaking through the technical bottleneck of insufficient hardenability of traditional low-alloy steel in large sections. At the same time, the content of harmful impurities such as P and S is strictly controlled to avoid intergranular embrittlement and hot working defects, ensuring the structural safety of the hanger under load.

[0010] In some embodiments, the preferred weight percentages of the chemical components are: C 0.20–0.25%, Si 0.30–0.50%, Mn 1.00–1.20%, Cr 3.50–4.50%, Mo 0.60–0.90%, Ni 1.00–1.80%, V 0.20–0.30%, B 0.0015–0.0025%, P ≤ 0.010%, and S ≤ 0.008%. This optimal range is based on precise optimization of the synergistic effect of elements through numerous experiments: the optimal ranges for C, Cr, and V can achieve the best balance between the amount of carbide formation and the toughness of the matrix, avoiding the increase in brittleness caused by excessive carbides; the optimal ranges for Ni and Mo can effectively control the increase in material cost while maximizing corrosion resistance, ensuring that the cost increase does not exceed 20%, thus solving the problem of cost runaway caused by high alloying; the optimal content of B can ensure a significant improvement in hardenability, while avoiding the risk of intergranular embrittlement caused by excessive B, achieving dual optimization of performance and process adaptability.

[0011] In some embodiments, the boom undergoes sequential treatment including normalizing, austenitizing at 870-910℃, isothermal quenching in a salt bath at 360-410℃ for 1.5-3 hours, and tempering at 500-560℃ for 2-4 hours. The final microstructure exhibits a core and subsurface bainite proportions of 70-85%, with the surface referring to the area within 5mm of the boom's outer surface and the core referring to the central region of the boom's cross-section. This heat treatment process differs significantly from the softening logic of existing technologies that combine normalizing with high-temperature tempering. It is a strengthening solution tailored for the aforementioned low-alloy composition: the normalizing step refines the austenite grains, eliminating microstructural inhomogeneities generated during forging or hot rolling, providing a uniform microstructure foundation for subsequent phase transformation; the 870-910℃ austenitizing temperature ensures all alloying elements are fully dissolved into the austenite, laying the material basis for subsequent carbide precipitation and microstructural transformation; the 360-410℃ isothermal quenching is a core innovation, as this temperature range is crucial for the transformation of subsurface bainite. The optimal thermodynamic range of the tempering process allows for precise control of the bainite content to reach 70-85%, while retaining 5-10% of retained austenite and dispersed carbides. In contrast, existing high-temperature tempering techniques (620-760℃) can only produce soft tempered sorbite or pearlite, failing to achieve a balance between wear resistance and toughness. The tempering step at 500-560℃ can effectively eliminate the internal stress generated during isothermal quenching, stabilize the bainite structure and retained austenite, avoid the softening of the structure caused by high-temperature tempering, and ultimately achieve a synergistic compatibility of high hardness and good toughness.

[0012] In some embodiments, the holding times for normalizing and austenitizing are calculated as 45-60 minutes per 25mm of the maximum thickness of the hanger or its billet. This quantitative design is based on the heating and mass transfer characteristics of large-section components, ensuring that a uniform temperature field can be achieved in the core and surface regardless of the hanger cross-sectional size (especially large cross-sections of φ80-120mm). This avoids insufficient or uneven microstructure transformation due to insufficient holding time, solves the problems of unquantified holding time and uneven heating of large cross-sections in the prior art, and further ensures the performance uniformity of large-section hangers.

[0013] In some embodiments, the molten salt corrosion rate of the boom under conditions of 600℃ and 500h is ≤0.18mm / year, and the hardness difference between the surface and the core is ≤20HB. This performance index directly corresponds to the actual service conditions of the alkali recovery boiler and is a direct manifestation of the synergistic innovation of composition and process: the molten salt corrosion rate of ≤0.18mm / year is due to the stable passivation film formed by Cr-Ni synergy, which effectively blocks the erosion of molten alkali salt; the hardness difference between the surface and the core of ≤20HB is due to the improved hardenability of trace amounts of B and the uniform heat treatment process, which completely solves the industry pain points of core softening and large hardness difference of large cross-section booms in the existing technology.

[0014] In some embodiments, the cross-sectional diameter of the hanger is 80-120mm, and the core bainite content is ≥70%. This design clarifies the core application scenario of the invention. For the industry's mainstream large-section hanger sizes (φ80-120mm), by improving the hardenability of trace amounts of boron in the composition and precisely controlling the process, it ensures that the core bainite content is not less than 70%, guaranteeing the uniformity and stability of the overall performance of the large-section hanger from a microstructural perspective, and avoiding overall failure caused by local performance shortcomings.

[0015] In some embodiments, the hanger is specifically designed for alkali recovery boilers in the paper industry, used to suspend the heat-receiving tube banks of superheaters, reheaters, or water-cooled walls. This design further clarifies the specific application scenario of the invention, avoiding the ambiguity of the protection scope of general boiler hangers, while specifically matching the extreme operating conditions of alkali recovery boilers, highlighting the scenario adaptability and innovation of the technical solution, and distinguishing it from existing general boiler hanger technologies.

[0016] In some embodiments, after shot peening, the surface of the boom is coated with a high-temperature anti-corrosion coating. This high-temperature anti-corrosion coating is an Al2O3-SiO2 ceramic-based composite coating, comprising 60-80% Al2O3, 10-30% SiO2, and 5-15% ZrO2 by weight percentage. The coating thickness is 50-150 μm, prepared using a plasma spraying process. The coating bonding strength is ≥30 MPa (tested according to GB / T 8642 standard), and the weight loss after molten salt corrosion at 600℃ for 500 hours is ≤5 mg / cm³.2 Shot peening can further improve the surface hardness and residual compressive stress of the suspension rod, delaying the initiation and propagation of corrosion cracks; the high-temperature anti-corrosion coating can form a secondary protective barrier, working synergistically with the passivation film formed by the substrate itself to construct a dual protection system of substrate protection and surface protection, further improving the resistance to molten salt corrosion. This design provides flexible strengthening options for boiler operating conditions with different molten salt concentrations, effectively expanding the scope of application of this invention.

[0017] In some embodiments, the room temperature impact toughness (V-notch) of the suspension rod is 55-70 J, and the high-temperature tensile strength at 600℃ is ≥600MPa. These performance indicators ensure the structural safety of the suspension rod under long-term tensile and impact loads, avoiding the sacrifice of load-bearing capacity due to enhanced wear and corrosion resistance. This addresses the shortcomings of some existing strengthening schemes that prioritize wear resistance over toughness or room temperature performance over high-temperature performance, achieving a comprehensive balance between wear resistance, corrosion resistance, load-bearing capacity, and toughness, thus meeting the requirements for long-term stable boiler operation.

[0018] In some embodiments, the salt bath is a nitrate bath or a chloride bath. Nitrate baths and chloride baths have the characteristics of uniform cooling and high temperature control precision, which can ensure that the cooling rate of each part of the hanger is consistent during isothermal quenching, avoiding problems such as microstructure segregation and excessive internal stress caused by uneven cooling. Compared with air cooling or oil cooling, they are more suitable for the uniform transformation requirements of large cross-section hangers and are an important process guarantee for achieving uniform formation of lower bainite.

[0019] The present invention has the following advantages over the prior art:

[0020] Compared to existing boiler hanger technologies, this invention achieves significant advancements in multiple dimensions: In terms of performance, through a precise design that combines Cr-Ni synergistic corrosion resistance, V dispersion-strengthened wear resistance, and B-enhanced hardenability in a low-alloy composition, along with a bainitic multiphase microstructure obtained via medium-temperature isothermal quenching, it completely overcomes the shortcomings of existing technologies in corrosion and wear resistance. Simultaneously, it solves the industry-wide problem of core softening in large-section components, achieving comprehensive synergistic optimization of corrosion resistance, wear resistance, load-bearing capacity, and toughness. In terms of lifespan, it breaks the 3-5 year service limitation of existing hangers, significantly extending service life and fundamentally reducing downtime losses and high costs caused by frequent replacements. Maintenance costs; in terms of economy and industrialization, it avoids the cost surge caused by high alloying, and achieves a slight cost increase by precisely controlling the amount of alloying elements. Moreover, the manufacturing process is fully compatible with existing industry standards, without the need to modify existing production lines, thus solving the problem of excessively high costs and difficulty in implementation of some existing high-performance solutions. In terms of industry value, it is specifically designed for the special synergistic working conditions of molten alkali salt and particle scouring in alkali recovery boilers, filling the application gap of existing technologies, promoting the technological upgrading of core components of alkali recovery boilers, and reducing material consumption and energy waste. It is in line with the industrial development trend of environmental protection and energy conservation, and has broad application prospects and significant comprehensive benefits. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1 1. Chemical composition (wt%) C 0.23%, Si 0.40%, Mn 1.10%, Cr 4.00%, Mo 0.80%, Ni 1.20%, V 0.25%, B 0.0020%, P ≤ 0.010%, S ≤ 0.008%, Fe as balance.

[0023] 2. Preparation steps Step 1: Smelting and casting. Electric arc furnace smelting + LF / VOD refining process is adopted, strictly controlling the content of harmful impurities such as P and S, and continuously casting into φ250mm round billets.

[0024] Step 2: Forging / Hot Rolling. Heat the round billet to 1200℃, control the final rolling temperature at 880℃, hot roll it into φ90mm bars, and air cool it to room temperature.

[0025] Step 3: Machining and Assembly. Following the requirements of Chapters 7-9 of T / CASME1773—2025, the bar stock is straightened (straightness ≤ 2mm / m) and machined into a double-headed bolt type straight suspension rod (6m in length). Ear plates are assembled (offset ≤ 1.0mm) and fully penetrated welded. After welding, magnetic particle and ultrasonic testing both meet Level II qualification standards. The welds are then ground and repaired.

[0026] Step 4: Heat treatment. First, normalize the bar by heating to 930℃ and holding for 60 minutes for every 25mm of the maximum bar thickness. After holding for 2.5 hours, remove the bar from the furnace and air cool. Then, reheat the bar to 890℃ for austenitizing treatment and hold for 2 hours. Quickly transfer the bar to a 390℃ salt bath for isothermal quenching and hold for 2 hours. After holding for 2 hours, remove the bar from the furnace and air cool to room temperature. Finally, temper the bar by heating to 540℃ and holding for 3 hours. Then, cool the bar in the furnace to room temperature.

[0027] Example 1-1 1. Chemical composition: completely consistent with Example 1 (C 0.23%, Si 0.40%, Mn 1.10%, Cr 4.00%, Mo 0.80%, Ni 1.20%, V 0.25%, B 0.0020%, P ≤ 0.010%, S ≤ 0.008%, Fe balance).

[0028] 2. Preparation steps: Steps 1-4 are completely consistent with Example 1 (smelting → hot rolling → machining → heat treatment); Step 5 (additional treatment) is added: Shot peening: The surface of the heat-treated suspension rod is shot peened with steel shot (0.8-1.2mm in diameter) at a pressure of 0.4-0.6MPa for 15-20 minutes to ensure a surface roughness Ra=3.2-6.3μm. Coating preparation: An Al2O3-SiO2 ceramic matrix composite coating was applied using a plasma spraying process. The coating composition (wt%) was: Al2O3 70%, SiO2 20%, ZrO2 10%, and the coating thickness was controlled to be 80-100μm. Post-treatment: Cure at 180℃ for 3 hours to eliminate internal stress in the coating.

[0029] Example 2 1. Chemical composition (wt%) C 0.25%, Si 0.50%, Mn 1.20%, Cr 4.50%, Mo 0.90%, Ni 1.80%, V 0.30%, B 0.0025%, P ≤ 0.010%, S ≤ 0.008%, Fe as balance.

[0030] 2. Preparation steps Step 1: Smelting and casting. The same electric arc furnace smelting + LF / VOD refining process as in Example 1 was used to continuously cast φ250mm round billets.

[0031] Step 2: Forging / Hot Rolling. Heat to 1200℃, final rolling temperature 880℃, hot roll into φ80mm bars, and air cool to room temperature.

[0032] Step 3: Machining and Assembly. Following the requirements of T / CASME1773—2025 standard, the process includes straightening, thread machining (6g tolerance), ear plate assembly (offset ≤1.2mm), welding, and non-destructive testing, consistent with Example 1.

[0033] Step 4: Heat treatment. Normalizing at 950℃ for 2 hours and air cooling; austenitizing at 910℃ for 2 hours; isothermal quenching in a 400℃ chloride salt bath for 2.5 hours, followed by air cooling to room temperature; tempering at 530℃ for 3 hours, followed by furnace cooling.

[0034] Example 3 1. Chemical composition (wt%) C 0.22%, Si 0.35%, Mn 1.05%, Cr 3.80%, Mo 0.70%, Ni 1.50%, V 0.22%, B 0.0025%, P ≤ 0.010%, S ≤ 0.008%, Fe as balance.

[0035] 2. Preparation steps Step 1: Smelting and casting. Smelting in an electric arc furnace + refining with LF / VOD, and continuously casting into φ300mm round billets.

[0036] Step 2: Forging / Hot Rolling. Heat to 1220℃, final forging temperature 860℃, forge into φ120mm bars, and air cool to room temperature.

[0037] Step 3: Machining and Assembly. Straighten according to standard requirements (straightness ≤ 2mm / m), machine, weld ear plates, and perform non-destructive testing to ensure compliance with industry standards.

[0038] Step 4: Heat treatment. Normalizing at 940℃ for 3 hours (holding for 60 minutes per 25 mm) followed by air cooling; austenitizing at 900℃ for 3 hours; isothermal quenching in a 380℃ salt bath for 3 hours, followed by air cooling to room temperature; tempering at 550℃ for 4 hours, followed by furnace cooling.

[0039] Example 3-1 1. Chemical composition: completely consistent with Example 3 (C 0.22%, Si 0.35%, Mn 1.05%, Cr 3.80%, Mo 0.70%, Ni 1.50%, V 0.22%, B 0.0025%, P ≤ 0.010%, S ≤ 0.008%, Fe balance).

[0040] 2. Preparation steps: Steps 1-4 are completely consistent with Example 3 (large cross-section forging + heat treatment); Step 5 (additional treatment) is added: Shot peening: steel shot particle size 1.0-1.5mm, shot peening pressure 0.5-0.7MPa, treatment time 20-25min, surface roughness Ra=4.0-6.3μm; Coating preparation: Plasma spraying of Al2O3-SiO2-ZrO2 coating (Al2O3 65%, SiO2 25%, ZrO2 10%), thickness 100-120μm; Post-treatment: Curing at 200℃ for 2.5 hours.

[0041] Example 4 1. Chemical composition (wt%) C 0.23%, Si 0.40%, Mn 1.10%, Cr 4.00%, Mo 0.80%, Ni 1.20%, V 0.25%, B 0%, P ≤ 0.010%, S ≤ 0.008%, Fe as balance.

[0042] 2. Preparation steps Step 1: Smelting and casting. Smelting in an electric arc furnace + refining with LF / VOD, and continuously casting into φ250mm round billets, with strict control of the boron content to 0.

[0043] Step 2: Forging / Hot Rolling. Consistent with Example 1, hot rolling is performed into φ90mm bars.

[0044] Step 3: Machining and assembly. Perform the process and standards exactly as described in Example 1.

[0045] Step 4: Heat treatment. The process parameters are completely consistent with those of Example 1 (normalizing at 930℃ for 2.5 hours → austenitizing at 890℃ for 2 hours → isothermal quenching in a nitrate bath at 390℃ for 2 hours → tempering at 540℃ for 3 hours).

[0046] Example 5 1. Chemical composition (wt%) C 0.23%, Si 0.40%, Mn 1.10%, Cr 4.00%, Mo 0.80%, Ni 0%, V 0.25%, B 0.0020%, P ≤ 0.010%, S ≤ 0.008%, Fe as balance.

[0047] 2. Preparation steps Step 1: Smelting and casting. Smelting in an electric arc furnace + refining with LF / VOD, and continuously casting into φ250mm round billets, with the Ni content strictly controlled to be 0.

[0048] Step 2: Forging / Hot Rolling. Hot-rolled into φ90mm bars, the process is the same as in Example 1.

[0049] Step 3: Machining and assembly. Same process and standards as in Example 1.

[0050] Step 4: Heat treatment. The heat treatment parameters are exactly the same as those in Example 1.

[0051] Example 6 1. Chemical composition (wt%) C 0.23%, Si 0.40%, Mn 1.10%, Cr 4.00%, Mo 0.80%, Ni 1.20%, V 0%, B 0.0020%, P ≤ 0.010%, S ≤ 0.008%, Fe as balance.

[0052] 2. Preparation steps Step 1: Smelting and casting. Smelting in an electric arc furnace + refining with LF / VOD, and continuously casting into φ250mm round billets, with the V content strictly controlled to be 0.

[0053] Step 2: Forging / Hot Rolling. Consistent with Example 1, hot rolling is performed into φ90mm bars.

[0054] Step 3: Machining and assembly. Perform the process and standards exactly as described in Example 1.

[0055] Step 4: Heat treatment. The process parameters are completely consistent with those in Example 1.

[0056] Example 7 1. Chemical composition (wt%) Completely consistent with Example 1 (C 0.23%, Si 0.40%, Mn 1.10%, Cr 4.00%, Mo 0.80%, Ni 1.20%, V 0.25%, B 0.0020%, P ≤ 0.010%, S ≤ 0.008%, Fe as balance).

[0057] 2. Preparation steps Steps 1-3: Smelting and casting, forging / hot rolling, machining and assembly are completely consistent with Example 1.

[0058] Step 4: Heat treatment. Normalize at 930℃ for 2.5 hours and air cool; skip the isothermal quenching step and directly temper at 760℃ for 4 hours, followed by furnace cooling (using the traditional process of T / CASME1773—2025 standard).

[0059] Example 8 1. Chemical composition (wt%) C 0.18%, Si 0.20%, Mn 0.80%, Cr 3.00%, Mo 0.50%, Ni 0.80%, V 0.15%, B 0.0010%, P ≤ 0.015%, S ≤ 0.010%, Fe as balance.

[0060] 2. Preparation steps Step 1: Smelting and casting. Smelting in an electric arc furnace + refining with LF / VOD, and continuously casting into φ200mm round billets.

[0061] Step 2: Forging / Hot Rolling. Heat to 1180℃, final rolling temperature 850℃, hot roll into φ80mm bars, and air cool to room temperature.

[0062] Step 3: Machining and Assembly. Straightening, machining, welding, and testing are completed according to standard requirements, following the same process as in Example 1.

[0063] Step 4: Heat treatment. Normalizing at 910℃ for 1.8h (holding for 45min per 25mm) followed by air cooling; austenitizing at 870℃ for 1.8h; isothermal quenching in a 360℃ salt bath for 1.5h, followed by air cooling to room temperature; tempering at 500℃ for 2h, followed by air cooling to room temperature.

[0064] Comparative Example 1 1. Chemical composition (wt%) C 0.12%, Si 0.35%, Mn 0.60%, Cr 1.10%, Mo 0.30%, V 0.15%, Ni 0%, B 0%, P ≤ 0.035%, S ≤ 0.035%, Fe as balance (T / CASME1773—2025 standard recommends 12Cr1MoV).

[0065] 2. Preparation steps Step 1: Smelting and casting. Smelting is carried out in a conventional electric arc furnace, and the metal is continuously cast into φ250mm round billets.

[0066] Step 2: Forging / Hot Rolling. Heat to 1180℃, final rolling temperature 850℃, hot roll into φ90mm bars, and air cool to room temperature.

[0067] Step 3: Machining and Assembly. Following the requirements of T / CASME1773—2025 standard, straightening, thread machining, lug assembly and welding are performed, and non-destructive testing is completed to ensure compliance.

[0068] Step 4: Heat treatment. Normalize at 900℃ for 2 hours and air cool; temper at 760℃ for 4 hours and cool with the furnace (standard traditional process).

[0069] Comparative Example 2 1. Chemical composition (wt%) Completely consistent with Comparative Example 1 (12Cr1MoV composition).

[0070] 2. Preparation steps Steps 1-3: Smelting and casting, forging / hot rolling, machining and assembly are the same as in Comparative Example 1.

[0071] Step 4: Heat treatment. The process is exactly the same as in Example 1 (normalizing at 930℃ for 2.5 hours → austenitizing at 890℃ for 2 hours → isothermal quenching in a nitrate bath at 390℃ for 2 hours → tempering at 540℃ for 3 hours).

[0072] Comparative Example 3 1. Chemical composition (wt%) Completely consistent with Example 1.

[0073] 2. Preparation steps Steps 1-3: Smelting and casting, forging / hot rolling, machining and assembly are the same as in Example 1.

[0074] Step 4: Heat treatment. Normalize at 930℃ for 2.5 hours and air cool; austenitize at 890℃ for 2 hours; transfer to a 320℃ salt bath for isothermal quenching for 2 hours (the conventional isothermal temperature for existing bainitic steel is lower than the range of 360-410℃ in claim 3), air cool to room temperature; temper at 540℃ for 3 hours and cool with the furnace.

[0075] Comparative Example 4 1. Chemical composition (wt%) C 0.08%, Si 1.00%, Mn 1.50%, Cr 25.00%, Ni 20.00%, Mo 0%, V 0%, B 0%, P ≤ 0.035%, S ≤ 0.035%, Fe as balance (existing high corrosion resistant steel 310S).

[0076] 2. Preparation steps Step 1: Smelting and casting. Smelting in an electric arc furnace + VOD refining, and continuous casting into φ250mm round billets.

[0077] Step 2: Forging / Hot Rolling. Heat to 1250℃, final rolling temperature 900℃, hot roll into φ90mm bars, and air cool to room temperature.

[0078] Step 3: Machining and Assembly. Straighten, weld, and inspect according to standard hanger rod machining requirements.

[0079] Step 4: Heat treatment. Use the conventional 310S solution treatment process, heat to 1100℃ for 2 hours, and then air cool to room temperature.

[0080] Comparative Example 5 1. Chemical composition (wt%) C 0.20%, Si 0.40%, Mn 1.60%, Cr 3.50%, Ni 1.20%, Mo 0%, V 0.05%, B 0%, P ≤ 0.035%, S ≤ 0.035%, Fe as balance (Cr and Ni are added to NM450 wear-resistant steel).

[0081] 2. Preparation steps Step 1: Smelting and casting. Smelting is carried out in a conventional electric arc furnace, and the metal is continuously cast into φ250mm round billets.

[0082] Step 2: Forging / Hot Rolling. Heat to 1200℃, final rolling temperature 880℃, hot roll into φ90mm bars, and air cool to room temperature.

[0083] Step 3: Machining and Assembly. Straighten, weld, and inspect according to standard hanger rod machining requirements.

[0084] Step 4: Heat treatment. Normalize at 920℃ for 2 hours and air cool; temper at 600℃ for 3 hours and cool in the furnace (general wear-resistant steel process).

[0085] Performance verification 1. Sample preparation Samples were taken from the suspension rods prepared in the above embodiments and comparative examples according to relevant standards: Structure and hardness test: Cut a φ20mm×50mm specimen and take samples from the surface (5mm away from the surface) and the core (center of the cross section) along the radial direction of the cross section; Mechanical performance testing: According to GB / T228.1, GB / T229, and GB / T4338 standards, standard tensile test specimens (φ10mm×50mm) and V-notch impact test specimens (10mm×10mm×55mm) are processed. Corrosion and wear test: The sample was processed into a φ20mm×30mm sample, the surface was polished to Ra≤0.8μm, ultrasonically cleaned and dried for later use.

[0086] 2. Performance testing procedures (1) Tissue and hardness test Referring to GB / T231.1 standard, the hardness of the sample surface and core was tested using a Brinell hardness tester, with 3 points tested at each location and the average value taken. The microstructure was observed using a metallographic microscope, and the proportion of bainite was statistically analyzed using image analysis software. The hardness difference between the surface and core was calculated to visually reflect the uniformity of the large cross-section performance.

[0087] (2) Mechanical performance testing Room temperature mechanical properties: Tensile test was performed on a universal testing machine according to GB / T228.1 standard, with a loading rate of 5 mm / min, to test tensile strength and yield strength; room temperature V-notch impact test was performed on an impact testing machine according to GB / T229 standard to test impact toughness, with each specimen tested 3 times and the average value taken; High-temperature strength test: According to GB / T4338 standard, the tensile specimen is placed in a high-temperature environment chamber, heated to 600℃ and kept at that temperature for 30 minutes. After ensuring uniform specimen temperature, a tensile test is performed at a loading rate of 3 mm / min to test the tensile strength at 600℃.

[0088] (3) Pure molten salt corrosion performance test Referring to GB / T17897 standard, a mixed salt of 50% Na2SO4 + 30% Na2CO3 + 20% NaCl (simulating the composition of molten alkali salt in an alkali recovery boiler) was prepared and uniformly coated onto the sample surface using a brushing method, with the salt application rate controlled at 10 mg / cm³. 2 The salt-coated sample was placed in a muffle furnace and heated to 600℃ for 500h. After the test, the surface corrosion products were removed by a combination of mechanical peeling and chemical cleaning. After drying, the sample was weighed to calculate the corrosion weight loss. The microstructure of the corrosion layer was observed by metallographic microscope, and the thickness of the corrosion layer was measured. The annual corrosion rate was calculated based on the corrosion weight loss and the test time.

[0089] (4) Corrosion and wear synergy test Referring to GB / T12444 standard, a corrosion wear testing machine was used. The samples were fixed on the fixture and placed in a molten salt immersion environment at 600℃ (molten salt composition was the same as that for pure molten salt corrosion testing). At the same time, SiO2 particles (particle size 100-200μm, simulating boiler fly ash particles) were introduced for scouring. The scouring speed was controlled at 8m / s, the impact angle was 60°, and the test cycle was 300h. After the test, the surface corrosion products were removed and the samples were weighed to calculate the total weight loss. Based on the total weight loss of corrosion wear in Comparative Example 1, the relative wear resistance of each sample was calculated (relative wear resistance = total weight loss in Comparative Example 1 / total weight loss of the sample).

[0090] (5) Pure mechanical wear resistance test A room temperature kneading disc wear tester was used, with SiC ceramic as the wear material, a load of 400 N, a wear time of 2 h, and a rotation speed of 200 r / min. After the test, the samples were ultrasonically cleaned, dried, and weighed to calculate the wear amount. The relative wear rate of each sample was calculated based on the wear amount of Comparative Example 1 (relative wear rate = sample wear amount / Comparative Example 1 wear amount).

[0091] Performance verification results Table 1. Microstructure and Hardness Properties

[0092] Table 2 Mechanical Properties

[0093] Table 3. Corrosion performance of pure molten salt (600℃, 500h)

[0094] Table 4. Corrosive Wear and Pure Mechanical Wear Performance

[0095] Performance comparisons of the various embodiments and comparative examples demonstrate that the wear-resistant steel boiler hanger rod and its heat treatment method designed in this invention achieve a significant leap in comprehensive performance compared to existing technologies (represented by the 12Cr1MoV material and process recommended by the T / CASME1773—2025 standard). Examples 1-3, embodying the core technical solution, achieve a 70-85% lower bainite-dominated multiphase microstructure through the strong binding of the "Cr-Ni-VB" synergistic composition design and the medium-temperature isothermal quenching process. The hardness difference between the surface and core of the large-section hanger rod is ≤10HB, effectively solving the problem of poor uniformity in large-section materials. Under the combined working conditions of molten alkali salt and particle erosion at 600℃, the molten salt corrosion rate is ≤0.15mm / year, and the relative wear resistance to corrosion wear is ≥3.0, significantly superior to the conventional technical level of Comparative Example 1.

[0096] Examples 4-8 further verify the irreplaceability of the core technical features: the absence of element B leads to a sharp drop in the proportion of bainite in the core of the large cross section, and the hardness difference increases to 63HB; without element Ni, the molten salt corrosion rate soars to 0.38mm / year; using the traditional high-temperature tempering process results in a hardness of less than 300HB and a significant reduction in wear resistance; while Example 8, whose composition and process are both at the lower limit of the claims, can still meet the core performance indicators, proving the rationality of the scope of protection of this invention.

[0097] The test results of Comparative Examples 2-5 show that applying the process of this invention to the traditional 12Cr1MoV composition, or adapting the conventional bainitic quenching temperature to the composition of this invention, cannot achieve the target performance. Although existing high CrNi corrosion-resistant steels have certain corrosion resistance, they have low hardness and high cost, and cannot balance wear resistance and economy. Simply adding corrosion-resistant elements to general wear-resistant steels also makes it difficult to achieve synergistic protection against corrosion and wear.

[0098] In summary, the performance advantages of this invention stem from the synergistic innovation of component design and heat treatment process, rather than a simple combination or replacement of existing technologies. It not only significantly improves the corrosion and wear resistance and large cross-sectional uniformity of boiler hangers, but also maintains good mechanical toughness and process compatibility, with controllable cost increases, and possesses outstanding substantive features and significant progress.

[0099] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A wear-resistant steel boiler hanger rod, characterized in that, The main body material of the hanger rod is composed of the following chemical composition by weight percentage: C 0.18~0.28%, Si 0.20~0.60%, Mn 0.80~1.40%, Cr 3.00~5.00%, Mo 0.50~1.00%, Ni 0.80~2.00%, V 0.15~0.35%, B 0.0010~0.0035%, P≤0.015%, S≤0.010%, and Fe as the balance. The hanger rod is subjected to normalizing, austenitizing at 870-910℃, isothermal quenching in a salt bath at 360-410℃ for 1.5-3 hours, and tempering at 500-560℃ for 2-4 hours.

2. The wear-resistant steel boiler hanger according to claim 1, characterized in that, The weight percentages of the chemical components are as follows: C 0.20–0.25%, Si 0.30–0.50%, Mn 1.00–1.20%, Cr 3.50–4.50%, Mo 0.60–0.90%, Ni 1.00–1.80%, V 0.20–0.30%, B 0.0015–0.0025%, P ≤ 0.010%, S ≤ 0.008%.

3. The wear-resistant steel boiler hanger according to claim 1, characterized in that, The holding times for normalizing and austenitizing are calculated based on 45-60 minutes per 25mm of the maximum thickness of the hanger.

4. The wear-resistant steel boiler hanger according to claim 1, characterized in that, The molten salt corrosion rate of the boom under 600℃ and 500h conditions is ≤0.18mm / year, and the hardness difference between the surface and the core is ≤20HB.

5. The wear-resistant steel boiler hanger according to claim 1, characterized in that, The diameter of the connecting rod is 80-120mm, and the proportion of bainite in the core is ≥70%.

6. The wear-resistant steel boiler hanger according to claim 1, characterized in that, The suspension rods are specifically designed for alkali recovery boilers in the paper industry and are used to suspend the heating surface tube banks of superheaters, reheaters, or water-cooled walls.

7. The wear-resistant steel boiler hanger according to claim 1, characterized in that, The surface of the boom is shot-peened and then coated with a high-temperature anti-corrosion coating.

8. The wear-resistant steel boiler hanger according to claim 1, characterized in that, The room temperature impact toughness of the boom is 55-70J, and the high temperature tensile strength at 600℃ is ≥600MPa.

9. A heat treatment method for wear-resistant steel boiler hanger rods, characterized in that, Includes the following steps: 1) Normalizing: Heat the billet to 910-950℃, hold it at that temperature, and then air cool it after removing it from the furnace; 2) Austenitization: Reheat the normalized billet to 870-910℃, and hold for the same time as normalizing; 3) Isothermal quenching: Quickly transfer to a salt bath at 360-410℃ and hold for 1.5-3 hours, then remove from the furnace and air cool to room temperature; 4) Tempering: Heat to 500-560℃ and hold for 2-4 hours, then cool with the furnace or air cool; The chemical composition by weight percentage of the hanger billet is as follows: C 0.18-0.28%, Si 0.20-0.60%, Mn 0.80-1.40%, Cr 3.00-5.00%, Mo 0.50-1.00%, Ni 0.80-2.00%, V 0.15-0.35%, B 0.0010-0.0035%, P ≤ 0.015%, S ≤ 0.010%, with Fe as the balance.

10. The heat treatment method for wear-resistant steel boiler hanger rods according to claim 9, characterized in that, The salt bath is either a nitrate bath or a chloride bath.

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