High-temperature-resistant and corrosion-resistant composite coating for surface of zinc pot roller and preparation method

Abstract

The invention discloses a high-temperature-resistant and corrosion-resistant composite coating for the surface of a zinc pot roller and a preparation method, the composite coating comprises a WB-metal working layer and a WC-boride surface layer, and the components of the WB-metal working layer comprise W, B and metal elements; and the WC-boride surface layer comprises the following components: W, C and boride. The method comprises the following steps: firstly, pretreating a roll surface substrate, and preparing a working layer and a surface layer by adopting high velocity oxy-fuel spraying equipment; and the roller surface is brushed with confining liquid, and the high-temperature-resistant and corrosion-resistant composite coating on the surface of the zinc pot roller is obtained after low-temperature heat treatment. The composite coating is compact in microscopic structure and low in porosity, the bonding strength of the coating and a roller surface base body is high, and the composite coating has good comprehensive performance such as abrasion resistance, high-temperature corrosion resistance and adhesion resistance, meets the production requirements of a key spare part zinc pot roller of a hot-dip coating production line, and is particularly suitable for surface strengthening treatment of a hot-dip coating high-aluminum zinc aluminum magnesium production line zinc pot roller. The service life is prolonged, and the strip steel product quality is improved.

Description

Technical Field

[0001] The invention relates to the technical field of composite coatings and preparation thereof, and in particular to a high temperature resistant and corrosion resistant composite coating for the surface of a zinc pot roller and a preparation method thereof. Background Art

[0002] With the development of steel materials and coating technology, higher requirements are put forward for the corrosion resistance of coated steel. Traditional hot-dip galvanized steel can no longer meet the application requirements. Highly corrosion-resistant 55%Al-Zn, Zn-5%Al and zinc-aluminum-magnesium (Zn-Al-Mg) alloy coatings have become the focus of coating material development. In particular, Zn-Al-Mg alloy coatings have become the best choice for coated steel plates due to their high corrosion resistance and port corrosion protection. However, due to the stronger corrosion and higher temperature of the molten zinc-aluminum-magnesium liquid in the zinc pot, especially for the hot-dip high-aluminum zinc-aluminum-magnesium production line, the key spare parts of the existing zinc pot, the zinc pot roller, can no longer meet the production and use requirements.

[0003] At present, ordinary hot-dip galvanizing zinc pot rollers use supersonic flame spraying to prepare coatings such as tungsten carbide and boride. However, for hot-dip high-aluminum zinc-aluminum-magnesium production lines, the molten liquid temperature is higher and the corrosiveness is stronger. The existing coatings cannot meet production requirements. As a passive roller, the zinc pot roller relies on the friction between the surface of the strip and the zinc pot roller surface to make the zinc pot roller and the strip run at the same speed. However, sometimes due to the influence of many factors such as changes in the zinc liquid composition, the use of the zinc pot roller, and changes in process speed, the transmission friction between the strip and the zinc pot roller is insufficient, and the strip and the zinc pot roller slide relative to each other, scratching the surface of the steel strip. Zinc slag is easy to adhere to the zinc pot roller, which will also scratch the surface of the steel plate or cause indentations. At the same time, the zinc pot roller also frequently jumps or does not rotate, affecting production efficiency.

[0004] Chinese patent document CN1978705A discloses a surface gradient protective coating and its preparation method, which adjusts the content ratio of MoB-based and CoCr-based components through the system design of the protective coating, prepares a buffer transition thermal spray coating material, and obtains a gradient coating with excellent thermal expansion matching between the roller material and the surface protective coating. However, in actual use, the roller surface is seriously zinc-adhered, which has a great impact on the quality of the strip. Chinese patent document CN107523780A discloses a composite protective coating for a sinking roller for hot dip plating and its preparation method, which has CoCrW as a base layer, a transition layer of CaO・SiO2 and CoCrW mixed in proportion, and CaO・SiO2 as a working layer. The composite coating has good high-temperature aluminum-silicon liquid erosion resistance and adhesion performance, but the amorphous state when the coating is formed makes the coating prone to stress cracking or peeling, and the service life cannot meet production requirements. Chinese patent document CN111424229A discloses a method for preparing a composite coating resistant to liquid metal alloy corrosion. The composite dense coating with a thickness of more than 0.5 mm, which uses metal molybdenum as a bonding layer, 2CaO・SiO2 ceramics as a working layer, and ZrO2・Y2O3 ceramics as a surface layer, meets the requirements for the use of sinking rollers and stabilizing rollers in a continuous hot-dip aluminum-silicon production line. However, for high-aluminum-zinc-aluminum-magnesium molten liquid, after adding Mg, the corrosion is stronger and cannot meet the production requirements. In addition, the production cost of thicker coatings is higher and the production efficiency is lower. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a high-temperature resistant and corrosion-resistant composite coating for the surface of a zinc pot roller and a preparation method thereof. The composite coating and the preparation method thereof overcome the defects of the traditional zinc pot roller surface coating. The composite coating has a dense microstructure, low porosity, high bonding strength between the coating and the roller surface substrate, and has good comprehensive properties such as good wear resistance, high-temperature corrosion resistance, and anti-adhesion. The composite coating also maintains the required roughness to prevent relative sliding and scratching of the strip surface, thereby meeting the production requirements of the zinc pot roller, a key spare part of the hot-dip production line, and is particularly suitable for the surface strengthening treatment of the zinc pot roller of a hot-dip high-aluminum zinc-aluminum-magnesium production line, thereby extending its service life and improving the quality of the strip product.

[0006] To solve the above technical problems, the high temperature resistant and corrosion resistant composite coating for the surface of the zinc pot roller of the present invention comprises a WB-metal working layer and a WC-boride surface layer, wherein the weight percentage of the components of the WB-metal working layer is 20-30% of metal elements, 3.5-4% of B, the remainder is W, and the powder particle size is 15-45 μm; the weight percentage of the components of the WC-boride surface layer is 15-25% of borides, 3.5-4% of C, the remainder is W, and the powder particle size is 53-75 μm.

[0007] Furthermore, the metal element in the WB-metal working layer is a mixture of two or more of Co, Cr, Mo, and Ni, and the boride in the WC-boride surface layer is one or a mixture of two of MoB2, ZrB2, WB, and TiB2.

[0008] A method for preparing the composite coating comprises the following steps: Step 1: Pre-treat the roller surface substrate, machine it to the size requirements before spraying, degrease it and clean it, without any bumps, pores or cracks, and use an automatic sandblasting machine to sandblast it. The roller surface roughness after sandblasting is Ra6-9μm; Step 2: preheat the component powders of the WB-metal working layer at 100-120° C. for 90-120 min, and prepare the working layer using supersonic flame spraying equipment. The spraying process parameters are powder feeding rate 80-110 g / min, oxygen 1850-1950 scfh, kerosene 5.5-6.0 gph, powder feeding gas 20-23 scfh, spraying distance 330-380 mm, and coating thickness 0.05-0.10 mm. Step 3: preheat the component powder of the WC-boride surface layer at 100-120° C. for 90-120 min, and use supersonic flame spraying equipment to prepare the surface layer on the surface of the WB-metal working layer. The spraying process parameters are powder feeding rate 70-100 g / min, oxygen 1900-2000 scfh, kerosene 5.7-6.2 gph, powder feeding gas 20-23 scfh, spraying distance 330-380 mm, coating thickness 0.03-0.05 mm, and the roller surface roughness after spraying is Ra7-9 μm; Step 4: Use sealing liquid to evenly brush the roller surface, and the immersion is uniform without foreign matter defects, and low-temperature heat treatment is performed to obtain a high-temperature resistant and corrosion-resistant composite coating on the surface of the zinc pot roller.

[0009] Since the high temperature resistant and corrosion resistant composite coating and preparation method for the surface of the zinc pot roller of the present invention adopt the above technical scheme, that is, the composite coating includes a WB-metal working layer and a WC-boride surface layer, the components of the WB-metal working layer include metal elements, B and W; the components of the WC-boride surface layer include boride, C and W. The method first pre-treats the roller surface substrate, and respectively prepares the WB-metal working layer and the WC-boride surface layer by supersonic flame spraying equipment; the roller surface is evenly brushed with a sealing liquid, and after low temperature heat treatment, the high temperature resistant and corrosion resistant composite coating on the surface of the zinc pot roller is obtained. The composite coating and preparation method overcome the defects of the traditional zinc pot roller surface coating. The composite coating has a dense microstructure, low porosity, high bonding strength between the coating and the roller surface substrate, good comprehensive properties such as wear resistance, high temperature corrosion resistance, and anti-adhesion, and maintains the required roughness to prevent relative sliding and scratching of the strip surface. It meets the production requirements of the zinc pot roller, a key spare part of the hot-dip production line, and is particularly suitable for the surface strengthening treatment of the zinc pot roller of the hot-dip high-aluminum zinc-aluminum-magnesium production line, extending its service life and improving the quality of the strip product. DETAILED DESCRIPTION

[0010] The high temperature resistant and corrosion resistant composite coating for the surface of a zinc pot roller of the present invention comprises a WB-metal working layer and a WC-boride surface layer, wherein the weight percentage of the components of the WB-metal working layer is 20-30% of metal elements, 3.5-4% of B, the balance is W, and the powder particle size is 15-45 μm; the weight percentage of the components of the WC-boride surface layer is 15-25% of borides, 3.5-4% of C, the balance is W, and the powder particle size is 53-75 μm.

[0011] Preferably, the metal element in the WB-metal working layer is a mixture of two or more of Co, Cr, Mo, and Ni, and the boride in the WC-boride surface layer is one or a mixture of two of MoB2, ZrB2, WB, and TiB2.

[0012] A method for preparing the composite coating comprises the following steps: Step 1: Pre-treat the roller surface substrate, machine it to the size requirements before spraying, degrease it and clean it, without any bumps, pores or cracks, and use an automatic sandblasting machine to sandblast it. The roller surface roughness after sandblasting is Ra6-9μm; Step 2: preheat the component powders of the WB-metal working layer at 100-120° C. for 90-120 min, and prepare the working layer using supersonic flame spraying equipment. The spraying process parameters are powder feeding rate 80-110 g / min, oxygen 1850-1950 scfh, kerosene 5.5-6.0 gph, powder feeding gas 20-23 scfh, spraying distance 330-380 mm, and coating thickness 0.05-0.10 mm. Step 3: preheat the component powder of the WC-boride surface layer at 100-120° C. for 90-120 min, and use supersonic flame spraying equipment to prepare the surface layer on the surface of the WB-metal working layer. The spraying process parameters are powder feeding rate 70-100 g / min, oxygen 1900-2000 scfh, kerosene 5.7-6.2 gph, powder feeding gas 20-23 scfh, spraying distance 330-380 mm, coating thickness 0.03-0.05 mm, and the roller surface roughness after spraying is Ra7-9 μm; Step 4: Use sealing liquid to evenly brush the roller surface, and the immersion is uniform without foreign matter defects, and low-temperature heat treatment is performed to obtain a high-temperature resistant and corrosion-resistant composite coating on the surface of the zinc pot roller.

[0013] The composite coating has a dense microstructure, low porosity, high bonding strength between the coating and the roller surface substrate, good high-temperature corrosion resistance, anti-adhesion and other comprehensive properties, meets high roughness requirements, and is particularly suitable for surface strengthening treatment of zinc pot rollers in hot-dip high-aluminum zinc-aluminum-magnesium production lines. The WC-Co coating commonly used in hot-dip galvanizing rollers will decompose at temperatures exceeding 540°C and is not suitable for molten high-aluminum zinc-aluminum-magnesium molten liquid above 600°C. The composite coating and preparation method use metal tungsten boride with better stability as the surface strengthening working layer. The molten high-aluminum zinc-aluminum-magnesium liquid is prone to diffusion corrosion along the metal phase in the composite coating. When the B content is controlled at a lower ratio (B3.5-4%, not more than 4%), the metal phase and WB form an η phase. The η phase has good resistance to molten metal liquid corrosion, prevents the molten metal liquid from diffusing into the composite coating, and a certain content of metal elements helps to further improve the corrosion and erosion resistance of the composite coating. Borides such as MoB2, ZrB2, WB, TiB2, etc. have good high temperature resistance, wear resistance, and corrosion resistance, especially resistance to high temperature molten metal liquid erosion. The addition of 15-25% boride ceramic phase in the surface layer of the composite coating enhances the wear resistance, scratch resistance and adhesion resistance of the composite coating. The higher roughness ensures that the zinc pot roller and the strip steel run at the same speed, preventing relative sliding, avoiding scratches on the strip steel surface, extending the service life, and meeting the requirements of production site use.

Claims

1. A high temperature resistant and corrosion resistant composite coating for the surface of a zinc pot roller, characterized in that: It comprises a WB-metal working layer and a WC-boride surface layer, wherein the weight percentage of the WB-metal working layer is 20-30% of metal elements, 3.5-4% of B, the balance is W, and the powder particle size is 15-45 μm; the weight percentage of the WC-boride surface layer is 15-25% of boride, 3.5-4% of C, the balance is W, and the powder particle size is 53-75 μm.

2. The high temperature resistant and corrosion resistant composite coating for the surface of the zinc pot roller according to claim 1, characterized in that: The metal element in the WB-metal working layer is a mixture of two or more of Co, Cr, Mo, and Ni, and the boride in the WC-boride surface layer is one or a mixture of two of MoB2, ZrB2, WB, and TiB2.

3. A method for preparing the composite coating according to claim 1 or 2, characterized in that The steps include: Step 1: Pre-treat the roller surface substrate, machine it to the size requirements before spraying, degrease it and clean it, without any bumps, pores or cracks, and use an automatic sandblasting machine to sandblast it. The roller surface roughness after sandblasting is Ra6-9μm; Step 2: preheat the component powders of the WB-metal working layer at 100-120° C. for 90-120 min, and prepare the working layer using supersonic flame spraying equipment. The spraying process parameters are powder feeding rate 80-110 g / min, oxygen 1850-1950 scfh, kerosene 5.5-6.0 gph, powder feeding gas 20-23 scfh, spraying distance 330-380 mm, and coating thickness 0.05-0.10 mm. Step 3: preheat the component powder of the WC-boride surface layer at 100-120° C. for 90-120 min, and use supersonic flame spraying equipment to prepare the surface layer on the surface of the WB-metal working layer. The spraying process parameters are powder feeding rate 70-100 g / min, oxygen 1900-2000 scfh, kerosene 5.7-6.2 gph, powder feeding gas 20-23 scfh, spraying distance 330-380 mm, coating thickness 0.03-0.05 mm, and the roller surface roughness after spraying is Ra7-9 μm; Step 4: Use sealing liquid to evenly brush the roller surface, and the immersion is uniform without foreign matter defects, and low-temperature heat treatment is performed to obtain a high-temperature resistant and corrosion-resistant composite coating on the surface of the zinc pot roller.