CN109468634B - Process method for recovering precision of rolling mill step pad by laser cladding technology - Google Patents

Abstract

The invention belongs to the field of laser repair, and particularly relates to a process method for recovering the precision of a rolling mill step pad by using a laser cladding technology. The method is realized by surface derusting, detection before repair, surface fatigue layer removal by processing, detection after processing, fusion covering process determination (comprising process parameters and alloy powder composition), detection after fusion covering, rough and fine machining and detection after repair, and the method is simple and convenient to operate and greatly reduces the labor intensity; the method has the characteristics of restoring the original design size precision and increasing the surface corrosion resistance and wear resistance, and improves the overall use efficiency; the influence on the surface is small, large deformation cannot be caused, and the surface is smooth and uniform and has high glossiness after being processed by the grinding machine; the product is tracked and detected after being repaired, the size precision of the step pad can be recovered after laser cladding, the operation cost is low, the processed surface has no crack during nondestructive inspection, the normal use can be met, and the service life of the product is prolonged by more than 3 times.

Description

Process method for recovering precision of rolling mill step pad by laser cladding technology

Technical Field

The invention relates to a process method for recovering the precision of a rolling mill step pad by a laser cladding technology, belonging to the field of laser repair.

Background

The step pad is a device which is arranged in a frame in a hot continuous rolling way in a steel mill and is used for adjusting the height of a lower supporting roll. There are integral (a ladder pad comprises a plurality of steps) or split type (every is a thickness dimension, the polylith cushion constitutes the ladder) two kinds, there is certain height dimension difference in each step face, it has two kinds to make the material to have high alloy structure steel and martensite stainless steel, the main material is 34CrNi3Mo, the form of case hardening has carburization, nitridation and surface quenching etc., there are iron scale and a large amount of water-washed brush steam corrosion and scouring that splash at a high speed between the rolling slab temperature range 600~1200 ℃ of during operation, receive the effect of roll vertical direction 'round trip' rolling force itself, so main damage form is: surface wear, crushing, corrosion, and the like.

With the continuous development of the steel industry in China, at present, most of step pads operate under the condition of overload, the fault rate is increased continuously, the step pads need to be replaced when the average abrasion loss is 2-3mm in the process of maintenance every year, 168 step pads are arranged on one continuous casting and rolling plate line, more than 80% of the continuous casting and rolling plate line need to be replaced, the cost for replacing a new step pad is about 17 ten thousand, more than 8 million yuan per step pad is needed for replacing all the step pads of one plate line, more than 100 step pads in steel mills in China are replaced every year, and therefore the cost is huge every year. In order to reduce the cost and change waste into valuable, it is necessary to restore the dimensional accuracy of the step pad.

Therefore, selecting a reasonable process method for restoring the dimensional accuracy of the step pad to ensure the repaired step pad to have corrosion resistance and improve the surface hardness and wear resistance is a problem to be solved urgently at present.

The laser cladding repair technology is an advanced remanufacturing technology and is rapidly popularized and widely applied in recent years.

Laser surface cladding is non-contact machining (heating a workpiece with an intense laser beam without touching the workpiece) and the input heat is controllable (the heat input into the substrate is controlled by controlling the output power of the laser, the size of the spot diameter and the scanning speed). The laser surface cladding has the characteristics of high energy density, compact cladding quality, high bonding strength, low dilution rate of cladding layer tissues, small heat affected zone and the like, and the adopted standard laser repair method can solve the welding residual stress and cracking tendency caused by other welding methods. Therefore, the method is very suitable for local treatment of parts with high quality requirements, and is particularly suitable for repairing parts with complex geometric shapes and small deformation requirements after repair.

Laser forming is a remanufacturing technology which prepares a new material on the surface of a base material by laser cladding and forms metallurgical bonding with the base body.

Because the high-temperature alloy is generally selected during manufacturing of the traditional domestic step pad, and the size of the traditional domestic step pad is not restored by a mature method at present, the applicant invents a process method for laser restoration precision of the step pad through theoretical analysis and a large number of experiments, and prepares a special material to be applied to the step pad by combining with an advanced remanufacturing technology of laser cladding, so that the problems can be effectively solved.

The applicant searches and verifies that: the laser cladding technology is adopted to recover the dimensional accuracy of the step pad, no precedent is made at home, and no relevant report is seen at abroad. Therefore, the search for suitable process parameters of step pad laser repair by laser cladding technology still requires further creative research work by those skilled in the art.

Disclosure of Invention

The invention aims to solve the problems in the prior art, provides a process method for recovering the precision of a rolling mill step pad by a laser cladding technology through repeated research and improvement, adopts a 5 kilowatt gas laser to carry out laser treatment on the step pad, is provided with a liftable working platform for lifting the laser, is used for adjusting various types of step pads with different heights, and carries out early and later processing treatment by a milling machine, a grinding machine and the like.

The technical scheme provided by the invention is as follows: a process method for recovering the precision of a rolling mill step pad by a laser cladding technology comprises the following process steps.

(1) And (5) removing rust on the surface.

The surface of the step pad is often seriously rusted after long-term use, so that the surface of the step pad needs to be subjected to rust removal treatment for facilitating detection and determining the damage condition, and the rust removal method comprises polishing, sand blasting, high-pressure water gun cleaning and the like.

(2) And (5) detecting before repairing.

The method comprises the steps of detecting the hardness and the size of a step pad before repairing, wherein the size can determine the damage amount of the step pad, the thickness of a fatigue-removing layer and the thickness of a cladding layer can be determined by matching with layered hardness detection, and nondestructive flaw detection is carried out on the step pad so as to ensure that the step pad does not have crack defects influencing repairing; if a large area crack is detected on the surface, even a new crack is penetrated, the step pad cannot be repaired.

(3) And processing and removing the surface fatigue layer.

And (3) removing a surface fatigue layer by milling, wherein the fatigue layer mainly comprises an original surface hardening layer (a quenching layer, a carburization layer and a nitriding layer) and a surface corrosion layer (with corrosion pits).

(4) And (5) detecting after processing.

And (3) carrying out size and hardness detection on the step pad after the fatigue layer is removed to determine that the fatigue layer is removed according to the preset processing amount or the size of the step pad after actual processing is carried out to finally determine the number and thickness of laser cladding layers, carrying out nondestructive flaw detection on the surface and determining that the defect of the repaired surface which does not influence the laser cladding is detected.

(5) And (4) determining a cladding process.

And determining the number and thickness of the metal powder and the cladding layer according to the design surface hardness and the thickness of the hardened layer of the original step pad or the hardness and the thickness of the functional layer required by the technical protocol.

In the cladding process, preheating and slow cooling treatment are carried out to avoid cracking of a cladding layer, cladding is carried out by adopting a composite functional layer process, the size thickness of a bottom layer FM1 is strictly controlled, the phenomenon that the hardness index of a processed surface layer is influenced due to overlarge cladding thickness of the bottom layer is avoided, and surface layer FM2 laser cladding is reserved according to the size of a drawing, wherein the thickness of the surface layer FM2 laser cladding is about 1 mm; the step pad is subjected to laser cladding by a 5-kilowatt gas laser, and a liftable working platform is firstly arranged for lifting the laser so as to ensure that the heights of the processing surfaces are consistent, pneumatic powder feeding is adopted in the laser cladding process, and the component control is uniform. The cladding technological parameters are as follows: power: 2000-10000W, spot diameter: Φ 2-25mm, scanning speed: 200 and 1000mm/s, and adopts pneumatic powder feeding to protect the molten pool with argon gas in the cladding process.

The laser cladding bottom layer alloy powder FM1 comprises the following components in percentage by mass: 0.02-1% of C, Cr: 10-25%, Si: 0.2-3.5%, Ni: 15-40%, Mo 0.5-2.5%, Mn 0.2-1.5%, Nb 0.05-1%, B: 0.02-0.5% and the balance of Fe.

The laser cladding surface layer alloy powder FM2 comprises the following components: cr: 8-30%, Ni: 10-25%, C: 0.2-4%, Fe 5-20%, Mn: 0.5-2.5%, W: 3-5%, Si: 0.2-3.5%, V: 0.2-1%, Cu: 0.1-0.5%, Mo 0.3-3%, Ti: 0.1-0.5%, Al: 0.02-0.5%, rare earth element less than or equal to 0.1% and Co in balance.

Wherein the rare earth element is one or more of La, Y, Nd and Ce.

(6) And (5) detecting after cladding.

And carrying out size detection after cladding, determining that the cladding allowance meets the processing requirement, and carrying out nondestructive flaw detection to ensure that the cladding layer has no defects such as cracks.

(7) And (5) carrying out rough and fine machining.

The integral type step pad is large in size area, a gantry type guide rail grinding machine is needed to carry out grinding machining, machining cost is high, the upper surface and the lower surface of the repaired step pad are required to be ground, and original design size precision and surface smoothness are restored after grinding.

(8) And (5) detecting after repairing.

In order to ensure the quality of finished products, the processed step pad needs to be subjected to size and hardness detection and nondestructive flaw detection.

Wherein, in the FM1 alloy material: the addition of the element C forms various carbides with Cr, Mo and W elements, and has the double effects of grain boundary strengthening and structure stability, the addition of the element C can dissolve Mo and enhance the performance of the alloy, when the content of the element C is less than 1%, although the formed carbides are less, when the content exceeds the value, the carbides are more beneficial to strengthening the alloy, but the addition of more element C is unfavorable to the toughness of the alloy, but the toughness of the Fe-based alloy powder is known to be insufficient, so the addition amount of the element C is complementary with the Fe-based alloy powder; the addition of Cr element enhances the corrosion resistance and the abrasion resistance of the alloy, increases the surface strength and the oxidation resistance of the metal, but a large number of tests show that the content of Cr element cannot be too high, more than 25 percent of Cr element is easy to temper and embrittle, and if the content of Cr element is less than 10 percent, the Cr element cannot resist high temperature and resists oxidation and corrosion; the addition of the Si element can not only reduce the melting point of the alloy, enlarge the solid-liquid phase line temperature area, form a low-melting eutectic, perform deoxidation and reduction functions and slag-forming functions, play a role in hardening and strengthening a coating and improving the operation process performance, but also reduce the melting point of powder to below 1300 ℃, thereby protecting a powder nozzle and further playing a good role in the operation and cost control of actual production; the addition of the Ni element can play a role in wear resistance and corrosion resistance; the addition of Mo element improves the electrode potential of the matrix, improves corrosion resistance and increases metal toughness; the addition of Mn not only has the function of increasing rigidity and hardness, but also can desulfurize and deoxidize the coating and improve the metal performance, but the Mn content of more than 2.5 percent is easy to embrittle and generate cracks; the addition of the B element can refine the matrix and the carbide, form high-hardness oxide with a plurality of metal elements and resist heat; niobium (Nb) can refine crystal grains, reduce temper brittleness and improve strength; the Fe-based alloy not only can reduce the cost, but also can improve the resistance to a high-temperature carburization environment and control thermal expansion, but also has poor toughness, so the Fe-based alloy is matched with other elements to form a coating which has a good metallurgical surface, compact coating, no pore or crack in deformation and good corrosion resistance and wear resistance.

Wherein, in the FM2 alloy material: the Co-based alloy has better high-temperature resistance and corrosion resistance, and the addition of the Cr element increases the surface strength and oxidation resistance of the metal; si is added to increase the wettability of the alloy powder to form a self-fluxing alloy, the melting point of the powder can be reduced, and a powder nozzle is protected, but the experiment shows that the alloy powder with excessive Si content has fine cracks; the addition of the Ni element can reduce the cost, improve the cladding performance of the alloy powder and improve the toughness of the coating; co and Cr generate stable solid solution, a small amount of C element of 0.2-4% is added at the moment, so that metastable carbides such as chromium carbide, tungsten carbide and the like are dispersed and distributed on the alloy matrix, the coating has higher hardness, wear resistance, corrosion resistance and high-temperature oxidation resistance, and the content range is suitable for matching with cobalt-based alloy, so that powder can be uniformly fed, and the uniform heating of the powder is facilitated; the cost is reduced by adding Fe element, the content of Fe element is controlled below 20%, and if the content of Fe element is high, the hardness of the coating is reduced; the addition of the W element can enable the alloy coating to resist high temperature and maintain mechanical properties; the addition of the V element is beneficial to improving the microhardness and the wear resistance of the matrix; the addition of trace Cu element can reduce the generation of cracks; the addition of Ti element can make the structure compact, refine the grain strength and prevent intergranular corrosion; the performance of the coating can be enhanced by adding a small amount of Al element, but when the adding content is more, the performance of the coating is improved, but the elongation of the coating is reduced, and fine cracks are generated; the addition of the rare earth elements can refine grains, improve alloy structure, prevent crack resistance, better combine with the parent metal during cladding, improve surface flatness and reduce processing amount.

The invention has the beneficial effect.

(1) And a complete process method is provided for recovering the dimensional accuracy of the step pad.

(2) The technology aims at the characteristics of program control and simple and convenient operation of the gas laser, and is operated by utilizing equipment such as a milling machine, a grinding machine and the like, so that the labor intensity is greatly reduced, and the requirement on dimensional precision is improved.

(3) The bottom layer FM1 and the surface layer FM2 are selected according to the damage amount in laser cladding, so that the method has the characteristics of restoring the original design size precision and increasing the surface corrosion resistance and wear resistance, improves the characteristics of large abrasion loss, surface corrosion and the like of the step pad, and improves the overall use efficiency.

(4) The laser cladding has small heat input during laser cladding, small influence on the surface, no great deformation, smooth and uniform surface and high glossiness after being processed by a grinding machine.

(5) The laser cladding bottom layer material FM1 and the surface layer material FM2 form a gradient composite material, the material performance of the bottom layer powder FM1 and the closeness degree of the repair product material are more than 80%, so the bonding force and the bonding strength of the parent metal are very good; surface powder FM2 mainly increases the surface and resistance to wear, corrosion resistance, and high temperature resistant is anti-oxidant, tracks to the product after repairing and detects, can resume the size precision of ladder pad after laser cladding, and the running cost is low, and the surface nondestructive test crack-free after the processing can satisfy normal use to improve the life of product more than 3 times.

Detailed Description

Example 1X bench mark pad laser treatment restored precision.

The base material of the step pad is 34CrNi3 Mo.

(1) And carrying out sand blasting and rust removal on the surface of the step pad to expose the metal surface.

(2) Machining is carried out in advance, and the corrosion, wear surface and fatigue layer are removed (the machining is carried out to the lowest point of corrosion, and then the machining is carried out for 0.3-0.5 mm).

(3) Hardness detection and fatigue layer thickness judgment

The fatigue layer can be removed when the hardness HB is less than or equal to 290, the size measurement abrasion loss is about 5mm, nondestructive inspection is carried out, no crack is observed on the surface by naked eyes, and the laser repair can be judged when a small number of air holes (less than 5 air holes which are less than phi 2 are allowed on each square decimeter).

(4) And (3) detection after processing: and (3) after removing the fatigue layer by early-stage machining, discovering pores, and performing laser repair welding on the pores, wherein the repair welding process comprises the following steps.

Materials: metal powder FM 1.

And secondly, manually cleaning the air holes by using an electric tool, and carrying out nondestructive inspection and visual inspection on the air holes.

Thirdly, prefabricating powder: and pre-preparing metal powder into the cleaned air holes in advance.

Fourthly, laser cladding: the technological parameters are as follows: power: 4000W, spot diameter: and phi 5mm, manually turning off light and stopping controlling light to perform cladding.

Fifthly, the thickness of the base surface is required to be 0.5-1mm higher than that of the original base surface after full repair welding.

Sixthly, manually grinding the repair welding part, wherein the grinding is required to be carried out: the planeness is less than or equal to 0.2 mm.

And seventhly, nondestructive flaw detection after grinding has no defects of cracks, air holes and the like, and the laser cladding condition is met.

(5) Carrying out laser cladding on the processing surface of the step pad by adopting a gas laser, wherein the laser cladding process comprises the following steps: materials: bottom layer metal powder FM1, surface layer metal powder FM 2; observing the quality and power change of the light; powder feeding needs to be uniform; fourthly, attention is paid to cleaning oxide skin during cladding; fifthly, when cladding the two ends, making the two ends into right angles to ensure the processing size; sixthly, laser cladding process parameters are as follows: power: 3200W, spot diameter: 5mm, scanning speed: 550mm/s, adopting pneumatic powder feeding, and keeping the single-layer cladding thickness to be 1-1.2mm, in the cladding process, using bottom layer powder FM1 to restore the size and reserving 1mm as a surface layer, using surface layer powder FM2 as an anti-corrosion wear-resistant layer, and keeping the cladding thickness to be 1-1.5mm higher than that of the finished product drawing.

(6) And (4) detecting the actual size after cladding by 1.3mm larger than the standard size of a drawing, and carrying out nondestructive inspection without cracks.

(7) And (3) roughly processing the laser cladding surface according to a drawing, reserving a finish machining allowance single surface of 0.2-0.25mm, and performing finish machining by using a grinding machine to meet the requirements of the tolerance precision (the planeness is less than or equal to 0.15, the verticality is less than or equal to 0.15 and the parallelism is less than or equal to 0.15) of the original design size and the surface smoothness Ra0.8.

(8) And (3) detection after repair: the dimensional deviation is +/-0.06 mm, the form and position tolerance is not more than 0.12, the surface roughness is Ra0.8, the glossiness reaches N6 level, the visual inspection of nondestructive inspection does not have obvious defects such as cracks, air holes and the like, the hardness of 9 points detected on the processed surface after repair is HRC 32-47, and the average hardness is 38.7; after the machine is used for three years, the annual abrasion loss is less than 0.10mm, and the abrasion resistance is integrally improved.

Wherein, FM1 selects the material ratio as follows: 0.65% of C, Cr: 12%, Si 2%, Ni: 20%, Mo 1.2%, Nb: 0.4%, Mn 0.5%, B: 0.25%, Fe: and (4) the balance.

FM2 comprises the following materials: cr: 23%, Ni: 17%, C: 1%, 16% of Fe, Mn: 1.2%, W: 3.5%, Si: 1.5%, V: 0.45%, Cu: 0.35%, Mo:2.2%, Ti: 0.25%, Nd: 0.03%, Al: 0.1% and the balance of Co.

Example 2X bench mark pad laser treatment restored precision.

The base material of the step pad is 34CrNi3 Mo.

(1) And cleaning and derusting the step pad.

(2) Before repairing, size and hardness detection are carried out, abrasion loss is determined, and after nondestructive inspection is determined, laser repairing can be carried out (after the size is detected, the abrasion loss is determined to be about 2.5 mm).

(3) And (4) carrying out mechanical processing to remove the fatigue layer such as corrosion and abrasion on the surface.

(4) The fatigue layer is removed by mechanical processing in the early stage, and the surface of the processed part is subjected to nondestructive flaw detection after processing, so that the defects of cracks, air holes and the like are avoided.

(5) Carrying out laser cladding on the processing surface of the step pad by adopting a gas laser, wherein the laser cladding process comprises the following steps: materials: bottom layer metal powder FM1, surface layer metal powder FM 2; secondly, observing the quality and power change of the observation light; thirdly, the powder feeding is uniform; fourthly, attention is paid to cleaning oxide skin during cladding; fifthly, the two ends are cladded to be right-angled, so that the machining size is ensured; sixthly, laser cladding technological parameters are as follows: power: 3600W, spot diameter: Φ 4.5mm, scanning speed: 450mm/s, adopting pneumatic powder feeding, and enabling the single-layer cladding thickness to be 0.8-1 mm), in the cladding process, using bottom layer powder FM1 to restore the size, reserving 1mm as a surface layer, using surface layer powder FM2 as an anti-corrosion wear-resistant layer, selecting the optimal laser cladding parameters for other process parameters, and ensuring that the cladding thickness is 1-1.5mm higher than that of a finished product drawing.

(6) And (4) detecting the actual size after cladding, wherein the actual size is 1.2mm larger than the size of the drawing, and performing nondestructive inspection to avoid the defects of cracks and the like on the surface.

(7) And (3) roughly processing the laser cladding surface according to a drawing, reserving a fine processing allowance single surface of 0.15-0.20mm, and performing post fine processing by using a grinding machine to ensure that the step pad meets the requirements of the tolerance precision (flatness is less than or equal to 0.15, verticality is less than or equal to 0.15 and parallelism is less than or equal to 0.15) and surface smoothness (Ra0.8) of the original design size.

(8) And (3) detection after repair: the size deviation is +/-0.07 mm, the form and position tolerance is not more than 0.10, the surface roughness is Ra0.8 and reaches N6 level, the defects of cracks, air holes and the like are not detected by naked eyes in nondestructive inspection, 10 points are detected on the processed surface after repair, the hardness is HRC 30-45, and the average hardness is 37.2; after the machine is used for two years, the annual abrasion loss is less than 0.1 mm. The wear resistance is greatly improved.

Wherein, FM1 selects the material ratio as follows: 0.4% of C, Cr: 16%, Si 2.5%, Ni: 25%, Mo:0.7%, Nb: 0.45%, Mn 0.8%, B: 0.3%, Fe: and (4) the balance.

FM2 comprises the following materials: cr: 20%, Ni: 15%, C: 1%, Fe 15%, Mn: 1.2%, W: 3.5%, Si: 1.5%, V: 0.45%, Cu: 0.25%, Mo:2.2%, Ti: 0.2%, Al: 0.05%, Y: 0.05 percent and the balance of Co.

Through two examples and field tracking detection in an unscheduled period every year, the annual size abrasion loss is less than 0.1mm, which shows that the problems of corrosion, crushing and abrasion repair of the step pad are really and effectively solved by adopting a laser cladding technology, the integral size precision requirement of the step pad can be recovered, the normal use of the step pad in steel rolling can be met, the effect of changing waste into valuable is achieved, a large amount of cost is saved, and the service life is prolonged by more than 3 times.

Claims (1)

1. A process method for recovering the precision of a rolling mill step pad by a laser cladding technology is characterized by comprising the following process steps:

(1) surface rust removal

Carrying out surface rust removal on the stepped pad in a polishing, sand blasting and high-pressure water gun cleaning mode;

(2) pre-repair detection

Performing hardness, size detection and nondestructive flaw detection on the step pad before repair, determining the damage amount of the step pad, the thickness of the fatigue removing layer and the thickness of the cladding layer, and ensuring that the step pad does not have crack defects influencing repair;

(3) processing and removing surface fatigue layer

Removing the surface fatigue layer by milling;

(4) post-process inspection

Carrying out size and hardness detection and nondestructive flaw detection on the step pad after the fatigue layer is removed;

(5) determination of cladding Process

Determining the number and thickness of metal powder and cladding layers according to the surface hardness and hardened layer thickness of the original step pad design or the hardness and functional layer thickness required by a technical protocol;

in the cladding process, in order to avoid cracking of a cladding layer, preheating and slow cooling treatment are carried out, and cladding is carried out by adopting a composite functional layer process; FM1 is alloy powder for bottom layer cladding, FM2 is alloy powder for surface layer cladding, and the cladding technological parameters are as follows: power: 2000-10000W, spot diameter: Φ 2-25mm, scanning speed: 200 and 1000mm/s, adopting pneumatic powder feeding, and protecting a molten pool with argon in the cladding process;

(6) post-cladding detection

Carrying out size detection and nondestructive flaw detection after cladding;

(7) rough and fine machining

Carrying out rough milling and grinding on the clad step pad to achieve the dimensional accuracy and surface roughness required by a drawing;

(8) post-repair detection

Carrying out size and hardness detection and nondestructive flaw detection on the processed step pad;

the laser cladding bottom layer alloy powder FM1 comprises the following components: 0.02-1% of C, Cr: 10-25%, Si: 0.2-3.5%, Ni: 15-40%, Mo:0.5-2.5%, Mn:0.2-1.5%, Nb:0.05-1%, B: 0.02-0.5% and the balance of Fe;

the laser cladding surface layer alloy powder FM2 comprises the following components: cr: 8-30%, Ni: 10-25%, C: 0.2-4%, Fe:5-20%, Mn: 0.5-2.5%, W: 3-5%, Si: 0.2-3.5%, V: 0.2-1%, Cu: 0.1-0.5%, Mo:0.3-3%, Ti: 0.1-0.5%, Al: 0.02-0.5%, rare earth element less than or equal to 0.1%, Co: the balance;

wherein the rare earth element is one or more of La, Y, Nd and Ce.