阅读说明：本技术 一种球墨铸铁与低碳钢的激光焊接方法 (Laser welding method for nodular cast iron and low-carbon steel ) 是由 石岩 张培学 刘佳 于 2020-12-28 设计创作，主要内容包括：本发明提供了一种球墨铸铁与低碳钢的激光焊接方法,属于激光加工技术领域。本发明首先用激光对球墨铸铁待焊接表面进行激光表面热处理进行去石墨化,球墨铸铁待焊接表面的石墨在激光作用下大部分烧蚀成气体溢出,另一部分溶解在组织中,在激光热处理过程中,熔池温度梯度很大,形成极大的过冷度,达到了马氏体生成的条件,并伴随着碳化物的生成,从而使球墨铸铁待焊接表面的石墨减少,获得表面局部去石墨化球墨铸铁。将去石墨化表面与低碳钢待焊接表面对接,然后实施激光焊接,可以有效避免激光焊接过程中焊接接头气孔、裂纹缺陷的产生,显著提升焊接接头强度。(The invention provides a laser welding method of nodular cast iron and low-carbon steel, and belongs to the technical field of laser processing. The method comprises the following steps of firstly carrying out laser surface heat treatment on the surface to be welded of the nodular cast iron by using laser to remove graphitization, ablating most of graphite on the surface to be welded of the nodular cast iron into gas under the action of the laser to overflow, dissolving the other part of the graphite in a tissue, and forming a great supercooling degree due to great temperature gradient of a molten pool in the laser heat treatment process to achieve the condition of martensite generation and reduce the graphite on the surface to be welded of the nodular cast iron along with the generation of carbide, thereby obtaining the surface partially-graphitized nodular cast iron. The graphitized surface is butted with the surface to be welded of the low-carbon steel, and then laser welding is carried out, so that the generation of air holes and crack defects of a welding joint in the laser welding process can be effectively avoided, and the strength of the welding joint is obviously improved.)

1. The laser welding method of the nodular cast iron and the low-carbon steel is characterized by comprising the following steps of:

carrying out laser surface heat treatment on the surface to be welded of the nodular cast iron, wherein most of graphite on the surface to be welded is ablated into gas to overflow, and the other part of graphite is dissolved in the structure to form a graphite removal layer, so that the nodular cast iron with the surface partially subjected to graphitization removal is obtained;

annealing the surface partially-graphitized nodular cast iron to obtain annealed surface partially-graphitized nodular cast iron;

and carrying out laser welding on the annealed surface locally-graphitized ductile cast iron and the low-carbon steel.

2. The laser welding method according to claim 1, wherein the laser power of the laser surface heat treatment is 500 to 700W, the scanning speed is 150 to 300mm/min, and the positive defocus amount is 5 to 25 mm.

3. The welding method of claim 1, further comprising applying a light absorbing coating to the surface to be welded of ductile iron before the laser surface heat treatment.

4. Welding method according to claim 3, characterised in that the light-absorbing coating consists of C powder and MoS₂Dispersing the powder in absolute ethyl alcohol to obtain the powder; the C powder and MoS₂The mass ratio of the powder is 1: 1.

5. The welding method according to claim 1, wherein the annealing temperature is 250 to 300 ℃ and the holding time is 1.5 to 2.5 hours.

6. The welding method according to claim 1, wherein the power of the laser welding is 3000-5000W, the welding speed is 1-3 m/min, the negative defocusing amount is 1-5 mm, and the shielding gas flow is 20-30L/h.

7. The welding method according to claim 1, characterized in that the ductile iron comprises, in mass percent: 3.70-4.00% of C, 2.15-2.93% of Si, 0.46-0.66% of Mn, 0.010-0.016% of S, 0.027-0.035% of P, 0.027-0.050% of Mg, 0.026-0.043% of Re and the balance of Fe; the carbon equivalent of the nodular cast iron is 4.3-4.6.

8. The welding method of claim 1, wherein the low carbon steel comprises, in mass percent: 0.17-0.23% of C, 0.17-0.37% of Si, 0.80-1.10% of Mn, 1.00-1.30% of Cr, less than or equal to 0.030% of S, less than or equal to 0.030% of P, less than or equal to 0.30% of Ni, Cu: less than or equal to 0.30 percent, 0.04 to 0.10 percent of Ti and the balance of Fe.

9. The welding method according to claim 1, further comprising, before the laser surface heat treatment, polishing the surface to be welded of the ductile iron with sand paper, cleaning the polished surface with an alcohol solution, and blow-drying.

10. The welding method of claim 1, further comprising, prior to the laser welding, planarizing the surface to be welded of the annealed surface partially graphitized ductile iron.

Technical Field

The invention relates to the technical field of laser processing, in particular to a laser welding method of nodular cast iron and low-carbon steel.

Background

The nodular cast iron is lighter than steel by about 10%, has no residual stress, has less defects during processing, has better damping property, wear resistance, notch sensitivity and the like than steel, has great advantage in price and is used as a combined gear ring part. The steel as the gear part is more beneficial to carburization and quenching treatment to improve the strength, hardness and wear resistance of the gear, thereby prolonging the service life of the gear. The nodular cast iron is used as the combined gear ring part, and the steel is used as the gear part, so that the cost can be effectively reduced, and the development direction of future light weight is met. Due to the existence of a large amount of graphite in the nodular cast iron, a large amount of carbon is dissolved into a molten pool in the welding process of the nodular cast iron and steel and is separated out in the form of ledeburite in the rapid cooling process after welding, so that welding cracks and air holes are generated and the mechanical property is reduced.

The method for welding the cast iron and the steel commonly used at present mainly comprises friction welding, brazing, diffusion welding, electron beam welding, laser-arc composite welding, laser welding and the like, wherein the method for fusion welding of the electron beam welding, the laser-arc composite welding, the laser welding and the like has the advantages that a large amount of carbon is dissolved into a molten pool in the welding process due to the high carbon equivalent of the nodular cast iron, a fusion area is influenced by the diffusion of the carbon of a base material to form carbon enrichment, and a brittle ledeburite layer is easily formed, so that the fracture is caused. In the non-melting welding methods such as friction welding, brazing, diffusion welding and the like, the friction welding and the diffusion welding have the defects of low production efficiency, special requirements on welding pieces, difficulty in controlling welding quality and the need of welding under a vacuum condition. While the strength of brazed joints is generally lower, especially joints that have not been treated by a particular process.

The laser-MIG composite welding performance of ductile cast iron and ferritic stainless steel is carried out in Xuzhou construction (Xuzhou construction, Liuxiangyu, Hangzhou Xiang, and the like, laser-MIG composite welding performance [ J ] Shenyang industry university report, 2012(5):496 and 503.) and the like, and the welding joint is analyzed by filling 3 welding wires with different nickel mass fractions, although the welding joint has no cracks and is well formed, a large number of ledeburite bodies exist in the welding joint, so that the tensile strength is not high. The laser welding of cast iron for differential gears and carburized steel is carried out by Jiyonggyu (Yu J, Jung T, Kim S, et al. laser welding of cast iron and hardened steel for differential gear [ J ]. Journal of Mechanical Science & Technology,2011,25(11): 2887-.

Disclosure of Invention

The invention aims to provide a laser welding method of nodular cast iron and low-carbon steel, which solves the problems of cracks, air holes and the like in the welding process of the nodular cast iron and the low-carbon steel.

In order to achieve the above object, the present invention provides the following technical solutions:

the invention provides a laser welding method of nodular cast iron and low-carbon steel, which comprises the following steps:

carrying out laser surface heat treatment on the surface to be welded of the nodular cast iron, wherein most of graphite on the surface to be welded is ablated into gas to overflow, and the other part of graphite is dissolved in the structure to form a graphite removal layer, so that the nodular cast iron with the surface partially subjected to graphitization removal is obtained;

annealing the surface partially-graphitized nodular cast iron to obtain annealed surface partially-graphitized nodular cast iron;

and carrying out laser welding on the annealed surface locally-graphitized ductile cast iron and the low-carbon steel.

Preferably, the laser power of the laser surface heat treatment is 500-700W, the scanning speed is 150-300 mm/min, and the positive defocusing amount is 5-25 mm.

Preferably, before the laser surface heat treatment, a light-absorbing coating is coated on the surface to be welded of the ductile iron.

Preferably, the light-absorbing coating consists of C powder and MoS₂Dispersing the powder in absolute ethyl alcohol to obtain the powder; the C powder and MoS₂The mass ratio of the powder is1:1。

Preferably, the annealing treatment temperature is 250-300 ℃, and the heat preservation time is 1.5-2.5 h.

Preferably, the laser welding power is 3000-5000W, the welding speed is 1-3 m/min, the negative defocusing amount is 1-5 mm, and the protective gas flow is 20-30L/h.

Preferably, the nodular cast iron comprises the following components in percentage by mass: 3.70-4.00% of C, 2.15-2.93% of Si, 0.46-0.66% of Mn, 0.010-0.016% of S, 0.027-0.035% of P, 0.027-0.050% of Mg, 0.026-0.043% of Re and the balance of Fe; the carbon equivalent of the nodular cast iron is 4.3-4.6.

Preferably, the low-carbon steel comprises the following components in percentage by mass: 0.17-0.23% of C, 0.17-0.37% of Si, 0.80-1.10% of Mn, 1.00-1.30% of Cr, less than or equal to 0.030% of S, less than or equal to 0.030% of P, less than or equal to 0.30% of Ni, Cu: less than or equal to 0.30 percent, 0.04 to 0.10 percent of Ti and the balance of Fe.

Preferably, before the laser surface heat treatment, the method further comprises the steps of polishing the surface to be welded of the ductile cast iron smoothly by using abrasive paper, cleaning the polished surface by using an alcohol solution, and drying.

Preferably, before the laser welding, the method further comprises the step of flattening the to-be-welded surface of the annealed surface partially-graphitized ductile iron.

The invention provides a laser welding method of nodular cast iron and low-carbon steel, which comprises the following steps: carrying out laser surface heat treatment on the surface to be welded of the nodular cast iron, wherein most of graphite on the surface to be welded is ablated into gas to overflow, and the other part of graphite is dissolved in the structure to form a graphite removal layer, so that the nodular cast iron with the surface partially subjected to graphitization removal is obtained; annealing the surface partially-graphitized nodular cast iron to obtain annealed surface partially-graphitized nodular cast iron; and carrying out laser welding on the annealed surface locally-graphitized ductile cast iron and the low-carbon steel.

The method comprises the following steps of firstly carrying out laser surface heat treatment on the surface to be welded of the nodular cast iron by using laser to remove graphitization, ablating most of graphite on the surface to be welded of the nodular cast iron into gas under the action of the laser to overflow, dissolving the other part of the graphite in a tissue, and forming a great supercooling degree due to great temperature gradient of a molten pool in the laser heat treatment process to achieve the condition of martensite generation and reduce the graphite on the surface to be welded of the nodular cast iron along with the generation of carbide, thereby obtaining the ball-milled cast iron with the surface partially removed graphitization. The graphitized surface is butted with the surface to be welded of the low-carbon steel, and then laser welding is carried out, so that the generation of air holes and crack defects of a welding joint in the laser welding process can be effectively avoided, and the strength of the welding joint is obviously improved.

Drawings

FIG. 1 is a process flow diagram of a laser welding method of the present invention;

FIG. 2 is a metallographic picture of partially surface-graphitized ductile cast iron obtained after the laser surface heat treatment in example 1;

FIG. 3 is a drawing graph of a ductile iron and low carbon steel weldment of example 1;

FIG. 4 is a metallographic picture of a weld of nodular cast iron and mild steel in example 1;

FIG. 5 is a tensile fracture metallographic graph of ductile iron and low carbon steel in example 1;

FIG. 6 is a graph showing a comparison of the tensile strengths of the base metal and the weld members in example 1;

FIG. 7 is a metallographic image of a weld between ductile iron and low-carbon steel in comparative example 1 without surface laser heat treatment.

Detailed Description

The invention provides a laser welding method of nodular cast iron and low-carbon steel, which comprises the following steps:

carrying out laser surface heat treatment on the surface to be welded of the nodular cast iron, wherein most of graphite on the surface to be welded is ablated into gas to overflow, and the other part of graphite is dissolved in the structure to form a graphite removal layer, so that the nodular cast iron with the surface partially subjected to graphitization removal is obtained;

annealing the surface partially-graphitized nodular cast iron to obtain annealed surface partially-graphitized nodular cast iron;

and carrying out laser welding on the annealed surface locally-graphitized ductile cast iron and the low-carbon steel.

According to the method, the surface to be welded of the nodular cast iron is subjected to laser surface heat treatment, most of graphite on the surface to be welded is ablated into gas to overflow, and the other part of graphite is dissolved in the tissue to form a graphite removal layer, so that the surface partially-graphitized nodular cast iron is obtained.

In the invention, the nodular cast iron preferably comprises, by mass, 3.70-4.00% of C, 2.15-2.93% of Si, 0.46-0.66% of Mn, 0.010-0.016% of S, 0.027-0.035% of P, 0.027-0.050% of Mg, 0.026-0.043% of Re and the balance of Fe; the carbon equivalent of the nodular cast iron is preferably 4.3-4.6.

Before the laser surface heat treatment, the nodular cast iron is preferably processed into required specifications, then the surface to be welded of the nodular cast iron is polished smooth by abrasive paper, and then the polished surface is cleaned by alcohol solution and dried by blowing.

After blow-drying, the invention preferably coats the surface to be welded of the ductile iron with a light-absorbing coating, waits for the coating to dry, and then carries out laser surface heat treatment. In the present invention, the light-absorbing coating is preferably composed of C powder and MoS₂Dispersing the powder in absolute ethyl alcohol to obtain the powder; in the present invention, the C powder and MoS₂The mass ratio of the powders is preferably 1: 1. The invention is used for the C powder and the MoS₂The particle size of the powder is not particularly limited, and may be one known in the art. In the present invention, the C powder and MoS₂The ratio of the total mass of the powder to the amount of absolute ethanol is preferably 2g:1 mL.

In the present invention, the light absorbing coating is preferably applied in such an amount that the thickness of the coating layer is 0.1 to 0.2 mm.

Because the nodular cast iron has higher reflectivity to laser, the surface to be welded of the nodular cast iron is coated with a layer of light absorption coating, so that the absorption effect to the laser is enhanced. During the laser surface heat treatment, the light-absorbing coating material is vaporized and removed from the ductile iron.

In the invention, the laser power of the laser surface heat treatment is preferably 500-700W, and more preferably 550-650W; the scanning speed is preferably 150-300 mm/min, and more preferably 180-250 mm/min; the positive defocusing amount is preferably 5-25 mm, and more preferably 10-20 mm. The surface laser heat treatment is preferably carried out by using a carbon dioxide laser.

Most of graphite on the surface to be welded of the ductile iron is ablated into gas to overflow under the action of laser, the other part of graphite is dissolved in a structure, the temperature gradient of a molten pool is large in the heat treatment process of the laser surface, the extremely high supercooling degree is formed, the condition of martensite generation is achieved, and along with the generation of carbides (mainly comprising cementite, ferrite and austenite), C elements on the surface layer are reduced, a graphite removing layer is formed, and the positive effect of reducing air holes and crack defects in the subsequent laser welding is achieved.

After the nodular cast iron with the surface partially subjected to graphitization is obtained, annealing is carried out on the nodular cast iron with the surface partially subjected to graphitization to obtain the nodular cast iron with the annealed surface partially subjected to graphitization.

In the invention, the annealing temperature is preferably 250-300 ℃, and more preferably 290-300 ℃; the heat preservation time is preferably 1.5-2.5 h, and more preferably 2 h. The annealing according to the invention is preferably carried out in an air atmosphere. In the present invention, the annealing is preferably performed in a medium-high temperature box-type resistance furnace. The invention removes the residual stress existing in the ungraphitized layer by annealing, and reduces the hardness of the ungraphitized layer. After annealing, the invention preferably cools to room temperature along with the furnace to obtain the nodular cast iron with locally-graphitized annealed surface.

After the partially graphitized ductile cast iron with the annealed surface is obtained, the partially graphitized ductile cast iron with the annealed surface is subjected to laser welding with low-carbon steel.

Before laser welding, the method preferably performs flattening treatment on the to-be-welded surface of the annealed surface partially-graphitized ductile iron. The invention has no special requirements on the specific implementation mode of the planarization treatment, and any mode capable of realizing planarization, such as machining, can be adopted.

Before laser welding, the method preferably also comprises the steps of processing the low-carbon steel into a required specification, polishing the surface to be welded of the low-carbon steel smoothly, cleaning the polished surface with an alcohol solution, and drying.

In the present invention, the low carbon steel preferably includes, in mass percent: 0.17-0.23% of C, 0.17-0.37% of Si, 0.80-1.10% of Mn, 1.00-1.30% of Cr, less than or equal to 0.030% of S, less than or equal to 0.030% of P, less than or equal to 0.30% of Ni, Cu: less than or equal to 0.30 percent, 0.04 to 0.10 percent of Ti and the balance of Fe.

According to the invention, the annealed surface local-graphitization-removing nodular cast iron and the low-carbon steel are preferably clamped on a welding table, argon is used as shielding gas, and then a high-power laser is adopted for laser welding.

In the invention, the power of the laser welding is preferably 3000-5000W, more preferably 3500-4500W, and even more preferably 3800-4200W; the welding speed is preferably 1-3 m/min, and more preferably 1.5-2.5 m/min; the negative defocusing amount is preferably 1-5 mm, more preferably 2-4 mm, and further preferably 2.5-3.5 mm; the flow rate of the protective gas is preferably 20-30L/h, and more preferably 22-28L/h. The present invention preferably employs a disk laser for the laser welding.

FIG. 1 is a process flow diagram of a laser welding method of the present invention. As shown in figure 1, the invention firstly uses a machining method to machine low-carbon steel and nodular cast iron into required specifications, then uses sand paper to polish the surfaces to be welded of the nodular cast iron and the low-carbon steel smoothly, then uses alcohol solution to clean the polished surfaces, and dries the surfaces for standby; coating a light absorption coating on the surface to be welded of the nodular cast iron, and then carrying out laser surface heat treatment to form a de-graphitization layer to obtain the nodular cast iron with the partially de-graphitization surface; placing the nodular cast iron with the surface partially subjected to graphitization removal into a heating furnace for heat preservation and annealing, and then cooling the furnace to room temperature to obtain the nodular cast iron with the annealed surface partially subjected to graphitization removal; carrying out leveling treatment on the welding surface of the partially graphitized ductile cast iron on the annealed surface; and finally, clamping the annealed surface locally-graphitized ductile cast iron and the low-carbon steel on a welding table, and performing laser welding by using a disc laser by using argon as shielding gas.

The laser welding method of ductile iron and low carbon steel according to the present invention will be described in detail with reference to the following examples, which should not be construed as limiting the scope of the present invention.

The ductile iron 450 used in the following examples had the following composition: 3.70-4.00% of C, 2.15-2.93% of Si, 0.46-0.66% of Mn, 0.010-0.016% of S, 0.027-0.035% of P, 0.027-0.050% of Mg, 0.026-0.043% of Re, and 4.3-4.6% of carbon equivalent; the low-carbon steel adopts 20CrMnTi, and comprises the following specific components: 0.17-0.23% of C, 0.17-0.37% of Si, 0.80-1.10% of Mn, 1.00-1.30% of Cr, less than or equal to 0.030% of allowable residual S, less than or equal to 0.030% of allowable residual P, less than or equal to 0.30% of allowable residual Ni, and Cu: the allowable residual content is less than or equal to 0.30 percent, and the content of Ti is 0.04-0.10 percent.

Example 1

Firstly, processing the nodular cast iron 450 and 20CrMnTi into a sample with required specification, polishing the to-be-welded surfaces of the nodular cast iron 450 and 20CrMnTi with sand paper to be smooth, cleaning the surface of the sample with alcohol solution, and drying the sample;

coating light absorption paint on the to-be-welded surface of the nodular cast iron 450, and waiting for the light absorption paint to dry to form a coating with the thickness of 0.1-0.2 mm; wherein, the preparation of the light-absorbing coating is as follows: 50% of C powder and 50% of MoS₂Proportioning the powder, and diluting with absolute ethyl alcohol (99.5%) to prepare the light-absorbing coating; subjecting the surfaces to be welded coated with the light-absorbing coating to CO₂Carrying out laser surface heat treatment, wherein the laser power is 600W, the scanning speed is 200mm/min, the positive defocusing amount is 15mm, and a graphitization removing layer with the thickness of 0.75mm is formed to obtain surface partially graphitized ductile iron 450; the de-graphitized layer has no pores and crack defects.

Step three, placing the nodular cast iron 450 with the surface partially subjected to graphitization removal into a heating furnace, keeping the temperature at 300 ℃ for 2h for annealing, and then cooling the furnace to room temperature to obtain the nodular cast iron 450 with the annealed surface partially subjected to graphitization removal;

step four, carrying out flattening treatment on the welding surface of the annealed surface partially de-graphitized nodular cast iron 450, so as to facilitate butt joint of the subsequent laser welding;

clamping the annealed surface locally-graphitized ductile cast iron 450 and 20CrMnTi on a welding table, using argon as shielding gas, and then performing laser welding by using a disc laser;

laser welding technological parameters are as follows: laser power 4000W, welding speed 2.4m/min, negative defocusing amount 2mm, and protective gas flow 24L/h; the carbon content in the finally obtained welding seam is obviously controlled, the graphite removal layer has a good carbon removal effect, the defects of pores, cracks and the like of the welding seam are effectively controlled, and the welding joint has good mechanical properties.

Example 2

Firstly, processing the nodular cast iron 450 and 20CrMnTi into a sample with required specification, polishing the to-be-welded surfaces of the nodular cast iron 450 and 20CrMnTi with sand paper to be smooth, cleaning the surface of the sample with alcohol solution, and drying the sample;

coating light absorption paint on the to-be-welded surface of the nodular cast iron 450, and waiting for the light absorption paint to dry to form a coating with the thickness of 0.1-0.2 mm; wherein, the preparation of the light-absorbing coating is as follows: 50% of C powder and 50% of MoS₂Proportioning the powder, and diluting with absolute ethyl alcohol (99.5%) to prepare the light-absorbing coating; subjecting the surfaces to be welded coated with the light-absorbing coating to CO₂Carrying out laser surface heat treatment, wherein the laser power is 600W, the scanning speed is 300mm/min, the positive defocusing amount is 25mm, and a graphitization removing layer with the thickness of 0.3mm is formed to obtain surface partially graphitized ductile iron 450; the de-graphitized layer has no pores and crack defects.

Step three, placing the nodular cast iron 450 with the surface partially subjected to graphitization removal into a heating furnace, keeping the temperature at 250 ℃ for 1.5 hours for annealing, and then cooling the furnace to room temperature to obtain the nodular cast iron 450 with the annealed surface partially subjected to graphitization removal;

step four, carrying out flattening treatment on the welding surface of the annealed surface partially de-graphitized nodular cast iron 450, so as to facilitate butt joint of the subsequent laser welding;

clamping the annealed surface locally-graphitized ductile cast iron 450 and 20CrMnTi on a welding table, using argon as shielding gas, and then performing laser welding by using a disc laser;

laser welding technological parameters are as follows: laser power is 3000W, welding speed is 1m/min, negative defocusing amount is 1mm, and protective gas flow is 20L/h; the carbon content in the finally obtained welding seam is obviously controlled, the graphite removal layer has a good carbon removal effect, the defects of pores, cracks and the like of the welding seam are effectively controlled, and the welding joint has good mechanical properties.

Example 3

Firstly, processing the nodular cast iron 450 and 20CrMnTi into a sample with required specification, polishing the to-be-welded surfaces of the nodular cast iron 450 and 20CrMnTi with sand paper to be smooth, cleaning the surface of the sample with alcohol solution, and drying the sample;

coating light absorption paint on the to-be-welded surface of the nodular cast iron 450, and waiting for the light absorption paint to dry to form a coating with the thickness of 0.1-0.2 mm; wherein, the preparation of the light-absorbing coating is as follows: 50% of C powder and 50% of MoS₂Proportioning the powder, and diluting with absolute ethyl alcohol (99.5%) to prepare the light-absorbing coating; subjecting the surfaces to be welded coated with the light-absorbing coating to CO₂Carrying out laser surface heat treatment, wherein the laser power is 700W, the scanning speed is 150mm/min, the positive defocusing amount is 5mm, and a graphitization removing layer with the thickness of 0.9mm is formed to obtain surface partially graphitized ductile iron 450; the de-graphitized layer has no pores and crack defects.

Step three, placing the nodular cast iron 450 with the surface partially subjected to graphitization removal into a heating furnace, keeping the temperature at 275 ℃ for 2.5 hours for annealing, and then cooling the furnace to room temperature to obtain the nodular cast iron 450 with the annealed surface partially subjected to graphitization removal;

step four, carrying out flattening treatment on the welding surface of the annealed surface partially de-graphitized nodular cast iron 450, so as to facilitate butt joint of the subsequent laser welding;

clamping the annealed surface locally-graphitized ductile cast iron 450 and 20CrMnTi on a welding table, using argon as shielding gas, and then performing laser welding by using a disc laser;

laser welding technological parameters are as follows: 5000W, the welding speed is 3m/min, the negative defocusing amount is 5mm, and the protective gas flow is 30L/h; the carbon content in the finally obtained welding seam is obviously controlled, the graphite removal layer has a good carbon removal effect, the defects of pores, cracks and the like of the welding seam are effectively controlled, and the welding joint has good mechanical properties.

Comparative example 1

The only difference from example 1 is that the laser surface heat treatment was not performed.

And (3) performance testing:

1. microscopic observation was performed on the surface-partially-graphitized spheroidal graphite cast iron 450 of example 1, and the result is shown in fig. 2. FIG. 2 shows that the structure of the graphitized layer is basically free of defects such as air holes and cracks by the laser heat treatment, and the thickness of the graphitized layer is 0.75 mm.

2. The ductile iron and low carbon steel welded parts of example 1 were processed into tensile test pieces, and the tensile test results are shown in fig. 3. As can be seen from fig. 3, the maximum force applied to the specimen at the time of breaking can be 16000N or more.

3. The weld zones of the ductile iron and low-carbon steel weld joints of example 1 were prepared into metallographic parts for observation, and the results are shown in fig. 4. As can be seen from FIG. 4, the ductile iron and the low-carbon steel form good metallurgical bonding, and the bonding part is basically free of defects such as air holes, cracks and the like.

4. The ductile iron and low carbon steel welded joint tensile fracture piece was prepared into a metallographic piece for observation, and the results are shown in fig. 5. It can be seen from fig. 5 that the ductile iron and low carbon steel weld joint fractures at the de-graphitized layer, rather than at the center of the weld joint, demonstrating that the ductile iron and low carbon steel form a good metallurgical bond.

5. The ductile iron, the low-carbon steel and the ductile iron and low-carbon steel welded pieces were subjected to a tensile test, respectively, and the results are shown in fig. 6. As can be seen from fig. 6, the tensile strength of the ductile iron base metal is 450MPa, the tensile strength of the low-carbon steel base metal is 760MPa, the tensile strength of the welded part can reach 500MPa, and the tensile strength of the welded part is higher than that of the ductile iron base metal, which indicates that the welded part obtained by the welding method of the present invention has excellent tensile strength.

6. The weld zones of the ductile iron and the low carbon steel of comparative example 1 were observed by a microscope, and the results are shown in fig. 7. As can be seen from fig. 7, the nodular cast iron was directly welded to the low-carbon steel without performing the laser surface heat treatment for graphitization removal, and the weld zone had pores and crack defects.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.