CN103273200A - Laser cladding restoring method for die steel - Google Patents

Abstract

The invention provides a laser cladding restoring method for die steel. The method comprises a first step of collecting data, specifically, collecting a hardened zone size H of an HAZ, a valid softening zone size S of the HAZ, a weld width W of the HAZ and a weld depth P of the HAZ, a second step of establishing a Higuchi model and optimizing technological parameters to obtain welding joint characteristic data, and a third step of correcting and optimizing the Higuchi model, inputting the welding joint characteristic data into the corrected and optimized Higuchi model to obtain a weld pass overlap rate in an optimal layer and optimal energy among layers and sending the data to a welder and restoring the die steel. The Higuchi model is optimized and improved firstly, and the die steel is restored through the double-layer tempering technology based on a laser cladding method, so that the weld pass overlap rate in the optimal layer and the optimal energy among the layers are obtained. A die can be fast restored without subsequent heating treatment. The laser cladding restoring method for the die steel is simple, easy to achieve, high in efficiency and high in accuracy and quality, restoring time is saved, and economic benefits are improved.

Description

Laser cladding repair method for die steel

technical field

The invention relates to the field of laser cladding repair, in particular to a method for laser cladding repair of mold steel.

Background technique

Molds often require welding repairs due to failures such as surface wear, peeling, and cracks during service, as well as design changes or processing errors during mold manufacturing. In the traditional welding repair process (such as argon arc welding), due to the large amount of heat input, the surface layer of the mold material forms a heat-affected zone (HAZ) with a coarse structure, high hardness and low toughness. In order to improve the structure and properties of the HAZ in the repaired area, it is inevitable to carry out long-term high-temperature post-weld tempering heat treatment (PWHT). Although PWHT is very beneficial to reduce the hardness value of HAZ and improve its toughness, it usually brings a series of problems, such as the need to add PWHT equipment and increase the cost, and the mold repair takes a long time and causes long-term equipment shutdown. Therefore, it is of significant economic benefit to develop a new process for mold welding repair without PWHT.

By searching the existing literature, it can be seen that Canonico D A et al. proposed the half bead technique (half bead technique) in the paper "Half bead welding technique", Albuquerque D, Victor HC et al. in the paper "Effect of nonmetallic inclusion and banding on the Success of the two-layertemper bead welding technique" proposed double-layer tempered bead technology, Lundin C proposed controlled deposition technology in the paper "Controlled Deposition Techniques for Improvement of Fabrication and ServicePerformance of Cr-Mo Steels", etc. The common feature of these processes is to use the tempering effect of the subsequent weld bead in the layer and between the layers to the HAZ of the previous weld bead to obtain a repaired heat-affected zone with hardness and toughness that meet the requirements, so as to achieve the purpose of eliminating the PWHT process. Among them, the double-layer tempered weld bead technology is a widely used repair technology. The difficulty lies in how to determine the best matching welding heat input combination of the first layer and the second layer (tempered layer) to obtain the optimal tempered layer. The tempering effect of the weld bead on the HAZ of the first pass. At present, it is generally obtained by trial and error based on the principle of actual welding experience, which requires repeated tests, and the accuracy of the data is poor, and the effect is not ideal. However, the Higuchi process optimization model proposed in recent years can obtain better interlayer heat input combination simply and economically through theoretical derivation based on actual welding repair data. However, this method is mainly aimed at the traditional arc welding repair method, and does not consider the influence of the overlap rate during multi-pass welding. Experiments show that the tempering effect of subsequent welds on the previous welds with different overlap rates It is not the same, and in multi-pass welding, the height of the cladding layer is also different under different lap rates.

Contents of the invention

Aiming at the defects in the prior art, the object of the present invention is to provide a laser cladding repair method for mold steel.

The invention provides a laser cladding repair method for die steel, the method comprising the following steps:

Step 1, data collection: Obtain microhardness values along the 30 degrees from the center of the cladding weld section and 3 straight lines across the HAZ, and draw the hardness distribution curve by taking the average value of the microhardness values to obtain the hardening of the HAZ The zone size H and the effective softening zone size S; the melting width W and the melting depth P measured by an optical microscope;

Step 2, establishing the Higuchi model, optimizing the process parameters, and obtaining the weld characteristic data;

Step 3, modifying and optimizing the Higuchi model, bringing the weld feature data into the revised optimized Higuchi model to obtain the optimal welding bead overlap rate in the layer and the optimal energy between layers, and the obtained optimal welding bead overlap in the layer The optimal energy of the rate and interlayer is sent to the welding machine, and the data is used as the process parameter to repair the mold steel;

The steps of setting up the Higuchi model are as follows:

Step 2.1, divide the interval: divide the HAZ into 4 micro-areas: coarse-grained area, fine-grained area, critical area and effective tempering area;

Step 2.2, select the size of R, P, H and S process parameters;

In step 2.3, the Higuchi model can be established by analyzing the relationship between the relative position and size of the HAZ micro-intervals of the second layer of tempered weld bead and the first layer of weld bead.

Preferably, in step 2.1, the melting point of the coarse-grained region is 1000°C, the melting point of the fine-grained region is 912-1000°C, the melting point of the critical region is 727-912°C, and the melting point of the effective tempering region is 550-727°C.

Preferably, in step 2.1, the coarse-grained region, the fine-grained region and the critical region are collectively referred to as the hardened region, and the definition of the effective tempering region is related to specific repair materials.

Preferably, in step 2, the weld seam characteristic data is the hardened zone size H of the heat-affected zone, the effective softened zone size S, the fusion width W, the penetration depth P, the single-pass cladding layer area V ₀ , and the cladding layer average Thickness R', optimal welding bead lap ratio a, average thickness R' of multi-pass welding cladding layer.

Preferably, in step 3, when the modified and optimized Higuchi model is applicable to multi-pass cladding, the optimal weld bead overlap rate in the layer is when the offset distance of the subsequent weld bead relative to the previous weld bead is equal to the size of the tempering zone The overlapping rate of welding beads in the layer, the average thickness R' of the multi-pass cladding layer of the first layer is calculated according to the following formula:

R'=V/[(1-a)*W]

Where V is the cladding material melted per unit time, a is the welding bead overlap rate in the layer, and W is the width of the melting zone;

The heat-affected zone is divided into a hardening zone and a softening zone. In multi-run welding, the subsequent weld pass has a tempering effect on the previous weld pass. If the offset distance L of the subsequent weld pass relative to the previous weld pass is equal to the size S of the tempering zone, The area of the untempered area will become zero, obviously at this time the overlap rate α between the front and rear weld beads is optimal, and its calculation formula is a=1-S/W;

In multi-pass welding, the layer heights of weld passes with different overlap ratios are different. Therefore, the Higuchi model is improved as follows: the single-pass fusion height R is replaced by the multi-pass cladding layer thickness R' considering the influence of the overlap rate. In the case of certain process parameters such as laser power and cladding rate, the volume V ₀ of the cladding material melted per unit time is constant, assuming that the lapping rate is α, and the welding width of a single bead is W, the average cladding layer is The relationship between the thickness R' and the overlap ratio α is: R'=V ₀ /((1-α)*W)

The modified Higuchi double-layer tempering process parameter model is as follows:

Δ ₁ ＝A ₂ -A ₁ ＝(P ₂ +H ₂ +S ₂ )-(R′ ₁ +P ₁ +H ₁ )＞0

Δ ₂ =B ₁ -B ₂ =(R′ ₁ +P ₁ )-(P ₂ +H ₂ )>0

a=1-S/W

R'=V ₀ /((1-a)*W)

in,

A ₁ =R ₁ +P ₁ +H ₁ , A ₂ =P ₂ +H ₂ +S ₂ ,

B ₁ =R ₁ +P ₁ , B ₂ =P ₂ +H ₂ ,

P ₁ is the penetration depth of the first cladding layer, and P ₂ is the penetration depth of the second cladding layer;

R ₁ is the cladding layer thickness of the first layer, R ₂ is the thickness of the second cladding layer;

H ₁ is the hardened zone size of the first cladding layer, H ₂ is the hardened zone size of the second cladding layer;

S ₁ is the effective softening zone size of the first cladding layer, and S ₂ is the effective softening zone size of the second cladding layer.

It can be seen from the above model that Δ ₁ gives the lower limit value of the interlayer energy density combination, and Δ ₂ in the model gives the upper limit value of the interlayer energy density combination, and the overlapping ratio a gives the layer Optimum overlap between the subsequent weld pass and the preceding weld pass for internal tempering. And R' means that the melting height is different under different overlapping ratios. R' in the model gives the calculation method of the average melting height of multi-pass laser cladding under the optimal overlapping ratio;

In the process optimization model above, the four formulas contain a total of 12 variables, which cannot directly obtain the optimal energy density combination between layers, but can only obtain the value range of the energy density combination between layers under different overlapping ratios a, so further steps are needed deal with.

Preferably, in step 3, the characteristic data of the weld seam are brought into the revised optimized Higuchi model to obtain the optimal welding bead lap rate in the layer and the optimal energy between layers:

Step 1: Take P, H, S, V, W, optimal weld bead lap rate a and cladding layer thickness R′ under different energy densities, and calculate the limiting conditions Δ ₁ and Δ ₂ , to screen energy density combinations satisfying Δ ₁ >0 and Δ ₂ >0 at the same time. Specifically, select 4 commonly used process parameters with different energy densities to conduct single-pass laser cladding process experiments, and then determine the process parameters of each group. The model data P, H, S, V, W of die steel, while the fusion width W, penetration depth P, and cladding volume V can be directly measured by metallographic microscope and image software. Since the size values of the hardening zone H and the softening zone S cannot be obtained directly through the metallographic contrast, they can be obtained indirectly through the hardness distribution curve. Specifically, the hardness can be measured in the HAZ zone from the centerline of the cladding zone and 30 degrees left and right, and the hardness can be counted distribution, and then determine the size of H and S at different energy densities.

According to the model data S and W obtained from the experiment, the theoretical optimal welding bead lap rate a corresponding to different laser cladding energy density values can be obtained from the formula a=1-S/W. Obviously, when the energy density is different, the optimal The bead lap ratio a will vary.

Based on the model data V, W and the overlap rate a obtained from the experiment, according to the formula R′=V ₀ /((1-α)*W), calculate the cladding layer’s thickness under different energy densities and different overlap rates. Thickness R', based on P, H, S, V, W under different energy densities and the calculated optimal weld bead lap rate a and cladding layer thickness R', calculate the limiting condition _Δ1 under different energy density combinations and the condition Δ ₂ , all energy density combinations satisfying the conditional formulas Δ ₁ >0 and Δ ₂ >0 are obtained when different overlapping ratios are obtained.

Step 2: further screen the energy density combinations selected in step 1 to obtain the optimal energy density combination. The specific principles for determination are as follows: (1) The energy density of the first layer is small; (2) Under the premise of Δ ₂ >0, Choose a larger value of _Δ1 ; (3) On the premise of uniform thickness of the cladding layer, choose a larger overlap ratio.

Based on the above principles, the optimal energy density combination that satisfies the conditions can be obtained. Under this process parameter, the laser cladding repair of multi-pass double-layer tempering can be carried out on the mold steel, which can realize the rapid recovery of mold steel without subsequent high-temperature tempering heat treatment. Repair, its structure and properties are not inferior to or even better than the structure and properties of tempering heat treatment after welding.

Preferably, in step one, the calculation formulas of Δ ₁ and Δ ₂ are as follows:

Δ ₁ =A ₂ -A ₁ =(P ₂ +H ₂ +S ₂ )-(R ₁ +P ₁ +H ₁ )>0,

Δ ₂ =B ₁ −B ₂ =(R ₁ +P ₁ )−(P ₂ +H ₂ )>0.

The restriction condition Δ ₁ is to ensure that the heat input value of the tempered weld bead is large enough relative to the first weld bead, so that its effective tempering zone (S ₂ ) can "cover" and "soften" the hardening of the first weld bead HAZ area (H ₁ ), and the larger the positive value of Δ ₁ , the better the tempering effect. The restriction condition _Δ2 is to ensure that the hardened zone formed by the first weld bead will not be hardened again under the heat of the tempered weld bead.

Preferably, in step 2, the optimal energy density combination simultaneously satisfies the following conditions:

(1) The energy density of the first layer is small;

(2) On the premise of Δ ₂ > 0, choose a larger Δ ₁ value;

(3) On the premise of uniform cladding layer thickness, select a larger overlap rate.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The double-layer tempering laser cladding repair method for mold steel provided by the present invention can accurately control the heat input and optimal process parameters between the front and rear welds and the interlayer welds, and realize rapid mold without subsequent heat treatment. repair.

(2) The present invention also relates to the laser cladding repair method of multi-pass welding in double-layer tempering. Due to the influence of the overlapping rate in the process, the present invention adopts quantitative calculation of the optimal lapping rate of the weld bead in the layer, and multiple The method of the average cladding layer height of road welding, the Higuchi model is optimized and improved, and then the mold steel is repaired by double-layer tempering technology based on the laser cladding method, and the HAZ of the previous welding seam is adjusted by the rear welding seam. Tempering effect, using the tempering effect of the second layer weld on the HAZ of the first layer weld, through the improved Higuchi optimization model, the accurately matched welding bead overlap rate within the layer and the optimal heat input ratio between layers are obtained , Accurately realize rapid mold repair without subsequent heat treatment.

(3) The method of the present invention is simple, easy to implement, high in efficiency, high in accuracy, high in quality, saves repair time, and improves economic benefits.

Description of drawings

Other characteristics, objects and advantages of the present invention will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings:

Figure 1 is a schematic diagram of the distribution and microstructure transformation of each micro-area in the heat-affected zone;

Figure 2 is a schematic diagram of the principle of the double-layer tempering weld bead technology;

Fig. 3 is a schematic diagram of multiple laps in a layer;

Figure 4 is a schematic diagram of the hardness measurement position of the Higuchi test sample.

Detailed ways

The present invention will be described in detail below in conjunction with specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

Example 1

This embodiment relates to a laser cladding repair method for mold steel, the method comprising the following steps:

Please refer to Figure 1 for a schematic diagram of the distribution of each micro-area in the heat-affected zone, where the temperature of A ₁ is 727°C, which represents the eutectoid transition temperature. A ₂ represents the Curie point of ferrite. A ₃ temperature range 727～912℃, the end line of ferrite transformation to austenite (heating) or the beginning line of austenite transformation to ferrite (cooling), A ₄ range temperature 1394～1495℃, high temperature iron The end line of transformation from ferrite to austenite (cooling) or the beginning line of transformation from austenite to high-temperature ferrite (heating), A _cm temperature range 727 ~ 1148 ℃, the solubility curve of carbon in austenite, also It becomes the precipitation line of cementite. Please refer to Figure 2 for the schematic diagram of the double tempered weld bead technology, where A ₁ =R ₁ +P ₁ +H ₁ , A ₂ =P ₂ +H ₂ +S ₂ , B ₁ = R ₁ +P ₁ , B ₂ =P ₂ +H ₂ , please refer to Figure 3 for the schematic diagram of "multiple overlapping".

The invention is adopted on die steel AISI P20, and the laser cladding material adopts self-made alloy powder with a particle size of 100-200 mesh. The laser cladding equipment used in the experiment includes a 3.5kW semiconductor laser (the spot width is 6mm, and the energy of the laser beam is Gaussian and high-hat distribution on the fast axis and slow axis respectively), FANUC robot and coaxial powder feeding system, etc. The powder feeding rate is 15g/min. The protective gas is pure argon with a flow rate of 10L/min.

(1) Data collection: Acquire microhardness values along the 1, 2, and 3 straight lines across the HAZ as shown in Figure 4 (dot spacing 0.1mm), take the average value to draw the hardness distribution curve, and select 550HV as P20 The average hardness value of the quenched steel structure is used to determine the hardened zone size H and the effective softened zone size S of the HAZ; the fusion width W and penetration depth P are measured by an optical microscope; the single-pass cladding layer area _V0 is measured by image software, It is used to calculate the average thickness R' of the cladding layer. According to the overlapping ratio calculation formula of the modified Higuchi optimization model and the multi-pass welding cladding average thickness calculation formula, the optimal overlapping ratio a and fusion height R′ can be obtained respectively. The results of Higuchi test data are shown in Table 2.

(2) Establish the Higuchi model, optimize the process parameters, and obtain the weld characteristic data;

The base material used in this embodiment is quenched P20 steel, the quenching temperature is 860°C, heat preservation is 20min, and oil cooling is performed.

Using the cladding process parameters shown in Table 1, four groups of single-pass Higuchi samples with different laser cladding energy density values were obtained.

Table 1 Higuchi test laser cladding process parameters

Table 2 Higuchi test data results of P20 steel laser cladding

(3) Modify and optimize the Higuchi model, bring the weld feature data into the revised optimized Higuchi model for derivation, and then obtain the optimal overlap rate of weld bead in the layer and the optimal energy between layers.

(a) Determine the optimal welding bead lap rate in the layer

It can be seen from Table 2 that when the energy density of laser cladding varies in the range of 5-13.3kJ/ ^cm2 , the theoretical optimal welding bead lap rate is in the range of 62%-76%, which is greater than the 50% lap rate traditionally used. . Under the premise of obtaining a uniform cladding layer thickness, a larger overlap rate is selected to obtain a greater tempering effect on the heat-affected zone of the previous weld bead in the same layer. Therefore, considering the actual welding conditions, 70% is selected as the optimal lap rate of the weld bead in the layer.

(b) Derivation of the optimal interlayer energy density combination

According to the Higuchi laser cladding optimization model, in order to achieve the optimal interlayer tempering effect, the interlayer energy density combination needs to meet the model conditions Δ ₁ and Δ ₂ , and the corresponding cladding layer thickness is calculated according to the model condition R′, Among them, the optimal in-layer welding bead lap rate is 70% selected above, and the formulas used in this derivation are listed as follows:

Δ ₁ =A ₂ -A ₁ =(P ₂ +H ₂ +S ₂ )-(R′ ₁ +P ₁ +H ₁ )>0

Δ ₁ =B ₁ -B ₂ =(R′ ₁ +P ₁ )-(P ₂ +H ₂ )>0

R'=V ₀ /((1-a)*W)

It can be seen from the calculation that when the overlap rate is 70%, only the cladding energy density combinations 5&8.3, 5&10, 5&13.3 and 8.3&13.3 kJ/cm ² can meet the requirement of Δ ₁ > ₀ , and it is not difficult to find that all the combinations that meet the conditions have selected a lower energy density value of the first layer and a higher energy density value of the tempering layer than the first layer, because a smaller energy density value of the first layer can obtain a smaller size The heat-affected zone of the first layer cladding layer can be tempered to a greater degree by choosing a larger energy density value of the tempering layer. For the constraint condition Δ ₂ , except for the combination of 5&13.3kJ/cm ² , all other combinations can satisfy Δ ₂ >0. This limitation is to ensure that the hardened zone formed by the first layer of weld bead will not be hardened again under the heat of the tempered layer of weld bead, and the energy density of the first layer is in the range of 5 to 13.3kJ/ ^cm2 . With a sufficiently large cladding layer thickness, re-hardening will only occur when the interlayer energy density combination is 5&13.3kJ/cm ² , that is, the extreme case where the thickness of the first cladding layer is the smallest and the hardening zone of the tempered layer is the largest. .

Table 3 shows the combination of interlayer energy density that satisfies the two constraints at the same time. It can be seen from the table that when the optimal overlap rate is 70%, there are 5&8.3, The three groups of 5&10 and 8.3&13.3kJ/cm ² are based on the principle that the energy density value of the first layer should be as small as possible under the premise of obtaining good forming and the energy density value of the tempering layer should be as large as possible under the premise of satisfying the restrictive conditions. It can be known that 5&10kJ/cm2 ² is the expected best interlayer energy density combination.

Table 3 When the overlap rate is 70%, the energy density combination that satisfies the conditional formula

According to Higuchi's modified model, the optimal interlayer energy density combination of P20 die steel is 5&10kJ/cm ² . Using this energy density combination to repair P20 mold steel with double-layer tempered laser cladding can obtain a repaired heat-affected zone with a uniform tempered sorbite structure and an average hardness of about 400HV. The repair effect is better than that required for subsequent tempering Traditional single layer mold repair process for heat treatment.

To sum up, the present invention optimizes the original Higuchi model, considers the problem of the optimal overlap rate between the welds in the multi-pass welding layer in the actual repair process, and also corrects its fusion rate during multi-pass welding. high calculation method. Based on the process parameter optimization model, the optimal process parameters of double-layer tempered laser cladding can be accurately predicted. Only through the theoretical derivation of a small amount of actual welding repair related data, the optimal interlayer energy input combination can be obtained simply and economically, so that the material can be repaired by double-layer multi-pass laser cladding only through an appropriate energy combination, and no follow-up High-temperature tempering heat treatment can obtain the basic consistency repair effect of the heat-affected zone microstructure properties and hardness of the repaired area with the base metal. The restoration quality is improved, the restoration time is saved, and the economic benefit is improved. The cost is greatly reduced, the repair time is saved, and it has significant economic benefits.

Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims (8)

1. The laser cladding repair method of the die steel is characterized by comprising the following steps of:

step 1, data acquisition: obtaining microhardness values along the left and right sides of the center of the cross section of the cladding weld joint by 30 degrees respectively and traversing 3 linear directions of the HAZ, and drawing a hardness distribution curve by taking the average value of the microhardness values to obtain the size H of a hardening area and the size S of an effective softening area of the HAZ; measuring the fusion width W and the fusion depth P by an optical microscope;

step 2, establishing a Higuchi model, and optimizing process parameters to obtain weld joint characteristic data;

step 3, correcting the optimized Higuchi model, substituting the weld characteristic data into the corrected optimized Higuchi model to obtain the optimal inner weld bead lap joint rate and the optimal interlayer energy, and sending the obtained optimal inner weld bead lap joint rate and the optimal interlayer energy to a welding machine to repair the die steel by taking the obtained data as process parameters;

the steps for establishing the Higuchi model are as follows:

step 2.1, dividing the regions: the HAZ was divided into 4 micro-zones: a coarse crystal region, a fine crystal region, a critical region and an effective tempering region;

step 2.2, selecting R, P, H and S process parameter sizes, wherein R, P, H and S are respectively the sizes of a melting height, a melting depth, a hardening area and an effective softening area;

and 2.3, establishing the Higuchi model by analyzing the relation between the relative position and the size of each micro-area of the HAZ of the second tempering welding layer welding bead and the first welding bead.

2. The laser cladding repair method of the die steel according to claim 1, wherein in step 2.1, the melting point of the coarse crystal region is 1000 ℃, the melting point of the fine crystal region is 912-1000 ℃, the melting point of the critical region is 727-912 ℃, and the melting point of the effective tempering region is 550-727 ℃.

3. The method for repairing die steel by laser cladding according to claim 1, wherein in step 2.1, the coarse crystal area, the fine crystal area and the critical area are collectively called as a hardening area, and the effective tempering area is defined in relation to the repairing material.

4. The laser cladding repair method of die steel according to claim 1, wherein in step 2, the weld joint characteristic data are a hardened zone size H, an effective softened zone size S, a weld width W, a weld depth P, and a single pass cladding layer area V of a heat affected zone₀The average thickness R 'of the cladding layer, the optimal weld bead overlap ratio a and the average thickness R' of the multi-pass welding cladding layer.

5. The laser cladding repair method for die steel according to claim 1, wherein in step 3, when the modified optimized Higuchi model is applied to multi-pass cladding, the optimal in-layer weld bead overlap ratio is the in-layer weld bead overlap ratio when the offset distance of the subsequent weld bead from the previous weld bead is equal to the size of the tempering area, and the average thickness R' of the multi-pass cladding layer of the first layer is calculated according to the following formula:

R′=V/[(1-a)*W]

wherein V is a cladding material melted in unit time, a is an overlap ratio of an inner weld bead, and W is a weld width.

6. The laser cladding repair method for die steel according to claim 1, wherein in step 3, the weld joint characteristic data is substituted into the modified optimized Higuchi model to obtain the optimal inner weld bead lap ratio and the optimal interlayer energy specifically as follows:

step one, P, H, S, V, W, the optimal weld bead overlap ratio a and the cladding layer thickness R' under different energy densities are taken, and the limiting condition delta is calculated through a Higuchi optimal process parameter model₁And Δ₂Screening while satisfying Δ₁> 0 and Delta₂Energy density combinations > 0;

and step two, further screening the energy density combination screened out in the step one to obtain the optimal energy density combination.

7. The method for repairing die steel by laser cladding according to claim 6, wherein in the first step, the calculation formulas of Δ 1 and Δ 2 are as follows:

Δ₁=A₂-A₁=(P₂+H₂+S₂)-(R₁+P₁+H₁)>0，

Δ₂=B₁-B₂=(R₁+P₁)-(P₂+H₂)>0，

wherein,

A₁=R₁+P₁+H₁，A₂=P₂+H₂+S₂，

B₁=R₁+P₁，B₂=P₂+H₂，

P₁for the penetration of the first cladding layer, P₂The melting depth of the second cladding layer;

R₁thickness of cladding layer as first layer, R₂The thickness of the second cladding layer;

H₁the size of the hardening zone of the first cladding layer, H₂The size of the hardening zone of the second cladding layer;

S₁for effective softening of the first cladding layer to remove dimensions, S₂The effective softening zone size of the second cladding layer.

8. The laser cladding repair method of die steel according to claim 6, wherein in step two, the optimal energy density combination simultaneously satisfies the following conditions:

(1) the energy density of the first layer is small;

(2) at a₂On the premise of more than 0, a larger delta is selected₁A value;

(3) on the premise of uniform thickness of the cladding layer, a larger lap joint rate is selected.

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