CN103273200A - Laser cladding restoring method for die steel - Google Patents
Laser cladding restoring method for die steel Download PDFInfo
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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
Technical Field
The invention relates to the field of laser cladding repair, in particular to a laser cladding repair method for die steel.
Background
The dies often need to be welded and repaired due to surface wear, spalling, cracks and other failures during service, and design changes or processing errors during die fabrication. In the traditional welding repair process (such as argon arc welding), a Heat Affected Zone (HAZ) with thick structure, high hardness and low toughness is formed on the surface layer of the die material due to large heat input. In order to improve the organization and performance of the HAZ in the repair area, it is inevitable to perform a high temperature post weld tempering heat treatment (PWHT) for a long time. Although PWHT is very beneficial in reducing the HAZ hardness value and improving its toughness, it also generally presents a number of problems, such as increased cost due to the need to add PWHT equipment, lengthy tool repair time resulting in long tool downtime, etc. Therefore, the development of a new die welding repair process without PWHT has obvious economic benefits.
As can be seen from a search of the existing literature, Canonico D A et al have proposed Half bead technology in the paper "Half bead technology", Albuquerque D, Victor HC et al have proposed double-layer tempering bead technology in the paper "Effect of nonmetallic inclusion and cladding on the success of the two-layer bead technology", Lundin C has proposed Deposition control technology in the paper "Controlled Deposition technology for Improvement of the surface and service Performance of Cr-Mo Steels", and so on. The common characteristic of the processes is that the tempering effect of the post-weld bead in and between layers on the HAZ of the pre-weld bead is utilized to obtain a repair heat affected zone with the hardness and toughness meeting the requirements, thereby realizing the purpose of avoiding PWHT process. The difficulty of the double-layer tempering welding bead technology is how to determine the best-matched welding heat input combination of the first layer and the second layer (tempering layer) so as to obtain the optimal tempering effect of the tempering layer welding bead on the first layer welding bead HAZ. At present, the welding method is generally obtained by a trial and error method according to an actual welding experience principle, repeated tests are needed, the data accuracy is poor, and the effect is not ideal. In the Higuchi process optimization model proposed in recent years, theoretical derivation is carried out based on actual welding repair data, and better interlayer heat input combination can be obtained simply, conveniently and economically. However, the method mainly aims at the traditional arc welding repair method, and the influence of the lap joint rate of multi-pass welding is not considered, and experiments show that the tempering effect of subsequent passes on previous passes is different in different lap joint rates, and the heights of cladding layers are different under the conditions of different lap joint rates in multi-pass welding.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a laser cladding repair method for die steel.
The invention provides a laser cladding repair method of die steel, which comprises the following steps:
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;
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.
Preferably, 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 ℃.
Preferably, in step 2.1, the coarse crystalline regions, the fine crystalline regions and the critical regions are collectively referred to as hardening regions, and the definition of the effective tempering region is related to the specific repair material.
Preferably, in step 2, the weld characteristic data are the hardened zone size H, the effective softening zone size S, the fusion width W, the fusion depth P and the single-pass cladding layer area V of the 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.
Preferably, in step 3, when the modified optimized Higuchi model is suitable for 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 relative to 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 inner weld bead lap joint rate, and W is the width of a melting zone;
the heat affected zone is divided into a hardened zone and a softened zone, when a plurality of welding passes are carried out, the subsequent welding passes have tempering effect on the previous welding passes, if the offset distance L of the subsequent welding passes relative to the previous welding passes is equal to the size S of the tempering zone, the area of an untempered area becomes zero, obviously, the lap joint rate alpha between the previous welding passes and the next welding passes is optimal at the time, and the calculation formula is a = 1-S/W;
and in the multi-pass welding, the layer heights of the welding beads with different lap joint rates are different. The Higuchi model was therefore modified as follows: the single pass weld height R is replaced by a multi-pass cladding thickness R' that takes into account the effect of overlap ratio. Under the condition of certain process parameters such as laser power, cladding rate and the like, the volume V of the fused cladding material in unit time0Is constant, provided with an overlap jointThe ratio is alpha, the single-pass fusion width is W, and the relation between the average thickness R' of the cladding layer and the lap ratio alpha is as follows: r' = V0/((1-α)*W)
The modified Higuchi double-layer tempering process parameter model is as follows:
Δ1＝A2-A1＝（P２+H２+S２）-(R′1+P1+H1)＞0
Δ2＝B1-B2＝(R′1+P1)-(P2+H2)＞0
a=1-S/W
R'=V0/((1-a)*W)
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.
From the above model, Δ1The lower limit of the interlayer energy density combination is given, and Δ in the model2The upper limit value of the energy density combination between layers is given, and the lap ratio a is given after the tempering in the layersOptimum lap joint rate between the successive passes. R 'represents that the melting height is different under the condition of different lap joint rates, and R' in the model provides a calculation method of the average melting height of the multi-channel laser cladding under the condition of the optimal lap joint rate;
in the above process optimization model, the 4 formulas contain 12 variables, which cannot directly obtain the inter-layer optimal energy density combination, and only can obtain the value ranges of the inter-layer energy density combinations at different lap joint rates a, so that further processing is required.
Preferably, in step 3, the step of substituting the weld characteristic data into the modified optimized Higuchi model to obtain the optimal inner weld bead overlap ratio and the optimal interlayer energy specifically includes:
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 Delta2And (3) energy density combination more than 0, specifically, 4 groups of commonly used process parameters with different energy densities are selected to perform a single laser cladding process experiment, model data P, H, S, V, W of the die steel under each group of process parameters is determined, and the fusion width W, the fusion depth P and the cladding volume V can be directly measured by a metallographic microscope and image software. The size values of the hardening zone H and the softening zone S can not be directly obtained through metallographic contrast, and can be indirectly obtained through a hardness distribution curve, specifically, the hardness of the HAZ zone can be measured from the center line of the cladding zone and 30 degrees on the left and right, the hardness distribution is counted, and the sizes of the H and the S under different energy densities are further determined.
According to model data S and W obtained through experiments, theoretical optimal weld bead lap joint rate a corresponding to different laser cladding energy density values can be obtained through a formula a =1-S/W, and obviously, the optimal weld bead lap joint rate a is different when the energy densities are different.
The model data V, W and the lap ratio a obtained from the experiment were calculated according to the formula R' = V0V ((1- α) × W), calculated at different energy densities, noneThe thickness R 'of the cladding layer at the same overlapping rate is calculated according to P, H, S, V, W at different energy densities and the calculated optimal welding bead overlapping rate a and the thickness R' of the cladding layer, and the limiting condition delta at different energy density combinations is calculated1And condition Δ2All satisfy the conditional formula delta when obtaining different lap joint rates1> 0 and Delta2Energy density combinations > 0.
Step two, further screening the energy density combination selected in the step one to obtain the optimal energy density combination, wherein the determination principle is as follows: (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.
Based on the principle, the optimal energy density combination meeting the conditions can be obtained, under the process parameters, the die steel is subjected to multi-channel double-layer tempering laser cladding repair, the die steel can be quickly repaired without subsequent high-temperature tempering heat treatment, and the structure and the performance of the die steel are not lower than or even better than those of the die steel subjected to tempering heat treatment after welding.
Preferably, in step one, Δ is1And Δ2The calculation formula of (a) is as follows:
Δ1=A2-A1=(P2+H2+S2)-(R1+P1+H1)>0，
Δ2=B1-B2=(R1+P1)-(P2+H2)>0。
limitation condition Δ1Is to ensure that the heat input value of the tempering course is sufficiently large relative to the first course so that the effective tempering area (S) is obtained2) Capable of "covering" and "softening" the hardened zone (H) of the first weld pass HAZ1) And Δ1A larger positive value means a better tempering effect. And the limitation condition delta2It is to ensure that the hardened zone formed by the first pass is not in the tempered layerThe weld bead is hardened again by the heat.
Preferably, in the second step, 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.
Compared with the prior art, the invention has the following beneficial effects:
(1) the double-layer tempering laser cladding repair method for the die steel can accurately control the heat input quantity and the optimal process parameters between the front and rear welding beads and the interlayer welding bead, and realize the rapid repair of the die without subsequent heat treatment.
(2) The invention also relates to a multi-pass welding double-layer tempering laser cladding repairing method, which adopts a method for quantitatively calculating the optimal lapping rate of the inner welding bead and the average cladding layer height of multi-pass welding because of the influence of the lapping rate in the process, optimizes and improves a Higuchi model, then adopts a double-layer tempering technology to repair the die steel based on the laser cladding method, utilizes the tempering effect of the subsequent welding bead on the HAZ of the previous welding bead, utilizes the tempering effect of the second welding bead on the HAZ of the first welding bead, obtains the accurately matched lapping rate of the inner welding bead and the ratio of the optimal heat input quantity between layers through the improved Higuchi optimizing model, and accurately realizes the rapid repairing of the die without subsequent heat treatment.
(3) The method is simple, easy to implement, high in efficiency, high in accuracy and quality, saves the repairing time and improves the economic benefit.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is a schematic diagram of the distribution and texture transformation of micro-zones in a heat affected zone;
FIG. 2 is a schematic diagram of a double-tempering bead technology;
FIG. 3 is a schematic view of multiple lap joints in a layer;
FIG. 4 is a schematic diagram of the position of hardness measurement of Higuchi test samples.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. All falling within the scope of the present invention.
Example 1
The embodiment relates to a laser cladding repair method of die steel, which comprises the following steps:
the distribution of each micro-area in the heat affected zone is schematically shown in FIG. 1, wherein A1The temperature is 727 ℃ representing the eutectoid transition temperature. A. the2Indicates the curie point of ferrite. A. the3The temperature range is 727-912 ℃, the ending line (heating) of ferrite transformed into austenite or the starting line (cooling) of austenite transformed into ferrite4The temperature is 1394-1495 ℃, the finishing line (cooling) of the transformation from the high-temperature ferrite to the austenite or the starting line (heating) of the transformation from the austenite to the high-temperature ferrite is AcmThe temperature range is 727-1148 ℃, the solubility curve of carbon in austenite also becomes a precipitation line of cementite, and the schematic diagram of the technical principle of the double-layer tempering welding bead is shown in the figure2, wherein A1=R1+P1+H1,A2=P2+H2+S2，B1=R1+P1,B2=P2+H2FIG. 3 shows a schematic diagram of "multi-pass lapping".
The invention is used on die steel AISI P20, and the laser cladding material is self-made alloy powder with the granularity of 100-200 meshes. The laser cladding equipment used for the experiment comprises a 3.5kW semiconductor laser (the width of a light spot is 6mm, and the energy of a laser beam is respectively distributed in a Gaussian manner and a high-cap manner on a fast axis and a slow axis), a FANUC robot, a coaxial powder feeding system and the like. The powder feeding rate was 15 g/min. The protective gas is pure argon, and the flow rate is 10L/min.
(1) Collecting data: obtaining microhardness values (dotting distance is 0.1 mm) along 1,2 and 3 straight lines which traverse the HAZ as shown in FIG. 4, taking the average value of the microhardness values to draw a hardness distribution curve, and selecting 550HV as the average hardness value of the quenched structure of the P20 steel for determining the hardened zone size H and the effective softened zone size S of the HAZ; the fusion width W and the fusion depth P are measured by an optical microscope; area V of single-pass cladding layer0Measured by image software, for calculating the average thickness R' of the cladding layer. And respectively obtaining the optimal lap joint rate a and the weld height value R' according to a lap joint rate calculation formula of the modified Higuchi optimization model and an average thickness calculation formula of a multi-pass weld cladding layer. Results of Higuchi test data are shown in table 2.
(2) Establishing a Higuchi model, and optimizing process parameters to obtain weld joint characteristic data;
the substrate adopted by the embodiment is quenched P20 steel, the quenching temperature is 860 ℃, the temperature is kept for 20min, and the oil cooling is carried out.
4 groups of single-pass Higuchi samples with different laser cladding energy density values were obtained by using the cladding process parameters as shown in table 1.
TABLE 1Higuchi test laser cladding Process parameters
TABLE 2P 20 Steel laser cladding Higuchi test data results
(3) And correcting the optimized Higuchi model, and substituting the weld characteristic data into the corrected optimized Higuchi model for derivation to obtain the optimal inner weld bead overlap ratio and the optimal interlayer energy.
(a) Determining an optimum weld bead overlap rate within a layer
As can be seen from Table 2, the laser cladding energy density is 5-13.3 kJ/cm2When the range is changed, the theoretical optimal weld bead overlapping rate is in the range of 62-76%, and is greater than the traditional 50% overlapping rate used conventionally. On the premise of obtaining a uniform cladding layer thickness, a larger lapping rate is selected to obtain a larger tempering effect of the back weld bead in the same layer on the heat affected zone of the front weld bead, so that 70% is selected as the optimal lapping rate of the inner weld bead in consideration of the actual welding condition.
(b) Derivation of optimal inter-layer energy density combinations
According to the optimized Higuchi laser cladding model, the interlayer energy density combination needs to meet the model condition delta to realize the optimal tempering effect between layers1And Δ2The corresponding thickness of the cladding layer is calculated according to the model condition R', wherein the lapping rate of the inner weld bead in the optimal layer is 70% selected previously, and the formulas used in the derivation are listed as follows:
Δ1＝A2-A1＝(P2+H2+S2)-(R′1+P1+H1)＞0
Δ1＝B1-B2＝(R′1+P1)-(P2+H2)＞0
R′＝V0/((1-a)*W)
as can be seen by calculation, when the lap ratio is 70%, the limiting condition Δ is satisfied1Only cladding energy density combination 5&8.3、5&10、5&13.3 and 8.3&13.3 kJ/cm2Can satisfy Δ1And > 0, and it is not difficult to find that all combinations that satisfy the conditions select a lower energy density value for the first layer and a higher energy density value for the temper layer than for the first layer, because a smaller energy density value for the first layer can achieve a smaller sized heat affected zone, and a larger energy density value for the temper layer can achieve a greater degree of tempering of the first cladding layer HAZ. For the limiting condition Δ2Except for 5&13.3kJ/cm2All combinations other than the combination can satisfy Δ2Is greater than 0. The limiting condition is to ensure that the hardening zone formed by the first layer of welding bead cannot be hardened again under the heat action of the tempering layer of welding bead, and the energy density value of the first layer is 5-13.3 kJ/cm2Within the range, enough thickness of the cladding layer is obtained, and only the energy density combination between the layers is 5&13.3kJ/cm2In the extreme case of the first cladding layer having the smallest thickness and the tempering layer having the largest hardening zone, the re-hardening phenomenon occurs.
Table 3 shows the combinations of interlayer energy densities satisfying both the two restrictions, and it can be seen from the table that the combinations of interlayer energy densities satisfying both the two restrictions are 5 in total at an optimum lap joint ratio of 70%&8.3、5&10 and 8.3&13.3kJ/cm2Three groups, based on the principle that the energy density value of the first layer is as small as possible under the premise of obtaining good forming and the energy density value of the tempering layer is as large as possible under the premise of meeting the limiting conditions, 5 can be known&10kJ/cm2To anticipate the best interlayer energy density combination.
Energy density combinations satisfying the conditional formula at 370% overlap ratio
The optimal interlaminar energy density combination of the P20 die steel determined according to the Higuchi correction model is 5&10kJ/cm2. The energy density combination is selected to carry out double-layer tempering laser cladding repair on the P20 die steel, a repair heat affected zone with the structure of uniform tempering sorbite and the average hardness of about 400HV can be obtained, and the repair effect is superior to that of the traditional single-layer die repair process needing subsequent tempering heat treatment.
In conclusion, the original Higuchi model is optimized, the problem of the optimal lap joint rate between inner welding beads of a plurality of welding layers in the actual repair process is considered, and the calculation method of the weld height during the plurality of welding is also modified. Based on the process parameter optimization model, the optimal process parameters of double-layer tempering laser cladding can be accurately predicted. The optimal interlayer energy input combination can be simply, conveniently and economically obtained only by theoretical derivation of a small amount of actual welding repair related data, so that the material can be subjected to double-layer multi-channel laser cladding repair only through a proper energy combination, and the repairing effect that the microstructure performance and hardness of a heat affected zone of a repairing zone are basically consistent with those of a base metal can be obtained without subsequent high-temperature tempering heat treatment. The repair quality is improved, the repair time is saved, and the economic benefit is improved. Greatly reduces the cost, saves the repair time and has obvious economic benefit.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes and modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the 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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