CN114293113A

CN114293113A - High-thermal-conductivity alloy powder for SLM (Selective laser melting), high-thermal-conductivity die steel and SLM forming process of high-thermal-conductivity die steel

Info

Publication number: CN114293113A
Application number: CN202111673638.8A
Authority: CN
Inventors: 刘桐; 骆良顺
Original assignee: Anhui Hate 3d Technology Co ltd
Current assignee: Anhui Hate 3d Technology Co ltd
Priority date: 2021-12-31
Filing date: 2021-12-31
Publication date: 2022-04-08
Anticipated expiration: 2041-12-31
Also published as: CN114293113B

Abstract

The invention discloses high-thermal-conductivity alloy powder for an SLM (selective laser melting), which comprises the following components in percentage by weight: 0.05 to 0.1 percent of C, 3 to 3.5 percent of Ni, 0.8 to 1 percent of Al, 0.8 to 1 percent of Cu, 1 to 1.5 percent of Mn, 0.4 to 0.5 percent of Mo, 0.3 to 0.4 percent of Cr, 0 to 0.1 percent of Si and the balance of Fe. The invention also discloses an SLM forming process of the high-thermal-conductivity die steel, which comprises the following steps: and (3) taking the high-thermal-conductivity alloy powder for the SLM, spreading the powder, and then carrying out selective laser melting and forming to obtain the high-thermal-conductivity die steel. The invention also discloses high-thermal-conductivity die steel. The alloy powder has high thermal conductivity and can be used for SLM forming; and a proper SLM forming process is provided, so that the die steel has good thermal conductivity, compactness and mechanical property.

Description

High-thermal-conductivity alloy powder for SLM (Selective laser melting), high-thermal-conductivity die steel and SLM forming process of high-thermal-conductivity die steel

Technical Field

The invention relates to the technical field of selective laser melting, in particular to high-thermal-conductivity alloy powder for an SLM (Selective laser melting), high-thermal-conductivity die steel and an SLM forming process thereof.

Background

The Selective Laser Melting (SLM) technology belongs to the 3D printing technology and is an important development direction of advanced manufacturing technology. The selective laser melting technology comprises the steps of firstly designing a three-dimensional modeling diagram of a part to be printed by utilizing UG, Pro/e, CATIA and other software in a computer, then carrying out slicing layering processing on a drawn three-dimensional model of the part by using slicing software to obtain data information of each section, then guiding the obtained section information into a forming device, converting the three-dimensional manufacturing into two-dimensional plane manufacturing, controlling a laser beam to carry out melting sintering processing on powder at a corresponding position in each layer of spread powder by the device according to the guided section information, and stacking layer by layer to finally obtain the required solid metal part.

Compared with the traditional manufacturing process, the selective laser melting technology does not need a die and an original blank, so that a large amount of raw materials can be saved, and the material consumption is reduced to below 50 percent of the original material consumption. The SLM technology breaks through the bottleneck of manufacturing complex geometric structure parts (such as closed complex inner cavity, thin-wall structure, and curved inner flow channel structure), and these complex structural parts are difficult to be manufactured by the traditional material reduction manufacturing method and the deformation forming method, but can be easily realized by the SLM technology. The SLM technology can be used for manufacturing a conformal cooling mold with a complex shape structure and a mold with high thermal conductivity.

Nowadays, it is necessary to replace the common mold with the conformal cooling mold. However, the conventional machining method for manufacturing the conformal cooling water channel mold often has the problems of multiple working procedures, high cost, low forming precision, high cost and even difficult machining, and the SLM technology has the characteristics which are not possessed by the conventional machining method due to the self-forming mode, so that the conformal cooling water channel mold with a complex shape structure can be manufactured, which means that the mold manufactured by the SLM technology can have more uniform heat dissipation capability, the part forming period can be obviously shortened, and considerable social and economic benefits are generated. The materials currently on the market for SLM mold production are mainly maraging steel and maraging stainless steel, but the large amount of alloying elements added to these steels to obtain ultra-high strength of 2GPa results in thermal conductivity of these steels being generally lower than 20W/(mK), which means that the production efficiency of the mold will be greatly limited.

Therefore, the thermal conductivity of the die steel manufactured by SLM molding needs to be improved, and the mechanical property of the die steel needs to be improved; the SLM technology is used for completely melting metal powder, the melted metal is rapidly cooled, solidified and formed, and the mechanical properties of the formed part can be greatly influenced by the density of the formed part, laser power, scanning speed, scanning distance, powder laying thickness, wind field direction, scanning strategy, substrate preheating temperature and other process parameters in the SLM technology; it is therefore desirable to provide a suitable SLM forming process to prepare the die steel.

Disclosure of Invention

Based on the technical problems in the background art, the invention provides high-thermal-conductivity alloy powder for an SLM (selective laser melting), high-thermal-conductivity die steel and an SLM forming process thereof; aiming at the problem that the thermal conductivity of the existing material for preparing the SLM mold is generally lower than 20W/(mK), the invention provides alloy powder with high thermal conductivity for SLM molding; and a proper SLM forming process is provided, so that the die steel has high compactness and mechanical property and good thermal conductivity.

The invention provides high-thermal-conductivity alloy powder for an SLM (selective laser melting), which comprises the following components in percentage by weight: 0.05-0.1% of C, 3-3.5% of Ni, 0.8-1% of Al, 0.8-1% of Cu, 1-1.5% of Mn, 0.4-0.5% of Mo, 0.3-0.4% of Cr0.1%, 0-0.1% of Si and the balance of Fe.

The carbon content is reduced, Ni, Al and Cu are added, the alloy is strengthened through the composite action of the Ni, the Al and the Cu, Al element and the Ni can form a NiAl phase, and the hardness of the material can be improved through the interactive precipitation of the NiAl phase and the Cu-rich phase; by adopting the design idea of low-carbon low-alloying and second-phase strengthening alloy, the toughness and plasticity of the alloy are improved, and the alloy has higher thermal conductivity, strength and hardness, so that the requirement of high-thermal conductivity die steel is met, and the alloy is suitable for selective laser melting forming.

Preferably, the particle size of the alloy powder is 15-53 μm.

Preferably, the alloy powder has a D50 of 33-35 μm.

Preferably, the bulk density of the alloy powder is 3.8 to 4.2g/cm³。

Preferably, the fluidity of the alloy powder is 15 to 16.5s/50 g.

The invention also provides an SLM forming process of the high-thermal-conductivity die steel, which comprises the following steps: and (3) taking the high-thermal-conductivity alloy powder for the SLM, spreading the powder, and then carrying out selective laser melting and forming to obtain the high-thermal-conductivity die steel.

In the SLM forming process, the performance of the formed part is affected by the laser power, the scanning speed and the scanning distance. And the influence of three factors of laser power, scanning speed and scanning distance on the density is not independent, and each factor is influenced by the other two factors when acting on the density, and interaction exists among the three factors.

Therefore, proper laser selective melting process parameters need to be selected, so that the die steel has high compactness and mechanical properties and good thermal conductivity. The alloy powder is a self-designed formula, and the SLM forming process needs to be started from zero, and the inventor determines a proper SLM process through a plurality of experiments.

Preferably, the laser power is 240-320W, the scanning speed is 850-1150mm/s, and the scanning pitch is 0.11-0.15 mm.

Preferably, the laser power is 280-320W, the scanning speed is 850-1000mm/s, and the scanning interval is 0.11-0.15 mm.

Preferably, the laser power is 310W, the scanning speed is 930mm/s, and the scanning interval is 0.12 mm.

The powder spreading thickness is too small, so that the remelting frequency of each layer is too much, burning loss occurs, the production efficiency is seriously reduced, if the powder spreading thickness is too large, more heat input is needed to melt the powder, the particle size range of the alloy powder is 15-53 mu m, and the powder spreading thickness is set to be more than or equal to 35 mu m in comprehensive consideration.

Preferably, the thickness of the spread powder is 40-60 μm.

Preferably, the dusting thickness is 50 μm.

Preferably, after the selective laser melting and forming, the aging treatment is carried out to obtain the high-thermal-conductivity die steel.

After selective laser melting and forming, the inventor selects a proper aging process, so that the heat conductivity and the mechanical property of the die steel can be further improved.

Preferably, the aging temperature is 475-.

Preferably, the ageing temperature is 500 ℃ and the ageing time is 4 h.

The invention also provides the high-thermal conductivity die steel which is prepared according to the SLM forming process of the high-thermal conductivity die steel.

Has the advantages that:

aiming at the problem that the thermal conductivity of the existing material for preparing the SLM mold is generally lower than 20W/(mK), the invention designs an alloy formula, and provides alloy powder with high thermal conductivity for SLM molding; in addition, because the alloy powder is a self-designed formula, research on the SLM (melt flow modeling) forming process of the alloy powder is a blank and needs to be started from zero; according to the invention, by designing appropriate laser selective melting process parameters, the die steel has high density and mechanical properties and good thermal conductivity.

Drawings

Fig. 1 is a scanning electron micrograph of the high thermal conductivity alloy powder of example 1 at 500 times and 1500 times, wherein a is 500 times and b is 1500 times.

FIG. 2 is a side surface profile of a molded sample under different process parameters, wherein a-d are laser powers of 240, 280, 320 and 360W in sequence, e-h are scanning speeds of 700, 850, 1000 and 1150mm/s in sequence, and i-l are scanning pitches of 0.09, 0.11, 0.13 and 0.15mm in sequence.

FIG. 3 is an internal profile chart of a molded sample under different process parameters, wherein a-d are laser powers of 240, 280, 320 and 360W in sequence, e-h are scanning speeds of 700, 850, 1000 and 1150mm/s in sequence, and i-l are scanning pitches of 0.09, 0.11, 0.13 and 0.15mm in sequence.

FIG. 4 is an X-ray diffraction spectrum of a high thermal conductivity alloy powder, an SLM molded article in a printed state and a heat treated state, wherein AF is the printed state and SAT is the heat treated state.

FIG. 5 is a metallographic photograph of the high thermal conductivity mold steel in the printed state and in the heat treated state, where a is the printed state and at 50 magnification; b is in a heat-treated state with a magnification of 500.

FIG. 6 is a SEM magnified photograph of a high thermal conductivity die steel as printed.

FIG. 7 is an SEM magnified photograph of a high thermal conductivity die steel in a heat treated state.

FIG. 8 is a photograph of a high thermal conductivity die steel with SEM magnification of 30000 times in the heat treated state.

Detailed Description

The technical solution of the present invention will be described in detail below with reference to specific examples.

The tensile property test is carried out by using an AGXplus electronic universal testing machine with the specification of 20Kn produced by Jinshima according to the national standard GB/T228-2002 indoor tensile test method for metal materials.

A hardness measuring instrument is an HVS-1000A type hardness tester, and a hardness measuring experiment is carried out according to the standard GB/T230 Rockwell hardness test of metal materials.

The performance of the powder was tested using a Mastersizer 3000E powder particle size analyzer, an ONH-3000 oxy-nitrogen hydrogen analyzer, and a BT-1001 intelligent powder comprehensive property tester, respectively.

Example 1

Adding raw materials according to a formula (the components comprise, by weight, 0.05% of C, 3.4% of Ni, 0.8% of Al, 1% of Cu, 1.5% of Mn, 0.1% of Si, 0.45% of Mo, 0.33% of Cr and the balance of Fe), and preparing high-heat-conductivity alloy powder by using Anhui three-dimensional atomization powder preparation equipment, wherein in order to prevent a nozzle from being blocked by rapid solidification of metal droplets in an atomization process, a large-caliber nozzle is selected, atomization is carried out after the temperature of liquid metal reaches 1500 ℃, and an atomization medium is nitrogen; finally, high-thermal-conductivity alloy powder is prepared, and the composition detection, the powder performance detection and the electron microscope scanning are carried out on the alloy powder, and the results are shown in tables 1-2 and figure 1.

As can be seen from fig. 1: the sphericity of the powder is high, a small amount of elliptical powder and satellite powder exist, the small amount of small-particle-size powder is adhered to the large-particle-size powder, and the cooling speed of liquid drops in the atomization powder preparation process is extremely high, so that the grain size of the powder is smaller than 10 mu m, and the grains are equiaxial crystals formed by growth of extremely small cellular crystals or dendrites.

Table 1 example 1 chemical composition of high thermal conductivity alloy powder (% by weight)

C	Ni	Al	Cu	Mn	Mo	Cr	Fe
								0.05-0.1	3-3.5	0.8-1	0.8-1	1-1.5	0.4-0.5	0.3-0.4	Bal.

Table 2 powder properties of the high thermal conductivity alloy powder of example 1

Example 2

Taking the high-thermal-conductivity alloy powder of the embodiment 1, designing an experiment, using HIT-M150 laser selective melting molding equipment of a 3D printing die special machine produced in Hartt three-dimensional mode, in order to avoid oxidation of the metal powder after laser melting, performing the whole molding process in a sealed molding chamber of a system, continuously introducing argon protective gas with the purity of 99.9%, and providing an oxygen-free environment for the molding process while blowing away floating magazines; the laser power, the scanning speed and the scanning distance of the SLM forming process are adjusted to prepare the die steel, the powder spreading thickness is 50 mu m, the compactness of the die steel forming samples of each group is inspected, and the results are shown in table 3 and fig. 2-3.

As can be seen in fig. 2-3: with the increase of the laser power, the appearance of the side surface of the sample has obvious difference, the boundary between the molten pool and the molten pool becomes fuzzy gradually from clear, and simultaneously, the convex molten pool with the spheroidization tendency is less and less. When the power is changed from 240W to 360W, obvious pore defects exist in the sample, the pores in the sample are irregular shapes such as long strips and triangles at low power, and the pores in the sample are mostly circular or nearly circular at high power. Obviously, when the laser power is low, the heat input by the laser is insufficient, so that the molten pool metal liquid is low in temperature and has large surface tension, the molten pool is spheroidized, and the molten metal cannot fill all places, so that arc-shaped and triangular pores are formed inside the molten pool; when the laser power is high, the metal liquid is gasified due to excessive heat absorbed by the powder, and the keyhole effect occurs;

when the speed is 700mm/s, arc-shaped cracks can be seen at the interface of the molten pool and the molten pool on a side SEM picture, large thermal stress is generated due to excessive heat input, and cracks are generated between the relatively weak molten pool and the molten pool under the action of the large thermal stress;

when the scanning distance is 0.09mm, the lapping rate between the molten pools is large, so that the heat absorbed by a single molten pool is extremely large, the dynamic viscosity of molten metal in the molten pool is small due to high temperature of the molten pool, and the molten pool is unstable and is reflected on the molten pool shapes with different sizes.

TABLE 3 SLM Molding Process and die Steel Density of molded samples of example 2

Experiment number	Laser power/W	Scanning speed/mm.s^-1	Scanning distance/mm	Density/%
					1	240	850	0.11	99.857
2	280	850	0.11	99.786
					3	320	850	0.11	99.813
4	360	850	0.11	99.529
					5	320	700	0.11	99.666
6	320	850	0.11	99.813
					7	320	1000	0.11	99.928
8	320	1150	0.11	99.763
					9	320	850	0.09	99.776
10	320	850	0.11	99.813
					11	320	850	0.13	99.915
12	320	850	0.15	99.865

As can be seen from table 3: the relative density of all the formed parts is more than 99 percent, when the laser power, the scanning speed and the scanning distance are respectively 360W, 850mm/s and 0.11mm, the formed part density is the lowest and is only 99.529 percent, and when the laser power, the scanning speed and the scanning distance are respectively 320W, 1000mm/s and 0.11mm, the formed part density is the highest and is 99.928 percent;

when the laser power is in the range of 240-320W, the density change of the formed part is small, and when the laser power is increased to 360W, the density is sharply reduced, because the over-high laser power can cause unstable molten pool and generate droplet splashing to cause inclusion and burning defects. As the scanning speed and the scanning pitch increase, the density tends to increase first and then decrease. When the scanning speed is low and the scanning distance is small, the molten pool absorbs more heat, the range of the lap joint area is large, the molten pool is also unstable, and the lap joint area is easy to burn, so that the density is low; when the scanning speed is high and the scanning distance is large, the molten pool absorbs less heat, the molten pool spheroidization tendency is severe, all areas are difficult to be paved to cause gaps, and the compactness is also low;

as shown in Table 3, when the laser power, the scanning speed and the scanning pitch are respectively in the ranges of 240-.

Example 3

Further experiments were designed to obtain more optimal process parameters, with the results shown in table 4.

TABLE 4 SLM Molding Process and die Steel compaction of example 3

Experimental number	Laser power/W	Scanning speed/mm.s^-1	Scanning distance/mm	Density/%
					1	300	850	0.11	99.937
2	320	1000	0.11	99.943
					3	300	1000	0.13	99.730
4	280	1000	0.15	98.292
					5	280	1150	0.13	98.918
6	300	1150	0.15	98.128
					7	320	850	0.13	99.931
8	300	1150	0.11	99.841
					9	280	850	0.13	99.916
10	280	1000	0.11	99.890
					11	300	1000	0.13	99.829
12	320	1150	0.13	99.122
					13	320	1000	0.15	98.897
14	300	1000	0.13	99.539
					15	300	850	0.15	99.672
16	310	930	0.12	99.962

As can be seen from table 4: the relative density of all the formed parts is more than 99%, and when the laser power, the scanning speed and the scanning distance are respectively 310W, 930mm/s and 0.12mm, the density of the formed parts is the highest and is 99.962%.

Example 4

The powder of the alloy with high thermal conductivity in example 1 is taken, the powder spreading thickness is 50 μm according to the process parameters of experiment number 16 in example 3, the SLM forming is carried out to obtain a forming sample (marked as a printing state), then the forming sample is subjected to solid solution at 900 ℃ for 30min, water quenching is carried out to room temperature, then heat preservation and aging are carried out at 500 ℃ for 4h, and air cooling is carried out to room temperature to obtain die steel (marked as a heat treatment state).

The results of the examination of the high thermal conductivity alloy powder, the printed state, and the heat-treated state are shown in FIGS. 4 to 8.

As can be seen from fig. 4: no matter in a powder state, a printing state or a heat treatment state, only the body-centered cubic ferrite alpha peak exists in the X diffraction spectrum of the high-thermal conductivity die steel, but the austenite diffraction peak cannot be seen, so that the main phase composition of the high-thermal conductivity die steel in the three states does not exist, and considering that the atomization powder preparation process and the SLM forming process are both rapid solidification processes, the main phase composition can be inferred to be martensite, the die steel has good hardenability, and the full martensite structure is easy to obtain.

As can be seen from fig. 5: the appearance of a molten pool can be clearly seen through a printed metallographic photograph, wherein a dark color area is a molten pool boundary, a light color area is the inside of the molten pool, the color difference is generated because the molten pool boundary has high nucleation rate due to the rapid solidification of the molten pool and generates a large amount of fine grains, because the magnification is small and the grains in the fine grains area are dense, the inside of the molten pool has the formation condition of columnar crystals due to the slow solidification, the inside of each molten pool is composed of a limited number of large columnar crystals, and the density degree of the brown grain boundary after corrosion is relatively low and the molten pool appears light color; after heat treatment, the clear boundaries of columnar crystals and fine crystals completely disappear, the columnar crystals and the fine crystals are converted into isometric crystals with the grain size of less than 10 mu m, and the structure can be judged to be lath martensite by combining the cooling condition, the XRD result and the structure morphology.

The existence of fine crystalline zones at the boundary of the molten pool and columnar crystalline zones inside the molten pool can be seen more clearly from fig. 6a) enlarged 1000 times, the existence of equiaxed crystalline zones at the center of the molten pool is not seen, and the width of the fine crystalline zones is about 20 μm, which indicates that the solidification speed of the molten pool is extremely high. Fig. 6b) and 6c) are SEM photographs of a columnar crystal region inside the molten pool in which the existence of martensite laths is clearly seen and a fine crystal region at the boundary of the molten pool in which the grain size is too small to be seen, respectively, after being magnified 10000 times.

From fig. 7a) magnified 1000 times, it can be seen that the grain size is within 20 μm, and the grain size is significantly increased compared to the printed state because the sample is subjected to a solution treatment at 900 ℃ and austenite grows during the solution treatment; it can also be seen that within each grain there are 1-3 clusters of martensite laths, the width of which is limited by the grain size, all around 10 μm, which is much smaller than the as-cast state. Fig. 7b) is an SEM image magnified 10000 times, showing more visually the martensite lath population and lath bundles, but no martensite laths, the width of the lath bundles being in the range of 1-3 μm. Different from the printing state, a large amount of dispersed spherical particles with fine sizes appear in the interior of the crystal grains after heat treatment, the size of the spherical particles is approximately measured and found to be within 100nm, and the particles can be judged to be a precipitated phase in the aging process and be a NiAl phase or a Cu-rich phase by combining the components of the die steel.

FIG. 8 is a photograph of a high thermal conductivity die steel with SEM magnification of 30000 times in the heat treated state. The existence of precipitated phases can be seen more clearly in fig. 8, where spectrum 1 is plotted on the particles and spectrum 2 is plotted on the matrix.

The results of the energy spectrum analysis of spectrogram 1 and spectrogram 2 are shown in Table 5.

TABLE 5 content (wt%) of alloy elements at different positions

Spectrogram	Al	Cr	Mn	Fe	Ni	Cu	Total amount of
								Spectrogram 1	1.45	0.6	1.88	90.46	3.95	1.67	100.00
Spectrogram 2	2.15	0.99	2.05	89.21	3.83	1.77	100.00

From table 5 it can be seen that the Al content in spectrum 1 is 1.45% which is significantly lower than 2.15% of spectrum 2.

Tensile properties and hardness were measured for the high thermal conductivity die steel in the as-printed and heat treated states, respectively, and compared to the cast (as-cast, untreated) of the formulation of example 1, and the results are shown in table 6.

TABLE 6 mechanical Properties of high-thermal-conductivity die steels in different states

Sample (I)	Tensile strength Ts (MPa)	Elongation El (%)	Hardness (HRC)
				Printing state	1041	12.4	31.8
In a heat-treated state	1364	10.6	45.2
				As-cast condition	871	15.7	29.5

As can be seen from Table 6, the strength of the SLM-formed die steel after the heat treatment of solution treatment and aging treatment is increased from 1041MPa to 1364MPa, the increase rate is 31.0%, the hardness is increased from 31.8HRC to 45.2HRC, and the elongation is reduced from 12.4% to 10.6%. In combination with the previous analysis of the texture in the printed state and in the heat-treated state, it is not difficult to draw conclusions: the NiAl phase and the Cu-rich phase which are dispersed and precipitated during aging are the reasons for greatly improving the strength and the hardness of the sample after heat treatment. Compared with the as-cast state, the strength and the hardness of the SLM forming die steel are improved slightly and obviously, and the reason that the strength and the hardness of the SLM forming sample are higher than those of the casting sample is considered to be that the crystal grain size of the SLM forming part is generally less than 20 micrometers.

Respectively measuring the density, specific heat and thermal diffusion coefficient of the high-thermal-conductivity die steel in a printing state and a heat treatment state at each experimental temperature point, and according to a formula lambda ═ alpha rho C_p(Note: α -thermal diffusivity, cm)²s^-1(ii) a Rho-density g cm^-3；C_p-specific heat capacity J/(g · K); λ -thermal conductivity W/(m · K)), the thermal conductivity at each experimental temperature point was calculated, and the results are shown in table 7.

TABLE 7 thermal conductivity (W/(m.K))

Temperature of	25	100	200	300	400	500
							Printing state	27.016	29.31	31.222	32.548	33.2	33.029
In a heat-treated state	31.695	33.665	35.302	36.920	36.297	35.444

As can be seen from table 7: the thermal conductivity of the die steel is increased and then reduced along with the temperature rise no matter in a heat treatment state or a printing state, and the thermal conductivity of the die steel after the heat treatment is higher than that in the printing state within the temperature range of 0-500 ℃, because SLM forming is a rapid solidification process, solid solution atoms are precipitated from a matrix without time due to extremely rapid cooling speed, so that the number of solid solution atoms in the die steel in the printing state is large, lattice distortion caused by a large number of solid solution atoms can cause electron scattering, after the heat treatment of solid solution and aging, a large number of solid solution elements are precipitated from the matrix, free electron scattering caused by lattice distortion caused by solid solution is reduced, and the phenomenon that the thermal conductivity is improved after the heat treatment is generated. Comparing the thermal conductivity of the die steel in the as-cast state with the thermal conductivity of the as-printed state, it can be seen that the thermal conductivity of the as-printed state is lower than that of the as-cast state at a lower temperature, which can also be explained by electron scattering caused by solid solution atoms, and the thermal conductivity of the as-printed state and that of the as-cast state is almost the same at a higher temperature, which indicates that in the temperature range of 0-500 ℃, when the grain size does not exceed a certain critical value, the influence of the change of the grain size on the thermal conductivity is small, and the influence of the number of solid solution atoms on the thermal conductivity is maximum and exceeds that of the second phase;

under the condition of 100 ℃, the thermal conductivity of the printing state is 29.31 (W/m.K), the thermal conductivity is improved to 33.67 (W/m.K) after heat treatment, and compared with the existing 18Ni300 commonly used for manufacturing die steel for 3D printing, the thermal conductivity is improved by over 50 percent.

In summary, the following steps:

the SLM process parameters for the alloy powders described in example 1 were: the laser power is 240-320W, the scanning speed is 850-1150mm/s, and the scanning distance is 0.11-0.15 mm; the preferable technological parameters are as follows: the laser power is 310W, the scanning speed is 930mm/s, the scanning distance is 0.12mm, and the density of the formed part is 99.962 percent.

The high thermal conductivity die steel powder, the printing state and the heat treatment state are all martensite structures. The crystal grains in the molten pool of the printing-state high-thermal-conductivity die steel comprise a large amount of fine grains and columnar grains, the fine grains are mainly positioned at the boundary of the molten pool, and the width of a fine grain region is about 20 mu m; columnar crystals are located inside the molten pool, and no equiaxed crystals are observed in the center of the molten pool.

After the SLM-formed high-thermal-conductivity die steel is subjected to 900 ℃ solid solution and 500 ℃ aging treatment, columnar crystals and fine crystals disappear and become isometric crystals with the grain size of 10-20 mu m, dispersed fine precipitated phases are precipitated in the grains, EDS (electron-dispersive spectroscopy) analysis results show that the precipitated phases can be NiAl phases, the strength of the high-thermal-conductivity die steel after heat treatment is improved from 1041MPa in a printing state to 1364MPa, and the hardness of the high-thermal-conductivity die steel is improved from 31.8HRC to 45.2HRC due to the strengthening effect of the precipitated phases.

The thermal conductivity of the high-thermal-conductivity die steel in a printing state is remarkably improved after heat treatment, and the main reason is that the heat diffusion coefficient of the material is increased by the large amount of solid solution atoms after the heat treatment, so that the thermal conductivity is improved, and the deterioration of the thermal conductivity by the solid solution is higher than that of the second relative thermal conductivity. After heat treatment, the room temperature thermal conductivity is as high as 31.695W/(m.K), which is higher than the thermal conductivity of 18Ni300 by more than 50%.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.

Claims

1. A high thermal conductivity alloy powder for SLM, characterized by comprising, in weight percent: 0.05 to 0.1 percent of C, 3 to 3.5 percent of Ni, 0.8 to 1 percent of Al, 0.8 to 1 percent of Cu, 1 to 1.5 percent of Mn, 0.4 to 0.5 percent of Mo, 0.3 to 0.4 percent of Cr, 0 to 0.1 percent of Si and the balance of Fe.

2. A high thermal conductivity alloy powder for SLM as claimed in claim 1, characterized in that the grain size of the alloy powder is 15-53 μm.

3. A high thermal conductivity alloy powder for SLM as claimed in claim 1 or 2, characterized in that the D50 of the alloy powder is 33-35 μm.

4. A high thermal conductivity alloy powder for SLM according to any one of claims 1 to 3, characterized in that the loose packed density of the alloy powder is 3.8-4.2g/cm³。

5. A high thermal conductivity alloy powder for SLM according to any one of claims 1 to 4, characterized in that the fluidity of the alloy powder is 15-16.5s/50 g.

6. The SLM forming process of the high-thermal-conductivity die steel is characterized by comprising the following steps of: taking high-thermal-conductivity alloy powder for the SLM according to any one of claims 1 to 5, laying the powder, and then carrying out selective laser melting forming to obtain the high-thermal-conductivity die steel.

7. The SLM forming process of the high thermal conductivity die steel as claimed in claim 6, wherein the laser power is 240-320W, the scanning speed is 850-1150mm/s, and the scanning pitch is 0.11-0.15 mm; preferably, the laser power is 280-320W, the scanning speed is 850-1000mm/s, and the scanning interval is 0.11-0.15 mm; preferably, the laser power is 310W, the scanning speed is 930mm/s, and the scanning interval is 0.12 mm.

8. The SLM forming process of the high-thermal-conductivity die steel as claimed in claim 6 or 7, wherein the powder spreading thickness is more than or equal to 35 μm; preferably, the powder spreading thickness is 40-60 μm; preferably, the dusting thickness is 50 μm.

9. The SLM forming process of the high-thermal-conductivity die steel as claimed in any one of claims 6-8, wherein after selective laser melting forming, aging treatment is carried out to obtain the high-thermal-conductivity die steel; preferably, the aging temperature is 475-; preferably, the ageing temperature is 500 ℃ and the ageing time is 4 h.

10. A high thermal conductivity die steel produced by the SLM forming process of the high thermal conductivity die steel according to any one of claims 6 to 9.