CN115595510B

CN115595510B - Iron-manganese alloy with high work hardening capacity, and preparation method and application thereof

Info

Publication number: CN115595510B
Application number: CN202211234913.0A
Authority: CN
Inventors: 吴宏; 刘佩峰; 刘波; 廖楚庭; 陈含蝶; 马雪茹
Original assignee: Central South University
Current assignee: Central South University
Priority date: 2022-10-10
Filing date: 2022-10-10
Publication date: 2023-07-28
Anticipated expiration: 2042-10-10
Also published as: CN115595510A

Abstract

The invention relates to an iron-manganese alloy with high work hardening capacity, and a preparation method and application thereof, and belongs to the technical field of preparation of medical high-strength iron-manganese alloy. In the ferromanganese alloy, the Mn content is 17.5-18.5wt%, the oxygen content is less than or equal to 0.03wt% and the balance is iron; the yield strength of the ferromanganese alloy is 220-300MPa, and the ultimate tensile strength is 870-998MPa. The ferromanganese takes Fe-Mn prealloy powder as a raw material; preparing a printing blank by adopting a 3D printing technology, and then performing heat treatment at 450-700 ℃ in a protective atmosphere; the product is obtained, and the parameters of 3D printing are as follows: the laser power is 200-220W, and the scanning speed is 680-720mm/s. The invention can ensure the product to have certain yield strength, and simultaneously greatly improve the tensile strength of the product, thereby achieving the purpose of improving the work hardening capacity of the product. The invention has simple and controllable components, strong work hardening capacity of the product and is convenient to be used as biomedical materials.

Description

Iron-manganese alloy with high work hardening capacity, and preparation method and application thereof

Technical Field

The invention relates to an iron-manganese alloy with high work hardening capacity, and a preparation method and application thereof, and belongs to the technical field of preparation of medical high-strength iron-manganese alloy.

Background

Among metal biomaterials, biodegradable alloys have received increasing attention in orthopedic implant applications over the last decade. It is a novel bioactive material that provides stable mechanical support for 3 to 6 months and is fully absorbed by the human body for 1 to 2 years without adverse pathophysiological and toxicological effects, which means that not only is the cost of secondary surgery reduced, but also the pain of the patient is alleviated. Among such medical metals, iron-based metals, particularly iron-manganese (Fe-Mn) based alloys, have excellent mechanical properties and workability, and in the limit of solubility, the addition of Mn makes Fe substrates more susceptible to corrosion, increasing their degradation rate in physiological media; mn is also an essential trace mineral required for normal brain and nerve function and bone and connective tissue formation in humans (ref: M.Aschner, T.R.Guilarte, J.S.Schneider, W.Zheng, manganese: recent advances inunderstanding its transport and neurotoxicity [ J ], toxicol. Appl. Pharmacol. [ J ].221 (2007) 131-147). Therefore, the excellent mechanical, degradation and biocompatibility make Fe-Mn alloy as a candidate degradable bone implant material.

On the other hand, bone substitutes require a reasonably personalized design for complex and diverse bone defect sites. Laser Powder Bed Fusion (LPBF) is a promising 3D printing technology that, when combined with Computer Aided Design (CAD), can produce complex layered structures with high dimensional accuracy, short processing time, and the like. Therefore, compared with the traditional manufacturing process, the preparation method is an ideal preparation method of the bone implant material, and has great potential in the field of iron-based degradable metals. Since the degradation rate of Fe-Mn alloy is greatly increased when Mn is more than 29% by weight, few reports on additive manufacturing of Fe-Mn alloy are focused on 30Mn and 35Mn series alloys, and high Mn content tends to generate certain neurotoxicity. According to Herawan et al, it is reported that a dual-phase structure (i.e., gamma-fcc phase/alpha' -bcc phase + epsilon-hcp phase) is more easily formed when the Mn content is less than or equal to 20wt.%, and that the phase interface hinders shear deformation to improve mechanical properties, and the highest tensile strength value of 702MPa (reference: H.Hermawan, D.Dube, D.Mantovani, degradable metallic biomaterials: design and development of Fe-Mn alloys for stents [ J ], journal of Biomedical Materials Research Part A93A (1) (2008) 1-11) can be achieved for the dual-phase Fe-Mn alloy reported in the conventional powder metallurgy process. At the same time, the potential difference between the different phases eventually increases the tendency to corrosion, which has been demonstrated in our recent work in the subject group (ref: P Liu, H Wu et al, microstructure, mechanical properties and corrosion behavior of additively-manufactured Fe-Mn alloys [ J ], materials Science & Engineering A852 (2022) 143585). In addition, the present subject group also uses Fe and Mn element powder to print out dual-phase Fe-Mn alloy in 3D (as in patent 2021107262170); however, the ultimate tensile strength of the product obtained by the patent is only 855-858MPa.

Compared to conventional processes such as casting, powder metallurgy, etc., LPBF has a finer microstructure and higher tensile strength due to an extremely fast cooling rate. However, heat flow and temperature gradients opposite to the build direction can lead to micro-structure non-uniformity and extreme residual stresses, which can undoubtedly lead to early mechanical failure and reduced plasticity. In view of the above facts, it is necessary to perform appropriate heat treatment on the print sample to reduce the residual stress, obtaining a uniform tissue. The current literature on heat treatment of Fe-Mn alloys is very limited to powder metallurgy. Dehestani et al prepared alloys by sintering FeMn mixed powder and studied the effect of heat treatment temperature on the structure and mechanical properties, and found that more epsilon-martensite phase precipitated after heat treatment than the original sample. However, the tensile strength of the alloy was not improved either by heat treatment at 700℃or 900 ℃ (ref: mahdi Dehestani, kevin Trumble, han Wang, haiyan Wang, lia A. Stanci, effects of microstructure and heat treatment on mechanical properties and corrosion behavior of powder metallurgy derived Fe-30Mn alloy [ J ], materials Science & Engineering A703 (2017) 214-226). The current literature report of the temporary absence of heat treatment of LPBFed Fe-Mn alloys predicts that the microstructure changes induced in the L-PBF material after heat treatment will be different from its sintered or cold rolled counterparts due to its unique microstructure.

Meanwhile, up to now, no report is made on how to improve the work hardening capacity of the product while ensuring the yield strength of the silicon-free ferromanganese alloy with the Mn content of less than 20% as a research object.

Disclosure of Invention

Based on the patent 2021107262170, the invention further researches and explores the attempts for enhancing the mechanical property and the work hardening capacity of the product; the invention is based on the attempted optimization scheme.

The ferromanganese alloy with high work hardening capacity is disclosed by the invention; in the ferromanganese alloy, the Mn content is 17.5-18.5wt%, the oxygen content is less than or equal to 0.03wt% and the balance is iron; the yield strength of the ferromanganese alloy is 220-300MPa, and the ultimate tensile strength is 870-998MPa. In the present invention, the yield strength and the ultimate tensile strength are measured at room temperature.

In the present invention, work hardening capacity = ultimate tensile strength-yield strength of the test specimen; the greater the difference in ultimate tensile strength and yield strength, the higher the work hardening capacity.

The invention ensures that the product has certain yield strength, namely 220-300MPa, and is used for providing enough mechanical support during implantation; under the condition of ensuring yield strength, the invention improves the ultimate tensile strength of the product, thereby achieving the purpose of improving the work hardening capacity of the product. The stronger the work hardening ability of the product, the stronger the ability to adapt to deformation, thereby having advantages in both implantation stability and safety.

The ferromanganese alloy with high work hardening capacity is disclosed by the invention; the ferromanganese takes Fe-Mn prealloy powder as a raw material; preparing a printing blank by adopting a 3D printing technology, and then performing heat treatment at 450-700 ℃ in a protective atmosphere; the product is obtained, and the parameters of 3D printing are as follows: the laser power is 200-220W, and the scanning speed is 680-720mm/s;

the structure of the printing blank mainly consists of needle-shaped martensite (alpha'), cellular subgrain and columnar subgrain;

the finished product is still very stable compared with the printing blank, the dimension is unchanged, but finer needle-shaped alpha' martensite is uniformly distributed in the matrix. The phase volume fraction of epsilon martensite in the finished product (65.16 vol.%) is greater than the phase volume fraction of epsilon martensite in the green print (62.09 vol.%).

After optimization, the ferromanganese alloy with high work hardening capacity is prepared; after heat treatment, the yield strength of the product is 294-296MPa, the ultimate tensile strength is 995-997MPa, and the elongation at break is 16.2-16.3%. Compared with a printing blank, the printing blank has the advantages of improving yield strength, ultimate tensile strength and elongation at break, and more importantly: the work hardening capacity is further improved on the basis of the printing blank.

The invention relates to a preparation method of an iron-manganese alloy with high work hardening capacity, which is prepared by adopting 3D printing and heat treatment in a matching way; the method comprises the following steps:

taking Fe-Mn prealloy powder as a raw material; preparing a printing blank by adopting a 3D printing technology, and then performing heat treatment at 450-700 ℃ in a protective atmosphere; the product is obtained, and the product is obtained,

in the Fe-Mn pre-alloy powder, the content of Mn is 18-18.5wt%, the oxygen content is less than or equal to 0.03wt% and the balance is iron;

the parameters for 3D printing are: the laser power is 200-220W, and the scanning speed is 680-720mm/s.

The tensile strength of the product is greater than or equal to 884MPa.

Preferably, the method for preparing the high-strength ferromanganese alloy by adopting 3D printing and heat treatment is characterized in that the particle size of Fe-Mn prealloy powder is 15-53 mu m.

In industrial application, the Fe-Mn prealloy powder is spherical Fe-Mn prealloy powder prepared by an air atomization method.

Preferably, the invention relates to a preparation method of an iron-manganese alloy with high work hardening capacity; the parameters for 3D printing are: the laser power is 210W, and the scanning speed is 700mm/s.

Preferably, the invention relates to a preparation method of an iron-manganese alloy with high work hardening capacity; in 3D printing, the scan pitch was 80 μm and the layer thickness was 30 μm.

Preferably, the invention relates to a preparation method of an iron-manganese alloy with high work hardening capacity; the prealloyed powder consists essentially of fcc austenite phase (γ) and hcp martensite phase (ε), while the green print consists essentially of hcp martensite phase and bcc martensite phase.

Preferably, the invention relates to a preparation method of an iron-manganese alloy with high work hardening capacity; the structure of the printing blank mainly consists of needle-shaped martensite, cellular subgrain and columnar subgrain.

Preferably, the invention relates to a preparation method of an iron-manganese alloy with high work hardening capacity; the columnar sub-crystals will grow along the direction of the heat flow.

Preferably, the invention relates to a preparation method of an iron-manganese alloy with high work hardening capacity; the heat treatment temperature is 645-655 ℃, the heat preservation time is 80-100min, and the cooling mode is furnace cooling.

Preferably, the invention relates to a preparation method of an iron-manganese alloy with high work hardening capacity; after heat treatment, the cellular and columnar sub-crystals are still very stable, with no change in size, but finer acicular martensite is uniformly distributed in the matrix, compared to the print. The phase volume fraction of epsilon martensite in the finished product (65.16 vol.%) is greater than the phase volume fraction of epsilon martensite in the green print (62.09 vol.%).

Preferably, the invention relates to a preparation method of an iron-manganese alloy with high work hardening capacity; after heat treatment, the product has stronger work hardening capacity than a printing blank, and the mechanical property is also greatly improved.

After optimization, the yield strength of the printing blank is 205-207MPa, the ultimate tensile strength is 883-885MPa, and the elongation at break is 15.8-15.85%.

After optimization, the yield strength of the heat-treated product is 294-296MPa, the ultimate tensile strength is 995-997MPa, and the elongation at break is 16.2-16.3%. In the exploration process of the invention, the temperature of heat treatment is 645-655 ℃, the heat preservation time is 80-100min, and the yield strength, ultimate tensile strength and elongation at break of the product are all improved (relative to a printing blank) when the product is cooled along with a furnace, which is greatly beyond the current prediction.

After the product is optimized, the fracture mode is ductile fracture after the product is pulled off after heat treatment.

Applications of the ferromanganese alloy designed and prepared according to the present invention with high work hardening capacity include use in bioimplant materials.

Principle and advantages

The invention attempts to make Fe-Mn alloy for the first timeThe mechanical property and the work hardening capacity of the product are improved by adopting a mode of combining 3D printing and heat treatment, and the principle that the stacking fault energy is obviously influenced by the Mn content is utilized (when Mn is less than or equal to 18wt percent, the stacking fault energy is lower than 20 mJ/m) ² The phase transition induced plasticity TRIP and the twinning induced plasticity TWIP effect are easy to occur simultaneously, and the Fe-18Mn alloy (nominal composition) is successfully prepared by combining a 3D printing technology. The extremely fast cooling speed of the alloy generates unbalanced phase transformation in the matrix, and finally forms an epsilon-alpha' double-phase martensitic structure. While the product is uniformly distributed with epsilon and alpha 'phases under optimized heat treatment conditions, the alternating epsilon (hard phase) and alpha' (soft phase) distributions form back stress reinforcement, providing additional work hardening capacity (in the present invention work hardening capacity = ultimate tensile strength-yield strength; the greater the difference in ultimate tensile strength to yield strength, the higher the work hardening capacity), in addition to the TWIP and TRIP effects providing significant work hardening. Therefore, on the basis of the earlier work, the 3D printing technology is combined with the subsequent heat treatment, and finally the Fe-18Mn alloy with very excellent work hardening capacity is obtained, and the ultimate tensile strength is obviously improved. The invention provides a product with excellent work hardening capacity, which has the advantages that: when implanted into a human body, the implant has good fatigue performance while providing enough mechanical support, and adapts to deformation caused by cyclic loading, so that the high work hardening capacity can ensure the stability and safety of the implant.

Drawings

FIG. 1 shows the density and 5 for the different laser process parameters (corresponding to the volume energy density) of example 1 ^# 、11 ^# 、17 ^# Representative polished surface topography (corresponding to low, medium, and high volumetric energy densities, respectively) of the sample;

FIG. 2 shows XRD patterns of the raw materials used in examples 1, 2, 3 and comparative examples 1, 2, 3, 4 and the obtained products;

FIG. 3 is an SEM micrograph of the corresponding products of examples 1, 2, 3 and comparative example 1;

FIG. 4 is a graph of tensile engineering stress strain for the corresponding products of examples 1, 2, 3 and comparative example 1;

FIG. 5 is a graph showing the stretch-break topography of the products obtained in examples 1, 2 and comparative example 1;

FIG. 6 is a graph showing the stretch-break topography of the products obtained in comparative examples 2, 3, 4.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail with reference to the accompanying drawings.

Example 1

The Fe-Mn alloy rod was aerosolized to obtain spherical Fe-Mn prealloyed powder (particle size: 15-53 μm, composition see Table 1) for use. Laser powder bed melting equipment (LPBF, supplied by Hunan Hua Shu high-tech Co., ltd.) is used to scan the alloy powder layer by layer (oxygen content in the forming bin is lower than 100 ppm), and the laser power setting interval is: 120-270W, the scanning speed setting interval is: 600-800mm/s, all samples are scanned at a distance of 80 μm and have a layer thickness of 30 μm; the different laser process parameter numbers are shown in table 1, and finally, a scanning direction tensile member with the thickness of 1.5mm and a cube with the length, width and height of 10mm are printed for subsequent performance analysis.

TABLE 1

Effect of the invention

1. Volumetric energy Density (VED, J/mm) ³ ) The best response to the energy input during printing is calculated by the formula ved=p/v×h×t (P represents laser power, v represents scan speed, h represents scan pitch, t represents layer thickness). Figure 1 shows the density, measured by archimedes' displacement method, of different laser process parameters (corresponding volumetric energy density) and the corresponding polished surface topography. It can be seen that at low energy density, the density ranges from 97.05% to 98.69%, and in combination with the results of fig. 1a and table 2, many unfused holes appear on the polished surface, and the mass percentage of Mn element is only about 14wt.% due to insufficient energy input; likewise, at too high an energy density, the density ranges from 98.13% to 98.40%, in combination with fig. 1c and 98.40Table 2 the results, polishing at too high an energy input, show the formation of many spherical pores, which are caused by Mn sublimation, and the final Mn content is only 15wt.%. Relatively speaking, at moderate energy input (corresponding to 7 ^# To 12 ^# Sample) the density of the sample can reach more than 99.2 percent, especially for 11 percent ^# The compactness of the sample, namely the sample with the laser process parameter of 210W,700mm/s, reaches 99.94%. In combination with the results of fig. 1b and table 2, the sample surface was almost fully dense with no obvious hole defects, and the Mn content measured at this laser parameter was 17.8wt.%, substantially close to the Mn content of the original powder (18.3 wt.%). In summary, the optimal laser process parameters for the Fe-Mn alloy samples are: the laser power was 210W and the scanning speed was 700mm/s (designated As-build sample).

TABLE 2

Sample of	Mn(wt.％)	O(wt.％)	Fe(wt.％)
				Fe-18Mn prealloyed powder	18.3	0.02	Bal.
2 ^#	14.4	0.07	Bal.
				5 ^#	14.2	0.09	Bal.
11 ^#	17.8	0.03	Bal.
				13 ^#	15.2	0.07	Bal.
17 ^#	14.8	0.13	Bal.

2. As can be seen from the XRD results of FIG. 2, there is a certain difference between the As-build sample and the prealloyed powder. The prealloyed powder consisted essentially of fcc austenite phase (γ) and hcp martensite phase (ε), while the As-build sample consisted essentially of hcp martensite phase and bcc martensite phase (α'), the volume fraction of ε phase being 62.09vol.% As measured by an electron back-scattering diffraction device (FE-SEM, quanta 250FEG, america). The extremely rapid rate of cold flow of the alloy after melting typically results in an unbalanced phase change, with a phase change of γ→ε occurring at Mn levels of 12-30 wt.%, and a phase change of ε→α' occurring at 12-18 wt.%. The Fe-Mn alloy rod is dispersed into fine liquid drops through high-speed air flow after being melted, and then FeMn pre-alloy powder is obtained through quick cooling, so that a part of high Wen austenite phase is unstable and is converted into epsilon martensite phase, the Mn content of an As-building sample is lower than 18wt.%, and after the high-temperature austenite phase is formed in the LPBF process, gamma- & gtepsilon- & gtalpha' phase transformation is generated through quick cooling, and a part of epsilon martensite phase is reserved, and therefore, the main peak strength of martensite is reduced compared with that of the pre-alloy powder.

3. As shown in FIG. 3, the scanning surface microstructure image (SEM) of the As-build sample mainly comprises needle-shaped martensite, cellular subgrain and columnar subgrain, the interfaces of epsilon and alpha' phases are clear when observed at low multiples, and cellular subgrain and columnar subgrain with different orientations are formed when observed at high multiples, which is mainly caused by uneven temperature gradient distribution and different growth modes of the subgrain, and generally the columnar subgrain grows along the opposite direction of heat flow.

4. As shown in FIG. 4, the tensile engineering stress strain curve of the As-build sample is lower in the fault energy (< 20 mJ/m) due to the Mn content of about 18 wt% ² ) In addition to dislocation slip during deformation, there is also twinning and phase transformation, so there is significant work hardening during stretching. The ultimate tensile strength is greatly improved compared with the original yield strength. Table 3 lists the mechanical property data of As-build samples, which have higher tensile strength (884 MPa) and elongation at break (15.81%) than the current powder metallurgy prepared dual phase Fe-Mn alloy. In inventive example 1, the work hardening capacity of the As-build samples obtained was already relatively high.

TABLE 3 Table 3

5. FIG. 5 shows the stretch-break morphology of As-build samples, both from low and high power, with large areas of cleaved breaks and randomly distributed ductile fosters found. Since the epsilon phase and alpha 'phase are clearly demarcated in fig. 3, the hard epsilon phase results in a cleavage fracture mode, while the alpha' phase results in a ductile fracture mode, thus resulting in uneven fracture surfaces in various fracture modes.

Example 2

The ferromanganese prealloy powder is scanned layer by adopting LPBF equipment, the laser power is 210W, the scanning speed is 700mm/s, the scanning interval is 80 mu m, the scanning layer thickness is 30 mu m, and a scanning direction stretching piece with the thickness of 1.5mm and a cube with the length, width and height of 10mm are printed. Sealing the stretching piece and the cube in a quartz tube filled with argon, then placing the quartz tube into a muffle furnace for heat treatment, wherein the heating rate is 10 ℃/min, the temperature is 650 ℃, the heat preservation time is 90min, the cooling mode is furnace cooling, and the quartz tube is named as HT650 sample and is subjected to subsequent performance analysis.

Effect of the invention

1. The XRD results of the HT650 sample are shown in FIG. 2, also consisting of epsilon martensite phase and alpha ' martensite phase, with a decrease in alpha ' peak intensity and an increase in epsilon peak intensity compared to the As-building sample, which means that the epsilon phase volume fraction is increased, and is more easily identified, as measured by an electron back-scattering diffraction device (ebsd), with a epsilon phase volume fraction of 65.16vol.%, which is mainly related to the alpha '. Fwdarw.epsilon reverse phase change that occurs under heat treatment conditions, where the furnace cooling rate is slower, leaving more epsilon martensite.

2. As can be seen from the SEM results of fig. 3, the cellular and columnar sub-crystals are still stable and the size is not changed under the 650 ℃ heat treatment condition (low temperature annealing). Unlike the As-build sample, finer acicular α' martensite is uniformly distributed in the matrix.

3. As shown in FIG. 4, the tensile engineering stress-strain curve of HT650 is higher than that of the As-build sample, whether it is yield strength (295 MPa), tensile strength (996 MPa) or elongation at break (16.28%). Quantitative results of HT650 mechanical properties are listed in Table 4, since the epsilon phase volume fraction of the HT650 sample is slightly higher than that of the As-build sample, in addition to the deformation mechanism enhancement described in example 1, additional work hardening is formed due to the different degree of softness and more uniform distribution of the epsilon phase and alpha' phase, back stress (HDI) is generated in alternating soft and hard regions, the interaction between back stress and normal stress, and more mobile dislocations are accumulated at soft and hard interfaces. In summary, HT650 has a stronger work hardening capacity than the As-build sample, while mechanical properties are also the best of all heat treated samples. In all the studies, the work hardening capacity of the product was further improved on the basis of the As-build sample after heat treatment of example 2. This elevation is also only reflected in this embodiment.

TABLE 4 Table 4

4. Fig. 5 shows the tensile fracture morphology of HT650 samples, which shows that the entire fracture surface is very flat and many fine ductile pits can be seen at high multiples, indicating that the primary fracture mode is ductile fracture with uniform tissue distribution, which also verifies that the thermal treatment at 650 ℃ improves the fracture elongation.

Example 3

The ferromanganese prealloy powder is scanned layer by adopting LPBF equipment, the laser power is 210W, the scanning speed is 700mm/s, the scanning interval is 80 mu m, the scanning layer thickness is 30 mu m, and a scanning direction stretching piece with the thickness of 1.5mm and a cube with the length, width and height of 10mm are printed. Sealing the stretching piece and the cube in a quartz tube filled with argon, then placing the quartz tube into a muffle furnace for heat treatment, wherein the heating rate is 10 ℃/min, the temperature is 850 ℃, the heat preservation time is 90min, the cooling mode is furnace cooling, and the quartz tube is named as HT850 sample and is subjected to subsequent performance analysis.

Effect of the invention

1. The XRD results of the HT850 samples are shown in fig. 2, also consisting of epsilon martensite phase and alpha 'martensite phase, with a slight decrease in alpha' peak intensity compared to HT650, the volume fraction of epsilon phase as measured by ebsd being 69.44vol.%.

2. As can be seen from the SEM results of fig. 3, the structure morphology of the products obtained in examples 1 and 2 is completely different from that of the products obtained in examples 1 and 2, the cellular and columnar sub-crystals of the HT850 sample have completely disappeared, and instead the lath martensite is cross-distributed, and the lath epsilon martensite width is increased compared to the original sample. Outside the lath-shaped regions are all alpha' martensite.

3. The tensile engineering stress-strain curve of HT850 is shown in FIG. 4, the strength and plasticity are reduced (tensile strength 889MPa, elongation at break 11.61%) compared with the HT650 sample, the strength is slightly improved and the elongation at break is significantly reduced compared with the As-building sample, and the corresponding quantitative results of mechanical properties are shown in Table 5. While the tissue distribution is more uniform, thicker, denser lath epsilon martensite makes the overall strength inferior to the HT650 sample, while the stress concentration area increases, resulting in a decrease in material plasticity.

TABLE 5

Comparative example 1

The ferromanganese prealloy powder is scanned layer by adopting LPBF equipment, the laser power is 210W, the scanning speed is 700mm/s, the scanning interval is 80 mu m, the scanning layer thickness is 30 mu m, and a scanning direction stretching piece with the thickness of 1.5mm and a cube with the length, width and height of 10mm are printed. The tensile member and the cube were sealed in an argon filled quartz tube and then placed in a muffle furnace for heat treatment at a heating rate of 10 ℃/min, a temperature of 1050 ℃, a holding time of 90min, and a cooling mode of furnace cooling, which was designated as HT1050 sample, and the subsequent performance analysis was performed.

Effect of the invention

1. From the XRD results of fig. 2, it is seen that the HT1050 sample is also composed of epsilon martensite phase and alpha' martensite phase, and that the phase volume fraction of the HT850 sample is not different.

2. From the SEM high-magnification morphology of fig. 3, it can be seen that HT1050 samples likewise cross-distribute lath epsilon martensite, but continue to grow in width, with alpha' martensite outside the lath regions.

3. The tensile engineering stress-strain curve of HT1050 is shown in FIG. 4, and the strength-plasticity is reduced (tensile strength 636MPa, elongation at break 7.17%) compared to all samples, and the corresponding quantitative results are listed in Table 6, where the mechanical properties of the samples are the worst, which is related to the dense epsilon martensite distribution with increased thickness.

TABLE 6

4. Fig. 5 shows the tensile fracture morphology of the HT1050 samples, which demonstrates poor plasticity of the HT1050 samples, as seen at low magnification, although the entire fracture surface is flat, instead the entire surface is cleaved to fracture, with very few ductile pits present.

Comparative example 2

The ferromanganese prealloy powder is scanned layer by adopting LPBF equipment, the laser power is 210W, the scanning speed is 700mm/s, the scanning interval is 80 mu m, the scanning layer thickness is 30 mu m, and a scanning direction stretching piece with the thickness of 1.5mm and a cube with the length, width and height of 10mm are printed. Sealing the stretching piece and the cube in a quartz tube filled with argon, then placing the quartz tube into a muffle furnace for heat treatment, wherein the heating rate is 10 ℃/min, the temperature is 450 ℃, the heat preservation time is 90min, the cooling mode is furnace cooling, and the quartz tube is named as HT450 sample and is subjected to subsequent performance analysis.

Effect of the invention

1. From the XRD results of fig. 2, it is seen that HT450 samples are also composed of epsilon martensite phase and alpha 'martensite phase, and epsilon peak intensity is reduced compared to HT650 samples, because the reverse alpha' →epsilon phase transformation is incomplete by lowering the heat treatment temperature.

2. Table 7 lists the mechanical properties of HT450 samples, with a 72MPa decrease in yield strength compared to HT650, a 86MPa decrease in ultimate tensile strength compared to HT650, and lower elongation at break (13.45%) than the As-build and HT650 samples.

TABLE 7

3. From the tensile fracture morphology of fig. 6, HT450 is primarily a mixed mode of ductile fracture and fracture-splitting, with less planar fracture surfaces.

Comparative example 3

Other conditions were consistent with example 2; the difference is that: the heat treatment temperature was 550℃and was designated as HT550 samples. The XRD results are shown in FIG. 2, and are not significantly different from those of HT450 samples. The tensile experiments gave 251MPa, 912MPa and 15.17% elongation at break, respectively, yield strength, ultimate tensile strength and elongation at break, which, despite their excellent strong plastic properties, were still lower than the HT650 samples, not the optimal heat treatment parameters. The fracture morphology in fig. 6 shows that the HT550 sample still had an uneven cleaved fracture surface.

Comparative example 4

Other conditions were consistent with example 2; the difference is that: the heat treatment temperature was 750℃and was designated as HT750 samples. The XRD results are shown in FIG. 2, and are not significantly different from those of HT450 samples. The tensile experiment shows that the yield strength, the ultimate tensile strength and the breaking elongation are 269MPa, 871MPa and 13.71 percent respectively, the mechanical properties are lower than those of an As-building sample and an HT650 sample, and the thermal treatment parameters are not optimal. From the stretched fracture morphology of fig. 6, the fracture mode is still dominated by cleavage fracture.

Claims

1. An iron-manganese alloy with high work hardening capacity, characterized in that: in the ferromanganese alloy, the Mn content is 17.5-18.5wt%, the oxygen content is less than or equal to 0.03wt% and the balance is iron;

the ferromanganese takes Fe-Mn prealloy powder as a raw material; preparing a printing blank by adopting a 3D printing technology, and then performing heat treatment for 80-100min at 645-655 ℃ in a protective atmosphere; the product is obtained, and the parameters of 3D printing are as follows: the laser power is 200-220W, and the scanning speed is 680-720mm/s;

the structure of the printing blank consists of needle-shaped martensite, cellular subgrain and columnar subgrain;

compared with a printing blank, the product has stable cellular subgrain and columnar subgrain, and the size is unchanged, but needle-shaped alpha 'martensite is uniformly distributed in a matrix, and the size is smaller than the needle-shaped alpha' martensite in the printing blank; the phase volume fraction of epsilon martensite in the product is greater than the phase volume fraction of epsilon martensite in the green print, as compared to the green print;

after heat treatment, the yield strength of the product is 294-296MPa, the ultimate tensile strength is 995-997MPa, and the elongation at break is 16.2-16.3%; compared with the printing blank, the printing blank has the advantages that the yield strength, the ultimate tensile strength and the breaking elongation are improved, and the difference between the ultimate tensile strength and the yield strength of the finished product is larger than the corresponding value of the printing blank.

2. A high work hardening capacity ferromanganese alloy according to claim 1, wherein: the particle size of the Fe-Mn prealloyed powder is 15-53 mu m.

3. A high work hardening capacity ferromanganese alloy according to claim 1, wherein:

the parameters for 3D printing are: the laser power was 210W, the scanning speed was 700mm/s, the scanning pitch was 80 μm, and the layer thickness was 30. Mu.m.

4. A high work hardening capacity ferromanganese alloy according to claim 1, wherein:

the yield strength of the printing blank is 205-207MPa, the ultimate tensile strength is 883-885MPa, and the elongation at break is 15.8-15.85%.

5. Use of a high work hardening ferromanganese alloy according to any one of claims 1 to 4, wherein: including use as a bioimplant material.