CN115976393A - Method for preparing high-performance powder metallurgy low-alloy steel by master alloy approach - Google Patents
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Abstract
The invention discloses a method for preparing high-performance powder metallurgy low-alloy steel by a master alloy way, belonging to the field of powder metallurgy. The invention designs a novel method for preparing high-performance powder metallurgy low-alloy steel by a master alloy way, aiming at the problem that the prior powder metallurgy low-alloy steel has insufficient comprehensive performance caused by the defects of pores, original particle boundaries and the like. The invention comprises the design of master alloy components, the preparation of master alloy powder and matrix iron powder, the powder mixing and the hot isostatic pressing sintering process. The powder metallurgy low-alloy steel material with good performance can be obtained through the coordination of component design and preparation process. The powder metallurgy low alloy steel prepared by the invention has uniform structure, no obvious pore and original particle boundary defects, no fracture appearance along the particles, and obviously improved plasticity. Compared with the traditional preparation method of sintering forming-large plastic deformation treatment, the method can be widely applied to the near net shape preparation of the complex special-shaped low-alloy steel member.
Description
Technical Field
The invention relates to the field of powder metallurgy, in particular to a method for preparing high-performance powder metallurgy low-alloy steel by a master alloy approach.
Background
The low alloy steel is widely applied to the fields of weaponry, aerospace and the like due to the excellent characteristics of high strength, high hardness, good plasticity and toughness and the like. With the continuous deepening of the green manufacturing concept, higher requirements are put forward on the aspects of material utilization, energy conservation, environmental protection and the like in the manufacturing process. However, for complex components such as low alloy steel elastomer head materials and rocket engine casings, a preparation process of casting/forging and machining is usually adopted, which easily causes serious material waste and energy consumption. Under the background, the powder metallurgy near-net forming technology is widely concerned, can obtain workpieces with the final shape and size, greatly reduces the workload of subsequent machining, and is particularly suitable for preparing large thin-wall and complex revolving body components. Therefore, the powder metallurgy near-net forming technology is an ideal technology for realizing green manufacturing of low-alloy steel complex components.
However, there are often porosity problems in powder metallurgy products that severely affect the mechanical properties of the product. In addition, as the powder raw material inevitably forms an oxide layer on the surface of the powder particles in the processes of preparation, storage and the like, and further a great number of defects (called as original particle boundaries) that the oxides are distributed in a chain shape along the particle boundaries are formed in the product, the plasticity and toughness of the product can be seriously weakened. The existence of the two powder metallurgy defects restricts the development and the application of the powder metallurgy low alloy steel.
The documents "Effect of density and processing conditions on oxide transformations and mechanical properties in Cr-Mo-alloyed PM steles, M.V.Sundaram, E.Hryha, D.Chasoglou, et al, metallic and Materials transformations A2022; 53A. "preparing Cr-Mo powder metallurgy steel with different densities. The results show that the density is from 7.3g cm -3 Reduced to 6.8g cm -3 The tensile strength of the material is reduced from 1600MPa to 1200MPa.
The literature "Ductity in hot differential compressed 250-grade marking steel, R.M.German, J.E.Smugeresky: metallurgical transformations A1978;9A "adopting rotary electrode atomization to prepare prealloy 250-grade maraging steel powder, and carrying out hot isostatic pressing sintering to obtain a sintered product. The results show that the tensile strength is comparable to that in the as-forged state, but the elongation is extremely low. This is mainly due to the presence of the original grain boundary defects causing peel breaks along the grains in the specimen during the stretching process.
At present, the pore problems are mainly eliminated through the improvement of powder metallurgy technology and process optimization. Aiming at the original grain boundary defect, the current mature improvement measure is mainly to change the distribution state of inclusions at the original grain boundary by carrying out large plastic deformation on a sintered blank, thereby improving the bonding strength among grains and achieving the purpose of improving the plastic toughness.
The documents "Effect of thermal Engineering on the microstructure and mechanical properties of hot alcoholic compressed super alloy Inconel 718, G.A.Rao, M.Srinivas, D.S.Sarma; 383 p.201-212 "and" documents Properties of marking Steel 300Produced by powder metallurgical, L.F.V.Swam, R.M.Pelloux, N.J.Grant; 17, p.33-45', and the like respectively carry out hot rolling treatment on the Inconel 718 high-temperature alloy in the hot isostatic pressing state and the Maring 300 Maraging steel, the original grain boundary is obviously damaged, and the elongation after fracture is obviously improved. However, such improvements result in significant changes in the shape of the sintered compact and the advantages of powder metallurgy near-net shape are lost.
Based on the above, the field urgently needs to develop a novel preparation method of powder metallurgy low alloy steel, which can effectively solve the problems of the defects of pores and original particle boundaries in powder metallurgy products and avoid subsequent large plastic deformation treatment; provides a new scheme for green manufacturing of complex low-alloy steel components.
Disclosure of Invention
The invention provides a method for preparing high-performance powder metallurgy low-alloy steel by a master alloy approach, which aims at the problems of pores and original particle boundary defects in a powder metallurgy component on the basis of the current situation that a near-net-shaped component is difficult to perform large plastic deformation by taking green manufacturing of a complex low-alloy steel component as a background. The invention aims to optimize a near net shape powder hot isostatic pressing process to obtain a sintered material without pore defects, and simultaneously provides a new way for regulating and controlling original particle boundary defects in a sintering process, thereby avoiding subsequent large plastic deformation treatment and realizing the near net shape preparation of high-performance powder metallurgy low-alloy steel.
The invention discloses a method for preparing high-performance powder metallurgy low alloy steel by a master alloy way, which comprises the following steps of:
(1) Designing the components of the master alloy: according to the components Fe-1.1Cr-1.2Mn-1.15Si-1.7Ni-0.25Mo-0.1V-0.28C of the 30CrMnSiNi2A steel, increasing all alloy elements according to the same proportion to obtain the components of a master alloy: fe-x (1.1 Cr-1.2Mn-1.15Si-1.7Ni-0.25 Mo-0.1V-0.28C), wherein x is defined as a proportionality coefficient;
the proportionality coefficient x should be strictly controlled to be selected within 3-7; the proportion coefficient is too low, the solidus temperature of the master alloy is higher, the solid-liquid phase interval is narrower, and the process control is difficult to carry out; the proportionality coefficient is too high, and the uniform diffusion is difficult to realize during sintering. In the present invention, the proportionality coefficient may preferably be 3 to 3.5.
(2) Preparing master alloy powder and matrix iron powder: preparing a master alloy ingot by taking a Fe-M intermediate alloy block and a pure Fe block as raw materials, and then pulverizing to obtain master alloy powder; preparing matrix iron powder by taking pure Fe as a raw material;
(3) Powder mixing: weighing the obtained master alloy powder and matrix iron powder according to the mass ratio of 1 (x-1), filling the master alloy powder and the matrix iron powder into a mixing tank, introducing protective atmosphere, and mixing on a three-dimensional mixer to obtain mixed powder;
taking 30 crmnsii 2A steel as an example, let a g master alloy powder and (x-1) × a g matrix iron powder be weighed respectively, taking Cr as an example, nominal composition of Cr in the mixed powder can be expressed as: 1.1 × a/(a + (x-1) =1.1, consistent with the composition in 30CrMnSiNi2A steel.
(4) And (3) hot isostatic pressing sintering: the mixed powder is filled in a steel sheath, and then vacuum degassing and seal welding are carried out; placing the sealed and welded sheath in a hot isostatic pressing machine, heating to the required sintering temperature of 1100-1350 ℃ at the heating rate of 5-15 ℃/min, keeping the temperature and the pressure for 1-4 h under the pressure of 50-200 MPa, and cooling along with the furnace to obtain a powder metallurgy low alloy steel material; defining the sintering temperature as T and the heat preservation time as T, wherein the selection of the sintering temperature T and the heat preservation time T is related to a proportionality coefficient:
wherein, in order to ensure that the proper liquid phase quantity is generated in the sintering process, when the unit of the sintering temperature is ℃ (centigrade), the sintering temperature T and the proportionality coefficient x should satisfy the following relation: when x is more than or equal to 3 and less than or equal to 5, T is more than or equal to 1375-35x and less than or equal to 1500-50x; when x is more than 5 and less than or equal to 7, T is more than or equal to 1375-35x and less than or equal to 1340-20x;
wherein, in order to ensure that the master alloy powder and the matrix iron powder are fully diffused in the sintering process and simultaneously avoid excessive growth of crystal grains, when the unit of the heat preservation time is h (hour), the heat preservation time t and the proportionality coefficient x should satisfy the following relation: t is more than or equal to 1/2 (x-1) and less than or equal to 1/2 (x + 1).
Preferably, in the method for preparing the high-performance powder metallurgy low-alloy steel by the master alloy route, in the second step, M in the Fe-M intermediate alloy block is at least one element selected from Cr, mn, ni, si, mo, V, C and the like.
As a preferred scheme, the method for preparing the high-performance powder metallurgy low-alloy steel by the master alloy approach comprises the following steps of preparing master alloy powder and matrix iron powder from a master alloy ingot and a pure Fe ingot by an atomization powder preparation technology; the atomization powder preparation technology comprises one of water atomization, gas atomization and plasma rotating electrode atomization; to ensure that the powder has a low oxygen content, gas atomization and rotary electrode atomization techniques are preferred.
In the second step, the master alloy powder and the matrix iron powder are sieved, and the particle size range of the master alloy powder obtained by sieving is preferably 10-75 μm, more preferably 15-50 μm, even more preferably 20-50 μm, and even more preferably 20-40 μm; the particle size range of the base iron powder obtained by sieving is preferably 10 to 105 μm, more preferably 15 to 75 μm, still more preferably 20 to 50 μm, and still more preferably 20 to 40 μm.
According to the method for preparing the high-performance powder metallurgy low-alloy steel by the master alloy way, the protective atmosphere in the step three is argon atmosphere, and the material mixing time is preferably 2-6 hours, and further preferably 3-5 hours.
According to the method for preparing the high-performance powder metallurgy low-alloy steel by the master alloy way, the heating rate of hot isostatic pressing in the step four is preferably 8-12 ℃/min.
Preferably, in the method for preparing the high-performance powder metallurgy low-alloy steel by the master alloy route, the pressure of the hot isostatic pressing in the step four is preferably 75-175 MPa, and more preferably 100-150 MPa.
Preferably, in the method for preparing the high-performance powder metallurgy low-alloy steel by the master alloy route, when the proportionality coefficient x is 3, the holding time of the hot isostatic pressing in the step four is preferably 80-120 min, and more preferably 100-120 min.
Principles and advantages
Principle of
At present, the application bottlenecks of the near-net-shaped powder metallurgy low-alloy steel component are as follows: the powder metallurgy component usually has defects such as pores, original particle boundaries and the like, and the mechanical property of the product is seriously influenced; it is difficult to find a defect control method that is compatible with near net shape manufacturing. The invention provides a method for preparing high-performance low-alloy steel by a master alloy way. Aiming at the problem of pores, the invention proposes to solve the problem by utilizing the high temperature and high pressure of the hot isostatic pressing technology; aiming at the problem of original grain boundary, the invention provides that a local liquid phase is formed on the surface of powder in the sintering process, and the continuous distribution form of oxide along the grain boundary is destroyed by the formation of the liquid phase; however, the higher solidus temperature (1440 ℃) and the narrower solid-liquid temperature range (40 ℃) of the prealloyed 30CrMnSiNi2A steel powder bring great challenges to hot isostatic pressing equipment and process control. Therefore, the innovative thinking of the invention is that on one hand, a master alloy approach is adopted to replace a pre-alloying approach, so as to prepare the master alloy powder with high alloy content (with lower solidus temperature and wider solid-liquid phase temperature interval), and the master alloy powder is mixed with the matrix iron powder in proportion to realize the formation of local liquid phase at lower sintering temperature; on the other hand, through the mutual matching and regulation of the proportionality coefficient, the sintering temperature and the sintering time, the full diffusion among the powder, the effective damage of the original particle boundary and the nearly full densification of the green body are realized. Namely, the powder metallurgy low-alloy steel material with good performance and the near-net-shape powder metallurgy preparation method matched with the material are developed through the design of the components of the master alloy and the cooperative optimization of the preparation process.
Advantages of
Compared with the prior art, the invention mainly has the following specific advantages:
1. the green manufacturing of the complex low alloy steel component can be realized, the workload of subsequent processing treatment can be effectively reduced, the production efficiency is improved, and the manufacturing cost is reduced.
2. The method solves the problem of the common defects of pores and original particle boundaries in the powder metallurgy low-alloy steel component, does not need to carry out the traditional large plastic deformation treatment, and realizes the integration of sintering forming and powder metallurgy defect control.
3. The powder metallurgy low-alloy steel material with good performance is obtained by the coordination of the optimization of the components of the master alloy and the sintering process.
Drawings
FIG. 1 shows the metallographic structure, inclusion distribution and tensile fracture characteristics of powder metallurgy low alloy steel prepared by process optimization in example 5 using a master alloy approach; wherein a is a metallographic structure diagram, has uniform structure and consists of granular bainite and martensite; b is an inclusion distribution diagram, and no obvious original grain boundary defect can be observed; c is the tensile fracture morphology, which consists of crystal-crossing quasi-cleavage and toughness dimples.
FIG. 2 is a metallographic structure, inclusion distribution, and tensile fracture characteristics of the powder metallurgy low alloy steel prepared by the prealloying method in comparative example 1; wherein a is a metallographic structure diagram and consists of uniform granular bainite; b is an inclusion distribution diagram, and obvious original grain boundary defects can be observed; c is the tensile fracture morphology, and obvious peeling fracture characteristics along the particles can be observed.
FIG. 3 shows metallographic structures, inclusion distributions and tensile fracture characteristics of powder metallurgy low alloy steels prepared by a master alloy approach and unreasonable powder particle size combinations in comparative example 4; wherein a is a metallographic structure diagram, and extremely uneven structure characteristics can be observed; b is an inclusion distribution diagram, and no obvious original grain boundary defect can be observed; c is the tensile fracture morphology, consisting of transgranular cleavage, transgranular quasi-cleavage and ductile dimple.
Detailed Description
The following examples and comparative examples are intended to further illustrate the present disclosure, but not to limit the present invention.
Example 1
(1) Designing the components of the master alloy: according to the composition Fe-1.1Cr-1.2Mn-1.15Si-1.7Ni-0.25Mo-0.1V-0.28C of 30CrMnSiNi2A steel, increasing all alloy elements according to the same proportion, and selecting a proportionality coefficient x as 3 to obtain the composition of a master alloy: fe-3.3Cr-3.6Mn-3.45Si-5.1Ni-0.75Mo-0.3V-0.84C;
(2) Preparing master alloy powder and matrix iron powder: preparing an ingot casting by using Fe-Cr, fe-Mn, fe-Si, fe-Ni, fe-Mo, fe-V, fe-C intermediate alloy blocks and pure Fe blocks according to the components of the master alloy; further adopting a gas atomization powder preparation technology to prepare master alloy powder and matrix iron powder from the master alloy and the pure iron cast ingot; then screening the master alloy powder and matrix iron powder to obtain powder with the granularity of 25-50 mu m;
(3) Powder mixing: weighing the obtained master alloy powder and matrix iron powder according to the mass ratio of 1:2, filling into a mixing tank, introducing argon for atmosphere protection, and mixing for 3 hours on a three-dimensional mixer to obtain mixed powder;
(4) And (3) hot isostatic pressing sintering: the mixed powder is filled in a steel sheath, and then vacuum degassing and seal welding are carried out; and (3) placing the sealed and welded sheath in a hot isostatic pressing machine, heating to 1350 ℃ of the required sintering temperature at the heating rate of 10 ℃/min, preserving heat and pressure for 1h under the pressure of 150MPa, and cooling along with the furnace to obtain the powder metallurgy low alloy steel material.
Inclusions in the sample are distributed dispersedly, and obvious original grain boundary defects are not formed; the relative density reaches 99.5 percent, and the product is nearly fully dense. The powder has good matching of the grain diameter and the sintering process, fully diffused elements and uniform structure, and consists of granular bainite and martensite. The room-temperature mechanical properties of the alloy are as follows: the tensile strength is 1335MPa, the elongation after fracture is 15.9 percent, and the performance is better; the fracture morphology is mainly based on crystal-crossing quasi-cleavage and ductile dimple fracture, and no obvious fracture morphology along particle peeling is found.
Example 2
(1) Designing the components of the master alloy: according to the components Fe-1.1Cr-1.2Mn-1.15Si-1.7Ni-0.25Mo-0.1V-0.28C of the 30CrMnSiNi2A steel, increasing all alloy elements according to the same proportion, and selecting a proportionality coefficient x to be 4 to obtain the components of the master alloy: fe-4.4Cr-4.8Mn-4.6Si-6.8Ni-1.0Mo-0.4V-1.12C;
(2) Preparing master alloy powder and matrix iron powder: preparing an ingot according to the components of the master alloy by using Fe-Cr, fe-Mn, fe-Si, fe-Ni, fe-Mo, fe-V, fe-C intermediate alloy blocks and pure Fe blocks; further adopting a gas atomization powder preparation technology to prepare mother alloy powder and matrix iron powder from the mother alloy and the pure iron cast ingot; then screening the master alloy powder and matrix iron powder to obtain powder with the granularity of 25-50 mu m;
(3) Powder mixing: weighing the obtained master alloy powder and matrix iron powder according to the mass ratio of 1:3, filling into a mixing tank, introducing argon for atmosphere protection, and mixing for 3 hours on a three-dimensional mixer to obtain mixed powder;
(4) And (3) hot isostatic pressing sintering: the mixed powder is filled in a steel sheath, and then vacuum degassing and seal welding are carried out; and (3) placing the sealed and welded sheath in a hot isostatic pressing machine, heating to the required sintering temperature of 1250 ℃ at the heating rate of 10 ℃/min, preserving heat and pressure for 2h under the pressure of 150MPa, and cooling along with the furnace to obtain the powder metallurgy low alloy steel material.
Inclusions in the sample are distributed dispersedly, and obvious original grain boundary defects are not formed; the relative density reaches 99.6 percent, and the product is nearly fully dense. The powder has good matching of the grain diameter and the sintering process, fully diffused elements and uniform structure, and consists of granular bainite and martensite. The room-temperature mechanical properties of the alloy are as follows: the tensile strength is 1310MPa, the elongation after fracture is 15.3 percent, and the performance is better; the fracture morphology is mainly based on crystal-crossing quasi-cleavage and ductile dimple fracture, and no obvious fracture morphology along particle peeling is found.
Example 3
(1) Designing the components of the master alloy: according to the composition Fe-1.1Cr-1.2Mn-1.15Si-1.7Ni-0.25Mo-0.1V-0.28C of 30CrMnSiNi2A steel, increasing all alloy elements according to the same proportion, and selecting a proportionality coefficient x to be 6 to obtain the composition of a master alloy: fe-6.6Cr-7.2Mn-6.9Si-10.2Ni-1.5Mo-0.6V-1.68C;
(2) Preparing master alloy powder and matrix iron powder: preparing an ingot according to the components of the master alloy by using Fe-Cr, fe-Mn, fe-Si, fe-Ni, fe-Mo, fe-V, fe-C intermediate alloy blocks and pure Fe blocks; further adopting a gas atomization powder preparation technology to prepare mother alloy powder and matrix iron powder from the mother alloy and the pure iron cast ingot; then screening the master alloy powder and matrix iron powder to obtain powder with the granularity of 25-50 mu m;
(3) Powder mixing: weighing the obtained master alloy powder and matrix iron powder according to the mass ratio of 1:5, filling into a mixing tank, introducing argon for atmosphere protection, and mixing for 3 hours on a three-dimensional mixer to obtain mixed powder;
(4) And (3) hot isostatic pressing sintering: the mixed powder is filled in a steel sheath, and then vacuum degassing and seal welding are carried out; and (3) placing the sealed and welded sheath in a hot isostatic pressing machine, heating to the required sintering temperature of 1200 ℃ at the heating rate of 10 ℃/min, preserving heat and pressure for 3h under the pressure of 150MPa, and cooling along with the furnace to obtain the powder metallurgy low alloy steel material.
Inclusions in the sample are distributed dispersedly, and obvious original grain boundary defects are not formed; the relative density reaches 99.4 percent, and the product is nearly fully dense. The powder has good matching of the grain diameter and the sintering process, fully diffused elements and uniform structure, and consists of granular bainite and martensite. The room-temperature mechanical properties of the alloy are as follows: the tensile strength is 1330MPa, the elongation after fracture is 15.6 percent, and the performance is better; the fracture morphology is mainly based on crystal-crossing quasi-cleavage and ductile dimple fracture, and no obvious fracture morphology along particle peeling is found.
Example 4
(1) Designing the components of the master alloy: according to the composition Fe-1.1Cr-1.2Mn-1.15Si-1.7Ni-0.25Mo-0.1V-0.28C of 30CrMnSiNi2A steel, increasing all alloy elements according to the same proportion, and selecting a proportionality coefficient x as 3 to obtain the composition of a master alloy: fe-3.3Cr-3.6Mn-3.45Si-5.1Ni-0.75Mo-0.3V-0.84C;
(2) Preparing master alloy powder and matrix iron powder: preparing an ingot according to the components of the master alloy by using Fe-Cr, fe-Mn, fe-Si, fe-Ni, fe-Mo, fe-V, fe-C intermediate alloy blocks and pure Fe blocks; further adopting a gas atomization powder preparation technology to prepare master alloy powder and matrix iron powder from the master alloy and the pure iron cast ingot; then screening the master alloy powder and matrix iron powder to obtain powder with the granularity of 25-50 mu m;
(3) Powder mixing: weighing the obtained master alloy powder and matrix iron powder according to the mass ratio of 1:2, filling into a mixing tank, introducing argon for atmosphere protection, and mixing on a three-dimensional mixer for 3 hours to obtain mixed powder;
(4) And (3) hot isostatic pressing sintering: the mixed powder is filled in a steel sheath, and then vacuum degassing and seal welding are carried out; and (3) placing the sealed and welded sheath in a hot isostatic pressing machine, heating to 1350 ℃ at the heating rate of 10 ℃/min, keeping the temperature and the pressure for 2 hours under the pressure of 150MPa, and cooling along with the furnace to obtain the powder metallurgy low alloy steel material.
Inclusions in the sample are distributed dispersedly, and obvious original grain boundary defects are not formed; the relative density reaches 99.7 percent, and the product is nearly fully dense. The powder has good matching of the grain diameter and the sintering process, fully diffused elements and uniform structure, and consists of granular bainite and martensite. The room-temperature mechanical properties of the alloy are as follows: the tensile strength is 1360MPa, the elongation after fracture is 16.8 percent, and the performance is better; fracture morphology is mainly based on crystal-crossing quasi-cleavage and toughness dimple fracture, and no obvious fracture morphology along particle peeling is found.
Example 5
(1) Designing the components of the master alloy: according to the components Fe-1.1Cr-1.2Mn-1.15Si-1.7Ni-0.25Mo-0.1V-0.28C of the 30CrMnSiNi2A steel, increasing all alloy elements according to the same proportion, and selecting a proportionality coefficient x as 3 to obtain the components of the master alloy: fe-3.3Cr-3.6Mn-3.45Si-5.1Ni-0.75Mo-0.3V-0.84C;
(2) Preparing master alloy powder and matrix iron powder: preparing an ingot casting by using Fe-Cr, fe-Mn, fe-Si, fe-Ni, fe-Mo, fe-V, fe-C intermediate alloy blocks and pure Fe blocks according to the components of the master alloy; further adopting a gas atomization powder preparation technology to prepare master alloy powder and matrix iron powder from the master alloy and the pure iron cast ingot; then screening the master alloy powder and matrix iron powder to obtain powder with the granularity of 20-40 mu m;
(3) Powder mixing: weighing the obtained master alloy powder and matrix iron powder according to the mass ratio of 1:2, filling into a mixing tank, introducing argon for atmosphere protection, and mixing for 3 hours on a three-dimensional mixer to obtain mixed powder;
(4) And (3) hot isostatic pressing sintering: the mixed powder is filled in a steel sheath, and then vacuum degassing and seal welding are carried out; and (3) placing the sealed and welded sheath in a hot isostatic pressing machine, heating to 1350 ℃ of the required sintering temperature at the heating rate of 10 ℃/min, preserving heat and pressure for 2h under the pressure of 150MPa, and cooling along with the furnace to obtain the powder metallurgy low alloy steel material.
Inclusions in the sample are distributed dispersedly, and obvious original grain boundary defects are not formed; the relative density reaches 99.7 percent, and the product is nearly fully dense. The powder has good matching of the grain diameter and the sintering process, fully diffused elements and uniform structure, and consists of granular bainite and martensite. The room-temperature mechanical properties of the alloy are as follows: the tensile strength is 1380MPa, the elongation after fracture is 17.7 percent, and the performance is better; the fracture morphology is mainly based on crystal-crossing quasi-cleavage and ductile dimple fracture, and no obvious fracture morphology along particle peeling is found.
Comparative example 1
(1) Designing the components of the master alloy: according to the composition Fe-1.1Cr-1.2Mn-1.15Si-1.7Ni-0.25Mo-0.1V-0.28C of 30CrMnSiNi2A steel, the proportional coefficient x is selected to be 1, namely, a prealloying way is selected for preparation;
(2) Preparing pre-alloy powder: preparing an ingot according to the components of the 30CrMnSiNi2A steel by adopting Fe-Cr, fe-Mn, fe-Si, fe-Ni, fe-Mo, fe-V, fe-C intermediate alloy blocks and pure Fe blocks; further preparing the ingot into pre-alloyed powder by adopting a gas atomization powder preparation technology; then sieving the pre-alloyed powder to obtain powder with the granularity of 20-40 mu m;
(3) And (3) hot isostatic pressing sintering: the mixed powder is filled in a steel sheath, and then vacuum degassing and seal welding are carried out; and (3) placing the sealed and welded sheath in a hot isostatic pressing machine, heating to 1350 ℃ of the required sintering temperature at the heating rate of 10 ℃/min, preserving heat and pressure for 2h under the pressure of 150MPa, and cooling along with the furnace to obtain the powder metallurgy low alloy steel material.
As the prealloyed 30CrMnSiNi2A steel powder is adopted, a liquid phase cannot be formed at the temperature, dense inclusions form original grain boundary defects along grain boundaries, the relative density reaches 99.3 percent, and the density is close to full compactness. The room temperature structure of the alloy is mainly granular bainite structure; the room-temperature mechanical properties of the alloy are as follows: the tensile strength is 1230MPa, the elongation after fracture is 11.9 percent, and the performance is poor; fracture morphology significant exfoliation fracture morphology along the particle was observed.
Comparative example 2
(1) Designing the components of the master alloy: according to the composition Fe-1.1Cr-1.2Mn-1.15Si-1.7Ni-0.25Mo-0.1V-0.28C of 30CrMnSiNi2A steel, increasing all alloy elements according to the same proportion, and selecting a proportionality coefficient x of 2 to obtain the composition of a master alloy: fe-2.2Cr-2.4Mn-2.3Si-3.4Ni-0.5Mo-0.2V-0.56C;
(2) Preparing master alloy and matrix powder: preparing an ingot according to the components of the master alloy by using Fe-Cr, fe-Mn, fe-Si, fe-Ni, fe-Mo, fe-V, fe-C intermediate alloy blocks and pure Fe blocks; further adopting a gas atomization powder preparation technology to prepare master alloy powder and matrix iron powder from the master alloy and the pure iron cast ingot; then screening the master alloy powder and matrix iron powder to obtain powder with the granularity of 20-40 mu m;
(3) Preparation of mixed powder: weighing the obtained master alloy powder and matrix iron powder according to the mass ratio of 1:1, filling into a mixing tank, introducing argon for atmosphere protection, and mixing on a three-dimensional mixer for 3 hours to obtain mixed powder;
(4) And (3) hot isostatic pressing sintering: the mixed powder is filled in a steel sheath, and then vacuum degassing and seal welding are carried out; and (3) placing the sealed and welded sheath in a hot isostatic pressing machine, heating to 1350 ℃ of the required sintering temperature at the heating rate of 10 ℃/min, preserving heat and pressure for 2h under the pressure of 150MPa, and cooling along with the furnace to obtain the powder metallurgy low alloy steel material.
Because the proportional coefficient is selected to be lower, a liquid phase is not formed at 1350 ℃, and obvious original grain boundary defects are formed; the relative density reaches 99.4 percent, and the product is nearly fully dense. The room-temperature mechanical properties of the alloy are as follows: the tensile strength is 1250MPa, the elongation after fracture is 11.2 percent, and the performance is poor.
Comparative example 3
(1) Designing the components of the master alloy: according to the composition Fe-1.1Cr-1.2Mn-1.15Si-1.7Ni-0.25Mo-0.1V-0.28C of 30CrMnSiNi2A steel, increasing all alloy elements according to the same proportion, and selecting a proportionality coefficient x of 8 to obtain the composition of a master alloy: fe-8.8Cr-9.6Mn-9.2Si-13.6Ni-2.0Mo-0.8V-2.24C;
(2) Preparing master alloy and matrix powder: preparing an ingot casting by using Fe-Cr, fe-Mn, fe-Si, fe-Ni, fe-Mo, fe-V, fe-C intermediate alloy blocks and pure Fe blocks according to the components of the master alloy; further adopting a gas atomization powder preparation technology to prepare master alloy powder and matrix iron powder from the master alloy and the pure iron cast ingot; then screening the master alloy powder and matrix iron powder to obtain powder with the granularity of 20-40 mu m;
(3) Preparation of mixed powder: weighing the obtained master alloy powder and matrix iron powder according to the mass ratio of 1:7, filling into a mixing tank, introducing argon for atmosphere protection, and mixing for 3 hours on a three-dimensional mixer to obtain mixed powder;
(4) And (3) hot isostatic pressing sintering: the mixed powder is filled in a steel sheath, and then vacuum degassing and seal welding are carried out; and (3) placing the sealed and welded sheath in a hot isostatic pressing machine, heating to 1150 ℃ of the required sintering temperature at the heating rate of 10 ℃/min, preserving heat and pressure for 4h under the pressure of 150MPa, and cooling along with the furnace to obtain the powder metallurgy low alloy steel material.
The inclusions are seen to be distributed dispersedly, and obvious original grain boundary defects are not formed; the relative density reaches 99.2 percent, and the product is nearly fully dense. Because the proportionality coefficient exceeds the limited range, serious tissue nonuniformity phenomenon is formed; the room-temperature mechanical properties of the alloy are as follows: tensile strength is 1150MPa, elongation after fracture is 8.5%, and performance is extremely poor.
Comparative example 4
(1) Designing the components of the master alloy: according to the composition Fe-1.1Cr-1.2Mn-1.15Si-1.7Ni-0.25Mo-0.1V-0.28C of 30CrMnSiNi2A steel, increasing all alloy elements according to the same proportion, and selecting a proportionality coefficient x as 3 to obtain the composition of a master alloy: fe-3.3Cr-3.6Mn-3.45Si-5.1Ni-0.75Mo-0.3V-0.84C;
(2) Preparing master alloy and matrix powder: preparing an ingot casting by using Fe-Cr, fe-Mn, fe-Si, fe-Ni, fe-Mo, fe-V, fe-C intermediate alloy blocks and pure Fe blocks according to the components of the master alloy; further adopting a gas atomization powder preparation technology to prepare master alloy powder and matrix iron powder from the master alloy and the pure iron cast ingot; then screening the master alloy powder and matrix iron powder to respectively obtain the master alloy powder with the granularity of 20-40 mu m and the matrix Fe powder with the granularity of 75-150 mu m;
(3) Preparation of mixed powder: weighing the obtained master alloy powder and matrix iron powder according to the mass ratio of 1:2, filling into a mixing tank, introducing argon for atmosphere protection, and mixing for 3 hours on a three-dimensional mixer to obtain mixed powder;
(4) And (3) hot isostatic pressing sintering: the mixed powder is filled in a steel sheath, and then vacuum degassing and seal welding are carried out; and (3) placing the sealed and welded sheath in a hot isostatic pressing machine, heating to 1350 ℃ at the heating rate of 10 ℃/min, keeping the temperature and the pressure for 2 hours under the pressure of 150MPa, and cooling along with the furnace to obtain the powder metallurgy low alloy steel material.
Inclusions in the sample are distributed dispersedly, and obvious original grain boundary defects are not formed; the relative density reaches 99.4 percent, and the product is nearly fully dense. The powder grain size collocation is unreasonable, the element diffusion is uneven, and a mixed structure consisting of pearlite, ferrite, bainite and martensite is formed. The room-temperature mechanical properties of the alloy are as follows: the tensile strength is 1260MPa, the elongation after fracture is 11.4 percent, and the performance is poor; the fracture morphology is mainly based on crystal-crossing cleavage, crystal-crossing quasi-cleavage and ductile dimple fracture, and no obvious fracture morphology along particle peeling is found.
Comparative example 5
Designing the components of the master alloy: according to the composition Fe-1.1Cr-1.2Mn-1.15Si-1.7Ni-0.25Mo-0.1V-0.28C of 30CrMnSiNi2A steel, increasing all alloy elements according to the same proportion, and selecting a proportionality coefficient x as 3 to obtain the composition of a master alloy: fe-3.3Cr-3.6Mn-3.45Si-5.1Ni-0.75Mo-0.3V-0.84C;
(2) Preparing master alloy and matrix powder: preparing an ingot casting by using Fe-Cr, fe-Mn, fe-Si, fe-Ni, fe-Mo, fe-V, fe-C intermediate alloy blocks and pure Fe blocks according to the components of the master alloy; further adopting a gas atomization powder preparation technology to prepare master alloy powder and matrix iron powder from the master alloy and the pure iron cast ingot; then screening the master alloy powder and matrix iron powder to obtain powder with the granularity of 20-40 mu m;
(3) Preparation of mixed powder: weighing the obtained master alloy powder and matrix iron powder according to the mass ratio of 1:2, filling into a mixing tank, introducing argon for atmosphere protection, and mixing for 3 hours on a three-dimensional mixer to obtain mixed powder;
(4) And (3) hot isostatic pressing sintering: the mixed powder is filled in a steel sheath, and then vacuum degassing and seal welding are carried out; and (3) placing the sealed and welded sheath in a hot isostatic pressing machine, heating to the required sintering temperature of 1200 ℃ at the heating rate of 10 ℃/min, preserving heat and pressure for 2h under the pressure of 150MPa, and cooling along with the furnace to obtain the powder metallurgy low alloy steel material.
Because the selected sintering temperature is low, a local liquid phase is not formed on the surface of the powder, and dense inclusions form original grain boundary defects along grain boundaries; the relative density reaches 99.3 percent, and the product is nearly fully dense. The structure consists of granular bainite and martensite; the room-temperature mechanical properties of the alloy are as follows: the tensile strength is 1210MPa, the elongation after fracture is 10.5 percent, and the performance is poor; fracture morphology is dominated by fracture along the particle.
Comparative example 6
(1) Designing the components of the master alloy: according to the composition Fe-1.1Cr-1.2Mn-1.15Si-1.7Ni-0.25Mo-0.1V-0.28C of 30CrMnSiNi2A steel, increasing all alloy elements according to the same proportion, and selecting a proportionality coefficient x as 3 to obtain the composition of a master alloy: fe-3.3Cr-3.6Mn-3.45Si-5.1Ni-0.75Mo-0.3V-0.84C;
(2) Preparing master alloy powder and matrix iron powder: preparing an ingot casting by using Fe-Cr, fe-Mn, fe-Si, fe-Ni, fe-Mo, fe-V, fe-C intermediate alloy blocks and pure Fe blocks according to the components of the master alloy; further adopting a gas atomization powder preparation technology to prepare mother alloy powder and matrix iron powder from the mother alloy and the pure iron cast ingot; then screening the master alloy powder and matrix iron powder to obtain powder with the granularity of 20-40 mu m;
(3) Powder mixing: weighing the obtained master alloy powder and matrix iron powder according to the mass ratio of 1:2, filling into a mixing tank, introducing argon for atmosphere protection, and mixing for 3 hours on a three-dimensional mixer to obtain mixed powder;
(4) And (3) hot isostatic pressing sintering: the mixed powder is filled in a steel sheath, and then vacuum degassing and seal welding are carried out; and (3) placing the sealed and welded sheath in a hot isostatic pressing machine, heating to 1350 ℃ at the heating rate of 10 ℃/min, keeping the temperature and the pressure for 0.5 hour under the pressure of 30MPa, and cooling along with the furnace to obtain the powder metallurgy low alloy steel material.
Inclusions in the sample are distributed dispersedly, and obvious original grain boundary defects are not formed; due to the low pressure and the low holding time, the relative density is only 98.1 percent, and micropores exist. In addition, the diffusion of elements is insufficient and the structure is less uniform. The room-temperature mechanical properties of the alloy are as follows: tensile strength is 1150MPa, elongation after fracture is 7.8 percent, and performance is extremely poor.
TABLE 1
| Description of the preferred embodiment | Mechanical properties | Degree of tissue homogeneity | Primary grain boundary defects | Degree of densification |
| Example 1 | 1335MPa,15.9％ | Is relatively uniform | Is not obvious | Near full densification |
| Example 2 | 1310MPa,15.3％ | Is relatively uniform | Is not obvious | Near full densification |
| Example 3 | 1330MPa,15.6％ | Is relatively uniform | Is not obvious | Near full densification |
| Example 4 | 1360MPa,16.8％ | Is relatively uniform | Is not obvious | Near full densification |
| Example 5 | 1380MPa,17.7％ | Is relatively uniform | Is not obvious | Near full densification |
| Comparative example 1 | 1230MPa,11.9％ | Uniformity | Is obvious | Near full densification |
| Comparative example 2 | 1250MPa,11.2％ | Is relatively uniform | Is obvious to | Near full densification |
| Comparative example 3 | 1150MPa,8.5％ | Extremely uneven | Is not obvious | Near full densification |
| Comparative example 4 | 1260MPa,11.4％ | Unevenness of | Is not obvious | Near full densification |
| Comparative example 5 | 1210MPa,10.5％ | Is relatively uniform | Is obvious | Near full densification |
| Comparative example 6 | 1150MPa,7.8％ | Is less uniform | Is not obvious | Has pores |
The properties, the homogeneity of the structure and the degree of defects of the powder metallurgy low alloy steels prepared in the listed examples and comparative examples are compared in the attached table 1.
Claims (9)
1. A method for preparing high-performance powder metallurgy low alloy steel by a master alloy way is characterized by comprising the following steps:
(1) Designing the components of the master alloy: according to the composition Fe-1.1Cr-1.2Mn-1.15Si-1.7Ni-0.25Mo-0.1V-0.28C of 30CrMnSiNi2A steel, increasing all alloy elements according to the same proportion to obtain the composition of a master alloy: fe-x (1.1 Cr-1.2Mn-1.15Si-1.7Ni-0.25 Mo-0.1V-0.28C), wherein x is defined as a proportionality coefficient;
the proportionality coefficient x should be controlled to 3-7;
(2) Preparing master alloy powder and matrix iron powder: preparing a master alloy ingot by taking a Fe-M intermediate alloy block and a pure Fe block as raw materials, and then pulverizing to obtain master alloy powder; preparing matrix iron powder by taking pure Fe as a raw material;
(3) Powder mixing: weighing the obtained master alloy powder and matrix iron powder according to the mass ratio of 1 (x-1), and mixing the materials in a protective atmosphere; obtaining mixed powder;
(4) And (3) hot isostatic pressing sintering: the mixed powder is filled in a steel sheath, and then vacuum degassing and seal welding are carried out; placing the sealed and welded sheath in a hot isostatic pressing machine, heating to the required sintering temperature of 1100-1350 ℃ at the heating rate of 5-15 ℃/min, preserving heat and pressure for 1-4 h under the pressure of 50-200 MPa, and cooling along with the furnace to obtain a powder metallurgy low alloy steel material; defining the sintering temperature as T and the heat preservation time as T, wherein the selection of the sintering temperature T and the heat preservation time T is related to a proportionality coefficient:
when the unit of the sintering temperature is DEG C, the sintering temperature T and the proportionality coefficient x should satisfy the following relation: when x is more than or equal to 3 and less than or equal to 5, T is more than or equal to 1375-35x and less than or equal to 1500-50x; when x is more than 5 and less than or equal to 7, T is more than or equal to 1375-35x and less than or equal to 1340-20x;
when the unit of the heat preservation time is h, the heat preservation time t and the proportionality coefficient x should satisfy the following relation: t is more than or equal to 1/2 (x-1) and less than or equal to 1/2 (x + 1).
2. The method for preparing the high-performance powder metallurgy low-alloy steel by the master alloy way according to the claim 1, wherein the method comprises the following steps: and step two, M in the Fe-M intermediate alloy block is selected from at least one element of Cr, mn, ni, si, mo, V and C.
3. The method for preparing the high-performance powder metallurgy low-alloy steel by the master alloy way according to the claim 1, wherein the method comprises the following steps: the second step of milling adopts the atomization milling technology; the atomization powder preparation technology comprises one of water atomization, gas atomization and plasma rotating electrode atomization; to ensure that the powder has a low oxygen content, gas atomization and rotary electrode atomization techniques are preferred.
4. The method for preparing the high-performance powder metallurgy low-alloy steel by the master alloy way according to the claim 1, wherein the method comprises the following steps: in the second step, the master alloy powder and the matrix iron powder are screened, the granularity range of the master alloy powder obtained by screening is preferably 10-75 μm, and the granularity range of the matrix iron powder obtained by screening is preferably 10-105 μm.
5. The method for preparing the high-performance powder metallurgy low-alloy steel by the master alloy route according to claim 4, wherein the master alloy route comprises the following steps: the particle size range of the master alloy powder obtained by sieving is more preferably 15 to 50 μm.
6. The method for preparing the high-performance powder metallurgy low-alloy steel by the master alloy route according to claim 4, wherein the master alloy route comprises the following steps: the particle size range of the base iron powder obtained by sieving is more preferably 15 to 75 μm.
7. The method for preparing the high-performance powder metallurgy low-alloy steel by the master alloy way according to the claim 1, wherein the method comprises the following steps: and step three, the protective atmosphere is argon atmosphere, and the mixing time is preferably 2 to 6 hours, and further preferably 3 to 5 hours.
8. The method for preparing the high-performance powder metallurgy low-alloy steel by the master alloy way according to the claim 1, wherein the method comprises the following steps: and fourthly, the heating rate of the hot isostatic pressing is preferably 8-12 ℃/min.
9. The method for preparing the high-performance powder metallurgy low-alloy steel by the master alloy way according to the claim 1, wherein the method comprises the following steps: the pressure of the hot isostatic pressing in the fourth step is preferably 75 to 175MPa, and more preferably 100 to 150MPa.
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