CN107868899B - Permeable steel for injection molding and preparation method thereof - Google Patents

Abstract

The invention provides breathable steel, which consists of 1-5 wt% of Cu, 0.2-0.4 wt% of C, 12-15 wt% of Cr, 0.5-1 wt% of Mo, 0.3-0.5 wt% of V and the balance of Fe. The invention also provides a preparation method of the breathable steel, which comprises the following steps: carrying out ball milling on iron-based pre-alloy powder containing C, Cr, Mo and V to obtain modified pre-alloy powder; mixing atomized spherical Cu powder, water-based binder and modified pre-alloyed powder, granulating and drying; and (4) putting the granulated powder into a die for pressing, and putting the pressed green body into a sintering furnace for sintering. The air-permeable steel prepared by the method has the advantages of high passing amount, excellent mechanical property, narrow and controllable aperture range, excellent corrosion resistance and the like.

Description

Permeable steel for injection molding and preparation method thereof

The technical field is as follows:

the invention relates to high-flux breathable steel for an injection mold and a preparation method thereof.

Technical background:

the air permeable steel is formed by sintering fine-particle spherical powder stainless steel at high temperature, and tiny exhaust holes are uniformly distributed in each direction inside the air permeable steel and are commonly used for exhaust of an injection mold.

During the injection molding process, high-pressure plastic melt is injected into a mold cavity, and if gas in the mold cavity cannot be exhausted or is not exhausted in time, various injection molding defects and adverse effects are easy to occur, such as: 1) the plastic melt can not fill the cavity; 2) high-pressure gas permeates into the plastic to cause quality defects of air holes, cavities, loose tissues and the like. 3) The gas compression and temperature rise cause melt decomposition, burning, local carbonization and scorching phenomena. 4) The melt entering each cavity has different speeds, so that a flow mark and a fusion mark are easy to form, and the mechanical property of an injection molding piece is reduced. 5) The mold filling speed is reduced, the production efficiency is reduced, and the energy consumption is increased. The mold exhaust insert is made of the breathable steel, so that gas can be rapidly exhausted, the injection molding quality is improved, and the problem of energy consumption is solved.

Injection molding is a high-pressure, high-speed and precise molding process, and the application of the breathable steel to an injection mold needs to meet the following requirements: 1) the thickness of the breathable steel for the die is usually more than 8mm, the on-way resistance caused by the thickness is increased to cause insufficient flux, and the flux is required to be high enough to ensure that gas is exhausted in time; 2) the pore size is small and controllable, and cannot be higher than the overflow value of plastics, for example, the pore size of the breathable steel is required to be lower than 20 μm when polyethylene is injection molded, and part of plastics can be moderately increased to 100 μm; 3) can bear the injection molding pressure of 150MPa, so the fatigue strength is higher than 150MPa, and the static tensile property is not lower than 450 MPa. 4) Has certain corrosion resistance, and can resist atmospheric corrosion and organic acid gas corrosion. At present, metal porous materials are mostly used in the filtration industry, but the tensile strength is not higher than 150MPa, and the thickness is about 2mm generally, so that a breathable steel material which is suitable for injection molds and has high flux, small pore diameter and excellent mechanical property needs to be developed.

The porous steel is a sintered metal powder porous material with integrated structure and function, the throughput of the porous steel is in a mutual restriction relation with mechanical property and pore size, generally, the smaller the pore size is, the more excellent the mechanical property is, and the lower the throughput is.

The invention content is as follows:

the invention aims to provide the high-throughput breathable steel which has the advantages of excellent mechanical property, narrow and controllable aperture range and excellent corrosion resistance.

The technical scheme adopted by the invention for solving the technical problems is as follows: a kind of injection moulding uses the powder metallurgy process to prepare, its composition is 1-5 wt% Cu, 0.2-0.4 wt% C, 12-15 wt% Cr, 0.5-1 wt% Mo, 0.3-0.5 wt% V, the surplus is Fe;

wherein Cu is added as atomized spherical powder, the particle size of the powder is 10-20 μm, and other elements are added as pre-alloyed powder.

The pore diameter of the air permeable steel is 10-100 mu m, the throughput is more than 1L/cm2 min bar, the tensile strength is more than 450MPa, and the micro Vickers hardness is more than 500 HV.

Another technical problem to be solved by the present invention is to provide a method for preparing a gas permeable steel for injection molding, comprising the steps of:

1) powder modification: carrying out ball milling on the pre-alloyed powder containing 0.2-0.4 wt% of C, 12-15 wt% of Cr, 0.5-1 wt% of Mo and 0.3-0.5 wt% of V iron base to obtain modified pre-alloyed powder, wherein the particle size of the powder after ball milling is 60-150 mu m;

3) mixing powder: weighing 1-5 wt% of atomized spherical Cu powder prepared in the step 1), and uniformly mixing the atomized spherical Cu powder with the prealloyed powder in the step 1);

4) and (3) granulating: adding water-based binder into the mixed powder according to the mass ratio of 1:10-13.5, stirring for 20-40min at 35-48 ℃, and then granulating;

5) and (3) drying: granulating the powder, placing in vacuum state of more than 20%, introducing warm air of 40-45 deg.C, and drying for more than 2 hr;

6) pressing and sintering: putting the granulated powder into a die for pressing, wherein the pressing pressure is 200-300 MPa, the pressed green body is placed in a sintering furnace for sintering, the sintering temperature is higher than 1200 ℃, and the sintering time is at least 2 hours to obtain a blank piece;

7) cutting and forming: the cut surface after cutting and forming can produce the plugged hole, can adopt the electric spark to process the trompil.

The breathable steel is prepared by adopting a powder metallurgy process, Cu is added as atomized spherical elemental Cu powder, and the rest metal is added as pre-alloy powder. The prealloying powder is irregular powder, is uniformly mixed and bonded with Cu powder after ball milling modification, and is pressed, sintered and molded. Adding 0.2-0.4 wt% of C to ensure that the breathable steel matrix has high mechanical properties; the addition of 12-15 wt% of Cr ensures that the breathable steel matrix material has corrosion resistance, the addition of 0.5-1 wt% of Mo improves the tempering stability and red hardness of the material, the addition of 0.3-0.5 wt% of V can avoid the growth of structure crystal grains during sintering, and can also control the growth of crystal grains of the breathable steel in the subsequent heat treatment process, thereby improving the strength and toughness of the material.

The aperture of the air-permeable steel matrix is mainly regulated and controlled by the grain diameter and the shape of the pre-alloyed powder, the shape of the pre-alloyed powder is smooth after ball milling, and the aperture of the air-permeable steel can be more accurately regulated and controlled by regulating and controlling the grain diameter range of the spherical powder. In addition, the particle size of the atomized spherical Cu powder is 10-20 microns, and the in-situ generated holes are not larger than 20 microns.

In addition, Cu is dissolved in Fe to improve the corrosion resistance of the steel, particularly atmospheric corrosion resistance, strength, particularly yield strength, impact toughness, hardenability and the like, although the solid solubility of Cu in gamma-Fe is 7.23 wt% at 1100 ℃, the solid solubility of Cu in α -Fe is only about 1.5 wt% at room temperature, so that Cu is excessively high to cause segregation and aggregation to reduce the mechanical property, and the Cu content is controlled within 1-5 wt%.

The invention has the following beneficial technical effects:

the permeable steel has high flux, excellent mechanical property and small pore diameter range, excellent mechanical property, adjustable pore diameter and smooth pore channel, can be widely applied to the exhaust process in an injection mold, and solves various defects caused by poor exhaust.

Secondly, the breathable steel has excellent corrosion resistance, particularly resistance to atmospheric and organic gases, due to the synergistic effect of Cr and Cu.

And thirdly, when the thickness of the product is larger than 50mm, the product still has obvious air permeability.

Detailed Description

The method for producing the air-permeable steel and the properties of the air-permeable steel obtained by the production method will be specifically described below by way of specific examples.

Example 1.

Performing ball milling on the iron-based prealloyed powder containing 0.2 wt% of C, 13 wt% of Cr, 0.5 wt% of Mo and 0.3 wt% of V, wherein the particle size of the powder is between 60 and 80 mu m, and the particles become smooth after 6h of ball milling. And then adding atomized spherical Cu powder with the particle size range of 10 mu m and a water-based binder into the modified pre-alloyed powder for mixing, wherein the addition amount of Cu is 3%, and granulating and drying the mixed powder. And (3) putting the granulated powder into a die for pressing, wherein the pressing pressure is 250MPa, and the pressed green body is placed in a sintering furnace for sintering, and the sintering temperature is 1200 ℃. The gas throughput of the prepared permeable steel is more than 1L/cm2 min-bar (the test thickness is 15mm), the tensile strength is more than 600MPa, the micro Vickers hardness is more than 500HV, the pore size of more than 95 percent of micropores is between 10 and 20 mu m, and the pores are smooth.

Example 2.

Carrying out ball milling on iron-based prealloyed powder containing 0.3 wt% of C, 14 wt% of Cr, 0.6 wt% of Mo and 0.4 wt% of V, wherein the particle size of the powder is 80-100 mu m, and carrying out ball milling for 10 hours to enable the particles to be smooth; then adding atomized spherical Cu powder with the particle size range of 15 mu m and a water-based binder into the modified pre-alloyed powder for mixing, wherein the addition of Cu is 5%, and granulating and drying the mixed powder; and (3) putting the granulated powder into a die for pressing, wherein the pressing pressure is 300MPa, and the pressed green body is placed in a sintering furnace for sintering, and the sintering temperature is 1200 ℃. The gas throughput of the prepared permeable steel is more than 1.5L/cm2 min-bar (the test thickness is 20mm), the tensile strength is more than 550MPa, the micro Vickers hardness is more than 500HV, the pore size of more than 95 percent of micropores is between 25 and 50 mu m, and the pores are smooth.

Example 3.

Ball-milling iron-based prealloyed powder containing 0.4 wt% of C, 15 wt% of Cr, 1 wt% of Mo and 0.5 wt% of V, wherein the particle size of the powder is 100-150 mu m, and ball-milling for 20 hours to enable the particles to be smooth; then adding atomized spherical Cu powder with the particle size range of 20 mu m and a water-based binder into the modified pre-alloyed powder for mixing, wherein the addition of Cu is 5%, and granulating and drying the mixed powder; and (3) putting the granulated powder into a die for pressing, wherein the pressing pressure is 200MPa, and the pressed green body is placed in a sintering furnace for sintering at the sintering temperature of 1250 ℃. The gas throughput of the prepared permeable steel is more than 2L/cm2 min-bar (the test thickness is 18mm), the tensile strength is more than 450MPa, the micro Vickers hardness is more than 500HV, the pore size of more than 95 percent of micropores is between 50 and 100 mu m, and the pores are smooth.

Claims (1)

1. A preparation method of permeable steel for injection molding adopts a powder metallurgy process, and is characterized in that: the material of the air permeable steel consists of 1-5 wt% of Cu, 0.2-0.4 wt% of C, 12-15 wt% of Cr, 0.5-1 wt% of Mo, 0.3-0.5 wt% of V and the balance of Fe; wherein Cu is added as atomized spherical powder having a particle size10-20 μm, other elements are added as pre-alloyed powder; the pore diameter of the permeable steel is adjustable between 10 and 100 mu m, and the permeability coefficient is more than 1L/cm²Min-bar, tensile strength greater than 450MPa, micro Vickers hardness greater than 500 HV;

the preparation method comprises the following steps:

1) powder modification: carrying out ball milling on the pre-alloyed powder containing 0.2-0.4 wt% of C, 12-15 wt% of Cr, 0.5-1 wt% of Mo and 0.3-0.5 wt% of V iron base to obtain modified pre-alloyed powder, wherein the particle size of the powder after ball milling is 60-150 mu m;

3) mixing powder: weighing 1-5 wt% of atomized spherical Cu powder prepared in the step 1), and uniformly mixing the atomized spherical Cu powder with the prealloyed powder in the step 1);

4) and (3) granulating: adding water-based binder into the mixed powder according to the mass ratio of 1:10-13.5, stirring for 20-40min at 35-48 ℃, and then granulating;

5) and (3) drying: granulating the powder, placing in vacuum state of more than 20%, introducing warm air of 40-45 deg.C, and drying for more than 2 hr;

6) pressing and sintering: putting the granulated powder into a die for pressing, wherein the pressing pressure is 200-300 MPa, the pressed green body is placed in a sintering furnace for sintering, the sintering temperature is higher than 1200 ℃, and the sintering time is at least 2 hours to obtain a blank piece;

7) and (5) cutting and forming.