CN104148657B - A kind of method utilizing intercrystalline corrosion to prepare high-compressibility alloy steel powder by spraying etc. - Google Patents
A kind of method utilizing intercrystalline corrosion to prepare high-compressibility alloy steel powder by spraying etc. Download PDFInfo
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- CN104148657B CN104148657B CN201410444914.7A CN201410444914A CN104148657B CN 104148657 B CN104148657 B CN 104148657B CN 201410444914 A CN201410444914 A CN 201410444914A CN 104148657 B CN104148657 B CN 104148657B
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Abstract
The invention discloses a kind of method utilizing intercrystalline corrosion to prepare high-compressibility alloy steel powder by spraying etc., before smelting molten steel terminates to carry out water atomization pulverization, carbon is added in smelting molten steel, control and regulate C content to be 0.8% ~ 2.0%, carry out the sensitization of intercrystalline corrosion chemical composition, then water atomization pulverization.Then, under argon shield, at 750 DEG C ~ 850 DEG C temperature, alloy comminuted steel shot carries out intercrystalline corrosion heat treatment sensitization; Last in adjustable atmosphere furnace, first adopt high-temperature vapor blackening, form passivating film on powdered alloy steel surface; Intermittently pass into the high temperature decarbonization method of oxidizing gas under adopting argon shield again, alloy comminuted steel shot carries out intercrystalline corrosion.The present invention can reduce the adverse effect of sponge iron loose structure to pressed density greatly, and the alloy steel powder by spraying etc. hardness obtained is low, thus improves compressibility.
Description
Technical field
The present invention relates to the preparation of powdered alloy steel, specifically refer to a kind of method utilizing intercrystalline corrosion to prepare high-compressibility alloy steel powder by spraying etc., belong to powder metallurgical technology.
Background technology
Compressibility is one of most important processing performance of steel powder product, and when the condition such as pressing pressure, mold tooling is constant, powder compressibility directly decides density and the mechanical property thereof of part.Nineteen sixty-five, the U.S. takes the lead in adopting hydraulic atomized technology to produce mild steel powder, and obtained powder forming is poor, powder green compact intensity is low, is difficult to practical application.The beginning of the seventies in last century, Germany was by high temperature reduction technique, obtained compressibility and formability all shows excellent water-atomized iron powder.P/m Iron Base extrudate density reaches 7.2g/cm
3after, its hardness, tensile strength, fatigue strength, toughness etc. all can increase in geometric progression with the increase of density.Central South University Li Songlin, Cui Jianmin etc. disclose the patent (application number: 201110275149.7) of " a kind of high-compressibility water-atomized iron powder and preparation method ".This patent take steel scrap as raw material, by controls such as raw alloy constituent content, smelting molten steel composition, high temperature reductions, iron powder purity is reached: C≤0.01%, O≤0.15%, S≤0.01%, Mn+P+Si≤0.20%, Cr+Ni+Cu≤0.1%, microhardness≤the 90HV of particle, the straight iron powder compressibility after process reaches 7.20g/cm
3(uniaxially suppressing under 600MPa).But density is at 7.20g/cm at present
3above auto industry high-quality sintered alloy steel construction part still dependence on import or traditional machining.Reason is:
China lacks the raw material that quality is high, impurity content is low.The raw material that Sweden He Genasi adopts is the distinctive carbonyl iron refined ore of Sweden.The raw material that Canadian Quebec metal dust company adopts is the byproduct-high-carbon pure iron water of smelting titanic iron ore, and the quality of raw material molten iron is high, impurity content is low, limits its production technology be not suitable for carrying out large-scale production in China to the rigors of raw material.The domestic steel scrap that nearly all adopts does raw material, and steel scrap is various in style, and the raw scrap material of alloying element content extremely low (Cr+Ni+Cu≤0.1%) is few, and selected difficulty is higher.
The alloying element purifying costs such as Cr, Ni, Cu are high.The element purifying such as C, O, S, P can carry out in smelting molten steel and high temperature reduction operation, and the alloying element purifying costs such as Cr, Ni, Cu will be multiplied.
The alloying element uniformity such as Cr, Ni, Cu are added poor when preparing steel construction part.When preparing steel construction part with straight iron powder, the alloyed powder containing elements such as Cr, Ni, Cu need be added.Alloyed powder is mixing with straight iron powder, is carrying and produce segregation unavoidably in suppression process.In sintering circuit, uniform alloyization also needs long-time high temperature diffusion annealing, easily causes grain coarsening.In actual production technique, in order to avoid grain coarsening, be often in the pseudo-alloy state of mechanical mixture in sintered article between alloyed powder and straight iron powder, limit the raising of product properties.
Alloying in smelting molten steel, uniform composition, this is the significant advantage of water atomization comminuted steel shot.But water atomization comminuted steel shot hardness is high, and compressibility is low, be difficult to practical application.Adopt traditional high annealing, decarburization and feed purification, its hardness requirement cannot be met.Although can form the sponge iron of loose structure after powder surface redox, can reduce hardness, but the loose structure of sponge iron cannot be eliminated completely in compacting and sintering, thus reduces the density of goods.
Summary of the invention
For prior art above shortcomings, the object of this invention is to provide a kind of method utilizing intercrystalline corrosion to prepare high-compressibility alloy steel powder by spraying etc., this method can reduce the adverse effect of sponge iron loose structure to pressed density greatly, the alloy steel powder by spraying etc. hardness obtained is low, thus improves compressibility.
Technical scheme of the present invention is achieved in that
Utilize intercrystalline corrosion to prepare a method for high-compressibility alloy steel powder by spraying etc., step is as follows,
1) composition is determined: the component requirements processing the sintered alloy steel construction part obtained as required, determines the composition of its raw material alloy steel powder by spraying etc.;
2) smelting molten steel: by the 1st) composition of alloy steel powder by spraying etc. determined of step gets the raw materials ready and carries out smelting molten steel;
3) intercrystalline corrosion chemical composition sensitization: before smelting molten steel terminates to carry out water atomization pulverization, add carbon in smelting molten steel, controls and regulates C content to be 0.8% ~ 2.0%;
4) water atomization pulverization;
5) intercrystalline corrosion heat treatment sensitization: under argon gas atmosphere protection, alloy comminuted steel shot carries out intercrystalline corrosion heat treatment sensitization at 750 DEG C ~ 850 DEG C temperature, and heat treatment sensitization time is 1h ~ 5h;
6) intercrystalline corrosion: in adjustable atmosphere furnace, first adopts high-temperature vapor blackening, forms 0.1 μm ~ 3.0 μm passivating films on powdered alloy steel surface; Adopt argon gas atmosphere to protect lower interval to pass into the high temperature decarbonization method of oxidizing gas again, alloy comminuted steel shot carries out intercrystalline corrosion; The temperature of intercrystalline corrosion is 500 DEG C ~ 850 DEG C, and each logical oxidizing gas time is 0.01h ~ 0.5h, and the intermittent time is 0.1h ~ 1.0h, and intercrystalline corrosion total time is 0.5h ~ 5.0h; Logical oxidizing gas content 1% ~ 20%;
7) high temperature reduction, then carry out follow-up pulverizing, grinding and screening process and namely obtain high-compressibility alloy steel powder by spraying etc.
Further, the oxidizing gas in step 6) is H
2the combination of O vapour, oxygen or both arbitrary proportions.
Further, the 3rd), in the sensitization of step intercrystalline corrosion chemical composition, C content controls as 0.8-1.2%.
Further, the 5th) optimum condition of step intercrystalline corrosion heat treatment sensitization is that temperature 780 DEG C ~ 850 DEG C, the time is 2h ~ 3h.
Further, the 6th) optimum condition of step intercrystalline corrosion is, passivation film thickness 0.1 μm ~ 1.5 μm; Intercrystalline corrosion temperature is 650 DEG C ~ 800 DEG C, and each logical oxidizing gas time is 0.1h ~ 0.3h, and the intermittent time is 0.2h ~ 0.5h, and total time is 1.5h ~ 4.0h; Logical oxidizing gas content 5% ~ 15%.
Compared to existing technology, the present invention has the following advantages:
1, after intercrystalline corrosion, the sponge iron that comminuted steel shot surface grain boundary structure is formed after being reduced by the crystal boundary be not corroded and corrosion oxidation product forms, and the loose structure of sponge iron weakens the adhesion between surface layer grain.Under pressing pressure, surface layer grain intercrystalline fracture, the fine particle of generation can be filled in space, improves compressibility.
2, between this method comminuted steel shot surface layer grain, still there is stronger adhesion, be equivalent to additional fine particle uniform close and be wrapped in coarse granule surface, less on the impact of apparent density of powder, mobility and particle segregation.
3, the fine particle that the present invention suppresses generation has been intercrystalline corrosion, and crystal boundary is few, and intensity low (under pressing pressure, its crystal boundary can destroy completely, forms monocrystal), the inhibition of crystal boundary to plastic deformation is little, is easy to plastic deformation.
4, compared with surface oxidation embrane method, intercrystalline corrosion scope is little, accelerates intercrystalline corrosion, suppresses general corrosion, and the loose structure formed after at utmost can reducing corrosion product reduction is to the adverse effect of pressed density.
Detailed description of the invention
The present invention utilizes intercrystalline corrosion to prepare alloy steel powder by spraying etc., and intercrystalline corrosion scope is little, accelerates intercrystalline corrosion, suppresses general corrosion, forms the loose structure of sponge iron to the adverse effect of pressed density after can reducing corrosion product reduction to greatest extent.
The technology of the present invention route is substantially identical with existing water atomized steel powder technology path.Difference is: the present invention increases C content in smelting molten steel, forms hypereutectoid steel.At the above heat-treatment of annealing of eutectoid temperature, C separates out the cementite forming netted (or spheroidization) at crystal boundary, increases the carbon content of crystal boundary, strengthens the component difference of crystal boundary and crystals, increases powdered alloy steel Susceptibility To Intergranular Corrosion.Concrete technology is as follows:
1) composition is determined: the component requirements processing the sintered alloy steel construction part obtained as required, determines the composition of its raw material alloy steel powder by spraying etc.;
2) smelting molten steel: by the 1st) composition of alloy steel powder by spraying etc. determined of step gets the raw materials ready and carries out smelting molten steel;
3) intercrystalline corrosion chemical composition sensitization: before smelting molten steel terminates to carry out water atomization pulverization, add carbon in smelting molten steel, controls and regulates C content to be 0.8% ~ 2.0%;
4) water atomization pulverization;
5) intercrystalline corrosion heat treatment sensitization: under argon gas atmosphere protection, alloy comminuted steel shot carries out intercrystalline corrosion heat treatment sensitization at 750 DEG C ~ 850 DEG C temperature, and heat treatment sensitization time is 1h ~ 5h; By this annealing temperature, softening quenching structure, coarsened grain, and make C separate out formation netted (or spheroidization) cementite at crystal boundary;
6) intercrystalline corrosion: in adjustable atmosphere furnace, first adopts high-temperature vapor blackening (passing into water vapour between 450 to 550 DEG C), forms 0.1 μm ~ 3.0 μm passivating films on powdered alloy steel surface; Adopt argon gas atmosphere to protect lower interval to pass into the high temperature decarbonization method of oxidizing gas again, alloy comminuted steel shot carries out intercrystalline corrosion; The temperature of intercrystalline corrosion is 500 DEG C ~ 850 DEG C, and each logical oxidizing gas time is 0.01h ~ 0.5h, and the intermittent time is 0.1h ~ 1.0h, and intercrystalline corrosion total time is 0.5h ~ 5.0h; Logical oxidizing gas content is 1% ~ 20% of total gas volume fraction; Oxidizing gas of the present invention is H
2the combination of O vapour, oxygen or both arbitrary proportions.
7) high temperature reduction, then carry out follow-up pulverizing, grinding and screening process and namely obtain high-compressibility alloy steel powder by spraying etc.
The present invention is in existing alloy steel powder by spraying etc. preparation technology, add step 3), 5) and 6), step 3), 5) and 6) intercrystalline corrosion that realizes finally makes product be had high-compressibility, therefore the control of these three steps is comparatively large to Influence on test result, belongs to committed step of the present invention.
3rd), in the sensitization of step intercrystalline corrosion chemical composition, C content preferably controls to be 0.8% ~ 1.2%.
5th) optimum condition of step intercrystalline corrosion heat treatment sensitization is, (be more preferably 800 DEG C ~ 820 DEG C, the time is 2h ~ 3h to temperature 780 DEG C ~ 850 DEG C.
6th) optimum condition of step intercrystalline corrosion is, passivation film thickness 0.1 μm ~ 1.5 μm; Intercrystalline corrosion temperature is 650 DEG C ~ 800 DEG C, and each logical oxidizing gas time is 0.1h ~ 0.3h, and the intermittent time is 0.2h ~ 0.5h, and total time is 1.5h ~ 4.0h; Logical oxidizing gas content 5% ~ 15%.
The preferred embodiment of the present invention is:
3rd), in the sensitization of step intercrystalline corrosion chemical composition, C content is 1.0% ~ 1.2%.5th) step intercrystalline corrosion heat treatment sensitization condition is, temperature 800 DEG C ~ 820 DEG C, the time is 2h ~ 3h.6th) step intercrystalline corrosion condition is, passivation film thickness 0.3 μm ~ 1.0 μm; Intercrystalline corrosion temperature is 700 DEG C ~ 850 DEG C, and each logical oxidizing gas time is 0.2h ~ 0.3h, and the intermittent time is 0.5h, and total time is 3h ~ 4.0h; Logical oxidizing gas content 10% ~ 12%.
Because alloy steel powder by spraying etc. technology of preparing is through the development of decades, comparative maturity, so the present invention does not all elaborate to other step existing (comprising equipment, technical process and technical parameter etc.).
The present invention adopts high-temperature water vapor black-emitting technology, forms fine and close passivating film, suppress general corrosion on powdered alloy steel surface.
Under high temperature neutral atmosphere, the carbon in comminuted steel shot to surface passivation membrane diffusion, with the oxygen generation decarburization deoxygenation in passivating film.Through chemical composition and heat treatment sensitization, crystal boundary C content is high, and grain boundary decision belongs to short circuit diffusion, diffusion rate is far above crystals, therefore the passivating film deoxidation speed of powdered alloy steel grain boundaries is faster, and namely first the passivating film of grain boundaries is destroyed, and can accelerate intercrystalline corrosion.Continue to increase the intermittent time (i.e. the decarburization time of neutral atmosphere), the passivating film in other place, surface also starts to destroy, and is difficult to suppress general corrosion.Intermittent time is key process parameter.
Under high temperature oxidation stability atmosphere, the carbon in comminuted steel shot is to surface passivation membrane diffusion, and oxidizing gas to powder diffusion inside, oxidation and the decarburizing reaction of iron occurs by passivating film.The above-mentioned passivating film remained can hinder the diffusion of oxidizing gas, suppresses general corrosion.Form the loose structure of sponge iron after the deoxidation of grain boundaries passivating film, form oxidizing gas mass transfer channel, can react with from the iron on the darker crystal boundary in surface, formation oxide-film.Continue to increase the logical oxidizing gas time, the oxide-film of grain boundaries thickens, and oxidizing gas is strengthened by the resistance of oxide-film, grain boundary corrosion (oxidation) rate reduction.The logical oxidizing gas of interval, can shorten the general corrosion time, reduce general corrosion.The logical oxidizing gas time is key process parameter.
The oxidation product of sponge iron is more loose, and the oxidation of grain boundaries is expanded, and CO or CO that decarburization deoxygenation generates
2gas, all can leave mass transfer channel for oxidizing gas, and therefore the intermittent time does not need the oxidation product being formed to sponge iron the last time to carry out deoxidation next time.So repeatedly crystal boundary deoxidation can be passed through destroy passivating film and oxidation reaction (i.e. the logical oxidizing gas of interval) method, accelerate intercrystalline corrosion, suppression general corrosion.
By the subsequent high temperature reduction reduction of operation and decarburization, eliminate its impact on product properties.
Intercrystalline corrosion method improves the principle of water atomization comminuted steel shot compressibility:
After intercrystalline corrosion, the sponge iron that comminuted steel shot surface grain boundary structure is formed after being reduced by the crystal boundary be not corroded and corrosion oxidation product forms, and the loose structure of sponge iron weakens the adhesion between surface layer grain.Under pressing pressure, surface layer grain intercrystalline fracture, the fine particle of generation can be filled in space, improves compressibility.Compared with additional fine particle, there is following significant advantage.
According to the closeest filling theory of Horsfield, in coarse granule, add fine particle step by step, can effective reduce orifice porosity, improve powders compression performance.But additional fine particle, can reduce apparent density and the mobility of powder, increase frictional resistance when suppressing, in powder transhipment, filling and suppression process, produce particle segregation.And still there is between comminuted steel shot surface layer grain described in project stronger adhesion, and be equivalent to additional fine particle uniform close and be wrapped in coarse granule surface, less on the impact of apparent density of powder, mobility and particle segregation.
According to Hall-petch formula (s
s=s
0+ kd
-1/2) known, crystal boundary plays inhibition to plastic deformation, and crystal boundary is more, and namely crystal grain is thinner, and the yield strength of material is higher.Additional tiny water atomized steel powder, crystal grain is tiny, and yield strength is high, is difficult to plastic deformation.And the fine particle suppressing generation described in project has been intercrystalline corrosion, crystal boundary is few, and intensity low (under pressing pressure, its crystal boundary can destroy completely, forms monocrystal), the inhibition of crystal boundary to plastic deformation is little, is easy to plastic deformation.
In addition, compared with surface oxidation embrane method, intercrystalline corrosion scope is little, accelerates intercrystalline corrosion, suppresses general corrosion, and the loose structure formed after at utmost can reducing corrosion product reduction is to the adverse effect of pressed density.
As seen through the above analysis, intercrystalline corrosion method can improve water atomization comminuted steel shot compressibility.
The above embodiment of the present invention is only for example of the present invention is described, and is not the restriction to embodiments of the present invention.For those of ordinary skill in the field, other multi-form change and variations can also be made on the basis of the above description.Here cannot give exhaustive to all embodiments.Every belong to technical scheme of the present invention the apparent change of amplifying out or variation be still in the row of protection scope of the present invention.
Claims (5)
1. utilize intercrystalline corrosion to prepare a method for high-compressibility alloy steel powder by spraying etc., it is characterized in that, step is as follows,
1) composition is determined: the component requirements processing the sintered alloy steel construction part obtained as required, determines the composition of its raw material alloy steel powder by spraying etc.;
2) smelting molten steel: by the 1st) composition of alloy steel powder by spraying etc. determined of step gets the raw materials ready and carries out smelting molten steel;
3) intercrystalline corrosion chemical composition sensitization: before smelting molten steel terminates to carry out water atomization pulverization, add carbon in smelting molten steel, controls and regulates C content to be 0.8% ~ 2.0%;
4) water atomization pulverization;
5) intercrystalline corrosion heat treatment sensitization: under argon gas atmosphere protection, alloy comminuted steel shot carries out intercrystalline corrosion heat treatment sensitization at 750 DEG C ~ 850 DEG C temperature, and heat treatment sensitization time is 1h ~ 5h;
6) intercrystalline corrosion: in adjustable atmosphere furnace, first adopts high-temperature vapor blackening, forms 0.1 μm ~ 3.0 μm passivating films on powdered alloy steel surface; Adopt argon gas atmosphere to protect lower interval to pass into the high temperature decarbonization method of oxidizing gas again, alloy comminuted steel shot carries out intercrystalline corrosion; The temperature of intercrystalline corrosion is 500 DEG C ~ 850 DEG C, and each logical oxidizing gas time is 0.01h ~ 0.5h, and the intermittent time is 0.1h ~ 1.0h, and intercrystalline corrosion total time is 0.5h ~ 5.0h; Logical oxidizing gas content is 1% ~ 20% of total gas volume fraction;
7) high temperature reduction, then carry out follow-up pulverizing, grinding and screening process and namely obtain high-compressibility alloy steel powder by spraying etc.
2. the method utilizing intercrystalline corrosion to prepare high-compressibility alloy steel powder by spraying etc. according to claim 1, is characterized in that: the oxidizing gas in step 6) is H
2the combination of O vapour, oxygen or both arbitrary proportions.
3. the method utilizing intercrystalline corrosion to prepare high-compressibility alloy steel powder by spraying etc. according to claim 1 and 2, is characterized in that: the 3rd) in the sensitization of step intercrystalline corrosion chemical composition, and it is 0.8 ~ 1.2% that C content controls.
4. the method utilizing intercrystalline corrosion to prepare high-compressibility alloy steel powder by spraying etc. according to claim 1 and 2, is characterized in that: the 5th) optimum condition of step intercrystalline corrosion heat treatment sensitization is, temperature 780 DEG C ~ 850 DEG C, the time is 2h ~ 3h.
5. the method utilizing intercrystalline corrosion to prepare high-compressibility alloy steel powder by spraying etc. according to claim 1 and 2, is characterized in that: the 6th) optimum condition of step intercrystalline corrosion is, passivation film thickness 0.1 μm ~ 1.5 μm; Intercrystalline corrosion temperature is 650 DEG C ~ 800 DEG C, and each logical oxidizing gas time is 0.1h ~ 0.3h, and the intermittent time is 0.2h ~ 0.5h, and total time is 1.5h ~ 4.0h; Logical oxidizing gas content is 5% ~ 15% of total gas volume fraction.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| DE3277966D1 (en) * | 1982-11-02 | 1988-02-18 | Sumitomo Metal Ind | Process for producing alloy steel powder |
| JPH0784604B2 (en) * | 1987-08-21 | 1995-09-13 | 吉川工業株式会社 | Method for producing iron powder for sinter shrinkage body |
| SE9602835D0 (en) * | 1996-07-22 | 1996-07-22 | Hoeganaes Ab | Process for the preparation of an iron-based powder |
| CN102689008A (en) * | 2011-03-23 | 2012-09-26 | 杰富意钢铁株式会社 | Method of finish heat treatment of iron powder and apparatus for finish heat treatment |
| CN102350497B (en) * | 2011-09-16 | 2013-02-06 | 中南大学 | High-compressibility water atomization iron powder and preparation method thereof |
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