CN104148657A - Method for preparing high-compressibility water atomization alloy steel powder through intergranular corrosion - Google Patents
Method for preparing high-compressibility water atomization alloy steel powder through intergranular corrosion Download PDFInfo
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- CN104148657A CN104148657A CN201410444914.7A CN201410444914A CN104148657A CN 104148657 A CN104148657 A CN 104148657A CN 201410444914 A CN201410444914 A CN 201410444914A CN 104148657 A CN104148657 A CN 104148657A
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Abstract
The invention discloses a method for preparing high-compressibility water atomization alloy steel powder through intergranular corrosion. The method comprises the steps of adding carbon into smelted molten steel before water atomization powder preparation after smelting of molten steel is completed, controlling and regulating the content of C to range from 0.8 percent to 2.0 percent, performing intergranular corrosion chemical component sensitization, and performing water atomization powder preparation; performing intergranular corrosion thermal treatment sensitization on alloy steel powder at the temperature of 750 DEG C-850 DEG C under protection of argon; forming a passive film on the surface of the alloy powder in an adjustable atmosphere furnace through a high-temperature steam blackening technology; performing intergranular corrosion on the alloy steel powder through a high-temperature decarbonization method introducing oxidizing gas intermittently under protection of argon. By means of the method, adverse effect on pressed density caused by cellular structures of sponge iron can be reduced greatly, the obtained water atomization alloy steel powder is low in hardness, and therefore, compressibility is improved.
Description
Technical field
The present invention relates to the preparation of powdered alloy steel, specifically refer to a kind of method of 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 in the situation that the conditions such as pressing pressure, mold tooling are constant, powder compressibility is directly determining 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 the powder forming that makes is poor, powder green compact intensity is low, is difficult to practical application.The beginning of the seventies in last century, Germany passed through high temperature reduction technique, had obtained compressibility and formability and had all showed 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 be with the increase of density geometric progression and increase.The Li Songlin of Central South University, Cui Jianmin etc. disclose the patent (application number: 201110275149.7) of < < high-compressibility water-atomized iron powder and preparation method > >.This patent be 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≤90 HV of particle, the straight iron powder compressibility after processing reaches 7.20g/cm
3(600MPa places an order and axially suppresses).But density is at 7.20g/cm at present
3high-quality sintered alloy steel construction part still dependence on import or traditional machining for above auto industry.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.Byproduct-high-carbon pure iron water that the raw material that Canadian Quebec metal dust company adopts is smelting titanic iron ore, the quality of raw material molten iron is high, impurity content is low, the harshness of raw material is required to limited its production technology and be not suitable for carrying out large-scale production in China.The domestic steel scrap that nearly all adopts is done 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.
While preparing steel construction part, add the alloying element uniformities such as Cr, Ni, Cu poor.While preparing steel construction part with straight iron powder, need to add the alloyed powder that contains the elements such as Cr, Ni, Cu.Alloyed powder and straight iron powder are unavoidable mixing, in conveying and suppression process produces segregation.In sintering circuit, uniform alloyization also needs long-time high temperature diffusion annealing, easily causes grain coarsening.In actual production technique, for fear of grain coarsening, in sintered article, the pseudo-alloy state in mechanical mixture often between alloyed powder and straight iron powder, has limited the raising of product properties.
Alloying in smelting molten steel, composition is even, and 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, cannot meet its hardness requirement.Though after powder surface redox, can form the sponge iron of loose structure, reduce hardness, but the loose structure of sponge iron compacting and sintering in cannot eliminate completely, thereby reduction goods density.
Summary of the invention
For prior art above shortcomings, the object of this invention is to provide a kind of method of 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 obtaining is low, thereby 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: process as required the composition requirement of the sintered alloy steel construction part obtaining, determine the composition of its raw material alloy steel powder by spraying etc.;
2) smelting molten steel: by the 1st) composition of the definite alloy steel powder by spraying etc. of step is got the raw materials ready and carries out smelting molten steel;
3) intercrystalline corrosion chemical composition sensitization: finish to carry out, before water atomization pulverization, to add carbon in smelting molten steel at smelting molten steel, controlling and regulating C content is 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 ℃～850 ℃ temperature, and heat treatment sensitization time is 1h～5h;
6) intercrystalline corrosion: in adjustable atmosphere furnace, first adopt high-temperature vapor blackening, form 0.1 μ m～3.0 μ m passivating film on powdered alloy steel surface; Adopt the lower high temperature decarbonization method of oxidizing gas that intermittently passes into of argon gas atmosphere protection, alloy comminuted steel shot carries out intercrystalline corrosion again; The temperature of intercrystalline corrosion is 500 ℃～850 ℃, and the logical oxidizing gas time is 0.01h～0.5h at every turn, 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 and process and 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 is controlled as 0.8-1.2%.
Further, the 5th) optimum condition of step intercrystalline corrosion heat treatment sensitization is, 780 ℃～850 ℃ of temperature, and the time is 2h～3h.
Further, the 6th) optimum condition of step intercrystalline corrosion is, passivation film thickness 0.1 μ m～1.5 μ m; Intercrystalline corrosion temperature is 650 ℃～800 ℃, and the logical oxidizing gas time is 0.1h～0.3h at every turn, 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, comminuted steel shot top layer grain boundary structure is comprised of the crystal boundary not being corroded and the rear sponge iron forming of corrosion oxidation product reduction, and the loose structure of sponge iron has weakened 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 and be evenly closely 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, intensity low (under pressing pressure, its crystal boundary can destroy completely, forms monocrystal), and crystal boundary is little to the inhibition of moulding distortion, is easy to moulding distortion.
4, compare with surface oxidation embrane method, intercrystalline corrosion scope is little, accelerates intercrystalline corrosion, suppresses general corrosion, can at utmost reduce the adverse effect of the rear loose structure forming of corrosion product reduction to pressed density.
The specific embodiment
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, can reduce to greatest extent the adverse effect of loose structure to pressed density that forms sponge iron after corrosion product reduction.
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 that forms 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: process as required the composition requirement of the sintered alloy steel construction part obtaining, determine the composition of its raw material alloy steel powder by spraying etc.;
2) smelting molten steel: by the 1st) composition of the definite alloy steel powder by spraying etc. of step is got the raw materials ready and carries out smelting molten steel;
3) intercrystalline corrosion chemical composition sensitization: finish to carry out, before water atomization pulverization, to add carbon in smelting molten steel at smelting molten steel, controlling and regulating C content is 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 ℃～850 ℃ temperature, and heat treatment sensitization time is 1h～5h; By this annealing temperature, softening quenching structure, coarsened grain, and make C separate out and form netted (or spheroidization) cementite at crystal boundary;
6) intercrystalline corrosion: in adjustable atmosphere furnace, first adopt high-temperature vapor blackening (passing into water vapour between 450 to 550 ℃), form 0.1 μ m～3.0 μ m passivating film on powdered alloy steel surface; Adopt the lower high temperature decarbonization method of oxidizing gas that intermittently passes into of argon gas atmosphere protection, alloy comminuted steel shot carries out intercrystalline corrosion again; The temperature of intercrystalline corrosion is 500 ℃～850 ℃, and the logical oxidizing gas time is 0.01h～0.5h at every turn, and the intermittent time is 0.1h～1.0h, and intercrystalline corrosion total time is 0.5h～5.0h; Logical oxidizing gas content is total gas volume fraction 1%～20%; 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 and process and obtain high-compressibility alloy steel powder by spraying etc.
The present invention is in existing alloy steel powder by spraying etc. preparation technology, increased 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 larger on result impact, belongs to committed step of the present invention.
The 3rd), in the sensitization of step intercrystalline corrosion chemical composition, it is 0.8%～1.2% that C content is preferably controlled.
The 5th) optimum condition of step intercrystalline corrosion heat treatment sensitization is, (more preferably 800 ℃～820 ℃, the time is 2h～3h for 780 ℃～850 ℃ of temperature.
The 6th) optimum condition of step intercrystalline corrosion is, passivation film thickness 0.1 μ m～1.5 μ m; Intercrystalline corrosion temperature is 650 ℃～800 ℃, and the logical oxidizing gas time is 0.1h～0.3h at every turn, 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:
The 3rd) in the sensitization of step intercrystalline corrosion chemical composition, C content is 1.0%～1.2%.The 5th) step intercrystalline corrosion heat treatment sensitization condition is, 800 ℃～820 ℃ of temperature, and the time is 2h～3h.The 6th) step intercrystalline corrosion condition is, passivation film thickness 0.3 μ m～1.0 μ m; Intercrystalline corrosion temperature is 700 ℃～850 ℃, and the logical oxidizing gas time is 0.2h～0.3h at every turn, 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 existing other step (comprising equipment, technical process and technical parameter etc.).
The present invention adopts high-temperature water vapor black-emitting technology, on powdered alloy steel surface, forms fine and close passivating film, suppresses general corrosion.
Under high temperature neutral atmosphere, the carbon in comminuted steel shot spreads to surface passivated membrane, with the oxygen generation decarburization deoxygenation in passivating film.Through chemical composition and heat treatment sensitization, crystal boundary C content is high, and crystal boundary diffusion 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 first the passivating film of grain boundaries is destroyed, and can accelerate intercrystalline corrosion.Continue to increase the intermittent time (being the decarburization time of neutral atmosphere), other local passivating film of 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 spreads to surface passivated membrane, and oxidizing gas to powder diffusion inside, oxidation and the decarburizing reaction of iron occurs by passivating film.The above-mentioned passivating film remaining can hinder the diffusion of oxidizing gas, suppresses general corrosion.After the deoxidation of grain boundaries passivating film, form the loose structure of sponge iron, form oxidizing gas mass transfer channel, can react with 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 strengthens by the resistance of oxide-film, grain boundary corrosion (oxidation) rate reduction.Intermittently logical oxidizing gas, can shorten the general corrosion time, reduces 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 the CO of the generation of decarburization deoxygenation
2gas, all can be for oxidizing gas leaves mass transfer channel, and therefore the intermittent time does not need the oxidation product that is formed to sponge iron the last time to carry out deoxidation next time.So can pass through repeatedly crystal boundary deoxidation, destroy passivating film and oxidation reaction (i.e. intermittently logical oxidizing gas) method, accelerate intercrystalline corrosion, inhibition general corrosion.
By reduction and the decarburization of follow-up high temperature reduction operation, eliminate its impact on product properties.
Intercrystalline corrosion method improves the constrictive principle of water atomization comminuted steel shot:
After intercrystalline corrosion, comminuted steel shot top layer grain boundary structure is comprised of the crystal boundary not being corroded and the rear sponge iron forming of corrosion oxidation product reduction, and the loose structure of sponge iron has weakened 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.Compare with additional fine particle, there is following significant advantage.
According to the closeest filling theory of Horsfield, in coarse granule, add step by step fine particle, can effectively reduce porosity, improve powders compression performance.But additional fine particle, can reduce apparent density and the mobility of powder, and frictional resistance while increasing compacting produces particle segregation in powder transhipment, filling and suppression process.And described in project, between comminuted steel shot surface layer grain, still there is stronger adhesion, and be equivalent to additional fine particle and be evenly closely 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 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 moulding distortion.And the fine particle that described in project, compacting generates has been intercrystalline corrosion, crystal boundary is few, intensity low (under pressing pressure, its crystal boundary can destroy completely, forms monocrystal), and crystal boundary is little to the inhibition of moulding distortion, is easy to moulding distortion.
In addition, compare with surface oxidation embrane method, intercrystalline corrosion scope is little, accelerates intercrystalline corrosion, suppresses general corrosion, can at utmost reduce the adverse effect of the rear loose structure forming of corrosion product reduction to 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 to be only explanation example of the present invention, and is not the restriction to embodiments of the present invention.For those of ordinary skill in the field, can also make on the basis of the above description other multi-form variation and changes.Here cannot give all embodiments exhaustive.Every still row in protection scope of the present invention of apparent variation that technical scheme of the present invention amplifies out or change that belong to.
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: process as required the composition requirement of the sintered alloy steel construction part obtaining, determine the composition of its raw material alloy steel powder by spraying etc.;
2) smelting molten steel: by the 1st) composition of the definite alloy steel powder by spraying etc. of step is got the raw materials ready and carries out smelting molten steel;
3) intercrystalline corrosion chemical composition sensitization: finish to carry out, before water atomization pulverization, to add carbon in smelting molten steel at smelting molten steel, controlling and regulating C content is 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 ℃～850 ℃ temperature, and heat treatment sensitization time is 1h～5h;
6) intercrystalline corrosion: in adjustable atmosphere furnace, first adopt high-temperature vapor blackening, form 0.1 μ m～3.0 μ m passivating film on powdered alloy steel surface; Adopt the lower high temperature decarbonization method of oxidizing gas that intermittently passes into of argon gas atmosphere protection, alloy comminuted steel shot carries out intercrystalline corrosion again; The temperature of intercrystalline corrosion is 500 ℃～850 ℃, and the logical oxidizing gas time is 0.01h～0.5h at every turn, 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 and process and obtain high-compressibility alloy steel powder by spraying etc.
2. the method for 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 for 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, C content is controlled as 0.8-1.2%.
4. the method for 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, 780 ℃～850 ℃ of temperature, and the time is 2h～3h.
5. the method for 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 μ m～1.5 μ m; Intercrystalline corrosion temperature is 650 ℃～800 ℃, and the logical oxidizing gas time is 0.1h～0.3h at every turn, and the intermittent time is 0.2h～0.5h, and total time is 1.5h～4.0h; Logical oxidizing gas content 5%～15%.
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Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0108175B1 (en) * | 1982-11-02 | 1988-01-13 | Sumitomo Metal Industries, Ltd. | Process for producing alloy steel powder |
| JPH01132703A (en) * | 1987-08-21 | 1989-05-25 | Yoshikawa Kogyo Co Ltd | Manufacture of iron powder for sintering shrinkage body |
| CN1228726A (en) * | 1996-07-22 | 1999-09-15 | 赫加奈斯公司 | Process for preparation of iron-based powder |
| CN102350497A (en) * | 2011-09-16 | 2012-02-15 | 中南大学 | High-compressibility water atomization iron powder and preparation method thereof |
| 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 |
-
2014
- 2014-09-03 CN CN201410444914.7A patent/CN104148657B/en not_active Expired - Fee Related
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0108175B1 (en) * | 1982-11-02 | 1988-01-13 | Sumitomo Metal Industries, Ltd. | Process for producing alloy steel powder |
| JPH01132703A (en) * | 1987-08-21 | 1989-05-25 | Yoshikawa Kogyo Co Ltd | Manufacture of iron powder for sintering shrinkage body |
| CN1228726A (en) * | 1996-07-22 | 1999-09-15 | 赫加奈斯公司 | Process for preparation of 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 |
| CN102350497A (en) * | 2011-09-16 | 2012-02-15 | 中南大学 | High-compressibility water atomization iron powder and preparation method thereof |
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