Background technology
High nitrogen stainless steel has good mechanical, corrosion resisting property, and nitrogen is strong austenite stable element, and the source is abundant, can partly or entirely replace the nickel in the austenitic stainless steel, and the conserve expensive resource reduces cost; Nitrogen is effective solution strengthening element, has increased the refined crystalline strengthening effect, can significantly improve stainless intensity.Nitrogen can also improve the decay resistance of steel when significantly improving stainless mechanical property, particularly local decay resistance is as anti-spot corrosion, crevice corrosion and intercrystalline corrosion etc.Nickel ion is a carcinogenic elements, and the free nickel high nitrogen austenitic stainless steel has thoroughly solved the quick problem of nickel, and biocompatibility is good, economizes on resources environmental friendliness.High nitrogen stainless steel becomes the preferred material of sustainable development, is very promising new material.
The preparation technology of high nitrogen stainless steel mainly contains: pressurized Induction Melting, high temperature insostatic pressing (HIP) melting, high pressure plasma melting, pressurization electroslag melting, back-pressure casting, the nitriding of electroslag heating-high pressure, powder metallurgy etc.Compare with the melting high nitrogen stainless steel, powder metallurgic method prepares high nitrogen stainless steel and has numerous advantages, comprises obtaining evening chemical composition and microstructure, can add nitrogen in different phase, and it is flexible etc. to have the possibility, the technology that reach high nitrogen-containing very.Therefore, the method just is being widely used in the research of nitrogenous/high nitrogen stainless steel.
The method that powder metallurgic method is produced high nitrogen stainless steel has: the common metal powder is carried out sintering nitriding processing after with different powder metallurgy manufacturing process such as process formings such as mold pressing, injection moulding; Produce the high nitrogen stainless steel powder earlier, adopt preparation high nitrogen stainless steel material goods such as different metallurgy forming process for powder such as die forming, injection moulding, high temperature insostatic pressing (HIP), powder forging rolling, hot extrusion, explosive forming then.The preparation method of high nitrogen stainless steel powder has atomization, element powders mixing method, mechanical alloying method, fluidized-bed method etc.Specifically comprise:
(1) injection molding method: utilization powder injection molding technologies such as Rawers are made nitrogenous 316L stainless steel (Rawers J., Croydon F., Krabbe R., Duttinger N.TensileCharacteristics of Nitrogen Enhanced Powder Injection Moulded 316LStainless Steel.Powder Metallurgy, 1996,39:125-129).
(2) hot extrusion method: people such as Simmons are contained in compacting in the carbon steel pipes of certain size, drying with a certain amount of nitrogenous powder, corresponding temperature when being heated to steel pipe with high nitrogen steel solution heat treatment then.After insulation a period of time, hot extrude is pressed onto required size under certain extruding force, heat-treats (Simmons J.W., Kemp W.E. after the end, Dunning J.S.The P/MProcessing of High-Nitrogen Stainless Steel.JOM, 1996 (4): 20);
(3) Aeroform method: Zhou Candong etc. utilize Aeroform method prepare nitrogenous 35CrMoV steel (Zhou Candong. the preparation of high nitrogen 35CrMoV steel and research [D]. Shanghai: publishing house of Shanghai University, 2002:52.).
(4) hot isostatic pressing method: U.S. Crucible company adopts this method to produce the powder metallurgy high nitrogen stainless steel material, the technological parameter that it adopted is that sintering temperature is 1130 ℃, pressure is 100MPa, be incubated 4 hours (G.O.Rhodes, W.B.Eisen. " High Nitrogen CorrosionResistant Austenitic Stainless Steels Produced by HIP P/M Processing, " Materials Science Forum 1999:635-648.).
But for high nitrogen steel, particularly high nitrogen steel part, its height is tough, high corrosion-resistant can be to be based upon on the basis of high nitrogen-containing, high density, high composition structural homogenity.Height/nitrogenous steel part sintered density that conventional powder metallurgy process is produced is lower, and nitrogen content is lower, and composition tissue odds is even, compare with nonnitrogenous stainless steel, though intensity has a more substantial increase, impact flexibility significantly descends, and this is fatal defective to some powdered metal parts.Adopt hot isostatic pressing method need prepare jacket, this obviously is inapplicable for the lighter part series products of weight, does not also disclose the preparation method of the part series products of nitrogenous/high nitrogen stainless steel in the prior art.
Summary of the invention
The object of the present invention is to provide a kind of preparation method of powder metallurgy nitrogen/high nitrogen containing stainless steel parts, adopt the sintering isostatic pressing process, can prepare high density, composition even tissue, high performance nitrogenous/the high nitrogen stainless steel part.
In order to achieve the above object, the present invention is achieved in that
A kind of preparation method of powder metallurgy nitrogen/high nitrogen containing stainless steel parts, adopt the sintering isostatic pressing process, may further comprise the steps: static pressure such as raw material preparation, moulding, ungrease treatment and sintering, wherein in static pressure steps such as sintering, heating rate is 3-10 ℃/min, and sintering atmosphere is the mixed atmosphere of pure nitrogen gas or nitrogen and hydrogen, argon gas, and its nitrogen pressure/dividing potential drop is consistent with the solubility of nitrogen in this alloy system, sintering temperature is 1200-1450 ℃, and temperature retention time is 10-120min;
Density greater than 90-95% after, pressure is increased to 3-10MPa, nitrogen partial pressure is constant in the pressurization, with argon gas and hydrogen partial pressure, temperature retention time is 60-240min;
Density is greater than after 99%, step-down and cooling fast.
Described sintering atmosphere is high pure nitrogen or the nitrogen of 0.15MPa and mist or the nitrogen of 0.15MPa and the mist of argon gas of hydrogen of 0.01-0.15MPa, and wherein nitrogen partial pressure is 0.01-0.1MPa.
Described nitrogenous/particle mean size of high nitrogen stainless steel powder is 20-100 μ m.
Described nitrogenous/particle mean size of high nitrogen stainless steel powder is 30-50 μ m.
Described moulding be the injection, the compacting, the extruding in a kind of.
Described ungrease treatment is a kind of or its combination in solvent degreasing, heating degreasing, the catalysis degreasing.
Described powder of stainless steel composition is by weight percentage: Cr 12-20, and Mn 1.0-20, Mo0.5-5, Si 0.3-1.0, N 0.4-1.0, all the other are Fe.
Described powder of stainless steel satisfies one of following performance:
Particle mean size is 9.1 μ m, and apparent density is 4.0gcm
-3, tap density is 4.6gcm
-3, D10 is 3.5 μ m, and D50 is 9.00 μ m, and D90 is 16 μ m, and the percentage by weight of N is 0.85.(D10, D50, D90 are that the cumulative particle sizes percentile of a sample reaches 10%, 50%, 90% o'clock pairing particle diameter).
Stainless steel parts has one of following performance: relative density>99%, R
P0.2〉=500MPa, Rm 〉=850MPa, δ
0.5〉=35%, the percentage by weight of N content 〉=0.85.
Technology of the present invention is to adopt nitrogenous/high nitrogen stainless steel powder, obtain part blank through methods such as injection moulding, mold pressing or extruding, adopt suitable sintering isostatic pressing process, utilize the sintering equal pressing equipment to regulate nitrogen partial pressure in the sintering process in real time, nitrogen content, the composition structural homogenity of control part material, and reach high density, with preparation high-performance height/nitrogen-contained stainless steel powdered metal parts, its key problem in technology is:
Raw material is nitrogenous/the high nitrogen stainless steel powder be good fluidity than fine powder
In order to obtain higher-density, adopt than fine powder and higher sintering temperature, long temperature retention time.Particle mean size is 20-100 μ m, for injection moulding, generally adopts the following powder of average grain diameter 30 μ m, and the sintering temperature of austenitic stainless steel is approximately 1350 ℃.Greater than 100 μ m, the flowability of powder is difficult to reach requirement; Adopt thinner powder (less than 20 μ m), can under lower sintering temperature, obtain higher density really, but the cost of powder significantly improves.
Nitrogen partial pressure in the control sintering atmosphere
The sintering temperature of powder of stainless steel part is generally at 1200-1400 ℃.General sintering temperature, Fe-Cr alloy just are in δ-ferrite zone, and the solubility of nitrogen significantly reduces (below 0.3%), adopt conventional sintering process, can not prepare nitrogen content higher, be evenly distributed, the high nitrogen steel of high density part.Adopt the sintering equal pressing equipment can obtain the gas pressure intensity of 6-10MPa, suitably increase nitrogen partial pressure, can suppress δ-ferrite and form, increase the solubility of nitrogen, the nitrogen content that obtains expecting.After the sintered density more than part reaches 90-95%, the interconnected pore disappears, and applies the higher gas pressure intensity of 3-10MPa again, keeps nitrogen partial pressure constant, with dividing potential drops such as argon gas.Can obtain like this near 100% densification, the uniform high-performance powder metallurgy high nitrogen stainless steel of nitrogen content controlled distribution part.Because it is more even that composition is organized, and do not have violent phase transformation, shrinkage factor is consistent more, and dimensional accuracy significantly improves, and this has special significance for injection moulding.
The preparation method's of powder metallurgy nitrogen/high nitrogen containing stainless steel parts of the present invention detailed step is:
Material powder: nitrogenous/the high nitrogen stainless steel powder, particle mean size 20-100 μ m.The chemical composition of stainless steel powder according to percentage by weight (wt%) is: Cr 12-20, and Mn 1.0-20, Mo 0.5-5, Si 0.3-1.0, N 0.4-1.0, all the other are Fe.
Moulding: with metal dust and binding agent routinely powder metallurgical technique mix, adopting technological formings such as injection, compacting, extruding then is part blank.
Degreasing: adopt technologies such as solvent degreasing, heating degreasing, catalysis degreasing, or it is compound, the powder metallurgy degreasing process removes the binding agent in the pressed compact routinely.
Static pressure such as sintering: the heating rate that adopts 3-10 ℃/min, high pure nitrogen at 0.01~0.15MPa, or the mist of the nitrogen of the mist of the nitrogen of 0.15MPa and hydrogen or 0.15MPa and argon gas, wherein nitrogen partial pressure is 0.01~0.1MPa, be warming up to 1200-1450 ℃ of sintering, temperature retention time is 10-120min; Make the density of part blank improve pore closure simultaneously, in pressure process, form pressure reduction inside and outside the blank, reach the purpose of further densification.According to the solubility of nitrogen in alloy system, adjust nitrogen partial pressure in good time, keep the solubility of intensification sintering process material nitrogen and the basically identical of nitrogen partial pressure, the content of blank nitrogen is not taken place than great fluctuation process, guarantee not generate δ-ferritic phase, cause the big ups and downs of nitrogen content to descend in high temperature section.After the relative density that reaches more than 92%, increase gas pressure intensity to 3-10MPa, wherein nitrogen partial pressure is 0.01~0.1MPa, and pressurization keeps nitrogen partial pressure constant, and with dividing potential drops such as argon gas, insulation 60-240min is until near 100% densification.Fast cooling reduces gas pressure intensity, keeps nitrogen partial pressure and the nitrogen basically identical in alloy system solubility.Like this, the part nitrogen content that makes can control to high level, composition even tissue, density height, good toughness, distortion is little, precision is high, corrosion resistance is good.
The present invention is suitable for the powder blank, also is applicable to that employing obtains the sintering of highdensity part blank with compacting or method moulding such as extruding than fine powder, with produce the high-performance powder metallurgy that high density, nitrogen content be evenly distributed nitrogenous/the high nitrogen stainless steel part.
Compared with prior art, beneficial effect of the present invention is:
1. employing powder metallurgical technique, direct prepared in batches high nitrogen stainless steel part, materials saving;
2. adopt nitrogenous/high nitrogen stainless steel powder to prepare high nitrogen steel, nitrogen distributes more even;
3. adopt the sintering isostatic pressing technology can significantly improve the density of goods, obtain high nitrogen stainless steel goods near 100% density;
4. adopt the sintering isostatic pressing technology, the part nitrogen content is controlled, the composition even tissue, and dimensional accuracy improves, and intensity, toughness, corrosion resistance obviously improve.
The specific embodiment
Following examples are used to further specify the present invention, and non-limiting its scope.
Embodiment one
Raw material: the nitrogen-contained stainless steel powder, composition (percentage by weight): 16.74%Cr, 12.02%Mn, 2.08%Mo, 0.5%Si, 0.8%N, all the other are iron; Particle mean size 9.1 μ m, apparent density 4.0gcm
-3, tap density 4.6gcm
-3, D10=3.5 μ m, D50=9.00 μ m, D90=16 μ m, N wt%=0.85%; Adopt the thermoplasticity wax-based binder, the powder charging ratio is 55%.
It is even that powder and binding agent are added hot milling, and granulation then makes equigranular injection material; Wherein binding agent is by 70% paraffin, 29% high density polyethylene (HDPE), and 1% stearic acid (all being weight percentage) is formed.Mould is loaded on carries out injection moulding on the injection machine, make part blank.The blank that obtains is soaked certain hour in organic solvent, guarantee molten the removing of wax more than 80%.Dry in vacuum drying chamber, temperature is 100 ℃, and the time is 120min.Utilize resistance furnace after the oven dry or directly in static pressure stoves such as sintering, adopt in the 0.05MPa high pure nitrogen atmosphere and carry out hot degreasing.Degreasing finishes, and in the 0.05MPa blanket of nitrogen, is warming up to 1350 ℃ with 5 ℃/min heating rate and carries out sintering, insulation 120min, density to be sintered reaches greater than 92%, and the interconnected pore disappears substantially, increases gas pressure intensity to 9MPa, wherein nitrogen partial pressure is 0.08MPa, all the other are partial pressure of ar gas, keep 180min, and the part sintered density is near 100%, reduce pressure, fast cooling.Whole process keeps nitrogen partial pressure consistent with the solubility of alloy system nitrogen, does not make significantly fluctuation of nitrogen content generation in the alloy, does not generate δ-ferrite.Can obtain relative density>99%, R at last
P0.2〉=500MPa, Rm 〉=850MPa, δ
0.5〉=35%, the sintered part(s) of N wt%=0.85%.And the austenitic stainless steel 316L of density 99%, R
P0.2=220MPa, Rm=510MPa, A%=45%; The martensitic precipitation 17-4PH of density 99%, Rm=1090MPa, R
P0.2=950MPa, A%=8%.The yield strength of high nitrogen stainless steel is higher than 316L far away, and toughness does not significantly descend, and corrosion resistance is higher than 316L.Though martensitic precipitation 17-4PH has higher intensity, toughness, corrosion resistance are relatively poor.High-nitrogen austenitic stainless steel has the highest tough combination, and corrosion resistance is best, excellent combination property.
Embodiment two
The moulding degreasing process of raw material and part is with embodiment one, after degreasing finishes, in static pressure such as sintering, adopt the nitrogen of 0.15MPa and the mist of hydrogen, wherein nitrogen partial pressure is 0.1MPa, be warming up to 1400 ℃ with 7 ℃/min heating rate and carry out sintering, insulation 120min, density to be sintered reaches greater than 95%, the interconnected pore disappears substantially, increase gas pressure intensity to 9MPa, wherein nitrogen partial pressure is 0.1MPa, and all the other are partial pressure of ar gas, keep 180min, the part sintered density reduces pressure near 100%, fast cooling.Whole process keeps nitrogen partial pressure consistent with the solubility of alloy system nitrogen, does not make significantly fluctuation of nitrogen content generation in the alloy, does not generate δ-ferrite.Can obtain relative density>99%, R at last
P0.2〉=550MPa, Rm 〉=920MPa, δ
0.5〉=15%, the sintered part(s) of N wt%=0.95%.