CN101851735B - Strengthening process of nodular cast iron and finished product thereof - Google Patents
Strengthening process of nodular cast iron and finished product thereof Download PDFInfo
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- CN101851735B CN101851735B CN2010101532801A CN201010153280A CN101851735B CN 101851735 B CN101851735 B CN 101851735B CN 2010101532801 A CN2010101532801 A CN 2010101532801A CN 201010153280 A CN201010153280 A CN 201010153280A CN 101851735 B CN101851735 B CN 101851735B
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Abstract
A strengthening process for nodular cast iron includes such steps as cleaning nodular cast iron, putting it in carburizing furnace, carbonitriding at 800-840 deg.C while adding methanol and ammonia gas (80-120 drops/min) in volume of cracked methanol gas (1-5%), maintaining the carbon potential at 0.8-1.2% for 2-4 hr, quenching to obtain finished product, and features that the carbonitriding process includes such steps as sequentially preparing its metallographic structure including surface layer, sub-layer and matrix, the surface layer is granular or continuous compound layer, the sub-layer is acicular martensite, residual austenite and graphite, and the matrix is fine acicular martensite, residual austenite and graphite. The invention can not only improve the scratch resistance, the wear resistance and the contact fatigue strength of the nodular cast iron parts, but also effectively prevent the full decarburization of the nodular cast iron during carbonitriding, and has smaller process difficulty and lower production cost.
Description
Technical field
The present invention relates to a kind of thermal treatment process of spheroidal graphite cast iron, relate in particular to a kind of reinforcing process and finished product thereof of spheroidal graphite cast iron, specifically be applied to make the part such as spheroidal graphite cast iron rocking arm, tappet of engine.
Background technology
The surface intensified technique of spheroidal graphite cast iron part generally includes only and forms the compound of local chill, hard surfacing, nitriding, carbonitriding, surface rolling reinforcement and these technologies, quench as chill, fillet rolling and reinforcing or the like behind the ductile iron crankshaft carbonitriding, do not comprise carbonitriding technology, because carbonitriding technology is applied to the spheroidal graphite cast iron part usually to be considered to draw a snake and add feet to it---traditional understanding is thought: the spheroidal graphite cast iron part is carburizing or carbonitriding not, enough hardenabilitys are also arranged, simple hard surfacing is enough to improve its wear resistance.But in some field, need simultaneously on the small-sized complex structural member of resistance to marring, wear resistance, contact fatigue strength as engine rocker, tappet, air valve yoke and injector plate etc., handle without carbonitriding technology, and the spheroidal graphite cast iron part that direct quenching is handled is because the no compound layer in surface, crystal grain is thick, and its resistance to marring, wear resistance can not satisfy service requirements; Though there is compound layer on the surface of nitriding or carbonitriding spheroidal graphite cast iron part, its subsurface hardness is low, and anti-contact fatigue strength can not meet the demands; The chill machinability of local cold shock spheroidal graphite cast iron part is relatively poor, causes difficulty often for the machining of small-sized responsible parts such as engine rocker, air valve yoke.Comparatively speaking, the carbonitriding of spheroidal graphite cast iron part low temperature then can take into account performance requriements and process for machining performance requriementss such as resistance to marring, wear resistance, contact fatigue strength simultaneously, has certain advantage.
In addition, because the carbon content and the silicone content of spheroidal graphite cast iron are higher than soft steel and low-carbon alloy converted steel far away, therefore the decarburizing tendency of spheroidal graphite cast iron under heating condition is very big, and Heating temperature is high more, easy more decarburization, in case and spheroidal graphite cast iron decarburization, just form the Decarburized layer of pure ferrite tissue easily on the surface of spheroidal graphite cast iron part, this moment is if will eliminate this pure ferrite tissue, just must heat carburizing in the temperature more than 880 ℃, and then carry out carbonitriding again at 800-840 ℃, this has not only increased technology difficulty and cost greatly, and make and infiltration layer and the alligatoring of matrix quenching structure have reduced the part performance.
The Chinese patent Granted publication number is CN100513646C, Granted publication day is that the patent of invention on July 15th, 2009 discloses a kind of heat treatment process for automobile gear shifting box synchronizer gear sheath, this technology comprises: carbonitriding, press quench, cleaning, tempering, detection, when device fails, in the carbonitriding step, carburizing temperature is 780-850 ℃, and carbon potential is 0.5-1.0%, and the nitrogen add-on is 5-12m
3/ h, the methyl alcohol add-on is 4-7L/h, the propane add-on is 0.5-0.9m
3/ h, the ammonia add-on is 0-30L/h, though carburizing temperature that this patent process using is lower and corresponding carbon potential and carbonitriding atmosphere medium are so that control carbonitriding speed, thereby when guaranteeing during equipment failure, to be incubated for a long time, oxidation, decarburization or the infiltration layer that still can prevent the tooth cover parts are dark excessively, but the tissue that this patent technology forms is followed successively by high carbon martensite and residual austenite, middle carbon martensite, low carbon martensite, and because this patent technology is when carburizing temperature is low, carbon potential is lower, be carburizing temperature when being 800 ℃, carbon potential is 0.55 ± 0.05%; When carburizing temperature was 785 ℃, carbon potential was 0.55 ± 0.05%, thereby can't form the carbide bright layer on the surface of spheroidal graphite cast iron part, i.e. compound layer can't improve resistance to marring, wear resistance and the contact fatigue strength of spheroidal graphite cast iron part.In addition, this patent technology is not considered the strong decarburizing tendency of spheroidal graphite cast iron part in heat-processed, do not take to take precautions against accordingly technological measure yet, this carrying out for the carbonitriding technology of spheroidal graphite cast iron part is very unfavorable, when especially the cementing furnace of taking when carbonitriding was periodic cementing furnace such as forvacuum gas carbruizing furance, common open well formula or box gas carbruizing furance, what the taking of anti-decarburization technological measure showed was even more important.
Summary of the invention
The present invention has overcome the deficiency of technology such as existing spheroidal graphite cast iron direct quenching, nitriding, carbonitriding or local cold shock, with quench treatment after the carbonitriding of spheroidal graphite cast iron part, form the compound layer of granular or continuous distribution successively on spheroidal graphite cast iron part top layer, latent needle-like martensite containing nitrogen, residual austenite and graphite, fine acicular martensite, residual austenite and graphite, thus resistance to marring, wear resistance and the contact fatigue strength of spheroidal graphite cast iron part improved simultaneously.The present invention is a kind of new spheroidal graphite cast iron reinforcing process and goods thereof.
For realizing above purpose, spheroidal graphite cast iron reinforcing process of the present invention may further comprise the steps successively:
The first step: the spheroidal graphite cast iron part is cleared up, cleaned, remove dirts such as surface scale, rust staining, greasy dirt;
Second step: the spheroidal graphite cast iron part after will clearing up, cleaning is put into and is carried out the carbonitriding processing in the cementing furnace, described carbonitriding is handled and is meant adding methyl alcohol and ammonia under 800-840 ℃ temperature condition, the add-on of methyl alcohol be 80-120 drip/minute, the adding volume of ammonia is the 1%-5% of the splitting gas volume of aforementioned methyl alcohol, add-on by control propane is 0.8%-1.2% to keep carbon potential simultaneously, and the treatment time is 2-4 hour;
The 3rd step: will put the quenching of carrying out in the oil under the normal temperature into through the spheroidal graphite cast iron part that carbonitriding is handled, and promptly make spheroidal graphite cast iron part finished product after the quenching.
Described cementing furnace is common pit gas carburizing furnace or box gas carbruizing furance; Described second step may further comprise the steps successively:
At first, the temperature of first rising cementing furnace is carried out the retort carburizing then to 800-840 ℃ under this temperature condition, until the furnace atmosphere carbon potential greater than 0.8%;
Secondly, spheroidal graphite cast iron part with cleaning, after cleaning is packed in the cementing furnace and is covered bell, be rapidly heated then to 760 ℃-800 ℃ with by the ferritic-austenitic two-phase region, heat-up rate is more than or equal to 15 ℃/min, after furnace temperature arrives 760 ℃-800 ℃, carry out exhaust-gas disposal, promptly under 760 ℃-800 ℃ temperature condition, add methyl alcohol, open the venting port exhaust simultaneously fully, the add-on of methyl alcohol be 120-220 drip/minute, the treatment time continues 30 minutes;
Once more, continue the interior temperature of rising stove earlier to 800-840 ℃, then the spheroidal graphite cast iron part being carried out carbonitriding handles, described carbonitriding is handled and is meant adding methyl alcohol and ammonia under 800-840 ℃ temperature condition, the add-on of methyl alcohol be 80-120 drip/minute, the adding volume of ammonia is the 1%-5% of the splitting gas volume of aforementioned methyl alcohol, and the add-on by control propane is 0.8%-1.2% to keep carbon potential simultaneously, and the treatment time is 2-4 hour;
Described cementing furnace is the forvacuum cementing furnace; Described second step may further comprise the steps successively:
At first, the temperature of first rising cementing furnace is carried out the retort carburizing then to 800-840 ℃ under this temperature condition, until the furnace atmosphere carbon potential greater than 0.8%;
Secondly, to clear up, spheroidal graphite cast iron part after the cleaning is packed in the cementing furnace and is covered bell, be rapidly heated then to 760 ℃-800 ℃ with by the ferritic-austenitic two-phase region, heat-up rate is more than or equal to 15 ℃/min, opening vacuum pump simultaneously bleeds, when furnace temperature arrives 760 ℃-800 ℃, carry out exhaust-gas disposal again after vacuum tightness reaches 50-266Pa in the stove, promptly close vacuum pump earlier, splash into methyl alcohol simultaneously, when furnace pressure returns to the above 20-30mm water column of normal pressure, open the venting port exhaust again, the add-on of methyl alcohol be 120-220 drip/minute, the treatment time continues 5-20 minute;
Once more, continue the interior temperature of rising stove earlier to 800-840 ℃, then the spheroidal graphite cast iron part being carried out carbonitriding handles, described carbonitriding is handled and is meant adding methyl alcohol and ammonia under 800-840 ℃ temperature condition, the add-on of methyl alcohol be 80-120 drip/minute, the adding volume of ammonia is the 1%-5% of the splitting gas volume of aforementioned methyl alcohol, and the add-on by control propane is 0.8%-1.2% to keep carbon potential simultaneously, and the treatment time is 2-4 hour;
Described cementing furnace is the continous way cementing furnace; Described second step may further comprise the steps successively:
At first, set and keep the Heating Zone Temperature of cementing furnace be 760-800 ℃, carbonitriding district temperature be 800-840 ℃, carbonitriding district carbon potential be the add-on of 0.8%-1.2%, methyl alcohol be 80-120 drip/minute, and the adding volume of ammonia is the 1%-5% of the splitting gas volume of aforementioned methyl alcohol;
Secondly, to clear up, spheroidal graphite cast iron part after the cleaning pack into the travelling belt or the charging tray of cementing furnace, set line speed or push-plate cycle then to guarantee that the spheroidal graphite cast iron time of part in the carbonitriding district is 2-4 hour, the subsequent start-up cementing furnace is handled the spheroidal graphite cast iron part is carried out carbonitriding, described carbonitriding is handled and is meant adding methyl alcohol and ammonia under 800-840 ℃ temperature condition, the add-on of methyl alcohol be 80-120 drip/minute, the adding volume of ammonia is the 1%-5% of the splitting gas volume of aforementioned methyl alcohol, simultaneously by control propane add-on to keep carbon potential 0.8%-1.2%, the treatment time is 2-4 hour.
Described the 3rd step is: will put the quenching of carrying out in the oil under the normal temperature into through the spheroidal graphite cast iron part of carbonitriding processing earlier, and again the spheroidal graphite cast iron part be carried out low-temperaturetempering below 220 ℃ after the quenching, and can make spheroidal graphite cast iron part finished product after the low-temperaturetempering.
A kind of finished product of reinforcing process of above-mentioned spheroidal graphite cast iron, the metallographic structure of described spheroidal graphite cast iron part finished product comprises top layer, sublevel and matrix successively, described top layer is the compound layer of granular or continuous distribution, thickness is 0.0025-0.005mm, described sublevel is latent needle-like martensite containing nitrogen, residual austenite and graphite, thickness is 0.04-0.10mm, and described matrix is fine acicular martensite, residual austenite and graphite.
Compared with prior art, beneficial effect of the present invention is:
1. because in the reinforcing process and finished product thereof of a kind of spheroidal graphite cast iron of the present invention, the spheroidal graphite cast iron part low temperature carbonitriding and quenching have been carried out successively, not only formed compound layer on the spheroidal graphite cast iron surface, and refinement the martensitic stucture of spheroidal graphite cast iron carbonitrided case, thereby on the spheroidal graphite cast iron part, from outward appearance to inner essence formed the top layer successively, sublevel and matrix, described top layer is the compound layer of granular or continuous distribution, thickness is 0.0025-0.005mm, described sublevel is latent needle-like martensite containing nitrogen, residual austenite and graphite, thickness is 0.04-0.10mm, and described matrix is a fine acicular martensite, residual austenite and graphite.This tissue and spheroidal graphite cast iron part directly quench, form behind nitriding or the reinforcing process such as carbonitriding, local cold shock organize all inequalityly, improved the use properties or the processing characteristics of spheroidal graphite cast iron part greatly:
With respect to the spheroidal graphite cast iron part that direct quenching is handled, spheroidal graphite cast iron goods of the present invention have overcome the former surface and have not had problems such as compound layer, martensitic stucture be thick, thereby had better resistance to marring, wear resistance and contact fatigue strength.
With respect to the spheroidal graphite cast iron part of nitriding or carbonitriding processing, spheroidal graphite cast iron goods of the present invention have overcome the former time top layer and the low problem of matrix hardness, thereby have had better contact fatigue strength.
Spheroidal graphite cast iron part with respect to local cold shock reinforcement, spheroidal graphite cast iron goods of the present invention are before the mechanical workout moulding, surface hardness is low, therefore the mechanical processing technique performance is better, be applicable to complex-shaped more, the part that the position is many, area is big that needs reinforcement is as parts such as engine rocker, air valve yoke, tappets.
Therefore, the present invention has not only improved resistance to marring, the surface abrasion resistance of spheroidal graphite cast iron part, and has improved the contact fatigue strength of spheroidal graphite cast iron part, thereby has improved the performance of spheroidal graphite cast iron part, has enlarged its range of application, has saved production cost.
2. owing to taking common pit gas carburizing furnace or box gas carbruizing furance in the reinforcing process of a kind of spheroidal graphite cast iron of the present invention and the finished product thereof, when the forvacuum cementing furnace carries out carbonitriding to the spheroidal graphite cast iron part, before carbonitriding technology carries out, fully taken into account the strong decarburizing tendency of spheroidal graphite cast iron part in heat-processed, thereby taked to prevent accordingly the decarburization technological measure, promptly by the control heat-up rate, exhaust temperature, measures such as exhaust velocity, effectively prevented the generation of the especially full decarburization situation of spheroidal graphite cast iron part decarburization before carbon potential recovers in the cementing furnace, stoped pure ferrite to organize the formation of Decarburized layer, save operation, and reduced technology difficulty and the production cost that the spheroidal graphite cast iron part is carried out carbonitriding.Therefore the present invention has not only considered the strong decarburizing tendency of spheroidal graphite cast iron part in heat-processed, has taked corresponding anti-decarburization technological measure, and can prevent effectively that full decarburization, the technology difficulty of spheroidal graphite cast iron part in heat-processed is less, production cost is lower.
Description of drawings
Fig. 1 is the technological operation schema of embodiments of the invention 1.
Fig. 2 is the weave construction synoptic diagram of the finished product of embodiments of the invention 1.
Embodiment
The present invention is further detailed explanation below in conjunction with description of drawings and embodiment
A kind of reinforcing process of spheroidal graphite cast iron, described reinforcing process may further comprise the steps successively:
The first step: the spheroidal graphite cast iron part is cleared up, cleaned, remove dirts such as surface scale, rust staining, greasy dirt;
Second step: the spheroidal graphite cast iron part after will clearing up, cleaning is put into and is carried out the carbonitriding processing in the cementing furnace, described carbonitriding is handled and is meant adding methyl alcohol and ammonia under 800-840 ℃ temperature condition, the add-on of methyl alcohol be 80-120 drip/minute, the adding volume of ammonia is the 1%-5% of the splitting gas volume of aforementioned methyl alcohol, add-on by control propane is 0.8%-1.2% to keep carbon potential simultaneously, and the treatment time is 2-4 hour;
The 3rd step: will put the quenching of carrying out in the oil under the normal temperature into through the spheroidal graphite cast iron part that carbonitriding is handled, and promptly make spheroidal graphite cast iron part finished product after the quenching.
Described cementing furnace is common pit gas carburizing furnace or box gas carbruizing furance; Described second step may further comprise the steps successively:
At first, the temperature of first rising cementing furnace is carried out the retort carburizing then to 800-840 ℃ under this temperature condition, until the furnace atmosphere carbon potential greater than 0.8%;
Secondly, spheroidal graphite cast iron part with cleaning, after cleaning is packed in the cementing furnace and is covered bell, be rapidly heated then to 760 ℃-800 ℃ with by the ferritic-austenitic two-phase region, heat-up rate is more than or equal to 15 ℃/min, after furnace temperature arrives 760 ℃-800 ℃, carry out exhaust-gas disposal, promptly under 760 ℃-800 ℃ temperature condition, add methyl alcohol, open the venting port exhaust simultaneously fully, the add-on of methyl alcohol be 120-220 drip/minute, the treatment time continues 30 minutes;
Once more, continue the interior temperature of rising stove earlier to 800-840 ℃, then the spheroidal graphite cast iron part being carried out carbonitriding handles, described carbonitriding is handled and is meant adding methyl alcohol and ammonia under 800-840 ℃ temperature condition, the add-on of methyl alcohol be 80-120 drip/minute, the adding volume of ammonia is the 1%-5% of the splitting gas volume of aforementioned methyl alcohol, and the add-on by control propane is 0.8%-1.2% to keep carbon potential simultaneously, and the treatment time is 2-4 hour;
Described cementing furnace is the forvacuum cementing furnace; Described second step may further comprise the steps successively:
At first, the temperature of first rising cementing furnace is carried out the retort carburizing then to 800-840 ℃ under this temperature condition, until the furnace atmosphere carbon potential greater than 0.8%;
Secondly, to clear up, spheroidal graphite cast iron part after the cleaning is packed in the cementing furnace and is covered bell, be rapidly heated then to 760 ℃-800 ℃ with by the ferritic-austenitic two-phase region, heat-up rate is more than or equal to 15 ℃/min, opening vacuum pump simultaneously bleeds, when furnace temperature arrives 760 ℃-800 ℃, carry out exhaust-gas disposal again after vacuum tightness reaches 50-266Pa in the stove, promptly close vacuum pump earlier, splash into methyl alcohol simultaneously, when furnace pressure returns to the above 20-30mm water column of normal pressure, open the venting port exhaust again, the add-on of methyl alcohol be 120-220 drip/minute, the treatment time continues 5-20 minute;
Once more, continue the interior temperature of rising stove earlier to 800-840 ℃, then the spheroidal graphite cast iron part being carried out carbonitriding handles, described carbonitriding is handled and is meant adding methyl alcohol and ammonia under 800-840 ℃ temperature condition, the add-on of methyl alcohol be 80-120 drip/minute, the adding volume of ammonia is the 1%-5% of the splitting gas volume of aforementioned methyl alcohol, and the add-on by control propane is 0.8%-1.2% to keep carbon potential simultaneously, and the treatment time is 2-4 hour;
Described cementing furnace is the continous way cementing furnace; Described second step may further comprise the steps successively:
At first, set and keep the Heating Zone Temperature of cementing furnace be 760-800 ℃, carbonitriding district temperature be 800-840 ℃, carbonitriding district carbon potential be the add-on of 0.8%-1.2%, methyl alcohol be 80-120 drip/minute, and the adding volume of ammonia is the 1%-5% of the splitting gas volume of aforementioned methyl alcohol;
Secondly, to clear up, spheroidal graphite cast iron part after the cleaning pack into the travelling belt or the charging tray of cementing furnace, set line speed or push-plate cycle then to guarantee that the spheroidal graphite cast iron time of part in the carbonitriding district is 2-4 hour, the subsequent start-up cementing furnace is handled the spheroidal graphite cast iron part is carried out carbonitriding, described carbonitriding is handled and is meant adding methyl alcohol and ammonia under 800-840 ℃ temperature condition, the add-on of methyl alcohol be 80-120 drip/minute, the adding volume of ammonia is the 1%-5% of the splitting gas volume of aforementioned methyl alcohol, simultaneously by control propane add-on to keep carbon potential 0.8%-1.2%, the treatment time is 2-4 hour.
Described the 3rd step is: will put the quenching of carrying out in the oil under the normal temperature into through the spheroidal graphite cast iron part of carbonitriding processing earlier, and again the spheroidal graphite cast iron part be carried out low-temperaturetempering below 220 ℃ after the quenching, and can make spheroidal graphite cast iron part finished product after the low-temperaturetempering.
A kind of finished product of reinforcing process of above-mentioned spheroidal graphite cast iron, the metallographic structure of described spheroidal graphite cast iron part finished product comprises top layer, sublevel and matrix successively, described top layer is the compound layer of granular or continuous distribution, thickness is 0.0025-0.005mm, described sublevel is latent needle-like martensite containing nitrogen, residual austenite and graphite, thickness is 0.04-0.10mm, and described matrix is fine acicular martensite, residual austenite and graphite.
The present invention takes the reason of carbonitriding technology to be to spheroidal graphite cast iron:
In the process of carbonitriding because carbon, nitride are separated out at original austenite subgrain boundary, crystal boundary or intracrystalline, stoped thick martensitic formation, thereby refinement crystal grain, refinement spheroidal graphite cast iron quenching top layer martensitic stucture; Because the C of spheroidal graphite cast iron, Si content are higher, during carbonitriding, C, N are little in the concentration gradient on top layer, carbonitriding temperature in addition is 800 ℃-840 ℃, with respect to 840-880 ℃ of general carbonitriding, temperature is lower, causes the spread coefficient of atom less, therefore C, N atom be easily at the surface enrichment of spheroidal graphite cast iron, thereby form the compound layer of granular or continuous distribution easily on the surface.
With respect to the spheroidal graphite cast iron part that direct quenching is handled, problem such as spheroidal graphite cast iron goods of the present invention have overcome the former surface and do not had compound layer, and martensitic stucture is thick, thus have better resistance to marring, wear resistance and contact fatigue strength.
With respect to the spheroidal graphite cast iron part of nitriding or carbonitriding processing, spheroidal graphite cast iron goods of the present invention have overcome the former time top layer and the low problem of matrix hardness, thereby have had better contact fatigue strength.
Spheroidal graphite cast iron part with respect to local cold shock reinforcement, spheroidal graphite cast iron goods of the present invention are before the mechanical workout moulding, surface hardness is low, therefore the mechanical processing technique performance is better, be applicable to complex-shaped more, the part that the position is many, area is big that needs reinforcement is as parts such as engine rocker, air valve yoke, tappets.
Therefore, the present invention has not only improved resistance to marring, the surface abrasion resistance of spheroidal graphite cast iron part, and has improved the contact fatigue strength of spheroidal graphite cast iron part, thereby has improved the performance of spheroidal graphite cast iron part, has enlarged its range of application, has saved production cost.
In addition,, inferior top layer and matrix are quenched to " bainite+residual austenite+graphite ", can further improve its toughness, then will obtain better use properties as carrying out the isothermal quenching complex intensifying after the spheroidal graphite cast iron carbonitriding.
The present invention must be rapidly heated before spheroidal graphite cast iron is carried out carbonitriding technology and the deflated cause description is as follows fast:
At first, because the carbon content and the silicone content of spheroidal graphite cast iron are higher than soft steel and low-carbon alloy converted steel far away, decarburizing tendency when therefore spheroidal graphite cast iron heats is very big, and Heating temperature is high more, easy more decarburization, when the spheroidal graphite cast iron part heats in " ferritic-austenitic " two-phase matrix temperature range, the easier Decarburized layer that forms the pure ferrite tissue on the surface of spheroidal graphite cast iron part, this moment is if will eliminate this layer tissue, just must be in the heating of the temperature more than 880 ℃ carburizing, and then carrying out carbonitriding again at 800-840 ℃, this will cause microstructure coarsening, and this has increased technology difficulty and cost greatly.
Therefore the carbonitriding technology of spheroidal graphite cast iron is compared with the carbon nitrogen technology of soft steel part, one of its key distinction on working method for the former need prevent carbon potential recover before part decarburization, particularly decarburization entirely.
Because the general cementing furnace that adopts of carbonitriding technology is the forvacuum cementing furnace, vacuum cementation furnace, continous way cementing furnace and common gas carbruizing furance, wherein forvacuum cementing furnace and vacuum cementation furnace are because its inside can be createed vacuum environment by bleeding, therefore be particularly suitable for deaeration in condenser, also just be particularly suitable for the taking of anti-decarburization technological measure in the spheroidal graphite cast iron carbonitriding process, spended time is also less, be generally 5-20 minute, and when adopting common gas carbruizing furance to carry out the carbonitriding of spheroidal graphite cast iron, because vacuum pump less is bled, compare forvacuum cementing furnace and vacuum cementation furnace of its anti-decarburization process time seems longer, is generally 30 minutes.Described anti-decarburization technology is generally after part advances stove passes through the two-phase region by measures such as control heat-up rates to be rapidly heated, then by the control exhaust temperature, measures such as exhaust velocity are to carry out quick exhaust, promptly strengthen air charge rate, thereby recover the furnace atmosphere carbon potential as far as possible in the short period of time, thereby prevent the decarburization of spheroidal graphite cast iron part, the method that wherein strengthens exhaust velocity is generally the quick exhaust of low temperature, promptly when reducing exhaust temperature, increase the speed that splashes into of methyl alcohol, shorten time of exchanging gas, as under 760 ℃-800 ℃ temperature condition, adding methyl alcohol, open simultaneously the venting port exhaust fully, the add-on of methyl alcohol be 120-220 drip/minute, the treatment time continues 30 minutes.
Embodiment 1: take the common pit gas carburizing furnace of 60Kw to carry out the carbonitriding of spheroidal graphite cast iron, the spheroidal graphite cast iron part of test is the spheroidal graphite cast iron QT600-2 rocking arm on certain engine, and referring to Fig. 1, Fig. 1 is the technological operation schema, and testing sequence is as follows successively:
The first step: the spheroidal graphite cast iron part is cleared up, cleaned, remove dirts such as surface scale, rust staining, greasy dirt;
Second the step: at first, the temperature of first rising periodic cementing furnace is carried out the retort carburizing then to 800-840 ℃ under this temperature condition, until the furnace atmosphere carbon potential greater than 0.8%;
Secondly, part after will clearing up earlier, cleaning is packed in the common gases cementing furnace and is covered bell, be rapidly heated then to 760 ℃-800 ℃ with by the ferritic-austenitic two-phase region, heat-up rate is more than or equal to 15 ℃/min, after furnace temperature arrives 760 ℃-800 ℃, carry out exhaust-gas disposal, promptly under 760 ℃-800 ℃ temperature condition, add methyl alcohol, open the venting port exhaust simultaneously fully, the add-on of methyl alcohol be 120-220 drip/minute, the treatment time continues 30 minutes;
Once more, continue the interior temperature of rising stove earlier to 800-840 ℃, then the spheroidal graphite cast iron part being carried out carbonitriding handles, described carbonitriding is handled and is meant adding methyl alcohol and ammonia under 800-840 ℃ temperature condition, the add-on of methyl alcohol be 80-120 drip/minute, the adding volume of ammonia is the 1%-5% of the splitting gas volume of aforementioned methyl alcohol, and the add-on of controlling propane simultaneously is to keep carbon potential 0.8%-1.2%, and the treatment time is 2-4 hour;
The 3rd step: will put the quenching of carrying out in the oil under the normal temperature into through the spheroidal graphite cast iron part that carbonitriding is handled, and promptly make spheroidal graphite cast iron part finished product after the quenching.
Embodiment 2: adopt the continous way cementing furnace to carry out the carbonitriding of spheroidal graphite cast iron, its technology may further comprise the steps successively:
The first step: the spheroidal graphite cast iron part is cleared up, cleaned, remove dirts such as surface scale, rust staining, greasy dirt;
Second step: at first, set and keep the Heating Zone Temperature of cementing furnace be 760-800 ℃, carbonitriding district temperature be 800-840 ℃, carbonitriding district carbon potential be the add-on of 0.8%-1.2%, methyl alcohol be 80-120 drip/minute, and the adding volume of ammonia is the 1%-5% of the splitting gas volume of aforementioned methyl alcohol;
Secondly, to clear up, spheroidal graphite cast iron part after the cleaning pack into the travelling belt or the charging tray of cementing furnace, set line speed or push-plate cycle then to guarantee that the spheroidal graphite cast iron time of part in the carbonitriding district is 2-4 hour, the subsequent start-up cementing furnace is handled the spheroidal graphite cast iron part is carried out carbonitriding, described carbonitriding is handled and is meant adding methyl alcohol and ammonia under 800-840 ℃ temperature condition, the add-on of methyl alcohol be 80-120 drip/minute, the adding volume of ammonia is the 1%-5% of the splitting gas volume of aforementioned methyl alcohol, simultaneously by control propane add-on to keep carbon potential 0.8%-1.2%, the treatment time is 2-4 hour.
The 3rd step: will put the quenching of carrying out in the oil under the normal temperature into through the spheroidal graphite cast iron part that carbonitriding is handled, and promptly make spheroidal graphite cast iron part finished product after the quenching.
Embodiment 3: adopt the forvacuum cementing furnace to carry out the carbonitriding of spheroidal graphite cast iron, its technology may further comprise the steps successively:
The first step: the spheroidal graphite cast iron part is cleared up, cleaned, remove dirts such as surface scale, rust staining, greasy dirt;
Second step: at first, the temperature of first rising periodic cementing furnace is carried out the retort carburizing then to 800-880 ℃ under this temperature condition, reach more than 0.8% until the furnace atmosphere carbon potential;
Secondly, to clear up earlier, part after the cleaning is packed in the forvacuum cementing furnace and is covered bell, be rapidly heated then to 760 ℃-800 ℃ with by the ferritic-austenitic two-phase region, heat-up rate is more than or equal to 15 ℃/min, opening vacuum pump simultaneously bleeds, when furnace temperature arrives 760 ℃-800 ℃, carry out exhaust-gas disposal again after vacuum tightness reaches 50-266Pa in the stove, promptly close vacuum pump earlier, splash into methyl alcohol simultaneously, when furnace pressure returns to the above 20-30mm water column of normal pressure, open the venting port exhaust again, the add-on of methyl alcohol be 120-220 drip/minute, the treatment time continues 5-20 minute.
Once more, continue the interior temperature of rising stove earlier to 800-840 ℃, then the spheroidal graphite cast iron part being carried out carbonitriding handles, described carbonitriding is handled and is meant adding methyl alcohol and ammonia under 800-840 ℃ temperature condition, the add-on of methyl alcohol be 80-120 drip/minute, the adding volume of ammonia is the 1%-5% of the splitting gas volume of aforementioned methyl alcohol, and the add-on of controlling propane simultaneously is to keep carbon potential 0.8%-1.2%, and the treatment time is 2-4 hour;
The 3rd step: the spheroidal graphite cast iron part after carbonitriding handled is put oil quenching into, again the spheroidal graphite cast iron part is carried out low-temperaturetempering below 220 ℃ after the quenching, can make spheroidal graphite cast iron part finished product after the low-temperaturetempering.
Referring to Fig. 2, Fig. 2 is the synoptic diagram of organizing of spheroidal graphite cast iron finished product among the embodiment 1, as seen from the figure, the metallographic structure of spheroidal graphite cast iron part finished product comprises the top layer successively, sublevel and matrix, the top layer is the compound layer of granular or continuous distribution, thickness is 0.0025-0.005mm, sublevel is latent needle-like martensite containing nitrogen, residual austenite and graphite, thickness is 0.04-0.10mm, matrix is a fine acicular martensite, residual austenite and graphite, the martensite containing nitrogen of sublevel is obviously than the fine acicular martensite refinement of matrix as can be seen from Figure, so sublevel has better low-temperaturetempering stability.
Test as the engine rocker of manufactured materials adopting the spheroidal graphite cast iron part finished product after carbonitriding technology also quenches, after the test of 500 hours full speed of engine full load, surface of friction pair little polishing scratch of only taking a favourable turn, the greatest wear amount is less than 0.02mm, do not see the contact fatigue vestige, satisfy the motor performance requirement.
Claims (3)
1. the reinforcing process of a spheroidal graphite cast iron is characterized in that described reinforcing process may further comprise the steps successively:
The first step: the spheroidal graphite cast iron part is cleared up, cleaned, remove surface scale, rust staining, greasy dirt;
Second step: adopt common pit gas carburizing furnace or box gas carbruizing furance; Described second step may further comprise the steps successively:
At first, the temperature of first rising cementing furnace is carried out the retort carburizing then to 800-840 ℃ under this temperature condition, until the furnace atmosphere carbon potential greater than 0.8%;
Secondly, spheroidal graphite cast iron part with cleaning, after cleaning is packed in the cementing furnace and is covered bell, be rapidly heated then to 760 ℃-800 ℃ with by the ferritic-austenitic two-phase region, heat-up rate is more than or equal to 15 ℃/minute, after furnace temperature arrives 760 ℃-800 ℃, carry out exhaust-gas disposal, promptly under 760 ℃-800 ℃ temperature condition, add methyl alcohol, open the venting port exhaust simultaneously fully, the add-on of methyl alcohol be 120-220 drip/minute, the treatment time continues 30 minutes;
Once more, continue the interior temperature of rising stove earlier to 800-840 ℃, then the spheroidal graphite cast iron part being carried out carbonitriding handles, described carbonitriding is handled and is meant adding methyl alcohol and ammonia under 800-840 ℃ temperature condition, the add-on of methyl alcohol be 80-120 drip/minute, the adding volume of ammonia is the 1%-5% of the splitting gas volume of aforementioned methyl alcohol, and the add-on by control propane is 0.8-1.2% to keep carbon potential simultaneously, and the treatment time is 2-4 hour;
The 3rd step: will put the quenching of carrying out in the oil under the normal temperature into through the spheroidal graphite cast iron part of carbonitriding processing earlier, and again the spheroidal graphite cast iron part be carried out low-temperaturetempering below 220 ℃ after the quenching, and can make spheroidal graphite cast iron part finished product after the low-temperaturetempering.
2. the reinforcing process of a spheroidal graphite cast iron is characterized in that described reinforcing process may further comprise the steps successively:
The first step: the spheroidal graphite cast iron part is cleared up, cleaned, remove surface scale, rust staining, greasy dirt;
Second step: adopt the forvacuum cementing furnace; Described second step may further comprise the steps successively:
At first, the temperature of first rising cementing furnace is carried out the retort carburizing then to 800-840 ℃ under this temperature condition, until the furnace atmosphere carbon potential greater than 0.8%;
Secondly, to clear up, spheroidal graphite cast iron part after the cleaning is packed in the cementing furnace and is covered bell, be rapidly heated then to 760 ℃-800 ℃ with by the ferritic-austenitic two-phase region, heat-up rate is more than or equal to 15 ℃/minute, opening vacuum pump simultaneously bleeds, when furnace temperature arrives 760 ℃-800 ℃, carry out exhaust-gas disposal again after vacuum tightness reaches 50-266Pa in the stove, promptly close vacuum pump earlier, splash into methyl alcohol simultaneously, when furnace pressure returns to the above 20-30mm water column of normal pressure, open the venting port exhaust again, the add-on of methyl alcohol be 120-220 drip/minute, the treatment time continues 5-20 minute;
Once more, continue the interior temperature of rising stove earlier to 800-840 ℃, then the spheroidal graphite cast iron part being carried out carbonitriding handles, described carbonitriding is handled and is meant adding methyl alcohol and ammonia under 800-840 ℃ temperature condition, the add-on of methyl alcohol be 80-120 drip/minute, the adding volume of ammonia is the 1%-5% of the splitting gas volume of aforementioned methyl alcohol, and the add-on by control propane is 0.8-1.2% to keep carbon potential simultaneously, and the treatment time is 2-4 hour;
The 3rd step: will put the quenching of carrying out in the oil under the normal temperature into through the spheroidal graphite cast iron part of carbonitriding processing earlier, and again the spheroidal graphite cast iron part be carried out low-temperaturetempering below 220 ℃ after the quenching, and can make spheroidal graphite cast iron part finished product after the low-temperaturetempering.
3. finished product of the reinforcing process of any described spheroidal graphite cast iron among the claim 1-2, it is characterized in that: the metallographic structure of described spheroidal graphite cast iron part finished product comprises top layer, sublevel and matrix successively, described top layer is the compound layer of granular or continuous distribution, thickness is 0.0025-0.005mm, described sublevel is latent needle-like martensite containing nitrogen, residual austenite and graphite, thickness is 0.04-0.10mm, and described matrix is fine acicular martensite, residual austenite and graphite.
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