SE123799C1

SE123799C1 -

Info

Publication number: SE123799C1
Authority: SE
Publication date: 1948-01-01

Description

Uppfinnare: H. Loevenstein. Inventor: H. Loevenstein.

Prioritet begard frcEn den 13 september 1945 (Anlerilcas f5renta slater). Priority was given on 13 September 1945 (Anlerilca's f5renta slater).

Foreliggande uppfinning hanfor sig till ythardning av jarnlegeringar, narmare bestamt nitrerhardning av kromhaltiga jarnlegeringar, vilka ha en benagenbet att bilda en passiv oxidhinna ph sina ytor. Sarskilt innefattar uppfinningen behandling av austenitiskt krom- stal och rostfritt kromnielstal med hog kromhalt saint rostfritt jam. The present invention relates to surface hardening of iron alloys, more particularly to nitrous hardening of chromium-containing iron alloys which have a bone bite to form a passive oxide film on their surfaces. In particular, the invention comprises the treatment of austenitic chromium steel and stainless chromium steel with high chromium content saint stainless jam.

Hittills anvanda nitreringsprocesser for ythardning innefatta i allmanhet behandling av en jarnlegering av speciell sammansattning med ammoniakgas vid forhojd temperatur, vanligen mom omradet f190---550° C. De fOr hardning avsedda jarnlegeringsforemalen maskinbearbetas vanligen far att de skola erUlla sin slutliga form och sina slutliga dimensioner, innan de underkastas nitreringsbehandlingen. Detta forfarande liar funnit stor anvandning i praktiken, men pa senare tiden ha svarigheter uppstatt vid forfarandets tillampning for hogvarcliga krom- och kronanickel-jarnlegeringar. Om dessa legeringar icke underkastas en sarskild forbehandling bildas antingen intet hardskikt ails inom rim-hg behandlingstid, eller ocks& blir hardskiktet for grunt resp. erhaller for lag hardhetsgrad for att kunna motsvara de onskade andamalen. Hitherto used nitriding processes for surface hardening generally involve the treatment of an iron alloy of special composition with ammonia gas at elevated temperature, usually in the range f190 --- 550 ° C. dimensions, before being subjected to the nitriding treatment. This method has been widely used in practice, but in recent times difficulties have arisen in the application of the process to high-grade chromium and crown nickel-iron alloys. If these alloys are not subjected to a special pretreatment, either no hard layer is formed within a reasonable treatment time, or the hard layer becomes too shallow resp. obtain for law degree of hardness to be able to correspond to the desired andamalen.

Svarigheterna med nitrering av hogyardiga krom-jarnlegeringar hero pa att legeringens yta innehaller en inert eller »passiv hinna, som Or sammansatt av krorhoxid. Det har foreslagits att Ora de hagvardiga krom-jarnlegeringarna mottagliga far nitrering genom en behandling, som innefattar ,etsning av de nitreringen underkastade foremalen med en vatgasutvecklande syra, t. ex. klorvatesyra. Denna behandling uppfyller visserligen det onskade andamalet men medfor att en extra atgard tillkommer for fOremalens framstallning, varmed foljer extra kostnader. Vidare nodvandiggores att arbetsstycket omedelbart maste inff3ras i nitreringsugnen efter den namnda behandlingen, enar oxidhinnan el- jest anyo bildas, da den utsattes for luf tens inverkan. Forsavitt icke sarskilda forsiktighetsatgarder vidtagas, bli de erhallna resultaten salunda icke likformiga. The similarities with nitration of high-grade chromium-iron alloys are that the surface of the alloy contains an inert or "passive film", which is composed of chlorine oxide. It has been suggested that the susceptible chromium-iron alloys be susceptible to nitration by a treatment which comprises etching the nitrates subjected to the formalin with a water gas generating acid, e.g. chloroacetic acid. Although this treatment fulfills the desired purpose, it entails that an extra action is added for the production of the object, which entails extra costs. Furthermore, it is necessary that the workpiece must be introduced immediately into the nitriding furnace after the said treatment, otherwise the oxide film is formed, as it is exposed to the action of the air. If no special precautionary measures are taken, the results obtained will thus not be uniform.

Andra losningar av detta problem ha forsOkts med stone eller mindre framgang. En elektrolytisk reningsbehandling, atfoljd av tvattning om-edelbart fore arbetsstyckets inforande i nitreringsugnen, liar med framgang forsokts i praktiken. liven i detta fall uppsta emellertid extra arbetsmoment och okade kostnader. Other solutions to this problem have been tried with stone or less progress. An electrolytic cleaning treatment, followed by washing immediately before inserting the workpiece into the nitriding furnace, has been successfully attempted in practice. In this case, however, extra work steps and increased costs arise.

Hogvardiga krom-jarnlegeringar ha ocksa med framgang nitrerats genom att det passiva oxidskiktet f8rst reduceras genom be-handling med viite i den sign, dar nitreringen sedan utfores. Detta fOrfarande medf Or tillfredsstallande nitreringsresultat men erfordrar extra apparatur for ammoniakens spanning, sa att derma avger vatgas f Or reduktion av oxidhinnan, varjamte ugnens kapacitet nedbringas. High-grade chromium-iron alloys have also been successfully nitrated by first reducing the passive oxide layer by treatment with white in the sign where the nitriding is then carried out. This process gives satisfactory nitration results but requires additional equipment for the ammonia voltage, so that it emits hydrogen gas to reduce the oxide film, and the capacity of the furnace is reduced.

Det nitrerhardskikt, som erhalles pa Mgvardiga krom-jarnlegeringar, medelst de nu namnda forfaringssatten, Or relativt grunt for en given nitreringsbehandling. Enligt nyligen gjorda ran i praktiken i samband med nitrering av ett austenitiskt, varmeresistent, hOgvardigt krom-nickel-volframstal, erhalles ett hardskiktsdjup av 0,1-0,15 mm genom nitrering under 50 timmar vid 538° C 'efter en forberedande ,elektrolytisk behandling. The nitride hard layer obtained on heavy chromium-iron alloys by the now mentioned method is relatively shallow for a given nitriding treatment. According to recent practice in connection with nitration of an austenitic, heat-resistant, high-grade chromium-nickel tungsten number, a hard layer depth of 0.1-0.15 mm is obtained by nitration for 50 hours at 538 ° C 'after a preparatory, electrolytic treatment.

FOreliggande uppfinning ham till andamal att majliggora ett nitreringsforfarande, som kan tillampas for olika hogvardiga krom- jarnlegeringar, inkluderande sadana med austenitisk struktur, sarskilt rostfria stal air typen med hog kromhalt samt austenitiska Iragvardiga krom-nickelst01, varvid man genom detta forfarande i huvudsak undviker de ovannamnda olagenheterna och svarigheterna. ELI ytterligare andamal Or att genomfora nitreringsprocessea p0 sadant satt, att hogyardiga krom-jarnlegeringar kunna nitre- — l23799 — ras med tillfredsstallande resultat utan flagon vasentlig tidsspillan och endast med ringa iikning av kostnaderna, jainfOrt med det brukliga nitreringsfiirfarande, som tillampas for Ifigvardiga krom-aluminiunistal. Vidare ayser uppfinningen att mojligg8ra nitreringsprocessens tillampning for hogvardiga krom-jarnlegeringar ph sadant satt, att ett nitrerhardskikt rued vfisentligt okat djup kan erhallas under en given nitreringsperiod, jfimfort med de resultat, som erhallits medelst kfinda forfaranden. Slutligen avser uppfinningen iiven att genomfora nitreringsprocessen pa sadant sail, all lokala ytdelar av de h8gvardiga kromjarnlegeringsforemalen nitreras utan att nagot skyddsskikt behover anbringas pa de delar, som icke skola nitreras, eller att pa annat satt behandla dessa delar for att tundra dem att antaga ett nitrerhardskikt saint utan att antaga ett nitrerhardskikt samt utan minskning av dessa onitreracle ytdelars motstandsfOrmaga mot korrosion. The present invention aims at enabling a nitriding process which can be applied to various high-quality chromium-iron alloys, including those having an austenitic structure, especially stainless steel type with high chromium content and austenitic irradiated chromium-nickel steel, thereby essentially avoiding the process the above-mentioned illegality and liabilities. ELI further andamal Or to carry out the nitriding process in such a way that high-grade chromium-iron alloys can be nitrided with satisfactory results without significant waste of time and only with little calibration of the costs, compared with the usual nitriding procedure which is applied to aluminum plant. Furthermore, the invention seeks to enable the nitriding process to be applied to high quality chromium-iron alloys in such a way that a nitriding hard layer having a substantially increased depth can be obtained during a given nitriding period, as well as with the results obtained by existing methods. Finally, the invention relates to carrying out the nitriding process on such a sail, all local surface parts of the high-grade chromium-iron alloy materials are nitrided without any protective layer having to be applied to the parts which are not to be nitrated, or to otherwise treat these parts to tundra to assume a nitriding hard layer. saint without assuming a nitrile hard layer and without reducing these onitreracle surface parts' resistance to corrosion.

Det har befunnits att de nu namnda flndamdlen kunna uppnas och att man kan erhalla hogvardiga krom-jarnlegeringar med ett nitrerhfirdskikt av goda egenskaper i brukliga typer av nitreringsugnar och inom det normala ()mild:let for nitreringstemperaturerna, om nitreringen utfores i narvaro av vissa metaller inklusive kisel i intiin beroring med den yta pa arbetsstycket, som skall nitreras. De metaller, som har befunnits medfOra detta gynnsamma resultat, aro sadana, vilkas oxider ha hagre bildningsvarme an kromoxiden, Cr203. Lampligen har metallen sadan smaltpunkt, att den forblir i fast tillstand vid den temperatur, vid vilken nitreringsforfarandet utfores. Da forfarandet enligt uppfinningen anvandes, kunna arbetsstyckena forberedas for nitreringsbehandlingen pa vilket sorn heist brukligt satt. Det Or ej nodvandigt att infora nagot sarskilt arbetsmoment fOr att behandla arbetsstyckets ytor i och for deras forberedande for nitreringen. It has been found that the above-mentioned fine dams can be obtained and that high-quality chromium-iron alloys with a nitriding layer of good properties can be obtained in conventional types of nitriding furnaces and within the normal () temperature of the nitriding temperatures, if the nitriding is carried out in the presence of certain metals. including silicon in intiin contact with the surface of the workpiece to be nitrated. The metals which have been found to give this favorable result are those whose oxides have a better heat of formation than the chromium oxide, Cr2 O3. The lamp has such a melting point that it remains in a solid state at the temperature at which the nitriding process is carried out. When the method according to the invention is used, the workpieces can be prepared for the nitriding treatment in which way it is customary. It is not necessary to introduce any particular work step to treat the workpiece surfaces in and for their preparation for nitriding.

De speciella metaller, som ha befunnits vara verksamma, kunna anvandas i samband med lamplig modifikation av nitreringsprocessen. Vanligtvis genomfares nitreringen genom att arbetsstyckena placeras i nitreringsugnen, varvid de delar, som skola nitreras, tackas med ett relativt find pulver av nagon av de speciella metallerna, varefter en kvaveutvecklande gas bringas aft stromma genom ugnen pa sadant satt, att gasen kommer i be-raring med metallen och arbetsstycket. Forfarandet kan aven tillampas vid de modifikationer av nitreringsprocessen, dar nitreringsbeframjande medel anvandas, exempelvis i form av amider enligt svenska patentet nr 120 005. The special metals which have been found to be active can be used in connection with appropriate modification of the nitriding process. The nitriding is usually carried out by placing the workpieces in the nitriding furnace, filling the parts to be nitrided with a relatively fine powder of any of the special metals, after which a nitrogen-evolving gas is caused to flow through the furnace in such a way that the gas enters with the metal and the workpiece. The process can also be applied to the modifications of the nitriding process where nitriding promoters are used, for example in the form of amides according to Swedish Patent No. 120,005.

De metaller, som falla inom ramen for uppfinningen, och som provats samt befunnits lampliga for anvandning i samband med det nya forfarandet, utgoras av magnesium, kal cium, aluminium och kisel saint blandningar och legeringar av dessa metaller. En kiselaluminiumlegering och en kisel-kalciumlegering ha befunnits giva goda resultat. En legering av aluminium och magnesium i ungefar lika proportioner finnes tillganglig i marknaden och kan anvandas. Denna legering har den for foreliggande andamal gynnsamma egenskapen att den Or myeket sprod och latt kan s8nderdelas i pulverform. The metals which fall within the scope of the invention, and which have been tested and found suitable for use in connection with the new process, consist of magnesium, calcium, aluminum and silicon saint mixtures and alloys of these metals. A silicon-aluminum alloy and a silicon-calcium alloy have been found to give good results. An alloy of aluminum and magnesium in approximately equal proportions is available in the market and can be used. This alloy has the favorable property for the present purpose that it can be very dispersed and easily decomposed into powder form.

Nitreringsforfarandet kan genomforas i en bruklig nitreringsugn genoni att ugnen upphettas till en temperatur inom nitreringsomradet, d. v. s. mellan e:a 475° C och 600° C, varefter denna temperatur bibehalles, medan ammoniakgasen bringas att strOmma genom reaktionszonen. Ammoniakens stromning regleras ph sficlant salt, att de utstrommande gasernas dissoeiationsgrad Mies vid lampligt varde. Pa senare tiden är det bruklig praxis att installa dissociationsgraden till ungefar 30-40 %. Foreliggande uppfinning kan emellertid lika val genomforas med andra varden ph ammoniakens dissociation. &Isom exempel pa forfarandets genomforande i samband med finfordelat metallpulver mO namnas, att ett prov av en rostfri shitlegering, innehallande 18 % krona och 8 % nickel jamte mindre halter av andra bestandsdelar, placerades i en nitreringsugn och tacktes med en finfordelad kisel-kalciumlegering med en halt av 30 % kalcium, samt underkastades behandling med ammoniak vid 575° C under 24 timmar. Efter uttagning frail ugnen samt darefter foljande kylning befanns provet ha en hardhet av 94,5--95 enligt Rockwell 15 N-slcalan, till skillnad fran dess ursprungliga hardhet, uppgaende till 77 enheter enligt samma skala. Tvarsektioner av detta prov preparerades och undersoktes mikroskopiskt samt befunnos ha ett nitrerhardskikt av goda egenskaper, som strackte sig ned till ett djup av 0,15 mm. The nitriding process can be carried out in a conventional nitriding furnace by heating the furnace to a temperature within the nitriding range, i.e. between 475 ° C and 600 ° C, after which this temperature is maintained, while allowing the ammonia gas to flow through the reaction zone. The flow of ammonia is regulated ph sficlant salt, that the degree of dissociation of the effluent gases Mies at appropriate value. In recent times, it has been common practice to set the degree of dissociation to about 30-40%. However, the present invention can be practiced equally with other values of dissociation of ammonia. As an example of the implementation of the process in connection with finely divided metal powder, it is mentioned that a sample of a stainless steel alloy, containing 18% crown and 8% nickel as well as minor contents of other constituents, was placed in a nitriding furnace and charged with a finely divided silicon-calcium alloy. content of 30% calcium, and was subjected to treatment with ammonia at 575 ° C for 24 hours. After removal from the furnace and subsequent cooling, the sample was found to have a hardness of 94.5--95 according to Rockwell 15 N-slcalan, in contrast to its original hardness, amounting to 77 units according to the same scale. Cross sections of this sample were prepared and examined microscopically and were found to have a nitrile hard layer of good properties, extending down to a depth of 0.15 mm.

Enligt uppfinningen har det befunnits att metallpulvrets effekt varierar med partikelstorleken, och att ett mera finfordelat pulver Or verksammare On ett grovre pulver. Det har Oven befunnits att metallpulvrets partikelstorlek blir av storre betydelse, da oxidernas bildningsvarme narmar sig kromoxidens. Ett prov av ett rostfritt stal, som nitre-rats under 24 timmar vid 575° C i beroring riled ett kiselpulver, som Or grovre On vad som motsvarar siktning genom en sikt med 40 maskor, gay en ythardhet av 79,5 enheter, medan ythardheten uppgick till 90,5--91,5 enheter oh nitreringen utf8rdes under i Ovrigt identiska forhallanden i narvaro av ett kiselpulver, motsvarande en sikt av 300 maskor. Detta inflytande av metallpartiklarnas storIek kan mojligen hero pa att beroringen mellan arbetsstycket och metaIlen blir intimare em pulvret Or mera finfardelat. Troligen heror effekten Oven atminstone delvis p0 att kon- — —3 centrationen av yardet okas ph eller nara de metallytor, som underkastas nitrering. Vilken forklaringen an Sr, leder ett mere finfordelat pulver till battre resultat, varfOr uppfinnaren ej anser sig vara bunden yid den ovan giyna teoretiska forklaringen. Liknande prov air rostfritt krom-nickelsthl nitrerades under samma forhallanden i beroring med aluminium, magnesium samt en legering ay kisel och aluminium, innehallande 50 % aluminium. Resultaten ay alla dessa prov anges foljande tabell: Pray M etall p ulveUrsprunglig Slutlig hardhet Hardskiktsdjup r No.,ha rdhetRockwell 15Nmm NS 1 Si-Ca-legering (30 Ca) NU 1 Al NG 1 Mg 77 94,5-90, 77 91,5-92 0, 76 91,5-93 0, 76 79.5-8* 76 90,5-91,* 76 89,5-90,* Nk 1 Si (grov) NK 2 Si (fin) NP 1Si-Al-legering (50 !', Al) * Djupet icke upprnatt. According to the invention, it has been found that the effect of the metal powder varies with the particle size, and that a more finely divided powder is more effective on a coarser powder. It has also been found that the particle size of the metal powder becomes of greater importance, as the heat of formation of the oxides approaches that of chromium oxide. A sample of a stainless steel, which has been nitrated for 24 hours at 575 ° C in contact riled a silicon powder, which amounted to 90.5--91.5 units and the nitration was carried out under otherwise identical conditions in the presence of a silicon powder, corresponding to a sieve of 300 meshes. This influence on the size of the metal particles may possibly mean that the contact between the workpiece and the metal becomes more intimate with the powder or more finely divided. The effect is probably at least partly due to the fact that the concentration of the yard increases the pH or near the metal surfaces which are subjected to nitration. Which explanation depends on a more finely divided powder leading to better results, which is why the inventor does not consider himself bound by the above theoretical explanation. Similar samples of stainless chromium-nickel steel were nitrated under the same conditions in contact with aluminum, magnesium and an alloy of silicon and aluminum, containing 50% aluminum. The results of all these tests are given in the following table: Pray M etall p ulveOriginal Final hardness Hard layer depth r No., hardness Rockwell 15Nmm NS 1 Si-Ca alloy (30 Ca) NOW 1 Al NG 1 Mg 77 94.5-90, 77 91 , 5-92 0, 76 91.5-93 0, 76 79.5-8 * 76 90.5-91, * 76 89.5-90, * Nk 1 Si (coarse) NK 2 Si (fine) NP 1Si- Al alloy (50! ', Al) * Depth not reached.

Forfarandet enligt uppfinningen kan Sven genomforas genom anyandning av de ovan angiyna metallerna i form av en tunn belaggning ph arbetsstyckets yta. Goda resultat ha uppnatts med belaggningar, vilka paforts de f8r nitrering avsedda ytorna genom sprutning. Ett prov ay ett rostfritt stal, innehallande 18 % krom och 8 % nickel, forsags Over en del av den for nitrering avsedda ytan med ett tunt sprutskikt av aluminium och nitrerades darefter i naryaro av ammoniak vid 575° C under 24 timmar. Provets ursprungliga hardhet uppgick till 75 enheter. Efter nitreringen uppvisade provet en ythiirdhet, ef ter aylagsnande av aluminiumskiktet, uppghende till 90-91 enheter i de ytor, som thekts med aluminium. De delar av ytan, som icke tackts med aluminium, uppvisade i huvudsak ingen Mining av hardheten gentemot deras ursprungliga tillstand fore nitreringen. The process according to the invention can be carried out by using the above-mentioned metals in the form of a thin coating on the surface of the workpiece. Good results have been obtained with coatings which are applied to the surfaces intended for nitration by spraying. A sample of a stainless steel, containing 18% chromium and 8% nickel, was coated over a portion of the surface to be nitrated with a thin spray layer of aluminum and then nitrated in naryaro of ammonia at 575 ° C for 24 hours. The initial hardness of the sample was 75 units. After nitration, the sample showed a surface density, after application of the aluminum layer, amounting to 90-91 units in the surfaces covered with aluminum. The parts of the surface which were not covered with aluminum showed essentially no Mining of the hardness compared to their original state of nitriding.

Den pasprutade belaggningen eller det pulverformiga skiktet av den anvanda metallen kan phforas pa endast en del av arbetsstyckets yta. Arbetsstyeket hardas da endast vid de ytor, som aro i berOring med metallen. Forfarandet innebar ett bekvamt satt att selektiyt harda olika delar ay ett enda arbetsstycke och samtidigt undvika att de ytor, som skola forbli onitrerade, underkastas en behandling, som skulle kunna inverka skadligt ph den dath anbragta passiva hinnan, varfor dessa ytor kvarlamnas med hela sin ursprungliga fOrmaga att motsth. korrosion eller skalning. FOr forbranningsmotorer avsedda yentiler av ea stallegering, innehhllande ungefar 13-15 % krom, fi5rses exempelvis med ett nitrerhiirdskikt utmed de delar av yentilen, som aro utsatta for glidfriktion., exempelvis en del av yentilspindeln och halsen, fOr att minska notningen pit dessa stallen. Det Sr Omsk-mart att ventilens ovriga delar forbli onitrerade. Detta resultat kan uppnas genom att belagga de delar av ventilytan, som skola bardas, exempelvis med ett tunt aluminiumskikt, som lamnar resten ay ytan obelagd. Da arbetsstycket sedan underkastas nitreringsbehandlingen, forbli ytans obelagda delar onitrerade ph grund av att de aro forsedda med det passiva skiktet, medan ett nitrerhardskikt bildas under ytans belagda delar. Dit en metall enligt fOreliggande uppfinning anvandes i form av ett overdrag eller en belaggning, som pa-Rifts genom sprutning eller ph annat salt, bor belaggningen vara tillrSckligt tunn eller poros for att det aktiva kvayet skall kunna genomtranga densamma och shlunda astadkomma effektiv nitrering av den underliggande legeringsmetallen. Tunna belaggningar med en tjoeklek av storleksordningen 0,125 mm eller mindre ha befunnits vara effektiva. Belaggningen behover icke vara noggrant likformig I avseende A sin tjocklek och behover ej vara sammanhangande. Stift- eller bulthal och liknande bristfalligheter inverka icke namnvart pa det framstallda hardskiktets likformighet. The spray-coated coating or powder layer of the metal used can be applied to only a part of the surface of the workpiece. The workpiece is then hardened only at the surfaces which are in contact with the metal. The procedure was convenient in that it selectively hardened different parts in a single workpiece and at the same time avoided that the surfaces which were to remain unnitrated were subjected to a treatment which could adversely affect the dath applied passive membrane, so that these surfaces were left with all their original fOrmaga att motsth. corrosion or peeling. For internal combustion engine yantiles of a stable alloy, containing about 13-15% chromium, is provided, for example, with a nitride layer along the parts of the yentyl which are subjected to sliding friction, for example a part of the yentil spindle and neck, to reduce the notch in these stalls. It Sr Omsk-mart that the other parts of the valve remain unnitrated. This result can be achieved by coating the parts of the valve surface which are to be shaved, for example with a thin aluminum layer, which leaves the rest of the surface uncoated. As the workpiece is then subjected to the nitriding treatment, the uncoated parts of the surface remain unnitrated due to the fact that they are provided with the passive layer, while a nitrile hard layer is formed below the coated parts of the surface. Where a metal according to the present invention is used in the form of a coating or coating which is applied by spraying or other salt, the coating should be sufficiently thin or porous for the active quail to penetrate it and thus achieve efficient nitriding of the underlying alloy metal. Thin coatings with a thickness of the order of 0.125 mm or less have been found to be effective. The coating need not be exactly uniform in respect of its thickness and need not be coherent. Pin or bolt hall and similar defects do not have a significant effect on the uniformity of the hard layer produced.

Belaggningen kan och bOr vanligtvis aylagsnas fran arbetsstycket, sedan nitreringen fullbordats. Die exempelvis aluminium anvandes sasom belaggningsmaterial, kan belaggningen avlagsnas genom behandling mcd en utspadd natriumhydroxidl8sning, exempelvis en 5 % losning. The coating can and should usually be removed from the workpiece after the nitriding has been completed. If, for example, aluminum is used as the coating material, the coating can be removed by treatment with a dilute sodium hydroxide solution, for example a 5% solution.

Uppfinningen Sr icke begransad till de ovan angiyna speciella nitreringsforfarandena, vilka endast anforts sasom exempel. Uppfinningen kan Sven tillampas for kromhaltiga jamlegeringar av annan sammansattning an Tad som ovan nanints sh.som exempel. Salunda kan uppfinningen ifragakomma hi. a. for ka rostfria stal, rostfritt jarn och hOgyardigt kromgjutjarn, i vilka olika andra legeringstillsatser forefinnas fOrntom krom eller krom och nickel. Behandlingens varaktighet kan amen variera, alltefter fordringarna for det speciella arbetsstycke, som &sail behandlas. The invention is not limited to the special nitration procedures indicated above, which are given by way of example only. The invention can be applied to Sven for chromium-containing jam alloys of other composition than Tad as above nanints sh. As an example. Thus, the invention can be called hi. a. for stainless steels, stainless iron and high-grade chromium cast iron, in which various other alloying additives are found in addition to chromium or chromium and nickel. The duration of the treatment may vary, depending on the requirements for the special workpiece, which & sail is treated.

Claims

Patent claim:

1. Salt that nitrides hard chromium-containing iron alloys with a surface which contains a sh high chromium content that a passive or inert, nitriding chromium oxide film is bitten, may be characterized by the fact that said alloy warms up nitriding temperature in contact with a metal! including silicon, whose slides have a higher heat of formation than the chromium oxide, in the presence of a cold-releasing gas, whereby the skin is deposited as a nitride-hardened surface is formed on the alloy.

2. according to claim 1, characterized in that the alloy is subjected to a preparatory treatment for removal of the inert membrane of chromium oxide and a nitriding treatment either simultaneously or sequentially at a temperature between 470 G and 600 ° C, and that the nitrogen-releasing gas 1 mainly horses of gaseous ammonia.

MRI according to claim 1 or 2, It is claimed that the metal whose oxides have a higher formation value for the chromium oxide is selected from the metals aluminum, potassium, magnesium and silicon or alloys ay tya or more of these metals.

4. According to any one of claims 1 to 3, it is characterized in that the metal whose oxides have a higher formation yarine than the chromium oxide is fused to the iron alloy in finely divided form.

5. A seat according to any one of claims 1 to 4, characterized in that the metal whose oxides have a higher formation heat than the chromium oxide, in the form of a coating or a coating, is applied only to the surface parts of the mold which are intended to be nitrated, while the rest of the mold surface parts of the cooling lambs free. Stockholm 1910. Kling '. Bektr. P. A. Norstedt Stiller 490089