DE1758424A1 - Chrome-nickel steel with increased corrosion resistance - Google Patents

Description

~ 1326

Gebr. Böhler & Co · Aktiengesellschaft in

Vienna

Chrome-nickel steel with increased corrosion resistance

The invention relates to a chrome Niokel steel with increased corrosion resistance both in the unwelded and in the welded state compared to reducing acting, ohlorionenhaltigen and in particular oxidizing acting attack media, such as ζ · Β · nitric acid.

It is known that an austenitic stainless steel, in addition to 15 to 25 # Cr, 7 to 2o # nickel, o, oo5 to o, 2 i "carbon, ο to 4 fi Mo tnd o, 1 bia 5 1> manganese» 2 , 5 to 6 j6 contains silicon, has increased resistance to stress corrosion cracking and that steels of essentially the same type show increased resistance to solutions of nitric acid

4-

they have a sensitive part in the welded state * Due to the effects of heat during welding, this occurs in the area adjacent to the weld seam a highly intergranular susceptible zone in which the silicon-containing steel in nitric acid is also absent additional oxidizing agents, such as hexavalent chromium or trivalent iron, are increasingly removed A white silicon oxide occurs at these points, under which the corrosion continues · This susceptible « Zone has nothing to do with the well-known intergranular susceptible zone on welded, non-stabilized 18/8 chrome nickel Steels with increased »carbon content to do» this is known to be caused by chroocarbide cleavage on the

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Grain boundaries triggered. In the siliceous steels considered here, the carbon content is so much reduced that this separation does not occur. Bs represents but, after detailed metallurgical investigations, they contributed under the influence of the heat of welding these high-silicon steels in the temperature range 85o ° C an intermetallic precipitation on the grain boundaries in which chromium and silicon are strongly secured are · This leads to a depletion of these elements in the vicinity of the grain boundaries · Ba these two elements However, what is decisive for the resistance in nitric acid are ι the grain boundary fringes that are depleted in it are increasingly attacked by nitric acid and formation occurs the zone susceptible to grain decay at a certain distance on both sides of the weld seam

Since it is generally not possible to avoid welding steel in chemical apparatus engineering, it is practical to use it the silicon-containing austenitic ChronHETickel steels with increased corrosion resistance depending on the solution to this problem caused by the welding

Our investigations have shown that the or · delays in this type of steel in the temperature range of about 85 © ° 0 occurring intermetallic Korngrenzenaussoheidungen and to the same extent so AUOH enhanced corrosion adjacent to the weld reduced can be avoided, "if the S ^x ahl accounted for o »o4 to 0.3 j (, preferably *» o8 to q / ji contains nitrogen *

The chromium Kiokel steel according to the invention with increased corrosion resistance in both ungesohweißten as AUOH in gesohweißten state is thus characterized daduroh that he max ο, Ji 25 carbon »1.5 toi" 1 © Jf, preferably 2 -. 8 Jf silicon, ο up to 1o Jf manganese »13 The 3o J * chromium, 4 to 3o Jt Niokel, ο to 1o Jf molybdenum and o ₉ o4 to o.3 Jf -nitrogen _{t the} rest of bis iron and unavoidable impurities» contains ·

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As particularly against redmeierend acting or · ohlorionenhaltigen attack media, both in the unwelded resistant as well as in the welded condition steel to a further characteristic of the invention, such a proposed according to which a maximum of o, 15 i "carbon ι 2 to 6 i" silicon, ο to 6 i » Manganese, 16 to 25 fi chromium, 10 to 25 fi nickel, 2 to 6 $> molybdenum and 0.08 to o.2 i» nitrogen, the remainder bison and unavoidable impurities, contains ·

In the case of this steel, too, in the absence of nitrogen there is a very pronounced tendency to precipitate intermetallic phases i * the neighborhood of the Weld seams and thus increased exposure to attack media such as ζ · Β · sulfuric acid ·

For best results in terms of Beetändigkeit against oxidizing acting attack media, particularly nitric acid, both in the non-welded as well as in the welded condition, a steel is recommended, which is characterized in that it ma ximal o, 15 # Kohlenioff, 2 to 6 $> Silicon , ο to 6 <f> manganese, 16 to 25 t chroy, 1o to 25 1 » nickel and o, o8 to o, 2 i» nitrogen, the remainder iron and unavoidable impurities ρ contains ·

A series of tests carried out with a series of steel coarse with increasing nitrogen content showed, after welding tests as well as after similarly carried out corrosion tests in boiling concentrated nitric acid, dilute hydrochloric and sulfuric acid, a clear superiority of the chrome kickel steels according to the invention.The same picture resulted after the extraction to η 11oo ^{Steel samples subjected to a subsequent tempering treatment of 5 minutes to 10 hours at 0} C in water, whose notched impact strength was determined in terms of the duration of the tempering and whose weight loss was determined in boiling concentrated nitric acid after 3 to 48 hours of cohesion * The steels show the best results o, 11 and o, 16 ji nitrogen to % with nitrogen contents above o, 22 i * it appears essential

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which is disadvantageous in particular to the mechanical behavior To avoid the formation of chromium nitrides

Composition of the steels * Chair No. C Si Mn Or Il I

1 0.03 3.9 0.72 18.5 14.7 0.04

2 0.04 4.1 0.67 18.3 14.9 0.08

3 0.02 4.4 0.58 18.1 15.5 0.11

4 0.03 4.3 0.71 18.4 15.8 0.16

5 0.04 4.4 0.56 17.6 15.4 0.19

0098ti5 / 085B

Claims (1)

Claims 1 · Chrome-Ηicke1 steel with increased corrosion resistance both in the unwelded and in the welded state, characterized in that it contains a maximum of 0.25 # carbon, 1.5 to 1o <fi _9, preferably 2 to 8 % silicon, 0 to 1o Jt Manganese, 13 to 3o * chromium, 4 to? O # nickel, 0 to 1o Ji molybdenum and 0.04 to 0.3 $> nitrogen, heat iron and inevitable impurities, contains · 2 »ChronHtfiokel steel according to claim 1 with increased resistance to reducing agents and chlorine ion-containing attack media,» although in the unshelded as well as in the welded state, characterized in that it contains a maximum of 0.15 £ carbon, 2 to 6 <f> silicon, ο to 6 # manganese, 16 to 25 i * chromium, 1o to 25 £ nickel, 2 to 6 ^ molybdenum and 0.08 to 0.2 f> nitrogen, best iron and unavoidable impurities, contains » 3 _e Ohrom-flicke1 steel according to claim 1 with increased resistance to oxidizing attack media, in particular nitric acid, both in the unwelded and in the welded state, characterized in that it contains a maximum of 0.15 Ji carbon, 2 to 6 jt silicon, ο to contains 6 i * Maugan, 16 bie 25 i chromium, 1o to 25 $ Lickel and 0.08 to 0.2 Ji nitrogen isen Best ^B and unavoidable impurities, 4 »Use of the chrome-nickel steel according to the claims 1 to 3 as welding filler material, in particular for the welding of similar materials, with the proviso, that it contains up to 2o £ D # lta-ferrite Public company patent office 009885/0856