Stabilizing treatment of SS plate /components

[Prakash Hegde]

Hi! Friends

Why some of the client spec ask for

Stabilizing treatment (At lower temperature than solution annealing i.e. about 900C) of already solution annealed plate but not Welded SS components

Especially  304H,347,321

Regards

Hegde

[Vishwas Keskar Welding Manager WELDING]

Dear Sir 

At @ 900-940 Deg C , the Carbon will react  with Ti /Nb/Cb to form its carbides . This   results into no Carbon or very less Carbon will be available  to form Chromium Carbide which is  detrimental to corrosion resistance.

Thanks and regards

Vishwas - IWE

International Welding Engineer 

[Sankaran Sp]

Dear  Mr.Prakash,

stabilized heat treament is required for stablized staniless steel only, not for all SS grades.

stabilizing alloys of Like : Nb/Cb, Ti ,Zr & others are speciafiaclly added in the normal SS aloys to avoid senstitization, after solution heat treatement we don't know about whether these stabilzed alloys are setteld in grain boundry or in the core. hence to ensure the stabilized alloys in grain boundry this stabilized heat treatment is essential, as per ASTM A 182 ot ASTM A 351 this stabilized heat teratment is given as subimentary variable for forging & casting respectively. During stabilized heat treatement soaking hour to given as 4 hour (min).          

 

Regards,

Sankaran.SP

Welding & Metallurgy expert

Coimbatore, India. 

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[james gerald]

Basically it is performed to form TiC and/ NbC and so no further C available for IGC attack/

Thanks & Regards

J.Gerald Jayakumar

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[james gerald]

Just to add, the purpose of this HT is to form stable TiC & NbC and hence the name stabilization HT

Thanks & Regards

J.Gerald Jayakumar

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[james gerald]

Mainly avoids WELD DECAY.

Thanks & Regards

J.Gerald Jayakumar

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[Kannayeram Gnanapandithan]

Is Zr is stabilize element, of so, what is classification of ASS. 

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[james gerald]

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[james gerald]

chromium depletion in the surrounding area. Corrosion is therefore limited to zones where niobium carbide has been re-dissolved, i.e. zones in the immedi ate vicinity of the weld. These zones are rather narrow and this type of inter granular corrosion attack is thus called knife line corrosion. Its appears only in stabilized aus tenitic materials in both the HAZ of the base metal and the HAZ of the weld metal in multi-layer welds or where there are two or more parallel weld deposits. Fig. 88 shows the appearence of some typical welded joints where intergranular corrosion has taken place according to Schabereiter [253]. After welding, these specimens were annealed in the temperature range of550-600° C and then subject ed to the Strauss test. In the unstabilized, corrosion susceptible materials (upper micrographs), intergranular corrosion attack occurs over the whole area of the weld metal (Fig. 88a) and the base metal (Fig. 88b). The specimens were taken from the top run of a single V but weld of 20 mm thickness. Intergranular corrosion attack is only visible in the deformed part of the bent specimen, where the area attacked by intergranular corrosion has opened up. In niobium stabilized weld metal (ratio of stabilization- % Nb : % C = approx. 10 : 1), intergranular knife line corrosion Fig. 88. Different types of intergranular corrosion in weldments after prolonged annealing in the temperature range of around 5500 C obtained in the Strauss test according to Schabereiter [253]. Upper micrographs-Unstabilized chromium-nickel steels of the type AISI 308; a inter granular corrosion in the IC prone weld metal, b intergranular corrosion in the heat affected zone of the IC prone base metal. Lower micrographs-Niobium stabilized chromium-nickel steel of type AISI 347. c knife line corrosion in the heat affected zone between the three beads of the top layer ofintergra.nular corrosion prone weld metal, d knife line corrosion in the HAZ of the intergranular corrosion prone base metal gerr...@yahoo.com 4.1 Carbide Precipitations in Stainless Steels 123 appears in the heat affected zone between the three beads of the top layer of the weld (Fig. 88c). The bead in the middle which had been deposited last, produced knife line corrosion in the heat affected zone ofthe previously deposited outer beads of the top layer. If the weld metal is sufficiently resistant to intergranular corrosion attack, but the base metal is not, corrosive attack will be limited to the heat affected zone of the base metal on both sides of the weld (Fig. 88d). The occurrence of knife line corrosion in the HAZ after annealing in the temperature range of 500-700° C can be avoided by lowering the carbon content to below 0.04% with a simultaneous overstabilization to at least one and a halftimes the normal stabilization ratio (with titanium> 8 X % C, with niobium> 15 X % C). Heat treatments of 10-15 hours in the temperature range of 500-600° C are most critical. If annealing takes place at higher temperatures, a smaller degree of over stabilization will normally be suffice since re-diffusion of chromium in the depleted zones is already apparent in such cases. Fig. 89 shows the areas of grain decay caused by intergranular corrosion in austenitic weld metal with different chromium contents and varying stabi lization ratios which clearly shows the influence of alloying elements. The behav iour of stabilized austenitic weld metal is mainly governed by the combined effect of the three elements carbon, niobium and chromium which are interdependent with regard to their effect on knife line corrosion. An additional factor to be consid ered in this context is the fact that niobium contents above 1% will increase the hot cracking sensitivity and chromium contents above 20% will increase the tendency towards sigma phase precipitation. Therefore, an increase in these two elements is limited and for a change in content we must always consider the overall property requirement of the weld metal. mOr-----,------,------.------, 500~----~------~----~~--=-~~ 0,1 Time in hours Fig. 89. TTC diagram of the beginning of inter granular corrosion attack with consideration to knife line corrosion in austenitic weld metals with different contents of chromium and nio bium. Chemical composition in %: No.1: C= 0.027, Si= 0.63, Mn= 1.55, Cr= 17.97, Ni= 9.00, Nb = -; No.2: C= 0.027, Si = 0.74, Mn = 1.71, Cr= 20.07, Ni = 10.02, Nb = -; No.3: C = 0.033, Si = 0.70, Mn = 1.75, Cr = 21.20, Ni = 11.08, Nb = 0.30; No.4: C = 0.035, Si = 0.85, Mn=1.58, Cr=17.98, Ni=8.97, Nb=0.55; No.5: C=0.031, Si=0.62, Mn=1.78, Cr = 19.96, Ni = 10.14, Nb = 0.65

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