[MW:1122] RE: 1121] SS-CS Welding

Galv corrosion has be considered during material selection by process, it has noting to do with type 309 (its almost same either you weld with 308 or 309)

 

In joining austenitic stainless steel to carbon or low-alloy steel for service applications involving exposure to temperatures

not exceeding 370 °C (700 °F), it is good practice to use a stainless steel filler metal with a total alloy content high

enough to prevent the formation of martensite in the weld after dilution by the base metal and to preserve residual

amounts of ferrite to minimize the possibility of hot cracking resulting from welding under severe restraint. Dilution is the

change in chemical composition of a welding filler metal caused by the admixture of the base metal or previously

deposited weld metal in the deposited weld bead. It is normally measured by the percentage of base metal or previously

deposited weld metal in the weld bead.

The Schaeffler diagram is particularly useful when examining what filler metal is suitable for joining dissimilar metals.

The example in Fig. below shows the joining of a carbon steel (point A) to a type 304 austenitic stainless steel (point B) using

type 309 as the filler metal (point D). Point C shows what the composition of the weld metal would be if these items were

joined without a filler metal. If we assume that each base metal is fused to the same extent, point C will lie halfway

between A and B. Because the welding is done using type 309 filler metal, the composition of the weld metal will lie

along the line CD, depending on the degree of dilution. At point E a suitable weld metal composition is obtained, that is,

an austenitic structure with 8 to 9% ferrite (Ferrite Number). This weld metal will be crack resistant, in contrast to that

obtained at point C, which is very sensitive to cracking because of martensite formation. Types 309 and 309L (25Cr-

12Ni) filler metals are most widely used for joining carbon or low-alloy steel to austenitic stainless steel; they normally

contains about 8 to 15 FN. Types 304Cb, 309Mo, 309MoL, and 312 (29Cr-9Ni) are progressively more strongly ferritic.

Satisfactory welds are also obtained with nickel-chromium-iron filler metal and these filler metals allow the service

temperature to exceed 370 °C (700 °F) and minimize some stress relieving problems.

 

Source: ASM

 -----Original Message-----
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com]On Behalf Of renjith shankar
Sent: Tuesday, September 16, 2008 5:40 AM
To: Materials-Welding (E-mail)
Cc: Bathula Raghuram (Mumbai - PIPING)
Subject: [MW:1121] SS-CS Welding

Gents,   This is for a technical clarification. Please advice.   Sub: For SS-CS welding normally we are using 309. i.e. this weld metal will protect the parent SS & CS as a separation media, in order to avoid those 2 metals from direct contact. (Pease correct if I am wrong). As per my knowledge if SS & CS will become in direct contact means, there is a possibility of galvanic corrosion. So my doubt is whether this weld metal will act as protection media against that? (By using this 309, manufacture's mainly concentrating on its tensile strength type phenomena or giving more priority to take precaution against these type corrosion.) I would like to get metallurgical explanation   Regards Renjith

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