Re: [MW:31335] Effect of high delta ferrite FN number (12-13) on welding of SS 304 L material

I suppose Karthik's explanation is how to reduce the Delta Ferrite within the Limits.

My views as below.

1. The first phase to form from the Liquid metal say at temperature of 1400-1495 degC is Delta ferrite and which upon cooling will transform to secondary Austenite. To have the delta ferrite increased it is always preferable to have low Heat Input which results in Faster cooling and hence more Delta ferrite. Also if the Interpass temperature is restricted to 100degC, instead of normal 175degC recommended for SS 304L it results in faster cooling and hence Delta ferrite is increased.

2. High Heat Input will increase the formation of Sigma phase as the time spent in the range of 600-900 degC is more.

3. Your achieved Ferrite in the range of 12-13FN may be an concern when you are subjected it to PWHT or operating at High temperature or very low temperatures. 

4. Effect of sigma phase can be understood by the below snap shot.

Thanks & Regards

J.Gerald Jayakumar

On Tuesday, 18 August, 2020, 08:21:15 pm GMT+7, 'karthik s' via Materials & Welding <materials-welding@googlegroups.com> wrote:

Hi, it's due to high heat input and interpass temperatures should control within 100 degree Celsius. Person should monitor each pass and record amp, interpass temperature and all wps parameters. Check your wps and pqr within the above temperature limits and actual welding parameters .

Karthik

Sent from my iPhone

On 18 Aug 2020, at 17:04, 'james gerald' via Materials & Welding <materials-welding@googlegroups.com> wrote:



Delta Ferrite in the range of 12-13 FN will affect during.

1. High temperature operation beyond 350degC

2. Since SS 304L also used at sub-zero temperatures presence of ferrite in the range 12-13 FN will affect the Impact properties

3. Results in formation of Sigma phase as it results in low notch toughness.

4. Affects the General atmospheric corrosion resistance of SS 304L

Some snap shots to support above.

<1597741832665blob.jpg>

On Tuesday, 18 August, 2020, 02:36:11 pm GMT+7, Aakash <harenathjha@gmail.com> wrote:

Hello Expert ,

please explain and also provide relevant documents  about effect of higher delta ferrite on SS 304L materials 

Regards

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