I have to agree with everything mentioned, and would like to commend Chuck once again with his explanation as to why some area's are magnetic and why some are not...
I also concurr with Chuck's explanation regarding the use of E310-17 as opposed to let's say E316L however, It's not my Navy Chuck!;) It's OUR NAVY!!!;) Second to NONE - Still!!! Seriously though - from an economical & strategic perspective, I can think of three different types of problems that come to mind with respect to an excessive amount of ferrite content must be taken into account when it comes to designing with stainless steels for use on both surface & submersible naval vessels... One is Corrosion... Two is embrittlement at high temperatures... Three is the fact that the USN would have to perform alot, and I mean alot more "degaussing" than they already do in order to lower the electromagnetic signatures on both their Surface Ships & Submarines for a variety of reasons for which I will not get into because, I do'nt want to "let the horse out of the barn" so to speak! There may exist other problems but with the lousy weather outside, I can only think of three.
js55 also makes some very good points especially when it concerns the potential for variances in the FN's in the welds... Farshid, if you really want to dig more into the issue then get an Elcometer 111-7F ferrite indicator which is accurate to + or - 10% of the reading or (YES! the readings are in ferrite numbers in accordance to WRC & IIW recommendations) + or - 1FN, so long as it's properly calibrated unlike the "Coin" shaped type magnet that Farshid probably used...
Anywho, check out this interesting article on shot peening with respect to minimizing SCC in 300 grades of stainless steel:
http://www.shotpeening.org/ICSP/icsp-1-54.pdfNotes on Ferrite Numbers & Calibration from Elcometer Inspection Equipment...
"After much testing around the world, it has been decided that it is impossible to determine accurately the true ferrite content of stainless steel weld metals. Previous figures of percentage content were very dependent on their source, the measuring instrument used ands its calibration. So Ferrite Numbers were established to define ferrite quantity and are related to the ferrite quantity of an equivalently magnetic weld metal."
"The calibration of a gauge is such that the ferrite reading can be related to the seperation of the gauge's magnet from low carbon mild steel plate. The primary standard is thickness and the secondary standard is ferrite samples, and the Calibration Certificate supplied with the Elcometer 111-7F relates the gauge reading to both standards." ANSI/AWS A4.2-97, ("Standard Procedures for Calibrating Magnetic Instruments to Measure the Delta Ferrite Content of Austenitic and Duplex Austenitic-Ferritic Stainless Steel Weld Metal.") is the standard used to calibrate in order to maintain traceability to internationally recognized secondary standards.
Here's an interesting article that farshid might want to review:
http://www.egmrs.org/EJS/PDF/vo291/151.pdfThen there is an alternative to the Elcometer 111-7F...
Here's the webpage & .pdf on the Fischer "Feritscope" MP30E which is convenient because it shows readings in both percentage of ferrite or in FN's starting from 0.1 to about 90FN:
http://www.helmut-fischer.com/ProductDetail.asp?PN=603-712http://www.helmut-fischer.com/globalfiles/DE_Ferit_MP30E_0605_EN.pdfThen of course like js55 mentioned, there are the "Money is no object" methods of Positive Material Identification instruments which include: 1.The "XMET 3000TX" Portable Alloy Analyzer from Metorex (Finland), Metal Master 2000, Model 898 Alloy Analyzer from NITON and Model XMET3000 from Metorex. These analyzers can analyze alloying elements in Carbon Steel, Alloy Steel or Stainless Steel, Tool Steels, Ni Alloys, Cobalt Alloys and Copper Alloys. The elements that can be analyzed are Cr, Ni, Mo, Mn, Fe, Ti, Nb, Zn, Cu, Co, W, V, Sn, Pb, Ta, etc. The identification is done on basis of major alloying elements only and grade of material is reported by our inspection engineer. Please note that this instrument will not analyze elements like C, S, P, Si, Al, B etc and hence material like 316L and 316 can not be segregated by these instruments. Here's an article in AWS "Inspection Trends" that covers X-ray Fluorescence FP-XRF analyzers:
http://www.niton.com/documents/inspectiontrendsarticle0104.pdfHere's another one that talks specifically about stainless steel PMI:
http://www.niton.com/documents/cnxstainless.pdfHere's a "nifty" Niton XLi/XLp 800 Series alloy analyzer specifically designed for in service PMI applications:
http://www.niton.com/Content/alloy_analysis/alloy_inservice.aspHere's the "XMET 3000TX:
http://www.oxford-instruments.co.uk/wps/wcm/connect/Oxford+Instruments/Products/X-ray+Fluorescence/X-MET3000TX+in+Metal+Recycling/X-MET3000TX+in+Metal+Recyclinghttp://www.oxford-instruments.co.uk/wps/wcm/resources/file/eb6a410811a4b6a/X-MET3000TX_Scrap_brochure.pdf2.The "ARC-MET 8000" MobileLab Portable Spectrometer
This portable spectrometer is ideal for PMI and can determine all elements in Carbon Steel, Alloy Steel & Stainless Steel. It can be used to analyze Ferrous and Non Ferrous materials including Nickel, Cobalt Aluminum and Copper base alloys along with Carbon. Low Alloy and Stainless Steels. Separate calibration will be provided for each matrix. Thus this is a very precise instrument and is used in lab as well as field operations. It uses Argon Gas for Ferrous samples where determination of elements like C, S, P and Si is essential to determine exact grade. It can analyze elements including Fe, C, Si, Mn, Cr, Mo, Ni, Al, Co, Cu, Nb, Ti, V, W, Pb, and Zr.
ARC-MET8000 MobileLab Optical Emission analyser is designed to identify all the key elements in metals - especially where highest accuracy and/or the analysis of light elements like C, Al, S, P, Mg, Si is needed and when sorting low alloys and aluminums. Ideal, for example, for separation of 316 H (>0.04% C) and 316 L (<0.03% C). Use one unit throughout the whole production cycle! Classification of raw material (recycling metal), QC of semimanufactured products, QC of final product.
Recognizing that carbon analysis in steels is of primary concern in many material verification functions, and e.g. in welding work, ARC-MET8000 has the unique capability of measuring carbon in both air and argon modes. ARC-MET8000 offers: Accurate results using Air or Argon measurements,
Fast grade identification and assay,Only one probe with an integrated display
Low level carbon analysis using Air burn in a few seconds,Battery operation,
long cable between main unit and probe, and convenient mobility
Unique to ARC-MET8000: the probe is the heart of the system. Ideal for ferrous and non-ferrous metals:
Low alloy steels, Stainless steels, Tool steels, Low alloy (white) cast iron, Aluminum alloys, Titanium alloys, Nickel alloys, Cobalt alloys, Copper alloys, Zinc alloys, Magnesium alloys... Other metals can also be added.
Reference: Oxford Instruments:
http://www.oxinst.com/wps/wcm/connect/Oxford+Instruments/Products/Optical+Emission+Spectroscopy/ARC-MET8000/ARC-MET8000http://www.oxinst.com/wps/wcm/resources/file/eb2dc70735e235f/ARC-MET8000_brochure_June_2005.pdfSo now that you've got a sampling of the methods currently used in determining weld metal alloy verification specifically involving the stainless steel grades, I hope you choose the method best suited for your needs... Btw, you can rent some of the equipment described above as an option to purchasing the equipment outright. If you want to know where? Do a google search!
Respectfully,
Henry