Welding Journal - April 2012 - (Page 18)

BRAZING Q&A Q: We are brazing high-temperature alloys together with nickel-based brazing filler metals (AMS 4777), and have had problems with parts failing in service due to cracks right through the brazed joints. The vacuum furnaces we use for brazing appear to be fine, and cross-section evaluation of the failed parts showed that joint clearances were about 0.006 in. (0.15 mm) in the joints before they cracked. Why are these joints failing in service if we’re doing our best to keep the parts really clean before and during brazing, and our vacuum brazing cycle appears to be correct according to our customer specification requirements? BY DAN KAY Fig. 1 — Variations in centerline structures in Ni-brazed joint, from extreme (right side of photo) to almost none at far left. (ASM Metal Progress magazine, Dec. 1967.) It can even occasionally happen during regular cooling from the brazing temperature when the part is first being brazed. The famous photomicrograph in Fig. 1 clearly shows how a hard centerline matrix forms along the center of the joint (since solidification moves from the edge of the base-metal/brazed-joint interface toward the center of the joint). Note that this polished sample was very smooth, with no holes, etc. Thus, the dark structure down the center of the horizontal joint is merely a smooth layer that etches to a different shade of color than the rest of the alloy in the joint. The last phases to solidify when brazing with nickel-based brazing filler metals (BFMs) will be those phases that are A: You are experiencing a problem that many brazing shops face, namely that of correctly dealing with joint-clearance issues during nickel-brazing processes. The hard, nonductile metallurgical phase-structures that form upon solidification of Ni-brazed joints must be carefully controlled, or else they can, and often do, result in cracks inside the joint during stressful service involving either mechanical or thermal cycling (or both). STAINLESS STEEL 300 SERIES Do you have to pickle or passivate stainless steel? WE CAN HELP. QWP has the products and over 30 years of experience in pickling and passivation. QWP, Inc. Introduces Metal Surface Treatments with Antox Products. The Antox Chemical Products are certified to ISO 9001. The Antox products degrease/pickle/passivate, stainless steel, aluminum and titanium. Products are available in paste, spray, bath, and electrochemical form. SOME OF OUR NEW PRODUCTS ARE: Antox 21EP Plus–Pickling Paste for stainless steel, will emit 80% less fumes than most standard pickling pastes. Excellent for confined areas. Antox 23EP Plus–Pickling Spray – same as above but in spray form, is colorized so operator can see which areas are covered. Antox 76E–Brush on or Spray on for stainless steel, aluminum and Titanium. Will degrease, pickle, and passivate. steel small areas. Antox 2001T can be shipped by UPS. P.O. Box 60467 King of Prussia, PA 19406 (610) 331-1607 Fax: (610) 783-0446 E-mail: JRC@QWPINC.NET Give us a call to discuss your application. Antox 2001T–Pickling paste that is fast and easy for stainless Warehouse Location: 730 Commercial Lane Honey Brook, PA 19344 Visit us at our web site: www.qwpinc.net For info go to www.aws.org/ad-index 18 APRIL 2012 http://www.qwpinc.net http://www.qwpinc.net http://www.aws.org/ad-index

Table of Contents for the Digital Edition of Welding Journal - April 2012

April 2012 - TOC Listing
Unlocking Your Gas Metal Arc Welding Potential - A study sponsored by the National Shipbuilding Research Program investigated low-cost modifications to equipment or parameters that improved welding performance - P. A. Blomquist
Community College Welding Program Update - Many community colleges around the country are equipping future workers with the skills manufacturers need D. Postlethwaite
Modern Power Source Technology Drives Process Improvement - New technology in weld monitoring is making it easier to access the data by all the appropriate personnel and understand how it should be applied to benefit weld quality - T. McEllis
Building a Welding Career from the Ground Up - A thirty-two-year career welder shares her passion for the profession with others in hopes of inspiring them to expand their skills and knowledge
How Today’s Power Sources Aid Pulsed GMAW - The advanced welding machines of today can deliver power to the arc in almost any form and can react with split-second timing to avoid adverse arc phenomena - L. Barley
Fiber Lasers Perform Precision Cutting for Medical Devices - There are many methods to cut thin tubular structures often used in medical devices, but fiber lasers are emerging as the precision machines of choice
Arc Characteristics in Pulsed-GMA Welding with Acute - Groove Angles The characteristics of a joint tracking sensor were monitored under conditions of different groove angles and root openings - R-H. Kim et al.
Design of Experiment and Goal Programming Application for the GMAW Process - This study was conducted to determine critical gas metal arc welding variables and ways to optimize them - Y. T. Iç et al.
Predictive and Measurement Methods for Delta Ferrite Determination in Stainless Steels - The advantages and limitations of predictive measurement methods for δ ferrite are outlined - M. A. Valiente Bermejo
Susceptibility of IN740 to HAZ Liquation Cracking and Ductility-Dip Cracking - Conditions that lead to cracking susceptibility of nickel-based IN740 were simulated to determine an action for its prevention - J. E. Ramirez
Editorial
Washington Watchword
Press Time News
News of the Industry
Aluminum Q&A
Brazing Q&A
Product & Print Spotlight
Coming Events
Certification Schedule
Welding Workbook
Society News
Interpretations D1.1
Guide to AWS Services
Personnel
Welding School Profiles
Classifieds
Advertiser Index

Welding Journal - April 2012