1、 STD-AWS PRGT-ENGL 1999 = 0784265 0539359 207 American Welding Society The Practical Reference Guide for - STDmAWS PRGT-ENGL 1997 0784265 05193b0 T2 m THE PRACTICAL REFERENCE GUIDE for WELDING TITANIUM Compiled/Edited/Writen by Eugene G. Hornberger Consultant Hampton, Virginia This publication is de
2、signed to provide information in regard to the subject matter covered. It is made available with the understanding that the publisher is not engaged in the rendering of professional advice. Reliance upon the information contained in this document should not be undertaken without an independent verif
3、ication of its application for a particular use. The publisher is not responsible for loss or damage resulting from use of this publication. This document is not a consensus standard. Users should refer to the applicable standards for their particular application. American Welding Society 550 N.W. L
4、eJeune Road, Miami, Florida 33126 STD-AUS PRGT-ENGL 1999 07842b5 0519361 965 = ACKNOWLEDGMENT The American Welding Society extends appreciation to John Monsees, Consultant, International Titanium Association, Boulder, Colorado, for both his technical review of, and advice on, this document. Photocop
5、y Rights Authorization to photocopy items for internal, personal, or educational classroom use only, or the internal, personal, or educational classroom use only of specific clients, is granted by the American Welding Society (AWS) provided that the appropriate fee is paid to the Copyright Clearance
6、 Center, 222 Rosewood Drive, Danvers, MA 01923, Tel: 978-750-8400; online: http: O 1999 by the American Welding Society. All rights reserved. Printed in the United States of America. - STDoAWS PRGT-ENGL 1999 = 0784265 0519362 8TL D TABLE OF CONTENTS Page No . Basic Safety Precautions . iv Introduct
7、ion 1 Weld Cleaning 2 Gas Shielded Arc Welding Processes 2 Welding in the Open . 3 Primary Gas Shielding 3 Secondary Gas Shielding 3 Backing Gas Shielding 4 Joint Design 5 Welding in a Chamber 4 Gas Tungsten Arc Welding . 6 Gas Metal Arc Welding . 7 Equipment 7 Welding Consumables 7 Filler Metal Tra
8、nsfer 7 Welding Conditions . 7 Plasma Arc Welding 8 Laser Beam Welding 9 Resistance Welding 9 Other Welding Processes 9 Electron Beam Welding . 9 References . 10 iii STD-AWS PRGT-ENGL 3999 I 07842b5 0539363 738 m BASIC SAFETY PRECAUTIONS Bum Protection. Molten metal, sparks, slag, and hot work surfa
9、ces are produced by welding, cutting, and allied processes. These can cause burns if precautionary measures are not used. Workers should wear protec- tive clothing made of fire-resistant material. Pant cuffs, open pockets, or other places on clothing that can catch and retain molten metal or sparks
10、should not be worn. High-top shoes or leather leggings and fire-re- sistant gloves should be worn. Pant legs should be worn over the outside of high-top shoes. Helmets or hand shields that provide protection for the face, neck, and ears, and a head covering to protect the head should be used. In add
11、ition, appropriate eye protection should be used. Electrical Hazards. Electric shock can kill. However, it can be avoided. Live electrical parts should not be touched. The manufacturers instructions and recommended safe practices should be read and understood. Faulty installation, improper grounding
12、, and incorrect operation and maintenance of electrical equipment are all sources of danger. All electrical equipment and the workpiece should be grounded. The workpiece lead is not a ground lead. It is used only to complete the welding circuit. A separate connection is required to ground the workpi
13、ece. The workpiece should not be mistaken for a ground connection. Fumes and Gases. Many welding, cutting, and allied processes produce fumes and gases which may be harmful to health. Avoid breathing the air in the fume plume directly above the arc. Do not weld in a con- fined area without a ventila
14、tion system. Use point-of-welding fume removal when welding galvanized steel, zinc, lead, cadmium, chromium, manganese, brass, or bronze. Do not weld on piping or containers that have held hazardous materials unless the containers have been inerted properly. Compressed Gas Cylinders. Keep caps on cy
15、linders when not in use. Make sure that gas cylinders are chained to a wall or other structural support. Do not weld on cylinders. Radiation. Arc welding may produce ultraviolet, infrared, or light radiation. Always wear protective cloth- ing and eye protection to protect the skin and eyes from radi
16、ation. Shield others from light radiation from your welding operation. AWS also recommends a personal copy of ”Arc Welding Safely,” “Fire Safety in Welding and Cutting,” “Safety in Welding, Cutting, and Allied Processes,” and “Standard for the Production, Processing, Handling, and Storage of Titaniu
17、m.” iv STDDAWS PRGT-ENGL 1977 = 0784265 05193b4 b74 m Introduction Titanium need not be ail that hard to weld! In industrial sectors the common opinion is that titanium alloys are difficult to weld. While it is true that titanium alloys can be embrittled by careless welding tech- niques, it is equal
18、ly true that these materials are much more weldable than their reputation sug- gests. Difficulties in welding titanium and titanium alloys originate from several basic sources. The high reactivity of titanium with other materials, poor cleaning of parts before joining, and inade- quate protection du
19、ring welding can lead to con- tamination, porosity and embrittlement of the completed joints. Titanium is one of the most common metals occur- ring in the earths crust. Particularly in North America, there is an abundance of titanium ores available for commercial exploitation. Pure tita- nium is a s
20、ilvery-colored metal that melts at approx- imately 3035F. It is as strong as steel, but half its weight with excellent corrosion resistance. Tradi- tional applications are in the aerospace and chemi- cal industries. Titanium and titanium alloys have a number of de- sirable properties and, when suita
21、bility combined, these properties make the metal the best material for a variety of service applications. These proper- ties include: Excellent fatigue resistance. Good notch toughness. Stability over a wide temperature range. Low coefficient of thermal expansion. Low thermal conductivity Outstandin
22、g corrosion characteristics for some of the most troublesome industrial chemicals. Excellent resistance to erosion and cavitation from high velocity fluid flow. No scaling below SOOOF, although discoloration of the metal may occur. Inert in electrochemical operations, when charged as an anode in an
23、electrochemical circuit. Titanium has a strong affinity for oxygen, and it forms a tight microscopic oxide film on freshly pre- pared surfaces at room temperature. Titanium tends to oxidize rapidly when heated in air above 1200F. At elevated temperatures it has the propen- sity for dissolving discre
24、te amounts of its own oxide into solution. For these reasons, the welding of titanium requires the use of protective shielding, such as an inert gas atmosphere, to prevent contam- ination and embrittlement from oxygen and nitro- gen, Titanium reacts with air to form oxides, and at elevated temperatu
25、res it will readily oxidize and discolor. The color of the welds can be used as an indication of the effectiveness of the shielding and resulting weld quality. Good shielding and cleaning will produce bright metallic, silvery welds, while the presence of straw, blue, gray, and white surface colors i
26、ndicate increasing amounts of weld contam- ination. Weld contamination is usually the result of faulty or inadequate trailing or back up shielding, excessive heat input, or too high a rate of travel when welding. Titaniums relatively low coefficients of thermal ex- pansion and conductivity minimize
27、the possibility of distortion during welding. Pure titanium is quite ductile (15 to 25% elongation), and has a relatively low ultimate tensile strength (approximately 30 ksi) at room temperature. Add- ing limited amounts of oxygen and nitrogen in solid solution will strengthen titanium markedly, but
28、 it will also embrittle the metal if present in ex- cessive quantities. The sensitivity of titanium and titanium alloys to embrittlement imposes limitations on the joining processes that may be used. Small amounts of car- bon, oxygen, nitrogen, or hydrogen impair ductility and toughness of titanium
29、joints. As little as 5000 parts per million of these elements will embrittle a weld beyond the point of usefulness. Titanium has a high affinity for these elements at elevated tem- peratures and must be shielded from normal air at- mospheres during joining. Consequently, joining processes and proced
30、ures that minimize joint con- tamination must be used. Dust, dirt, grease, finger- prints, and a wide variety of other contaminants also can lead to embrittlement and porosity when the titanium or filler metal is not properly cleaned prior to joining. When heated to joining temperatures, titanium an
31、d titanium alloys react with air and most elements and compounds, including most refractories. Therefore titanium and titanium alloys are welded with the inert gas shielded processes. See Table 1. There are basically three types of alloys distin- guished by their microstructure. AWS Practical Refere
32、nce Guide 1 STD-AWS PRGT-ENGL 1999 W Ti-0.15 02 Ti-0.20 02 Ti-0.35 02 Ti-6AI-4V Ti-0.20 02-0.2Pd Ti-3AI-2.5V Ti-6AI-4V ELI Table 1. Commonly used titanium alloys and recommended filler metals. ERTi-1 Commercially pure ERTi-2 Commercially pure ERTi-4 Commercjally pure ERTi-SELI Aircraft alloy ERTi-7
33、Commercially pure ERTi-9 Tube components ERTi-5ELI Low interstitials 1 Grade ASTM I Composition I Filler I Comments 1 23 I 25 I Ti-6AI-4V-0.06Pd I Matching I Corrosion grade I (1) Titanium. Commercially pure (98 to 99.5% Ti) or strengthened by small additions of oxygen, ni- trogen, carbon, and iron.
34、 These alloys are readily weldable. (2) Alpha Alloys. These are largely single-phase al- loys containing up to 7% aluminum and a small amount (0.3%) of oxygen, nitrogen, and carbon. The alloys are welded in the annealed condition. (3) Alpha-Beta Alloys. These have a characteristic two-phase microstr
35、ucture formed by the addition of up to 6% aluminum and varying amounts of beta- forming constituents-vanadium, chromium, and molybdenum. The alloys are readily welded in the annealed condition. Weld Cleaning Prior to welding titanium components, it is essen- tial that the weld joints and weld wire b
36、e free of mill scale, oil, grease, dirt, grinding dust, and any other contaminants. Grease and oil accumulated on titanium parts during machining and other opera- tions must be removed prior to joining to avoid contamination. Scale-free titanium often is de- greased only; titanium having an oxide sc
37、ale is de- greased prior to descaling operations. Degreasing may be accomplished in any of the following ways: Steam clean. Alkaline wash or dip in a dilute solution of so- dium hydroxide. Solvent wash with methyl ethyl ketone, methyl alcohol, toluene, acetone, or other chlorine-free solvents. Hand
38、wipe with solvent-dampened, clean lint- free cloths immediately before welding. Plastic gloves are recommended for this type of opera- tion. Reaction between solvents and some of the compounds in rubber gloves can leave deposits on the joint that can cause porosity. Light scales are formed on titani
39、um at temperatures up to about 1100F. The scale is generally thin and can be removed by chemical pickling. Pickling is normally accomplished in an aqueous solution of 2 to 4% hydroflouric acid and 30 to 40% nitric acid, followed by appropriate rinsing with deionized water and drying. Ordinary tap wa
40、ter should not be used to rinse titanium parts. Caution: Hydro- flouric acid or its solutions should not be permitted to contact the skin. It can cause serious, painful ul- cers if not washed off immediately. Joint surfaces should be cleaned at least 1 inch from the weld joint. Most sheet and plate
41、are cut either by shearing, plasma arc cutting or oxygen cutting. Torch-cut edges must be ground back to remove all traces of oxidation. Care must be taken so that the final grinding passes are light and do not generate sufficient heat to produce oxidation on the surface of the metal. Any contaminat
42、ion from grinding must be removed by filing or by a rotary carbide burr. Joint edges should be brushed using stainless steel brushes and wiped with acetone just prior to welding to rid the surface of oil, fingerprints, grease, paint, and other foreign matter from tita- nium surfaces. Chlorides and o
43、ther cleaning resi- dues on titanium can lead to stress corrosion- cracking when the components are heated above 550F. Hydrocarbon residues can result in contami- nation and embrittlement of the titanium. Hydrogen absorption by titanium alloys is gener- ally not a problem at temperatures up to 140F.
44、 However, after pickling and rinsing of the part, it should be handled with lint-free gloves during as- sembly. Oxide scale formed at temperatures above 1100F is difficult to remove chemically. Mechanical methods such as vapor blasting and grit blasting should be used for scale removal. All part han
45、dling after cleaning and before joining must be controlled. So called “white glove” opera- tions are often used to prevent contamination after careful cleaning. Cleaned parts should be joined 2 AWS Practical Reference Guide - STD=AWS PRGT-ENGL 1999 - 07842b5 05193bb 447 within a few hours or wrapped
46、 with lint-free and oil-free wrapping for storage until needed. Some re- cleaning of material that has been in storage may be required before certain joining operations. Preweld cleaning operations should be accom- plished immediately prior to welding. If grinding or sanding operations are used to c
47、lean the titanium, extreme care must be taken to prop- erly remove and store the titanium dust. Titanium is extremely flammable and becomes even more flammable as the particles become smaller (i.e., through grinding and sanding). See “Standard for the Production, Processing, Handling, and Storage or
48、 Titanium.“ 1 Gas Shielded Arc Welding Processes The gas shielded arc welding processes are well suited for joining titanium and titanium alloys, pro- vided the gas shielding arrangement adequately protects the weld area from the atmosphere. (Note: Regular welding grade of argon is not adequate; gas
49、 should have at least a -40“ dew point and less than 50 ppm impurities.) The three processes nor- mally used are gas tungsten arc, gas metal arc, and plasma arc welding. All three processes can be per- formed using manual, mechanized, semiautomatic, or automatic equipment. Manual, mechanized, and automatic welding can be performed in the open, or in an inert gas-filled chamber. Semiautomatic weld- ing is usually done in the open. Manifolds, regulators, hoses, tubing, torches, and other associated equipment must be clean, leak- free
