1、Guide to WeldabilityCarbon and Low Alloy Steels550 N.W. LeJeune Road, Miami, FloridaGUIDE TO WELDABILITY:CARBON andLOW ALLOY STEELSHow to get the needed resultsand stay out of troubleWritten byFritz Saenger, Jr., P.E., IWEThis publication is designed to provide information in regard to the subject m
2、atter covered. It is made availablewith the understanding that the publisher is not engaged in the rendering of professional advice. Reliance uponthe information contained in this document should not be undertaken without an independent verification ofits application for a particular use. The publis
3、her is not responsible for loss or damage resulting from use of thispublication. This document is not a consensus standard. Users should refer to the applicable standards for theirparticular application.iiPhotocopy RightsAuthorization to photocopy items for internal, personal, or educational classro
4、om 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 Center, 222 Rosewood Drive,Danvers, MA 01923, Tel: 978-750-8400; online: http:/.ISBN: 0-8
5、7171-000-5 2005 by the American Welding Society. All rights reserved.Printed in the United States of America.Cover photomicrographs courtesy of the AWS Welding Journal, and welding a structure with the SMAWprocess photograph courtesy of the AWS Welding Handbook, Vol. 2, 8th Edition, “Welding Process
6、es.”INTRODUCTIONACKNOWLEDGMENTSMost of the information in this reference guide is condensed from information in the current edition of TheWelding Handbook and Welding Metallurgy, Linnert Volume 1, both published by The American WeldingSociety. Additional sources include AWS D1.1/D1.1M:2004, Structur
7、al Welding CodeSteel, Jeffersons Weld-ing Encyclopedia, 18th Edition, The Lincoln Electric Company Procedure Handbook of Arc Welding, and theASM Handbook, Volume VI.You are responsible for the operation of an independent fabricationshop, a similar facility within a manufacturing organization, or ama
8、intenance facility in a factory of any type. “Things” are broughtto you to fabricate or repair. This guide is intended to help youask the right questions, and from the answers, select the method,materials, and procedures that will produce the result desired fromyour “customer,” or direct you to more
9、 comprehensive guidance thatmay be needed to produce the desired results.iiiTABLE OF CONTENTSPage No.CHAPTER 1The Questions (you need to ask) 1What is the product and how will it be used?1What is the material?1What specifications or codes apply to the welding rods or electrodes (wires), and to thefi
10、nished product, if any?1Are there welding procedure requirements? Make sure you understand what is required! .1What are the postweld requirements?.1CHAPTER 2Key Background Information3What is Steel?.3Why is Steel a Unique Structural Material?3Common Steels You May Encounter .6What if no information
11、or identification is available?.6Properties of SteelWhat the “Numbers” Mean 6Some Additional Important Terms 6Alloying Elements in Steels.11WeldabilityWhat is it?14CHAPTER 3What Happens When You Weld .19Where Does the Welding Heat Go? .19The Weld Zones 19Shrinkage, Residual Stresses, and Distortion
12、.20Restraint, Preheat and Interpass Temperatures, and Hydrogen Control.21Other Effects of Welding .22CHAPTER 4Selection of Proper Welding Filler Metal (Rods, Electrodes, etc.) .29CHAPTER 5Metallurgically-Related Weld Discontinuities (Defects) and Typical Causes31Cracking .31Porosity.31Inclusions .34
13、CHAPTER 6Weld Examination and Testing.35The Weld Cross Section .35Mechanical TestsWhat They Can Tell You .35CHAPTER 7Postweld Treatments.39CHAPTER 8Good Practice Reminders.41A Basic Welding Procedure Worksheet 41A Qualified Procedure Should be Used by a Qualified Welder 41CHAPTER 9Additional Informa
14、tion and Guidance .43APPENDIX 1Alternative Methods for Determining Preheat (and Preventing Cracking).45APPENDIX 2Additional Filler Metal Recommendations 51ivLIST OF TABLESTable Page No.2.1 Composition and Strength Requirements of Typical ASTM Carbon Steels.72.2 Typical SAEAISI Compositions 82.3 ASTM
15、 Specifications for High-Strength Low-Alloy Structural Steels 92.4 ASTM Specifications for High-Strength Low-Alloy Steels for Pressure-Vessel Plate 102.5 Composition of Selected Heat-Treatable Low-Alloy (HTLA) Steel112.6 Properties for Steel and/or Welds122.7 Effects of Common Alloying Elements at L
16、evels Used in Carbon and Low-Alloy Steels .122.8 Carbon Equivalent of Some Steels from Tables 2.12.5.173.1 Prequalified Minimum Preheat and Interpass Temperature .233.2 Minimum Preheat and Interpass Temperature for Three Levels of Restraint .264.1 Recommended Base Metal-Filler Metal Combinations for
17、 Matching ElectrodeTensile Strengths Nominally of 70 ksi (483 MPa) Minimum305.1 Common Causes and Potential Solutions to Cracking335.2 Common Causes of and Remedies for Porosity .33A2.1 Recommended Base MetalFiller Metal Combinations for Matching ElectrodeTensile Strengths Nominally of 8090 ksi (552
18、620 MPa) Minimum51A2.2 Recommended Base MetalFiller Metal Combinations for Steels with TensileStrengths Nominally of 100 ksi (689 MPa) Minimum .52A2.3 Suggested Welding Filler Metals for Exposed Applications of ASTM A 242 and A 588 Steels 53vLIST OF FIGURESFigure Page No.2.1 Structural changes in lo
19、w carbon steel weld metal on cooling from liquid .42.2 Pattern of dendritic growth from a crystal during solidification.42.3 Grain size and shape in solidified metal are determined by the manner in whichthe branches of dendrites meet .52.4 Weld cross section showing grains.52.5 Schematic illustratio
20、n of (A) Substitutional and (B) Interstitial solid solutions 52.7 Typical tensile specimens: (A) Rectangular and (B) Round132.8 Typical tensile test specimen before and after testing to failure, showing maximumelongation.132.9 Stress/strain diagram for complete history of a metal tension test specim
21、en from thestart of loading and carried to the breaking point .142.10 Charpy V-notch impact specimen 153.1 Schematic showing the different discrete regions present in a single-pass weld193.2 Effect of weld geometry and relative plate thickness on heat flow characteristics.203.3 Multi-pass weld in C-
22、Mn steel plate 1-1/2 in. (40 mm) thick showingpositions of individual weld beads and their heat-affected zones lying both inweld metal and in base metal203.4 Longitudinal shrinkage in a butt joint (distribution of longitudinal residual stress, sx,is also shown).213.5 Types of distortion 225.1 Crack
23、types of weld related cracking.326.1 Specimen and test orientation of the guided bend test .366.2 Schematic illustration of typical guided bend test fixtures.366.3 Typical tension test specimens for the evaluation of welded joints 378.1 Basic Welding Procedure Worksheet.42viBASIC SAFETY PRECAUTIONSB
24、urn Protection. Molten metal, sparks, slag, and hot work surfaces are produced by welding, cutting, andallied 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 o
25、n clothing that cancatch and retain molten metal or sparks should not be worn. High-top shoes or leather leggings and fire-resistant gloves should be worn. Pant legs should be worn over the outside of high-top shoes. Helmets orhand shields that provide protection for the face, neck, and ears, and a
26、head covering to protect the headshould be used. In addition, appropriate eye protection should be used.Electrical Hazards. Electric shock can kill. However, it can be avoided. Live electrical parts should not betouched. The manufacturers instructions and recommended safe practices should be read an
27、d understood.Faulty installation, improper grounding, and incorrect operation and maintenance of electrical equipmentare all sources of danger.All electrical equipment and the workpiece should be grounded. The workpiece lead is not a ground lead. Itis used only to complete the welding circuit. A sep
28、arate connection is required to ground the workpiece. Theworkpiece should not be mistaken for a ground connection.Fumes and Gases. Many welding, cutting, and allied processes produce fumes and gases which may beharmful to health. Avoid breathing the air in the fume plume directly above the arc. Do n
29、ot weld in a con-fined area without a ventilation 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 haveheld hazardous materials unless the containers have been inerted properly
30、.Compressed Gas Cylinders. Keep caps on cylinders when not in use. Make sure that gas cylinders arechained 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
31、 to protect the skin and eyes from radiation. Shield others from light radiation fromyour welding operation.The use of filtering masks or airline respirators will be required if it is determined that personnel are beingexposed to excessive pollutants.Additional information on welding safety may be o
32、btained from the American Welding Society, 550 N.W.LeJeune Road, Miami, FL 33126. ANSI Z49.1, Safety in Welding, Cutting, and Allied Processes, and theAWS Safety and Health Fact Sheets are available online and free of charge on the AWS website:http:/www.aws.org/technical/facts/.Carbon and Low Alloy
33、SteelsAWS Guide to Weldability 1CHAPTER 1The Questions (you need to ask)What is the product and how will it be used?In other words, what does the product do? Is theweld a simple connection that bears a light static(non-fluctuating) load, or are the welds subject tohighly fluctuating loads so that a
34、small defect couldgrow into a crack and cause a catastrophic failure?Will it be subjected to low temperatures, e.g., win-ters in the north where temperatures well below0F can be encountered? (Some steels become brittleat such temperatures.)What is the material?Find out what specification is used to
35、purchase thesteel. Some of the more common types of steel arediscussed in Chapter 2. If there is no specification, askif the material is “plain carbon steel” or “mild steel,”or (at the other extreme) “tool steel.” In most cases,the former materials are relatively easy to weld andsomewhat “forgiving.
36、” The latter materials requireextreme care if they are to be welded satisfactorily.There are some simple tests to help determine thegeneral class of material that you have, but there isno substitute for the actual composition or the pur-chasing specification.What specifications or codes apply to the
37、 welding rods or electrodes (wires), and to the finished product, if any?Most general fabrication is covered by agreementbetween the customer and the fabricator, with ap-plicable specifications on drawings and relatednotes. However, you need to know if the work iscovered by a code or specification t
38、hat has legalstanding and/or requires approval of a third party,which may require qualification of procedures, op-erators, materials, or other factors. Examples are theAWS D1.1/D1.1M:2004, Structural Welding CodeSteel, the American Society of Mechanical Engineers(ASME) Pressure Vessel Code, various
39、U.S. MilitaryStandards, and others. If you see reference to suchcodes and standards on drawings, notes, or specifi-cations, you and your customer need to reach anagreement on how these requirements will be han-dled. Certification, qualification, or conformance tosuch “third party” requirements is co
40、vered in detailby each code, and is outside the scope of this guide.Are there welding procedure requirements? Make sure you understand what is required!Your customer may require the use of: a specific welding process, a specific welding material (type and perhapseven the brand or manufacturer), a sp
41、ecific range of welding conditions, “qualified” welding operators (qualified by whomand to what standard?), a written welding procedure subject to the cus-tomers approval.NOTE: Even if your customer does not require a formalprocedure, you should consider preparing one. Then, testyour operators to en
42、sure that they can produce satisfac-tory welds using the procedure. A sample form for pre-paring an internal record or “control document” isincluded in Part 8 of this guide. Such a record has manybenefits, especially if the job is to be repeated. The controldocument can be particularly useful if the
43、re are problemswith the finished product on inspection or in service.What are the postweld requirements?Postweld requirements are as follows: Specific inspection and/or testing of the finishedproduct, A specific post-weld heat treatment, e.g., stressrelief, Painting, plating, or other surface treatm
44、ent.2 AWS Guide to WeldabilityCarbon and Low Alloy SteelsNOTESCarbon and Low Alloy SteelsAWS Guide to Weldability 3CHAPTER 2Key Background InformationWhat is Steel?Steel is by far the worlds most widely used struc-tural material, largely because it is relatively inex-pensive to produce. Steel also c
45、an be modified toperform in a wide variety of applications by theaddition of small amounts of other materials, calledalloying, and by a wide range of heat treatments andmechanical treatments, e.g., hot and cold rolling.The steels covered by this guide contain more than90% iron (Fe), iron that is usu
46、ally produced bysmelting iron ore in blast furnaces or the melting ofsteel scrap. The iron produced has a high level ofcarbon (C), typically as much as 3%, and if pouredinto a mold it will solidify into cast iron. Cast iron isstill widely used for machine bases, engine blocks,and other applications
47、where its ability both to ab-sorb vibration and to provide dimensional stabilityare valuable characteristics. However, because of itsstructure, cast iron cannot be rolled into thin sec-tions, is difficult to weld, and is unable to handlebending stressesall of which limit its use. Con-verting this ir
48、on into steel by processes that reducethe carbon content well below 1% and allow theintroduction of small amounts of other elements,results in a wide range of materials that are thebasis for most of the steel products we use today.Why is Steel a Unique Structural Material?Steel is uniquely valuable
49、because of phase transfor-mationa fundamental characteristic of iron that isfound in only a few other metals (most of which arenot suitable for general use). All metals in solidstate have a distinct crystal structure, i.e., the ar-rangement of the atoms of the metal and any otherelements that may be present. Iron is different be-cause its crystal structure changes as it is heatedand cooled. These changes in crystal structure,along with the resulting changes in mechanicalproperties (e.g., strength, ductility, and toughness),can be greatly
