"Preface Readers of Welding Metallurgy in their comments about previous Volumes 1 and 2 of the Third Edition have offered helpful suggestions toward betterment of future editions. All offerings from students@ engineers@ experienced welding personnel@ and educators have been carefully weighed by the author in planning this present revision. A principal aim in carrying out this work was to acquire updated information wherever available@ but input from readers prompted several changes. One change will be found in the sequence of chapters@ which now provides more logical progression from the structures and properties of metals@ through the mechanics and effects of heating for welding@ and finally to metallurgical description of typical welds in steel. Also@ the remodeled text now includes additional material of a fundamental nature to assist in developing broader@ analytical explanations for the chemical and physical events that arise in welding. The need for this assistance had been voiced by readers who are confronted with the complex technology of welding@ but who have not had exposure to chemistry and physics of the depth needed to rationalize the phenomena encountered. Relationships between fundamental features of metals and their behavior in welding are pointed out to encourage development of more complete understanding of each particular happening in welding. This kind of awareness of the factors involved and the mechanics entailed aids greatly when a decision must be made regarding the most effective measure for dealing with a given troublesome situation. Several features of the new text deserve comment. Metric practice has been employed as the principal system for dimensions and quantities because of expanding usage world-wide; however@ U.S. customary units are in parentheses following SI units throughout the text and are included in most tables and figures. The text does not include references to particular articles in periodicals@ reports@ and books that served as resources because of the great number from which information was extracted. Instead@ keywords from the International Welding Thesaurus are included in the text to guide readers to helpful literature for additional details whenever needed. Widely available computerized search services cognizant of these keywords can produce lists of relevant references@ including those published henceforth. Each chapter concludes with a short list of selected publications under the heading ""Suggested Reading."" These are recent publications that provide broader range of coverage of the area being reviewed in the chapter. Colleagues and organizations that assisted the author in collecting and preparing material for publication are so large in number that individual recognition here is not practical. The author is keenly aware of the great importance of this support. In the course of time@ sincere appreciation will be expressed to contributors individually. Two organizations provided protracted help with their staffs and their facilities. The American Welding Society gave encouragement and assistance at every possible turn@ and waited patiently for completion of the author's manuscript. Mr. Robert L. O'Brien@ Director of Technical Services@ for AWS at the time@ arranged peer reviews to verify the manuscript's technical content. Mrs. Debbie Givens@ Publishing Coordinator for AWS@ deserves a note of appreciation for her diligence in arranging reproduction of the many line drawings of figures and graphs. A bright spot in the lengthy publishing procedure was the engaging of Mr. Alexander M. Saitta by AWS as Production Editor to handle editing and formatting of this substantially larger edition of Volume I. Alex@ a newcomer to the welding field@ quickly demonstrated ability to fuse his language knowledge with the idiom of welding technology. In providing assistance on shortening the manuscript@ Alex proposed the inclusion of ""Technical Briefs"" to avoid deletion of useful fundamental information ?? an effective format measure for which this author is very appreciative. The Welding Institute@ at Abington@ England@ with which the author was affiliated for many years as head of its North American Office@ was extremely generous with staff assistance@ and provided many photographs and photomicrographs for new illustrations. This new edition would have been very difficult to complete without the support received from TWI. Hopefully@ a revision of Volume II will receive similar support from the many colleagues and organizations during its preparation@ and can be issued in a fourth edition without undue delay."