1、 ELEVATED TEMPERATURE STATIC PROPERTIES OF WROUGHT CARBON STEEL!Prepared for the Metal Properties Council by G.V.Smith ASTM SPECIAL TECHNICAL PUBLICATION 503 List price$3.00 04-503000-40 AMERICAN SOCIETY FOR TESTING AND MATERIALS 1916 Race Street,Philadelphia,Pa.19103 BY AMERICAN SOCIETY FOR TESTING
2、 AND MATERIALS 1972 Library of Congress Catalog Card Number:74-185538 NOTE The Society is not responsible,as a body,for the statements and opinions advanced in this publication.Printed in Alpha,NJ.IVIarcli 1972 Introduction In terms of tonnage,carbon steel is the most important material employed in
3、boiler and pressure vessel service.This material,limited in the present context to less than 0.35%carbon,may be referred to as simple carbon steel,as it some-times is,only in a facetious sense,and,in fact,it exhibits complexities of behavior that match those of alloy steels.Carbon steel is employed
4、in a wide variety of applications,and although some progress towards simplifying the specification picture has been made in recent years,the 1968 edition of the ASME Boiler and Pressure Vessel Code still lists a total of 32 individual specifications pertaining to carbon steel and many of the specifi
5、-cations provide for several grades.(Many engineers believe that the multiplicity of specifications for steel is unwarranted.)Carbon steel is employed at temperatures ranging from below room temperature to as high as 1000F in ASME Code applications,and even higher in non-code applications.Consequent
6、ly,in establishing allowable stresses,not only are con-ventional short-time tensile properties required,but also the creep and rupture properties.In some applications,fracture toughness,in the sense of transition at ambient temperature,and/or fatigue strength may be of interest,but these latter prop
7、erties are beyond the scope of the present review.In this review,consideration will be given to the effects of small quantities of certain alloying elements,e.g.molybdenum and niobium,which by narrow definition would not normally be viewed as present in carbon steel.And,we shall restrict our interes
8、t almost entirely to the ferrite-pearlite microstructural condition;in principle,it is possible to develop other microstructural condi-tions,though in practice,the cooling rates that would be required cannot be achieved except in sections generally less than those of practical concern.From investiga
9、tions carried out over many years,we know that the elevated temperature properties of carbon steel may be sensitively affected by a number of variables,including chemi-cal composition,deoxidation practice and process-ing.Nevertheless,when the data available from tests of materials of commercial manu
10、facture are examined,as for example,in a recently published report on carbon steeltJ prepared by The Metal Properties Council(MPC),it becomes difficult or impossible to discern these individual effects.Information concerning some of the variables now thought to be important may be lacking,and always
11、 there is an uncontrolled,simultaneous variation of different factors.And,the problem of iso-lating the effects of individual variables is compounded by the large inherent scatter in behavior even amongst nominally identical lots.An important consequence of the sensitive dependence of elevated tempe
12、rature strength upon manufacturing variables is that the scatter band of strength is very wide;this,in turn,is reflected in the level of working stresses per-mitted,which must recognize not only this scatter,but more importantly,the minimum of the scatter band.If the individual variables could be id
13、enti-fied and their importance assessed,it should be possible,in principle,to prepare tighter*Consulting Engineer,Ithaca,New York.specifications leading to a reduction in the scatter and to an increase in the minimum expected level.Because it has not been possible to achieve this goal by study of th
14、e available test results,MPC is giving consideration to planning a statisti-cal-design test program for this purpose.A necessary first step is to put in proper per-spective what is already known;this review endeavors to perform such a service.In reviewing the properties and behavior of carbon steel
15、at elevated temperatures,it is con-venient to consider independently yield and tensile strength on one hand,and creep and rupture strength on the other.A third section considers ductility and toughness at temperature.Yield and Tensile Strengths Establishing Allowable Stresses Before giving considera
16、tion to the factors affecting yield and tensile strength at elevated temperatures,it may be of value to note how these properties are employed in setting allowable stresses at temperatures below that level at which creep becomes important.In the ASME Code,the maximum allowable stress is the least of the following properties,each multiplied by a fraction which may differ amongst the different Sections of the Code:1)specified minimum yield strength at room temperature 2)specified minimum tensile s
