ASTM_DS50-1973.pdf

EVALUATION OF THE ELEVATED TEMPERATURE TENSILE AND CREEP-RUPTURE PROPERTIES OF aCr-fcMo,ICr-Mo,and lfcCr-a Mo-Si STEELS Prepared for the METALS PROPERTIES COUNCIL by G.V.Smith ASTM DATA SERIES PUBLICATION DS 50 List price$8.25 05-050000-02 2).All of the data,including those from references 1 and 2,are identified in Table I as to ASTM speci-fication number,deoxidation practice,heat treat-ment,product form and size,grain size,and data source,in so far as these are known;the chemical compositions of the steels,other than those included in references 1 and 2,are given in Table II.Data representing the different product forms,plate,pipe,tube,bar and casting are included.No additional data for weld metal or weldments were received;the relatively few weld metal and weld joint data previously reported in reference 18 have not warranted evaluation.The tabular data as well as the evaluations for the three grades of steel considered in this report have been grouped separately,as follows:Part 1:1/2 Cr-1/2 Mo Steels Part 2:1 Cr-1/2 Mo Steels Part 3:1 1/4 Cr-1/2 Mo-Si Steels In evaluating the data of each Part,a dis-tinction is made in the early stages of the evaluation as to product form,but in the final stage of developing trend curves for the dependence of strength upon temperature for the individual steel grades,the similarity in results makes it seem appropriate to treat the data for different product forms as from single data populations.The properties that have been evaluated in this report are yield strength,tensile strength,creep strength and rupture strength.Elongation and reduction of area at fracture also are included in the report for both the tensile and rupture tests,when available.Yield Strength,Tensile Strength,Elongation and Reduction of Area The original tensile test results except for those previously reported in references 1 and 2 are tabulated in Table III.The tests weTe pre-sumed to have been conducted generally at strain rates within the limits stipulated in ASTM Recom-mended Practice E21,and the yield strengths to represent either 0.2%offset or the lower yield point.Unless otherwise noted,elongation at fracture was determined over a 2 inch gage length,and plate test specimens were taken from the quarter thickness position,as prescribed by ASTM Standard Specification A-20.Many of the reported results represent the average of duplicate tests.The yield and tensile strength data have been evaluated employing a normalizing procedure that has proved useful in prior evaluations(e.g.,see references 19-20).By this procedure,the ele-vated temperature yield and tensile strengths of individual heats are ratioed to the room tempera-ture yield and tensile strengths of the same lots.Then,by the method of least squares,the best fit curve is established for each set of such ratios to provide trend curves in ratio form defining the variation of strength with temperature.By means of the ratio trend curve,it is possible to compute strength-temperature trend curve for any specific room temperature strength level of interest,within the limits encompassed by the original data.Of most general interest is the curve corresponding to(or anchored to)the minimum strength specified in a procurement specification;such a curve may be expected to define the lower bound of values appropriate to that particular specified minimum strength at room temperature.The tensile test results for the different grades are plotted as dependent on temperature in Figs.4-6.In each plot,data representing the various product forms are differentiated.Part 1:1/2 Cr-1/2 Mo steels,Figs.4a,b,c The yield strength and yield strength ratio results are plotted in Fig.4a,the tensile strength and tensile strength ratio results are plotted in Fig.4b,and the elongation and reduction of area results are plotted in Fig.4c.The number of test results are relatively few,certainly as compared to the other two grades of this report,and inadequate to warrant attempting a differenti-ation amongst product forms.The ratioed yield and tensile strength data were evaluated by the method of least squares and the resulting best fit trend curves have been drawn on the plots,and included in Table Va.The tensile strength ratio trend curve falls immediately above room temperature and then rises to a peak at 500-600F before again trending to lower values.The rise at intermediate temperatures,also commonly observed in carbon and other low alloy ferritic steels,is attributable to dynamic strain aging.(21)Dynamic strain aging is also manifested in the minima in elongation and reduction of area in the same temperature range as that in which the tensile strength passes through its maximum,Fig.4c.Part 2:1 Cr-1/2 Mo steels,Figs.5a,b,c There were many more data available for this grade than for 1/2 Cr-1/2 Mo.The normalization procedure was quite effective in minimizing scatter for tensile strength,Fig.5b,but relatively inef-fective for yield strength,Fig.5a.The scatter in yield strength v