ASME STP-PT-075-2015 Effect of Thickness on the Transformation Behavior of Grade 91 Steel.pdf

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1、Effect of Thickness on the Transformation Behavior of Grade 91 SteelSTP-PT-075STP-PT-075 EFFECT OF THICKNESS ON THE TRANSFORMATION BEHAVIOR OF GRADE 91 STEEL Prepared by: Domenic Canonico Canonico and Associates Date of Issuance: June 30, 2015 This report was prepared as an account of work sponsored

2、 by ASME Pressure Technology Codes Identified as “High Heat” 11 Figure 2-6: Chemical Composition of Test Bar No. 2; Identified as “Low Heat” . 12 Figure 2-7: Cooling Curves for Five Thermocouples Embedded in Jominy Bars . 13 Figure 2-8: Grade 91 CCT Diagram 2 . 13 Figure 2-9: Comparison of Cooling R

3、ates from the First Study, Which Had a Failed Thermocouple at the 3.75 in. Location and the Successful Second Test 14 Figure 2-10: 1st Run Austenitized at 1940F 14 Figure 2-11: 2nd Run Austenitized at 1940F . 15 Figure 2-12: Jominy Hardness Data for High Heat Test Bars 1-2 Austenitized (1940F) and C

4、ooled 17 Figure 2-14: Microstructure at 0.25 in. from Quenched End; Austenitized (1940F) and Tempered (1410F) 18 Figure 2-15: Microstructure at 0.75 in. from Quenched End; Austenitized (1940F) and Cooled 19 Figure 2-16: Microstructure at 0.75 in. from Quenched End; Austenitized 20 Figure 2-17: Micro

5、structure at 1.5 in. from Quenched End; Austenitized (1940F) and Cooled 21 Figure 2-18: Microstructure at 1.5 in. from Quenched End; Austenitized (1940F) and Tempered (1410F) 22 Figure 2-19: Microstructure at 2.5 in. from Quenched End; Austenitized (1940F) and Cooled 23 Figure 2-20: Microstructure a

6、t 2.5 in. from Quenched End; Austenitized (1940F) and Tempered (1410F) 24 Figure 2-21: Microstructure at 3.75 in. from Quenched End; Austenitized (1940F) and Cooled 25 Figure 2-22: Microstructure at 3.75 in. from Quenched End; Austenitized (1940F) and Tempered (1410F) 26 Figure 3-1: Oak Ridge Nation

7、al Laboratory Jominy Test, Circa 1980 4 28 Figure 3-2: Continuous Cooling Transformation Diagram for 9 Cr 1 Mo: Austenitized at 1832F . 29 STP-PT-075: Effect of Thickness on the Transformation Behavior of Grade 91 Steel iv FOREWORD This report evaluates the effect of thickness on the transformation

8、behavior of Grade 91 steel alloy to further define the materials properties. Established in 1880, the American Society of Mechanical Engineers (ASME) is a professional not-for-profit organization with more than 135,000 members and volunteers promoting the art, science and practice of mechanical and

9、multidisciplinary engineering and allied sciences. ASME develops codes and standards that enhance public safety, and provides lifelong learning and technical exchange opportunities benefiting the engineering and technology community. Visit www.asme.org for more information. ASME Standards Technology

10、, LLC (ASME ST-LLC) is a not-for-profit Limited Liability Company, with ASME as the sole member, formed in 2004 to carry out work related to new and developing technology. ASME ST-LLCs mission includes meeting the needs of industry and government by providing new standards-related products and servi

11、ces, which advance the application of emerging and newly commercialized science and technology, and providing the research and technology development needed to establish and maintain the technical relevance of codes and standards. Visit www.stllc.asme.org for more information. STP-PT-075: Effect of

12、Thickness on the Transformation Behavior of Grade 91 Steel v ABSTRACT The chemical compositions of six heats of Grade 91 steel were determined and two heats with furthest apart chemical composition were selected as test samples for the cooling rate tests and the Jominy hardness tests. A Jominy test

13、apparatus was built in accordance with ASTM A255-10 1 and successfully tested. Six Jominy bars were machined, three from each of the two heats. Thermocouples were welded at five centerline locations in radial holes drilled along the length of one bar from each heat. Jominy cooling rate determination

14、s from 1940F were made at the five locations from each heat. Jominy cooling rate determinations were essentially identical between the two instrumented bars. Two Jominy bars from each Grade 91 heat were austenitized at 1940F and subjected to the Jominy test. Hardness per ASTM A255 was made on one ba

15、r, the second bar was tempered at 1410F and then the hardness tests were made. Photomicrographs were made at the five locations in the Jominy bars where the thermocouples were located. All of the microstructures showed 100% martensite; there was no indication of transformation to a microstructure ot

16、her than martensite. STP-PT-075: Effect of Thickness on the Transformation Behavior of Grade 91 Steel 6 1 INTRODUCTION The Grade 91 alloy has been extensively studied, yet many questions still remain unanswered. The excellent elevated temperature properties of Grade 91 are dependent on the alloy ach

17、ieving a tempered martensite microstructure after it is cooled from the austenitizing temperature. It must be tempered after cooling to assure an ideal microstructure. The question of the ability of Grade 91 to achieve such a microstructure through its entire thickness continues to be a subject of d

18、iscussion. Grade 91 is a deeply hardenable alloy that should produce a martensitic when air-cooled in very thick section sizes. This project will allow the determination to what thickness such a microstructure can be assured. Based on past studies of this alloy, it should be able to achieve its maxi

19、mum hardness through the entire four (4) inch length of a Jominy bar. This research project could assist in determining what section sizes can provide a martensitic microstructure when properly heat-treated. Many of the organizations that are ASME Accredited and use Grade 91 in their fabrication pra

20、ctices will benefit from the results of this research. BPV Committee on Power Boilers (I), BPV Committee on Materials (II), and BPV Committee on Construction of Nuclear Facilities Components (III) should find this information invaluable. In particular, any organization involved in supercritical and

21、ultra-super-critical boilers could be interested in this materials data. STP-PT-075: Effect of Thickness on the Transformation Behavior of Grade 91 Steel 7 2 TEST METHODOLOGY 2.1 Coupon Tests or Jominy bar The intent of this project was to determine whether a Jominy end quench test will permit the p

22、rediction of the microstructure produced when a Grade 91 bar is cooled from its austenitizing temperature. The test plan was divided into 7 tasks. The tasks were as follows: Task 1 was to build a Jominy Test apparatus and test it. Task 2 was to adapt a Jominy bar to accommodate five chromel-alumel t

23、hermocouples (TC) and to imbed the TCs at the mid-point of the longitudinal axis of the Jominy bar. Task 3 was to select two heats of Grade 91 whose product form had section sizes from which Jominy bars could be machined. Task 4 was to measure the cooling curves at the five locations in the Jominy b

24、ar. Task 5 was to conduct the Jominy tests on two bars from each heat. Task 6 was to prepare photomicrophs from the five locations in the Jominy bar where the cooling rates were measured. 2.2 Building and Testing a Jominy Test Apparatus The first task was to build a Jominy test apparatus. This was d

25、one in accordance with ASTM A255-10 1. When the test apparatus was fabricated, an initial test was conducted to assure it was operating correctly. Figure 2-1 and Figure 2-2 represent photographs of the Jominy apparatus and the quench test. The upper photograph shows the test apparatus and a quench i

26、n progress. The bottom photograph shows the desirable conical shape of the water during the quench. This is exactly the water distribution required for an appropriate quench. Figure 2-1: Initial Test of Jominy Bar Apparatus STP-PT-075: Effect of Thickness on the Transformation Behavior of Grade 91 S

27、teel 8 Figure 2-2: Desirable Conical Shape of Water during Quench 2.3 Designing a Jominy Bar The second task was to design a Jominy bar, so it could accommodate the thermocouples required to measure the cooling rates at the five locations. The locations selected, measured from the quenched end, were

28、 0.25 in., 0.75 in., 1.5 in., 2.5 in., and 3.75 in. Photographs showing the locations in a Jominy bar are shown in Figure 2-3. Figure 2-4 shows the manner whereby the TCs were embedded in the Jominy bar. The pairs of TC holes were drilled 0.10 inches apart and 0.093 inches in diameter to a depth of

29、0.375 inches. Then the holes were extended another 0.25 inches at 0.036 inches in diameter to accommodate the TC wires. Each hole was designed to accommodate a chromel or an alumel wire. The hole diameters were selected to accommodate ceramic insulation to the 0.375 in. depth and the bare TC wire be

30、yond that depth. The TC holes were 0.10 inches apart straddling each of the five axial distances from the quenched end. The TC wires were electro-discharged welded into their respective holes. A chromel wire was welded at the bottom of one of the holes and an alumel wire was welded to the bottom of

31、the adjacent hole. This match provided the chromel-alumel thermocouple needed to measure the temperature during the Jominy quench. STP-PT-075: Effect of Thickness on the Transformation Behavior of Grade 91 Steel 9 Figure 2-3: Thermocouple Locations, 0.25 in., 1.5 in., 2.5 in., and 3.75 in. from Quen

32、ched End of Jominy Bar Figure 2-4: Individual Thermocouple (Chromel/Alumel) Embedded in Jominy Bar STP-PT-075: Effect of Thickness on the Transformation Behavior of Grade 91 Steel 10 2.4 Selecting Two Heats of Grade 91 The third task was to select two Grade 91 heats to be used for Task 4 through 6.

33、Alstoms Materials Technology Center (MTC) supplied six samples of Grade 91 alloy with six different heats. MTC conducted material test to determine the chemical composition of those six Grade 91 alloy samples. The Grade 91 alloys with the heats that had the further apart chemical composition were ch

34、osen for additional testing. Test Bar No. Heat Supplier Heat Treatment Test 1-1 High Heat Wuhan Heavy Industry Casting however, the sample bar from the Wuhan Heavy Industry Casting Identified as “High Heat” STP-PT-075: Effect of Thickness on the Transformation Behavior of Grade 91 Steel 12 Figure 2-

35、6: Chemical Composition of Test Bar No. 2; Identified as “Low Heat” 2.5 Measuring the Cooling Curves The fourth task was to measure the cooling rates at the five locations identified in the second task. The second cooling rate test is shown in Figure 2-7. There is evidence of recalescence in the 1.5

36、 in. and 3.75 in. curves. The continuous cooling transformation (CCT) diagram obtained from Vallourec time (seconds) to reach specific temperature (F) for the first cooling rate trial above and the second cooling rate trial below. STP-PT-075: Effect of Thickness on the Transformation Behavior of Gra

37、de 91 Steel 15 Temperature F Distance from Quenched End of Jominy Bar-inches Time to Temperature in Seconds 0.25 0.75 1.5 2.5 3.75 1800 12 20 20 25 27 1600 18 25 40 42 60 1400 20 40 80 77 100 1200 22 45 105 140 150 1000 23 78 142 215 220 800 35 100 193 280 320 600 44 145 260 425 560 400 95 200 400 6

38、00 720 200 170 440 660 860 970 Figure 2-11: 2nd Run Austenitized at 1940F Note: The second cooling rate trial was conducted due to the loss of the thermocouple at the 3.75 inch location. 2.6 Continuing Jominy Tests on Two Bars from Each Heat The fifth task was to conduct Jominy tests on two bars fro

39、m each heat. The hardness tests on the first bar from each heat were to be conducted on the as-cooled bar (Austenitized at 1940F and quenched). The second bar was austenitized at 1940F, end-quenched in the conventional manner, and then tempered at 1410F. The results of the hardness tests for both th

40、e as-quenched and quenched and tempered bars are shown in Figure 2-12. The slightly higher carbon content (0.102 Wt %) in the Test Bars No.1 heat (Vs the 0.092% C) in Test Bar No.2 heat is evident in the higher hardness values observed in Test Bar No.1 heat. STP-PT-075: Effect of Thickness on the Tr

41、ansformation Behavior of Grade 91 Steel 16 Figure 2-12: Jominy Hardness Data for High Heat Test Bars 1-2 Austenitized (1940F) and Cooled STP-PT-075: Effect of Thickness on the Transformation Behavior of Grade 91 Steel 18 Figure 2-14: Microstructure at 0.25 in. from Quenched End; Austenitized (1940F)

42、 and Tempered (1410F) STP-PT-075: Effect of Thickness on the Transformation Behavior of Grade 91 Steel 19 Figure 2-15: Microstructure at 0.75 in. from Quenched End; Austenitized (1940F) and Cooled STP-PT-075: Effect of Thickness on the Transformation Behavior of Grade 91 Steel 20 Figure 2-16: Micros

43、tructure at 0.75 in. from Quenched End; Austenitized STP-PT-075: Effect of Thickness on the Transformation Behavior of Grade 91 Steel 21 Figure 2-17: Microstructure at 1.5 in. from Quenched End; Austenitized (1940F) and Cooled STP-PT-075: Effect of Thickness on the Transformation Behavior of Grade 9

44、1 Steel 22 Figure 2-18: Microstructure at 1.5 in. from Quenched End; Austenitized (1940F) and Tempered (1410F) STP-PT-075: Effect of Thickness on the Transformation Behavior of Grade 91 Steel 23 Figure 2-19: Microstructure at 2.5 in. from Quenched End; Austenitized (1940F) and Cooled STP-PT-075: Eff

45、ect of Thickness on the Transformation Behavior of Grade 91 Steel 24 Figure 2-20: Microstructure at 2.5 in. from Quenched End; Austenitized (1940F) and Tempered (1410F) STP-PT-075: Effect of Thickness on the Transformation Behavior of Grade 91 Steel 25 Figure 2-21: Microstructure at 3.75 in. from Qu

46、enched End; Austenitized (1940F) and Cooled STP-PT-075: Effect of Thickness on the Transformation Behavior of Grade 91 Steel 26 Figure 2-22: Microstructure at 3.75 in. from Quenched End; Austenitized (1940F) and Tempered (1410F) STP-PT-075: Effect of Thickness on the Transformation Behavior of Grade

47、 91 Steel 27 3 DISCUSSION OF THE RESULTS In 1980, while the Modified 9 Cr-1 Mo (Grade 91) was being optimized, Oak Ridge National Laboratory (ORNL) conducted Jominy bar tests that permitted a comparison between 21/4 Cr-1 Mo and Grade 91 steel. These results are shown in Figure 3-1. The results of th

48、at study, which are shown in Figure 3-1, were included in the data package submitted to the Section I Committee for the ASME Boiler and Pressure Vessel Code (BPVC) in June 1982, when ORNL requested a Code Case for Grade 91. The cooling rates for those Jominys were not measured, nor were any metallog

49、raphic studies made of those samples. Those studies proved the extreme hardenability of the Grade 91 alloy. The Grade 91 CCT diagram shown in Figure 3-1 is quite similar to that presented for Grade 9 in the Atlas of Continuous Cooling Transformation Diagrams for Engineering Steels 3. This CCT diagram is shown in Figure 3-2. It suggests that the onset of transformation to a microstructure other than martensite will occur at an overall cooling rate of about 0.8 F per second. (Austenitizing temperature is 1832F the temperat