Mechanical Behaviour stainless steel (1).pptx

this is about mechanical behaviour of Stainless Steel , Related to MAterials Engineering

1. MECHANICAL BEHAVIOUR OF STAINLESS STEELS Dr. Santanu Ray [email protected]

2. Yield Strength for Stainless Steel is usually taken as the stress which will produce 0.2 % permanent strain ( off-set ) Typical Stress – Strain Curve Typical Stress - Strain Curve Mechanical Behaviour : measure of response to applied force Yield Strength and Tensile Strength

3. Stainless Steels do not show clearly demarked Yield Point , the change from elastic behaviour to permanent plastic deformation is not usually easy to detect. % Elongation of gauge length, or % Reduction of Area in cross section are measure of Ductility Hardness : comparative values Very Hard 62 HRC 688 BHN Hard 48 HRC 455 BHN Medium 30 HRC 286 BHN Soft 90 HRB 185 BHN YIELD POINT

4. Toughness: capacity to yield plastically, measure of energy absorbed to cause fracture DUCTILE - BRITTLE TRANSITION Impact value > 35 Joule normally indicates “ tough “ behaviour

5. Room temperature YS and UTS for annealed Austenitic Grades AISI Type 301 304 304L 305 309 S 310 S 316 316 L YS , MPa 275 290 270 262 310 310 290 290 UTS , MPa 755 580 560 585 620 655 580 560

6. COMPARATIVE STRENGTH

7. COMPARATIVE DUCTILITY

8. Response to cold working Austenitic Stainless Steels Grade % Cold Work YS , MPa UTS , MPa 301 10 % 585 1035 30 % 1035 1275 50 % 1310 1445 304 10 % 480 685 30 % 825 860 50 % 1000 1100 310 10 % 470 744 30 % 854 965 50 % 1010 1145

9. Strength increase with Temper Rolling of Temper YS , MPa UTS , MPa 1 /4 Hard 515 860 1/2 Hard 760 1035 3/4 Hard 930 1205 Full Hard 965 1275 Strength increases due to work hardening , particularly , for 301 grade with partly unstable austenite AISI 301 grade

10. High Temperature Strength : Short time and Long time Short time properties at high temperature indicate Normal properties based on tensile test conducted at high temperature Long time properties at high temperature indicate Continuous slow deformation ( CREEP ) on long holding Usually at > 500 C for > 10,000 hour

11. Short time properties : Normal tensile test at required temperature Temp °C 304 YS TS 304L YS TS 316 YS TS 316L YS TS 321 YS TS 347 YS TS 150 191 465 180 431 205 510 176 450 156 475 224 480 260 166 445 152 409 173 500 149 435 131 468 198 437 370 150 445 140 400 157 500 134 435 121 468 182 426 480 137 428 130 382 152 475 123 415 116 468 176 426 595 125 365 116 327 144 407 109 360 112 400 173 402 705 112 266 = 245 134 298 = 272 102 276 161 324 815 79 145 = 142 112 172 = 168 95 141 113 168

12. Maximum allowable stress in tension for use in Unfired Pressure Vessel Allowable stress in MPa for different temperatures Grade 150°C 260 °C 370 °C 480 °C 595 °C 705 °C 815°C 304 103 86 74 65 52 17 5 304L 90 67 59 = = = = L grades suffer higher loss of strength with temperature

13. Creep : continuous slow deformation Three stages : Primary creep : for relatively short time , creep rate decreases Secondary creep : for long time , creep rate constant Tertiary creep : for short time , creep rate increases , eventual fracture Creep stress causes specific rate of deformation in given time ( in secondary creep stage ) at a specific temperature Rupture stress causes final fracture ( covering all creep stages ) in given time at a specific temperature

14. Typical data from Creep rate - Rupture time diagram Rupture time at 734 C 250 hours at 69 MPa , 22,000 hours at 27 MPa Creep rate at 734 C For 69 MPa : 0.001 % per hour : in 10,000 hour dimension increase by 1 % For 14 MPa : 0.00002 % per hour : in 10,000 hour increase by 0.2 % Maximum permissible stress for different Creep rates of 304 grade 538 °C 648 °C 734 °C 815°C 1% creep in 10 000 hours 138 MPa 56 MPa 25 MPa 19 MPa 1% creep in 100 000 hours 76 MPa 28 MPa 12 MPa 9 MPa

15. YS and UTS for different Austenitic grades at subzero temperature Temperature , C 304 304N 310 YS , MPa UTS , MPa YS , MPa UTS , MPa YS , MPa UTS , MPa - 50 3 36 1101 495 940 392 848 - 100 41 3 1280 615 1110 466 950 - 140 51 5 1365 665 1345 557 972 - 196 60 2 1610 850 1620 671 1138 Increase of Strength at lower temperature YS increase more for grades with higher Ni , N

16. EXCELLENT DUCTILITY and TOUGHNESS even at Low Temperature for Austenitic grades % Elongation : 60 % at 30 C , 40 % at -100 C Toughness : > 165 J at 30 C , 100 J at -196 C 304 grade used for cryogenic applications , 304N preferred for higher strength Toughness gets affected due to : Temper embrittlement at 600 – 850 C ( formation of sigma phase ) 2. Sensitisation at 550 – 850 C ( formation of chromium carbides )

17. FATIGUE due to fluctuating stress cycle Fatigue cracks can initiate , propagate with increasing cycles , final failure by fracture : Stress to failure is Fatigue Strength Fatigue properties depicted in S – N curve At higher stress , failure at lower cycles A : Grades with Fatigue or Endurance Limit B : Austenitic grades with Fatigue Strength Fatigue Strength for annealed Austenitic Stainless Steels Grade Fatigue Strength ( MPa ) 301 245 304 245 316 265 321 260

18. FERRITIC STAINLESS STEELS Only minor response to work hardening , cannot be heat treated High temperature strength falls off rapidly above 450 C Low creep strength above 450 C : Not recommended for load bearing Elongation : 20 – 30 % , Fatigue strength : 310 – 330 MPa Toughness : DBTT around 0 C , not recommended for low temperature

19. YS and UTS for annealed Ferritic Stainless Steels Steel Grade YS ( MPa) UTS ( MPa) 430 345 510 446 ( scale resistant ) 345 550 409M 320 500 Temp , C 430 446 18-2 Super Ferritic 409M 200 465 580 480 420 400 395 550 450 360 600 165 240 = 160 700 89 110 = = 800 45 55 =

20. MARTENSITIC STAINLESS STEELS Heat treatment required to develop strength 1. Austenitisation for adequate time , 2. Air cooling to get martensite , 3. Tempering to get optimum strength and toughness

21. Grade Tempering Temperature C Y S , MPa UTS , MPa % Elongation Hardness Toughness J 200 1000 1310 15 41HRC 315 965 1240 15 39HRC 47 410 425 538 1035 790 1345 1000 17 20 41HRC 31HRC 47 102 648 585 758 23 97HRB 136 760 415 620 30 89HRB 200 1380 1755 10 315 1345 1725 10 420 425 1380 1755 10 48HRC 14 538 1000 1170 15 648 585 790 20 200 315 1070 1035 1415 1345 15 15 43HRC 41HRC 41 431 425 1070 1415 15 43HRC 61 538 895 1035 18 34HRC 68 648 655 860 20 24HRC 440A 440B 440C 315 315 315 1655 1860 1895 1795 1930 1965 5 2 51HRC 55HRC 57HRC 5 4 3

22. Martesitic Stainless Steels : Role of tempering Elongation and toughness increase with tempering temperature Temper embrittlement around 400 - 600 C Strength decreases above 400 C