The document studies the effects of deep cryogenic treatment (CT) on tool steels, particularly AISI M2 and T42 high-speed steels, highlighting the influence of soaking time and temperature on wear resistance and microstructural changes. Key findings include improved wear resistance at optimal soaking times, increased carbide density, and the preservation of hardness uniformity, while noting that prolonged soaking (16 to 24 hours) may lead to a deterioration in wear properties. The research emphasizes the importance of soaking time and temperature in achieving desired material properties while documenting various experimental methodologies and results.

1. OPEN DEFENCE STUDY OF THE EFFECT OF DEEP CRYOGENIC TREATMENT ON TOOL STEELS BY C.L.GOGTE 27 TH JANUARY 2009 SUPERVISORS: 1.DR.R.K.PARETKAR 2.DR.D.R.PESHWE DEPARTMENT OF METALLURGICAL AND MATERIALS ENGINEERING, VISVESVARAYA NATIONAL INSTITUTE OF TECHNOLOGY, NAGPUR

2. WELCOME & GOOD MORNING!

3. CHAPTER I – INTRODUCTION CHAPTER II – HIGH SPEED STEELS CHAPTER III – LITERATURE REVIEW CHAPTER IV – CRYOGENICS & CRYOGENIC TREATMENT CHAPTER V – EXPERIMENTATION CHAPTER VI – RESULTS & DISCUSSION CHAPTER VII – CONCLUSIONS STUDY OF THE EFFECT OF DEEP CRYOGENIC TREATMENT ON TOOL STEELS

4. HIGH SPEED STEELS THE MOST IMPORTANT TOOL STEEL FAMILY CONVENTIONALLY TREATED BY HARDENING AND TEMPERING TO GET EXTREMELY HIGH HARDNESS AND CAN WITHSTAND HIGH TEMPERATURES GENERATED DURING MACHINING. WEAR RESISTANCE IS THE PROPERTY OF TOP PRIORITY

5. WITH SUBZERO………...

6. TEMP 0 C TIME HRS HARDENING (AUSTENITIZATION) TRIPLE TEMPERING CONVENTIONAL HEAT TREATMENT WITH SUBZERO COOLING OF HIGH SPEED STEELS SUBZERO COOLING TO -80 0 C TO -120 0 C, DEPENDING UPON COMPOSITION

7. CRYOGENIC TREATMENT (CT) A BRIEF INTRODUCTION CRYOGENIC TEMPERATURES < SUBZERO TEMPERATURES (~ -100 0 C) (M f ) USING DRY ICE LIQUID NITROGEN (LN 2 ) UPTO -196 0 C OR Ar OR He etc FIRST EXPERIMENTATION RESULTS ON TOOL STEELS AND OTHER METALLIC MATERIALS PRESENTED BY BARRON IN 1982 OUTCOME IMPROVED WEAR RESISTANCE

8. Influence of varied CT on the wear behavior. Concluded about existence of critical time duration for achieving best wear resistance for D2 steel through CT. Nature of precipitation of carbides during CT explained. D2 Das 45 et al, 2009 Quantification of property improvements and correlation with microstructural changes after CT. Differential contraction between matrix and the primary carbides was observed during CT. Change in the dislocation density during CT proved. M2 Kelkar 44 et al, 2007 Study of variation of tempering temperature during CT and its effect. The wear resistance was found to increase with increasing tempering temperature. M2 Leskovsek 43 et al, 2005 Investigation of fatigue life of weldments due to CT. Improvement in the fatigue life was observed. 304L Johan Singh 42 et al, 2004 Microstructural studies of changes before and after CT. Concluded that CT can facilitate formation of carbon clustering and increase the carbide density at the defects, which leads to precipitation of fine carbides during tempering after CT. M2 J.Y.Huang 41 et al, 2003 Investigations in to the effect of CT on microstructure, mechanical properties and dimensional stability. Highest fracture toughness and hardness were achieved, when retained austenite was totally transformed in to martensite. Shape distortion was observed after CT due to stresses. Precipitation of rod like fine carbides was detected after CT. M2 V.Leskovsek 40 et al, 2002 Study of CT effect by both field tests and laboratory tests. Field tests confirmed improvement in tool life and cost reduction by 50%, Laboratory tests confirmed wear resistance improvement by CT after conventional treatment M2, H13 Molinari 39 et al, 2001 Study of the structural change responsible for the improvement in the wear resistance due to CT . Concluded formation of η carbide during CT D2 F.Meng 38 et al, 1994 Validation of the effect of CT on different varieties of alloy steels. M2, and D2 Barron 14 R.F, 1982 OBJEFCTIVES AND CONCLUSIONS MATERIAL AISI RESEARCH BY

9. THE PROCESS 1. IMMEDIATELY AFTER HARDENING FOLLOWED BY MULTIPLE LOW TEMPERATURE TEMPERING OR 2. AFTER CONVENTIONAL HARDENING AND TEMPERING FOLLOWED BY MULTIPLE LOW TEMPERATURE TEMPERING. CRYOGENIC TREATMENT -

10. THIS ROUTE WAS FOLLOWED IN THIS WORK AS HSS M2 AND T42 ARE VERY SENSETIVE TO LOW TEMPERATURES. COMMERCIALLY, THIS ROUTE IS MORE PREFERRED. HARDENING 1230 0 C (1503K) TEMPERING 560 0 C (833K) CRYOGENIC TREATMENT AT –185 0 C (88K) LOW TEMPERATURE TEMPERING 150 0 C (423K) TIME HRS TEMPERATURE DEG C

11. AISI M2 AND AISI T42 HIGH SPEED STEELS PILOT EXPERIMENTATION 10.0 3.2 3.6 9.5 4.0 1.27 T42 NIL 1.8 5.0 6.4 4.2 O.9 M2 Co V Mo W Cr C ELEMENTS WT % TOOL STEEL AISI

12. CONVENTIONAL T42 500X T42 WITH CT FOR 24 HRS SOAKING PERIOD 500 X OPTICAL MICROSCOPY

13. PILOT RESULTS FOR AISI M2 -185/24 -185/8 -185/4 -185/2 -185/1 -140 -80 CON

14. PILOT RESULTS FOR AISI T42 -185/24 -185/8 -185/4 -80 -140 -185/1 -185/2 CON

15. PILOT RESULTS EFFECT OF CT ON HARDNESS 1 63.8 3 64.4 H 1 64.2 2 64.6 G 1 64.4 2 64.4 F 2 64 3 64.2 E 2 64.2 2 64 D 2 64 2 64 C 2 63.8 2 64 B - - 2 64.2 A RANGE (MAX – MIN) AFTER TREATMENT AND TEMPERING, AVERAGE BULK HARDNESS R c RANGE (MAX – MIN) CONVENTIONAL AVERAGE BULK HARDNESS R c SAMPLE IDENTIFICATION

16. There is increase in the amount of carbides, as inspected by optical microscopy There is no change in average hardness after CT and tempering but The steels achieve uniformity in hardness over the surface Implies uniform distribution of particles. The soaking time at the cryogenic treatment plays an important role in affecting the wear resistance of these steels. CONCLUSIONS OF PILOT WORK

17. PARAMETERS FOR FINAL EXPERIMENTATION To carry out the experimentation at the CT temperature as -185 0 C; To Soak the steel for the periods of 8, 16, and 24 hours at CT temperature; To evaluate the microstructure by the particle follow up method after conventional treatment, after CT, and after triple tempering; To analyze the microstructure using SEM, TEM, XRD at various stages; To evaluate the effect of treatment using wear and hardness measurement.

18. C CONVENTIONAL T42 AND ELEMENTAL MAPPING VC V Fe W A B C

19. (V,W)C EDS - COARSE CARBIDE Counts 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 keV 001 0 150 300 450 600 750 900 1050 1200 1350 1500 V Mo W

20. EDS - MATRIX 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 keV 0 300 600 900 1200 1500 1800 2100 2400 Counts C V Cr Fe Co Mo W V W Fe Cr W

21. W2C EDS - FINE CARBIDE 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 keV 0 300 600 900 1200 1500 1800 2100 2400 Counts C V V Fe Fe Co Mo W W W Cr

22. MICROSTRUCTURAL CHANGES SHAPE SIZE DISTRIBUTION CON + CT + TEMPER (8 HRS)

23. CONVENTIONAL AFTER CT AFTER TRIPLE TEMPER CRACK ELIMINATION CON + CT + TEMPER (8 HRS)

24. CONVENTIONAL AFTER CT AFTER TRIPLE TEMPER CON + CT + TEMPER (16 HRS)

25. CON + CT + TEMPER (24 HRS) CONVENTIONAL AFTER TEMPERING

26. 24 HOURS SOAKING PERIOD

27. VOIDS AROUND CARBIDES 24 HOURS SOAKING PERIOD

28. AREA FRACTION ANALYSIS INCREASE IN AREA FRACTION OF CARBIDES VALIDATES EARLIER RESEARCH

29. SIZE ANALYSIS THE CLUSTERS OF FINE CARBIDES ARE MISTAKEN FOR A SINGLE PARTICLE OF BIGGER SIZE. INCREASE IN THE SIZE OF THE PARTICLES IS AN INDICATION OF COARSENING OF THE PARTICLES

30. NUMBER OF PARTICLES AT DIFFERENT STAGES PRECIPITATION OF CARBIDES OCCURS FROM THE MATRIX, DURING HIGHER SOAKING PERIODS PAST RESEARCH SUPPORTS PRIMARY COARSE CARBIDES NOT AFFECTED (24 HOURS) PRECIPITATION OF ONLY CARBIDES

31. THE SAMPLES WITH CT AND AFTER TEMPERING SHOW MORE UNIFORM WEIGHT LOSS DURING WEAR

32. ε = 1 FOR CONTROL SAMPLE ε = 1.38 FOR 8 HOURS ε = O.957 FOR 16 HOURS ε = 0.8820 FOR 24 HOURS ε = W0 / W W0 – WT LOSS OF CONTROL SAMPLE W – WT LOSS OF OTHER SAMPLE

33. TEM INVESTIGATIONS ONLY PARTICLES LESS THAN 1 MICRON ANALYZED EDS (MATRIX) CONVENTIONAL T42 1 MICRON LATH MARTENSITE 01.80 02.90 MoK 02.00 06.10 W L 10.90 10.80 CoK 79.50 75.10 FeK 04.80 04.20 CrK 01.10 00.90 V K Atomic % Weight % Elem QUANTIFICATION

34. VC0.88 535 nm 785 nm 714 nm 500 nm CONVENTIONAL T42 12.50 14.40 MoK 20.10 44.10 W L 00.90 00.60 CoK 07.80 05.20 FeK 04.90 03.00 CrK 53.70 32.70 V K Atomic % Weight % Elem CARBIDE VC QUANTIFICATION EDS – AT 785 nm PARTICLE

35. (R2)2 / (R1)2 = 18.0625 ≈ ( 4 1 1) (R3)2 / (R1)2 = 14.0625 ≈ ( 3 2 1 ) R1 = 2 mm R2 = 8.5 mm R3 = 7.5 mm MEASURED Φ23 = 19 deg Φ13 = 78 deg CARBIDE IDENTIFICATION BY INDEXING (RATIO METHOD) Ref: Ramachandran et al (4 1 1) (1 1 4) (3 2 1) (0 0 0) PLANES MATCHED WITH THE CARBIDE VC0.88 WITH ANGLES Φ23 = 19.098 deg AND Φ13 = 79.07 deg, WHICH MATCHES WITH MEASURED ANGLES ± 5 DEG. SADP

36. 15.90 14.90 MoK 31.40 56.50 W L 05.60 03.20 CoK 39.00 21.30 FeK 05.00 02.50 CrK 03.10 01.50 V K Atomic % Weight % Elem a b c d M 6 C - Fe 3 W 3 C T42 WITH CT

37. a) Magnification 100k X b) Magnification 125k X Martensite in T42 with CT (8 Hours soaking period) and Triple tempering

38. a) b) c) d) Deformation bands Dislocations Magnification 100k X Magnification 28k X Magnification 35k X Magnification 35k X 1.2 μm 571 nm 607 nm 1 μm 514 nm

39. AFTER 8 HOURS SOAKING PERIOD MATRIX DISLOCATIONS MATRIX-CARBIDE INTERFACE DISLOCATIONS CARBIDE DISLOCATION CLOUDS AT THE MATRIX CARBIDE INTERFACE. Magnification 66k X Magnification 88k X

40. AFTER 8 HOURS SOAKING PERIOD AND TEMPERING SADP EDS (PARTICLE) IDENTIFICATION M 6 C (Fe 2 W 4 C) η CARBIDE 16.80 16.50 MoK 27.80 52.20 W L 46.30 26.40 FeK 05.60 03.00 CrK 03.60 01.90 V K Atomic % Weight % Elem PARTICLE SIZE Largest diameter – 700 nm Smallest diameter – 100 nm MAGNIFICATION 35k X EDS QUANTIFICATION

41. CT WITH 16 HOURS SOAKING PERIOD Deformation Bands in Martnsite a) Magnification 125k X b) Magnification 28k X Dislocation cloud

42. CT WITH 24 HOURS SOAKING PERIOD Magnification 28k X EDS - CARBIDE MC 13.20 15.80 MoK 17.40 39.80 W L 00.40 00.30 CoK 04.40 03.10 FeK 06.90 04.50 CrK 57.70 36.60 V K Atomic % Weight % Elem CARBIDE QUANTIFICATION MC TYPE OF CARBIDE

43. CT WITH 24 HOURS SOAKING PERIOD 01.30 02.10 MoK 01.30 04.10 W L 10.70 10.90 CoK 80.30 77.20 FeK 05.30 04.70 CrK 01.20 01.10 V K Atomic % Weight % Elem EDS - MATRIX Magnification 45k X QUANTIFICATION Carbide size: 400 nm Gap between particle edge and the matrix = 30 nm

44. OUTCOME OF TEM INVESTIGATIONS: Dislocation density around the carbide particles has been found to have increased in all the samples irrespective of soaking time. Martensite deformation bands at very high magnification detected after CT The presence of η carbide in the samples with 8 hours soaking period has been identified. Presence of this carbide is not reported in the literature. Presence of MC type of carbides less than 1 micron are detected. Evidence of detachment of even fine carbides from the matrix after 24 hours soaking period confirmed with SEM results. This effect causes fall in wear properties.

45. XRD INVESTIGATIONS: DIFFRACTION PATTERN OF CONVENTIONAL T42 30 40 50 60 70 80 90 100 110 Counts 0 200 400 600 V C0.88 V C (1 1 1) Mo2 C (0 2 2) W2C (1 0 2) MARTENSITE (1 1 0) Mo2 C (0 2 2) VC (5 3 0) Mo2 C (0 4 2) Cr23 C6 (9 1 1) Co (3 1 1)

46. PARTICLES IDENTIFICATION (PATTERN LIST) CONVENTIONAL T42 Co -0.059 Cobalt 12 00-001-1255 * Mo2 C 0.370 Molybdenum Carbide 16 01-071-0242 * Cr23 C6 -0.020 Chromium Carbide 4 00-035-0783 * W2 C 0.192 Tungsten Carbide 11 01-079-0743 * V C0.88 -0.376 Vanadium Carbide 13 01-077-2003 * V C -0.400 Vanadium Carbide 11 01-073-0476 * C0.08 Fe1.92 0.090 Martensite 37 00-044-1291 * Chemical Formula Displacement [°2Th.] Compound Name Score Ref. Code Visible

47. DIFFRACTION PATTERN FOR T42 AFTER CT (8 HRS) Counts Position [°2Theta] 30 40 50 60 70 80 90 100 110 0 200 400 600 V C0.88 V C Mo2 C W2 C MARTENSITE Mo2 C V C Mo2 C Cr7 C3 (10 0 ) Co T 2 cryo

48. PARTICLES IDENTIFICATION (PATTERN LIST) FOR T42 AFTER CT (8HRS) Cr7 C3 0.115 Heptachromium tricarbide 29 00-036-1482 * Co 0.068 Cobalt 12 00-015-0806 * W2 C 0.186 Tungsten Carbide 7 01-079-0743 * V C0.88 -0.333 Vanadium Carbide 11 01-077-2003 * V C -0.356 Vanadium Carbide 9 01-073-0476 * Mo2 C 0.313 Molybdenum Carbide 7 01-071-0242 * C0.08 Fe1.92 0.090 Martensite 37 00-044-1291 * Chemical Formula Displacement [°2Th.] Compound Name Score Ref. Code Visible

49. CONCLUSIONS CRYOGENIC TREATMENT OF AISI T42 AT –1850C (88K) THE RESPONSE OF AISI T42 HIGH SPEED STEEL TO CT WAS DIFFERENT FROM THAT OF WELL INVESTIGATED AISI M2 M2 STEEL NEEDS 24 HOURS SOAKING PERIOD AT CRYOGENIC TEMPERATURE OF -185 DEG C, WHEREAS T42 NEEDS 8 HOURS. THERE IS NO SIGNIFICANT CHANGE IN HARDNESS OF T42 AFTER CT. THE HARDNESS BECOMES MORE UNIFORM AFTER CT. THE AREA FRACTION OF CARBIDES INCREASES WITH SOAKING TIME OF CT FROM 8 TO 24 HOURS.

50. CONCLUSIONS… THERE IS INCREASE IN THE NUMBER OF PARTICLES WITH INCREASE IN SOAKING TIME DURING CT. THERE IS INCREASE IN PARTICLE SIZE WITH INCREASE IN SOAKING TIME DUE TO CLUSTERING OF CARBIDES DURING CT. DESPITE OF THIS PARTICLE BEHAVIOR, THE RELATIVE WEAR RESISTANCE OF T42 DETERIORATES AT HIGHER SOAKING PERIODS OF 16 AND 24 HOURS. MAXIMUM BENEFIT CAN BE DERIVED BY 8 HOURS SOAK DURING CT. THE CHANGE IN THE MORPHOLOGY OF COARSE PRIMARY CARBIDES FOUND, DURING CT FOR 8 HOURS. THE CHANGE DIMINISHED FOR 16 HOURS SOAK, AND NO CHANGE WAS DETECTED AFTER 24 HOURS SOAK.

51. CONCLUSIONS… THE CHANGE IN MORPGOLOGY IN TERMS OF ‘CORRECTION’ IN THE SHAPE WAS DETECTED DURING CT. THE CORRECTION COMPRISING OF ‘ROUNDING OFF’ OF THE CORNERS, SMOOTHENING OF THE EDGES, THEREBY DECREASING THE STRESS CONCENTTRATION SITES. THE CHANGE BEGINS DURING WARMING UP PERIOD AND CONTINUES THROUGH LOW TEMPERATURE TEMPERING. CHANGE IN THE DISTRIBUTION PATTERN OF FINE SECONDARY CARBIDES ALSO TAKES PLACE ALONGWITH THE CHANGE MENTIONED ABOVE. THERE IS NO CHANGE IN THE MORPHOLOGY OF CARBIDES DURING CT WITH 24 HOURS SOAKING TIME. THIS CLEARLY INDICATES THAT THE CHANGE FOUND DURING 8 HOURS SOAKING TIME DO NOT TAKE PLACE DURING SOAKING PERIOD.

52. CONCLUSIONS… THE MICRO-CRACKS PRESENT IN CONVENTIONALLY TREATED STEEL ARE ELIMINATED DURING CT. THIS WAS FOUND IN CT WITH ALL THE SOAKING PERIODS. THE CAUSE IS ATTRIBUTED TO CONTRACTION OF THE MATRIX DURING CT. CRACK ELIMINATION GREATLY DECREASES THE BRITTLENESS OF THE STEEL, HENCE HELPS ACHIEVING GREATER WEAR RESISTANCE. VOIDS ARE CREATED BETWEEN THE MATRIX-CARBIDE INTERFACE DURING CT WITH 24 HOURS SOAKING PERIOD. THIS CAUSES DETACHMENT OF COARSE AND FINE CARBIDES FROM THE MATRIX, DUE TO DIFFERENTIAL CONTRACTION OF THE MATRIX AND THE PARTICLES. THIS DETERIORATES THE WEAR RESISTANCE OF STEEL. THE GENERATION OF DISLOCATIONS IN THE MATRIX AND AT THE MATRIX-CARBIDE INTERFACE OBSERVED BY TEM. THIS CONFIRMS THAT STRESSES ARE INDUCED DURING SOAKING TIME OF CT.

53. CONCLUSIONS… THE TEM OBSERVATIONS SUPPORT THE HYPOTHESIS OF HUANG ET AL ABOUT GENERATION OF HIGH DISLOCATION DENSITY IN THE MARTENSITIC MATRIX AND THE MATRIX-CARBIDE INTERFACE IN HIGH SPEED STEEL. THE ALLOYING ELEMENTS AND CARBON CLUSTERS FORM AT THE DISLOATIONS IN THE MARTENSITIC MATRIX, AND UPON HEATING, PRECIPITATE OUT IN THE MATRIX AT THE SITES ON THE CARBIDE SURFACE. THIS CAUSES PRECIPITATION AND MORPHOLOGICAL CHANGE IN T42 STEEL. T42 STEEL DERIVES ADVANTAGE BY THE PRESENCE OF COBALT. IT ENHANCES THE PRECIPITATION OF CARBIDES.

54. CONCLUSIONS… PRECIPITATION OF η CARBIDE TAKES PLACE IN HIGH SPEED STEELS DURING CT. THESE FINE PARTICLS ENHANCE WEAR RESISTANCE OF STEEL. THE XRD ANALYSIS HAS REVEALED FORMATION OF Cr7C3 PARTICLES IN STEEL AFTER CT. THESE CARBIDES ARE HARDER AND IMPART HIGHER WEAR RESISTANCE TO STEEL THAN Cr23C6 , WHICH IS USUALLY PRESENT IN CONVENTIONALLY TREATED STEEL. THE RESPONSE OF HIGH SPEED STEEL TO CRYOGENIC TREATMENT DEPENDS ON ITS COMPOSITION. RULE FOR ONE STEEL CAN NOT BE APPLIED FOR OTHER STEEL.