Ni-Cr-Mo-V Effect of Heat Treatment Conditions and Minor Elements on Grain Size

of High Strength Ni-Cr-Mo-V Steel

* Muroran Research Laboratory

**Nakamura Jico Co., Ltd.

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**

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Takahiro Kato

Takeshi Sagawa

Dr. Kunihiko Hashi

Tsuyoshi Kato

Masakatsu Honma

Daisuke Kikuchi

1

Ni-Cr-Mo-V

We tried to refine the grain size of high strength Ni-Cr-Mo-V steel by modification of the heat treatment condition and adjustment of contents of minor elements. The grain size number of the Ni-Cr-Mo-V steel is from 5 to 6 after the conventional heat treatment. It is impossible to make the grain much finer only by a minor modification of the heat treatment condition. Repeating austenitizing and increasing heating rate are required for further refining the grain of the steel. Also, no grain refining effect is confirmed even if Al and N were added to the Ni-Cr-Mo-V steel. Thermodynamic analysis results showed that the amount of AlN precipitates decreases and the solvus temperature drops with increase in V content. Fine AlN precipitates were observed in the modified composition with low V content, although precipitation of AlN was hardly observed in the conventional Ni-Cr-Mo-V steel composition containing high amount of V. This study revealed that it is possible to refine the grain of Ni-Cr-Mo-V steel to grain size number larger than 8 by Al and N addition with decreasing V content for stable precipitation of AlN without change of the conventional heat treatment condition.

Synopsis

Ni-Cr-Mo-V 5 6 AlN Al N V AlN Solvus V AlN V AlN Al N AlN V 8

1mass%

1mass%2No.672016.11

Ni-Cr-Mo-V

AlN11-17, 19Nb 17-19 V 20, 21 AlN Nb Ni-Cr-Mo-V Al N N V Al 2 V Al N Nb N C V

Ni-Cr-Mo-V Nb AlN V Nb AlN

2.

2.1Vacuum Induction Melting: VIM

50kg 1513K 3.1 1 Steel Al N Steel AlNNb V

2.2 1

Quenching temperature: TQ 1113KR 0.01K/s

1.

Ni-Cr-Mo-V

Ni-Cr-Mo-V 1-45, 65-88-10C VNi Ni 8

Ni-Cr-Mo-V

2 : OM : SEM

3

Ni-Cr-Mo-V

Simulated CarburizingQuenching: Q 200mm 50mm Simulated Cooling 243K 453K 2

Q Water Quenching: W.Q.Steel 0.2m

5% 30min JIS G0551

Scanning Electron Microscope: SEM Transmission Electron Microscope: TEM

3.

3.1 2 453K Steel

SEMSEM 1m

3 Steel XRD M3C Steel V V SEM M3C

4 Steel Continuous Cooling Transformation: CCT Simulated Cooling Steel Ac1 927KAc3 1029K Simulated Cooling 0.02K/s

3XRD 6

5

4Steel 7

4No.672016.11

Ni-Cr-Mo-V

Normalizing: NSteelV Al N Steel Steel CCT

3.2 5 SteelTQ

NGS1053 1203K 1 TQ

6 Steel NGS 2 1 2

7 SteelR NGS 0.01K/s

Ni-Cr-Mo-V

8 Steel Steel

9 Steel

5

Ni-Cr-Mo-V

3.3Nb AlN

8 9 0.01K/s 1113K 18ks W.Q. Steel Steel NGSSteel NGS -1.3 Nb Al N V 10 V Steel NGS -1.6 Steel NGS 2.4 Steel Steel V Al N Ni-Cr-Mo-V V Al N

1113K W.Q. Steel TEM 10 M3C Steel 100nm V Steel 100nm V nm Nb

AlN Steel 100nm AlN V Nb AlN

TEM V Nb AlN

11 Thermo-Calc : TCFE7 1000 1400K V AlN %0.20C-0.08Si-0 . 5 8Mn-3 .70Ni -1 .78Cr- 0 . 2 4Mo - 0 . 02Al - 0 . 0 0 8N-Vmass%a V Steelb V Steel Al N 0.09 V AlN Solvus Q 1113K AlN V AlN N V AlN N AlN Al N AlN AlN Solvus Steel AlN bSteel 0.02mass% Al 0.008mass% N 1113K AlN Steel Al N Steel NGS 2.1V

12 0.01K/s1113K SteelSteel 1113K 2%Steel 1113K SteelVV

101113K Steel TEM

11AlN V V Thermo-Calc

121113K Steel

Austenite grain

Austenite fraction: 2%

6No.672016.11

Ni-Cr-Mo-V

131113K 60 300s Steel

2

141113K 60 300s Steel

7

Ni-Cr-Mo-V

13 14 50K/s 1113K 60 300s SteelNGS 12 Steel 0.01K/s 1113K 13 14 60s Steel

V

1110K 12 290s 13 60s 12

1113K Simulated cooling V V Steel NGS 60s 9.5 180s 6 Steel Steel60 300s Steel Steel SteelSteel

2 SteelSteel AlN Nb Steel AlN Nb Steel SteelNi V Steel

Al N AlN V Ni-Cr-Mo-V

8No.672016.11

Ni-Cr-Mo-V

4.

Ni-Cr-Mo-V Al N AlN V

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3 , , , , , : ,Vol.69 1983, S1407

4 , , , , , : ,Vol.69 1983, S1408

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18 , , , : , 57 1971, 533.19 : , 67 1996, 26.20K. Narita: Kobe Steel Eng. Rep., 7 1957, 5621 , , , , : , 76 1990, 1380.