Gr.8 is 9Ni type low carbon quenching and tempering steel, listed in the American standard of low temperature pipe A333 and low temperature heat exchanger pipe A334 two standards.Nickel is the most effective element to improve the low temperature toughness of steel -- GR.8 contains 9% Ni, which ensures its good toughness and[TJC STEEL] high strength at very low temperature, and its service temperature can be as low as -195℃.

 

National Standard

CHINA	GB/T 18984-2016	06Ni9DG
AMERICA	ASTM A333/A333M-11 ASTM A334/A334M-04a[TJC STEEL]	Grade 8
JAPAN	JIS G 3460:2013 JIS G 3464:2013	STPL 690
GERMANY	DIN EN 10216-4:2004	X10Ni9 1.5682

 

Component Specification

GRADE	Grade  8	06Ni9DG	STPL 690	1.5682
C	≤0.13	≤0.10	≤0.13	≤0.13
Si	0.13~0.32	0.10~0.35	0.10~0.35	0.15~0.35
Mn	≤0.90	≤0.90[TJC STEEL]	≤0.90	0.30~0.80
P	≤0.025	≤0.015	≤0.030	≤0.020
S	≤0.025	≤0.008	≤0.030	≤0.010
Ni	8.4~9.6	8.5~9.5	8.5~9.5	8.5~9.5
Mo	—	—	—	≤0.10
Cu	—	—	—	≤0.30
V	—	—	—	≤0.05

 

Heat Treatment

Gr.8 Heat treated to control the microstructure as follows before delivery.

 

① quenching + tempering

Heat evenly to 800℃±15℃;Heat preservation, the heat preservation time is proportional to the thickness of 2min/mm, and not less than 15min;Immerse in circulating water and quench.

The steel tubes were reheated evenly[TJC STEEL] to 565-605 ℃;Heat preservation, the heat preservation time is proportional to the thickness of 2min/mm, and not less than 15min;Air cooling, or water quenching with a cooling rate of not less than 165℃/h.

(2) secondary normalizing + tempering

Heat evenly to 900℃±15℃;Heat preservation, the heat preservation time is proportional to the thickness of 2min/mm, and not less than [TJC STEEL]15min;Air cooling.

Reheated to 790℃±15℃;Heat preservation, the heat preservation time is proportional to the thickness of 2min/mm, and not less than 15min;Then air cooling.

Heat evenly to 565-605 ℃;Heat preservation, the heat preservation time is proportional to the thickness of 2min/mm, and not less than 15min;Air cooling, or water quenching with a cooling rate of not less than 165℃/h.

 

Tensile Property

strength of extension MPa	≥690
yield strength MPa	≥515
Elongation (longitudinal) %	≥22a
	≥16b

A. Longitudinal strip test with a standard distance of 50mm and a wall thickness of ≥8mm, or all small-size samples tested with full section.

B. Standard round sample with a standard distance of 50mm or a smaller size sample with a standard distance of 4 times the diameter.

 

Impact toughness：

The minimum impact test temperature of the steel tube GR.8 is -195℃.The test results are determined by the average lateral expansion value of the impact sample relative to the notch.

Applications：

GR.8 is primarily used for the storage of structural materials for liquefied natural gas (LNG) terminals.LNG is stored at around -162 ° C and must be made from ultra-low temperature materials.Compared with other ultra-low temperature materials, GR.8 has lower cost than stainless steel and nickel-based alloy, higher strength than aluminum alloy and better low temperature toughness, and is currently the main material for large LNG storage tanks.