9%-nickel steel is a low alloy steel, which contains lower quantity of carbon and 9% of nickel. This steel after proper heat-treatment shows excellent tensile strength and toughness at extremely low temperatures as low as -200°C. This steel can be used for the construction of rather larger low temperature structures such as the storage vessels containing liquefied natural gases, etc.
Comparing to the stainless- and 36%-nickel steel (Invar), etc., 9%-nickel steel seems to be the most reasonable material if considered the strength available for designing. The total cost of 9%-nickel steel welded structures, however, is rather expensive. The most predom-inant reason of expensive cost attributed to the high prices of the welding materials used.
The nickel-base alloys such as Inconel, now, are mainly used for the welding of 9%-nickel steel. Weldability of 9%-nickel steel is superior, so that, heat-affected zone cracking, usually, do not occur when without preheating.
Melting point of the nickel-base alloy is lower about 100°C than 9%-nickel steel. So, the welding penetration is rather shallow. The affinity between weld-metal and base metal is not so good that, in some cases, the lack of penetration occurs easily. Further, the hot cracking sensitivity of high nickel alloy is rather remarkable, so the creater cracking occurs almost always when omitted crater treatment. Generally speaking, the usability of high nickel alloy welding electrode is not so good.
Now, several welding materials used for manual arc-, submerged arc- and gas shielded arc welding processes were developed.
