Electric heating – Metal heating – Weld rod composition
Patent
1994-11-09
1996-05-21
Shaw, Clifford C.
Electric heating
Metal heating
Weld rod composition
B23K 3522
Patent
active
055191860
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a filler material suitable for welding of a high-strength heat-resisting steel having high toughness, and more specifically to an inert gas arc welding wire which can form a weld metal having excellent creep properties, toughness and cracking resistance at high temperatures.
The inert gas arc welding is arc welding which is carried out in a gas atmosphere of an inert gas, such as argon or helium, or a gas atmosphere comprising the inert gas and, added thereto, a minor amount of an active gas. It is classified into two types, that is, TIG welding as nonconsumable electrode welding and MIG welding as consumable electrode welding. In TIG welding, a tungsten electrode is used, and a filler material is supplied separately from the electrode. On the other hand, in MIG welding, a welding wire (a filler material), as such, is used as an electrode.
BACKGROUND ART
The development of a ferritic heat-resisting steel as a steel product for high-temperature, high-efficiency energy plants, which has a very high creep strength and is less susceptible to stress corrosion cracking such as is observed in an austenitic stainless steel, has been strongly desired in the art, and such a ferritic heat-resisting steel has begun to be actually used.
As a filler material or a welding wire for use in welding of the above ferrite heat-resisting steel, for example, Japanese Unexamined Patent Publication (Kokai) No. 60-257991 proposes a welding wire for a 9Cr-Mo-base steel, which welding wire comprises C, Si, Mn, Cr, Mo and Ni in respective specified contents with at least one of Nb and V being added thereto in a total content of not more than 0.3%. Further, Japanese Unexamined Patent Publication (Kokai) No. 2-280993 proposes an 8-12Cr-base filler material or welding wire which comprises C, Si, Mn, Cr, Ni, Mo, W, V, Nb, Al and N in respective contents specified so as to give a Cr.sub.eq value of 13.
The above conventional filler materials or welding wires, however, cannot be expected to have a markedly improved creep strength and, further, have a drawback that .delta. ferrite precipitates in a martensitic phase to markedly lower the toughness. The .delta. ferrite is much softer than martensite as the matrix. A metallic structure comprising a hard martensitic matrix and, dispersed therein, .delta. ferrite has a very low impact toughness.
DISCLOSURE OF INVENTION
An object of the present invention is to eliminate the above drawbacks of the prior art and to provide a filler material or a welding wire which can form a weld metal having high creep strength and excellent toughness when used in welding of a high Cr ferritic heat-resisting steel.
In order to attain the above object of the invention, the present invention provides an inert gas arc welding wire for a high Cr ferritic heat-resisting steel, characterized by comprising, by weight, not more than 2.8%.
The greatest feature of the present invention is that W and B are added and the contents of the Mo and W are specified in the above respective ranges, thereby suppressing the formation of .delta. ferrite in a weld metal to markedly enhance the creep rupture strength and the toughness. The reasons for the limitation of each ingredient in the present invention will now be described.
C: 0.03 to 0.12%
C should be present in an amount of not less than 0.03% for ensuring the hardenability and strength and should be not more than 0.12% for preventing the deterioration of cracking resistance. The term "cracking" used herein is intended to mean that a weld metal cracks at a high temperature at the time of welding.
Si: not more than 0.5%
Si is added as a deoxidizer and contributes also to an improvement in oxidation resistance. However, when the Si content exceeds 0.5%, the toughness is lowered, so that the upper limit of the Si content is 0.5%.
Mn: 0.3 to 1.5%
Mn is necessary not only for deoxidation purposes but also for maintaining the strength. The lower limit of the Mn content is 0.3% in view of the amount necessary for the deoxidation.
REFERENCES:
patent: 3554791 (1971-01-01), Johnson et al.
patent: 4487744 (1984-12-01), DeBold et al.
patent: 4673123 (1987-06-01), Shin et al.
Sakurai Hideo
Tanaka Takashi
Nippon Steel Corporation
Shaw Clifford C.
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