High strength and high toughness welding material

BACKGROUND OF THE INVENTION 
Examples of conventional welding materials for use at temperatures as low 
as -90.degree. C. are 3.5% nickel alloy steel and austenite stainless 
steel. 
Welds with these materials, however, offer low yield strengths of 30-55 
Kgf/cm.sup.2, although they are durable at low temperatures, which 
precludes their use for rotary high-speed machinery which requires 
materials that can be used as welding materials in strong and durable 
states at low temperatures. Additional heat treatment-- quenching and 
tempering do not raise yield strength and impact value, VE-- 90 to permit 
such welds being used in parts subject to high r.p.m. 
SUMMARY OF THE INVENTION 
The present invention relates to a welding material, hereinafter referred 
to as welding wire, and more particularly to a welding material which may 
be used at temperatures as low as -90.degree. C. for a variety of welds of 
various machinery and tools. The welding material according to the present 
invention offers great strength durability, even when it is used in welds 
at -90.degree. C. 
DETAILED DESCRIPTION OF THE INVENTION 
The inventors have developed a welding material that is stronger and more 
durable than conventional welds at -90.degree. C., and have determined 
that 
(1) Increased Ni content in steel increases durability at low temperatures. 
(2) Addition of Cr and Mo increases the efficiency of the quenching and 
tempering steps. 
(3) The Cr+ MO content are critical factors in achieving strength and 
durability. 
The present invention is based on the above findings and provides a 
strong-- durable welding material characterized by containing the 
following elements in the weight percentage listed below. Hereinafter, the 
percentage is by weight. C: 0.05- 0.15%, Si: 0.25- 0.70%, Mn: 0.60- 1.80%, 
Ni: 4.5- 11.0%, Cr: 0.20- 1.20%, Mo: 0.20- 0.60%, Ti: 0.03- 0.12% and Cr+ 
Mo: from 0.40% to 0.030.times. (Ni%).sup.2, and the impurities, P and S, 
that are unavoidable are limited to less than 0.010% and Cu less than 
0.20%, and Sn, Sb and As less than 0.010%, and oxygen and nitrogen less 
than 100 ppm and the balance iron. 
The reasons for specifying the amount of the component elements in the 
welding material according to the present invention are as follows. 
Carbon is needed for raising the weld strength. For the reasons that proper 
strength can not be obtained if it is too low, and that cracks at high 
temperatures in the weldment are liable to develop if it is too low, it is 
in the range from 0.05- 0.15%. 
Silicon has a refining effect on the weld metal. If silicon is too low, the 
refining effect is not enough, and if it is too high, low temperature 
durability is reduced during quenching and tempering. For those reasons, 
silicon of 0.25- 0.70% is used. 
Mn has the same effect as silicon. For the same reasons as for silicon, 
manganese of 0.60- 1.80% is employed. 
Ni raises the low temperature durability and strength. If it is below 4.5%, 
low temperature durability at -90.degree. C. is insufficient in the weld 
metal that is subjected to quenching and tempering to 22 a yield strength 
of from 75- 100 Kgf/mm.sup.2. If Ni content is higher than 11%, the cost 
is no longer practical. The Ni content is therefore limited to the range 
of 4.5- 11%. 
Cr improves quenching, but its characteristics tend to reduced low 
temperature durability. The range of 0.20- 1.20% is considered to be 
preferable. If the content is lower than 0.20, the yield strength is low. 
If the content exceeds 1.20%, durability at -90.degree. C. is reduced. 
Mo also improves the quenching characteristics, and it also maintains 
strength after tempering. A range of 0.20- 0.60% is recommended. If the Mo 
content is below 0.20%, the yield strength is low, and a content of over 
0.60% offers no improved yield strength, only raising the alloy cost. 
As for the above-mentioned chromium and molybdenum, if the total of both 
elements is increased, strength of the weld metal is increased, but low 
temperature durability is decreased. To meet both the strength and low 
temperature durability requirements, it is important that the total of 
both elements fall between 0.40% and 0.30.times. (Ni%).sup.2 
(0.40%.ltoreq.Cr+Mo.ltoreq.0.030.times.(Ni%).sup.2). 
Titanium is an important element for achieving stability in metallurgical 
reactions and in the arc during welding. If it is lower than 0.03% in 
weight, its deoxidizing effect and contribution to arc stability will not 
be evident, and if it is over 0.12% in weight, it lessens arc stability 
and durability of the weld metal, its content is limited in the range of 
0.03- 0.12%. 
The unavoidable impurities, P, and S and Cu are likely to cause cracks to 
develop in the weld. It is therefore desirable to limit P and S contents 
to less than 0.010%, and Cu under 0.20%. Other impurities, Sn, Sb and As 
should be limited to less than 0.010%. Since oxygen and nitrogen reduce 
durability, content of each gas should be less than 100 ppm. 
Welding materials that are examples of the present invention with the above 
listed compositions are used as welding rods for gas-sealed arc welding, 
and the weld metals are subjected after welding to quenching and tempering 
.