| A cold cast iron welding rod with nickelless steel wire, which not only lowers the hardness of the HAZ than that of the weld metal, but also eliminates blowholes from the weld metal. A cold cast iron welding rod according to Claim 1, which is used in the dissimilar metal welding between an optional cast iron and each kind of steel (high tensile steel, tool steel, stainless steel or especially steel the adhesivity in molten state of which is very bad or steel the hardenability of which is strong) possible as well as in the welding of all kinds of cast iron such as gray cast iron, spheroidal graphite cast iron and high-duty cast iron A cold cast iron welding rod according to Claims 2, which totally remove the tendency of destruction of the HAZ in the steel as well as in the cast iron in case of the dissimilar metal welding between a cast iron and a steel. A cold cast iron welding rod according to Claims 1 and 2, the wire of which is low-carbon steel and the coating flux of which contains marble, magnesia clinker, fluorite, medium-carbon ferromanganese, FeSi75, Fe-Si-Ba, feldspar, mica and thermite powder. A cold cast iron welding rod according to Claim 4, in which the material for the wire is common low-carbon cast iron that contains less than 0.22% carbon and respectively less than 0.04% sulfur and phosphorous as well as low-carbon steel that contains less than 0.08% carbon. A cold cast iron welding rod according to Claim 4, in which the coating flux contains at mass percent 38 to 44% marble, 0 to 8% magnesia clinker, 10 to 21% fluorite, 0 to 15% medium-carbon ferromanganese, 0 to 8% FeSi75, 0 to 3% Fe-Si-Ba, 3 to 8% feldspar, 3 to 6% mica and 3 to 5% thermite powder. 7. A cold cast iron welding rod according to Claim 4, the wire of which is coated mechanically with the mixture of complex water glass (or soda water glass), the module of which is 2.6 to 2.7 and the density of which is 1.38 to 1.40, and the coating materials, when the mass ratio between the wire, coating materials and complex water glass (or soda water glass) is 70:30:9. 8. A cold cast iron welding rod according to Claim 7, in which the complex water glass contains potash one and soda one, and the mass ratio between them is 3:7 to 7:3. 9. A cold cast iron welding rod according to Claim 4, in which the drying temperature is 200 to 250 °C and the drying time is two hours in view of drying conditions for finishing. |
STEEL WIRE FOR REMOVING TENDENCY OF DESTRUCTION OF HAZ (HEAT AFFECTED ZONE) AND ELIMINATING BLOWHOLES FROM WELD METAL BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a cold cast iron welding rod with nickelless steel wire which removes the tendency of destruction of the HAZ (heat affected zone) by lowering the hardness of the HAZ than that of the weld metal and can ensure high pressure sealing of the weld metal by eliminating blowholes from it.
2. Description of the background
Cast iron contains so much carbon and silicon unlike steel, its intensity is weak, its plasticity is not good, its thermal conductivity is low and its metal brittleness is strong. Therefore it is very difficult to weld k cast iron.
A lot of cold or hot cast iron welding rods, which are nickel-based or not, such as nickel ones, monel ones, steel-nickel ones and low-carbon steel ones, have ever been developed to solve the tough problem in cast iron welding.
The best one among them all is recognized to be nickel-based cold cast iron welding rod the wire of which is 100% nickel.
In case of using any of the previous cold cast iron welding rods, in a greater or less degree, the hardness of the weld metal is always higher than that of the HAZ, and thus the tendency of destruction of the HAZ constantly remains.
It means that no welding with any cold cast iron welding rod can ensure reproduction of a manufacture on a level of its original performance and lifetime and it needs complicated and special welding and heat treatment to obtain comparatively reliable cast iron weld joint.
Moreover, the weld metal is not attached well to the base metal and a large number of blowholes are formed in the weld metal in comparison with steel welding, which makes the seal welding for preventing leak of water or oil impossible. Especially, it is known that it is completely impossible to reproduce the main large or extra-large cast iron accessories, which have some frequent destruction at the fixed places owing to a very great load, on a level of their original performance and lifetime.
Even the cast iron welding rod with 100% nickel wire, which is known as the best one among all the previous cold cast iron welding rods, is also impossible to overcome such a tough problem. In addition, the nickel-base welding rods are only being used in extremely limited fields because of their high manufacturing cost.
And much thermal energy is consumed during the drying process since the drying temperature of the previous basic welding rods is mostly 350 to 400 * C. The objective of the present invention is to manufacture, without any nickel and with lowering the drying temperature, a cold cast iron welding rod which can reproduce various kinds of cast iron accessories on a level of more than their original performance and lifetime regardless of the objects, ensure the sealing of the weld joint and make the dissimilar metal welding between steel and cast iron possible.
SUMMARY OF THE INVENTION
The cold cast iron welding rod according to the present invention lowers the hardness of the HAZ than that of the weld metal and eliminates blowholes from the weld metal on the basis of the molten metal modification principle and high speed deoxidation principle by formation and infiltration of a compound modifier during the welding metallurgical process. Eliminating blowholes from the weld metal leads to thorough assurance of sealing in the weld joint.
This welding rod shows the same effect in all kinds of cast iron, such as gray cast iron, spheroidal graphite and high-duty cast iron. And it also gives the solid weld joint with ensuring sufficiently the mechanical properties and performance of the original base metals in the dissimilar metal welding between an optional cast iron and each kind of steel (high tensile steel, tool steel, stainless steel or especially steel the adhesivity in molten state of which is very bad or steel the hardenability of which is strong). That's because the molten metal formed from the wire is firmly adhesive to the cast iron and the steel since it is modified by the compound modifier and its adhesivity is raised. In general, this molten metal is more strongly adhesive to the steel than the cast iron.
In case of doing the dissimilar metal welding between a cast iron and a steel by using the welding rod according to the present invention, there is no tendency of destruction of HAZ in the steel as well as in the cast iron at all. The cold cast iron welding rod according to the present invention is a basic one the wire of which is low-carbon steel and in which the main materials of coating flux are marble, magnesia clinker and fluorite.
Any common low-carbon steel which contains less than 0.22% carbon and less than 0.04% sulfur and phosphorus respectively is enough for the wire as well as low-carbon steel which contains less than 0.08% carbon.
For the formation of the compound modifier during the welding metallurgical process some medium-carbon ferromanganese, ferrosilicon, Fe-Si-Ba, feldspar, mica and thermite powder are added to the coating flux of the welding rod.
Medium-carbon ferromanganese, which has a comparatively great tendency to increase the hardness of the weld metal, is for preventing the hot tearing resulting from sulfur since cast iron has more sulfur than steel.
FeSi75 is used, instead of FeSi45, so that some silicon in it not only takes part in the reaction of deoxidation, but also helps the formation of the compound modifier in the weld metal.
Some barium in Fe-Si-Ba accelerates exceedingly the modification of the weld metal, lowers considerably the hardness of the weld metal and prevents the formation of some blowholes in the weld metal by getting some barium oxide to be created before the reaction between carbon and oxygen in the weld metal occurs and then without delay making it rise up with the slag.
Feldspar acts as an arc stabilizer and increases the liquidity of the slag. Mica is a main factor to decrease some linear wrinkles in the weld metal with aluminum oxide in it, increases the plasticity of the mechanical coating of the welding rod, stabilizes the electric arc and keeps the coating from tearing during the drying of the welding rod.
Thermite powder, in which Al:Fe 2 0 3 is 1:3, makes the expected metallurgical reaction occur sufficiently in the state that the weld metal is liquid and keeps some firm carbide from being formed in the weld metal since it plays a role of slowing down the solidification rate of the molten metal with some supplementary heat resulting from the thermit reaction in the basic slag. In case more than 5% thermite powder is added to the coating the hardness of the weld metal gets lower but the reaction rate of deoxidation is decreased due to the increase of the amount of residual iron oxide (FeO) in the weld metal and slag, and thus the tendency of formation of blowholes in the weld metal grows greater. Therefore, the amount of the thermite powder is limited to less than 5%.
The coating of the welding rod according to the present invention contains at mass percent 38 to 44% marble, 0 to 8% magnesia clinker, 10 to 21% fluorite, 0 to 15% medium-carbon ferromanganese, 0 to 8% FeSi75, 0 to 3% Fe-Si-Ba, 3 to 8% feldspar, 3 to 6% mica and 3 to 5% thermite powder.
The coating materials are crushed into fine particles the size of which is about 0.1 to 0.2mm, are mixed at the mass percent according to the present invention and are agitated well by an agitator. Then complex water glass (or soda water glass) the module of which is 2.6 to 2.7 and the density of which is 1.38 to 1.40 is added to the agitated coating materials, this mixture of complex water glass (or soda water glass) and coating materials are agitated again well, and so some coating flux is made. And the coating flux is coated mechanically on the wire, when the mass ratio between the wire, coating materials and complex water glass (or soda water glass) is 70:30:9. The complex water glass contains potash one and soda one, and the mass ratio between them is 3:7 to7:3.
In view of drying conditions for finishing the welding rod coated with the coating flux, the drying temperature is 200 to 250°C and the drying time is two hours.
During the welding metallurgical process some proper amount of a compound modifier is created in the circumstance of high temperature by calcium oxide, magnesium oxide, FeSi75 and Fe-Si-Ba in the coating, carbon in the base metal, iron in the molten metal and so on.
The molten metal is modified by the compound modifier and thus the mechanical property of the weld metal becomes better than one of the base metal. And the compound modifier causes the high speed deoxidation and the high speed separation of oxides (gaseous or solid) from the weld metal, and so microscopic blowholes are not formed in the weld metal at all. The reactions of desulfurization and dephosphorization of the weld metal also take place violently.
The welding rod according to the present invention is able to use in both alternating current and direct current, and at the time of welding the surface of the seam is smooth, the liquidity and separability of the slag are good and the side hollow of the seam doesn't appear. The advantages of the present invention are as follows:
First, the resistance to destruction of the HAZ in the base metal with high hardenability, which has been impossible to ensure with any previous cold welding rod, is ensured smoothly.
Secondly, blowholes, which are one of the toughest problems in cold cast iron welding, are completely eliminated from the weld metal, the hardness of the weld metal is lowered enough to mechanically process it and it can be given high mechanical properties since its particles become very fine.
Thirdly, the manufacturing cost of welding rod is curtailed a great deal since the resistance to destruction of the HAZ is higher without any nickel than in case of using the 100% nickel welding rod.
Fourthly, by a simple cold cast iron welding the main large or extra- large cast iron accessories which have frequent destruction at the fixed places owing to a very great load or various kinds of special cast iron manufactures which need to ensure high pressure sealing can be reproduced on a level of more than their original performance.
Fifthly, the dissimilar metal welding between a cast iron and a steel, in particular, a steel with very bad adhesivity in molten state or a high- tensile steel with very high hardenability, is made perfectly.
Sixthly, a large cast iron manufacture can be made easily in a way of welding, like steel.
BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 shows comparatively distribution diagrams of the hardness of cast iron weld joint in case of single bed welding in a gray cast iron (Cast 28-48) with an embodiment of the cold cast iron welding rod with nickelless steel wire according to the present invention and some previous cold cast iron welding rods.
Fig. 2 shows metallurgical microscopic photographs of the weld metal, HAZ and base metal in case of single bed welding in a gray cast iron (Cast 28-48) with an embodiment of the cold cast iron welding rod with nickelless steel wire according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Fig. 1 shows comparatively distribution diagrams of the hardness of cast iron weld joint in case of single bed welding in a gray cast iron (Cast 28-48) with an embodiment of the cold cast iron welding rod with nickelless steel wire according to the present invention and some previous cold cast iron welding rods.
In Fig. 1 diagram 1 is a distribution diagram of the hardness of cast iron weld joint for a low-carbon steel welding rod, diagram 2 for a monel (70% Ni + 30% Cu) welding rod, diagram 3 for a steel-nickel (70% Ni + 30% Fe) welding rod, diagram 4 for a nickel (100% Ni) welding rod and diagram 5 for an embodiment of the welding rod according to the present invention.
As can be seen in Fig. 1 , diagram 5 is most superior.
In case of using any of the previous cold cast iron welding rods the order of hardness in the weld joint is always base metal < weld metal < HAZ. But as to the welding rod according to the present invention the order of hardness in the weld joint is base metal < HAZ < weld metal.
A welding rod that the tendency of HAZ destruction is comparatively small among the previous cold cast iron ones is a nickel one with 100% nickel wire, but in diagram 4 in Fig. 1 the HAZ portion is still much higher and sharper than in diagram 5 for a welding rod according to the present invention and thus the tendency of HAZ destruction constantly remains to a certain degree.
But since, as can be seen diagram 5 in Fig. 1, in case of using the welding rod according to the present invention the hardness of the HAZ is lower than that of the weld metal the resistance to HAZ destruction is ensured fully and after all a reliable cast iron weld joint can be obtained.
Fig. 2 shows metallurgical microscopic photographs of the weld metal, HAZ and base metal in case of single bed welding in a gray cast iron (Cast 28-48) with an embodiment of the cold cast iron welding rod with nickelless steel wire according to the present invention.
The specimen was manufactured from the welded cast iron twelve hours after welding.
In Fig. 2 photographs 2a to 2d are metallurgical microscopic photographs of the weld metal, HAZ and base metal together at different places and the magnification is 100. And photograph 2e is a metallurgical microscopic photograph of the base metal, photograph 2f is of the HAZ, photograph 2g is of the weld metal and their magnification is 200.
As can be seen in Fig. 2, the structure of the weld metal is fine perlite + sorbite, the structure of the HAZ is perlite + sorbite + ferrite and the structure of the base metal is graphite + perlite + ferrite. There is no white pig iron in the weld metal or the HAZ.
It is clear that the weld metal has high mechanical properties since its particles are very fine and are distributed uniformly and it has no blowholes at all. The tensile strength of the weld metal in the cast iron weld joint is 480 to 520MPa in case of using the welding rod according to the present invention.
Some processing properties and the welding currents according to wire diameter are given respectively in Tables 1 and 2.
Table 1
Table 2