JPS6157902B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to cast iron that suppresses hardening during welding and has excellent weldability. In general, cast iron has a strong tendency to whiten the welded parts, so many cast products are made in one piece, even those with complex shapes, and there are few examples of welding. Only a few post-casting repairs and welding have been applied to repair damage during use. Therefore, if weldability is improved, it is expected that the applications for wear-resistant materials, anti-vibration materials, structural materials, etc. will be dramatically expanded. Traditionally, technologies to suppress hardening caused by white pig iron have focused on improving the composition of the welding rod, the composition of the sheathing material, the welding method, and the welding equipment, but each has its drawbacks, and they are caused by the increase in deposited metal and unmelted metal. In the thin solid-liquid mixed phase that exists near the interface of the base metal, an undiffused and incompletely diffused layer of graphitizing elements occurs, and this area solidifies into white iron due to the cooling effect from the base metal. From these points, there was a need for a technology to improve the weldability of the casting itself. The object of the present invention is to provide cast iron with excellent weldability by adding elements that suppress hardening during welding of castings. That is, the present invention has (1) C: 2 to 4.8%, Mn: 0.1 to 1.5%, Si: 2.5 to
Cast iron with excellent weldability characterized by consisting of 4.5%, Al: 1.0~4.0%, Sb: 0.05~1.0%, the balance being iron and unavoidable impurities. (2) c: 2~4.8%, Mn: 0.1~1.5%, Si: 2.5~
4.5%, Al: 1.0~4.0%, Sb: 0.05~1.0%,
Ti: Cast iron with excellent weldability characterized by consisting of 0.01-1.0% balance iron and unavoidable impurities. In the present invention, in order to improve weldability, it is necessary to prevent the deposited metal from becoming dull. In other words, the cast iron of the present invention is characterized by the addition of Al, Sb, and Ti compared to conventionally known cast irons, and these added elements are eluted into the interface between the base metal and the weld metal and into the weld metal. It is thought that it becomes a nucleus for graphite crystallization during solidification, promotes its growth, and prevents whitening. These elements also promote graphitization within the base metal, leading to the crystallization of primary graphite, which is effective in preventing whitening. That is, during welding, the undissolved portion of primary graphite moves and diffuses to the interface between the base metal and the weld metal and to the weld metal, and in the process of solidification, this portion becomes a nucleus for graphite crystallization and promotes its growth. It is thought that this prevents whitening. The cast iron according to the present invention will be explained in more detail below with reference to the table. Table 1 shows test piece material melting conditions,
Table 2 shows the shape of the test piece, Table 3 shows the chemical composition of the welding rod, and Table 4 shows the TIG welding conditions.

【table】

【table】

【table】

[Table] Table 5 shows C: 3.69-3.82%, Mn: 0.52-0.55
% base material and Si: 4 levels of welding base material in the range of 2.09 to 4.75%, using a hypereutectic welding rod, the first
TIG welding was performed under the conditions shown in Tables 2 and 3, and the characteristics of the welded parts were examined to evaluate weldability.

[Table] Table 5 shows the chemical composition of the weld base metal, the characteristics of the weld zone, and the overall evaluation.When Si: 2.51% or more, no whitening was observed at the interface between the base metal and the weld metal.
In the tensile test, it broke from the base material, and the hardness was below Hv = 300, which is easy to machine. But Si: 4.75%
The base material contained exceeds HRB=100, which is the hardness allowed for cast iron in the present invention. Table 6 shows C: 3.64-3.78%, Si2.57-2.62
%, Mn: 0.49 to 0.52% as a base material, Al: 0.9 to 4.2, four levels of welding surface materials were melted under the same conditions as in Table 1, and welded under the same conditions as in Tables 2, 3, and 4. Then, the characteristics of the welded part were investigated and weldability was evaluated.

[Table] Table 6 shows the chemical composition of the Al-containing weld base metal, the characteristics of the weld zone, and the overall evaluation.
In the Al range of 1.0 to 4.0%, no whitening was observed at the interface between the base metal and the weld metal, and fracture occurred at the base metal in the tensile test. Hard graphite crystallization that impairs welding workability is 1.0 to 4.0
%, it was so small that there was no problem, and it was not observed at less than 1.0%. The hardness was 1.0% or more, Hv = 300 or less, and machining was extremely easy. Therefore
A suitable Al content is 1.0 to 4.0%. Table 7 shows C: 3.64-3.74%, Si: 2.60-2.63
%, Mn: 0.48~0.52% as base material, Sb: 0.04~1.15
Four levels of welding materials in the range of % were melted under the same conditions as in Table 1, welded under the same conditions as in Tables 2, 3, and 4, the characteristics of the welded parts were examined, and weldability was evaluated.

[Table] Table 7 shows the chemical composition of the Sb-containing weld base metal, the characteristics of the weld zone, and the overall evaluation.
Sb: At 0.05% or more, whitening does not occur at the interface between the base metal and the weld metal. However, crystallization of irregular graphite was observed at 1.01%. In the tensile test, samples containing Sb in the range of 0.05 to 1.01% broke at the base metal. Hardness within the same range
Machining was possible at Hv=300 or less. Therefore, the appropriate Sb content is 0.05 to 1.00%. As shown in the above experimental examples, the elements Si, Al, and Sb were added to suppress hardening during welding of cast iron, and the suppression effect was investigated and found to be effective. The content of these elements is Si: 2.5~4.5%, Al: 1.0~
If the Si content is less than 4.0%, Sb: 0.05 to 1.0, and Si content is less than 2.1%, whitening at the interface between the base metal and the weld metal cannot be prevented. If the amount exceeds 4.5%, solid solution of Si in the ferrite crystal lattice increases, causing hardening and ductility inhibition. When Al is contained, whitening cannot be prevented if the amount is less than 1.0%. If it is more than 4.0%, due to excessive crystallization of primary graphite in the base material,
This leads to a decrease in the strength, and during welding, hard graphite crystallizes, impeding welding workability and worsening the appearance of the welded part. If Sb content is less than 0.05%,
Unable to prevent whitening. If it is more than 1.0%, the shape of graphite will change and the strength and ductility of the base metal and weld will be impaired. As described above, in the present invention, by coexisting Si, Al, and Sb in ordinary cast iron, cast iron with extremely high weldability can be obtained. By the way, pearlite may be precipitated in the base of the welding base material containing Sb, which may impede the ductility of the base material. To prevent this, Ti is added. Table 8 C: 3.56-3.61%, Si: 2.57-2.65
%, Mn: 0.49 to 0.54%, Sb: 0.95 to 1.03%, and Ti: 0.008 to 1.020%, four levels of welding materials were melted under the conditions shown in Table 1, and the precipitation status of pearlite,
The crystallization status of Ti inclusions was investigated.

[Table] As shown in Table 8, pearlite disappeared when Ti was 0.010% or more, and crystallization of Ti inclusions was observed when Ti was 1.020% or more. Therefore, in a welding base material containing 0.05 to 1.00% Sb, it is appropriate to contain 0.010 to 1.000% Ti.In addition to Ti, other elements such as Ni, Co, Cu, and B can be used to prevent pearlite precipitation. It is also possible to utilize these elements. It is well known that in the case of steel, C hardens the welded metal part and the heat affected zone and reduces toughness, so it is preferable that C be as low as possible. However, since cast iron already contains a large amount of graphite, it is completely impossible to adjust the amount of C that penetrates into the weld. Therefore, the influence of C on the weldability of cast iron is small. However, as shown in the structure of the present invention and some experimental examples, crystallization of primary graphite, residual undissolved primary graphite, and nucleation are necessary to prevent whitening of the weld zone. As a condition, it is necessary to have a hypereutectic structure, but if it is too hypereutectic, it will hinder welding work and deteriorate the welding characteristics. Therefore, based on the experimental results, C was defined as follows. That is, C: 2 to 4.8%. C: If it is 4.8% or more, the properties of the weld will deteriorate, so 4.8
Limited to the following. Example 1 Cast iron consisting of the elements with the chemical components shown in Table 9, the balance iron, and unavoidable impurities was melted under the conditions shown in Table 1, processed into the shape shown in Table 2, and processed into the chemical composition shown in Table 3. TIG welding was carried out under the conditions shown in Table 4 using a welding rod with different compositions, and various characteristics of the welded parts were investigated. As a result, no crystallization of white pig iron was observed, and fracture occurred in the base metal in the tensile test. Hardness was less than 300 Bitkers hardness and could be easily machined. In addition, no crystallization of woody graphite was observed. As mentioned above, this base material has excellent weldability. In addition, some pearlite precipitation was observed at the base of the metallographic structure of the base metal.

[Table] Example 2 A cast iron welding base material consisting of the elements with the chemical components shown in Table 10, the balance iron, and unavoidable impurities was melted under the conditions shown in Table 1, and processed into the shape shown in Table 2. ,
Using a welding rod having the chemical composition shown in Table 3, TIG welding was performed under the conditions shown in Table 4, and as in Example 1, various characteristics of the welded part were investigated. As a result, no crystallization of pearlite or Ti inclusions was observed at the base of the metallographic structure of the base material. In addition, no crystallization of white pig iron or wood graphite was observed in the welded area, and the hardness was less than 300 bits. As mentioned above, this welding base material has excellent weldability at the welded part and the properties of the base material itself.

[Table] The welding base metal of the present invention does not require heating after preheating, and can be welded without taking into account the welding method or welding equipment to prevent whitening. Further, welding can be performed without being restricted by the shape or thickness of the welding base material.

Claims (1)

[Claims] 1 C: 2 to 4.8%, Mn: 0.1 to 1.5%, Si: 2.5 to
Cast iron with excellent weldability characterized by consisting of 4.5%, Al: 1.0~4.0%, Sb: 0.05~1.0%, the balance being iron and unavoidable impurities. 2 C: 2~4.8%, Mn: 0.1~1.5%, Si: 2.5~
4.5%, Al: 1.0~4.0%, Sb: 0.05~1.0%, Ti:
A cast iron with excellent weldability characterized by consisting of 0.01 to 1.0%, the balance being iron and unavoidable impurities.