JPS5932236B2 - Manufacturing method of wear-resistant strong parts - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a member made of composite cast iron that has wear resistance, high strength, and high toughness by welding.

In recent years, low chromium cast iron, high chromium cast iron, nihard cast iron (trade name), etc. have come to be used in large quantities for wear-resistant parts of various types of crushers, etc., but this type of cast iron has high hardness carbide,
For example, although it has high hardness due to the precipitation of chromium carbide, its biggest drawback is that it lacks toughness, and if the residual thickness decreases due to wear during use, there is a risk of breakage in applications that are subject to impact, so there is a problem with breakage resistance. can be said to be inferior to tilt casting of composite cast iron.

Furthermore, this kind of wear-resistant alloyed cast iron has the disadvantage that weld cracking is likely to occur, making it difficult or impossible to repair weld overlays in areas where local wear has occurred, and in compound folded parts, casting cracks are likely to occur, resulting in lower yields. The problem is that it is bad and expensive.

The purpose of the present invention is to easily manufacture tilt-cast composite cast iron, which has excellent wear resistance on the surface layer and toughness on the inner layer, using the welding metallization method, and to use spheroidal graphite cast iron, which has higher strength and toughness than gray pig iron, as the base metal. Use white pig iron or low chromium cast iron, high chromium cast iron, nihard cast iron, as surface hardening layer.
In addition, by forming alloy cast iron with a high degree of wear resistance, it has better wear resistance and impact resistance than conventional tilt composite cast iron, and has better breakage resistance than conventional wear-resistant alloy cast iron. It is an object of the present invention to provide a method for manufacturing a member that compensates for the drawbacks and has both advantages, and furthermore, it is an object of the present invention to provide a member that has the advantage of being able to be reused and repaired for localized wear and reusable.

The present invention uses spheroidal graphite cast iron as the base material. Spheroidal graphite cast iron has excellent weldability, which makes it possible to carry out this method, and also has the advantage of being able to reuse the member by performing the above-mentioned recycled repair overlay. In addition, the present invention performs deep penetration to utilize the large amount of graphite contained in the base metal, spheroidal graphite cast iron. Normally, when hardening metallization by welding, the penetration depth is as small as possible, and the base metal is diluted. Weld the deposited metal in such a way as to minimize the amount of damage and maintain the original components, composition, hardness, and wear resistance of the deposited metal, and weld at least 2 to 3 layers to eliminate the effects of dilution of the base metal. However, the present invention is directed in the completely opposite direction, and actively promotes deep penetration into the base metal by using the filler metal, thereby reducing the amount of metal contained in the base metal. The idea is to make effective use of certain elements, especially graphite, in the formation of wear-resistant hardening metals.

That is, the present invention uses spheroidal graphite cast iron as a base material, and uses a filler metal or alloy powder containing mild steel or a metal that combines with carbon in the base material to form a high-hardness carbide, and then deposits the weld metal by further depositing. The point is that deep penetration metallization is performed with a wall thickness H of 7 mm or less and a penetration depth P≧1.5H into the base metal to form hardened metal in the metal fill and the weld area. As described above, the present invention aims to form hardened metal in the first layer of weld metal and its penetration area, so if an even thicker wall is desired, the first layer can be formed with a conventional surface hardened welding rod. A surface hardened metal is applied on top. Here, the filler metal refers to filler materials, such as automatic welding wire (solid wire, tubular wire), etc.

The method of the present invention includes, for example, 13%Cr, 17%Cr, 23%Cr,
(Welding conditions that actively obtain deep penetration using FbCr, 28% Cr welding wire, etc. are adopted, and the graphite of the base metal and Cr contained in the welding material, for example, are combined to precipitate chromium carbide to improve wear resistance.) This results in a hardened metal.

This carbide is not limited to Cr, but also W, Nb, Ti, B, etc.
It is also possible to form a high hardness carbide in the weld metal and the injected metal by adding alloying elements such as , etc., to combine the graphite contained in the base material graphite cast iron with these carbide forming elements. Alternatively, it is also possible to simply deposit the base material of spheroidal graphite cast iron using mild steel wire to obtain a white pig iron layer. In the present invention, the reason why spheroidal graphite cast iron is used as the base metal is as follows.

(1) Spheroidal graphite cast iron contains 2.8% to 4.0% graphite.

Since the method of the present invention actively utilizes penetration into the base material to form carbide in the hardened portion, spheroidal graphite cast iron with a high graphite content is an extremely desirable base material. (2)
Spheroidal graphite cast iron has high strength and ductility as a base material, and has better weldability than ordinary cast iron, so even if cracks occur in the hardened layer, it will not lead to fracture of the base material.

When cracks come into contact with spheroidal graphite, the spheroidal graphite acts as a kind of prevention of crack propagation, preventing the crack from propagating further into the base material. In the case of acicular graphite in ordinary cast iron, cracks easily propagate through the base material and lead to fracture.

(3) Ordinary cast iron is prone to cracking due to the difference in thermal expansion caused by rapid heating and cooling during welding, but spheroidal graphite cast iron has less thermal expansion than ordinary cast iron and is less prone to cracking.

In the present invention, the reason why the maximum thickness of one layer of welded metal is limited to 7 mm or less when performing deep penetration is 7u71!
When welding the above thickness onto spheroidal graphite cast iron without preheating,
This is because the shrinkage stress generated after welding increases, and cracking or peeling occurs along the hard cementite layer formed in the weld heat affected zone due to the notch effect at the bead toe. Therefore, in carrying out the present invention, the thickness of the welded metal is made as small as possible, preferably the thickness H is about 2 to 3 μ to reduce shrinkage stress, and the penetration depth is increased to increase the hardening depth. It is better to do so.

If a thicker wall is desired, a surface hardened welding rod is used to overlay the metal as described above. Further, in the present invention,
The reason why the penetration depth into the base metal is limited to P≧1.5H is as follows.

In the present invention, when a C: less than 1.7%, that is, a cast steel composition is formed on the base material spheroidal graphite cast iron, the difference in linear expansion coefficient between the hardened layer and the spheroidal graphite cast iron increases, and the difference between the penetration layer and the spheroidal graphite cast iron increases. Internal stress generated in the cementite portion at the boundary with cast iron during the contraction process after penetration may cause cracks or peeling along the brittle cementite layer. Therefore, in the present invention, a composite cast iron is formed in which the C content of the base material spheroidal graphite cast iron, the weld metal, and the welded part is 1.7% or more, which is a cast iron composition according to the Fe-C system phase diagram. I'm aiming for that. In this case, use a mild steel welding rod to deposit 3%≧C≧4.0 (Fb) on spheroidal graphite cast iron, and in order to obtain a hardened layer with C:1.7 (fl) or more, the penetration rate must be This is because it is necessary to set it to at least 60% or more.However, in order to obtain a penetration rate of 60% or more, the relationship between the thickness H of the weld metal and the penetration depth P into the base material spheroidal graphite cast iron. is represented by 1) below, and the thickness of one layer of welded metal is as described above in (2) below, so the hardened metal in the diagonally shaded area in Figure 1 surrounded by (1) and (2) above is The provision is within the scope of the present invention.

The present invention utilizes a hardened metal portion consisting of a thick welded metal and a penetration hardened portion as a wear-resistant layer. Therefore, if the thickness of the weld metal is 7 mm and the penetration rate is 60%, the thickness of the wear-resistant layer will be as follows. As mentioned above, since the present invention actively utilizes penetration into the base material spheroidal graphite cast iron, welding methods that provide deep penetration are preferred, such as submerged arc welding, MIG welding, carbon dioxide arc welding, Various automatic welding methods such as electric mouth gas welding are suitable.

Next, examples will be described.

The present invention was implemented in a guide chute of a coke oven.

The guide chute of a coke oven is a guide plate for coke when the coke is pushed out of the coke oven by the ram head and introduced into the fire extinguishing engine, and conventionally, a spheroidized graphite cast iron material such as JISF CD4O has been used, but it is prone to wear. It is a part. The experiment was conducted using the conventionally used FCD4O spheroidal graphite O.
Using cast iron as a base material, three types of guide chute members were prepared by the method of the present invention, on which hardened metals of 1 white pig iron composition, 2 low chromium cast iron composition, and 3 nihard cast iron composition were formed.

Its dimensions and shape are as shown in Fig. 2, and the above sample 1
, 2, 53, the types and components of the filler metals used to form the hardened metals are shown in Table 1, and the chemical components and mechanical properties of the base metals are shown in Table 2. All three types of weld metals were made by automatic submerged arc welding under the following welding conditions. The above three types were operated to obtain similar penetration rates. Fig. 3 shows a cross-sectional view of the shape of the overlay and the weld into the base material FCD4O material. The table below shows the dimensions of the metal fill (extra metal) height H, penetration depth P, bead width W, cross-sectional area of the metal fill part, cross-sectional area of the weld part, and penetration rate. . Table 4 shows the component values and the average hardness of the weld metal and the weld metal calculated from the chemical analysis values and penetration rates of the weld metal and the weld metal of these three types of samples.

As shown in the table above, the analytical values and calculated values are approximately similar, so once the chemical composition and penetration rate of the wire used and the base material spheroidal graphite cast iron are known, the chemistry of the hardened metal part obtained by implementing this method can be determined. The components can be roughly estimated.

Further, the hardness of the hardened metal portion is the average value at each point in the vertical direction, approximately at the center of the hardened metal portion for Samples 1, 2, and 3.
In addition, the hardness of the cementite layer formed in the weld heat affected zone was surprisingly low in the above experiment, and was in the range of Hv 35O to 450. This is thought to be due to the large amount of heat supplied and slow cooling due to the use of weeping welding, and the concern about cracks occurring along the cementite layer was eliminated. Above 3
As a result of a life test using various types of samples in an actual coke guide system, it was found that the conventional spheroidal graphite cast iron had a service life of about 3 months, whereas the white pig iron of sample 1 had a service life of about 3 months. The composite cast iron liner lasted about 5 months, the low chromium composite cast iron liner of sample 2 lasted about 6 months, and the nihard composite cast iron liner of sample 3 lasted about 8 months.
The above is a case in which the present invention is applied to the production of a guide chute for a coke oven, but the present invention can also be applied to various types of shoot liners, coke crushing nozzles, ore crushing rolls, and other members that require wear resistance and toughness. It can be implemented in production and produce results.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the wall thickness H and penetration depth P of weld metal within the range of the present invention. FIG. 2 is a perspective view showing the shape and dimensions of a coke oven guide chute member according to the method of the present invention used in an example. FIG. 3 is a sectional view showing an example of the shape of the welded metal and the welded part into the base material according to the method of the present invention. 1: base material, 2: weld metal, 3: weld metal, 4: cementite layer, 5: countersink for bolt.

Claims (1)

[Scope of Claims] 1. Spheroidal graphite cast iron is used as a base material, and a filler metal or alloy powder containing a metal that combines with mild steel or carbon of the base material to form a high-hardness carbide is used, and then further metallization is performed. Thickness H of welded metal is 7 mm or less, penetration depth into base metal P≧1.5
A method for manufacturing a wear-resistant and strong member, which is characterized by performing deep penetration metal filling (H) to form hardened metal in the metal filling and the weld area. 2. Spheroidal graphite cast iron is used as a base material, and a filler metal or alloy powder containing mild steel or a metal that combines with carbon in the base material to form a high-hardness carbide is used, and the thickness of the weld metal is increased by further depositing. is 7mm or less, penetration depth into base metal P≧1.5
Wear-resistant and strong, characterized by performing a deep penetration metal layer H, forming hardened metal on the metal layer and the weld area, and forming a surface-hardened metal layer on the metal layer with a surface-hardened welding rod. How to make parts.