Research on a new tool steel cold welding seam (2)

Fig. 3 is a TEM photograph of the microstructure of the weld bead, and it is understood that the base is a typical lath martensite. Since the lath martensite has a low carbon content, the substructure is a high-density dislocation and has a good overall performance, thereby contributing to improvement of weld toughness. The reason for obtaining low-carbon lath martensite in high-carbon welds is related to the early formation of large amounts of carbides. The content of Nb, Ti and V in the weld is high, and a large amount of uniform carbide is formed in the liquid droplet or molten pool to form a large amount of uniform carbide, so that the carbon content in the austenite matrix is ​​lowered, thereby avoiding the formation of brittle high carbon twin horse. Clan. On the other hand, the reduction of the carbon content of the matrix also reduces the precipitation of the network secondary carbide after the weld is solidified, and the splitting action on the substrate is alleviated.

image 3



Figure 4

b. Impact test and fracture observation

The weld no-notch impact test results are shown in Table 2, and the fracture morphology is shown in Figure 4. It can be seen from Table 2 and Figure 4 that the average impact toughness of the weld is 52 J/cm ² , and the fracture is an obvious dimple-like fracture, indicating that the weld toughness is good.

Table 2 Impact toughness of weld specimen (αk, J/cm ² )

c. defect repair test

The surface defects of the 9Cr2Mo roll were trimmed with an angle grinder. After trimming, the defect size was about 30 mm and the depth was 8-10 mm. The cold welding process is used for defect repair. The interlayer temperature is about 35 ° C. Each layer is hammered immediately after welding to eliminate stress, so as to improve the grain morphology, eliminate the as-cast defects and reduce the welding stress. Magnetic particle inspection was performed after welding, and no cracks were found in the weld and heat affected zone. The weld hardness is 56-60HRC, which is close to the surface hardness of the 9Cr2Mo base metal (60-61HRC).

4 Conclusion

Surfacing test and test analysis shows that the use of strong carbide elements can obtain diffused carbonized material points in the cold-weld weld of tool steel, which can significantly improve the hardness and wear resistance of the weld; at the same time, the low carbon obtained in the weld The lath martensite matrix is ​​advantageous for improving the toughness and crack resistance of the weld. The new high-carbon Ti-Nb-V-Re-Cr alloy cold-weld weld can meet the requirements of cold-welding repair of tooling. The cold-welding process is simple and practical, and easy to promote.

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