A method to solve the problem of high local hardness of cast iron castings after welding repair

Abstract

The invention discloses a method for solving the problem of high local hardness of cast iron castings after welding repair, which is applied to the repair of casting defects in the production process of cast iron castings. Nickel cored electrode, the welding repair current is 80-120A, the welding repair process is divided into several intermittent welding, each welding repair time is 4-10 seconds, until the welding repair of casting defects is completed; step 2: heat treatment, Put the whole cast iron casting repaired by the welding repair method in step 1 into the annealing furnace for high temperature tempering treatment. The tempering temperature rise rate is 30-150°C / h, and tempering is carried out at a temperature of 450-600°C Heat treatment heat preservation, heat preservation time is greater than 2 hours. The invention can not only reduce the local hardness of the welding repair area to a level that does not affect the processing, but also maintain the original mechanical properties of the casting, and improve production efficiency and economic benefits.

Description

technical field [0001] The invention relates to the technical field of defect repairing technology of cast iron castings, in particular to a method for solving the problem of high local hardness of cast iron castings after welding repair. Background technique [0002] The cast iron casting production process is relatively complicated, and a certain proportion of casting defects will inevitably appear in cast iron castings. If these casting defects appear in unimportant parts of the casting, they can be rescued by welding to meet the performance requirements and reduce the loss of quality costs. , but after the casting is repaired by welding, the hardness of the welding spot is extremely high (greater than 280HB). The high hardness makes machining difficult, and in severe cases, it will also lead to tool breakage, scrapping of the casting, and serious losses. Therefore, it is necessary to solve the welding repair The problem of high local hardness of castings. [0003] The s...

AI Technical Summary

Problems solved by technology

[0004] The existing technology mainly uses the method of normalizing heat treatment to solve the problem of high local hardness of cast iron castings after welding repair. The disadvantages of this method are:

[0005] 1. Due to the stacking of castings, it is difficult to achieve uniform cooling when the castings are blown and air-cooled after they are released from the furnace. Some castings cool quickly and some castings cool slowly. Some parts of the same casting cool quickly and some parts cool slowly. When the cooling is too fast, the hardness is too high and affects machining. When the cooling is too slow, the hardness is too low to meet the performance, resulting in serious quality problems;

[0006] 2. The heating temperature is high. The graphitization annealing temperature for eliminating cementite is usually greater than 900°C. Our original process requirement is 910-920°C. The surface of the casting is oxidized seriously, which greatly increases the difficulty of subsequent cleaning;

[0007] 3. Special equipment is required for normalizing, and the equipment investment and operation and maintenance costs are high. At the same time, internal stress is generated after the casting is normalized. After normalizing, the casting needs to be subjected to stress relief annealing heat treatment.

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