Scenario: 

The end customer required to test the HAZ of welding parts, but the width of the HAZ is only 1.5~2mm, which the Leeb impact device couldn’t test it due to the huge indentation.

Solutions:

According to Sinowon professional experience in the field of hardness testing, the better portable hardness tester for HAZ hardness should be ultrasonic hardness tester. With 2.46mm diameter UCI Oscillating Rod and 0.35mm width indentation, Sinowon UCI SU-300 with 50N manual probe can test the hardness of HAZ easily and accurately.

What's max hardness of HAZ?

The max hardness of HAZ is one of the important indexes for evaluating the weldability of steel, which is more accurate than carbon equivalence. Adopting the max hardness of HAZ as a factor to evaluate the weldability (including welding cold crack sensitivity), can not only reflect the role of chemical composition of steel, but also the role of different microstructure formed under the different welding process.

Hardness and strength have a certain corresponding relationship, which the strength is high, the corresponding hardness is also high. Therefore, the max hardness of HAZ will reflect the strength of HAZ. When the strength of the HAZ is too high, it will lead to the decrease of its plasticity, which it is easy to form cracks or crack is easy to expand. The hardness of different microstructure is different. In steel, the hardness of high-carbon martensite (twin martensite) is the highest, and the plasticity and toughness of high-carbon martensite are the worst, so the highest hardness of HAZ can also indirectly reflect the performance of the joint.

In welding parts such as steam turbine rotors, performance testing methods are limited because the workpiece cannot be damaged. Hardness, as a convenient and reliable means of detection, has significant advantages.