Abstract
Weldability testing is an essential part of welding process in the manufacture of structural components to ensure the reliability and durability of the weldments. The highest hardness test method (GB 4675.5-84) is one of the welding performance tests, by which the maximum hardness of the heat-affected zone (HAZ) of welds in ferrous materials can be determined. This paper briefly describes the principles, equipments, samples and procedures of the highest hardness test method in GB 4675.5-84, in order to provide the basic information for further studies of the weldability performance.
Key Words: Weldability Testing; Heat-Affected Zone; Highest Hardness; GB 4675.5-84;
1 Introduction
Highly reliable and durable weldments are need in the manufac¬ture of structural components, and weldability testing is one of the important processes to ensure the service requirements of weldments. The highest hardness test method (or referred to as HAZ highest hardness test, GB 4675.5-84) is used to determine the maximum hardness of the HAZ of welds in ferrous materials. This paper will discuss the principles, equipments, samples and procedures of the highest hardness test method in GB 4675.5-84.
2 Principles
The maximum hardness of the HAZ of welds can be observed through destructive testing, which is carried out to study the parameters such as the microstructure, hardness and metallurgical properties of the welds. According to GB 4675.5-84, the HAZ highest hardness test is based on the rockwell hardness test, by which the maximum hardness of the HAZ of welds can be measured.
The maximum hardness of the HAZ achieved through the highest hardness test is determined based on the hardness-distance curve. The hardness-distance curve is the graphical portrayal of the hardness versus the distance away from the weld centerline. The maximum hardness of the HAZ is determined by the highest value of the hardness-distance curve.
3 Equipments
In order to perform the highest hardness test method, the necessary equipments include a Rockwell hardness tester, an optical microscope, a cutting machine, digital caliper and a bezel. Generally speaking, the Rockwell hardness tester should satisfy the requirements such as having a minimum range of 15HRBs, control accuracy of 0.5HRB and a resolution of 0.1HRB.
In addition, the optical microscope should have a minimum magnification of 100x, with the maximum magnification being 800x. The cutting machine, digital caliper and bezel all should meet the requirements of GB 4675.5-84.
4 Samples
For preparing the samples for highest hardness test, the samples should be cut from the actual weldment, with the end of the weld being at least 5mm away from the nearest notch or weld fusion line. The cut samples should have smooth surface.
5 Procedures
The highest hardness test procedure of ferrous materials is in accordance with the following steps:
1. Measure the surface hardness of the sample by the Rockwell hardness tester.
2. If the surface hardness is lower than HRc 35, perform heat treatment on the sample and then measure the surface hardness again until it reaches HRc 35.
3. Cut the sample by the cutting machine at a distance of 1mm away from the surface.
4. Measure the hardness of the cut surface using the Rockwell hardness tester.
5. Place the sample on the bezel, and measure the hardness of the cut section at every 0.5mm intervals in the HAZ at five levels.
6. Calculate the maximum hardness of the HAZ through the hardness-distance curve.
7. Analyze the structure of the HAZ by the optical microscope.
8Conclusion
Weldability tests are conducted to evaluate and verify the performance of weldments. The highest hardness test method is an indispensable performance test which assesses the maximum hardness of the HAZ of welds in ferrous materials. In this paper, the basic principles, equipments, samples and procedures of GB 4675.5-84 has been discussed, which also provides the basic knowledge for further studies of the weldability performance.
