What is the microstructure of steel plates with the Japanese grade SS400?

Is it normal for the microstructure of this steel to show bainite?

SS400 is a common carbon structural steel, equivalent to China’s Q235 steel. During the hot working of materials, improper temperature control or overheating can result in Widmanstatten structure. Wei’s structure not only features large grains, but also causes a rapid decline in the metal’s ductility due to the fragile surfaces formed by numerous ferrite needles, which easily leads to embrittlement and cracking of welded joints in steels such as SS400 that are difficult to quench.

I’m facing a situation where a lining device made from this material caught fire once during use. After that, it was tested by a specialized testing agency, and the mechanical properties of the material as well as the results of its physical and chemical tests were all within normal ranges. However, the report indicated that the microstructure of the material was bainite; I’m not quite sure about this. What is the difference between bainite and bainitic structure? What does this mean?

This post was last edited by nj1952 on 2017-7-15 at 13:31. (1) In metallographic structures, bainite is also often referred to as bainitic structure. For example, austenitic stainless steel has an austenitic microstructure, also known as an austenitic structure. (2) Generally speaking, the formation of Widmanstatten structure in the overheated zone of the welding heat-affected zone is normal, as this is determined by the metallurgical processes associated with welding; moreover, the properties of a metal depend on its microstructure, which is a fundamental principle in metallurgy. Therefore, the structural changes in the weld zone and heat-affected zone of welded joints will inevitably affect the changes in their mechanical properties. Wei’s structure is often found in welds; it reduces toughness, but generally it does not affect usability. (3) But in your case, it’s not possible to give a simple reply; each situation needs to be dealt with on its own. For example, the technical parameters of the equipment (operating pressure, temperature, medium, specifications, material), the equipment’s structure (lining method), the cumulative operating time of the equipment, its performance during service before the fire occurred, whether major repairs have been carried out and which parts were repaired, the extent and scope of the fire damage to the equipment, the methods used for extinguishing the fire, the inspection items and sampling locations after the fire (areas where Widmanstatten structure appeared), the inspection conclusions, whether the equipment is intended to be reused, and the basic approach to repairing it for reuse, etc. (4) You mentioned that \"a specialized testing agency was consulted, and the mechanical properties of the material as well as the results of the physical and chemical tests were all within the normal range\". What were the test items? Were samples taken from the equipment itself? What were the test results?

This post was last edited by whr73229880 on 2017-7-15 at 16:02. Samples were taken from the equipment itself – samples with welds as well as those without welds. Of course, the goal was to determine whether the steel base part of the equipment could be reused, and the test results are those I mentioned above There has been no determination as to whether it can be reused. It had not been overhauled before; the tower body was lined with glass flake. Since there were non-flammable liquids at the bottom, the fire did not spread there, and it mainly affected the middle and upper parts of the tower.

(1) “It’s samples taken from the equipment – samples with welds and those without welds. Of course, we want to know whether the steel base part of the equipment can be reused; the test results are what I mentioned above.” Your response fails to clarify things, and the relevant questions from floor 5 also haven’t been addressed one by one, so it’s difficult to provide a reply. (2) It is recommended that enterprises entrust a boiler inspection agency to conduct a comprehensive inspection of the equipment, using its suitability for use as a criterion to determine whether it can be reused.