For low-temperature steel, is it necessary to conduct a hardness test after heat treatment?
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There are several low-temperature equipment units made of 16MnDR and 09MnNiDR materials. After heat treatment, is a hardness test required? The hardness of the welded joint shall not exceed 225HB. Some people believe that low-temperature steels have very good toughness, and since welding test plates for low-temperature equipment have already been prepared, there is no need to conduct hardness tests after heat treatment. What are everyone’s thoughts on this issue? Especially those forum members who are engaged in manufacturing work, let’s share our experiences.
In my opinion, there is no need to test hardness after heat treatment. For materials used in low-temperature containers, the focus is primarily on their low-temperature impact toughness, whereas hardness is an indicator related to strength; the need to consider hardness arises mainly in the case of containers subject to stress corrosion.
That makes sense as an interpretation. However, I’ve seen drawings from many engineering companies, where for ordinary carbon steel, carbon-manganese steel, Q245R, and Q345R, hardness testing requirements are specified in the drawings. The material of the equipment does not exhibit a tendency to stress corrosion; heat treatment was applied only due to thickness considerations.
In the past, many design firms required that hardness testing be carried out for heat treatment, with the aim of evaluating its effectiveness and providing an additional proof of that evaluation; however, it seems unnecessary nowadays. Some designs take into account the instability of the materials being used, fearing a tendency to stress corrosion; this is generally not indicated on the design drawings, but hardness testing after heat treatment is required. From a manufacturing perspective, there are some design intentions that we are not aware of.
If the drawings specify 16MnDR or 09MnNiDR, a hardness test shall be conducted after heat treatment, with the hardness of the welded joint not exceeding 225HB. Can this hardness value be achieved?
For the design, you can put forward your requirements. . . But at the same time, the testing methods and standards, as well as the acceptance criteria, should be mentioned. . . As for whether these qualification criteria can be met, it is a matter of the design quality. You should know whether there is any basis for making these requests, whether they are necessary, and whether they are feasible to implement. . You could say that the standards are the minimum requirements. . Then you have to make a request. . Practical requirements. .
Quality control does not require you to design everything and specify it all in order to achieve quality control goals. . . Process, process. Process. . . For these two materials. . . The hardness of the welded joint shall not exceed 225HB. This figure should be achievable. . .
For these two materials, if it is possible to easily achieve a weld joint hardness of no more than 225HB, then does the hardness requirement specified in the drawings lose its meaning?
225 is achievable. . It’s not something that can be achieved easily. . It is welded according to specific processes and undergoes proper heat treatment, which can generally be achieved. . If it’s 300, that’s easily achievable. . . .
I checked the material standards and welding specifications, and no requirement regarding hardness was mentioned. I’m not sure how to approach this appropriately in actual work.
Those other experts and professors haven’t even touched this; it’s still up to individuals to be self-disciplined. . . . Don’t ask for it. .