【JST-067】One-on-one consultation service for pipeline technology experts in flange forgings

Question to experts: In Table 3 of NB/T47008-2010, in the column for heat treatment conditions, are the heat treatment conditions listed there corresponding to the thickness values mentioned earlier? Why doesn’t the thickness distinction line at the front extend to the heat treatment status column, so as to provide a clearer representation? For example, for steel grade 20 with a nominal thickness of 120 mm, in what heat treatment condition should it be delivered? Steel grade 20, nominal thickness 60mm – in what heat treatment condition is it delivered? Thank you for the guidance!

Hello! The heat treatment conditions at the back correspond to the thickness at the front. There are three types of heat treatment conditions: N–normalizing, Q–quenching, and T–tempering. The heat treatment method used varies depending on the material, and it is not related to the thickness. The different thicknesses of the workpiece affect its mechanical properties.

Is it thickness-related again, or is it unrelated? Could you explain it in detail using the example I gave? Thank you so much!

Due to differences in thickness, the corresponding mechanical properties vary. However, they use the same heat treatment method, so it can only be indicated accordingly in the table. For example, for those with thicknesses of 120 mm and 60 mm as you mentioned, their heat treatment methods are both normalizing + tempering; thus, their heat treatment processes are the same. I’m not sure if you understand now?

I’m sorry, I haven’t come here to check for a while; I just see it now! What you mean is that different materials determine their respective heat treatment conditions, independent of thickness, right? I would like to discuss my doubts using specific examples: 1) For 20 steel with a thickness of 60 mm, I think normalizing followed by tempering should be used; however, for the same thickness of 120 mm, I have a different opinion. I think the standard here offers two heat treatment methods: normalizing, and normalizing + tempering. When the thickness is relatively thin, such as 60 mm, normalizing is sufficient to achieve the mechanical properties required by the standards. There is no need to use normalizing + tempering. 2) 16Mn forgings, with heat treatment conditions including normalizing, normalizing + tempering, and quenching + tempering (quenching and tempering); here one material comes in with multiple heat treatment options. How should this be understood? I’m sorry for troubling you again; I truly hope to get my doubts resolved! Thank you. The heat treatment status at this location isn’t indicated with horizontal lines like in the previous sections, so I find it quite confusing. Is the standard not specific enough, or does it mean that any heat treatment condition is acceptable? ?

I have a question: In HG20596-97, the flange thickness for PN0.6MPa is greater for DN600 than it is for DN700–1200. Why is that?

“I would like to discuss my doubts using specific examples: 1) For 20 steel with a thickness of 60 mm, I think normalizing followed by tempering should be used; however, for the same thickness of 120 mm, I have a different opinion. I think the standard here offers two heat treatment methods: normalizing, and normalizing + tempering. When the thickness is relatively thin, such as 60 mm, normalizing is sufficient to achieve the mechanical properties required by the standards. There is no need to use normalizing + tempering. 2) 16Mn forgings, with heat treatment conditions including normalizing, normalizing + tempering, and quenching + tempering (quenching and tempering); here one material comes in with multiple heat treatment options. How should this be understood? The heat treatment methods specified in the standards mean that for materials such as 16Mn, all three of these heat treatment methods can meet the requirements for using the product; that’s all there is to it. In practice, manufacturers choose the heat treatment method to use based on factors such as cost. I’m not sure if you understand now after saying this? The heat treatment status at this location is not indicated with a horizontal line like in the previous sections regarding thickness, so I find it quite confusing. Is the standard not specific enough, or does it mean that any heat treatment condition is acceptable? ? Any heat treatment condition will do

The thickness of the material affects the heat treatment time. I’m curious to know what the moderator thinks about the holding time for heat treatment according to NB/T47008–10. Are there different ranges or specifications for the holding time depending on the thickness of the material? for reference.