Nadca 207:2024

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Last year, a new version of Nadca 207:2024 was released. Compared to the 2022 version, where some new principles were implemented, especially regarding the design of the shape of the hardening inserts, there were no significant changes in this new version. New steels were added, and none were removed.

Finkl SUPERDIE
Metal Ravne SITHERM S353R
Gröditz 2343 VICTORY ESR
Kind & Co. (Kind Special Alloys) – CS1

However, because the new version would be boring, the authors added a new term: Maximum Controlling Cross Section. What is it? I didn’t understand its meaning at first glance either. So, I asked the authors directly, at Paolo US, now Aalbert.

Basically, it is an aid for furnace operators in determining the tempering time. This is set at 1 hour per 1″ insert thickness, i.e. approximately 25 mm. This is in the case where we cannot measure the core temperature Tc. The tempering time can therefore be estimated, not by thickness, but by Maximum Controlling Cross Section. This is for cases where the inserts do not have a uniform and unambiguous cross-section.

The example of an insert below has two completely different cross-sections. To avoid any doubt, the heat treater is tasked with tempering part according to the maximum cross-section, not the minimum. My understanding is that even though the thin part of the insert will have a lower hardness as a result, for the purpose of tempering the insert and for targeted resistance to thermal fatigue, it is important to temper the maximum cross-section correctly. The operator should imagine this as a ball stuck into the maximum cross-section

However, if we have the possibility to place a thermocouple Tc, then regardless of the above, we will follow the actual temperature in the core. If, for example, we achieve a piece temperature of Tc-Tfurnace = – 15 °C, the dwell time at the tempering temperature will start. It must be at least 2 hours. The longer the set time, the better, but the economy of the process will deteriorate. It has been verified that if we temper twice in a row at the same temperature, we lose 0.5 to 1 HRc of hardness after second one. A longer tempering time, e.g. 3 hours, will have a similar effect. If we want to have long-term reproducible results, the parameter dT, e.g. -15 °C, and the dwell time in minutes must be fixed the same for all tempering processes.

All changes in Nadca 207:2024 compared to Nadca 207:2022 are shown in the attached images.