ASTM A291 Tempering Temperature 1

[kpedde01]

Hello All:

ASTM A291 dictates the minimum tempering temperatures that shall be followed.

My questions

1. What is the reason for dictating the minimum tempering temperature ?

2. Can you go any lower on the tempering temperatures (when hardness is not achieved) and what are the risks in doing so.

Thanks for the help in advance.

 

[metengr]

The minimum tempering temperature is typically specified in most ASME/ASTM material specifications to ensure adequate ductility of the material for forming and service. Higher tempering temperatures will result in improved ductility and increased toughness. However, the downside is lower strength properties, so this is why a minimum tempering temperature is provided and not a maximum (in most cases). If you temper below the minimum tempering temperature this is a nonconformance with the requirements of the material specification. This means lower ductility, higher hardness and strength which could effect further forming, performance in service and weldability.

 

[EdStainless]

Under ASTM rules if you don't comply with ALL aspects of the specification then you do not meet it. Period.

I don't know what the minimum in A291 is, but many alloy steels have a range of intermediate temperatures that while they produce the expected strength they have very poor ductility. There are some specs that have been drafted to prevent people from falling into this range.

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P.E. Metallurgy, Plymouth Tube

 

[redpicker]

I always viewed the minimum tempering temperature as a way to insure adequate quenching response. If you are not meeting the minimum hardness when tempered at the minimum tempering temperature, your quench is not effective. While lowering the tempering temperature will raise the hardness, it doesn't fix the problem.

And, as stated, if you use too low a tempering temperature, the material will lack the toughness and ductility required. Fix the problem, not the symptoms.

 

[tbuelna]

The ASTM spec lists min tempering temperatures for different material classes, but it also lists mechanical property requirements for those material classes.