Carbon Material (SA516-70) to be Normalized and Tempered

Normalisation - Ferrite + pearlite - fine grained structure - high strength.

Tempering - The precipitated cementites (precipitation hardening) improve the strength with just a bit compromise on toughness. (the final result depends upon the tempering temperature)

The purpose of tempered material is to increase hardness. Before tempered, it need to be normalized first. The purpose of normalizing is to remove internal stress induced by welding, forging, forming, machining etc. Stress if not controlled leads metal to failure. In the normalized condition steel much tougher than any other condition. So before hardening steel, you should normalizing it first to ensure maximum desired result. Usually low carbon steel don't required normalizing.

16.4.11

Normalising of fabrication material is common and understandeable from the stress relieving point of view. If your customer has not gone overboard and loosely specified normalising and tempering, the following implications emerge:

1.Tempering is necessarily a post quenching treatment which would mean heating beyond 730 deg C will be involved.

2.This will have to be done for individual parts pre- fabrication.Welded fabrications are not quenched.Post quenching, you will have to temper for couple of hrs at temps usually in the 200 deg range.

3. After that, complete your fabrication and subject the assembly to normalisation.

There is merit in this approach but can be expensive. Viability will depend on local infrastructure available.Have you provided for this in your estimation? .If not, the only way out is get back to your customer, have detailed discussion and get a price correction.

Vinay Isloorkar, Pune India

Some grades of Mild carbon steels are heat treated to improve mechanical properties. They are known as heat treated carbon steels. The heat treatment is either Normalizing (or) Quenching & tempering.

In as rolled condition, they give a yield strength of around 450 N/mm2. In the heat treated condition, the Yield strength will go up to 690 N/mm2 along with excellent notch toughness. These materials available mostly in plate form, has excellent Weld-ability and welded with conventional welding processes.

When heavy sections of coarse grained steels are normalized, the microstructure becomes uniformly finer (ex: SA 515 Gr Steels) and it will improve their Notch Toughness, so that they meet the impact test requirements at sub zero temperatures.

Very heavy sections of fine grained steels are quenched and tempered, so that they acquire a microstructure whose toughness matches that of thinner normalized sections of those steels ( ex: ASTM 516 Gr. Steel over 75 mm thick)

Normalized grades can be welded as easily as mild steel without any spl. Precautions. In case of quenched and tempered steels, heat input control is necessary when saw process selected ( general practice for heavy sections) For example, for A 516 Gr, Steels it should be below 3.2 KJ/ mm.

The important consideration in welding all these heat treated steels is to select welding consumables and procedure that will give joints of matching strength and sub zero impact values.

For manual welding Low Hydrogen Electrodes (AWS E 7018 or -16) are suitable. For SAW (or) similar Processes, high Manganese ( 2 Mn %) or Mn-Mo wire with basic flux should be preferred.

Sridhar.

For ASME material SA-516, the code define the heat treatment requirements as follows, unless there is a need for special requirements specified by the purchaser and included in the contract/purchase order signed with the supplier:

5. Heat Treatment

5.1 Plates of 1.5" (40 mm) and under in thickness are normally supplied in the as-rolled condition. The plates may be ordered normalized or stress relieved, or both.

5.2 Plates over 1.5" (40 mm) in thickness shall be normalized.

5.3 When notch-toughness tests are required on plates 1.5" (40 mm) and under in thickness, the plates shall be normalized unless otherwise specified by the purchaser.

5.4 If approved by the purchaser, cooling rates faster than those obtained by cooling in air are permissible for improvement of the toughness, provided the plates are subsequently tempered in the temperature range 1100 to 1300 oF (595 to 705 oC).

Dear Sir,

Where does the material specifications actually specify the heat treatment temperature and holding time? Or is it fully under the mill's discretion as long as the material properties complies after the heat treatment?

Thank you kindly.

Thank you so much for all of answers

Subcontractor which is mill manufacturer to make steel says that one more process to tempering after normalizing so, more expensive while the material is more valuable.

No way to persuade end user to remove the requirement to be tempered ?

This project is not enough time to meet delivery due day so, the material which carry out both Normalizing and tempering will be supplied longer time than general required material.

Anyone who have good idea to solve this problem?

i want to increase the yield strength of Sa 516 to min 450 mpa

what process i have to follow . normalizing or hardened & tempered

& if anybody have heat treatment chart. pls share