It is approximately equivalent to 441 stainless. Ferritic stainless grades cannot be hardened through austentizing and quenching. But they can be softened by annealing. What is your goal in heat treating this grade? What type of heat treatment did you have in mind?
from my experiences, many of customers have unreal requirement to mechanical properties, but on this chase the mechanical properties requirements looks absolutely realistic. I guess these properties should be reached without heat treatment as well because heat treatment for alloy like this has no significant impact on mechanical properties.
Is it casting or any forged parts? How values of mechanical properties you reached?
lakk, now it makes a sense for me, our customer always request from our castings mechanical properties like from formed part (e.g. plate) made of the same material (maybe it is the same customer as in your case).
Please, realize the tensile test and let me know the results. Stainless steel castings usually have Rm, Rp0,2 and elongation level lower as formed products made of the same steel (e. g. stainless steel casting Rm is usually about 50 MPa lower in comparison with the minimal requested value for formed product, especially in this very low cabon grades).
"EN 1.4509 / AISI 441*
Grade 1.4509 is a Ti and Nb dual-stabilized ferritic grade with improved weldability. Corrosion resistance is often comparable to that of general austenitic grade 1.4301. It is used in a wide range of applications, such as elevator and indoor claddings, door frames, catering and appliance, tubes and heat exchangers.
Grade 1.4509 has good oxidation resistance up to 950°C and is therefore used in exhaust system applications, where it also offers a better general corrosion resistance than grade 1.4512." ( ref outokumpu)

Chemical composition (typical)EN 1.4509
C 0.02%, Cr 18%, Ti+Nb 0.6%, Bal Fe Cr Mn
For castings a suitable grade will be ASTM A 743 Gr CB30. The heat treatment recommended is heat to 790C and the furnace or air cool.
As a foundry, it will be difficult to have low Carbon , unless you have refining facilities. Also, remember that a casting will have coarse grains, chemical inhomogeneity, porosity etc. Thus, it is not adequate to maintain the chemistry of a wrought product and achieve similar mechanical properties in a casting. Caution must be exercised.
"Even,if you are a minority of one, truth is the truth."
