Standard-probe measured curve
Describes the medium response for the stated probe and test conditions. It is not the surface or core curve of a production workpiece.
Maximum Round-Bar Critical Diameter Calculator(DI + H)
Calculate the critical diameter Dc at which the center of an infinitely long round bar reaches 50% martensite under finite quench severity; also check a specified target diameter and back-calculate the required H.
Dc / DI
=
f(H · DI)
｜
H
:
in⁻¹
Geometry
Infinitely long round bar; not a universal size for arbitrary complex workpieces
Microstructural criterion
Grossmann critical diameter for 50% martensite at the center of a round bar
Numerical method
Numerical solution of the cylinder-center half-temperature relationship; the old simplified formula is not used
Input Parameters
mm
Must be greater than zero. DI should come from measured hardenability conversion or a composition calculation within its validity range.
Current: page example
in⁻¹
H must retain its unit. Use a known or calibrated value, or a clearly identified historical reference boundary.
Current: page example
mm
Compare under the same infinitely long round-bar, 50% martensite center criterion; first establish an equivalent size for a complex section.
Valid input. Calculating with the Grossmann model.
Calculation Results
Actual Round-Bar Critical Diameter Dc (50% Martensite at Center)
--
mm
DI
--
H
--
H × DI
--
Dc / DI
--
Ideal Limit and Finite-H Result
DI
--
Dc
--
Target-Diameter Check
!Waiting for calculation
Enter DI, H, and the target diameter to obtain an assessment.
Required H: --
Meaning of critical diameter: When the round-bar diameter equals Dc, the model predicts exactly 50% martensite at the center. Below Dc it predicts more than 50%; above Dc, less than 50%.
Production limits: The result excludes shape factors, surface heat-transfer variation, load shielding, bath degradation, temperature uniformity, and the effects of carbide state and segregation in the steel.
Theoretical relationship · process validation required
Method: Grossmann cylinder-center half-temperature relationship using the first cylindrical-series term and numerical root finding; the output definition matches the original critical-diameter criterion.
Units: DI is converted internally to inches and combined with H (in⁻¹) as the dimensionless H·DI group.
Verification: For the Grossmann 1942 example DI=2.40 in and H≈0.40, the model gives Dc≈1.06 in, consistent with approximately 1.05 in in the paper.
Data classification
Three data types must remain separate
Every curve and conclusion on this site is identified by how the data was obtained.
Software-predicted curve
Calculated from a stated model and inputs. It is a prediction, not measured production data.
Real-workpiece internal measured curve
Comes from internal points in the actual workpiece and is used to assess the real cooling process against post-quench hardness, microstructure and properties.
Unless explicitly identified and validated, one data type cannot be converted into or substituted for another.Read the technical method
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