Does the result represent the maximum size of any workpiece shape?

No. The result is the critical diameter for an infinitely long round bar under the Grossmann 50% martensite center criterion. Plates, rings, complex sections, and actual loads require separate geometric and process corrections.

Why is the actual critical diameter smaller than DI?

DI is defined at ideal infinite quench severity. Production H is finite, so the actual round-bar critical diameter Dc for the same steel is below DI and approaches DI as H increases.

Can increasing H solve a target diameter greater than or equal to DI?

Not under this model and the 50% martensite criterion. DI is the upper limit at infinite quench severity; change material hardenability, effective section, or the criterion rather than increasing H without limit.

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.

D_c / 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

Ideal Critical Diameter DI Calculate DI first →

Must be greater than zero. DI should come from measured hardenability conversion or a composition calculation within its validity range.

Current: page example

Grossmann H Review the H basis →

in⁻¹

H must retain its unit. Use a known or calibrated value, or a clearly identified historical reference boundary.

Current: page example

Target Round-Bar Diameter to Check

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)

H × DI

Dc / DI

Ideal Limit and Finite-H Result

100%

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.

Screen media H ranges against the target →

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.

Official ASTM A255 scope and information · Official GB/T 5216-2014 standard record