How to Determine if the Heat Treatment of H13 Material is Qualified

Hardness testing (48–52 HRC), metallographic analysis to verify the tempered martensitic structure, and confirmation of the furnace temperature curve and batch report are the main methods used to determine if the heat treatment of H13 material is qualified. Accurate judgment is ensured by combining these three approaches.

 

1. The Most Direct Indicator: Hardness Testing

Qualification Standard: Following tempering, the hardness must fall between 48 and 52 HRC;

Testing Procedure: After grinding, evaluate the hardness in non-critical regions of the workpiece (such the nozzle root) using a portable Leeb hardness tester;

Logic of Judgment:

<45 HRC: Unqualified, over-tempered, and possibly not completely quenched54 HRC: excessive residual stress, inadequate tempering, and cracking danger;

48–52 HRC: Preliminary qualifies and satisfies usage standards.

Practical Advice: To prevent misjudgment owing to local abnormalities, measure at least three places for each piece and calculate the average value.

 

2. Metallographic Analysis (Basis for Authoritative Judgment)

Acceptable/Unacceptable Microstructure Features

Matrix Organization

Dispersed carbides plus uniform tempered martensite

Network carbides, coarse martensite, or leftover ferrite

State of Grain Boundaries

Clear yet free of oxidation and microcracks

Microcracks (overheating), remelted spheres, and oxidation at the grain boundary

Distribution of Carbides

Precipitation that is regular and fine

Network distribution, agglomeration, and decreasing toughness

Testing Requirements: Use a metallographic microscope to examine the sample at a magnification of 400× or greater once it has been prepared. Critical workpieces should be tested and sampled.

 

3. Verification of Process Records (Process Traceability)

Furnace Temperature Profile: Verify that the heating and cooling rates are compliant and that the temperature is maintained during the quenching (1020–1050°C) and tempering (550–600°C) processes.

Batch Hardness Report: Give hardness test results covering workpieces at various locations for every furnace.

Service Provider Qualification: Give preference to heat treatment facilities with CQI-9 certification, whose procedures are uniform and their documentation is comprehensive.

"Hardness compliance + qualified microstructure + traceable records" are essential components of a closed-loop safety system.