How to plot the tempering curve of H13 material

Information on the temperature-hardness connection is needed to plot the tempering curve of H13 material. Several sets of tempering temperatures and accompanying hardness values are acquired through trials in the 550–600°C range, with 580°C serving as the reference point. Important process parameters, including two tempering cycles and holding time, are noted. The precise steps are as follows:

1. Acquisition of Experimental Data

Procedures and Guidelines

Temperature Gradient Setting

Choose 550°C, 560°C, 580°C, and 600°C as your four usual temperature points. There should be a minimum of three parallel samples for each group.

Standardized Tempering Procedure

At each temperature point, conduct two tempering cycles, holding each time for at least two hours. Before beginning the second tempering, let the air settle to room temperature following the first.

Testing for Hardness

Once the object has cooled to room temperature, measure three to five locations on it (the center, edge, and thickness boundary) using a portable hardness tester, then average the results.

Data Capturing

Record process variables like workpiece thickness, holding time, cooling method, and furnace temperature curve simultaneously.

Example Data: The measured hardness is 49.8~50.3 HRC following two hours × two temperings at 580°C.

2. The Method of Plotting Curves

Tempering temperature (°C) on the horizontal axis, with a range of 550–600°C;

Average hardness (HRC) on the vertical axis

Data Points: Plot each temperature point's average hardness value;

Trend Line: Join the data points to create a smooth curve that illustrates how hardness is gradually declining as temperature rises;

Annotation of Key Information:

"Two tempering cycles" should be annotated.

Note "Holding time ≥ 2 hours";

Put "580°C ± 5°C" as the suggested range.

Include a description of the microstructure (such as "Uniform tempered martensite + dispersed carbides").

Advice: Plot the curve using programs like Excel or Origin to ensure precise coordinates and thorough comments.

3. Verification and Application of Curves

Metallographic Evidence: The microstructure is confirmed to be homogenous tempered martensite + scattered carbides by metallographic investigation of the samples;

Process Archiving: To achieve traceability, keep each furnace's temperature curve and test data;

Process Optimization Reference: To prevent going into the brittle zone (>52 HRC) or softening zone (<48 HRC), find the hardness inflection point across the curve.

"Data authenticity, process controllability, and microstructure reliability" are the three safety principles that guaranty the curve's scientific dependability.