What are the common causes of mold heat treatment deformation?

The deformation of mold heat treatment is essentially the combined effect of thermal stress, tissue stress, original internal stress, and structural/process additional stress, resulting in dimensional expansion, bending, warping, and twisting. Below, we will organize the most common and core reasons for on-site comparison and investigation.

1、 Thermal stress (deformation caused by temperature difference)

Heating speed too fast
The surface undergoes thermal expansion first, followed by internal expansion, resulting in significant temperature difference stress.
The cooling rate is too fast or uneven
Water quenching, single-sided strong cooling, local spraying, highly prone to bending and warping.
Uneven furnace temperature and dense furnace loading
The workpiece is too close to the heating tube, and the heating/cooling of each part is inconsistent.
Insufficient burn through of large and thick items
The temperature difference between the inside and outside is large, and thermal stress is superimposed on tissue stress, resulting in more severe deformation.

2、 Organizational stress (phase change volume change)

Volume expansion from austenite to martensite transformation
During quenching, local deformation occurs first and then, resulting in pulling/squeezing, causing expansion, contraction or distortion.
Uneven distribution of carbides and banded segregation
High carbon die steels (1.2379, D2, SKD11, etc.) are particularly noticeable with irregular deformation.
High quenching temperature
The austenite grains are coarse, the hardenability is enhanced, and the structural stress is greater.
Insufficient tempering or insufficient tempering
Residual austenite continues to transform in the later stage, causing secondary deformation during use.

3、 Original internal stress of workpiece (buried before heat treatment)

Forging stress not eliminated
Untnealed or insufficiently annealed after forging, resulting in high internal stress.
Cutting/Grinding Stress
Large rough machining volume, fast feed rate, concentrated surface stress, and concentrated release of deformation after quenching.
Cold work hardening, straightening stress
Forced straightening and cold pressing in the early stage release internal stress during heating.

4、 Inherent deformation caused by the mold structure itself

Unequal thickness and abrupt changes in cross-section
Thick areas cool slowly, thin areas cool quickly, and the stress difference is huge.
Sharp corners, narrow slots, deep holes
Stress concentration not only causes deformation but also cracking.
Slender piece, cantilever, thin wall
Under hot conditions, poor rigidity and self weight sagging deformation are common.
asymmetric structure
Must bend or warp to one side.

5、 Improper craftsmanship and operation (most common on-site)

Failure to temper in a timely manner after quenching
The quenching stress is not eliminated, and the deformation continues to develop and even cracks.
Incorrect selection of cooling method
Both complex parts quenched with water and small parts quenched with oil can cause abnormal deformation.
Unreasonable clamping/placement method
Flat placement, single point support, inclined hanging, directly bent by self weight in a hot and soft state.
Inaccurate temperature control and insufficient insulation
Insufficient thorough burning leads to uneven tissue transformation and irregular deformation.

6、 Material factors

Poor hardenability of the material
There is a significant difference between the surface and the heart tissue, and the deformation is unstable.
Severe segregation and multiple inclusions in steel
The expansion and contraction of various parts are inconsistent, and the deformation is irregular.