Change in Hardness and Microstructure during Cumulative Heating of Tool Steel H13Kouji Tanaka1, Yuya Fukutomi1, Shuta Nishikawa2, Yuki Kodama3
1Department of Mechanical Engineering, Graduate School of Mechanical Engineering, Daido University
2Tokai Shiki Co. Ltd.,

3Daido Bunseki Research, Inc. Nagoya 457-8545, Japan

BackgroundHybrid Die

Experimental

Laser Metal Deposition (LMD)

High-cycle
production of die
casting

 High Building Speed
 Dissimilar Materials

AM for Hybrid Die

Sample Preparation
CSi Mn Cr Mo V Fe
H13 0.4 1.0 0.40 4.9 1.2 1.0 Bal.
LCS 0.3 0.1 1.6 1.9 1.0 0.6 Bal.

H13 (JIS SKD61)

Reduction of coolingtime by hybridizing
copper with die steel

Starting "as-depo" material

Cumulative heat treatment

Copper plate>1873K
10g

Laminated deposit 1mm×7 layers(a)Heat Affection during LMD

Φ 8x10㎜

Melt powders
as solidified

Thermocouple

600

200
00300

600

900

1200

Time , sCalculation of phase diagram

(b)

Ms

Ms

400

MILaser

Layer
guide

10s

800

microstructure: Coarse martensite

Cellular &Coarse martensite

Upper layers
A few heat input (γ)

10s

1000

Temperature, ºCTRUMPF

1200

1st heating to γγ

1200ºC×10s A.C.

γ+VC

1㎜

2nd heating to γ + VC

←αTemperature, ºC

Cu plate t8㎜
Tempered martensiteLower layers
Cumulative heat input（γ～α）

Microstructures of deposited H13in (a) upper layer, (b) lower layer

Objectiveγ→

M23C6α+VC α+VC+M23C6• Relation between hardness change and microstructure during cumulative heatingof tool steel H13 and low-Cr, Si modified steel investigated

M7C3

1000ºC×10s A.C.

M7C3+M23C6

3rd heating to critical temp.
820 ~ 850ºC ×10s A.C.
•α→γ transformation and•M7C3 / M23C6 precipitation

α+VC+M23C6+M6C

Heating to α + carbides
700, 600, … 300ºC

C mass %Calculated phase diagram for H13 (~0.4%C)• Softening with descending peak temp. interpreted by thermodynamic calculation

Results and Discussion
Change in hardness

Reverse transformation

Microstructure and precipitates
1000ºC (577Hv)

700

α' martensite

600

Vickers Hardness, Hv

2nd 1000ºC heating
γ + VC

after 1st 1200ºC heating …

α' martensite

400

3rd 820~850ºC heating

2.0mm

H13 Martensitic acicular microstructure Fine particles : VC (extracted and EDS analysis)

300

200300500

On cooling …
due to high hardenability of H13α’+VC0.2mm

LCS

500

700

900

H131100820ºC (314Hv)

LCSαγ + tempered α'

LCS 820ºC (545Hv)

Peak Heating Temperature, ºC

H13-0.1%Si

H13fresh α'

Change in hardness of as-depo samples after the cumulative
heating at peak tempertures from 1473K to 573K.

M7C3
M23C6αγ

M23C6

M23C6VCVCγVC

In case M7C3 suppressed ..
Equil. phase fraction at 1102K for chemicalcomposition of α’ after 1273K heating

 600Hv above 1000ºC equivalent as-Q
2.0mm

 H13 discontinuous Hv decrease after 820ºC
700ºC (310Hv)

 LCS still high Hv after 820ºC,
no further softening after 700ºC

 Low Si or low Cr promotes α'→γ transformation in cumulative heating

700ºC (434Hv)

Driving force for carbide prec.
H135Cr-1SiLCS

fresh α'2Cr-0.1Si
2.0mm

γ0.2mmTemperature, ºC

γ
γ+VC
γ+VC

α+VC

 partly acicular structure nano particles : unknown

Driving force (J/mol) for carbide precipitationfrom superheated α’ on heating to 973K

α+VC+M23C60.6

C mass % non acicular structure Facet particles : M7C3> 700ºC heating
Supersaturatedortempered α'LCS
351.992.2571.9
ー542.0Conclusion and Future Work

α+VC
α+VC+M23C60.2mm

M7C3
M23C6
M3C
M6C
M3C2

C mass %Metastable phase diagram for (a) H13 and (b) LCS
with the calculation condition of M7C3 suppressed.

• In the cumulative heatings, as-depo samples showed a discontinuous decrease after heated to 1093K for
SKD and 973K for LCS. The degree of softening was larger in SKD than in LCS.
• In low-Cr or low-Si tool steels, partial γ transformation took place on heating, which suppressed softening
by formation of fresh martensite and precipitation of nano-scale particles.