Heat Transfer Characteristics of Billet/Die Interface and Measures to Relieve Thermal Stress for Hot Forging Die

  • Baoshan Lu
  • Leigang WangEmail author
  • Zhe Geng
  • Yao Huang


The interfacial heat transfer coefficient (IHTC) shows the heat transfer capacity at the billet/die interface during the hot forming process, which affects the temperature gradient in the die that may potentially induce high thermal stress. Consequently, this determines the service life of the die. In this paper, a set of experimental equipments were used to identify the IHTC and the upsetting test of superalloy Inconel718 (GH4169) was carried out on the hot flat die to evaluate the IHTC characteristics after the billet heating and die preheating temperature, holding time, and billet deformation rate. The results indicated that the billet heating temperature has a minimal role in IHTC but the other components have a great impact on IHTC. Among them, the billet deformation rate has influenced the IHTC the most. In the die preheating temperature ranging from \(150\,^{\circ }\hbox {C}~\hbox {to}~400\,^{\circ }\hbox {C}\), it was found that the preheating temperature was proportional to IHTC. A high preheating temperature that leads to a high IHTC was found unfavorable in relieving the die surface thermal stress, and also weakened the die hardness and strength. The IHTC declined with the increase in the holding time as a result of the billet oxidation. Based on these findings, the composite ceramic and polymetallic heat-resistant coatings on the die surface were prepared, respectively, to relieve the thermal stress of die surface by reducing IHTC. It showed that both of the treated dies could effectively reduce the IHTC, blocking the transferred heat from the hot billet and making it applicable to the different hot forging events.


Hot forging die Interfacial heat transfer coefficient Nonlinear estimation method Relieving thermal stress Superalloy GH4169 

List of Symbols


Interfacial heat transfer coefficient \([\hbox {W/(m}^{2}{\cdot }\hbox {K})]\)


Thermal conductivity [\(\hbox {W/(m}{\cdot } \hbox {K})\)]


Coordinate through out the thickness (mm)


Internal heat source for the billet \(\hbox {(W/m}^{3})\)


Sensitivity coefficient \((\hbox {m}^{2}{\cdot } {}^{\circ }\hbox {C/W}\))


Interfacial heat flux at the time M \((\hbox {W/m}^{2}\))


Objective function

\(Y_{K,M }\)

Measured temperature at the location K and at the time M (\(^{\circ }\hbox {C}\))


Any known heat flux (\(\hbox {W/m}^{2}\))

\(T_{M-1} (\chi )\)

Temperature distribution at the time \(t_{M-1}\,(^{\circ }\hbox {C}\))

b1, b2, b3

Temperature measurement points of the billet (mm)

d1, d2, d3

Temperature measurement points of lower die (mm)


Temperature \(({}^{\circ }\hbox {C})\)


Specific heat [\(\hbox {KJ/(Kg}{\cdot } \hbox {K})\)]


Heat flux \(\hbox {(W/m}^{2})\)




Length of the model

Greek Symbols

\(\rho \)

Density (\(\hbox {Kg/m}^{3}\))

\(\bar{\sigma }\)

Equivalent stress (Pa)

\(\dot{\bar{\varepsilon }}\)

Equivalent strain rate (\(\hbox {s}^{-1}\))

\(\dot{\varphi }_{z}\)

Deformation rate (\(\hbox {s}^{-1}\))

\(\Delta T\)

Transient temperature difference at the interface (\(^{\circ }\hbox {C}\))

\(\tau \)

Time (s)



Total number of temperature measurement points



Time point


Location point



This work was financially supported by National Natural Science Foundation of China (Grant No. 51275216), Natural Science Foundation of Jiangsu Province, China (Grant No. BK20160353), Natural Science Foundation of Jiangsu Higher Education Institutions of China (Grant No. 16KJB460032), and Top-notch Academic Programs Project of Jiangsu Higher Education Institutions of China (Grant No. PPZY2015B186).


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Copyright information

© Springer Science+Business Media New York 2017

Authors and Affiliations

  • Baoshan Lu
    • 1
    • 2
  • Leigang Wang
    • 1
    Email author
  • Zhe Geng
    • 2
  • Yao Huang
    • 1
  1. 1.School of Materials Science and EngineeringJiangsu UniversityZhenjiangPeople’s Republic of China
  2. 2.Department of Precision Manufacturing EngineeringSuzhou Institute of Industrial TechnologySuzhouPeople’s Republic of China

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