Zhenguo Nie

Precision Measurement and Modeling of Quenching-Tempering Distortion in Low-Alloy Steel Components with Internal Threads

Abstract Distortion resulting from heat treatment may cause serious problems for precision parts. A precision component made from 30CrNi3Mo steel with internal threads distorts slightly after quenching-tempering treatment. Such a small distortion results in serious difficulties in the subsequent assembly process. The distortion of the internal thread was measured using semi-destructive testing with video measuring system. Periodic wavy distortions emerged in the internal threads after heat treatment. Then both XRD analysis and hardness testing were conducted. A numerical simulation of the complete quenching-tempering process was conducted by DANTE, which is a set of user subroutines that link into the ABAQUS/STD solver. The results from the simulations are in good agreement with the measurement in distortion, microstructure field, and hardness. The effects of the technological parameters including quenchant, immersion orientation, and grooves were discussed on the basis of the simulation results. Finally, strategies to significantly decrease distortion and residual stress are proposed.

Microstructure Evolution of Martensitic Stainless Steel in Laser Hot Wire Cladding With Multiple Heating Passes

Laser cladding is one of attractive and cost effective means for repairing or remanufacturing high value engineering components. The microstructure and property in laser cladding process with multiple heating passes were investigated by using experimental method. Single-pass cladding experiments were conducted to investigate the wire transfer behavior and further optimize the laser hot wire cladding process. Multiple layers were cladded on the surface of martensite stainless steel by using fiber laser. The microstructure of clad layer and heat affected zone was characterized using an optical microscope, SEM and EDS. The orientation imaging microscopy of grain structure was obtained by the electron backscatter diffraction technique. The gradient microhardness from the clad layer to the substrate was tested. The uneven temperature distribution and high cooling rate led to the forming of gradient microstructure, and further affect the mechanical property of the remanufacturing parts.

Dynamic Mechanical Behavior and Phase‐Based Constitutive Model of 20Cr12Ni4Mo3VNiN in Austenitizing Stage

Dynamic mechanical behavior is vital to the investigation of mechanism of material removal in heavy grinding process, especially for manufacturing the root of turbine blades. The effect of temperature on properties is a key factor in the process, which may reach above the point of phase transformation. In this paper, dynamic mechanical experiments were conducted in elevated temperatures starting ambient temperature through complete austenitizing point, even the overcooling austenite, with a strain rate ranging from quasi-static to 8000s−1 with Split Hopkinson Pressure Bar. Kinetics of austenization was involved to investigate the effect of phases on the property. A comprehensive constitutive model was proposed to describe the dynamic mechanical behavior with temperature, strain rate and phase fraction consideration. The model was validated through comparison between experimentation and computation.

Experimental Study and Modelling on the Grain Growth of Annealing Process in Fe-50%Ni Alloy

Fe-50%Ni alloy is widely used in industrial fields as its excellent magnetic performance, and the average grain size has a strong effect on magnetic performance. In this paper, Fe-50%Ni alloy specimens are annealed under the hydrogen protection and vacuum respectively at different temperatures and holding times. Metallographic observation and grain size measurement are both finished. The metallographic observation shows that grains grow up more easily and fast under the hydrogen atmosphere than in vacuum. Hydrogen can reduce the chemical activation energy, and decrease the impurity elements more easily. A new model is proposed to describe the grain size basing on the assumption that \(\overline {{D^2}} - \overline {D_0^2} \alpha {t^m}\) by experiments and \(\overline {{D^2}} - \overline {D_0^2} \alpha {e^{ - \tfrac{Q}{{RT}}}}\) by thermo dynamical theory. The fitting result shows that the new model can describe the grains growth process better than the classical one.

A FEM-Based Inverse Calculation Method for Determination of Heat Transfer Coefficient in Liquid Quenching Process

Heat transfer coefificient(HTC), as a criterion of cooling capacity of quenchant, is vital for quenching process modeling. However results generated directly by specific devices for measuring cooling process are temperature curve and cooling rate. In this paper a FEM-based inverse calculation method was proposed to achieve automatic optimization for HTC curve with measured temperature curves. The method was validated by comparing measurements from IVF Smart Quench with simulation results. The effect of concentration of the UCON quenchant on HTC curves has been investigated by using the proposed method. It is shown that as the concentration increases, the HTC peak value, as well as average value, decreases and the temperature corresponding to the peak shifts to high value. A frame-like part has been used to validate the accuracy and effectiveness of the methodology.

Numerical Simulation of the Austenitizing Process in Hypoeutectoid Fe-C Steels

For predicting of diffusive phase transformations during the austenitizing process in hypoeutectoid Fe-C steels, a two-dimensional model has been developed. The diffusion equations are solved within each phase (α and γ) using an explicit finite volume technique formulated using a square grid. The discrete α/γ interface is represented by special volume elements α/γ. The result showing the dissolution of ferrite particles in the austenite matrix are presented at different stages of the phase transformation. Specifically, the influence of the microstructure scale and heating rate on the transformation kinetics has been investigated. Final austenitization temperature calculated with this 2D model is compared with predictions of a simpler one dimensional (1D) front-tracking calculation.Copyright

Prediction of Distortion in Quenching-Tempering Processes for a SM256 Steel Component With Internal Thread

A steel component with internal thread has a few slight distortions when it undergoes quenching-tempering processes. These small distortions affect assembly severely in the precision engineering. Using FEA software with its user subroutines, the position and contour of distortions which will be confirmed by subsequent experimental measurement are simulated. This result reasonably explains the assemble difficulty in enterprise manufacturing, and then lots of suggestions are given for manufacturing improvements.Copyright