The Influence of Former Process Steps on Changes in Hardness, Lattice and Micro Structure of AISI 4140 Due to Manufacturing Processes

Abstract

The surface and subsurface conditions of components are critical for their functional properties. Every manufacturing process modifies the surface condition as a consequence of its mechanical, chemical, and thermal impact or combinations of the three. The depth of the affected zone varies for different machining operations and is related to the process parameters and characteristics. Furthermore, the initial material state has a decisive influence on the modifications that lead to the final surface conditions. With this knowledge, the collaborative research center CRC/Transregio 136 “Process Signatures” started a first joint investigation to analyze the influence of several machining operations on the surface modifications of uniformly premanufactured samples in a broad study. The present paper focusses on four defined process chains which were analyzed in detail regarding the resulting surface conditions as a function of the initial state. Two different workpiece geometries of the same initial material (AISI 4140, 42CrMo4 (1.7225) classified according to DIN EN ISO 683-2) were treated in two different heat treating lines. Samples annealed to a ferritic-perlitic microstructure were additionally deep rolled as starting condition. Quenched and tempered samples were induction hardened before further process application. These two states were then submitted to six different manufacturing processes, i.e., grinding (with mainly mechanical or thermal impact), precision turning (mainly mechanical), laser processing (mainly thermal), electrical discharge machining (EDM, mainly thermal) and electrochemical machining (ECM, (mainly chemical impact). The resulting surface conditions were investigated after each step of the manufacturing chain by specialized analysis techniques regarding residual stresses, microstructure, and hardness distribution. Based on the process knowledge and on the systematic characterizations, the characteristics and depths of the material modifications, as well as their underlying mechanisms and causes, were investigated. Mechanisms occurring within AISI 4140 steel (42CrMo4) due to thermal, mechanical or mixed impacts were identified as work hardening, stress relief, recrystallization, re-hardening and melting, grain growth, and rearrangement of dislocations.

High-Performance Applications of Metals and Alloys: Material Properties, Behaviour Modeling, Optimal Design and Advanced Processes

“…The collection includes papers regarding the most multifaced aspects of metals and their alloys as synthesis and treatments [1], experimental characterization [2][3][4], material models [2,5,6], and engineering applications [7,8], providing a clear cross-section of the wide variety of topics and research arguments under investigation in the scientific community now.…”

“…In the case of [1], for instance, the critical importance of surface and subsurface conditions in components and how various manufacturing processes influence them is investigated. As known, the depth of the affected zone depends on the machining operations and process parameters in ways that are not always easy to understand.…”

Experimental and Numerical Investigation on Effects of Pin Diameter on Multi-Point Forming

“…A multi-point forming die set with 7 × 7 matrices was constructed to perform experimental studies. All components of die set material were selected as AISI 4140 steel due to its mechanical properties [16]. A photo of the die set and constructed bottom die is shown in Figure 1.…”