Abstract
It was verified that SAE 4130 steel plates crack when laser beam welded at room temperature (RT). To overcome this problem, this work proposes a high temperature (HT) laser welding in order to reduce the residual stresses and create a bainitic structure instead of a martensitic one. A conventional post-welding heat treatment (PWHT) had been used as a comparison for HT. The centerline crack disappeared after a heat treatment of both in-situ (HT) or after inserting in a furnace (PWHT) at 500 °C for 10 minutes. The finite element analyses indicated a residual stress reduction from 163.70 to 3.72 MPa in the fusion zone (FZ) of the welds from RT to HT. The hardness obtained in FZ depends on the thermal cycle induced microstructure of the welds as 400 HV, 340 HV and 250 HV, for martensite (RT), tempered martensite (PWHT) and bainite (HT) micro-constituents. The proposed in-situ high-temperature laser beam welding method proved its usefulness to solve the center crack issue in SAE 4130 joints.
Highlights
A couple of reports dated about 70 years ago indicated the use of SAE 4130 steel in US space program components such as envelopes, pillars and combustion chambers[1,2]
The objective of the present work is to investigate the possibility of in-situ heat treatment of a SAE 4130 steel plate during laser beam welding (LBW) in comparison with conventional LBW with and without post-welding heat treatment (PWHT)
The kinetics of the carbides formation in SAE 4130 steel are sufficiently low to state the ferrite as the product phase from austenite, or alternatively, an athermal martensite glissile transformation appears at high cooling rates[6]
Summary
A couple of reports dated about 70 years ago indicated the use of SAE 4130 steel in US space program components such as envelopes, pillars and combustion chambers[1,2]. The application of this alloy in airspace increased through the years and today some bleeding air tubes in commercial aircrafts are made of it[3]. Chemical and petrochemical industries made a large use of this alloy because of the good strength and toughness, weldability and machinability. The alloy can be hardened by quenching from 900 °C in oil or water, but usually is tempered to attain a good balance between hardness and toughness[6]. According to ASM standard the tempering temperature range for this alloy ranges from 200 to 700 °C for periods of a few hours[6]
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