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. T… Show more
“…Considering an isotherm at 1000 °C, the cooling rates at 40 and 100 μm were 32'280 and 21'434 °C/s, respectively. These rates are high enough to inhibit any long-range diffusional phase transformation, which promotes martensite formation [18]. However, as seen before, there was a small fraction of allotriomorphic ferrite in the FZ, both in condition B and in C. This ferrite must be a residue of the original BM that did not have time to dissolve in the austenitic matrix.…”
AISI 4130 steels have been used in several engineering applications, although presenting limited hardenability in conventional heat treatments. This contribution is aimed at determining the final hardness and reciprocating wear coefficient of friction (COF) after a given laser surface treatment (LST) with or without a carbon coating (C). The results indicated that the bare (B, without coating) condition produced a deeper case depth as a result of the carbon-rich plasma shielding. The observed microstructural features in the cases B and C showed martensite transformation and cementite formation; the latter is entirely in the C condition. Simple calculations using Rosenthal’s formalism indicate a high cooling rate, estimated as 32
′
280°C/s 40 μm below the irradiated surface and a heat-affected zone bounded by the austenite locus. The hardness near to the surface was higher in case C than in case B, but the overall final hardness is more pronounced when the surface is bare (B) due to plasma shielding. On the other hand, the final COF was very low in the C case (0.1) compared to the B condition (0.6).
“…Considering an isotherm at 1000 °C, the cooling rates at 40 and 100 μm were 32'280 and 21'434 °C/s, respectively. These rates are high enough to inhibit any long-range diffusional phase transformation, which promotes martensite formation [18]. However, as seen before, there was a small fraction of allotriomorphic ferrite in the FZ, both in condition B and in C. This ferrite must be a residue of the original BM that did not have time to dissolve in the austenitic matrix.…”
AISI 4130 steels have been used in several engineering applications, although presenting limited hardenability in conventional heat treatments. This contribution is aimed at determining the final hardness and reciprocating wear coefficient of friction (COF) after a given laser surface treatment (LST) with or without a carbon coating (C). The results indicated that the bare (B, without coating) condition produced a deeper case depth as a result of the carbon-rich plasma shielding. The observed microstructural features in the cases B and C showed martensite transformation and cementite formation; the latter is entirely in the C condition. Simple calculations using Rosenthal’s formalism indicate a high cooling rate, estimated as 32
′
280°C/s 40 μm below the irradiated surface and a heat-affected zone bounded by the austenite locus. The hardness near to the surface was higher in case C than in case B, but the overall final hardness is more pronounced when the surface is bare (B) due to plasma shielding. On the other hand, the final COF was very low in the C case (0.1) compared to the B condition (0.6).
“…Finite element analysis revealed a significant reduction in residual stress from 163.70 MPa to 3.72 MPa in the fusion zone (FZ) of the welds when transitioning from RT to HT. The study concludes that the hardness in the FZ is influenced by the microstructure resulting from the thermal cycle, with values of 400 HV for martensite (RT), 340 HV for tempered martensite (PWHT), and 250 HV for bainite (HT) [ 11 ].…”
The kinetics and the effects of tempering on the corrosion resistance of AISI 4130 steel were studied. The tempering activation energy was close to that for the diffusion of C in α-iron. This implies that the tempering kinetics in this steel is controlled by carbon diffusion. By increasing the time and temperature of tempering, the corrosion current density (i corr ) in the polarization curves decreased whereas the diameter of the semicircular arc in the Nyquist plots increased, which implies higher corrosion resistance. The i corr was successfully related to hardness, which actually indicates the effect of microstructure.Based on these findings, the quench and tempering treatment was used to adjust both the hardness and corrosion resistance of the AISI 4130 steel.
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