Microstructural Evolution and Mechanical Behavior of Friction-Stir-Welded DP1180 Advanced Ultrahigh Strength Steel

Abstract

Friction stir lap welding of a DP1180 advanced ultrahigh strength steel was successfully carried out by using three welding tools with different pin lengths. The effects of the welding heat input and material flow on the microstructure evolution of the joints were analyzed in detail. The relationship between pin length and mechanical properties of lap joints was studied. The results showed that the peak temperatures of all joints exceeded A c3 , and martensite phases with similar morphologies were formed in the stir zones. These martensite retained good toughness due to the self-tempering effect. The formation of ferrite and tempered martensite was the main reason for the hardness reduction in heat-affected zone. The mechanical properties of the lap joints were determined by loading mode, features of lap interface and the joint defects. When the stir pin was inserted into the lower sheet with a depth of 0.4 mm, the lap joint exhibited the maximum tensile strength of 12.4 kN.

Experimental simulation research on TMCP of 30MnCr22 oil well pipe

“…Furthermore, according to the corresponding energy spectrum shown in figure 4(g), it can be found that Cr element existed in this carbide marked by red circle in figure 4(e). And from the selected area electron diffraction (SAED) pattern along the [562] zone axis of the carbide illustrated in figure 4(h), this carbide has an orthogonal structure which is just consistent with that of θ-Fe 3 C. Therefore, this carbide is confirmed to be θ-(Fe, Cr) 3 C. In fact, carbon atoms or other alloy elements still have a certain diffusion ability to segregate on dislocations or other crystal defects, and carbides can precipitate dispersedly after quenching, which is called the self-tempering phenomenon of martensite [21]. And the deformation strengthening effect of reducing is also helpful to diffusion and precipitation of carbides by supplying more precipitation sites.…”

Improving mechanical properties of friction-stir-spot-welded advanced ultra-high-strength steel with additional water cooling

“…Owing to the reversion and recrystallisation of deformed grains and tempering of martensite, fine ferrite was generated and carbide particles could be easily precipitated in this region (Figure 4(h)). Specified explanation of the microstructural evolution in the sub-HAZs could be found in our previous work [29].…”

Friction stir lap joining techniques effects on microstructure and tensile properties of high-strength automotive steel top hat sections

“…It was noticed that there was no visible thermomechanical affected zone (TMAZ) in the welds. The allotropic phase transitions that occurred during carbon steel friction stir welding remove the evidence of (TMAZ) [19]. The HAZ in the FSLW joint is divided into three zones, namely the crucial heat-affected zone (CHAZ), nuclear heat-affected zone (NHAZ), and peripheral heat-affected zone (PHAZ), as quoted by Mahdi Mahmoudiniya et al [4].…”

“…Z.W. Wang et al [19] also discussed the tool movement's influences on the joint's strength and fracture mode. As the TTS increases, because of the lower heat, the effective lap width reduces, reducing the joint's strength.…”

“…The microstructure and joint performance of AHSS FSLW joints have received relatively little research so far. Wang et al [19] applied FSLW to join DP1180 grade steel by utilizing constant tool rotation, welding speed, and tools with varying pin lengths and reported that the desired microstructural features (i.e., martensite with good toughness) and maximum fracture load of 12.4 kN were noticed in the stir zone (SZ) when the tool pin length is 1.57 mm and lower sheet penetration depth of 0.4 mm was used.…”