太原钢铁集团有限公司

To investigate the influence of the laser welding process on the microstructure evolution and mechanical properties of duplex stainless steel joints, low-nickel duplex stainless steel S32001 was taken as the research object, automatic laser welding was conducted, and the relationship between the microstructure and mechanical properties was studied. The results indicate that under different welding process parameters, the weld surface is well formed, the microstructure is composed of austenite and ferrite, and secondary austenite is precipitated in the weld metal zone and the heat-affected zone. The microhardness of the joint exhibits a “W-shaped” distribution, with the highest hardness in the weld metal zone, the lowest hardness in the heat-affected zone, and intermediate hardness in the base metal. When the heat input is 12 J/mm, the hardness of the joint reaches a maximum of 322.7 HV ± 9.3 HV. When the heat input is 21 J/mm, the tensile strength and elongation after fracture of the joint reach maximum values of 904.9 MPa and 52.70%, respectively. The morphology of the tensile fracture is composed of cleavage planes, voids, and dimples. Some micron-sized inclusions can be observed, and the fracture mode of the weld is quasi-cleavage fracture.

To address the issue that the pitting corrosion resistance of commercial 430 stainless steel varies significantly without systematic clarification on the root cause,cold-rolled 430 stainless steel sheets from four different steel mills(A,B,C,D)were selected in this study.Their pitting corrosion resistance was sys-tematically compared using immersion tests,critical pitting temperature(CPT)measurements,and pitting potential tests,combined with chemical composition and microstructural characterization.This investigation not only evaluated the theoretical predictability of the pitting resistance equivalent number(PREN),but also emphasized the decisive role of the actual microstructure on corrosion performance.Results show that A-430SS exhibits the best pitting corrosion resistance,with the highest average pitting potential(40.7 mV)in 3.5%NaCl solution and the highest CPT(57.3℃)in Cl⁻ solution of mass fraction 50×10⁻6,followed by B-430SS,while C-430SS and D-430SS show the poorest performance.Although B-430SS possesses the highest PREN value(17.61)due to its relatively high mass fraction of Cr(16.78%)and N(0.052%),its actual corrosion resistance is not optimal.Microstructural analysis reveals that A-430SS has excellent cleanliness with only 5 type-D inclusions,much lower than 23 in C-430SS and 20 in D-430SS,and a fully recrystallized,uniform and band-free microstructure,which effectively inhibits pitting nucleation.In contrast,the large number of inclusions and banded structure caused by incomplete recrystallization in B-430SS greatly weakens its com-positional advantage of high PREN.This study clarifies that microstructural defects can dominate the pitting corrosion resistance of commercial 430 stainless steel,invalidating the composition-based PREN prediction,and provides an important basis for the processing optimization and material selection of high-performance ferritic stainless steels.

To elucidate the mechanism by which low-degree carbonation influences the macroscopic strength of stainless-steel slag, carbonated slag samples with carbonation efficiency ranging from 1.21% to 11.68% were prepared by varying the carbonation duration in a closed reactor at 210 °C with a liquid-to-solid ratio of 20% and a CO2 partial pressure of 0.2 MPa. Mortar specimens were fabricated by blending the carbonated slag with P.I 42.5 reference cement at a 30% mass replacement ratio and curing under standard conditions for up to 28 days. The phase composition was characterized by thermogravimetric analysis coupled with derivative thermogravimetry and X-ray diffraction, the pore structure of hardened mortars was examined by mercury intrusion porosimetry, and the interfacial transition zone between the slag particles and the cement paste matrix was analyzed by scanning electron microscopy with backscattered electron imaging and energy-dispersive spectroscopy. The width of the interfacial transition zone was quantified using gray-value profiles extracted perpendicular to the particle boundaries, and its internal porosity and compositional homogeneity were assessed via threshold segmentation and standard deviation analysis. The results revealed a distinct U-shaped evolution of the 28-day compressive strength with increasing carbonation efficiency, featuring a strength minimum at 3.33% and a performance compensation point at 3.95%. The underlying mechanism governing this nonmonotonic behavior is based on the morphological evolution and spatial redistribution of the CaCO3 carbonation product. At carbonation efficiencies below 3.33%, the reaction is largely confined to the particle surfaces where the preferential consumption of free lime and its hydration product Ca(OH)2 generates CaCO3 in the form of isolated encapsulation layers. These discontinuous layers act as physical barriers that impede the hydration of the internal dicalcium silicate while simultaneously introducing harmful micron-scale pores into the matrix, thereby accounting for the initial strength decline observed at this stage. Once the carbonation efficiency surpasses 3.33%, the reaction front advances into the dicalcium silicate phase and the newly formed CaCO3 undergoes a critical morphological transition from isolated clusters to a continuous grid-like network. This structural transformation fundamentally alters the role of CaCO3 from a hydration inhibitor to a synergistic reinforcer: the interconnected carbonate framework fills and progressively refines the capillary pore system while its extensive surface area provides abundant heterogeneous nucleation sites that promote the dense precipitation and intimate intergrowth of the calcium-silicate-hydrate gel throughout the matrix. At a carbonation efficiency of 3.95%, these positive contributions fully offset the initial adverse encapsulation effects, restoring the compressive strength to a level comparable to that of the untreated slag. Further carbonation to 11.68% elevates the 28-day compressive strength to 42.2 MPa, corresponding to an enhancement of 24.5% relative to the untreated reference material. In parallel with these bulk matrix modifications, deep carbonation substantially changes the interfacial transition zone. The average width of this zone decreases from over 20 μm to below 6 μm, and its internal structure changes from a porous and compositionally heterogeneous layer into a densified, homogeneous composite region in which calcium carbonate and calcium-silicate-hydrate gel are intimately interwoven, thereby strengthening the particle-matrix bond. This study demonstrates that precise regulation of carbonation efficiency dictates the morphological fate of carbonation products which in turn governs the pore structure refinement and interfacial densification that collectively underlie the U-shaped strength response. These findings provide a mechanistic basis for carbonation-based resource utilization of stainless steel slag, where steering the process beyond the compensation threshold enables carbonation products to act as synergistic reinforcements rather than physical barriers.

This study systematically investigated the role of lanthanum (La) content (0–0.17 wt.%) on the inclusion and NbC evolution, grain refinement, strength and toughness variations of ferritic stainless steel Crofer 22 H. The optimal La content was determined to be 0.08 wt.%, which simultaneously enhanced the yield strength by ∼18% (342 vs. 290 MPa), tensile strength by ∼15% (489 vs. 424 MPa), and impact energy by ∼150% (23.34 vs. 9.26 J) compared to the La-free steel. These improvements were attributed to three key mechanisms as follows. (i) La modified coarse and angular TiN and MgAl2O4 into fine spherical La2O3, LaP, La2O2S, and LaN inclusions and promotes fine NbC precipitation around them, effectively reducing crack initiation sites. (ii) La segregation at grain boundaries (GBs) and the formation of (La,P,S)-bearing inclusions suppressed harmful P and S segregation, enhancing the GB cohesion and crack resistance. (iii) Apparent grain refinement via 0.08 wt.% La addition increased GB density, hindering dislocation motion and crack propagation. However, excessive La (0.17 wt.%) caused the coarsening and aggregation of the inclusions and NbC, degrading both strength and toughness despite comparable grain refinement. The study establishes 0.08 wt.% La as the critical threshold for optimizing the strength-toughness balance of the Crofer 22 H steel.

The stable operation of a rolling mill is crucial for the extremely thin strip rolling process. Moreover, the performance of the rolling mill directly dictates the quality of the extremely thin strip products. In view of the lack of research on the digital twin model and condition monitoring of twenty-high rolling mills, this paper takes the Sendzimir 280 mm twenty-high reversible rolling mill, an extremely thin strip rolling equipment, as the research object, and conducts digital twin modeling and visualization design for it. First and foremost, finite element analysis and vibration analysis were conducted on the rolling mill, based on which the finite element model and dynamics model of the twenty-high rolling mill were established. Secondly, through a comparison between the vibration data of the rolling mill obtained from simulation and those of the physical rolling mill, the accuracy of the simulation model was validated. Finally, a digital twin model of the rolling mill was constructed based on the finite element model and the dynamics model, and the digital twin model of the rolling mill was built using Unity (version 2022.3.57, Unity Technologies, San Francisco, CA, USA) software to complete the visualization design of the digital twin model. The results show that the digital twin platform of the rolling mill established in this paper achieves a high degree of similarity between the virtual rolling mill and the physical one, which proves the effectiveness of the platform and can meet the actual engineering requirements.