Novel mechanism for the modification of Al_2O_3-based inclusions in ultra-low carbon Al-killed steel considering the effects of magnesium and calcium

Many researchers have explored the inclusion modification mechanism to improve non-metallic inclusion modifications in steelmaking. In this study, two types of industrial trials on inclusion modifications in liquid steel were conducted using ultra-low-carbon Al-killed steel with different Mg and Ca contents to verify the effects of Ca and Mg contents on the modification mechanism of Al_2O_3-based inclusions during secondary refining. The results showed that Al_2O_3-based inclusions can be modified into liquid calcium aluminate or a multi-component inclusion with the addition of a suitable amount of Ca. In addition, [Mg] in liquid steel can further reduce CaO in liquid calcium aluminate to drive its evolution into CaO–MgO–Al_2O_3 multi-component inclusions. Thermodynamic analysis confirmed that the reaction between [Mg] and CaO in liquid calcium aluminate occurs when the MgO content of liquid calcium aluminate is less than 3 wt% and the temperature is higher than 1843 K.

Structure Character of M-A Constituent in CGHAZ of New Ultra-Low Carbon Bainitic Steel under Laser Welding Conditions

800 MPa grade new ultra-low carbon bainitic （NULCB） steel is the recently developed new generation steel. The microstructure in the coarse-grained heat affected zone （CGHAZ） of NULCB steel under laser welding conditions was investigated by thermal simulation. The influence of the cooling time from 800℃ to 500℃.t8/5 （0.3-30 s）, on the microstructure of the CGHAZ was discussed. The experimental results indicate that the microstructnre of the CGHAZ is only the granular bainite which consists of bainitic ferrite （BF） lath and M-A constituent while t8/5 is 0.3-30 s. The M-A constituent consists of twinned martensite and residual austenite, and the change of the volume fraction of the residual austenite in the M-A constituent is very small when t8/5 is between 0.3 and 30 s. The morphology of the M-A constituent obviously changes with the variation of t8/5.As t8/5 increases, tile average width, gross and shape parameter of the M-A constituent increase, while the line density of the M-A constituent decreases.

Studies of diamond-like carbon (DLC) films deposited on stainless steel substrate with Si/SiC intermediate layers

In this work, diamond-like carbon （DLC） films were deposited on stainless steel substrates with Si/SiC intermediate layers by combining plasma enhanced sputtering physical vapour deposition （PEUMS-PVD） and microwave electron cyclotron resonance plasma enhanced chemical vapour deposition （MW-ECRPECVD） techniques. The influence of substrate negative self-bias voltage and Si target power on the structure and nano-mechanical behaviour of the DLC films were investigated by Raman spectroscopy, nano-indentation, and the film structural morphology by atomic force microscopy （AFM）. With the increase of deposition bias voltage, the G band shifted to higher wave-number and the integrated intensity ratio ID/IG increased. We considered these as evidences for the development of graphitization in the films. As the substrate negative self-bias voltage increased, particle bombardment function was enhanced and the sp^3-bond carbon density reducing, resulted in the peak values of hardness （H） and elastic modulus （E）. Silicon addition promoted the formation of sp^3 bonding and reduced the hardness. The incorporated Si atoms substituted sp^2- bond carbon atoms in ring structures, which promoted the formation of sp^3-bond. The structural transition from C-C to C-Si bonds resulted in relaxation of the residual stress which led to the decrease of internal stress and hardness. The results of AFM indicated that the films was dense and homogeneous, the roughness of the films was decreased due to the increase of substrate negative self-bias voltage and the Si target power.

Experimental investigation of erosion rate for gas-solid two-phase flow in 304 stainless/L245 carbon steel

Erosion is one of the most concerning issues in pipeline flow assurance for the Oil&Gas pipeline industries,which can easily lead to wall thinning,perforation leakage,and other crucial safety risks to the steady operation of pipelines.In this research,a novel experimental device is designed to investigate the erosion characteristics of 304 stainless and L245 carbon steel in the gas-solid two-phase flow.Regarding the impacts on erosion rate,the typical factors such as gas velocity,impact angle,erosion time,particle material and target material are individually observed and comprehensive analyzed with the assistance of apparent morphology characterized via Scanning Electron Microscope.Experimental results show that the severest erosion occurs when the angle reaches approximate 30°whether eroded by type I or type II particles,which is observed in both two types of steel.Concretely,304 stainless steel and L245 carbon steel appear to be cut at low angles,and impacted at high angles to form erosion pits.In the steady operational state,the erosion rate is insensitive to the short erosion time and free from the influences caused by the“erosion latent period”.Based on the comparison between experimental data and numerical results generated by existing erosion models,a modified model with low tolerance(<3%),high feasibility and strong consistency is proposed to make an accurate prediction of the erosion in terms of two types of steel under various industrial conditions.

Effect of stabilizing elements Nb and Ti on the microstructure and properties of low carbon ferritic stainless steel

The effect of stabilizing elements, such as Nb and Ti, on the microstructure and properties of low carbon ferritic stainless steel （FSS） has been investigated. The results of the Thermo-calc simulation have shown that the interstitial elements, such as C and N, may be completely stabilized by the addition of Nb and Ti. With the increase of Nb and Ti contents ,the α ＋ γ two phases gradually transfer to a single α-phase under a high temperature condition ,and the content of the carbide M23 C6 gradually decreases. The microstructure has indicated that the combined addition of Nb and Ti can promote the recrystallization of the band structure and form more uniform equiaxed grains. Also, with the increase of Nb and Ti contents,the elongation, the r-value and the corrosion resistance of cold-rolled and annealed sheets are improved prominently. In comparison with the effect of Ti ,the addition of Nb is more beneficial to the increase of r-value and the corrosion resistance.

Conductive and corrosion behaviors of silver-doped carbon-coated stainless steel as PEMFC bipolar plates

Ni–Cr enrichment on stainless steel SS316 L resulting from chemical activation enabled the deposition of carbon by spraying a stable suspension of carbon nanoparticles; trace Ag was deposited in situ to prepare a thin continuous Ag-doped carbon film on a porous carbon-coated SS316 L substrate. The corrosion resistance of this film in 0.5 mol·L^（-1） H_2SO_4 solution containing 5 ppm F- at 80°C was investigated using polarization tests. The results showed that the surface treatment of the SS316 L strongly affected the adhesion of the carbon coating to the stainless steel. Compared to the bare SS316 L, the Ag-doped carbon-coated SS316 L bipolar plate was remarkably more stable in both the anode and cathode environments of proton exchange membrane fuel cell（PEMFC） and the interface contact resistance between the specimen and Toray 060 carbon paper was reduced from 333.0 m？·cm^2 to 21.6 m？·cm^2 at a compaction pressure of 1.2 MPa.

Electrochemical Investigation of Corrosion on AISI 316 Stainless Steel and AISI 1010 Carbon Steel: Study of the Behaviour of Imidazole and Benzimidazole as Corrosion Inhibitors

An electrochemical investigation of the corrosion on AISI 316 austenitic stainless steel and AISI 1010 carbon steel in sodium chloride solution (3.0 wt.%) was performed in the absence and presence of imidazole and benzimidazole corrosion inhibitors. The results showed that at any inhibitor concentration (25 ppm to 1000 ppm), there was an increase in the polarisation resistance of both steels. The highest efficiency of corrosion inhibition was obtained using imidazole at a concentration of 50 ppm for both steels, with values of 96% for the AISI 316 stainless steel and 73% for the AISI 1010 carbon steel.

Effect of an upward magnetic field on nanosized sulfide precipitation in ultra-low carbon steel

An induction levitation melting （ILM） refining process is performed to remove most microsized inclusions in ultra-low carbon steel （UCS）. Nanosized, spheroid shaped sulfide precipitates remain dispersed in the UCS. During the ILM process, the UCS is molten and is rotated under an upward magnetic field. With the addition of Ti additives, the spinning molten steel under the upward magnetic field ejects particles because of resultant centrifugal, floating, and magnetic forces. Magnetic force plays a key role in removing sub-micrometer-sized particles, composed of porous aluminum titanate enwrapping alumina nuclei. Consequently, sulfide precipitates with sizes less than 50 nan remain dispersed in the steel matrix. These findings open a path to the fabrication of clean steel or steel bearing only a nanosized strengthen- ing phase.

Deformation Behavior of Ultra-low Carbon Steel in Ferrite Region during Warm Processing

The hot deformation experiments of ultra-low carbon steel in ferrite range were carried out in a hot simulator in order to research hot deformation behaviors of ultra-low carbon steel in ferrite range at low temperature. The results show that the influences of deformation parameters on flow stress are different to those in austenitic deformation. The deformation characteristic parameters were calculated for ultra-low carbon steel in ferrite region. The flow stress equation for ultra-low carbon steel in ferritic deformation at low temperature was obtained.

Study on process of roll bonding stainless and carbon steel under non-vacuum condition

The non-vacuum roll bonding method of nickel plating on the base materials is put forward in accordance with the primary problems existed in the roll bonding of stainless/carbon steel. After nickel plating test on the base materials, the microstructure of nickel cladding is observed by scanning electron microscopy （SEM） at high, and room temperature, and the results show that the nickel cladding on base material can be protected from oxidation in the high temperature. Non-vacuum roll bonding tests of nickel plating on base materials are done by the roll bonding equipment, and the roll bonding plates of stainless/carbon steel are obtained. The microstructure and the elements distribution of non-vacuum roll bonding interface are analyzed by optical microscope （OM） and SEM. The results reflect that the nickel plating layer and the base materials bond well.

Mechanical Method Determining Precipitation in an Ultra-Low Carbon Bainitic Steel

Stress relaxation was chosen as the best method for monitoring the precipitation process. Tests were carried out on an ultra-low carbon bainitic steel containing Mn, Nb and B over 800~950℃. Specimens were solu- tion treated at 1250℃ for a certain holding period. A prestain of 20% was applied at a strain rate of 0.1/s. The exper- imental results are displayed by a set of stress vs. 1g(time) curves different from the typical stress relaxation curves. There are two singularities forming a stress plateau on the stress vs.1g(time) curves when precipitates could be observed. Suppose the first one is the start of precipitation (Ps), and the second represcnts the fihish (Pf). As a result Precipitation-Time-Temperature relationship is described as C-shape curves based on two points. This mechanical method is suitable and precise for measuring precipitates in microalloyed steels during hot working.

Optimum process of RH-MFB refining for ultra-low carbon steel

A mathematical model was established and applied to simulate thedecarburization of RH-MFB process in Pansteel Company. Study of theeffects of w_[C]0, w_[O]0, Ar flowrate, evaluation rate the MFB lanceblowing parameters on the decarburization process was car- Ried out.The results showed that this model could give the quantitativeunderstanding of the process, especially the behavior of MFB Lanceblowing. This model has realized the optimum process of RH-MFBrefining for ultra-low carbon steels in Pansteel.

Advanced manufacturing technologies of large martensitic stainless steel castings with ultra low carbon and high cleanliness

The key manufacturing technologies associated with composition, microstructure, mechanical properties, casting quality and key process control for large martensitic stainless steel castings are involved in this paper. The achievements fully satisfeid the technical requirements of the large 700 MW stainless steel hydraulic turbine runner for the Three Gorges Hydropower Station, and become the major technical support for the design and manufacture of the largest 700 MW hydraulic turbine generator unit in the world developed through our own efforts. The characteristics of a new high yield to tensile strength (R p0.2/R m ) ratio and high obdurability martensitic stainless steel with ultra low carbon and high cleanliness are also described. Over the next ten years, the large martensitic stainless steel castings and advanced manufacturing technologies will see a huge demand in clean energy industry such as nuclear power, hydraulic power at home and abroad. Therefore, the new high yield o tensile strength (R p0.2/R m ) ratio and high obdurability martensitic stainless steel materials, the fast and flexible manufacturing technologies of large size castings, and new environment friendly sustainable process will face new challenges and opportunities.

Structure change of 430 stainless steel in the heating process

The microstructure analysis was employed for the ferrific stainless steel （SUS430） with the carbon content from 0.029wt% to 0.100wt% under the simulated heating process condition. The higher carbon sample （430H） contains the duplex phase microstructure at the temperature of 1150℃; on the other hand, the lower carbon content sample （430L） does not touch two phase area even at the temperature of 1450℃ and has the single phase ferritic microstructure. The carbon content need be well controlled for the 430 ferritic stainless steel since it can significantly affect the heating process curve, and the heating process may not be done in the two phase area due to the uncontrolled carbon content. With the low carbon content and the proper soaking time, the grain size is not sensitive to the heating process temperature and the soaking time. In the present heat treatment experiments, the soaking time is about 10 min, and the processing parameters can be chosen according to the requirement of the gross energy, the efficiency and the continual forming. 2008 University of Science and Technology Beijing. All rights reserved.

Mathematical Model of Decarburization of Ultra Low Carbon Steel during RH Treatment

According to the balance of carbon and oxygen, a decarburization model for the RH treatment has been developed. in which the influence of the mass transfer of carbon and oxygen in the liquid steel and the stirring energy (ε) in the vacuum vessel on decarburization rate has been considered. The conclusion that the volumetric coefficients of the mass transfer of carbon is proportional to ε(1.5) is drawn. Industrical experiment proves this model is reliable. The influence of some factors on decarburization rate has been obtained. which can provide directions for RH treatment The decarburization behavior of steel with RH-OB treatment is also studied. The OB-or-not curve, the optimized OB time and OB amount are discussed.

Constitutive Modeling and Dynamic Recrystallization Mechanisms of an Ultralow-carbon Microalloyed Steel During Hot Compression Tests

The hot deformation behavior of an ultralow-carbon microalloyed steel was investigated using an MMS-200 thermal simulation test machine in a temperature range of 1073-1373 K and strain rate range of 0.01-10 s-1.The results show that the flow stress decreases with increasing deformation temperature or decreasing strain rate.The strain-compensated constitutive model based on the Arrhenius equation for this steel was established using the true stress-strain data obtained from a hot compression test.Furthermore,a new constitutive model based on the Z-parameter was proposed for this steel.The predictive ability of two constitutive models was compared with statistical measures.The results indicate the new constitutive model based on the Z-parameter can more accurately predict the flow stress of an ultralow-carbon microalloyed steel during hot deformation.The dynamic recrystallization(DRX)nucleation mechanism at different deformation temperatures was observed and analyzed by transmission electron microscopy(TEM),and strain-induced grain boundary migration was observed at 1373 K/0.01 s^-1.

Effect of Mn on the microstructure and property of 13Cr stainless steel

Mn is a weak element for austenite formation and its effect on martensitic stainless steel is seldom researched. The microstructure and property of 13Cr martensitic stainless steel with varied Mn content and low carbon content were studied. The research demonstrates that Mn enlarges the austenitic zone at a high temperature and increases the strength and hardness of martensitic stainless steel. Following the addition of Mn,the corrosion resistance property of low carbon 13Cr stainless steel only decreases slightly. The strength and hardness of low carbon 13Cr stainless steel containing Mn is similar to that of high carbon 13Cr stainless steel.

Microstructure of stainless steel weld in double-sided arc welding

Double-sided arc welding with a single power source can effectively increase the weld penetration, diminish distortion, improve welding speed and save energy. Compared to conventional arc welding processes, double-sided arc welding can generate a penetrating electromaguetic field to help to form fine dendritic microstrueture in the weld due to the symmetry of heating. Type 1Cr1SNi9Ti aastenitic stainless steel was bead-on-plate welded with double-sided arc welding and conventional plasma arc welding processes, respectively, and microstructure in the weld, heat-affected zone and base metal were examined. After analyzing the black carbon-enriched band in the weld during plasma arc welding with electron probe microanalyzer （ EPMA ） and X-ray diffraction （XRD） technology, it was found that the black band was shaped from the aggregation of ferrite in the fasion boundary. Hardness measurement showed that this black band does not apparently affect the microhardncss distribution in the weld.

“双碳”战略背景下不锈钢复合钢板结构减碳前景分析

为探究不锈钢复合钢板结构的减碳前景,本文分析了“双碳”战略背景下钢结构行业的发展趋势,包括智能建造快速发展、新兴产业提供广阔市场以及高性能钢材和高性能结构发展更为迅猛,指出不锈钢复合钢板结构可兼顾高性能、经济性以及减碳要求。基于全寿命周期评价理论,采用排放因子法,提出了不锈钢复合钢板结构的碳排放计算方法。结果表明:不锈钢复合钢板结构的全寿命周期碳排放量比钢结构少36%,比不锈钢结构少10%。用不锈钢复合钢板结构替代普通钢结构,可以有效减少碳排放;替代不锈钢结构可以在减碳的同时具有良好的经济性。

温度和应变幅对亚稳奥氏体不锈钢S321低周疲劳行为的影响

在室温和650℃的环境下对S321、S321H不锈钢进行了0.5%、0.7%、0.9%应变幅下的低周疲劳试验,并在室温下对S321和S321H开展了多个寿命点的疲劳加载历史试验,结合X射线衍射定量分析测算形变诱发马氏体的含量。结果表明:形变诱发马氏体的生成会导致奥氏体钢持续循环硬化,室温下合金在初次硬化后继续二次硬化,而在650℃下没有形变诱发马氏体生成,合金在初次硬化后进入循环稳定阶段。循环过程中,碳含量越低,形变诱发马氏体含量越多,合金的循环硬化程度更高。两种温度下,两种材料的疲劳寿命在低应变幅下都相差不大,应变幅越大,两种材料的疲劳寿命相差越大,因此,可以考虑服役条件为低应变幅时使用S321不锈钢代替S321H不锈钢。