不锈钢与碳钢混合轧制中的板形控制

简要介绍了不锈钢1780mm热连轧生产情况和板形控制技术。从板形控制的角度分析了不锈钢与碳钢混合轧制和集中轧制的区别。结合计算结果和生产实绩,分析了典型不锈钢与碳钢混合轧制过程的板形控制情况,发现了其中存在的板形控制问题并提出了具体的改进措施。研究表明,为了使不锈钢和碳钢都能达到良好的凸度和平直度目标,需要合理确定两种产品的轧制工艺条件,使二者在板形控制上相互匹配。     

Effect of strain rate and temperature on hot workability and flow behaviour of duplex stainless steel

The flow behaviour and processing map of a duplex stainless steel were studied via hot compressive tests in a temperature range of 1223–1473?K and a strain rate range of 0.01–30?s^??1. The effect of strain rate and temperature on the hot workability, strain partitioning and dominant flow behaviour of the alloy was systematically investigated. It is found that the softening mechanism of each constituent phase differs from each other. The ferrite is softened by dynamic recovery and continuous dynamic recrystallisation (CDRX), while the austenite is softened only by the limited discontinuous dynamic recrystallisation (DDRX). At lower strain rates (0.01 and 0.1?s^??1), the strain is mainly accommodated by ferrite due to its excellent softening capability, which causes the apparent activation energy Q_p to decline continuously with the increase in true strain. In this case, plastic deformation of the austenite rarely occurs, and at this time, DDRX of austenite is not observed. When the strain rate increases, CDRX of ferrite is weakened at a relative low temperature, which prompts the strain transfer into austenite and induces the strain hardening due to its restricted softening. Accordingly, interactions between the strain hardening in austenite and weakened softening of ferrite leads to one or more platforms of Q formed at the medium stage of deformation (1–30?s^??1). The processing map shows that two flow instability regions appear at high strain rate due to the lack of sufficient response time for dynamic restoration at the early deformation stage. As the strain increases, dynamic softening mechanism is activated at a higher temperature, resulting in a gradually narrowed flow instability region. Differently, a decrease in temperature suppresses dynamic softening of the alloy with a high strain rate, which deteriorates the hot workability of the alloy and induces microcrack formation after straining of 0.8.     

Simulation of the behaviour of voids in steel plates during hot rolling

The prime objective of the work is to predict the behaviour of voids in the steel slab during hot rolling and to assess the tendency of the void to closure, depending on the process parameters. The rigid-plastic thermal-mechanical finite-element program is used for the purpose. The model which simulates the general case of deformation of a single void in a matrix undergoing plastic deformation is developed. This model allows the investigation of the influence of the stress state on the void's behaviour. Finite element calculations carried out for the industrial hot plate rolling process supply information regarding the stress state during rolling depending on the process technological parameters. These data are used as boundary conditions in the void's closure model and, in consequence, allow the analysis of the influence of rolling technology on the void's behaviour.     

不锈钢线棒材的热轧生产

介绍了不锈钢线棒材热轧生产的特点及现代轧制技术。     

High-temperature deformation behaviour of duplex stainless steel with hard boronised layer

In order to understand the high-temperature deformation behaviour of alloy having hard surface layer,thermo-mechani-cally treated duplex stainless steel(DSS)is ...     

冷轧硬化对超级双相不锈钢S32750析出相的影响

 为了优化不同厚度冷轧板加热工艺,避免有害相析出,研究了冷硬化对S32750板材析出相的影响。超级双相不锈钢S32750钢板经不同冷轧加工变形后,在850 ℃下进行热处理。利用SEM、EDS、XRD及TEM研究了不同冷轧总压下率对析出相的影响规律。结果表明,随着总压下率的增大,相同退火时间内,析出相增多,当总压下率大于50%时铁素体相几乎全部被析出相覆盖。析出相以σ相为主,伴随着很少量的Cr2N、χ相和γ2。σ相和χ相析出在α/γ相界和铁素体相内,Cr2N析出在α/γ相界处,γ2伴随着σ相析出在铁素体内。随着冷轧总压下率增加,晶体内的位错密度增大,析出数量增加。     

Precipitation behaviour of a nitrogenated surface layer of 1.4462 duplex stainless steel

A duplex stainless steel sheet containing masses of 22%Cr-5.5%Ni-3%Mo was nitrogenated at 2 bar partial pressure of N₂ at 1200°C for 5 hours. Three zones, with different microstructures and nitrogen contents, were formed: a fully austenitic nitrogen rich zone, a transition zone composed of an austenitic matrix containing islands of remaining ferrite and a nitrogen enriched duplex inner zone. The exposures of the nitrogenated material at temperatures below the nitrogenation temperature caused precipitation of ε-(Cr,Fe)₂N hexagonal nitride and of sigma phase. The nitride precipitation occurred both continuously and discontinuously. TTT diagrams for the austenitic external zone and for the inner ferritic-austenitic zone have been proposed.     

双相不锈钢2205热轧钢带氧化铁皮显微分析

 应用OM、SEM、XRD技术,分析研究了双相不锈钢2205热轧钢带氧化铁皮显微结构特征,这是决定钢带酸洗效果的本质因素之一。结果表明：热轧后钢带表面氧化铁皮存在大量的裂纹以及局部伴有氧化铁皮部分脱落,有利于酸洗;氧化铁皮厚度一般为10 μm左右,但是存在局部区域氧化层增厚以及氧化铁皮向基体内部的嵌入;氧化铁皮中含有难以酸洗的铁橄榄石（Fe2SiO4）和尖晶石结构的Cr2O3·FeO等物相,增加了钢带表面氧化铁皮酸洗去除的难度。     

Microstructural and mechanical behavior of a duplex stainless steel under hot working conditions

In the hot deformation of the duplex stainless steels, the complexity of the microstructure evolution and mechanical response is increased as compared with those of single-phase ferritic or austenitic stainless steels. In the present work, plane strain compression and torsion deformation modes have been used to analyze the microstructural evolution and the mechanical behavior of a duplex stainless steel in as-cast and wrought conditions, as a function of spatial phase distribution, the nature of interface, and the relative mechanical properties of both phases. The law of mixtures has been used to explain the different flow curves obtained when changing the phase distribution and/or the deformation mode. On deforming as-cast microstructures, the deformation partitions vary heterogeneously between both phases and some austenite areas act as hard nondeforming particles. Cracks have been observed to occur at the interface of such regions, from relatively low strains, for which the initial Kurdjumov-Sachs orientation relationship between ferrite and austenite is still present.     

Modelling water cooling of steel strip during hot rolling

Several tests of water cooling of steel samples are presented in the paper. The water spray and quenching conditions are considered. The temperature variations during the tests are monitored using the thermocouples embedded in the side of the samples. The experimental time – temperature profiles are compared with the results of calculations based on the finite element model. Comparison of the theoretical and experimental results allowed to suggest heat transfer coefficients of 10000 W/m²K for water in quenching, 6000 W/m²K for the top surface during water spray cooling and 4000 W/m²K for the bottom surface during water spray cooling.     

316L/EH40不锈钢复合板热轧过程中晶粒组织的均匀性

 为了改善热轧不锈钢复合板晶粒组织的均匀性,采用正交试验优化设计方法设计数值模拟方案,研究轧制工艺参数对基层不均匀因子、基层平均晶粒尺寸、复层不均匀因子和复层平均晶粒尺寸的影响,分析各参数的影响显著性顺序,并采用综合平衡法得到优选参数组合,轧制压下率为60%,轧制温度为1 100 ℃,轧制速度为300 mm/s。对优化后的参数组合进行有限元模拟,得到了热轧过程中沿不锈钢复合板厚度方向晶粒尺寸的分布及其变化规律。通过试验与仿真模拟获得的晶粒尺寸进行对比验证,得出晶粒尺寸误差在5%以内,验证了有限元模型的正确性与可靠性。     

不锈钢热轧板带生产工艺及设备选型

根据热轧不锈钢工程设计中的经验总结并结合国内已建成的宽幅不锈钢生产厂的工艺设备情况,从轧线布置形式和主要设备技术性能方面分析了不锈钢热轧板带生产工艺及设备选型的主要特点,指出不锈钢热轧生产与碳钢生产在工艺设备选型方面的区别。认为采用R1＋F1~F7的工艺布置方式,较为经济、实用。为保证生产过程中的温度控制和产品质量,宽幅不锈钢粗轧机轧制力宜选择在42 000 kN以上,主电机功率12 000 kW以上。中间坯保温方式宜采用热卷箱形式。精轧机组前应设置小立辊轧机对带坯进行边部轧制。     

真空热轧法制备不锈钢复合板组织和力学性能

 为了研究轧制温度对复合板界面结合强度的影响,采用真空热轧法制备了不锈钢复合板,利用OM、EPMA观察分析了不锈钢复合板界面组织和合金元素扩散。结果表明,碳钢中碳、铁元素向不锈钢扩散,不锈钢中铬、镍等元素向碳钢扩散,界面处出现Si-Mn-O三元化合物,合金元素扩散随轧制温度的升高而趋于严重。远离界面碳钢的组织为铁素体和珠光体组织,靠近界面碳钢的组织为铁素体组织。碳钢至界面处硬度先减小后升高,界面至不锈钢内部硬度先升高后下降,距界面约40 μm碳钢侧的维氏硬度值最低约为121.8HV,距界面约20 μm不锈钢侧的维氏硬度值最高约为245.5HV。从1 100到1 300 ℃,剪切强度随轧制温度的升高而升高,1 300 ℃轧制获得的界面剪切强度为463 MPa,远远超过基体的剪切强度。     

超级双相不锈钢生产工艺实践

超级双相不锈钢S32760生产工艺流程为20tEAF→AOD→LF→30cm模铸。由于S32760成分设计中高铬、低磷、低硫、超低碳这一特点,冶炼后期钢水过氧化程度严重。为改善钢水洁净度、降低钢中氧质量分数,通过采取合理的脱氧造渣工艺,采用Al-Si-Ca复合脱氧,使钢中气体、夹杂物得到了有效控制,改善了钢水洁净度,成品钢中硫质量分数控制在0.002%以下,氧质量分数控制在0.004%以下。     

不锈钢典型夹杂物在轧制过程的衍变分析

不锈钢对冷板表面质量要求高,轧制过程中夹杂物是产生表面缺陷的主要原因之一。为了明确夹杂物对轧制过程表面缺陷的影响规律,通过中试模拟试验研究了热轧、退火和冷轧过程硬质镁铝尖晶石和低熔点硅酸盐2种典型夹杂物的变形特点,并采用数值模拟对冷轧过程夹杂物的变形机理进行了分析。结果表明,热轧过程高熔点的镁铝尖晶石不变形,低熔点的硅酸盐夹杂物在1 200～1 250℃热轧温度下为半熔融状态,具有良好的变形能力。硅酸盐夹杂物长宽比高、抗拉强度低,冷轧过程更容易断裂延伸,随着轧制的进行,断裂后夹杂物之间的距离逐渐增加,尺寸减小。相反,镁铝尖晶石不容易断裂、延伸,而且存在断裂延伸的临界尺寸,该临界尺寸随冷轧变形量的增加而减小。由于镁铝尖晶石容易造成不锈钢轧制缺陷,因此生产过程中应尽量避免其生成或控制其粒径。     

Microstructures of a powder metallurgy-hot-isostatically pressed super duplex stainless steel forming in industrial heat treatments

The microstructures of a powder metallurgy/hot-isostatically pressed super duplex stainless steel, designed and manufactured for massive components of paper machines, were studied after heat treatments simulating the industrial production. It was shown that copper precipitates in the ferrite phase as ɛ phase. Morphologically, the copper precipitates are of two types—nearly spherical particles of typical size from 30 to 50 nm, and rodlike particles 30- to 35-nm wide, and up to 700-nm long. The main observations on copper precipitation in modern super duplex stainless steels are similar to those in low-alloy steels. Copper particles were shown to be the nucleation sites for the formation of secondary austenite and to pin the boundaries of sigma phase.     

2205双相不锈钢连铸过程中夹杂物的形成机制

摘要：为了研究2205双相不锈钢连铸过程中夹杂物的特征及形成机制，从2205双相不锈钢连铸中间包和板坯上分别取试样，利用扫描电镜分析夹杂物的类型及形貌特征，并结合热力学计算探讨夹杂物的演变规律及其形成原因。结果表明，2205双相不锈钢中间包中存在大于10μm的夹杂物，中间包中夹杂物类型主要为CaO Al2O3和CaO Al2O3 MgO球形夹杂物，板坯中夹杂物尺寸都小于10μm，板坯中CaO Al2O3和CaO Al2O3 MgO球形夹杂物外面包裹了一层TiN。错配度和热力学计算表明凝固过程中CaO Al2O3和CaO Al2O3 MgO球形夹杂物为TiN的析出提供了形核质点。