Research on martensitic transformation of 304 stainless steel

采用光学显微镜、扫描电镜、磁性测量和力学分析等手段,研究了304奥氏体不锈钢形变过程中发生开裂的原因,研究发现开裂是由于形变过程中发生了马氏体相变,导致塑性变差引起的,开裂处的磁性率达到了22.9%。发生马氏体转变的原因是由于w（Ni）低于标准下限,其组织稳定性下降,在形变过程中诱发了马氏体转变。     

304不锈钢马氏体组织转变探讨

采用光学显微镜、扫描电镜、磁性测量和力学分析等手段,研究了304奥氏体不锈钢形变过程中发生开裂的原因,研究发现开裂是由于形变过程中发生了马氏体相变,导致塑性变差引起的,开裂处的磁性率达到了22.9%。发生马氏体转变的原因是由于w（Ni）低于标准下限,其组织稳定性下降,在形变过程中诱发了马氏体转变。     

Development and application of nitrogen-alloyed austenitic stainless steels in Baosteel

In recent years,nitrogen-alloyed stainless steels have been a research hotspot in the field of stainless steel product and technology. Nitrogen-alloyed austenitic stainless steels developed by Baosteel and their applications are introduced. These steels are nitrogen-controlled products 304 N and 316 LN,nitrogen containing economical products BN series and high-nitrogen stainless steel( HNS) series. The results show that the presence of nitrogen can significantly improve the strength and corrosion resistance of steel produced. By nitrogen alloying,economical austenitic stainless steels w ith considerably less nickel than 304 can be obtained; the corrosion resistances of these steels are almost the same as 304. Furthermore,by a scientific approach of nitrogen alloying,high-nitrogen steel of0. 8% nitrogen content is fabricated under the non-pressurized conditions,and the pitting potential of this steel is 1. 0 V. At present,nitrogen-alloyed steels developed by Baosteel are w idely utilized in the manufacture of cryogenic storage containers,transportation containers,and many household w ares.     

Development of nitrogen-alloyed stainless steel sheet products in Baosteel

Nitrogen plays a vitally important role for improving properties for stainless steels in many aspects.In this paper,the physical metallurgy behavior and the beneficial effects of nitrogen on corrosion resistance and other mechanical properties of stainless steels were summarised.Based on nitrogen alloying,various stainless steel products,such as austenitic,duplex and martensitic staniless steels were developed with enhanced properties,such as corrosion resistance,mechanical strength and weldability,among other things.     

固溶时效后高氮奥氏体不锈钢的物理化学相分析

采用物理化学相分析技术研究了高氮奥氏体不锈钢固溶时效后的碳、氮化物析出行为,确定了析出相的类型、粒度分布、含量及组成结构式.结果表明:氮含量低的1Cr22Mn15N0.6以M₂₃C₆型碳化物析出为主,氮含量高的1Cr22Mn15N0.9以(CrFe)₂N_1-x型氮化物析出为主,高氮奥氏体不锈钢中析出物的总量随时效时间的延长而增加.     

A constitutive model for transformation plasticity accompanying strain-induced martensitic transformations in metastable austenitic steels

We propose a constitutive model which describes the transformation plasticity accompanying strain-induced martensitic transformation in nonthermoelastic alloys. The model consists of two parts: a transformation kinetics law describing the evolution of the volume fraction of martensite and a constitutive law defining the flow strength of the evolving two-phase composite. The Olson-Cohen model for martensite volume fraction evolution is recast in a generalized rate form so that the extent of martensite nucleation is not only a function of plastic strain and temperature, but also of the stress state. A selfconsistent method is then used for predicting the resultant stress-strain behavior. The model describes both the hardening influence of the transformation product, and the softening influence of the transformation itself, as represented by a spontaneous transformation strain. The model is then implemented in a finite element program suitable for analysis of boundary value problems. Model predictions are compared with existing experimental data for austenitic steels. We present results from a few simple analyses, including tensile necking, illustrating the critical importance of stress state sensitivity in the evolution model.     

晶粒细化对奥氏体不锈钢高温力学性能的影响

摘要：对粗晶201LN奥氏体不锈钢采用60%冷变形结合700℃退火120s工艺制备超细晶奥氏体不锈钢,研究晶粒细化对奥氏体不锈钢高温力学性能的影响。利用光学显微镜、扫描电子显微镜、透射电子显微镜、电子背散射衍射技术对粗晶和超细晶奥氏体钢进行了组织表征,并使用万能试验机测试20和650℃环境下力学性能。结果显示粗晶奥氏体不锈钢经过冷变形结合退火工艺处理,平均晶粒尺寸由18μm细化为0.9μm,屈服强度由383MPa提高到704MPa,而伸长率由63.8%下降到46.3%,表明晶粒细化能有效提高奥氏体不锈钢屈服强度的同时较小损害塑性,TEM证实其形变机制均为形变诱导马氏体和孪生协同作用。当温度由20℃提高到650℃时,粗晶奥氏体不锈钢屈服强度和伸长率分别下降到180MPa和28.1%,超细晶奥氏体不锈钢屈服强度和伸长率分别为384MPa和24.2%。这表明在650℃高温环境下细晶强化作用仍然有效,粗晶和超细晶奥氏体不锈钢也有较好的塑性,其形变机制分别变为位错滑移和位错滑移+层错+孪生。     

Effect of heat treatment on the behavior ofδ-ferrite in B410D martensitic stainless steel

The morphology and the evolution ofδ-ferrite existing in B410D slabs,hot-rolled plates,annealed plates and quenched plates were studied through metallographic observation.Results show thatδ-ferrite forms during the solidification process and that it easily grows and increases in quantity during high temperature annealing.Band-shapedδ-ferrite in hotrolled plates is difficult to be eliminated by conventional heat treatment and hard to recrystallize.     

冷却速率对奥氏体不锈钢凝固过程影响的原位观察

通过采用激光共聚焦扫描显微镜对AISI304奥氏体不锈钢的凝固过程进行了原位动态观察研究.发现当冷却速率为0.05℃·s^-1时,奥氏体不锈钢以胞状晶方式凝固,其凝固模式为FA模式,即δ铁素体相先从液相中形核并长大,γ相在1 448.9℃时通过与液相发生包晶反应(L+δ→γ)在δ铁素体相界形成,当温度降到1 431.3℃时液相消失,δ铁素体相通过固态相变转变为γ相,富Cr贫Ni的残留铁素体位于胞状晶之间.当冷却速率为3.0℃·s^-1时,奥氏体不锈钢以枝晶方式生长,冷却到1346.4℃时包晶反应在液相与δ铁素体相界之间进行,其残留铁素体位于枝晶干,与冷却速率为0.05℃·s^-1时相比,其残留铁素体的数量增多,残留铁素体富Cr贫Ni的程度减轻.     

铸造奥氏体不锈钢的疲劳裂纹扩展

用紧凑拉伸试样研究了载荷比、单峰过载和两步高-低幅加载对Z3CN20-09M铸造奥氏体不锈钢疲劳裂纹扩展速率的影响.当应力强度因子范围相同时,疲劳裂纹扩展速率随载荷比的增大而增大.单峰过载使裂纹扩展速率先有短暂的增加后长距离的减速扩展,出现裂纹扩展迟滞现象.两步高-低幅加载时,若两步的最大载荷不同,第二步裂纹扩展也会出现迟滞现象.用两参数模型和Wheeler模型能够预测恒幅载荷和变幅载荷下的疲劳裂纹扩展行为.     

奥氏体不锈钢保护渣的研制

针对奥氏体不锈钢成分的特殊性及可能产生的夹杂物,提出了连铸保护渣的相应研制思路,以此开发的保护渣在宝钢集团浦钢公司进行了数十炉的工业试验。结果证明,研制的奥氏体连铸保护渣各项性能均取得了较为满意的结果,铸坯质量及轧制性能达到了用户要求。     

粉末锻造制备含氮奥氏体不锈钢

介绍粉末包套烧结-自由锻造法制备含氮钢的过程。它包括含氮粉末准备→装粉→烧结→包套焊封→自由锻造等技术措施。本工艺比较简单，易于操作，对相应设备要求低。通过本技术制备的含氮奥氏体不锈钢材料相对密度达99％以上，且氮含量能满足含氮钢要求，其拉伸性能与粉末注射成形、高压熔炼等工艺制得的含氮奥氏体材料相当。     

高碳高铬马氏体不锈钢铸锭开裂原因

基于金相分析、热力学计算、高温拉伸试验和高温共聚焦原位观察等一系列方法,对高碳高铬马氏体不锈钢8Cr17Mo2铸锭表面裂纹产生原因进行了研究。结果表明,铸锭的心部存在一定面积的中心疏松,成为裂纹源头;铸锭浇铸完毕后的冷却时间较短,心部余温仍处于塑性比较低的范围,在钢锭脱离锭模的过程中,在外部产生的机械应力作用下容易在中心疏松处萌生裂纹;在中温退火后空冷过程中仍然会发生马氏体相变,由于应力作用促进萌生的裂纹扩展,并延伸至铸锭表面,形成裂纹。     

热处理工艺对超级马氏体钢逆变奥氏体的影响

 试验采用光学显微镜、X射线衍射仪（XRD）、透射电镜（TEM）及能谱分析（EDS）等手段,研究不同铬含量的超级马氏体不锈钢在相同热处理工艺下逆变奥氏体含量、组织形貌及生长规律的异同。结果表明,13Cr和15Cr两试验钢经淬火＋回火后的显微组织为回火马氏体和逆变奥氏体,两试验钢中逆变奥氏体含量及尺寸均随着回火温度升高先增加再减小,且在650～700 ℃时达到最大。两试验钢内的逆变奥氏体在回溶过程中会对基体组织产生细化作用。通过对比发现,15Cr钢中的逆变奥氏体含量更多,尺寸更大,回溶时对基体的细化作用更明显。     

VOD冶炼超低碳马氏体不锈钢

利用40tVOD精炼炉脱碳冶炼00Cr13Ni4Mo超低碳马体不锈钢.通过合理控制炉内参数得到,吹氧时炉内真空度在26660 Pa左右,停吹氧时真空度在7998 Pa;开吹温度控制在1600℃左右,停吹温度在1750~1800℃左右;开吹时提高供氧强度至570 Nm³·h^-1左右,吹炼后期降低供氧强度至550 Nm³·h^-1左右,可以避免铬的大量氧化;控制氧枪高度在75mm;开吹供氩强度控制在48.4 NL³·min^-1,提高低碳区供氩量至117.5 NL³·min^-1,用以加快钢包内钢水环流速度.     

Technological application of the martensitic transformation of some austenitic stainless steels

The final heat treatment of austenitic stainless steels of types X 5 CrNi 18 9 (1.4301) and X 2 CrNi 18 10 (1.4306) normally is annealing at 1050°C and subsequent water quenching. The resulting structure is of a metastable fcc-type. Plastic deformation, especially at low temperatures, causes martensitic transformation of these metastable structures. The transformation is accompanied by a substantial flow stress increase. This strengthening mechanism should be used in practice, e.g. to save weight. The deformed structure consists of tetragonal α′-martensite, austenite and hcp ε-martensite. Whereas α′-martensite increases continuously with deformation, the content of ε-martensite reaches a maximum value at about 5% plastic strain at 77 K. The hcp phase is only detectable by means of X-ray analysis, whilst α′-martensite can be determined quantitatively by saturation magnetisation measurement. The flow stress increase during low temperature deformation of metastable austenitic stainless steels is based on normal work-hardening by dislocation accumulation, in addition to a distinct amount of work-hardening due to martensitic transformation. Analysis of the work-hardening behaviour in the range of stable deformation (T > M_D) can be used to predict the amount of normal work-hardening when deformation is performed in the instable temperature regime. Separation of the flow stress contributions according to the procedure described above enables the possible savings in weight to be predicted when using cryogenically stretched instable austenitic steels in comparison with stable grades deformed under the same conditions.     

淬火温度对不同铬含量的低碳马氏体不锈钢组织和性能的影响

摘要：为研究淬火温度对不同铬含量的马氏体不锈钢组织和性能的影响,采用高温共聚焦显微镜(CLSM)、光镜(OM)、扫描电镜(SEM)、万能拉伸机、显微硬度计等方法对材料组织和性能进行了测试及表征。随着淬火温度的升高,不锈钢淬火后的晶粒尺寸都变大,计算确定了13%Cr和14%Cr不锈钢的晶界迁移能分别为113.62和125.92J/mol。13%Cr不锈钢经过淬火后显微组织为板条马氏体,回火后的组织为回火马氏体。但是,14%Cr不锈钢在1200℃淬火后生成了板条马氏体和少量的高温铁素体,并且在回火后高温铁素体并未消失,会对后续性能产生影响。淬火温度对不锈钢的强度影响不大。不锈钢中的铬质量分数从13%增加至14%,马氏体不锈钢强度增加,但伸长率有所降低。马氏体不锈钢的硬度随淬火温度的升高而下降,这主要与晶粒尺寸有关。     

奥氏体不锈钢中硫含量的研究

通过对不同硫含量铸坯和成品硫化物夹杂大小以及等级进行分析,研究了奥氏体不锈钢中硫含量对性能的影响。结果表明,随着硫含量的增加,不锈钢铸坯和成品中最大夹杂物尺寸逐步增加,成品夹杂物等级也相应提高,当硫的质量分数不大于21×10~(-6)时,成品硫化物夹杂低于最小评级要求;奥氏体不锈钢冲击性能与硫含量呈反比例关系,当硫的质量分数高于75×10~(-6)时,可能导致304不锈钢脆断。     

Study on microstructure and mechanical properties of martensitic stainless steel 6Cr15MoV

Martensitic stainless steel containing 12%-18%Cr have high hardness due to high carbon content. These steels are common utilized in quenching and tempering processes for knife and cutlery steel.The properties obtained in these materials are significantly influenced by matrix composition after heat treatment,especially as Cr and C content.Comprehensive considered the hardness and corrosion resistance,a new type martensitic stainless steel 6Cr15MoV has been developed.This study emphatic researches the effect of heat treatment processes on microstructure and mechanical properties of 6Cr15MoV martensitic stainless steel.Thermo-Calc software has been carried out to thermodynamic calculation;optical microscope（OM）,scanning electronic microscope（SEM） and transmission electron microscope（TEM） have been carried out to microstructure observation;hardness and impact toughness test have been carried out to evaluate the mechanical properties.Results show that the equilibrium carbide in 6Cr15MoV steel is M₂₃,C₆ carbide,and finely distributed of M₂₃C₆ carbides can be observed on annealed microstructure of 6Cr15MoV stainless steel.6Cr15MoV martensitic stainless steel has a wider quenching temperature range,the hardness value of steel 6Cr15MoV can reach to 60.8 -61.6 HRC when quenched at 1060 - 1100℃.Finely distributed carbides will exist in quenched microstructure,and effectively inhabit the growth of austenite grain.With the increasing of quenching temperature,the volume fraction of undissolved carbides will decrease.The excellent comprehensive mechanical properties can be obtained by quenched at 1060-1100℃with tempered at 100-150℃,and it is mainly due to the high carbon martensite and fine grain size.At these temperature ranges,the hardness will retain about 59.2-61.6 HRC and the Charpy U-notch impact toughness will retain about 17.3-20 J.The morphology of impact fracture surface of tested steel is small dimples with a small amount of cleavage planes.The area of cleavage planes increases with the increasing of tempering temperature.     

Precipitation of carbide and its effects on the properties of nickel-saving austenitic stainless steel

In this work,the effects of temperature and cooling rate on the precipitation of carbides in nickel-saving metastable austenitic stainless steel were studied.The test results show that the temperature range of carbide precipitation in the test steel was 500-950℃,and 750℃was the most sensitive temperature.However,when completely solution treated samples were cooled from high to room temperature at a cooling rate of more than 50 K/s,no carbides precipitated.The carbide precipitates increased the yield strength but decreased the corrosion resistance of the steel,with little impact on toughness.