Controlled Rolling and Cooling Process for Low Carbon Cold Forging Steel

Effect of controlled rolling and cooling process on the mechanical properties of low carbon cold forging steel was investigated for different processing parameters of a laboratory hot rolling mill. The results show that the specimens with fast cooling after hot rolling exhibit very good mechanical properties, and the improvement of the mechanical properties can be attributed mainly to the ferrite-grain refinement. The mechanical properties increase with decreasing final cooling temperature within the range from 670 ℃ to 570 ℃ due to the finer interlamellar spacing of pearlite colony. The specimen with fast cooling after low temperature rolling shows the highest values of the mechanical properties. The effect of the ferrite grain size on the mechanical properties was greater than that of pearlite morphology in the present study. The mechanical properties of specimens by controlled rolling and cooling process without thermal treatment were greatly superior to that of the same specimens by the conventional rolling, and their tensile strength reached 490 MPa grade even in the case of low temperature rolling without controlled rolling. It might be expected to realize the substitution medium-carbon by low-carbon for 490 MPa grade cold forging steel with controlled rolling and cooling process.

Effect of Nb on the Microstructure and Properties of Cold Rolled and Annealed Mo Microalloyed Bainitic Steel

Two kinds of low carbon bainitic steels,Nb-free Mo bearing and Nb + Mo addition steels,were cold rolled and annealed to investigate the effect of micro-alloying element Nb on the microstructure and properties of Mo microalloyed low carbon high strength bainitic steel. No precipitates were observed in Nb-free Mo bearing steel,whereas,two types of precipitates,i.e.,Nb( C,N) and composite( Nb,Mo)( C,N),were observed in the Nb + Mo microalloyed steel,resulting in precipitation strengthening. The strength of Mo bearing steel was improved by addition of Nb under the same annealing conditions. The grain size of Nb addition steel was almost the same as Nb-free steel. Unlike the obvious grain refinement and precipitation strengthening in hot rolling,the increase in yield strength of Nb addition steels in cold rolling and annealing mainly results from the precipitation strengthening,while the effect of grain refinement strengthening can be almost ignored.

Correlation of morphological anisotropy and Lankford value of deep drawing sheets hot-rolled by compact strip production

Cold-rolled steel sheets in automotive applications require an excellent deep draw ability, which is characterized by the Lankford value （r-value）. In this study, a correlation was identified between r-value and pancake-shaped grain flatness which is indicated as the ratio of grain diameter in the rolling direction （RD） and normal direction （ND） of sheets （dr/dn）. A mathematical model （ r = e^0.345（dn^1/2-dr^1/2） ） was developed to calculate r-value by the microstructure of steel sheets hot-rolled by compact strip production （CSP）. It is shown that the r-value is higher, if the microstructure of steel sheet is of pancake-shaped grains elongated in the rolling direction. The calculated r-value is confirmed to fit exactly to the measured one from the large-scale production.

Influence of high deformation on the microstructure of low-carbon steel

Low-carbon steel sheets DC04 used in the automotive industry were subjected to cold rolling for thickness reduction from 20% to 89%. The desired thickness was achieved by successive reductions using a rolling mill. The influence of thickness reduction on the microstructure was studied by scanning electron microscopy. Microstructure evolution was characterized by the distortion of grains and the occurrence of the oriented grain structure for high cold work. A mechanism of grain restructuring for high cold work was described. The occurrence of voids was discussed in relation with cold work. The evolution of voids at the grain boundaries and inside the grains was also considered. To characterize the grain size, the Feret diameter was measured and the grain size distribution versus cold work was discussed. The chemical homogeneity of the sample was also analyzed.

Influence of Controlled Rolling and Cooling Process on the Mechanical Properties of Low Carbon Cold Forging Steel

In the present paper,controlled rolling and cooling processing was conducted by using a laboratory hot rolling mill.The influence of different processing parameters on the mechanical properties of low carbon cold forging steel was investigated.The results show that the faster cooling after the deformation (especially in low temperature rolling conditions) leads to the refinement of the ferrite grain.The specimen exhibits very good mechanical properties owing to the finer ferrite grains.The pearlite morphologies can also affect the mechanical properties of low carbon cold forging steel.The mechanical properties increase with decreasing final cooling temperature within the range from 650℃ to 570 ℃ due to the finer interlamellar spacing of pearlite colony.The mechanical properties of the specimens with fast cooling after the conventional rolling are not only better than those of the specimens with slow cooling after low temperature rolling,but also almost similar to those of the specimens with fast cooling after low temperature rolling.It is suggested that fast cooling after high temperature rolling (the conventional rolling) process would be of important industrial value.

Researches on the problems in the production of low nickel austenitic stainless steel

Problems encountered in the production of low nickel austenitic stainless steel have been studied. These problems primarily include the changes to the microstructure of the slab during the heating process, the formation and removal of deformation - induced martensite during cold rolling, and the effects of the annealing process on the surface oxide structure. A reasonable manufacturing process has been proposed on the basis of the research results and high-quality cold-rolled strips of low nickel austenitic stainless steel have been produced.

Effect of Thermomechanical Controlled Processing on Mechanical Properties of 490 MPa Grade Low Carbon Cold Heading Steel

Thermomechanical controlled processing （TMCP） of low carbon cold heading steel in different austenite conditions were conducted by a laboratory hot rolling mill. Effect of various processing parameters on the mechanical properties of the steel was investigated. The results showed that the mechanical properties of the low carbon cold heading steel could be significantly improved by TMCP without heat treatment. The improvement of mechanical properties can be attributed mainly to the ferrite grain refinement due to low temperature rolling. In the experiments the better ultimate tensile strength and ductility are obtained by lowering finishing cooling temperature within the temperature range from 650 ℃ to 550 ℃ since the interlamellar space in pearlite colonies become smaller. Good mechanical properties can be obtained in a proper austenite condition and thermomechanical processing parameter. The ferrite morphology has a more pronounced effect on the mechanical behavior than refinement of the microstructure. It is possible to realize the replacement of medium-carbon by low-carbon for 490 MPa grade cold heading steel with TMCP.

减少冷轧低碳钢轧材表面夹杂缺陷实践

针对冷轧低碳钢轧材表面夹杂缺陷问题,分析主要原因是结晶器保护渣卷入钢水导致,采取优化保护渣理化性能,优化铸机拉速、水口浸入深度和氩气流量等措施后,降低了卷渣风险,冷轧低碳钢表面夹杂缺陷指数由4降至1,提高了产品表面质量。

汽车薄板钢中游离渗碳体的评定方法解析

为了更好地对汽车薄板产品中游离渗碳体组织进行微观评价,结合国内外相关标准中的评定方法介绍了3种评定渗碳体的方法,即级别评定法、定量法和最大限定尺寸法。对每种方法的评定内容进行了详细说明,并分别采用3种方法对一般用冷轧碳钢薄板及钢带中的游离渗碳体进行评定,便于读者更好地理解和使用,为汽车板等产品质量的提升提供可靠的微观评价方法。

冷变形对超低碳贝氏体钢中逆转变奥氏体的影响

采用硬度测试、拉伸试验、金相检验、X射线衍射测试、透射电镜检测、能谱分析等方法研究形变对超低碳贝氏体钢中逆转变奥氏体和力学性能的影响。结果表明:随着冷轧变形量的增大,超低碳贝氏体钢的硬度与强度呈显著增大趋势;超低碳贝氏体钢中的奥氏体体积分数从未变形时的0.4%逐渐增大到变形量为90%时的14.85%;钢中的逆转变奥氏体主要分布在晶界处,其形态由未变形时的薄膜状向块状转变;奥氏体中的Ni元素和Mn元素质量分数随变形量的增大而减小,Ni元素质量分数由未变形时的59%下降到变形量为90%时的11.64%,Mn元素质量分数由未变形时的16%下降到变形量为90%时的3.48%。

冷轧厂薄带钢高效生产的问题及解决方案分析

热镀锌板具有抗腐蚀强、易于深加工、使用寿命长、成本低以及表面美观等特点,主要用于家用电器、汽车等产品的内部构件和面板应用。随着家电板、汽车板工业的发展,家电和汽车所用的镀锌板占全国钢产量的比例逐步提升。随着国内外家电板、汽车板轻质化和高质量的要求,客户对产品表面质量要求越来越严格。针对生产线在提速增产过程中出现的入口跑偏、工艺段带钢表面质量缺陷和薄带钢薄锌层产速受限问题,提出了相应的改进措施。优化后,不仅提高了产量,而且提高了产品质量。

超低碳钢冷轧卷“头部黑线”缺陷分析与控制

针对超低碳冷轧连退卷带头20~30 m内频繁出现黑线缺陷,导致了批量不合格品产生而影响订单交期的问题,采用金相显微镜、扫描电子显微镜等检测分析手段对缺陷进行了分析,并进行了铸坯端面预制缺陷轧制中间坯的工业试验验证,锁定了缺陷产生的原因。结果表明,“头部黑线”缺陷与保护渣卷渣类、氧化铝夹杂类和气泡类缺陷形貌区别明显,与基体无连接,呈分开状态,主要由Fe、Al元素组成,判断此缺陷为外来异物。通过全流程追溯,发现热轧成材率攻关后,超低碳钢中间坯切头量有所减少,无法将喷号焊丝全部切除,铸坯打号机的喷号焊丝压入导致该类“黑线缺陷”的产生。基于此,将超低碳钢热轧中间坯切割量控制在300mm,喷号机的压空压力使用标准调整为4 bar,冷轧卷头部黑线缺陷问题得到了有效改善,超低碳钢表面质量合格率提高了4.03%。

430铁素体不锈钢冷轧带钢表面黑带缺陷分析

采用扫描电子显微镜(SEM)及能谱分析(EDS)等方法对冷轧带钢表面黑带缺陷和连铸板坯表层碳化物的形貌、尺寸及分布进行了分析研究。结果表明:430不锈钢带钢表面黑带缺陷部位较正常区域有更高的碳含量,且出现贫铬元素,为明显的晶间腐蚀缺陷。分别使用A型和B型保护渣的430不锈钢铸坯边部和中部表层均存在颗粒状碳化物,碳化物区域深度不同,呈不连续的分布。因此,由于结晶器液面波动或保护渣熔速过慢导致熔渣层补充不足,富碳层与钢液和铸坯表面接触,造成铸坯表面覆碳,在后续轧制过程形成黑带缺陷。

带状色差对冷轧低碳钢板表面性能影响

研究冷轧低碳钢表面带状色差区域与正常区域的表面性能以及带状色差对产品性能的影响。采用表面接触角、红外光谱、X光电子能谱、辉光放电能谱、三维形貌以及电化学测试等方法,分析清洗前后冷轧钢板表面接触角、表面及表层元素组成、微观结构、电化学性能等。结果显示轧硬钢板和退火钢板清洗前后,表面接触角均由80°以上降至35°以下,说明表面残留物均可被清洗去除,达到润湿一致性表面。退火钢板表层10 nm内有C和Mn元素富集,其带状色差区域面粗糙度为0.588μm、面最大峰高为2.964μm、面最大谷深为-3.873μm,均高于正常区域。同时,带状色差区域的腐蚀电流、阻抗、晶面衍射峰和表面金相等数据显示与正常区域无显著差异。研究发现带状色差是根植产品表面的外观形貌特征,并非异物富集所致,差异从轧硬钢板遗传至退火钢板表面,主要体现为表面形貌的粗糙特征,不影响清洗性和电化学活性,也不改变钢板的晶面和金相组织。

3500mm炉卷轧机管线钢柔性轧制技术开发

介绍了管线钢柔性轧制的工艺和关键技术。通过低碳设计,并采用Nb、Ti微合金化,设计了一种合理的、低成本的化学成分体系,结合大变形量卷轧+超快速冷工艺,充分利用位错强化、细晶强化、析出强化和相变强化等手段,以卷轧的方式使用一块板坯生产6~16 mm厚度规格、母板长度达100~400 m的X52、X56、X60、X65四个级别管线钢钢板。产品组织均匀,尺寸合适,各项力学性能指标满足GB/T14164~2103标准,落锤性能满足0~-30℃落锤剪切面积≥85%的低温止裂韧性要求。此技术的应用明显减少了余坯和余材数量,组坯更灵活,降低运营成本,满足各类用户的需求。

新型铁路信号继电器重锤片的研制

重锤片是铁路信号继电器磁路系统衔铁组件中的一个零件,在继电器的机械负载和磁路平衡中起着配重的作用,用于保证继电器衔铁可靠落下。通过对比原重锤片的结构尺寸及材料,结合新工艺技术对重锤片的结构尺寸及材料重新研制,主要从重锤片研制的设计输入、理论计算、实物验证等内容,并对重锤片研制前后的实物进行对比分析。新型重锤片的成功研制将提高重锤片零件的防腐性能及应用环境,彻底取消电镀工序对环境质量的影响,同时提高零件的生产效率,缩短产品的生产周期。

薄板坯连铸连轧CSP线生产低碳钢板的力学性能特征

从对珠钢 CSP线试生产的低碳钢板 ZJ330的大生产产品力学性能统计、力学性能特征实测观察表明 ,CSP薄板坯连铸连轧线生产的热轧板和普通厚板坯连铸连轧线生产的热轧板在组织状态和力学性能特征等方面存在较明显的差异 ,主要表现在 :板材强度高 ,屈强比高 ,伸长率较高 ,各向异性小。初步搞清了薄板坯连铸连轧生产热轧薄板的力学特征 。

低碳钢的高温力学性能

利用Gleeble 1500热模拟实验机,采用加热法和凝固法两种加热变形制度,研究了实验用低碳钢的热塑性及强度,测定了该钢种的零塑性温度(ZDT)θd及零强度温度(ZST)θs,分析了其裂纹敏感性及断口组织·结果表明,凝固法所测结果更符合实际;实验钢的高温脆性温度范围为1300℃至熔点,在1100～1300℃范围内,此钢的断面收缩率均大于60%,具有良好的塑性·实验用低碳钢的高温脆性区较小,具有较强的抗高温裂纹特性·其θd和θs分别为1350℃和1400℃·

冷轧压下率对低碳铝镇静钢冷轧板深冲性能的影响

采用攀钢热轧板厂生产的低碳铝镇静钢热轧卷 ,在实验室进行了不同压下率对冷轧钢板深冲性能的影响试验。结果表明 ,冷轧压下率对常规力学性能和n值无明显影响 ,而对r值影响显著。对于含碳量 0 0 59%的低碳铝镇静钢 ,获得最大 r值的冷轧压下率为 73% ,而Δr值随冷轧压下率的提高单调减小。

热轧深冲钢板的分析和应用

在对比冷轧深冲钢的基础上 ,分析了工业试制的热轧深冲钢板的组织和性能。研究结果表明 :该钢的碳含量较低 ,相应的金相组织和晶粒度合适 ;厚度大于 2 mm的钢板未经冷轧和退火处理可达到与冷轧深冲钢板相当的成型性能 ,是代替冷轧深冲钢板冲压汽车零件的理想材料。该钢生产工艺简单 ,质量稳定 ,具有明显的经济效益和社会效益。