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.

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.

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.

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.

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。

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%。

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。

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。

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。

氧化铁皮在冷轧过程中的断裂行为

利用轧卡实验研究热轧低碳钢表面氧化铁皮在无酸洗冷轧过程中的断裂行为.结果表明,由于带钢在靠近辊缝处的弹性变形,带钢表面的氧化铁皮受拉应力作用发生断裂,裂纹垂直于轧制方向,越靠近辊缝裂纹密度越大.单道次轧制压下量小于16%时,氧化铁皮只发生断裂;压下量超过16%时,氧化铁皮开始出现脱落,当氧化铁皮受力超过其界面附着强度时,将发生氧化铁皮从带钢表面剥离和粉碎.同样的总压下量条件下,多轧制道次有利于保护氧化铁皮的完整性.

车辆用低碳深冲冷轧板表面缺陷成因探析与控制

车辆用连铸生产的低碳深冲冷轧板卷一度出现大量表面缺陷,其宏观特征为凹坑、残留的金属疤壳或两者共存。缺陷区有时出现板卷穿孔、线痕或两者兼有。利用特殊金相制样与分析技术辅以电子探针微区分析等手段,探讨了发生率较高且又难以消除的复合夹杂型(CN I’s)、A l2O3型以及表面裂纹型缺陷的本质及形成原因。据此提出有效的缺陷控制措施,结果表明:采用这些措施改进的连铸工艺后,板卷表面质量合格率达100%。

磷对超低碳冷轧钢带性能的影响

阐述在冷轧汽车钢的生产中,为了提高IF钢强度采用超低碳钢加磷的方法。为了解磷对超低碳钢性能的影响,试制了含磷和不含磷的两种超低碳冷轧钢带。通过对这两种冷轧钢带的力学性能、组织织构的对比分析,得出P使得超低碳钢的强度大幅度增加的同时,保持了良好的变形性,使得钢板在汽车厂加工后具有良好的使用性。

冷轧低碳钢快速加热过程中的相变规律

以两种不同成分冷轧低碳钢为研究对象,利用Gleeble-3800热/力模拟实验机,研究了冷轧低碳钢在快速加热条件下,加热速度、化学成分对加热过程中相变规律的影响及连续加热过程中奥氏体晶粒尺寸的演变.研究结果表明,随着加热速度的增加（5-500℃/s）,实验钢相变点的升高趋势先快后慢,100℃/s为转折点.在连续加热过程中存在奥氏体晶粒异常长大的温度转折点,为1 050℃;在850~950℃范围内,奥氏体平均晶粒尺寸均小于5μm;添加微合金元素有利于细化奥氏体晶粒.研究结果为利用快速加热、短时保温的方法获得冷轧超细晶钢提供了参考依据.

冷轧超低碳钢的析出相和氢穿透时间研究

介绍了加钛、稀土等超低碳钢的化学成分和合金特点,分析了钢中析出相的类型、尺寸和数量,测定了氢在钢中的穿透时间和扩散系数,研究了析出相对氢在钢中穿透时间的影响。结果表明,添加足量钛或复合添加稀土、钛和铌的超低碳钢既具有超深冲性能,又具有足够长的氢穿透时间,从而实现了成形性能和抗鳞爆性能的良好匹配。

低碳铝镇静钢冷轧板中孔洞缺陷特征分析

对生产中常见的低碳铝镇静钢冷轧板孔洞缺陷特征进行了宏观和微观分析。结果表明 :孔洞大致可分为三大类 ,正常拉裂类孔洞主要与基板中的夹杂有关 ;疤块孔洞与坑状孔洞为钢基掉块或异物压入基板形成 ,其它类孔洞形成主要与轧制工艺过程相关。

冷轧压下率对烘烤硬化钢板连续退火再结晶的影响

当使用过厚的热轧坯料和过高的冷轧压下率时 ,Nb +Ti处理的高强度烘烤硬化 (ELC BH)钢板的连续退火再结晶提前发生 ,同时晶粒长大速度减慢。

低碳铝镇静钢板面发黑现象分析

研究了经脱脂后低碳铝镇静钢罩式炉退火后板面的"丝状"发黑现象,并对发黑部位的微观形貌、元素成分、组织结构和产生机理进行了分析和探讨。分析发现"丝状"发黑现象是C在带钢上结晶生长的结果,发黑部位的物质是石墨。

CSP-低碳钢DC03冷轧板的组织和织构

研究了CSP工艺生产的0.04%C低碳钢DC032.9 mm热轧基板、0.9 mm的冷轧板和退火平整板的组织与织构。结果表明,热轧基板组织为铁素体+少量沿晶界分布的珠光体,铁素体基体中有少量40～100 nm MnS粒子,没有观察到AlN;冷轧板组织为含大量位错的带状铁索体-珠光体,{111}织构的择优取向较明显;退火平整板组织为铁素体和游离渗碳体,并观察到10～30 nm的析出相,{111}织构轴密度达5.15,{100}轴密度减为0.61。