Reduction of friction of steel covered with oxide scale in hot forging

The hot ring compression test of chrome steel covered with an oxide scale film is carried out to examine the effects of the oxide scale film on the hot forging characteristics through experiment and finite element analysis. The nominal coefficient of shear friction of the scale is estimated from the plastic deformation behavior of the chrome steel covered with oxide scale film. The estimated coefficient of shear friction of the oxide scale is found to be lower than that of the chrome steel. The plastic deformations and temperature changes of the chrome steel workpiece and the oxide scale layer are calculated using finite element analysis method to investigate the mechanism underlying the reduction in the friction during the hot forging of chrome steel covered with an oxide scale film. Low friction and thermal conductivity values of the oxide scale lead to low forging load in the hot forging of chrome steel covered with an oxide scale film.     

CSP板带热连轧中氧化铁皮的控制技术

在实验室对不同工艺不同厚度的CSP热轧钢板进行了酸洗速度、表面粗糙度、氧化皮厚度与组成等一系列实验,与传统热轧钢板进行了对比。研究发现CSP生产的钢板的氧化皮组成与传统热轧板接近,但氧化皮厚度、酸洗后钢板表面粗糙度均大于传统热轧钢板,酸洗速度快于传统钢板。     

Friction modelling and experimental observations in hot ring compression tests

Few studies have been undertaken to understand friction in hot metal forming, especially when addressing the critical issue of whether changing magnitudes of strain rate and temperature at the interface influence the level of friction. This paper describes an experimental investigation into friction under hot forming conditions using the ring compression test. The experiments shows how variations in temperature at the interface affected the frictional behaviour. Additional observations were made with regard to the suitability of using the ring compression test for hot metal forming, especially their ability to reproduce process conditions in hot rolling. Finite-element simulations of the ring compression test were also completed under similar temperatures as in the experiments. The correlation between the experimental measurements and the results of the process modelling is presented in the paper.     

通过估计冷却时的摩擦和传热预测热锻模的寿命

用模拟热锻现实生产条件下的两种润滑剂喷射模型试验可以估计传热系数和润滑剂黏附力,最新设计的热减径挤压试验能显示润滑剂条件和摩擦系数的关系及摩擦因素和模具温度的关系,该结果可以在预测模具磨损寿命的CAE系统中实现.     

Cr18Mn18N奥氏体不锈钢热镦裂纹分析和高温塑性研究

本文测定了Ｃｒ１８Ｍｎ１８Ｎ铸坯的高温塑性图和变形抗力图，研究了高氮奥氏体不锈钢的热加工工艺规范及高温热塑性，分析了该钢种在热镦过程中产生裂纹的原因。研究结果表明：Ｃｒｌ８Ｍｎ１８Ｎ钢的高温塑性具有脆性区、塑性区和二次脆性区。裂纹的形成主要与加热温度过高、终锻温度过低及热变形过程中碳氨化物的析出有关。结合高温塑性图和变形抗力图确定了热檄工艺参数：加热温度为１２３０℃～１２５０℃之间，保温３０ｍｉｎ，开锻温度为１２３０℃，终锻温度为９５０℃，一道次变形量应控制在５０％以内。     

Formation mechanism of surface scale defects in hot rolling process

Thick oxide scale on steel may result in serious surface defects on hot-worked products. Yield efficiency and productivity of processes are considerably deteriorated by formation of defects. It is highly demanded to establish a way to produce hot-worked steels free from surface defects by controlling oxide scale. The oxide scale shows various behaviors in hot rolling; (a) uniform deformation with matrix steel, (b) cracking, (c) fragmentation, (d) indentation to matrix steel, etc. Through observations using glass coating, it is found that the behavior strongly depends on the rolling temperature as well as the scale thickness before rolling. Temperature drop due to contact with cold rolls is found to cause the cracking and a major reason for the thickness dependence. It is found that the scale cracking is predictable using the estimated scale temperature and the ductile-brittle transition temperature of Wustite (FeO). Then, methodology to produce hot rolled steels without surface defects in industrial processes is presented.     

2Cr13钢异形模锻件淬火裂纹分析及热处理工艺优化

为解决一种2Cr13钢异形模锻件淬火回火后批次性表面开裂的问题,从复查工艺过程入手,通过计算机模拟工件淬火过程中表面应力状态变化,观察开裂工件显微组织及裂纹形貌,分析工件淬火开裂原因,并通过热处理试验验证了淬火制度对工件表层组织以及力学性能的影响。结果表明,2Cr13钢异形模锻件淬火后出现表面裂纹与锻件形状、淬火加热方式以及淬火温度有关,可通过增加锻件过渡区余量、采用到温入炉以及较低的淬火加热温度的方式降低淬火开裂风险。采用1000 ℃淬火,到温入炉作为产品优化后的热处理制度。     

SPHC热带氧化铁皮酸洗困难原因分析及对策

从SPHC带钢的成分、氧化铁皮厚度、氧化铁皮与基体结合面的粗糙度、酸洗试验、氧化铁皮的相结构分析入手,剖析了氧化铁皮酸洗困难的原因;在不影响带钢供冷轧所要求的力学性能和冷轧轧制力的情况下,通过调整热轧生产工艺,改善了SPHC带钢的酸洗质量。     

3Cr2W8V钢制尖嘴钳热锻模热处理工艺改进

某厂3Cr2W8V钢制热锻尖嘴钳热锻模的失效形式为早期开裂，模腔变形塌陷。根据金相显微分析模具热处理前后的显微组织特征，改进了锻后淬火热处理工艺，从而控制和保证模具达到一定的淬硬层深度，使模具寿命显著提高。     

45圆钢热顶锻裂纹原因分析

针对45圆钢热顶锻开裂问题,从宏观和微观两方面对裂纹原因进行分析,结果表明圆钢折叠缺陷是引起热顶锻裂纹的主要原因,同时局部脱碳加剧了顶锻开裂。可以通过严格执行检修和轧制制度,同时配合优化轧钢加热制度来消除热顶锻裂纹的发生。     

热轧不锈钢板带粗轧机架高速钢轧辊的研制

由于不锈钢热轧板带产线粗轧温度高、压下量大、轧辊咬入角大、辊面受挤压力和摩擦力更大等工况特点,原轧辊材质的应用受到了限制。介绍了热轧不锈钢板带粗轧新型高速钢轧辊的研制情况,主要介绍了其化学成分、热处理工艺、内层材质的设计及其组织性能。该新型高速钢轧辊在国内某1 780 mm不锈钢热轧产线粗轧机组的应用取得了较好效果,毫米轧制量为7 000 t/mm,下机辊表面光洁,表面粗糙度为1.3～1.6 μm。     

Study on Hot Ring Compression Test of Nimonic 115 Superalloy Using Experimental Observations and 3D FEM Simulation

In hot forging of Nimonic 115, it is desirable to determine friction coefficients. Changing magnitudes of temperature and type of lubricant at the surface of the workpiece and dies influence friction coefficient. This paper describes an experimental investigation of friction under hot forging conditions using the ring compression test. The 3D FEM simulations were used to derive the friction calibration curves and to evaluate material deformation, geometric changes, and load-displacement results. A series of ring compression tests were carried out to obtain friction coefficients for a number of lubricants including mica plate, glass powder, graphite powder, and dry condition. The experiments show how the variations in temperature at the interface affected frictional behavior. On the basis of these results, mica is recommended for hot forging of Nimonic 115 and its friction coefficient is approximately 0.3.     

核电用1Cr13厚壁管材内表面裂纹产生原因分析

分析了热轧后空冷产生的淬火效应、退火缓冷引起的回火脆性和轧制对裂纹生长方向的影响.不合理的热处理制度使材料发生马氏体相变和回火脆性,在冲击性冷轧后产生开裂.而轧制压扁造成的内表面切向拉应力是产生纵向裂纹的原因.     

4140钢热轧调质材生产工艺

以轧代锻生产φ254mm~φ310mm的大规格4140钢热轧材。通过对调质过程中淬火和回火工艺的控制消除了纵向裂纹的产生,并严格执行均匀45°倒角工艺,有效控制了环形裂纹的产生。所生产钢材的各项指标均达到了用户的要求。     

Three Dimensional Finite Element Simulation of Transient Heat Transfer in High Efficiency Deep Grinding

3D Finite Element simulations have been carried out to investigate transient heat transfer under high efficiency deep grinding (HEDG) conditions. The results have been compared to those obtained from 2D analytical models and experimental measurements. It has been found that the steady-state heat transfer condition can be readily obtained in HEDG after the maximum contact length is achieved and that side wall convective cooling has little effect on the grinding temperatures for thin steel plates. The temperature distribution on the workpiece across the grinding width in cylindrical grinding shows obvious slopes and film boiling of grinding fluid may occur at the trailing edge of grinding width. Good agreement has been found between the FE results and experimental observations. 3D FE simulation and 2D analytical modelling predict quite similar values for the maximum temperatures on the finished surface of the workpiece.     

热轧高强钢表面氧化铁皮的控制与改善

在热成型过程中,由于氧化铁皮抛丸清除不净,导致在加热后表面覆盖一层黑色氧化铁皮,影响加热温度的测量和精确控制。利用箱式加热炉、场发射电子显微镜和电子背散射衍射仪等设备,分析了460 MPa汽车桥壳用钢在两种不同热轧工艺条件下的氧化铁皮厚度、结构的变化规律。研究表明：工艺二(低温短时烧钢,高温终轧、卷取工艺)条件下的氧化铁皮结构更易抛丸去除,经抛丸、加热模拟试验后,表面无氧化铁皮覆盖物,满足测温要求。     

铁粉烧结圆环开式热锻综合试验研究

采用烧结圆环开式热锻试验方法,综合考察了中碳合金钢粉烧结材料热锻过程的摩擦因子、断裂应变极限和致密情况。提出了一种烧结－喷丸、－热锻新工艺、用以有效提高材料的断裂应变极限和锻后材料的表面密度。     

Ф55～Ф70圆钢粗轧650孔型改进

为满足市场需求,提高优质圆钢热项锻合格率,第三轧钢厂根据现有工艺装备条件,在投资不大的前提下,对使用1802连铸坯轧制Ф55～Ф70优质圆钢的粗轧650孔型进行适应性改进。     

柴油机凸轮轴热锻模热处理工艺改进

5CrMnMo制作的热锻模在工作条件下常出现磨损、断裂及变形失效,为使模具获得硬度和韧性良好配合,针对生产实际中的柴油机凸轮轴热锻模,改进了热处理工艺,采用渗硼强化模腔表面,淬火加高温回火强韧化模具基体的复合热处理方法,使热锻模寿命得到了较大提高。     

氧化皮对SS400热轧带钢耐蚀性的影响

通过热处理在SS400热轧带钢表面生成氧化皮,采用SEM、XRD和EDS等手段观察分析了氧化皮的组成及结构。结合极化曲线、电化学阻抗谱(EIS)及扫描Kelvin探针(SKP)测试,探讨了SS400热轧带钢表面氧化皮状态与其耐蚀性能之间的关系。结果表明,连续、致密和完整的氧化皮能减缓腐蚀的进行,起到保护钢基体的作用;随着腐蚀时间的增加,腐蚀电池的阴极区和阳极区的电位差增大,腐蚀加速进行,阴极区和阳极区趋于明显,且呈现局部腐蚀的特征,氧化皮对金属基体的保护作用减弱。