Modeling of Microstructure Evolution and Mechanical Properties of Steel Plates Produced by Thermo-Mechanical Control Process and Its On-line Application

An integrated metallurgical model was developed to predict microstructure evolution and mechanical properties of low-carbon steel plates produced by TMCP. The metallurgical phenomena occurring during TMCP and mechanical properties were predicted for different process parameters. In the later passes full recrystallization becomes difficult to occur and higher residual strain remains in austenite after rolling. For the reasonable temperature and cooling schedule, yield strength of 30 mm plain carbon steel plate can reach 310 MPa. The first on-line application of prediction and control of microstructure and properties (PCMP) in the medium plate production was achieved. The predictions of the system are in good agreement with measurements.

IMPROVED PROCESSING FOR MICROSTRUCTURES AND MECHANICAL PROPERTIES OF A COMMERCIAL PIPELINE STEEL

The transformation productions of hot-deformation simulation experiments were investigated using a Gleeble-1500 hot simulator for a commercial pipeline steel. Based on the investigation results, the improved thermo-mechanical control processing (TMCP) schedules containing a two stage multi-pass controlled rolling coupled with moderate cooling rates were applied to hot rolling experiments and acicular ferrite dominated microstructure was obtained. Microstructures and mechanical properties of hot rolled plates were related to TMCP processing, and regression equations describing the relation between processing parameters and mechanical properties in the current TMCP were developed, which could be used to predict mechanical properties of the experimental steel during commercially processing. It was found that with an increase in cooling rate after hot rolling, grain size in the microstructure became smaller, the amount of polygonal ferrite decreased and acicular ferrite increased, and accordingly mechanical properties increased.

TMCP工艺下Q390钢板厚度、温度场与组织演变的关系

采用TMCP工艺制备三种不同厚度的Q390热轧钢板,基于冷却温度场有限元分析揭示了厚度对组织演变和硬度的影响规律。结果表明:在相同冷却条件下,40 mm厚热轧钢板厚度方向组织存在明显差异,即边部以贝氏体为主,而心部为铁素体和珠光体,对应显微硬度差值约40 HV;13、20 mm厚热轧钢板厚度方向组织较为均匀,以贝氏体为主,显微硬度分布也相对均匀。温度场有限元分析表明厚板(40 mm)试样的心部组织铁素体+珠光体主要形成于空冷阶段;而对于其他厚度钢板,在水冷阶段,心部和边部获得较为一致的终冷温度和冷速,且均在贝氏体相变温度区间。

Study on gas metal arc welding of two types of TMCP steels

Gas metal arc welding experiments were conducted on two types of steels with 0.41% carbon equivalent(Ceq) and 0.31% Cequsing WER70T wire and 20% CO_(2)and 80% Ar as shielding gas.The two types of steels show satisfactory weldability.The transition temperatures of 50% upper shelf energy(Tk0.5) for Charpy-V impact test of both the welded joints are below-40 ℃.However, the toughness of the fusion line zone and heat-affected zone(HAZ) of the two steel joints exhibits differences, with the toughness of 0.41% Ceqsteel being better than that of 0.31% Ceqsteel.The Tk0.5of the fusion line zone and the HAZ of 0.41% Ceqsteel is below-60℃,whereas that of 0.31% Ceqsteel is above-40℃.The welded joint of 0.41% Ceqsteel has low hardness fluctuation, while that of 0.31% Ceqsteel exhibits a narrow, softened zone, which has no obvious influence on the tested tensile strength.The coarse grain heat-affected zone(CGHAZ)microstructure of 0.41% Ceqsteel is bainite, while that of 0.31% Ceqsteel is bainite with ferrite and minor pearlite.

TMCP态桥梁钢与316L不锈钢制备的爆炸复合板热处理工艺研究

介绍了研究控轧控冷(TMCP)生产的Q370qD桥梁钢和316L不锈钢制备的爆炸复合板热处理性能与组织演变过程。结果表明:316L/Q370qD(TMCP)爆炸焊接复合板低温退火后强度偏高延伸率较低,900℃高温退火后强度不合格、冲击值离散性大;优化热处理方案进行630~710℃退火,最终确认适宜的热处理温度区间为650~680℃、时间为1.5~2 h,大规格复合板退火(680℃/1.5 h退火后空冷)验证测试性能合格,后续生产处理效果良好,表明TMCP状态的Q370qD桥梁钢与316L不锈钢制备爆炸复合板具有可行性。

基于TMCP对套管钢30MnCr22的静态再结晶研究

基于热机械控制工艺(TMCP),以经济型P110石油套管钢30MnCr22为研究对象,在Gleeble-1500D热模拟实验机上进行了双道次热压缩实验,测得其在不同变形条件下的真应力-真应变曲线,研究了其高温静态再结晶规律。结果表明,30MnCr22钢在热变形过程中随着变形温度的升高、道次间隙时间的延长、变形程度的加大和应变速率的加快,静态再结晶体积分数增加,更容易发生静态再结晶。采用Origin软件对各种变形条件下的真应力-真应变曲线进行了分析,采用线性回归方法建立了30MnCr22钢的静态再结晶动力学模型。结合30MnCr22钢静态再结晶规律,分析了TMCP条件下无缝钢管的再结晶控制策略。

A Special TMCP Used to Develop a 800MPa Grade HSLA Steel

The effect of relaxation after finished rolling on structures and properties of four microalloyed steel with different content of Nb and Ti was investigated. By alloy designing and control rolling + relaxation-precipitation-control phase trail storm ati on (RPC) process, a new 800 MPa grade HSLA plate steel could be obtained, the microstructure is composite ultra-fine lath bainite/martensite. The tempering process and mechanical properties of this kind of HSLA steel were investigated. The yield strength can achieve 800 MPa, and the ductility and impact toughness is satisfied.

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.

Research on the SUS304 hot-rolled austenitic stainless steel strip by TMCP

To avoid intergranular corrosion and obtain microstructural homogenization, the conventional SUS304 austenitic stainless steel needs to be solution annealed after hot rolling. This study investigates the thermal-mechanical controlled process （TMCP） of SUS304 steel, especially the controlled rolling and online accelerated cooling procedures. The objective of this research is to reduce or even prevent carbide precipitation based on the description of the time- temperature-precipitation （TTP） curve. The dynamic and post-dynamic recrystallization behaviors of this steel ensured the homogenization of grains in this process due to, which was studied by the hot compression tests. The microstructure and the properties of the TMCP-produced SUS304 steel strip were compared with the conventional method of solution annealing. Based on the above results, the newly developed TMCP-produced SUS304 hot-rolled austenitic stainless steel strip has been successfully produced and it can be directly utilized in the cold rolling process without solution annealing.

Recent process in special steel,heat treatment and surface modification of automotive components

Demand of improving the mechanical properties and productivity of automotive components while minimizing environmental impact makes the development of special steel combined with advance heat treatment and surface modification technologies become an important research area. Recently,to reduce CO_2 emissions by saving the manufacturing time,the following new special steel and advance heat treatment methods were developed: (1 ) An anti-coarsening extra-fine case hardening steel for automobile gear was developed,whose carburizing temperature can be improved for conventional 930 - 950℃to 1 050℃without coarsening,and the carburizing time can be reduced by maximum 75%. (2) Various microalloyed steels for fracture splitting connecting rod were developed.By using the above-mentioned steel combined with Thermo Mechanical Control Process(TMCP) method,the manufacturing time can be reduced by 30%-40%. (3) Vacuum carburizing and mild carburizing combined with induction quenching are being developed to replace the traditional gas carburizing,and the CO_2 emissions can be reduced by 20%-40%. (4) Intensive quenching is another new quenching technology which can be defined as cooling usually with pure water quenchant or low concentration water/salt solutions at a rate several times higher than the rate of ' normal' or conventional quenching,and the conventional effective case hardening depth can be reduce greatly and carburizing time can reduced. In addition,the high pressure gas quenching for reducing the quenching distortion and dual shot-peening for improving fatigue strength of gear will also be discussed. In a word,the present paper will focus on how to use the interaction among the development of special steel, advance heat treatment and surface modification to improve the strength of automotive components while reducing the manufacturing cost and impact to environment.

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.

Q345C高强度厚板TMCP工艺

介绍了Q345C厚70 mm钢板的TMCP工艺,实现了对钢的强度、塑性和韧性的控制,研究了控制轧制工艺和钢的组织性能之间的关系,分析了钢的组织形貌.结果表明,采用该无热处理的未再结晶区大压下量TMCP工艺试验的厚板,轧后无论采用空冷还是加速冷却,力学性能都满足GB/T1591-94的要求,且厚度方向力学性能均匀性良好;加速冷却钢板铁素体晶粒细化更为明显,表面与心部铁素体晶粒尺寸稍有差异.为现场生产厚70mm钢板提供了有力的依据,节省了能源,降低了生产成本.

TMCP钢焊接热影响区局部脆化区断裂韧度测试

针对强度 (屈服点应力 )级别为 4 2 0～ 4 6 0MPa的三种TMCP钢 ,探讨通常的焊接热影响区局部脆化区断裂韧度测试方法的可行性及存在问题。由于多层焊热影响区组织复杂 ,需进一步研究确认试验中得到的断裂韧度能否代表局部脆化区的韧度。试验结果发现 ,对多层焊热影响区试样 ,试验后必须进行刨面 (Sectioning)分析 ,首先检查疲劳裂纹前沿是否位于所测试的目标区域 ;其次当有延性裂纹扩展时 ,检查延性裂纹扩展是否偏离目标区域。当满足这些条件时 ,所测试的断裂韧度才能代表目标区域的韧度值。同时也试验研究了焊缝强度匹配对热影响区断裂韧度的影响。

超细晶粒钢制备工艺及机制与传统控轧控冷(TMCP)钢的异同

总结对比了传统控轧控冷(或热机械控制处理,TMCP)钢与超细钢开发制备所用的新型TMCP工艺的特征及其冶金机制。轧前急冷、低温加工与大应变变形(强加工)是超细钢制备工艺的3个必要条件。TMCP的晶粒细化主要靠加工硬化奥氏体的静态铁素体转变。新工艺晶粒细化主要靠形变诱导动态铁素体相变。

TMCP技术在Q345B低合金化生产中的应用

采用TMCP控轧控冷技术,用普碳钢成分生产出了Q345B高强度热轧带钢。生产中通过调整中间坯厚度与成品厚度之比,同时控制终轧温度和卷取温度,将铁素体晶粒细化和珠光体相变强化相结合,得到了高强高韧性热轧钢板。钢板冷成型性和焊接性良好,实现了Q345B的合金减量化生产。

AR+正火工艺与TMCP+正火工艺生产桥梁钢对比分析

对比了AR+正火工艺、TMCP+正火工艺生产的Q370qE-Z25桥梁钢的组织性能。结果表明,TMCP+正火工艺生产的Q370qE-Z25桥梁钢力学性能较好,尤其是屈服强度较AR+正火工艺的高出约30MPa,从而有助于合理制定客户有特殊要求(如强度高于国家标准)桥梁钢的生产工艺。

TMCP工艺生产40mm厚700MPa级低碳贝氏体钢试验研究

介绍了微合金化结合TMCP+回火工艺生产40 mm 700 MPa级低碳贝氏体钢的实验过程。通过对40 mm厚700 MPa级低碳贝氏体钢合理的成分、工艺设计和关键工艺控制的研究分析,制定合理的TMCP+回火工艺,成功开发出40 mm厚规格700 MPa级低碳贝氏体钢。

B500BD13mm带肋钢筋四线切分轧制生产工艺开发

介绍了石横特钢棒材厂英标B500BD13mm热轧带肋钢筋四切分轧制生产工艺的设计。针对顶出口、切分刀粘铁、力学性能不稳定以及成品尺寸不符合标准问题,分别从提高轧机刚性、优化导卫结构、提高温度工艺控制精度和优化孔型、调整机架间张力的措施着手,实现了热轧带肋钢筋四切分的稳定轧制,最终形成工业化批量生产,年创效360万元,产品质量满足用户需求。

采用TMCP工艺生产700MPa级低碳贝氏体钢

以微合金化结合控轧、控冷工艺生产非热处理高强度钢,本文通过对700MPa级低碳贝氏体钢轧制工艺的研制分析,制定合理的轧制工艺。

GCr15轴承钢生产絮流分析研究

轴承钢作为关键的工业材料,具有优异的力学性能和耐磨性。但在轴承钢生产过程中存在絮流的问题,絮流严重影响着产品的质量、生产成本和企业竞争力。为进一步提升轴承钢的可浇性,对轴承钢的成分、过程控制工艺、性能和应用进行了系统研究,并采取了一系列有效措施,成功减少了絮流的产生,为轴承钢的进一步应用提供理论依据。