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.

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。

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。

Microstructure and mechanical properties of a Cr-Ni-W-Mo steel processedthermo-mechanical controlled processing

Experiments were conducted to evaluate the microstructure and tensile properties of a medium carbon Cr-Ni-W-Mo steel processedthermo-mechanical controlled processing(TMCP)with cooling at different conditions in water,oil,air or lime followedlow tempering.Compared to normal heat-treatment processing,TMCP with water-cooling after deformation enhances the yield strength and tensile strength of the steelabout 323 MPa and about 251 MPa,respectively,due to higher dislocation strengthening and grain boundary strengthening.Meanwhile,it increases the elongation by ;about 1.76%attributed to the increase in volume percentage of the retained austenite and the refined laths of tempered martensite.Slowing the cooling rate after deformation during TMCP leads to a decrease in the strength.This results the coupling effectsthe reduction in dislocation density and volume fraction of tempered martensite together with the coarseness in martensite sizes.However,cooling rate decreasing has less influences on ductility becathe improved elongation the increase in the volume fractions of both retained austenite and lower bainite together with dislocation density decreasing is compensatedthe reduced elongation coarsened grains.

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.

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.

Effect of M-A constituents formed in thermo-mechanical controlled process on toughness of 20CrNi2MoV steel

The effect of martensite–austenite(M–A)constituents formed in thermo-mechanical controlled process on impact toughness of 20CrNi2MoV steel was investigated.The variation in fraction,size and morphology of M–A constituent and its effect on toughness under different cooling rates were carried out.The result shows that there was no significant change in the fraction of M–A constituent under different cooling rates,but the distribution and size of M–A constituent were greatly influenced by cooling rate,which consequently influenced toughness.The amount of large blocky M–A constituents decreased from 4.7%to 1.7%,while that of elongated M–A constituents increased from 3.8%to 8.6%with the cooling rate increasing from 7 to 26°C/s,and the corresponding impact energy decreased from 132 to 84 J.The deterioration of impact toughness could be related to the increase in the elongated M–A constituents.The elongated M–A constituents existing along the prior austenite grain boundaries in samples of 26°C/s could easily lead to the formation of cleavage crack,which then results in the lower crack initiation energy than that of low cooling rate samples.

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.

50 mm低合金高强度结构钢Q460NC的生产实践

通过合理的成分设计和严格的加热、TMCP轧制工艺控制,充分利用细晶强化、析出强化等手段,保障了TMCP交货状态的50 mm厚Q460NC钢板的成功研发。钢板晶粒细小、性能稳定,屈服强度达到450 MPa~510 MPa,抗拉强度达到590 MPa~645 MPa,延伸率达到25%以上,板形及表面质量良好。

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.

低成本Q345系列厚钢板的控轧控冷(TMCP)工艺

以两种不同Mn含量的工业生产连铸板坯为原料,采取控轧控冷(TMCP)工艺,成功试制了20 mm厚低成本Q345钢板。研究表明,终冷温度显著影响试验钢的组织与性能,通过选择合适的终冷温度,两种试验钢的强韧性均能达到GB/T 1591-2008中Q345的要求。提出低成本Q345系列厚钢板的成分与工艺:Mn含量为0.9%(质量分数),两阶段轧制,精轧温度低于890℃,终轧温度为800～850℃,终冷温度为(600±20)℃。

TMCP特厚止裂钢板的显微组织和抗解理断裂性能

为开发超大集装箱船用止裂钢板,提出了一种低碳微合金SiMnCrNiCuMo钢,使用控轧控冷工艺(TMCP)试制出最大厚度为80 mm特厚钢板,使用埋弧焊接技术对最厚钢板进行了焊接评定,分析了钢板和焊接接头的显微组织。通过系列示波Charpy冲击试验研究了钢板及焊接热影响区粗晶区(CGHAZ)的韧脆转变行为,获得了各部位的韧脆转变温度(DBTT)及其解理断裂强度σf;分别测试了钢板及CGHAZ区-10℃的全厚度裂纹张开位移(CTOD),并且估算其启裂韧性(Kc);通过系列温度梯度宽板双重拉伸试验,获得了钢板在-10℃的止裂韧性(Kca)。结果表明:钢板的显微组织由不规则铁素体、针状铁素体、细化上贝氏体和弥散分布的马氏体奥氏体组成,平均晶粒尺寸小于7.0μm,其屈服强度大于500 MPa,韧脆转变温度低于-78℃。高的止裂性能导致冲击韧性的提高;提高σf值可降低钢板的DBTT及改善其低温韧性;在低温发生解理断裂的Charpy冲击试样和在低温区发生解理断裂的双重拉伸试样具有相同的临界事件。在焊接状态下,焊接接头的启裂韧性值低于母材钢板的止裂韧性值,因此,如果裂纹在低韧性的CGHAZ区起始,则该裂纹的扩展将在母材钢板处停止。

超声波无损检测检查法在TMCP板中的实际应用

针对海工平台中热机械控制工艺(Thermo Mechanical Control Process,TMCP)板材钢熔透焊焊接接头超声波检测实际中的应用方法做出讲解,通过现场直接对比法执行TMCP材料的相关超声波检验来代替传统检测方法,其检测方法的使用使缺陷位置的判定更准确,同时节约成本、提高效率,值得推广。

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.

JFE采用TMCP工艺生产韧性优良的高强H型钢

JFE制钢公司开发出采用先进的热机械控轧工艺（TMCP）生产高性能H型钢的技术。为了能够获得具有优良韧性的高强度H型钢，尽管可以通过采用适当的合金方案，但最重要的一点是在最佳热轧条件下进行热轧以及热轧后加速冷却，以获得精细的贝氏体显微结构。介绍最新开发的高性能H型钢的一些例予，诸如应用于高层建筑施工中的520MPa级（抗拉强度）H型钢，该型钢具有优良韧性、焊接性和抗震性等特点；而490MPa级（抗拉强度）H型钢，则具有优良的低温韧性特点。在特定的热轧条件下，合金设计可以使H型钢获得精细的显微结构，但加速冷却设备（Super—OLACS：型钢用在线加速冷却，OLACS是日本注册商标）在高性能H型钢开发中起到关键性作用。

基于TMCP工艺的低成本Q355B厚板开发

通过3轮试制,成功开发了TMCP工艺生产30.1~40 mm的Q355B,合金成分与原相比,去除了Nb元素,同时降低了Mn含量,实现吨钢合金降本60元以上,取得了良好的经济效益。大生产性能实绩表明,采用降Mn去Nb后的新成分,TMCP工艺生产的钢板屈服强度总体较原C-Mn-Nb成分体系干轧工艺略低,抗拉强度略高于后者,而韧性指标则稍差于后者,总体性能满足标准要求,为生产厂节约合金成本、降低生产成本提供了可能。

X100管线钢的组织性能

利用金相显微镜、扫描电镜、透射电镜等研究了X100管线钢的力学性能、显微组织、晶粒取向及析出物.实验结果表明,采用控轧控冷两阶段轧制工艺轧制出实验钢平均屈服强度达到724 MPa,屈强比0.87,夏比冲击功在-60℃仍有255 J,韧脆转变温度在-60℃以下.平均有效晶粒尺寸为2.43μm,大角度晶界占78.8%,尺寸在10 nm左右的析出物与位错相互缠结起到了良好的析出强化作用.