冷轧变形量对304不锈钢力学性能的影响

 研究304奥氏体不锈钢薄板的硬度随冷轧变形量的变化规律,为奥氏体不锈钢薄板工业生产提供指导。同时,采用金相显微镜、维氏硬度测量、X-射线衍射仪和透射电镜研究了不同变形量冷轧对304不锈钢显微组织和机械性能的影响。在室温对0.5mm厚退火板材进行冷轧,使冷轧变形量从10%增加到52%。结果表明,形变诱发马氏体相变是导致304不锈钢冷轧时产生加工硬化的主要原因,冷轧可以显著提高钢的强度和硬度。当冷轧变形至40%时,304不锈钢的维氏硬度是未变形时的2.2倍,屈服强度、抗拉强度分别增大到未变形时的4.2倍（880MPa）和1.8倍（1312MPa）。     

罩式退火铌微合金化汽车钢的强化机理

 通过比较相同冷轧与罩式退火工艺下Mn-Si系和铌微合金化2种汽车用低合金高强钢的显微组织与力学性能,研究微量铌在冷轧罩式退火低合金高强钢中的强化机理。利用OM、SEM、TEM和拉伸试验机分别对2种钢的显微组织与力学性能进行了表征。对比分析表明：相对热轧板来说,2种钢冷轧退火板的铁素体晶粒和第二相析出物的尺寸都有所长大,导致了强度降低。相对Mn-Si钢而言,铌微合金化钢热轧板和冷轧退火板中的铁素体晶粒和第二相析出物尺寸更细小,细小第二相析出物的数量也更多,在相同的伸长率水平下明显提高了强度。冷轧罩式退火板的强化机理分析表明,铌微合金化低合金高强钢的主要强化方式是细晶强化和NbC的沉淀强化;研究认为添加质量分数为0.025%的铌时细晶强化更强烈。     

Deformation Behavior of Fe-36Ni Steel during Cryogenic (123-173 K) Rolling

Microstructural evolution and mechanical properties of cryogenic rolled Fe-36Ni steel were investigated. The annealed Fe-36Ni steel was rolled at cryogenic temperature( 123-173 K) with 20%- 90% rolling reduction in thickness.The deformation process was accompanied by twinning at cryogenic temperature,and the mean thickness of deformation twins was about 200 nm with 20% rolling reduction. When the rolling reduction was above 40%,twinning was suppressed due to the stress concentration in the tested steel. Deformation microstructure of Fe-36Ni steel consisted of both twin boundaries and dislocations by cryogenic rolling( CR),while it only contained dislocations after rolling at room temperature( RT). The tensile strength of Fe-36Ni steel was improved to 930 MPa after 90% reduction at cryogenic temperature,while the tensile strength after 90% reduction at RT was only 760 MPa. More dislocations could be produced as the nucleation sites of recrystallization during CR process.     

1750mm冷连轧精冲钢的连续退火工艺

连续退火工艺制度是精冲钢冷连轧生产过程中的重要环节,对其成品组织性能有着极其重要的影响。在实验室进行轧制润滑试验研究,设计了多种连续退火工艺方案,采用CAS- 300连续退火试验机模拟连续退火试验,确定了C15/2精冲钢的再结晶温度为550℃。针对不同规格冷连轧精冲带钢,通过拉伸试验和显微组织鉴定,给出了适用于冷连轧生产实践的连续退火工艺制度。结果表明,退火后试样的屈服强度控制在(310±20)MPa,抗拉强度小于450MPa,伸长率大于30%,获得了良好综合力学性能的精冲钢组织。该研究完全满足工业生产实践的需求,对精冲钢冷连轧生产退火工艺研究具有重要意义。     

终轧温度对加Ti低合金Q355B钢板组织性能的影响

以钛微合金化的355 MPa级低合金高强度钢为研究对象,将试验钢分别在830、800、750、700 ℃系列温度下终轧,研究了终轧温度对显微组织和力学性能的影响。结果表明,随着终轧温度的降低,屈服强度和抗拉强度呈现不断升高的趋势,伸长率和冲击性能呈现先升高后下降的趋势,在Ar3温度附近终轧,钢板可获得最佳的综合力学性能。不同终轧温度下钢板基体组织均为铁素体+珠光体,在800 ℃终轧钢板晶粒最为均匀细小,830 ℃终轧钢板晶粒较800 ℃终轧相对粗大,750 ℃终轧钢板组织出现混晶现象,700 ℃终轧时,钢板晶粒已经拉长变形,一定程度上出现“纤维状铁素体”。充分细化晶粒可以减轻钢板中的带状组织。     

工艺参数对800 MPa热镀锌双相钢组织性能的影响

 在实验室试制了低Si 的C Mn Cr Mo系的800 MPa级冷轧热镀锌双相钢,研究了卷取温度、退火温度、退火时间等工艺参数对双相钢微观组织和力学性能的影响。试验结果表明：试验用钢在820~850 ℃退火,保温100 s以上,抗拉强度可以达到800 MPa级以上。随着退火温度的升高,强度升高,但综合性能以退火温度为820 ℃时为最佳。在820 ℃退火时,随着保温时间的增加,双相钢的强度显著增加,当保温时间超过100 s以后,强度增加缓慢。690 ℃高温卷取有利于获得最终力学性能良好的双相钢组织。     

Intercritical Rolling Induced Ultrafine Lamellar Structure and Enhanced Mechanical Properties ofMedium-Mn Steel

The medium-Mn steel with ferrite and austenite structure was rolled in the intercritical region down to dif- ferent rolling reduction. The microstructure and mechanical properties of the rolled steels were investigated by scan- ning electron microscopy, transmission electron microscopy, X-ray diffraction and tensile tests. It was found that the ferrite and austenite structure gradually evolved into an ultrafine structure from the random directional lath structure to lamellar structure with lath longitudinal direction parallel to the rolling direction with increasing rolling strain. It was found that the thickness of the laths was gradually refined with increasing rolling strain. The lath thickness is about 0. 15 9m stored with high density dislocations and the austenite volume fraction of the steel is about 24% after 80% rolling reduction. Furthermore, it was interesting to find that yield strength, tensile strength and total elongation of the 80% rolled medium-Mn steel are about 1000 MPa, 1250 MPa and 24%, respectively, demonstrating an excellent combination of the strength and ductility. Based on the microstructure examination, it was proposed that the grain refinement of the medium-Mn steels could be attributed to the duplex structure and the low rolling temperature. Analysis of the relationship between the microstructure and the mechanical properties indicated that the high yield strength mainly resulted from the ultrafine grain size and the high density dislocation, but the improved ductili- ty may be attributed to the large fractions of austenite retained after intercritical rolling.     

Effects of Process Parameters prior to Annealing on the Formability of Two Cold Rolled Dual Phase Steels

This study concerns the effects of coiling temperature after hot rolling and the degree of reduction during cold rolling on formability‐related properties of high strength cold rolled dual phase (DP) steels. The effect of coiling temperature on the final structure and properties of two cold rolled and annealed DP‐steels is investigated. Further, the effect of cold rolling reduction and its impact on the final properties of the material is studied. Aspects of the impact of the different process parameters on the ferrite to austenite and austenite to martensite transformation are discussed based on results from production scale experiments, tensile testing and metallographic examinations of the materials.     

Strain Effect on the Microstructure,Mechanical Properties and Fracture Characteristics of a TWIP Steel Sheet

Twinning-induced plasticity (TWIP) steels are a highly promising group of steels for the production of complex structural components in cold forming operations for car body manufacturing. In this work, the effect of cold rolling strain on the microstructure, mechanical properties and fracture characteristics of a TWIP steel sheet used for automobile body structure was studied by means of optical microscopy, scanning electron microscopy, electron back-scattered diffraction technique, microhardness measurement, tensile test and fractography. TWIP steel sheets were cold rolled with reductions of 0, 15 and 30%. An increase of the cold rolling strain led to an increase of deformation twinning activity in certain favourably oriented grains and resulted in significant increase in ultimate tensile strength and hardness of TWIP steel. However, the ductility of TWIP steel significantly decreased with increasing degree of cold rolling strain. The increase in the ultimate tensile strength was almost linear with the increase in cold rolling strain. After cold rolling reduction of 30%, the ultimate tensile strength increased by approximately 50%, whereas the elongation decreased by approximately 85%. The size and depth of the dimples in the fracture surface decreased with the increase of the twin boundaries at 30% cold rolling strain, leading to highly limited plasticity through the tensile testing.     

首钢热轧DP580双相钢的工业试生产

采用合金成本低廉的C-Mn-Cr化学成分设计,通过层流冷却段的水冷—空冷—水冷的三段式冷却模式和低温卷取,成功在1 580mm机组上试生产580MPa级热轧双相钢。对试生产钢卷进行了性能均匀性分析,结果表明:除去轧钢头部弱冷区域,整卷性能均匀,马氏体比例可稳定在10%左右。进而得出当前采用的恒速轧制方法有利于热轧双相钢力学性能均匀性控制的结论。试生产中在终轧后实施了2种不同的中间温度,轧制结果显示2种工艺方案下屈服强度和屈强比差距较大。     

冷轧退火板DP钢成材率低原因分析

摘要：以冷轧退火板DP980为研究对象,结合生产过程中的工艺过程参数,利用金相显微镜、电子显微镜、显微硬度计、室温拉伸试验机对热轧卷、冷硬卷、退火卷试样的显微组织、硬度、强度、伸长率等进行了分析。结果表明,热轧卷生产过程中,为了控制带尾抛钢稳定性而降低卷取速度,导致带尾卷取温度较低,力学性能不均,遗传到冷轧工序转变为厚度波动。目前,冷轧各工序通过切头尾的方法,对于此问题进行控制,也就导致了DP钢成材率较低。     

Metallurgical aspects in cold rolled high strength steel sheets

Cold rolled high strength steel sheets with yield strength from 300 to 500 N/mm² have been developed by using conventional equipment for producing commercial cold rolled steel sheet, that is, cold rolling, box annealing, and temper rolling. Effective alloying elements for strengthening are carbon, silicon, manganese, phosphorus, niobium, etc. The sheets up to 400 N/mm² yield strength grade are easily produced by selecting appropriate chemical compositions. The sheets with higher yield strength grade than 450 N/mm² are obtained by introducing the new idea that the steel with more than 2 pct manganese is annealed between A₁ and A₃ transformation temperatures, and moderately temper rolled. Increase of tensile strength does not affect deep drawability while it deteriorates stretch-forming and stretch-flanging properties. As for electric resistance spot welding, shear tension strength increases in proportion to tensile strength, but cross tension strength hardly increases or tends to decrease. These sheets have been applied to door beams and bumper reinforcements.     

Austempering of Hot Rolled SiMn TRIP Steels

 The austempering after hot rolling in hot rolled Si Mn TRIP (transformation induced plasticity) steels was investigated. The mechanism of TRIP was discussed through examination of the microstructure and the mechanical properties of this kind of steel. The results showed that the strain induced transformation to martensite of retained austenite occurs in hot rolled Si Mn TRIP steels. The sample exhibited a good combination of ultimate tensile strength and total elongation when it was held at the bainite transformation temperature after hot deformation. The stability of retained austenite increases with an increase in isothermal holding time, and a further increase in the holding duration resulted in the decrease of stability. The mechanical properties were optimal when holding for 25 min, and tensile strength and total elongation reached the maximum values (774 MPa and 33%, respectively).     

平整工艺对冷轧780MPa级双相钢力学性能的影响

采用不同的平整工艺对连续退火780 MPa级别的冷轧双相钢进行平整试验,研究了平整伸长率对连续退火780 MPa级别双相钢力学性能的影响,并建立了平整伸长率与780 MPa级别双相钢力学性能的函数关系模型。研究表明：随着平整伸长率的提高,780 MPa级别双相钢的屈服强度提高,抗拉强度保持不变,同时均匀伸长率和总伸长率均有所下降。     

Hot Mechanical Properties of 24Cr‐14Ni High Alloy Billets

24Cr‐14Ni alloys have gained importance in high temperature applications. Because of δ‐ferrite and α phase formation, 24Cr‐14Ni austenitic stainless steel billets are difficult to hot work. The mechanical properties at high temperature of such stainless steels are investigated on a hot tensile test machine according to hot‐rolling conditions, under different time and temperature regimes. These 24Cr‐14Ni stainless steels were also hot rolled under various reduction ratios. The influences of the reduction ratio on the hot mechanical properties and phase transformation from δ‐ferrite into σ phase in 24Cr‐14Ni stainless steels are discussed in detail. The results obtained can be a contribution to improve the hot rolling of this high alloy stainless steel.     

钒对耐火钢显微组织及高温性能的影响

 通常采用控轧控冷方式生产耐火钢Mo-Nb复合合金化。采用电子显微镜、相分析和三维原子探针等方法,研究了不同热轧工艺条件下钒对含钒耐火钢的室温和600 ℃拉伸性能的影响,探讨了微观组织与力学性能之间的关系。结果表明,添加钒后能形成细小弥散分布的析出物,配合控制贝氏体比例后能有效地提高室温和高温力学性能;钒在热轧态耐火钢中主要固溶于先共析铁素体内,再加热至600 ℃时热轧态被“隐藏”的钒存在明显的析出,进一步提高了含钒耐火钢的高温性能。     

The Effect of Cold Rolling on Microstructure and Mechanical Properties of a New Cr–Mn Austenitic Stainless Steel in Comparison with AISI 316 Stainless Steel

In the present study the effect of room temperature rolling on microstructure and mechanical properties of a new Cr–Mn austenitic stainless steel (containing 12 %Cr, 23 %Mn and 0.13 %C) and AISI 316 steel was investigated. The specimens of these steels were cold rolled at various thickness reductions of 0, 12, 25, 37 and 50 %. Microstructural investigations were carried out using optical microscopy, magnetic field test and X-ray diffraction technique. Hardness and tensile test methods were also done to evaluate the mechanical properties. Results showed that some of austenite phase transformed to martensite during cold rolling in the 316 steel, while there was no strain induced transformation in the Cr–Mn steel. It was also found that the newly developed steel had higher strength and higher specific strength than those of the 316 steel, while its ductility was the same as that of the 316.     

Effect of warm- rolling and intercritical annealing on microstructure and mechanical properties of medium- Mn steel

Effect of warm- rolling and subsequent intercritical annealing time at 650?? on microstructure and mechanical properties of a medium- Mn steel 0. 1C- 5Mn was investigated by using uniaxial tensile testing, transmission electron microscopy (TEM) and X- ray diffraction (XRD) analysis. The results show that a duplex microstructure having both equiaxed and lamellar morphologies of reverted austenite and ferrite is obtained after intercritical annealing of the warm- rolled steel sheet. The amount of reverted austenite and its size increase with increasing annealing time, which causes a decrease of the mechanical stability of austenite and thus an increase of ultimate tensile strength (UTS) while a decrease of yield strength, total elongation (TEL) and the product of UTS to TEL (UTS??TEL). An excellent combination of strength and ductility of 40GPa??% could be obtained after a short time annealing of 5min. The combination of strength and ductility (UTS??TEL) could be increased by about 20% for the warm- rolled steel sheet compared to that of the cold- rolled steel sheet. It is thus proposed that warm- rolling is a promising way to simplify the traditional multi- stage rolling and annealing processes of medium- Mn steels as well as further enhancing it mechanical properties.     

C-Mn-Cr-Nb系低合金钢抗氢致开裂性能

 研究了一种低C、低Mn、高Cr和高Nb低合金钢经控轧控冷及轧后回火处理后性能与组织的变化,并对试验钢进行了抗氢致开裂(HIC)试验。结果表明：与轧态相比,回火处理后试验钢的力学性能有较大提高,600℃左右回火后屈服强度由轧态519MPa增加到626MPa,抗拉强度由653MPa增加到705MPa,且韧性基本未降低,回火处理后组织仍以针状铁素体为主,回火后M/A岛尺寸减少。此外,轧态与回火态钢均能满足抗HIC试验衡量标准,回火处理后抗HIC性能优异。降低Mn质量分数能显著提高低合金钢抗HIC性能,提高Cr质量分数和Nb质量分数能有效强化低Mn钢的强度。     

Effect of different thermomechanical processing on structure and mechanical properties of electron beam melted niobium

Among the refractory metals and alloys, niobium and niobium alloys are used in variety of high temperature applications ranging from light bulbs to rocket engines because of its high melting and boiling point, lower density, good ductility at room temperature and high corrosion resistance. In this paper the effects of different thermomechanical processing on structure and mechanical properties of electron beam melted niobium ingot was investigated. The correlation among the different processing conditions and microstructure as well as mechanical properties have been investigated using optical microscope, SEM, UTM and microhardness testing. The results show that the cold forging response of EB melted ingot was very poor, where as oxidation resistant coated ingot and ingot sealed in evacuated stainless steel jacket were successfully forged at 900 °C. The cast and hot forged EBM niobium ingot was cold rolled without any intermediate annealing. The hot forged, cold rolled and annealed niobium sheets exhibit better strength as compared to cold rolled and annealed niobium sheets. The mechanical properties of all the niobium sheets processed by using different processing conditions are superior to the properties specified by ASTM standard.