试验高强度低合金钢Q420N(/％:0.16C,0.28Si,1.39Mn,0.015P,0.003S,0.11Cr,0.009N)的生产流程为120 t转炉-LF精炼-RH真空脱气-连铸300 mm×340 mm方坯-热连轧成Φ90 mm棒材.试验研究了普通轧制工艺(开轧1100～1150℃,终轧950～1000℃,上冷床900～ 950℃,冷却速度0.5 ～1.0℃/s)和控轧控冷工艺(开轧1100～1150℃,终轧800～ 850℃,上冷床700～750℃,冷却速度5.0～15℃/s)对Q420N钢热轧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和冷却速度的增大,Q420N钢材的显微组织得到改善,屈服强度明显增加;普通工艺轧制Q420N钢材屈服强度为325 ～340 MPa,晶粒度为6.0级,控轧控冷工艺轧制Q420N钢材屈服强度为495 ～515 MPa,晶粒度为9.0级,满足了标准要求,降低了生产成本.

针对某轧钢厂生产的Φ100 mm以下规格42CrMo钢热轧态硬度超标现象,研究了常规轧制工艺和控轧控冷工艺,分析了不同工艺参数对42CrMo钢金相组织与硬度的影响.通过优化工艺参数,将终轧温度控制在830～ 850℃,轧后保温罩冷却速率控制在0.1～0.2℃·s-1,出保温罩温度控制在400～500℃.结果表明:采用常规轧制工艺,42CrMo钢的硬度值普遍在290～330 HBW之间,金相组织主要为贝氏体;采用控轧控冷工艺,42CrMo钢的硬度值可控制在220 ～ 260 HBW之间,金相组织为铁素体与珠光体;通过优化在线轧制工艺参数,42CrMo钢热轧态硬度满足了标准要求,降低了生产成本,提高了钢材的市场竞争力.

为了进一步提高P91钢产品质量,采用扫描电镜、ASPEX等检测方法对P91钢探伤分层形成原因进行了分析.结果表明:炼钢工序形成的镁铝尖晶石、铝酸钙等非金属夹杂物残留在钢中,在加工过程夹杂物聚集处应力集中产生裂缝和分层.夹杂物级别和T.O含量这2项指标较差,反映出P91钢在控制钢液洁净度方面存在问题.通过优化精炼渣组成(w(CaO)=55％～60％、w(SiO2)=10％～15％、w(A12O3)=18％～23％)、应用氮气增氮工艺以及提高高品质镁碳砖抗侵蚀能力等措施,试制10炉P91钢夹杂物级别稳定控制在1级以下,w(T.O)均值由21.04×10-6降低到16.73×10-6,探伤分层机率降低,钢管成材率提高15％.

In order to reduce banded structure of gear steel 20CrMoH,three kinds of through-water cooling experiments on Φ80 mm bars were carried out in finish rolling.The results showed that in the process of through-water cooling before finish rolling,the finish rolling was in the two phase zone,with the banded structure level 2.5-3.0,while in the process of through-water cooling after finish rolling and the process of through-water cooling both before and after finish rolling,the finish rolling was in austenite phase zone,with the banded structure level 1.5-2.0.Especially when finish rolling was in austenite non-recrystallized zone,the banded structure level was 1.0-1.5.

The numerical simulation of process of four stand tandem KOCKS mill continuous rolling Ф16 mm GCr15 bearing steel bar from Ф21.5 mm stock has been carried out by using DEFORM-3D three-dimensional heavy deformation thermal-mechanical coupled with elastic-plastic finite element software. And the rolling process parameters for stock rolling in KOCKS mill roll pass including equivalent stress, equivalent strain, temperature field and rolling force of steel are analyzed. Results show that the deformation of steel bar in KOCKS mill occurs mainly at rough rolling passes, and that at finish passes is small, especially at last pass ； the spread of steel bar in KOCKS mill stands is uneven, that near the roller area is smaller and that near the roll gap is larger to form bulge ； and in KOCKS mill stands the equivalent strain reaches the center of steel bar, it is available to ensure the compact density of structure and internal quality of finishing products. The relative error between simulated value and measured value of rolling force at each pass in situ is less than 2%.

进行常规大气条件1.2t电渣炉和氩气保护气氛5.0r电渣炉重熔1Cr1 8Ni9Ti奥氏体不锈钢[/％:0.05～0.09C,17.13～ 18.24Cr,9.73～ 10.6Ni,5×(C-0.02)～0.80Ti]的生产试验,分析氩气保护气氛对钢中钛烧损的影响.结果表明,在70CaF2-30Al2 O3二元提纯渣配加5.0％ TiO2的条件下,常规大气条件1.2t电渣重熔锭平均钛烧损率为48.33％;氩气保护气氛5.0t电渣重熔锭平均钛烧损率为2.61％;同时5.0t电渣炉重熔时除用氩气保护气氛外采用同钢种底垫固渣引燃,钢锭底部涨[C]现象得到明显改善.

微纳结构超高强度钢是兼具高强度、高塑性和高韧性的一类重要高性能钢铁结构材料.超细马氏体、贝氏体组织对于其强度起了决定性作用,对塑性和韧性起决定作用的为残留奥氏体.因此,如何通过调整化学成分和热处理工艺等手段调控残留奥氏体微结构,来实现精细组织结构和优良综合力学性能,成为新一代钢铁材料研究领域重要的课题.首先从钢铁材料强韧化机制出发,指出微观组织的精细化及硬相与软相的合理调控,是发展新一代钢铁材料的重要途径.然后针对近年来发展起来的超级贝氏体钢、Q&P钢、Q-P-T钢等具有微纳组织结构的超高强度钢,从合金设计、热处理工艺及组织结构与力学性能、磨损性能和疲劳性能的关系等方面进行综述与分析,最后指出微纳结构超高强度钢有待进一步深入研究与开发的问题.

通过对轴承钢球化退火转变机理的分析、研究,制定出理想的大规格轴承钢GCr15连续炉球化退火的生产工艺.结果表明,大规格轴承钢在连续炉球化退火时,选择等温球化退火工艺最为有效;退火炉保温区的温度分别制定为810、800℃,等温区的温度分别制定为735、730、720℃,辊速调整到1.5 m/h,φ120 mm的GCr15轴承钢球化组织能达到2.2和3.0级.

According to the status of serious wearing of rough mill roller during 240 mm X 240 mm bloom of bearing steel GCr15 at rolling mill, the effect of stock reduction amount, roll hardness, thermal conductivity and friction factor at a time of forming pass on roll wearing rule has been simulated and analyzed by using Archard wear mathematical model. The simulated results show that the higher the hardness of roll, the stronger the roll wear resistance; the effect of thermal conductivity on wearing of roll is minor； as friction factor f＞0.25, the effect of friction factor on change of wearing of roll is obvious; as stock reduction amount △h＜50 mm , the effect of stock reduction amount on wearing of roll is also obvious. Based on obtained results, combined with rolling process in situ and material of roll, with the measures including modifying the used spheroidal graphite I roll [tensile strength≥400 MPa, HRC hardness 40, thermal conductivity 18 kW/(m2·℃ ) and friction factor/=0.3] to spheroidal graphite II roll [ tensile strength 3500 MPa, HRC hardness 45 , thermal conductivity 17 kW/(m2·℃) and friction factor/=0.2] , and decreasing the reduction amount from 70 mm to 50 mm, the rolling steel amount by single groove of roll increases from 10000 t before optimization to 18000-20000 t after optimization.

In order to solve the problem of serious mischcrystal , the SAE4320 steel was held at temperature range of 640-1000℃for 2 h and air cooled, the austenitic grain size of the SAE4320 was detected and analyzed by use of the simulation of carburizing process .Results show that the mischcrystal in SAE4320 bearing steel is caused by excessively low final rolling temperature .When the SAE320 steel with mischcrystal is held at 740-760 ℃for 2 h then air cooled, the austenitic grain size is up to 8.0-7.0 grade.

Abstract For the first time, investigation of twin evolution during austenite grain growth in an Fe–C–Mn–Si alloy was conducted with in-situ observation using high temperature laser scanning confocal microscopy during austenization. It was found that twins nucleated in austenite grains, some of which might disappear during isothermal holding, even as new twins might nucleate at grain boundaries. In addition, the effects of twins and austenite grains on bainite morphology were also examined. The twins can restrain the growth of bainite sheaves and smaller austenite grains result in shorter bainite laths. The investigation of dynamic evolution of twins and the analysis of the effect of austenite twins on bainite morphology can only be realized by means of in-situ observation.

The metallurgy effect of carburized bearing steel G20CrNi2MoA for railway(/%:0.19C,0.49Cr, 1.75Ni,0.23Mo,0.071 Al) by argon shielding atmosphere electroslag remelting(ESR) in closed hood and by normal atmospheric ESR has been tested and analyzed.Results show that the loss of Si and Mn of argon shield atmosphere ESR ingot (3%～12%and 4%～10%) is less than the loss of Si and Mn of normal atmospheric ESR ingot(15%-18%and 7%～10%);as the oxygen content in electrode of steel G20CrNi2MoA is 10×10~(-6),the oxygen content in argon shield atmosphere ESR ingot(15×10~(-6) ) is lower than that in normal atmospheric ESR ingot(21.3×10~(-6));and the metallurgical quality of argon shield atmosphere ESR ingot is obviously better than that of normal non gas shielding ESR ingot.

According to 30CrMnSiA of the fracture defects, scanning electron microscope（SEM）and optical micro- scope（OM） were used to observe and find large former crack in the fracture, crack deepness contains half of the tube, crack was originated from the former root crack, which is the former crack propagation. Because of the big grain in the root crack, alumina slag and decarburization nearby the crack, the crack is concerned with the pierced tube. Pierced tube crack, alumina slag and big grain cause improper breakage. And the rising temperature leads to the big grain and fracture.

The normalizing and fully annealing tests were performed on the two samples of carburized bearing steel G20CrNi2MoA,which has two kinds of original structures;the isothermal annealing test has been done on the sample with normal structure,it was observed and shown that band structure can be eliminated by normalizing,while fully annealing makes the band structure worse,and the higher the isothermal annealing temperature is,the worse the banded structure is,which happens more obviously when the temperature is above 650 ℃.

New LZ45CrV steel blooms(/%:0.43C,0.27Si,0.77Mn,0.007P,0.005S,0.55Cr,0.10V, 0.lOMo) of 260 mm×260 mm and 280 mm×280 mm for heavy load railway axle at daye special steel are pilot-produced by the flow sheet 60 t UHP EBT EAF-LF-VD-6.5 t ingot-850 primary mill rolling process.With process measures including EAF charging 45%hot metal and quality scrap,controlling end[C]≥0.15%and[P]≥0.005%,feeding aluminium wire in LF refining to control 0.035%～0.045%Al and VD vacuum treatment≥20 min,the oxygen content in LZ45CrV steel bloom is 8.5×10~(-6),rating of nonmetallic inclusions≤1.0,rating of grain size 7～8,and the mechanical properties of steel bloom meet the requirement of standard and design.

The quenching examination of φ26 mm rod of steel 60Si2CrVAT(/%:0.60C,0.63Mn,1.50Si, 1.08Cr,0.14V) at 870～950℃is simulated by DIL850L phase transition instrument with <Φ4 mm×10 mm small specimen. Simulated test results show that with quenching temperature increasing,the residual carbide in steel decreases,and quenching at 950℃the grains coarsen obvionsly,therefore the selected optimum heating temperature for quenching is 910℃.In condition of production examination,with optimum heat treatment process i.e.quenching at 910℃for 40 min and tempering at 420℃for 90 min,it is available for steel to get optimum comprehensive mechanical properties i.e.tensile strength R_m- 1 940 MPa,yield strength R_(p0.2)-1 740 MPa,elongation A_5- 9.5%and reduction of area Z- 36.5%.

通过计算铁素体形核孕育期和形核率探讨了等温温度对带状组织的影响机理,并观察了齿轮钢SAE8822H（/%:0.22C、0.20Si、0.98Mn、0.60Cr、0.46Ni、0.36Mo）在管式炉经930℃10 min降至703～579℃等温1h空冷,或710～570℃等温处理2 h炉冷后钢中带状组织演变。结果表明,贫、富溶质区铁素体形核孕育时间差和铁素体形核率差异是造成等温转变时产生带状的原因;等温温度降低时,贫、富溶质区的孕育期时间差缩短,相对形核率减少,带状减轻;齿轮钢SAE8822H在570℃等温可使带状组织消失,这时相对形核率为6.3%。

The steelmaking process flow sheet of ferrite heat resisting steel P91 for boiler(%;0.08～0.12C,8.0～9.5Cr,0.85～1.05Mo,0.18～0.25V,0.06～0.10Nb,0.030～0.070N) is 20 t EBT EAF + 10 t induction furnace mixing melting- LF-VOD(nitrogen blowing) - 3 t ingot mold casting.With bottom blowing nitrogen gas stirring in low vacuum (～26 000 Pa) to make sufficient and quick reaction between deoxidizer,slag-making materials and liquid,the[N]increases from(80～90)×10~(-6) to(120～140)×10~(-6),then by nitrogen bottom-blowing with(9～15)×10~(-6)/min increasing rate of N content in liquid,the[N]shall increases to 620×10~(-6),and the nitrogen content in steel products is about 500×10~(-6) to meet the requirement of standard.

Large inclusions have a significant impact on the fatigue life of bearing steel.The evaluation methods for inclusions in bearing steel were compared and analyzed.Bearing steel were tested by high frequence ultrasonic C-scan,and using metallographic method to validate the results.The results showed that the testing method of high frequence ultrasonic C-scan was effective for the testing of large inclusions in bearing steel.

Poor fluidity of casting liquid of steel GCr15 mainly shows that the liquid in ladle doesn't flow out or the flow rate of liquid in nozzle of tundish is small.The steelmaking statistic data show that with increasing concasting heats average [Al](0.01%to 0.03%),decreasing[Ti](0.003%to 0.007%) and increasing Mn/Si(1.45 to 1.60) in steel the fluidity of liquid increases,besides,the longer LF refining period(80 min) and lower superheating extent(25℃) is unfavourable to increase the fluidity of liquid.Improving the cleanliness of liquid,suitable increasing[Al]and Mn/Si,controlling refining time and superheating extent of liquid in tundish is effective to improve the fluidity of liquid of steel GCr15.