Research into Grinding Hardening of Microalloyed Non-quenched and Tempered Steel

Grinding hardening is a new technology of hardening steel piece surfaces with grinding heat generated in the grinding process instead of with a high or medium frequency induction heating method,which can effectively integrate grinding and surface hardening. Experimental studies were carried out on grinding hardening of non-quenched and tempered steel. Through grinding experiments with variable depths of cut and feeding rate,the variation in the depth of the hardening layer was studied and the microstructure of the hardening zone of the test pieces was subsequently ana-lyzed. In the end,the hardening effect of non-quenched and tempered steel was compared with that of 40Cr steel,which revealed the superiority of non-quenched and tempered steel in grinding hardening technology.

Development of non-quenched and tempered bolt steel

The 8.8 grade non-quenched and tempered bolt steel was studied according to the process conditions of wire rod plant and customer requirments.Three types of experimental steel grades were selected.10MnSiTi Nb and 20Mn2VTi(N) were chosen as the formal steel after several experimemts.

Morphological transformation of elongated MnS inclusions in non-quenched and tempered steel during isothermal heating

Elongated MnS inclusions in rolled non-quenched and tempered steel tend to cause the mechanical anisotropy of steel,deteriorate the mechanical properties and degrade the quality and service life of the steel products.To reveal the mechanisms of morphological transformation of strip-shaped MnS inclusions during isothermal heating,the effects of heat treatment time and temperature on the morphology,number density and size distribution of elongated MnS inclusions were systematically studied and discussed.A diffusion couple experiment was also conducted to clarify the diffusion mode of MnS inclusions.The experimental results showed that with the increase in isothermal heating time(from 0 to 10 h at 1473 K)and temperature(from 1173 to 1573 K for 3.0 h),the number density and average aspect ratio of MnS inclusions generally showed an increase and decrease trend,respectively,while the area fraction remained stable and only slightly fluctuated around 0.4%.In the diffusion couple,after the isothermal heating at 1473 K for 3.0 h,the elements Mn and S in the steel near the steel-MnS interface were very stable without any concentration gradient.The morphology change sequence of the elongated MnS inclusions in the rolled non-quenched and tempered steel during the isothermal heating was strip→cylinderization→spindle→spheroidization.Relationship between the diameter of MnS inclusion and the spacing between two MnS inclusions after splitting,and the fitting goodness of different n values under different experimental time and temperature confirmed that the driving force for the transformation of MnS inclusions during the isothermal heating was surface diffusion,instead of volume diffusion.

Review on regulation of MnS in non-qquenched and tempered steel

An overview of the current research status and control methods of MnS in non-quenched and tempered steel was provided.As a low-melting plastic inclusion,the morphology and distribution of MnS were influenced by various production processes.Therefore,control of MnS is a systematic problem that must be integrated into the entire production process.Based on the production process,the factors affecting the morphology and distribution of MnS in steel were introduced.The effects of oxygen activity,manganese,sulfur,and some alloys on MnS inclusion precipitation were summarized,mainly including MnS modification treatment and oxygen-sulfide composite precipitation control.It is believed that MnS precipitates during the solidification process of steel,and controlling the solidification cooling rate could effectively regulate the size and morphology of MnS,avoiding the precipitation of II-MnS.Additionally,by changing the deformation rate,deformation amount,deformation temperature during the hot deformation process,and heating time and temperature during heat treatment,the distribution and morphology of MnS could be improved.Through the fine control of the above process parameters,the number of II-MnS in steel could be effectively reduced,and their morphology could be improved,thereby enhancing the performance of non-quenched and tempered steel and promoting its wider application.Furthermore,applying laboratory research results to industrial production is an important direction for future research efforts in this field.

Effect of induction heating and tempering on properties and microstructures of quenched and tempered pipes

In this study,a C-Mn quenched steel tube was quickly tempered by induction heating,and the influence of the tempering temperature on its performance was studied and compared with that by traditional tempering. The results show that the yield strength of both is quite strong with regular changes in the tempering temperature,but that the tensile strength of the tube tempered by induction heating is higher than that tempered by traditional tempering by about 25 MPa,and the elongation after induction tempering is significantly higher than that after traditional tempering. The differences in the microstructures of tubes after induction and traditional tempering were compared by metallographic microscope,scanning electron microscopy,and transmission electron microscopy.Theoretical analysis was also performed. Compared with traditional tempering,a fine dispersion of precipitated carbides occurs after induction tempering,which is the main reason for the performance differences.

Theoretical calculation of the impact work in the alloying non-quenched and tempered steel

Coupled with hot-continuous rolling technology and based on the calculation of the finishing rolling impact work in the non-quenched and tempered Si-Mn steel, the calculations of the finishing rolling impact work in the alloying non-quenched and tempered steel with the elements of Cr, Ni, Mo, W, Cu, V, Nb and Ti are studied with the covalent electron number nA of the strongest bond in alloying phases, the smallest electron density difference ?ρ of phase interfaces, and the number of atom states σ (σ′) which keep the interface electron density continuous. The calculated results show that the finishing rolling impact work of the alloying non-quenched and tempered steel intensely depends on strengthening mechanisms. The solution strengthening, interface strengthening, precipita- tion strengthening of pearlite, and dispersion strengthening will result in the decrease of the finishing rolling impact work; the refinement strengthening, the precipitation strength- ening of V, Nb and Ti in α-Fe-C-V(Nb, Ti), and the residual austenite containing Ni on the boundary of α-Fe-C-Ni will increase the impact work; and the increments or decrements can be calculated with nA, ?ρ, σ (σ′) and weights of alloying elements. The calculation formulas of the finishing rolling impact work in this paper are intergraded with the sug- gested ones of the finishing rolling tensile strength, yield strength, and elongation of the non-quenched and tempered steel. The calculated results agree well with the measured ones.

Theoretical calculation of the finishing rolling impact work in non-quenched and tempered Si-Mn steel

Based on the hot-continuous rolling technology, the finishing rolling impact work α k of the non-quenched and tempered Si-Mn steel is theoretically calculated with the covalent electron number nA of the strongest bond in alloying phases, and the smallest interface electron density difference Δρ of alloying phase interface and the number of atom states σ which keep the interface electron density continuous. Calculations show that the solution strengthening, the precipitation strengthening, and the interface strengthening will result in the decrease of the finishing rolling impact work α k, and the effects of the number of atom states σ which keep the interface electron density continuous on the finishing rolling impact work α k are different. Taking the impact work and the number of atom states σ 0 keeping the electron density continuous of the phase interface α-Fe/α-Fe-C between α-Fe and α-Fe-C as reference values, the impact work of the interface will increase when σ of some interface is larger than σ 0; otherwise, the impact will decrease. Therefore, the finishing rolling impact work α k can be calculated with the impact value of the refined α-Fe matrix and the influence amounts caused by the solution strengthening, the precipitation strengthening, the interface strengthening, and the number of atom states σ which keep the interface electron density continuous. The calculated results agree well with the measured ones. In this paper, the effect of S on the impact work is also discussed.

Effect of Nb-V Microalloying on Microstructures and Mechanical Properties of Medium Carbon Non-Quenched and Tempered Steel

Based on optical microscope(OM),transmission electron microscope(TEM) and mechanical performance measurement,the microstructures and mechanical properties of Nb-V micro-alloying non-quenched and tempered steels have been studied.The results showed that the microstructure consists of ferrite and pearlite,in which there exists a lot of intragranular ferrite.Niobium carbide is the main form of carbonitrides,Nb-enriched carbonitrides refine grains,V-enriched carbonitrides have precipitation strengthening effect,which promotes the toughness of the studied steel.The mechanical properties for steels 1,2 and 3 have met the standards required by high load automobile crankshaft,in which the comprehensive property for No.2 is the best.

易切削非调质汽车用钢表面裂纹形成机理及工艺优化

易切削非调质汽车用钢采用410 mm×530 mm大断面连铸坯轧制成规格Φ130~220 mm的钢材,表面探伤合格率较低,钢材表面出现裂纹缺陷,通过对钢轧全流程系统分析发现为连铸坯表面角部横裂纹和星状裂纹所导致,其与结晶器铜管倒锥度及R角不合理、钢中硫化物形态及偏析聚集、保护渣理化指标适配性差、二次冷却系统工艺有待优化等方面原因有关。通过改进结晶器铜管倒锥度及R角、微钙化处理工艺改善钢中硫化物形态、调整结晶器保护渣的理化性能指标、优化二次冷却系统,酸洗试样表面质量合格率提高了近30%,铸坯表面磁粉探伤合格率提高至99.2%,连铸坯所对应轧材的表面探伤最高炉次达98.6%、最低炉次达92.4%,铸坯纵剖酸洗试样V型偏析改善明显,且碳、硫的中心偏析指数分别为1.04、0.97,符合±0.05的高标准均质化要求。

回火工艺对超深井用V150油套管强韧性的影响

采用力学性能测试、金相组织观察、透射电镜以及扫描电镜观察,研究不同回火工艺对超深井用V150油套管强韧性的影响。研究结果表明:650℃为实验钢最优的回火温度;随着回火时间的延长,实验钢强度和硬度不断下降,塑性和韧性不断提高;当回火时间为15-75 min时,强度满足V150钢级要求;当回火时间大于45 min时,韧度满足V150钢级要求;考虑强韧性的最优匹配,兼顾节能降耗,45-60 min为较合适的回火时间;随着回火次数的增加,油套管强度下降,韧性提高,经过650℃,45 min的2次回火后,淬火应力充分释放,残余奥氏体完全转变为回火组织,回火组织更加细小,实验钢有较好的强韧性配合,0℃横向冲击功超过110 J,强度仍能满足V150钢级的要求。

钢管在线水淬热处理工艺

介绍了天津市无缝钢管厂运用锻造热处理工艺理论及工艺模拟试验,在现有的热轧管生产线上实施在线内外喷水淬火和离线回火的调质工艺生产N80钢级光套管的情况。生产实践证明,在大生产模式的条件下实施该调质工艺,钢管的综合力学性能稳定,达到了预期效果。该工艺也是一种节能增效的工艺。

回火温度对超高强高韧V150套管组织性能的影响

采用力学性能测试、金相组织观察、透射电镜以及扫描电镜观察,研究不同回火温度对超深井用超高强高韧套管组织和力学性能的影响规律。研究结果表明:套管经580～700℃回火的组织均为回火索氏体,在580～630℃回火时组织比较稳定,仍然保持着淬火马氏体的位向和形状,在640℃回火时发生铁素体再结晶,在700℃回火时发生组织粗化;与热轧态相比,淬火回火后的塑性和韧性得到了很大提高,在580～700℃回火,未出现第二类回火脆性;随着回火温度的升高,套管的强度和硬度逐渐降低,塑性和韧性逐渐增加;650℃为套管最佳回火温度,回火组织均匀,铁素体再结晶充分,碳化物细小弥散分布,强度达到V150钢级,0℃时横向冲击功接近110 J,强韧性匹配达到最佳。

热处理工艺对12Cr1MoVG厚壁无缝钢管表面硬度的影响

分析了12CrlMoVG厚壁无缝钢管组织分布状态与硬度的关系；通过测定其CCT曲线，确定出Ф219mmx45mm规格12CrlMoVG厚壁无缝钢管的最佳热处理工艺：淬火970℃×60min、水淬20s，回火750℃×150min。生产结果表明：通过控制淬火时间，可减少铁素体的析出量，避免马氏体组织的大量析出，从而实现产品硬度的控制；新热处理工艺实现了12CrlMoVG厚壁无缝钢管硬度在161～182HB内的稳定控制，表面硬度合格率达100％，且其各项机械性能指标均满足标准要求。

33Mn2V非调质油井管钢的相变特性及其应用

研究了新型热轧非调质无缝油井管用 3 3 Mn2 V钢 ,实验确定了该钢在加热过程和 95 0℃奥氏体化后冷却过程的相变点 ,以及 110 0℃奥氏体化不变形条件下和 12 0 0℃奥氏体化并模拟实际穿管、轧管变形条件下的两种过冷奥氏体连续转变曲线。提出一种不同于业界至今仍普遍认同的观点 ,即“在线常化”技术不是生产 N80钢级非调质热轧油井管必不可少的工艺途径。

新型油井管钢33Mn2V的动态再结晶规律研究

采用 Gleeble- 15 0 0热 /力模拟仪压缩变形实验 ,研究了微合金非调质钢 3 3 Mn2 V的动态再结晶规律。绘制出其动态再结晶图 ,发现其发生动态再结晶的临界变形量较小。通过回归计算出其热变形方程式 ,确定了 σP、εP和 Z的关系 。

油井管钢33Mn2V静态再结晶的模拟研究

采用热 /力模拟技术研究了新型非调质油井管用钢 33Mn2 V在不同变形温度、变形速率、变形量和初始组织条件下的奥氏体静态再结晶行为。根据所得数据确定了其静态再结晶激活能 Q=115 .4 k J/ mol,并建立了 33Mn2 V钢静态再结晶量的经验模型 :X=1- exp[- 0 .2 2 314 (t/ t0 .2 ) 0 .4 8],t0 .2 =1.2 4 34- 1 0· d20 ·ε- 2 .36 87· ε- 0 .31 6 7· exp(QRT) ,式中道次间隔时间 t≥ 6 0 s时取 t=6 0 s。

油套管的服役条件及产品研制开发现状(上)

我国油井管制造厂和油田用户密切合作,结合油田实际,联合研发攻关,极大地推进了油井管的国产化进程,使油套管产量、品种规格和质量实现根本性转变。简要介绍了油套管柱的力学、环境服役条件及油套管失效的类型及原因。综述了油套管产品研发的进展和现状,建议进一步加强非API钢级、特殊螺纹连接油套管和特殊用途油井管的开发,提出应解决的突出技术问题并注意评价标准的建立和评价方法的科学性。

用非调质钢生产高强度油管的试验

为满足石油勘采工程对油管用钢的高要求,进行了用非调质钢CT80生产N80级高强度油管的工艺试验。试验表明,采用CT80钢生产N80级油管,各项性能指标满足APISpec5CT,5B规范要求,并可简化生产工艺和改善生产环境。

非调质油井管钢的开发应用

研究了轧制工艺对不同成分的非调质油井管钢组织与性能的影响 ,并分析了不同组织对韧性的影响。结果表明 ,中碳铁素体—珠光体型非调质钢完全满足 N- 80油井管的要求 ,在 95 0～ 85

无缝钢管强韧化处理工艺

对 34Mn2V无缝钢管进行现场采样 ,将热轧钢管试样进行正火和回火处理 ,测定了不同处理工艺参数下钢的力学性能。试验发现 ,采用 880℃正火、5 0 0℃回火的处理工艺 ,获得了良好的综合力学性能 ,完全满足美国API .SPEC标准中规定的N80性能级别要求。