硼对刃具钢组织与性能的影响

为研制开发适合水淬的新型刃具钢,采用显微组织观察、力学性能测试、热处理试验和磨粒磨损试验等技术手段,对比研究了含硼中碳钢与不含硼的65Mn钢热轧后与热处理后的显微组织和应用性能.结果表明:热轧态中碳含硼钢中存在较多铁素体相,强硬性更低,韧塑性更好;中碳含硼钢水淬回火后组织为回火马氏体,硬度可达50 HRC以上,高于油淬回火的65Mn钢,韧塑性和耐磨性也明显好于65Mn钢.中碳含硼钢完全适合水淬工艺,减少了工业污染,符合环保要求.     

焊后热处理对T92钢焊接接头组织及性能的影响

通过模拟现场热处理工艺,研究了T92钢焊接接头在不同回火温度下的组织和性能。结果表明,焊缝硬度和母材抗拉强度均随回火温度的升高而降低。接头处未回火的马氏体粗大,呈细针状;740-780℃回火,马氏体组织变细,板条特征明显;超过780℃,马氏体板条特征消失,表现为屈氏体组织;随回火温度升高,母材碳化物产生偏聚,铁素体含量增加;780℃以下回火母材力学性能满足ASME标准要求。     

Microstructural characterization of shielded metal arc weldments of a copper-bearing HSLA stee

Abstract

A systematic microstructural characterization in the heat-affected zone (HAZ) of two ASTM A710 grade A steel weldments (one preheated and the other pre–cooled), employing identical shielded metal arc welding conditions, has been performed. The microstructure in both the HAZ and the weld metal of both welds has been characterized by optical, scanning, and transmission electron microscopy in conjunction with microhardness traverses. No difference in microstructure was observed in the HAZ on comparing the preheated and non-preheated weldments. The only significant difference observed in the two weldments was the width of the HAZ, which is about 1 mm wider for a preheated weldment. Examination by transmission electron microscopy revealed the following microconstituents in the HAZ of both the weldments: polygonal ferrite, acicular ferrite, ferrite–carbide aggregates, ε-copper and fine cementite precipitates, martensite, tempered martensite, retained austenite, and transformation-twinned martensite. The microhardness traverse revealed almost identical hardness gradients in the two welds. The microstructural and microhardness data are discussed with regard to the preheating requirements for this alloy.

MST/118     

Influence of cementite spheroidization on relieving the micro-galvanic effect of ferrite-pearlite steel in acidic chloride environment

The corrosion behavior of the as-received steel and the spheroidized steel in acidic chloride environment was investigated. The results indicate the corrosion mode and corrosion rate of two steels are diverse due to their difference in microstructure. For as-received steel with ferrite-pearlite microstructure, severe localized corrosion happens on the pearlite regions, and plenty of cathodic cementite remains in the pits, further strengthening the micro-galvanic effect and accelerating the corrosion rate. While for spheroidized steel with tempered martensite microstructure, the nanosized cementite particles evenly distributed on the ferrite substrate are easy to fall off, which can significantly reduce the cementite accumulation on the steel surface, relieving the acceleration effect of micro-galvanic corrosion.     

钢材相似显微组织的分析与鉴别

在日常钢材的显微组织检验中,由于网状铁素体和网状二次渗碳体、针状铁素体和针状渗碳体、马氏体及其回火产物（回火马氏体、回火屈氏体和回火索氏体）、未溶铁素体和先共析铁素体、淬火屈氏体和回火屈氏体等显微组织的显微特征非常相似,容易出现误判。以常用碳钢为例,运用显微组织观察、显微硬度测试、化学试剂侵蚀等金相检验的普通手段,通过对显微组织形貌中的组织形态、分布、颜色进行直观比较,总结归纳出了上述几种相似显微组织的鉴别方法,以供金相检验人员参考。     

Comparison of magnetic Barkhausen noise and ultrasonic velocity measurements for microstructure evaluation of SAE 1040 and SAE 4140 steels

The aim of this study is to compare the performance of magnetic Barkhausen noise and ultrasonic methods for the evaluation of the microstructure of commercial steels. Following the austenitization of the specimens made of SAE 1040 and SAE 4140, various heat treatments were carried out to obtain microstructures consisting of martensite, tempered martensite, fine pearlite–ferrite, and coarse pearlite–ferrite. The microstructures were initially characterized by SEM investigation and hardness measurements. The magnitude and position of Barkhausen noise peaks were determined via a commercial system. The propagation rates of longitudinal waves were determined with the ultrasonic pulse-echo technique. Barkhausen noise response and sound velocity goes to minimum for the as-quenched martensite, and both tend to increase in the following sequence: tempered martensite, fine pearlite–ferrite, and coarse pearlite–ferrite. However, the magnetic features are more sensitive to the microstructure variations than to the sound velocity.     

The effect of tempering temperature on mechanical properties and microstructure of low alloy Cr and CrMo steel

Two low alloy Cr and CrMo steels with similar levels of carbon, manganese and chromium have been studied to determine the effect of tempering temperature on the mechanical properties and microstructure. The quenching and tempering of steels were carried out using a high-speed dilatometer. The steels were quenched at the average cooling rate of 30 K s-1 in the temperature range from 1123 to 573 K by flowing argon and tempered at 673, 823 and 973 K. The martensite of steels formed during quenching was of entire lath morphology with 2 vol% retained austenite. It was found that after tempering at 973 K the Cr steel contained only orthorhombic cementite, while the CrMo steel contained the cementite and hexagonal Mo2C particles in the ferrite matrix. At the same tempering conditions, the CrMo steel shows higher strength but lower ductility as compared to those of Cr steel. It is shown that this difference results from finer prior austenite grain, substructure within matrix and precipitate dispersion strengthening, primarily by Mo2C. Transmission electron microscopy (TEM) bright- and dark-field micrographs as well as selected area diffraction pattern analysis of orientation relationship showed that the cementite precipitated from the ferrite matrix. Fractography analysis showed that the morphology fracture surface was changed by increasing tempering temperature. Tempering at 973 K obtained ductile fracture by the microvoid coalescence mechanism.     

Quantitative measurement of cementite dissociation in drawn pearlitic steel

Fractional dissociation of cementite was quantified as a function of strain by measuring the volume change of cementite in the pearlitic steel. The amount of carbon dissolved into the ferrite was estimated from the decrease of cementite volume, to correlate with the hardness in different strain level. The hardness showed linear relationship with the carbon dissolved into the ferrite matrix, which is believed to contribute in strengthening the drawn wire. Defects introduced from the deformation were believed to lower the energy barrier of cementite break-ups and to enhance the dissolution of carbon into ferrite.     

L80 pipe steel microstructure assessment using ultrasonic testing

The potential exists to use ultrasonic shear velocity for real-time microstructure assessment of the quenching step in the heat treatment of L80 steel pipe. L80 steel samples were austenitised and subsequently cooled in different quench mediums (water, oil, heated oil, air and furnace) to produce microstructures ranging from primarily martensite to coarse ferrite/pearlite mixed structures. Following heat treatment, the samples were ultrasonically tested, tensile and hardness tested and metallographically examined. The shear wave velocity was observed to increase as the underlying microstructure of each sample changed from primarily martensite, to primarily bainite and finally to coarse ferrite + pearlite. The measured shear wave velocity exhibited an inverse linear dependence on both yield strength and microhardness.     

Precipitation behaviors of carbides and Cu during continuous heating for tempering in Cu-bearing medium C martensitic steel

The precipitation behaviors of carbides and Cu during continuous heating for tempering were investigated in Cu-bearing medium C martensitic steel by means of dilatometry, electrical resistivity, and transmission electron microscopy. The addition of 1.5 wt% Cu suppressed carbide precipitation during quenching from 900 °C, resulting in a large amount of solute C atoms in virgin martensite. The addition of Cu increased both the finish temperature of ε-carbide precipitation and the amount of ε-carbide precipitates during continuous heating. The precipitation of cementite was retarded and the amount of cementite precipitates increased by the addition of Cu. Retarded cementite precipitation in the Cu-bearing steel was attributed to sluggish Cu partitioning from cementite particles to the martensite matrix, the hindrance to the migration of cementite interfaces by Cu particles, and the slowed diffusions of C and Fe atoms. Cu precipitation was accelerated by cementite precipitation because cementite interfaces and the high Cu concentration near cementite particles provided nucleation sites for Cu precipitation. The hardness of the tempered Cu-bearing steel was higher than that of the tempered Cu-free steel at the temperatures of over 300 °C due to both Cu precipitation hardening and retarded cementite precipitation.     

13MnNiMoNbR与00Cr19Ni10异种钢焊接接头的组织与性能

首先将H309L焊丝堆焊在13MnNiMoNbR钢板坡口上,再将堆焊后的13MnNiMoNbR钢板与00Cr19Ni10钢板用H308L焊丝填充焊接,得到了13MnNiMoNbR与00Cr19Ni10异种钢焊接接头,并对接头的显微组织及硬度进行了分析。结果表明：13MnNiMoNbR钢板侧熔合线附近出现了粗大的铁素体组织,形成脱碳层,而H309L焊缝侧的奥氏体堆焊层熔合线附近出现了黑色的非常细小的碳化物析出层;由于碳化物的析出或是固溶碳,使H309L焊缝侧增碳层处的硬度明显升高。     

Numerical simulation and experimental investigation on the induction hardening of a ball screw

To improve the distribution of the hardened layer and avoid potential defects, the effects of induction hardening parameters on the hardened layer were researched using the finite element method (FEM). A FEM model of single coil induction hardening was built, and temperature curves on the surface region of a ball screw were attained by numerical simulation. The hardenability and phase transformation of 55CrMo steel were researched by experiment. The simulation and experimental results show that the temperatures Ac1 and Ac3 rise with increasing heating rate. Non-uniformity of temperature at the groove region can lead to non-uniformity of austenitization and hardness. High temperature can result in cracks, coarse grain size and overheating defects at the groove tip. Martensite produced during cooling transforms into tempered martensite due to the residual heat, and the remaining austenite transforms into martensite at a low cooling rate. A 5010-type ball screw cannot attain a hardened layer with the thickness of 2.5 mm at the groove bottom without defects at the groove tip by single coil induction hardening. Multiple induction coils with a certain gap would be helpful to improve the uniformity of temperature and hardness.     

硅对烧结M3∶2高速钢回火相及力学性能的影响

为研究硅对烧结高速钢力学性能的影响,采用真空热处理炉在1230℃对含0.4%碳粉及硅添加量在0～3.0%的M3∶2高速钢进行烧结,在500～600℃对烧结后的试样进行二次回火.采用X射线衍射仪,扫描电镜及能谱分析等手段研究了不同硅添加量对回火态高速钢的物相特征及力学性能的影响规律.物相分析结果表明,添加硅后,硅主要分布在回火马氏体及M6C碳化物中,而在MC碳化物中含量较低.回火马氏体组织中硅的含量随硅添加量的增加而增加,同时,硅的添加还显著影响回火马氏体组织中铁素体相的晶格常数,在硅添加量为0.7%时,铁素体相达到最大的晶格常数.力学性能测试结果表明,适量硅的添加可提高二次硬化效果,添加0.7%硅的高速钢在550℃二次回火后获得了最佳的硬度和弯曲强度.     

Suppression of hydrogen-induced blisters in SK4 carbon steel alloy by friction stir processing

The feasibility of using friction stir-processing technique as a microstructural refining method for preventing hydrogen-induced blisters of SK4 carbon steel alloy containing microstructure of hard cementite particles in a ductile ferrite matrix was examined. Amount and size of hydrogen-induced blisters decreased in the stirred layers with increasing rotation speed and completely disappeared when rotation speed attained 400 rpm because of the formation of a hard and fine microstructure consisting of pearlite, martensite, and retained austenite instead of that containing hard spheroidized cementite particles in a soft ferrite matrix. Interfaces between ferrite matrix and cementite particles were the preferential sites for the hydrogen blisters initiation.     

纳米贝氏体/马氏体钢的热稳定性

将低温贝氏体相变前淬火得到由马氏体、贝氏体铁素体和残余奥氏体组成的纳米贝氏体钢,使用扫描电镜(SEM)、X射线衍射(XRD)和透射电镜(TEM)等手段观察在不同温度回火的纳米贝氏体钢的显微组织和硬度变化,研究了预相变马氏体对纳米贝氏体钢热稳定性的影响。结果表明:含有马氏体的纳米贝氏体钢在中低温(473~773 K)回火后其硬度比回火前的高,回火温度高于823 K其硬度迅速下降到266.2HV(923 K)。预形成的马氏体在473~573 K回火后向附近的残余奥氏体排碳,后者的碳含量提高到峰值1.52%,提高了残余奥氏体的热稳定性,延迟后者在高温时的分解,从而提高了纳米贝氏体钢的高温热稳定性;回火温度高于723 K则残余奥氏体分解成碳化物,贝氏体铁素体粗化、回复形成新的铁素体晶粒。     

铁素体-珠光体型非调质钢的高周疲劳破坏行为

研究了三种碳和钒含量不同的铁素体-珠光型非调质钢的高周疲劳破坏行为,并与调质钢进行了对比.结果表明,铁素体-珠光体型非调质钢的高周疲劳性能与其微观组织特征有关.提高铁素体相硬度,其疲劳极限及疲劳极限比均提高,疲劳极限比最高可达0.60,远高于调质钢的0.50;热轧态粗大的网状铁素体-珠光体组织的疲劳性能较差,低于同等强度水平的高温回火马氏体组织。铁素体-珠光体型非调质钢疲劳破坏机制不同于调质钢,其疲劳裂纹基本上萌生于试样表面的铁素体/珠光体边界,并优先沿着铁素体/珠光体边界扩展;对于同等强度水平的调质钢,不存在像铁素体那样的软相,因而易在试样表层粗大的夹杂物处萌生疲劳裂纹.     

CYCLIC MECHANICAL BEHAVIOR AND MICROSTRUCTURE OF A 12Cr-Mo-V MARTENSITIC STAINLESS STEEL

Abstract— The low cycle fatigue properties of a 12Cr-IMo-V martensitic stainless steel are investigated at room temperature and correlated with its microstructure. The mechanical test results show that the behavior of this steel depends on the applied strain level. The SEM and TEM studies bring out the role of ferrite islands embedded in a tempered martensite lath matrix. Plastic deformation is essentially accommodated by ferrite; this results in extrusion formation on the surface specimen and a cellular dislocation structure. When the strain level is high, it requires a greater contribution of the tempered martensite, ferrite alone being unable to accomplish all the plastic deformation.     

NM360钢与Q345钢异种钢焊接接头组织与性能研究

为了解NM360钢与异种钢焊接应用过程中焊接接头的力学性能,本文对NM360调质钢和Q345热轧钢采用气体保护焊进行异种钢焊接,对焊接接头进行了力学性能试验及微观组织观察,并分析了NM360钢ICHAZ的软化机理.研究表明:Q345热轧钢焊接接头CGHAZ组织为贝氏体+魏氏组织,为HAZ硬度值最高的区域,FGHAZ和ICHAZ组织为P+F;NM360调质钢焊接接头CGHAZ组织为低碳马氏体,FGHAZ组织为低碳马氏体+少量的粒状贝氏体,晶粒细小,为HAZ硬度值最高的区域,ICHAZ组织为回火马氏体+铁素体+粒状贝氏体,铁素体组织是造成ICHAZ硬度值大幅度降低的原因.     

Microstructure of as-quenched 3.5NiCrMoV rotor steel. Part I. General structure and retained austenite

The microstructural features have been examined for 3.5NiCrMoV steam turbine rotor steel, in the as-quenched state and tempered at 500 °C. Quenching produces lath martensite, with bands of retained austenite at the lath boundaries and, to a lesser extent, at prior austenite grain-boundaries. Autotempering occurs during the quench, resulting in loss of tetragonality of the martensite and extensive carbide precipitation in the matrix and to a lesser degree at prior austenite grain boundaries, but not at lath boundaries. Tempering at 500 °C leaves the lath structure largely intact, but causes retained austenite to transform to bands of ferrite and cementite. This transformation does not correlate with the reduction in stress corrosion crack velocity which occurs on tempering. The strength of 3.5NiCrMoV steel in the as-quenched and 500 °C tempered conditions is most probably due to the combination of carbide precipitation strengthening and substructure strengthening.     

Hybrid Friction Stir Welding of High-carbon Steel

A high-carbon steel joint,SK5(0.84 wt% C),was successfully welded by friction stir welding(FSW),both without and with a gas torch,in order to control the cooling rate during welding.After welding,the weld zone comprised gray and black regions,corresponding to microstructural variation:a martensite structure and a duplex structure of ferrite and cementite,respectively.The volume fraction of the martensite structure and the Vickers hardness in the welds were decreased with the using of the gas torch,which was related with the lower cooling rate.