Effects of medium- and low-temperature carbides on the mechanical properties of a low-carbon steel

A steel with low mass contents of carbon (0.04 %) was quenched and aged at temperatures between 60 and 200°C. The increase in yield stress due to these aging treatments and other mechanical properties were analyzed. A rather direct correlation of results from internal friction with those for yielding exists. The precipitates which form during aging at the lowest temperatures are equally capable of improving the yield stress. Thus it is possible to improve the properties by modified “bake-hardening”. Comparisons with literature confirmed that the aging procedures influence the kinetics of precipitation and the resulting strength increase: intermediate aging at room temperature before the proper aging treatment are of advantage.     

Effect of laser processing on the microstructure of a structural low-carbon steel

The macro- and microstructures and the distribution of microhardness over the height and width of the remelted and heat-affected zones in structural low-carbon grade 20 steel (1020 AISI) are investigated after laser processing under various conditions, including the application of an electric arc.     

Effects of thermomechanical processing on the microstructure and mechanical properties of a Ti-V-N steel

Based on studies of austenite deformation behavior and continuous-cooling-transformation behavior of a Ti-V microalloyed steel by cam plastometer and quench-deformation dilatometer, respectively, plate rolling schedules were designed to produce (i) recrystallized austenite, (ii) unrecrystallized austenite, (iii) deformed ferrite + unrecrystallized austenite. The effects of austenite condition and cooling rate on the final microstructure and mechanical properties were investigated. To rationalize the variation in final ferrite grain size with different thermomechanical processing schedules, it is necessary to consider the kinetics of ferrite grain growth in addition to the density of ferrite nucleation sites. The benefit of dilatometer studies in determining the optimum deformation schedule and cooling rate for a given steel is domonstrated. A wide range of tensile and impact properties results from the different microstructures studied. Yield strength is increased by increasing the amount of deformed ferrite, bainite, or martensite, and by decreasing the ferrite grain size. Impact toughness is most strongly influenced by ferrite grain size and occurrence of rolling plane delaminations. B. Dogan, Formerly with CANMET, Ottawa, Canada,     

Effect of water quenching processing parameters on the mechanical properties of a cold-rolled C-Mn-containing steel sheet

Cold-rolled advanced high-strength steel sheets have become the material of choice for the automotive industry because of their unique attributes of high strength and balanced mechanical properties. High-hydrogen gas jet cooling and water quenching are the most commonly used ultrafast cooling technologies for producing martensite-containing high-strength steel sheets. The water quenching technology ensures the fastest industrial cooling rate of 1 000 K/s; therefore,it has the highest potential with respect to saving alloys. In this study,the water quenching of a C-Mn-containing steel sheet is simulated during continuous annealing to investigate the effect of water quenching and tempering parameters on its mechanical properties. The results reveal that at low quenching temperatures,the strength of the steel sheet decreases as the soaking temperature increases. However,at high quenching temperatures,a high soaking temperature corresponds to increased strength after quenching,regardless of whether the material was austenitized in the single austenite zone or the inter-critical zone. Therefore,a high quenching temperature always results in a high strength and a high yield ratio after quenching. Low-temperature overaging( tempering) considerably influences the yield strength and yield ratio,and the extent of this influence is correlated with the soaking temperature.     

Influence of scale removal on the mechanical properties of low-carbon steel

The influence of heat treatment and of the acidic and mechanical removal of rolling scale on the variation in mechanical properties of 1kp low-carbon steel wire rod is investigated.     

Thermomechanical processing of microalloyed powder forged steels and a cast vanadium steel

The effects of controlled rolling on transformation behavior of two powder forged (P/F) microalloyed vanadium steels and a cast microalloyed vanadium steel were investigated. Rolling was carried out in the austenitic range below the recrystallization temperature. Equiaxed grain structures were produced in specimens subjected to different reductions and different cooling rates. The ferrite grain size decreased with increasing deformation and cooling rate. Ferrite nucleated on second phase particles, deformation bands, and on elongated prior austenite grain boundaries; consequently a high fractional ferrite refinement was achieved. Deformation raised the ferrite transformation start temperature while the time to transformation from the roll finish temperature decreased. Cooling rates in the cast steel were higher than in P/F steels for all four cooling media used, and the transformation start temperatures of cast steels were lower than that of P/F steel. Intragranular ferrite nucleation, which played a vital role in grain refinement, increased with cooling rate. Fully bainitic microstructures were formed at higher cooling rates in the cast steel. In the P/F steels inclusions and incompletely closed pores served as sites for ferrite nucleation, often forming a ‘secondary’ ferrite. The rolling schedule reduced the size of large pores and particle surface inclusions and removed interconnected porosity in the P/F steels. Formerly Postgraduate Researcher in the Department of Metallurgy and Materials Science, UMIST/University of Manchester, United Kingdom     

Structure and mechanical properties of hot-deformed low-carbon martensitic steel

The structural changes in low-carbon martensitic 15Kh2G2NMFBA steel induced by its hot forging in the temperature range 1150–850°C have been studied. The calculated cracking resistance parameter I_c is in agreement with its experimental value. A relation is found between the lath sizes in the martensite structure and the change in the impact toughness characteristics. A combined regime of hot deformation and hot treatment of the low-carbon martensitic steel is proposed to form submicrometer-sized structural elements and high strength and impact toughness characteristics.     

Effect of alloying elements on the microstructure and properties of a hot-rolled low-carbon low-alloy bainitic steel

A two-level full factorial statistical experiment consisting of eight alloys was conducted to determine the effect of 2 pct cobalt, 1 pct nickel and 1 pct chromium on the hot-rolled microstructure and properties of a bainitic steel containing 0.2 pct C, 2 pct Mn, 1 pct Si, 0.75 pct Mo and 0.003 pct B. The results indicate that chromium induced the formation of the acicular bainitic structure while cobalt favored massive ferrite formation and resulted in islands of martensite and/or austenite. Nickel, when added singly, did not appear to influence the microstructure but in combination with chromium, enhanced the formation of the lower bainitic structure. The mechanical properties were statistically analyzed and statistical equations were obtained to predict optimized compositions. These equations indicate that chromium increased the toughness of these steels more than nickel. However, it was shown that with similar bainitic structures, nickel enhanced the toughness more than chromium. The results illustrate the short-coming of a pure statistical approach to the design of alloys.     

Effect of alloying elements on the microstructure and properties of a hot-rolled low-carbon low-alloy bainitic steel

A two-level full factorial statistical experiment consisting of eight alloys was conducted to determine the effect of 2 pct cobalt, 1 pct nickel and 1 pct chromium on the hot-rolled microstructure and properties of a bainitic steel containing 0.2 pct C, 2 pct Mn, 1 pct Si, 0.75 pct Mo and 0.003 pct B. The results indicate that chromium induced the formation of the acicular bainitic structure while cobalt favored massive ferrite formation and resulted in islands of martensite and/or austenite. Nickel, when added singly, did not appear to influence the microstructure but in combination with chromium, enhanced the formation of the lower bainitic structure. The mechanical properties were statistically analyzed and statistical equations were obtained to predict optimized compositions. These equations indicate that chromium increased the toughness of these steels more than nickel. However, it was shown that with similar bainitic structures, nickel enhanced the toughness more than chromium. The results illustrate the short-coming of a pure statistical approach to the design of alloys.     

Nonuniform structure and properties in hot-rolled low-carbon steel coils

The austenite phase transitions in the industrial production of hot-rolled steel coils are studied magnetometrically. Nonuniformity of the structure and mechanical properties of low-carbon steel strip over its length and width may be attributed to incomplete phase transitions in the strip on the output roller conveyer and nonuniformity of the subsequent coil cooling in regular production conditions. Inheritance of the structural inhomogeneity formed after hot rolling may be responsible for the thickness variation observed after cold rolling of the strip. Recommendations are made for reducing or eliminating the structural inhomogeneity so as to improve product quality.     

RE-Mg-Ti变质对铸造高速钢组织和性能的影响

用RE－Mg-Ti对低碳铸造高速钢（6W6Mo5Cr4V)模具进行变质处理,消除了钢中网状共晶碳化物,并细化了基体组织,还可减轻W、Mo元素偏析,变质处理后,高速钢硬度、红硬性和强度变化不大,断裂韧性（K1c）和疲劳裂纹扩展门槛值（△Kth）有所提高,冲击韧性（αk）提高1倍以上,耐磨性也明显提高,各项性能指标达到了锻造高速钢水平,RE－Mg-Ti变质低碳铸造高速钢,有望实现“以铸代锻”。     

Effects of processing on the transverse fatigue properties of low-sulfur AISI 4140 steel

The effects of inclusions due to steelmaking processes on the fatigue life of AISI 4140 have been investigated. The test matrix consisted of three commercially produced heats of AISI 4140 of comparable cleanliness: one was conventionally cast (CC), and two were inert gas-shielded/ bottom-poured (IGS). One of the IGS heats was calcium-treated to explore the effects of inclusion shape control (IGS/SC). All heats were hot-rolled and reduced over 95 pct to produce bar stock of 127 to 152 mm (5 to 6 in.) in diameter. Transverse axial specimens conforming to ASTM E466 were machined, quenched, and tempered to approximately 40 HRC, and they were fatigue tested in tension-tension cycling (R = 0.1). Test results and statistical analyses of the stress-life data show that the IGS grade has several times the fatigue strength of the CC grade at 10⁷ cycles. Lower-limit fatigue strengths calculated at a 99.9 pct probability were 518.5 MPa (75.2 ksi) for IGSvs 55.6 MPa (8.1 ksi) for the CC grade. The IGS/SC grade had the best performance at all stress and life levels. The results obtained indicate that fatigue performance can be improved by choosing a processing method that reduces the incidence of exogenous oxides and by controlling the shape of the sulfides.     

硼对低碳铝镇静钢酸洗钢板性能的影响

在宝钢工业生产中,通过对薄规格酸洗低碳铝镇静钢中添加（10～30）×10-4%硼合金的研究,分析了硼对钢力学性能、金相组织及表面质量的影响。结果表明,钢中添加（10～30）×10-4%的硼合金可使钢的屈服强度降低20 MPa,延伸率提高1.5%,屈强比降低5.7%;回归出屈服强度和延伸率与终轧温度、C含量、Mn含量、B含量的关系。添加适当硼合金有利于生产高表面质量低碳铝镇静钢酸洗板。     

Influence of cold forming on the tensile behavior and properties of low-carbon microalloyed steel

The tensile behavior and properties of cold formed low-carbon microalloyed steel with its microstructure of all ferrite and pearlite (F+P) were investigated.Bending and flattening deformations were carried out in the laboratory on hot-rolled sheets in order to simulate the cold forming process of steel sheets during pipe fabrication and sampling of high frequency straight bead welding pipes.A comparison of the tensile behavior and properties of the material made before and after cold forming indicates that cold deformation alters the tensile behavior and properties of the material to a certain degree depending on the manner of the cold deformation and the degree.The research on the Bauschinger effect indicates that for the steels investigated,when the plastic strain is small,the back stress increases rapidly with the increase of the plastic strain and then rapidly tends to saturation.The finite element analysis indicates that the change in the properties of the steel sheets due to cold forming is a result of the Bauschinger effect and work hardening.The mechanism of the change in the properties is also given in this study.     

Influence of rolling temperature on the austenite structure and properties of low-carbon microalloyed steel

In laboratory conditions, the influence of the temperature interval in the finishing stage of controlled rolling on the structure of hot-deformed austenite, the final microstructure, and the properties of low-carbon microalloyed steel is studied. Experiments show that reducing that temperature interval within the range T _nr-A _r3 reduces the grain size in the direction transverse to rolling and increases the number of deformational twins within the hot-deformed austenite grains. The effect is to improve the grain size and uniformity of the ferrite-bainite microstructure and hence to improve the mechanical properties of the thick sheet produced.     

Influence of controlled rolling on the structure and mechanical properties of low-carbon microalloy steel

The influence of the temperature and deformation in the finishing stage of rolling on the structure and properties of low-carbon microalloy steel is investigated. The microstructure and mechanical characteristics of the steel are studied as a function of the final temperature T _f.r in the finishing stage and the time interval between the last rolling cell and the accelerated-cooling system.