In this paper, ultrasonic （20 kHz） fatigue tests were performed on specimens of a high-strength steel in very high cycle fatigue （VHCF） regime. Experimental results showed that for most tested specimens failed in ...In this paper, ultrasonic （20 kHz） fatigue tests were performed on specimens of a high-strength steel in very high cycle fatigue （VHCF） regime. Experimental results showed that for most tested specimens failed in a VHCF regime, a fatigue crack originated from the interior of specimen with a fish-eye pattern, which contained a fine granular area （FGA） centered by an inclusion as the crack origin. Then, a two-parameter model is proposed to predict the fatigue life of high-strength steels with fish-eye mode failure in a VHCF regime, which takes into account the inclusion size and the FGA size. The model was verified by the data of present experiments and those in the literature. Furthermore, an analytic formula was obtained for estimating the equivalent crack growth rate within the FGA. The results also indicated that the stress intensity factor range at the front of the FGA varies within a small range, which is irrespective of stress amplitude and fatigue life.展开更多
The microstructure,strength,toughness and fatigue properties of an ultra-high strength steel 40CrMnSiMoVA have been investigated.The so-called meta-bainite,composed of thin re- tained austenite films within or between...The microstructure,strength,toughness and fatigue properties of an ultra-high strength steel 40CrMnSiMoVA have been investigated.The so-called meta-bainite,composed of thin re- tained austenite films within or between the bainitic ferrite lathes was found in the steel after isothermally quenched at 300℃ for 1h.In comparison with the martensite structure obtained by isothermally quenching in martensite range,the meta-bainite has more excellent strength and plasticity,lower notch sensitivity,stronger strain harden ability,higher fatigue strength, longer strain or impact fatigue life,slower crack propagation rate and more remarkable overload effect on increasing fatigue life.展开更多
This paper deals with microstructure and grain size of HAZ of 590 MPa high strength ship-structure steel with welding simulator. While t 8/5 time is short, 10CrNi3MoV steel’s microstructure of coarse grain heat-a...This paper deals with microstructure and grain size of HAZ of 590 MPa high strength ship-structure steel with welding simulator. While t 8/5 time is short, 10CrNi3MoV steel’s microstructure of coarse grain heat-affected zone (CGHAZ) is lath martensite structure and a small amount of twined martensite structure; while t 8/5 time is long, it is mainly granular bainite structure. After second thermal cycle with peak temperature between critical temperature Ac 1′ and Ac 3′, CGHAZ has the inheritance of coarse grain and coarse microstructure. Welding energy input (determined by t 8/5 time) has an effect on the inheritance of coarse microstructure, but no influence on the inheritance of coarse grain. In detail, with a shorter t 8/5 time, there is an inheritance of coarse microstructure and grains. With a longer t 8/5 time, there is only the inheritance of coarse grains. While t 8/5 increases, the scope of temperature of causing it diminishes. Therefore, the inheritance of coarse microstructure connects with the high speed of heating and cooling.展开更多
Fatigue properties of high-strength steels become more and more sensitive to inclusions with enhancing the ultimate tensile strength (UTS) because the inclusions often cause a relatively low fatigue strength and a lar...Fatigue properties of high-strength steels become more and more sensitive to inclusions with enhancing the ultimate tensile strength (UTS) because the inclusions often cause a relatively low fatigue strength and a large scatter of fatigue lives. In this work, four S–N curves and more than 200 fatigue fracture morphologies were comprehensively investigated with a special focus on the size and type of inclusions at the fatigue cracking origin in GCr15 steel with a wide strength range by different heat treatments after high-cycle fatigue (HCF). It is found that the percentage of fatigue failure induced by the inclusion including Al2 O3 and TiN gradually increases with increasing the UTS, while the percentage of failure at sample surfaces decreases conversely and the fatigue strength first increases and then decreases. Besides, it is interestingly noted that the inclusion sizes at the cracking origin for TiN are smaller than that for Al2 O3 because the stress concentration factor for TiN is larger than that for Al2 O3 based on the finite element simulation. For the first time, a new fatigue cracking criterion including the isometric inclusion size line in the strength-toughness coordinate system with specific physical meaning was established to reveal the relationship among the UTS, fracture toughness, and the critical inclusion size considering different types of inclusions based on the fracture mechanics. And the critical inclusion size of Al2 O3 is about 1.33 times of TiN. The fatigue cracking criterion could be used to judge whether fatigue fracture occurred at inclusions or not and provides a theoretical basis for controlling the scale of different inclusion types for high-strength steels. Our work may offer a new perspective on the critical inclusion size in terms of the inclusion types, which is of scientific interest and has great merit to industrial metallurgical control for anti-fatigue design.展开更多
提出了100 t EAF-LF-VD-CC-CR全流程控制齿轮钢氧含量的工艺措施;研究了0.00053%~0.00145%氧含量20MnCr5齿轮钢的旋转弯曲疲劳性能、断口和夹杂物尺寸。结果表明,钢中总氧含量越高,最大夹杂物尺寸也越大,疲劳强度越低,当[O]≤0.0010%时,...提出了100 t EAF-LF-VD-CC-CR全流程控制齿轮钢氧含量的工艺措施;研究了0.00053%~0.00145%氧含量20MnCr5齿轮钢的旋转弯曲疲劳性能、断口和夹杂物尺寸。结果表明,钢中总氧含量越高,最大夹杂物尺寸也越大,疲劳强度越低,当[O]≤0.0010%时,随[O]降低,疲劳强度升高幅度较小;试验钢在表层不产生疲劳裂纹的临界夹杂物尺寸为21μm,距表面深度30~430μm的浅层区域为相对安全区域,其中的夹杂物很难引起疲劳开裂。展开更多
基金supported by the National Basic Research Program of China (Grant 2012CB937500)the National Natural Science Foundations of China (Grants 11172304 and 11202210)
文摘In this paper, ultrasonic （20 kHz） fatigue tests were performed on specimens of a high-strength steel in very high cycle fatigue （VHCF） regime. Experimental results showed that for most tested specimens failed in a VHCF regime, a fatigue crack originated from the interior of specimen with a fish-eye pattern, which contained a fine granular area （FGA） centered by an inclusion as the crack origin. Then, a two-parameter model is proposed to predict the fatigue life of high-strength steels with fish-eye mode failure in a VHCF regime, which takes into account the inclusion size and the FGA size. The model was verified by the data of present experiments and those in the literature. Furthermore, an analytic formula was obtained for estimating the equivalent crack growth rate within the FGA. The results also indicated that the stress intensity factor range at the front of the FGA varies within a small range, which is irrespective of stress amplitude and fatigue life.
文摘The microstructure,strength,toughness and fatigue properties of an ultra-high strength steel 40CrMnSiMoVA have been investigated.The so-called meta-bainite,composed of thin re- tained austenite films within or between the bainitic ferrite lathes was found in the steel after isothermally quenched at 300℃ for 1h.In comparison with the martensite structure obtained by isothermally quenching in martensite range,the meta-bainite has more excellent strength and plasticity,lower notch sensitivity,stronger strain harden ability,higher fatigue strength, longer strain or impact fatigue life,slower crack propagation rate and more remarkable overload effect on increasing fatigue life.
文摘This paper deals with microstructure and grain size of HAZ of 590 MPa high strength ship-structure steel with welding simulator. While t 8/5 time is short, 10CrNi3MoV steel’s microstructure of coarse grain heat-affected zone (CGHAZ) is lath martensite structure and a small amount of twined martensite structure; while t 8/5 time is long, it is mainly granular bainite structure. After second thermal cycle with peak temperature between critical temperature Ac 1′ and Ac 3′, CGHAZ has the inheritance of coarse grain and coarse microstructure. Welding energy input (determined by t 8/5 time) has an effect on the inheritance of coarse microstructure, but no influence on the inheritance of coarse grain. In detail, with a shorter t 8/5 time, there is an inheritance of coarse microstructure and grains. With a longer t 8/5 time, there is only the inheritance of coarse grains. While t 8/5 increases, the scope of temperature of causing it diminishes. Therefore, the inheritance of coarse microstructure connects with the high speed of heating and cooling.
基金financially sup-ported by the National Natural Science Foundation of China(NSFC)(Grant Nos.52001310,52130002,and 51771208)the Strategic Pri-ority Research Program of the Chinese Academy of Sciences(Grant No.XDC04040502)+3 种基金the National Science and Technology Major Project(No.J2019-VI-0019-0134)Outstanding Postgraduate Inno-vative Research Project of Institute of Metal Research,CAS(No.1193002090)KC Wong Education Foundation(No.GJTD-2020-09)Institute of Metal Research Innovation Fund(No.2023-ZD01).
文摘Fatigue properties of high-strength steels become more and more sensitive to inclusions with enhancing the ultimate tensile strength (UTS) because the inclusions often cause a relatively low fatigue strength and a large scatter of fatigue lives. In this work, four S–N curves and more than 200 fatigue fracture morphologies were comprehensively investigated with a special focus on the size and type of inclusions at the fatigue cracking origin in GCr15 steel with a wide strength range by different heat treatments after high-cycle fatigue (HCF). It is found that the percentage of fatigue failure induced by the inclusion including Al2 O3 and TiN gradually increases with increasing the UTS, while the percentage of failure at sample surfaces decreases conversely and the fatigue strength first increases and then decreases. Besides, it is interestingly noted that the inclusion sizes at the cracking origin for TiN are smaller than that for Al2 O3 because the stress concentration factor for TiN is larger than that for Al2 O3 based on the finite element simulation. For the first time, a new fatigue cracking criterion including the isometric inclusion size line in the strength-toughness coordinate system with specific physical meaning was established to reveal the relationship among the UTS, fracture toughness, and the critical inclusion size considering different types of inclusions based on the fracture mechanics. And the critical inclusion size of Al2 O3 is about 1.33 times of TiN. The fatigue cracking criterion could be used to judge whether fatigue fracture occurred at inclusions or not and provides a theoretical basis for controlling the scale of different inclusion types for high-strength steels. Our work may offer a new perspective on the critical inclusion size in terms of the inclusion types, which is of scientific interest and has great merit to industrial metallurgical control for anti-fatigue design.
文摘提出了100 t EAF-LF-VD-CC-CR全流程控制齿轮钢氧含量的工艺措施;研究了0.00053%~0.00145%氧含量20MnCr5齿轮钢的旋转弯曲疲劳性能、断口和夹杂物尺寸。结果表明,钢中总氧含量越高,最大夹杂物尺寸也越大,疲劳强度越低,当[O]≤0.0010%时,随[O]降低,疲劳强度升高幅度较小;试验钢在表层不产生疲劳裂纹的临界夹杂物尺寸为21μm,距表面深度30~430μm的浅层区域为相对安全区域,其中的夹杂物很难引起疲劳开裂。
