Development of Plastic Region Tightening 1.6-GPa Ultra-High Strength Bolt with High Delayed Fracture Resistance

Hamada, Takahiro; Kobayashi, Daisuke; Oyanagi, Mitsushi; Tanabe, Tatsuhiko; Ando, Tomohiro; Honma, Tomonori; Kodama, Hitoshi

doi:10.4271/2019-01-1116

Cited by 2 publications

References 19 publications

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Stainless Steel Thermal Spray Coating of Cylinder Bores for VC-Turbo Engine

Hirayama¹,

Higuchi²,

Hoshikawa³

et al. 2021

SAE Int. J. Adv. & Curr. Prac. in Mobility

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<div class="section abstract"><div class="htmlview paragraph">Nissan’s variable compression turbo (VC-Turbo) engine has a multilink mechanism that continuously adjusts the top and bottom dead centers of the piston to change the compression ratio and achieve both fuel economy and high power performance. Increasing the exhaust gas recirculation (EGR) rate is an effective way to further reduce the fuel consumption, although this increases the exhaust gas condensation in the cylinder bores, causing a more corrosive environment. When the EGR rate is increased in a VC-Turbo engine, the combined effect of piston sliding and exhaust gas condensation at the top dead center accelerates the corrosive wear of the thermal spray coating. Stainless steel coating is used to improve the corrosion resistance, but the adhesion strength between the coating and the cylinder bores is reduced. Trial production of the coatings with different linear expansion coefficients was conducted, and the sensitivity of the linear expansion coefficient and adhesion strength was obtained. Consequently, the adhesion strength was found to have a maximum value with respect to the linear expansion coefficient. By contrast, the surface observation of this coating after the honing process showed an increase in surface porosity. The martensitic content in the coating was reduced, and the appropriate martensitic content and chemical composition with the optimal corrosion resistance, adhesion strength, and surface porosity were found. Using this coating (0.01C-12Cr-0.22Ni-0.35Mn), the corrosive wear at the top dead center was resolved. Consequently, the fuel economy was improved by more than 4% compared with that of the current VC-Turbo engine, which has already adopted a carbon-steel-based coating.</div></div>

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Stainless Steel Thermal Spray Coating of Cylinder Bores for VC-Turbo Engine

Hirayama¹,

Higuchi²,

Hoshikawa³

et al. 2021

SAE Int. J. Adv. & Curr. Prac. in Mobility

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Development of Mo-Free Ultra-High Strength 1.6-GPa Bolt with Delayed Fracture Resistance for Multi-Link Type Engine

Sekine,

Oyanagi,

Hamada

et al. 2024

SAE Technical Paper Series

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<div class="section abstract"><div class="htmlview paragraph">Mo-free 1.6-GPa bolt was developed for a Variable Compression Turbo (VC-Turbo) engine, which is environment friendly and improves fuel efficiency and output. Mo contributes to the improvement of delayed fracture resistance; therefore, the main objective is to achieve both high strength and delayed fracture resistance. Therefore, Si is added to the developed steel to achieve high strength and delayed fracture resistance. The delayed fracture tests were performed employing the Hc/He method. Hc is the limit of the diffusible hydrogen content without causing a delayed fracture under tightening, and He is the diffusible hydrogen content entering under a hydrogen-charging condition equivalent to the actual environment. The delayed fracture resistance is compared between the developed steel and the SCM440 utilized for 1.2-GPa class bolt as a representative of the current high-strength bolts. Owing to delayed fracture test, Hc/He of developed steel is 49.1 (Hc:3.39 ppm, He:0.069 ppm), and that of SCM440 is 4.14 (Hc:1.16 ppm, He:0.028 ppm). In the microstructure of the developed steel, cementite is dispersed by the addition of Si, and the film-like carbides that precipitated at the grain boundaries, causing delayed fracture, are suppressed. Therefore, Hc of the developed steel is higher than that of SCM440. Moreover, adding Si reduces the hydrogen diffusion rate; hence, the He of the developed steel is less than that of 1.2-GPa class bolt. Thus, we developed a novel 1.6-GPa tensile strength bolt that achieved higher hydrogen embrittlement resistance than the current high-strength bolt.</div></div>

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Development of Plastic Region Tightening 1.6-GPa Ultra-High Strength Bolt with High Delayed Fracture Resistance

Cited by 2 publications

References 19 publications

Stainless Steel Thermal Spray Coating of Cylinder Bores for VC-Turbo Engine

Stainless Steel Thermal Spray Coating of Cylinder Bores for VC-Turbo Engine

Development of Mo-Free Ultra-High Strength 1.6-GPa Bolt with Delayed Fracture Resistance for Multi-Link Type Engine

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