Stability of (Ti, M)C (M = Nb, V, Mo and W) carbide in steels using first-principles calculations

Thermomechanical processing of advanced high strength steels

Interphase precipitation of nanometer-sized carbides in a titanium–molybdenum-bearing low-carbon steel

The effects of Ti, Ti–Mo, and Ti–Nb microalloy additions on the precipitation strengthening in three experimental high-strength low-alloy steels have been investigated. The objective of this work was to study the carbide precipitation under the conditions of continuous cooling and interrupted cooling. It was found that titanium molybdenum complex carbide, (Ti, Mo)C, can strongly maintain nanometer-scaled sizes and has the largest contribution to the hardness as compared to titanium carbide, TiC, and titanium niobium complex carbide, (Ti, Nb)C. The result emphasizes that (Ti, Mo)C particles possess an excellent behavior of thermal stability.

Precipitation hardening of high-strength low-alloy steels by nanometer-sized carbides

Strengthening mechanisms of a new 700 MPa hot rolled Ti-microalloyed steel produced by compact strip production

A ferritic steel precipitation-strengthened by manometer-sized carbides was developed to obtain a high strength hot-rolled sheet steel having tensile strength of 780 MPa grade with excellent stretch flange formability. Manganese in a content of 1.5% and molybdenum in a content of 0.2 % were added to 0.04 % carbon Ti-bearing steel in order to lower austenite-ferrite transformation temperature for fine carbides and to retard generating of pearlite and large cementites, respectively. Tensile strength of hot-rolled sheet steel increased with titanium content and it was achieved to 800 MPa in a 0.09 % Ti steel. Microstructure of the 0.09 %Ti steel was ferrite without pearlite and large cementites. Fine carbides of 3 nm in diameter were observed in rows in the ferrite matrix of the 0.09 % Ti steel with transmission electron microscope. The characteristic arrangement of the nanometer-sized carbides indicates that the carbides were formed at austenite-ferrite interfaces during transformation. By energy dispersive X-ray spectroscopy, the carbides were found to contain molybdenum in the same atomic concentration as titanium. Crystal structure of the nanometer-sized carbides was determined to be NaCI-type by X-ray diffractometry. The calculated amount of precipitation-strengthening by the carbides was approximately 300 MPa. This is two or three times higher than that of conventional Ti-bearing high strength hot-rolled sheet steels. Based on the results obtained in the laboratory investigation, mill trial was carried out. The developed hot-rolled high strength sheet steel exhibited excellent stretch flange formability.

Development of High Strength Hot-rolled Sheet Steel Consisting of Ferrite and Nanometer-sized Carbides

A method of producing a welded steel pipe which comprises: (a) forming a steel strip having two edges in a cylindrical form so that the two edges face each other; (b) preheating the two edges of the steel strip to a temperature of a melting point or less by applying a high frequency electric current to the two edges; (c) pressing the two edges of the steel strip towards each other by contact with squeeze rolls to form a joint portion including a joint line; (d) radiating a high density energy beam sufficient to fuse a full thickness of the steel strip to a portion adjacent to a squeeze point to weld the joint portion; and (e) controlling an upset by applying the squeeze rolls sufficiently to reduce weld defects

Method for producing a steel pipe using a high density energy beam

The world's first 25 kW laser welding machines at its 24-inch pipe mill has been installed. The technology for the high-power laser pipe welding process that assures welds with the same properties as those of the base metal while maintaining high productivity has been started to develop. Key technologies for this process such as high power laser welding, high-accuracy seam tracking and nondestructive inspection have been successfully established. The results obtained are as follows.(1)The productivity of this process is much higher than conventional fusion weldings, e.g., SAW for less than steel plate 16 mm thick.(2)High energy density of laser beam helps to produce finely distributed oxides.(3)Fine oxide particles with a size of 0.1-0.2 μm were found in weld metal. And they also prevent the heat-affected zones from deteriorating low temperature toughness and so on, a problem that occurs in conventional fusion weldings.(4)The performance of the welds was as sound as the base metal by using the heat treatment process after high-power laser welding.(5)The characteristics of low temperature toughness and SSCC etc. of the laser welds are almost at the same level as the base metal.

https://www.jstage.jst.go.jp/article/qjjws1983/19/2/19_2_233/_pdf

Development of High Power Laser Pipe Welding Process

Effect of cold spray deposition on fatigue strength of arc-welded ultra-high strength steel sheet

Fatigue property of the fillet lap joint using arc welding is lower than that of as-received material, which is affected by the various factors such as the stress concentration on the toe due to its own shape and the residual stress retained as tension in the vicinity of the toe. The TIG arc was applied to the local heat treatment in the vicinity of the welded joint parallel to the bead after the MAG welding for sheet steels. The effects of the distance from the bead and the speed of TIG torch on the residual stress perpendicular to the bead were investigated in case of the 310 to 590 MPa class hot rolled steel sheets. This heat treatment in the condition of the distance, 15 mm, and the torch speed, 150 cm/min., changed the residual stress perpendicular to the bead in the vicinity of the toe from tension to zero. As the result, the fatigue strength of the fillet lap joint in the out-of-plane bending mode for each material successfully increased and the improvement in the fatigue strength incresed with increase of the strength of material. The endurance limit for the specimen without residual stress was estimated using the modified Goodman's diagram. The mechanism of the improvement in the fatigue strength by this heat treatment is discussed in view of the release of the residual stress induced by the arc welding.

https://www.jstage.jst.go.jp/article/qjjws1983/17/2/17_2_319/_pdf

Tsuyoshi Shiozaki

Papers

Development of High Strength Hot-rolled Sheet Steel Consisting of Ferrite and Nanometer-sized Carbides

Method for producing a steel pipe using a high density energy beam

Development of High Power Laser Pipe Welding Process

Effect of cold spray deposition on fatigue strength of arc-welded ultra-high strength steel sheet

Improvement of Fatigue Properties of Fillet Lap Joints by Applying. Local Heat Treatment with TIG Arc.