Anisotropy Of Impact Toughness Research Articles

Причины образования трещиноподобных дефектов в толстолистовой стали 09Г2С для резервуарных металлоконструкций

Determination of causes of crack-like defects in the heavy plate steel 09Г2С is a crucial task, the solution of which is aimed at improving the mechanical safety of oil storage steel vertical tanks. In order to determine the causes for the formation of a group of crack-like defects oriented towards rolling, revealed during grinding and magnetic inspection of the tank wall surface near the vertical weld, the analysis of the chemical composition and testing of the mechanical properties of heavy plate steel were carried out, including the determination of the anisotropy of impact toughness in the temperature range from +20 to –75 °С, analysis of metal microstructure in the area of defect formation on transversal sections and rolled surface. Impact bending tests of 09Г2С heavy plate steel after controlled rolling in longitudinal and transverse directions showed no anisotropy of impact toughness, as well as high purity of steel as for sulfur and titanium, which at higher content causes impact toughness anisotropy. The revealed features of metal microstructure near the defects made it possible to conclude that the crack-like defects were formed during the rolling of gas bubbles at the stage of preparing semi-finished rolled products for finishing rolling. One of the possible methods to prevent such defects from getting into finished rolled products is the use of automated systems of visual inspection of rolled products in the manufacturing process.

Fracture of a Main Pipeline 530 mm in Diameter Made of Low-Alloy 17GS Steel

The causes and character of the fracture of a section cut from a main gas pipeline 530 mm in diameter made of low-alloy 17GS steel have been investigated. The length of a longitudinal main crack in the base metal is 12 m. The gas pipeline failed due to stress corrosion cracking according to a hydrogen mechanism. Cracks originated on the outer surface of the pipe near corrosion pits. Preferred crack propagation along the boundaries of ferrite grains and pearlite colonies is revealed. The fraction of intergranular fracture is 6–9.5%. An anomalously high anisotropy of impact toughness is found in the place of plastic corrugation formation, Ka = 3.2–3.9.

Anisotropy in impact toughness of powder bed fused AISI 304L stainless steel

Anisotropy in impact toughness of powder bed fused AISI 304L stainless steel

Effect of delta ferrites on the anisotropy of impact toughness in martensitic heat-resistant steel

To avoid brittle failure of the final-stage turbine blades, it is necessary to understand the anisotropy mechanism in martensitic heat-resistant steel 10Cr12Ni3Mo2VN. This study focused on the effect of delta ferrites on the anisotropy of impact toughness by investigating the relationship between the microstructures and the anisotropy of impact toughness. It was mainly interested in the effect of banded delta ferrites on the transverse impact toughness of experimental steel after quenching and tempering. It was found that banded delta ferrites cause banded brittle cracks and induce tempered martensite matrix to fracture in quasi-cleavage mode, which leads to the embrittlement in transverse specimens and the anisotropy of impact toughness. The embrittlement caused by banded delta ferrites is unrelated to other precipitates such as M23C6-type carbides or MX-type precipitates. In addition, by removing the banded delta ferrites, it can eliminate the anisotropy of impact toughness in the experimental steel. It was also found that conventional heat treatment could not improve the isotropy of impact toughness since it has little influence on the content of banded delta ferrites. As suggested, the use of upsetting-stretching forging strategy promises a great of improvement of isotropy of impact toughness as it can remarkably reduce the amount of banded delta ferrites.

Microstructure and microtexture assessment of delamination phenomena in charpy impact tested specimens

In this article the delamination phenomena, which occurs in the X70 steel during fracture process from the Charpy impact tests, was investigated. Microstructure, microtexture and Taylor factor map analyses were performed by scanning electron microscopy, light microscopy and electron backscatter diffraction, respectively. In a cross-section of two fractured surface regions namely, in the perpendicular and parallel regions to the propagation fracture direction where delamination occurred, it was possible to notice that delamination showed a key role in the anisotropy of impact toughness between the L-T and T-L orientations. The results also revealed that the cause of the delamination can be attributed to the presence of microstructural banding and elongated ferrite grains aligned in a rolling direction. The presence of (100)[011] and (111)[110] crystallographic orientations, with Taylor factors close to 2.7 and 4.5, respectively, were identified in the delamination region. They contribute to the occurrence of cleavage delamination during the fracture process.

Ausforming effects on anisotropy of mechanical properties in HSLA martensitic steel

In order to clarify effects of prior pancaked austenitic structure on microstructure and mechanical properties of transformed martensite in ausformed steel, a super-thin pancaked austenite was processed by multi-pass rolling in a 0.03–2.6Mn-0.06Nb-0.01Ti (wt%) low alloy steel. The evolution of prior pancaked austenite grain during multi-pass rolling was studied using Ni-30Fe model alloy. Related with the structure and texture in the prior super-thin pancaked austenite in Ni-30Fe alloy, the texture and anisotropy of mechanical properties of transformed martensite in the studied ausformed steel were focused on. There were mainly three kinds of rolling texture components in the super-thin pancaked austenite: Goss {110}〈001〉, copper {112}〈111〉 and brass {110}〈112〉. They were further transformed into the weak {001}〈110〉 and strong {112}〈110〉, {111}〈112〉 texture components in the martensitic structure. The orientation relationship (OR) of lath martensite transformation from pancaked austenite in the ausformed steel deviated larger from the exact Kurdjumov-Sachs (K-S) OR than in the case of equiaxed austenite without deformation. The tensile and yield strengths of the ausformed martensitic steel first decreased and then increased as the angle between tension direction and rolling direction increased. The main reason for the anisotropy of strength was considered as the texture component {112}〈110〉 in martensite. However, the anisotropy of impact toughness was more complex and the main reasons for it are unknown.

Developing Efficient Charges for Making Ultra-Clean Steel

Structural steels used in products that are subjected to high temperatures and alternating loads in service must meet strict standards on their contents of phosphorus, sulfur, and nonferrous-metal impurities. It has been established that an increase in the steelmaking charge’s content of metallized materials directly affects the physico-mechanical properties of the product. In particular, such an increase improves the resistance of the steel to brittle fracture. Charges of different compositions have been developed and commercially tested to make ultra-clean steels for machine-building and special-metallurgy plants. Use of the charges is making it possible to reduce the total content of nonferrous-metal impurities in steel by a factor of 1.5 without significantly increasing the cost of the charge materials. Structural steel ‐ a material used in products that are subjected to large alternating loads and high temperatures ‐ must meet stringent requirements on its contents of sulfur and phosphorus (no more than 0.005% of each) and nonferrous-metal impurities (Cu  0.06%; As, Sn, Sb  0.005%). The steel’s contents of zinc, lead, and bismuth are also determined and included in the certification data. To prevent the rejection of continuous-cast semifinished products due to unsatisfactory ultrasonic inspection results or surface defects, the maximum allowable contents of Pb, Sb, Sn, Zn, and Bi are 0.0046% and 0.0065%, respectively [1]. However, the content of nonferrous metals in the steel of heats that were investigated reached 0.0112%. We made a study of the effect of the combined content of Cu, Sb, Sn, and As on property anisotropy and the coldshortness threshold for steel 20Kh2N4A, which is used to make shells. The contents of the other elements in the steel did not exceed the narrow prescribed ranges and all of the products were subjected to the same heat treatment. The test group of 40 heats was divided into two samples based on their combined contents of Cu, Sb, Sn, and As. The metal in each sample was characterized by a mechanical property distribution that was close to a normal distribution, which allowed us to use the methods of mathematical statistics with a 95% confidence level. The results of our analysis showed that a 30% increase in the combined content of the nonferrous-metal impurities increases the anisotropy of impact toughness 12%. Here, the absolute values of impact toughness in the longitudinal and transverse directions decrease by 10 and 21%, respectively. There is also a 25% drop in the cold-shortness threshold (Table 1). The main reason harmful impurities enter the steel is the scrap metal used in the charge. The scrap can be divided into three categories, depending on its origin: home scrap (metallurgical and foundry scrap); chips from machining; dormant scrap. The amount of dormant scrap in the scrap total and the steelmaking charge is continually increasing, which is accompanied by an increase in the content of contaminating elements in the finished steel and, accordingly, an increase in the amount of home scrap (HS) created. The technology traditionally used to make quality steel in the shops of special metallurgy plants and machine factories involves the use of a cold charge containing conversion pig iron, HS, and dormant scrap.