Work Of Crack Initiation Research Articles

Metal cold resistance of the low-alloy steels welding joint, micro-alloyed REM

ABSTRACT The effect of rare earth metals (REM), introduced into the electrode coating, on the mechanical properties, chemical composition and impact toughness at test temperatures from +20 to −70°C deposited metal and metal of welding joint on steel 10ХSND was studied. The components of fracture under impact tests are determined: the work of crack initiation (KST3) and work of fracture (KSTr). The character of the fracture surface of the damaged samples is studied. There is an increase in the impact toughness of a metal, micro-alloyed REM, in the investigated temperature range of the tests.

Tool steels of new generation

Some requirements are formulated for tool steels used to make tools with their durability being limited by strength and impact resistance rather than by wear resistance. It is shown that the high-speed steel belonging to a new hypereutectoid class is optimal for the above-mentioned application. The fracture mechanisms are considered for ledeburitic (R6M5) and hypereutectoid (11M5F) classes of tool steels. It is demonstrated that critical length crack formation in hypereutectoid steels takes place not only by means of elastic but also by means of considerable plastic deformation; on this account, the work of crack initiation in 11M5F considerably exceeds that of R6M5. The above-mentioned fact is due to the peculiarities of 11M5F steel microstructure characterized by extremely fine grain and the absence of eutectic carbides. Correlation between fracture work and deformation is established under static bending (on one hand) and impact strength (on the other hand) conditions.

Influence of alloying by rare-earth metals on the mechanical properties of 17g1s pipe steel

The positive influence of microadmixtures of rare-earth metals on the strength, plasticity, impact toughness, and cyclic crack-growth resistance of 17G1S pipe steel is discovered. The decomposition of the impact toughness into the work of crack initiation $$ {a_i} $$ and the work of crack propagation $$ {a_p} $$ made it possible to discover the following specific features in the temperature dependences of $$ {a_p} $$ : at elevated testing temperatures guaranteeing the ductile fracture of steel, the positive effect of alloying by REM is preserved. At the same time, at lowered temperatures of brittle fracture, this effect becomes negative and the work $$ {a_p} $$ decreases. Distilled water somewhat decreases the cyclic crack-growth resistance of steel and the positive effect caused by the REM admixtures manifests itself only in the increase in the cyclic fracture toughness of steel.

Effect of strain aging on the ductility of the two-layer steel 09G2S+12Kh18N10T and its welded joint

1. In the initial state, the base metal of the two-layer steel has the highest critical brittleness temperatures, while those of the fusion zone and zone of thermal influence are lower. After aging, the critical brittleness temperatures increase, especially T50 at 20°C. 2. The temperature dependencies of the specific work of crack initiation ai and propagation ap suggest that aging exerts the greatest influence on the specific work of crack initiation along the fusion boundary and on the specific work of crack propagation in the base metal.

Special features of fracture of full-profile railroad rails in impact bend testing

1. The work of crack initiation can be determined in the impact tests on the full-profile rail specimens. 2. The energy of fracture of the full-profile rail specimens is greatly scattered as a result of the presence of various external and internal stress raisers formed in the course of testing. 3. We proposed a mechanism of fracture of the-full-profile rail specimens in the impact tests which explain the reduction of the energy capactity of fracture as a result of splitting of part of the rail foot at the saart of the fracture process and the effect of the elastic wave reflected from the surface of the rail head.

Pseudoeutectoid in low-carbon unalloyed steel

1. Refinement of hot-rolled type St3sp steel contributes to the strengthening (for example, by 120 N/mm2). The resilience (by 10 J/cm2) and the fiber portion in the fracture (by 20%) are simultaneously increased in this case. 2. The presence in the structure of a pseudoeutectoid, whose amount ranges from 40 to 60%, depending on the regime, assumes decisive significances in the formulation of properties of low-carbon unalloyed steel after quenching from the rolling heat. 3. Quenching from the rolling heat promotes the strengthening of steel St3sp (by 60–80%), but simultaneously gives rise to loss of resilience due to a reduction in the work of crack initiation.

Properties of steel 16G2AF with microadditions of tellurium

1. With the addition of 0.001–0.0074% Te, the notch toughness (in the range of +20 to −100°) of samples of type 1 is 0.25–0.30 MJ/m2 higher than for the steel without tellurium. 2. The higher notch toughness resulting from the addition of tellurium is due to the increase in the work of crack initiation. 3. With 0.019% Te the notch toughness and work of crack initiation decline. 4. The quantity of ductile components in the fracture and the work of crack propagation are independent of the tellurium content at testing temperatures from 20 to −100°. 5. Despite the substantial cost of tellurium it is expedient to add tellurium to structural steels because of their high notch toughness at low temperatures.

Phase composition, microstructure, and mechanical properties of steel 20GTL with different titanium concentrations

1. After normalization of steel with excess titanium as compared with nitrogen, one observes three types of nitrides and carbonitrides: titanium nitrides that are present in the cast steel, high-carbon carbonitrides precipitated in the process of holding during normalization, and highly dispersed carbonitrides precipitated in the process of air cooling. 2. Additional treatment of steel 20GTL with SiCa has no effect on the work of crack propagation in the ductile condition or the ductile-brittle transition temperature but increases the work of crack initiation. 3. The best combination of mechanical properties is obtained for steel 20GTL with 0.02–0.03% Ti that is additionally treated with SiCa.

Low-temperature properties of strain-hardened austenitic stainless steels containing nitrogen

1. Low-carbon austenitic steels containing nitrogen are strengthened considerably by deformation at normal and low temperatures. The yield strength of stable austenitic steel 03Kh20N16AG6 at 77°K depends only on the preliminary deformation and is prctically independent of the temperature. 2. To ensure high strength of stable austenitic steels containing nitrogen the deformation can be conducted at room temperature. The absolute values of the strength characteristics of stable austenitic steel 03Kh20N16AG6 deformed 30% at room temperature and metastable steels 03Kh18N11 and 03Kh19AN12 deformed at low temperature are almost identical. 3. The ductility of stable austenitic steel 03Kh20N16AG6 strengthened by deformation at room temperature is quite adequate and the steel can be used for cryogenic equipment. Its yeild strength increases to 190 kgf/mm2 at 77°K and to 110 kgf/mm2 at room temperature. 4. The change in the fracture toughness of steel 03Kh19AN12 at 77°K after small preliminary deformations (up to 5%) depends mainly on the reduction of the work of crack initiation. The reduction of the work of crack propagation with increasing preliminary deformation is due mainly to inhibition of the formation of strain martensite. With over 30% martensite the initiation of fracture is facilitated.

Effect of nitrides, carbonitrides, carbides, and copper precipitates on the cold resistance of low-alloy steels

1. Aluminum nitride (0.079%) and vanadium nitride (0.125%) refine the grains in steels of the 17GS type and increase the yield strength by 4.5–7 kg/mm2, substantially increasing the toughness of the steel and also the work of crack initiation and crack propagation, which lowers the ductile—brittle transition temperature by 17–58°. 2. In contrast to nitrides, excess carbides, carbonitrides, and copper phase, which increase the strength characteristics, lower the toughness and raise the ductile—brittle temperature of the steels. 3. The embrittling effect of copper phase in steel of the 17GSND type is slight at copper concentrations up to 0.5%, but increases at larger copper concentrations.

Resistance to fracture of steel 35KhN3MFA for large machine parts

1. The difference in the structure of steel through the depth induced by incomplete hardenability of large rotors has a strong effect on the resistance to crack propagationap and ductile-brittle temperature T50, but has a negligible effect on the work of crack initiation and the standard mechanical properties. 2. To determine the resistance to fracture of large parts it is expedient to use samples with lateral notches.

Effect of quenching bath temperature on notch toughness of eutectoid steel with tempering at moderate temperatures

1. Changing the temperature of the quenching bath (20, 100, and 200°) affects the properties of martensite. With increasing temperatures at which martensite is formed the ductile characteristics improve (reduction in section, toughness) and the coercive force increases. 2. Tempering of martensite formed at different temperatures improves the ductile characteristics of the steel. The notch toughness (an) and its components (ai andap) increase with the tempering temperature. 3. In the range of tempering temperatures from 350 to 450° the resistance to crack propagation increases and the work of crack initiation decreases sharply.

Effect of cyanide coatings on the notch toughness of high-speed steel

1. A brittle hardened layer obtained by cyaniding lowers the toughness of high-speed steels due to reduction of deformation, i.e., the work of crack initiation is lowered.

Cold resistance of cast structural steel 30KhGMYuL after heat treatment

1. The best mechanical properties-low ductile-brittle transition temperature and high values of the work of crack initiation and crack propagation-are obtained after quenching of steel 30KhGMYuL from 860–880° and tempering at 600–650°. 2. The homogenizing temperature of cast steel 30KhGMYuL should not exceed 900°. 3. Steel 30KhGMYuL has a low susceptibility to reversible temper brittleness.

Fracture of aluminum and titanium alloys at low temperatures

1. Cooling to cryogenic temperatures leads to an increase in the irregularity of the distribution of deformation due to the stress gradient through the section and the bulk stresses in the notch zone. 2. Aluminum and titanium alloys undergo ductile fracture at low temperatures. However, at −196 and −269° there is an increase in the percentage of the block structure undergoing brittle fracture in the early stages of fracture (discontinuous flow), which is responsible for the deep cracks in the direction of the main crack or at sharp angles to it in aluminum alloys. 3. From the ratio of the work of crack proparation to the work of crack initiation it is possible to determine the variation of the mechanical properties with temperature for aluminum and titanium alloys cooled to −269°. With lowering of the temperature from 20 to −196°, Ap/Ai decreases due to the larger decrease of the work of crack propagation. With lowering of the temperature to −269° this ratio increases for aluminum alloys due to the greater reduction of the work of crack initiation. For titanium alloys Ap/Ai continues to decrease with lowering of the temperature to −269°.

Effect of cooling (to ?269 �C) on failure of steels Kh18N10T and Kh16N6 in impact bending

1. For the investigated steels the decrease of the work of fracture with a decrease of the test temperature to −296° is due mainly to a decrease of the work of fracture development. 2. The decrease of the work of crack initiation, which is related to decrease of the radius at the notch vertex, depends little on the cooling temperature. 3. By using the ratio Ad/Ai it is possible to evaluate more fully the performance capability of ductile materials under deep cooling conditions.

Effect of nitride phase on the toughness of quenched and tempered structural steel

1. Alloying of structural steel 20NM with aluminum, chromium, or vanadium nitride refines the austenite grains to grade 12-14. 2. The ductile-to-brittle transition temperature decreases most for quenched and tempered steel 20NM alloyed with aluminum nitride and jointly with aluminum, chromium, and vanadium nitrides. 3. Alloying of steel 20NM with nitrides increases the work of crack initiation. The work of crack propagation changes little.

Properties of steel 18Kh2N4VA melted by different methods

1. As compared with ordinary steel, the VI+EBR steel contains less oxygen, nitrogen, sulfur, tin, arsenic, antimony, and nonmetallic inclusions.The VAR steel contains fewer oxide and sulfide nonmetallic inclusions than ordinary steel. 2. The cleaner steel has a greater tendency to grain growth, which increases with temperature. 3. Under conditions of ductile fracture the fracture toughness of the VI+EBR steel is two to three times that of ordinary steel, although the ductile-to-brittle temperature (determined from the type of fracture) is the same as that of ordinary steel.The increase of the fracture toughness after remelting is due to the increase in the work of crack propagation. The work of crack initiation and the ductile-to-brittle temperature remain unchanged.

Ductility of steel refined with liquid synthetic slag

1. In steel refined with liquid synthetic slag and subjected to improvement the work of crack initiation is high and remains unchanged down to −80°. 2. At negative temperatures the work of crack initiation is substantially higher for the improved steel than for the normalized steel. 3. Improvement leads to a substantial increase in the work of crack propagationap at temperatures down to −80°.

Resistance to brittle fracture of case-hardened steel

1. The presence of a brittle case leads to a change in the type of macrofracture of samples subjected to impact tests — plastic deformation is prevented although the fine structure of the fracture remains unchanged. 2. A brittle case has no effect on the cold brittleness threshold. 3. In the presence of a brittle case there is no macroplastic deformation of the sample before formation of the crack (the work of crack initiation) or during propagation of the crack. 4. The impact toughness of samples with a brittle case characterizes the work of crack propagation alone.