Problems of application of standards in evaluation of microstructure of metals and alloys

The purpose of this work is to consider the problems of applying some standards containing reference scales of structures: 1763-68, 1778-70, 5640-68, 9391-80, 10 243-75, 13938.13-93, 22 838-77, 3443-87 (materials: oxygenated copper, pipe and structural steels, cast iron). It is shown that the normative base of standards for metallographic analysis is morally outdated. The main problem is the discrepancy between the increase in standards and real modern structures. Basically, microstructure standards use a magnification of 100 times, in particular, for the analysis of oxygenated copper, banding of the rolled metal structure, Widmanstätt structure, phosphide eutectic. The analysis of modern materials requires an increase of about 500...800 times. The magnification of 360…400 times, used in some scales, is also insufficient, in particular, for the analysis of structurally free cementite. Also, the quality of images of structures makes them difficult to use. A common disadvantage of the considered standard scales of structures is the absence of metrics in photographs, which does not correspond to the modern level of metallurgy and causes certain inconveniences when comparing structures. It is necessary to revise the standards governing the structure of metals and alloys. Research should be carried out to develop a new generation of standards based on the real structures of modern industrial alloys. It is also necessary to develop new methods of structure analysis. This applies primarily to analysis in image processing programs.

The quality of semi-finished steel

The article deals with the quality of structural steel supplied by metallurgical enterprises. It is shown that the pipes made of steel 20, used in the oil and gas industry, contain structurally free cementite in the structure, often in the form of a grid (points 4 and 5 according to GOST 5640–68). This structure is the cause of faulty production: the subsequent cold treatment pressure formed sags on the surface of the product, and there is a violation of the continuity of the material up to the formation of through cracks. Formation of structurally-free cementite in steel 40KHN2MA with structure of the top bainite which was formed at violation of regulations of heat treatment of a semi-finished product is also found. When nitriding with heating to 490 ° C and holding at this temperature, there was a decay of bainite with the formation of tertiary cementite along the grain boundaries. Discussed the possibility of culling the poor quality of delivery at the consumer. It is also noted that many enterprises have now abolished entrance control, which has the most negative consequences both in terms of product quality and safety, especially in the oil and gas industry.

PARTICULARS APPLICATION OF DUCTILE IRON CASTINGS

The results of analysis of the relationship of structure and mechanical properties of ductile cast ironpots with globular graphite form, experience and perspectives of their industrial application. It is shown thatthe growth in the production of castings of ductile iron is caused exclusively by a favorable combination ofphysical, mechanical, operational and technological properties of this material, as well as economicconsiderations.The main factors regulating the cast structure and level of physical, mechanical and operationalcharacteristics of ductile iron are: the quality of the initial melt modification modes (including composition,quantity, method and sequence of input and additives), chemical composition and rate of solidification of themetal.Heat treatment of ductile iron is more effective than iron with lamellar graphite , since graphitespherical than weakens the metal substrate than the plate . Castings from nodular iron are exposed tovarious types of heat treatment. The purpose of heat treatment - structurally free cementite decomposition inrelatively thin sections of the casting ( graphitizing joke ) or hardening of pearlite matrix ( normalization).Can be used combined heat treatment, the purpose of pursuing the expansion of structurally free cementitewith subsequent normalization.

Development of Hypereutectoid Steel with Nodular Graphite

This work studies the formation of cast structures in hypereutectoid steel modified by alloying modifiers (Fe30Si55Mg7Ca2REM4, Fe34Si55Mg9Ca2 and Fe63Ni30Mg7) together with inoculants Fe20Si60Ba20. It is found that at spheroidizing by 0.7 % Fe63Ni30Mg7 and inoculation by 1.5 % Fe20Si60Ba20 causes the formation of inclusions of nodular graphite with nodularity exceeding 90 % and a structurally-free cementite structure is obtained. The mechanical properties of the steel with nodular graphite modified by Fe63Ni30Mg7 and Fe20Si60Ba20 are as follows: tensile strength (σb) 660-680 МPа, yield strength (σ0.2) 520-540 МPа, percent elongation (δ) 5-8 %, impact strength (КС) 15-35 J/cm2, Brinell hardness (НВ) 241-255. After ferritic annealing these parameters were found to be σb =530-560 МPа, σ0.2=400-430 МPа, δ =20-24 %, КС=160- 180 J/cm2, 150-162 НВ.